Key Points
- "Partial tear" covers at least three populations: the knee with MRI signal change but a stable examination; the knee with arthroscopically confirmed fiber disruption of 25%–75%; and the knee that presents with instability and is found at arthroscopy to retain one bundle. Natural-history and surgical data from these three cannot be transferred among one another.
- Treatment decisions depend on whether the remaining fibers currently restrain anterior tibial translation and rotation, not on the tear proportion shown on MRI. Pivot-shift grade combined with the side-to-side laxity difference measured on the same instrument is the preoperative combination that best separates "functional remnant," "nonfunctional remnant," and "complete tear"; MRI readings of these three conditions overlap heavily: in an Antwerp retrospective series of 51 arthroscopically confirmed partial tears, MRI called the injury a partial tear in only 20%–50% of cases, and sensitivity in other studies mostly fell between 40% and 80%.
- Young age, participation in pivoting contact sports, arthroscopic disruption of more than half the fibers, already mildly increased anterior translation at first presentation, and a further twisting injury with giving way after the index injury are signals that recur when nonoperative treatment progresses to complete tear. In young active cohorts followed for 3–7 years, about 40% progress; progression may occur in the first year or only become apparent after a reinjury two or more years later, so follow-up cannot end after a three-month revisit. None of Linköping's 22 initially stable knees with injury of no more than half the ligament underwent reconstruction during 20 years of observation, but that cohort all had concomitant injuries, and 3 had undergone single-bundle suture.
- Patients managed without surgery need a plan with scheduled follow-up visits: pivot shift and laxity at three months, with earlier return for any episode of giving way; an increase in laxity measured on the same instrument under the same conditions, or conversion of the pivot shift from negative to positive, explains loss of residual-bundle competence better than repeat MRI.
- Selective single-bundle reconstruction that preserves the remnant reliably restores laxity and functional scores. Two randomized studies (a French multicenter series of 54 and a Turkish single-center series of 40) showed no difference in subjective scores; in the French study, anterior laxity at one year was about 0.6 mm less in the preservation group, a difference a commentator judged close to Rolimeter reading error, while the original authors replied that under a blinded randomized design measurement error does not negate between-group significance; the clinical and long-term meaning of this difference remains unsettled. The costs of the technique are greater difficulty in tunnel placement and extension loss from an overly thick graft.
- Direct primary-repair data for partial tears in this chapter come from two single-center, uncontrolled lines: pulley-anchor repair of 21 cases from the Chinese PLA General Hospital, and bone-marrow stimulation with or without suture from Gobbi's Italian group (an early 2009 report of 26 cases, expanded in 2018 to 50 cases with about 10 years of follow-up; the two reports overlap in patient numbers), of whom about one quarter underwent reconstruction for secondary instability at ten years. Randomized repair-versus-reconstruction data come from complete-tear populations: the Dutch dynamic-augmentation trial predominantly proximal tears, and the BEAR trial midsubstance tears with closed physes; the signal of high repair failure in adolescents comes from proximal complete avulsions. When used for partial tears, these data can serve only as reference from adjacent populations.
Scope of Application
The intended patient for this chapter is an isolated partial tear of the anterior cruciate ligament (ACL): no concomitant ligament injury, no cartilage injury requiring treatment, and no prior knee surgery. Direct studies of this population are scarce; most cohorts cited here mix concomitant injuries: knees with meniscal injury make up a substantial share of the natural-history data; 9 of Kocher's 45 cases had a grade II medial collateral ligament (MCL) sprain; at least 18 of Horsens' 41 cases involved the MCL; 9 of 40 in Adachi's augmentation group had concomitant MCL injury; and 10 of 168 in the French Arthroscopy Society series had grade II or higher cartilage injury. When these results are applied to isolated partial ACL tears, the influence of concomitant injury should be considered. Children and adolescents with open physes are discussed separately. Graft choice, tunnel technical detail, and rehabilitation protocols belong to Chapters 8, 9, and 11; this chapter discusses only those aspects that bear on treatment decision-making. Material drawn from complete tears, acute proximal-tear repair, cadaveric specimens, or the overall ACL-injured population is indirect evidence.
1. Three Populations Covered by "Partial Tear"
What clinicians call a partial tear does not refer to the same population across sources.
The first population is the knee whose MRI report reads "partial tear," "signal abnormality," or "partial fiber discontinuity," yet which is stable on examination. The 2023 ACL Study Group questionnaire sent to 135 active knee surgeons used such a case: a high-school athlete with an acute sport injury, MRI showing intraligamentous edema, normal range of motion, and negative Lachman and pivot-shift tests. Of 113 respondents (84%), 92% chose nonoperative management and 6 (5.4%) chose surgery[1]. Prognostic data for this population are the sparsest, because almost no one undergoes arthroscopy solely for diagnosis.
The second population is the knee with arthroscopically confirmed estimated fiber disruption of 25%–75%. Natural-history studies of the 1980s and 1990s all used this definition; the representative series is Noyes' 1989 prospective cohort: acute hemarthrosis knees underwent arthroscopy within six weeks of injury, and only knees whose residual fibers tightened under probe traction, resisted anterior tibial translation, and had a negative pivot shift were included, excluding disruption greater than 75%[2]. The French Arthroscopy Society's 2012 systematic review pooled 12 such studies and reported 436 cases, with inclusion defined as arthroscopic fiber continuity of 25%–75%[3]; the review's pooled headcount disagrees with its own tables—see the data note in Section 3.
The third population is the knee that presents with instability, is suspected preoperatively of a partial tear, and is found at arthroscopic exploration during reconstruction to retain one bundle. The French Arthroscopy Society's 2007 prospective multicenter study of 418 cases classified arthroscopic findings into four types: complete ligament disappearance 50%, posterolateral (PL) bundle retained 16%, stump healed to the posterior cruciate ligament (PCL) 23%, and anteromedial (AM) bundle retained 11%. Probe assessment rated residual-bundle mechanical quality as good in 17%; the proportion of good quality was 70% in the PL-retained group, 27% in those healed to the notch roof, and 13% in those healed to the PCL[4]. Among patients who need reconstruction, knees with one intact bundle are fewer still: of 156 reconstructions in Seoul, only 11 (7%) had one intact bundle (PL intact in 10, AM intact in 1), and another 35% had continuous remnant fibers that offered no resistance under the probe and could not be retained as a functional bundle[5]. Surgical data are most abundant for this population, but these patients have already been selected once by instability and cannot be used to estimate whether those with an MRI "partial tear" and a stable examination will later develop instability.
Definitions have evolved accordingly. Noyes defined by tear proportion[2]; DeFranco and Bach proposed a functional definition: Lachman asymmetric to the uninjured side, pivot shift negative under anesthesia, KT-1000 side-to-side difference within 3 mm, plus arthroscopic evidence, and stated explicitly that "a positive pivot shift, of whatever grade, is treated as functional insufficiency"[6]; the French Arthroscopy Society in 2010 proposed an arthroscopic definition—continuous fibers from tibial to femoral insertion—and advocated final diagnosis by arthroscopy while making clear that arthroscopy solely for diagnosis is not recommended[4]. Sonnery-Cottet and Colombet in 2016 combined four items: positive Lachman with a firm endpoint, small side-to-side laxity difference, MRI intraligamentous high signal, and arthroscopic partial tear[7]. The shared trend is to shift attention from tear proportion to residual-fiber function; treatment decisions likewise rest chiefly on residual-fiber function.
2. Clinical Assessment of Residual-Bundle Function
2.1 Bundle Division of Labor and Correspondence with Examination
The two bundles assume their principal roles over different ranges of flexion; this is the biomechanical basis for inferring which bundle is injured from the examination, and it also defines the limits of that inference. Cadaveric work shows that neither bundle is isometric: the AM bundle tightens in flexion and the PL bundle tightens near extension[8]; under a 134 N anterior load, the PL bundle carried a greater in situ force in full extension (67 ± 30 N) than the AM bundle (48 ± 16 N); by 30° of flexion the AM bundle dominated (81 ± 17 N versus 34 ± 23 N), and at 60° the AM bundle reached 90 ± 17 N[9]. Single-bundle sectioning experiments correspond: after AM section, anterior translation at 60° and 90° of flexion rose from 7.1 mm and 6.7 mm to 15.9 mm and 12.7 mm, and under a combined rotational load simulating the pivot shift anterior translation rose from 3.3 mm (0°) and 5.3 mm (30°) to 4.1 mm and 6.3 mm, not reaching statistical significance (P = .08); after PL section, anterior translation at 30° rose from 8.2 mm to 14.9 mm, and under combined rotational load to 9.8–11.7 mm[10]. These experiments are acute sharp sectioning in about 10 cadaveric specimens each and do not include elongation or degeneration of residual fibers.
The clinical picture inferred from this is that isolated AM tear presents with increased anterior drawer in flexion while the Lachman may be nearly normal and the pivot shift may be negative; isolated PL tear is the reverse—positive pivot shift with a possibly negative anterior drawer[8][11]. The outpatient findings described by Siebold and Fu are consistent: symptomatic AM tear presents with anterior instability, anterior drawer 1+, KT-1000 side-to-side difference 2–4 mm, Lachman 0–1+, pivot shift 0–1+; symptomatic PL tear presents with rotational instability during pivoting sports, no problem with walking or straight-line activity, pivot shift 1+, anterior drawer and Lachman 0–1+, KT-1000 side-to-side difference 1–3 mm[12]. Both papers by Petersen and Zantop and by Siebold and Fu are experiential summaries; Petersen himself wrote that clinical studies validating the correspondence between these signs and bundle identity did not then exist[11]. Dejour's 2013 series of 300 cases does not support correspondence between bundle identity and examination: AM-retained and PL-retained groups did not differ in Lachman, pivot shift, or stress-view laxity[13]. A more fundamental limit comes from cadaveric work: after AM section alone, three experienced examiners judging blindly were correct in only 13%, and 93% of errors were a judgment of intact; KT-1000 anterior translation rose by only 1.3 mm (not statistically significant), whereas complete section increased it by 5.2 mm[14]. What the examination can identify is the knee whose residual bundle is already insufficient; when residual-bundle function is still adequate, examination findings cannot be distinguished from those of a normal knee.
2.2 History and Physical Examination
The typical history of partial tear is injury during pivoting sport in a young person, with a relatively low-energy injury mechanism, mild subsequent symptoms, and little recurrent instability, so that presentation is late. In French Arthroscopy Society material, the mean interval from injury to presentation for partial tears was 5–7 months, versus more than 12 months for complete tears[7]; in Dejour's 300 cases, the mean interval from injury to surgery was 26 months for complete tears, 6.5 months for PL retention, 5 months for AM retention, and 19 months for healing to the PCL[13]. Late-presenting partial tears are often discovered only after a new twisting injury.
The Lachman test observes the amount of anterior translation and the endpoint. A firm endpoint indicates that fibers still take load; a soft endpoint indicates that residual fibers have ceased to function. Dejour's 300-case arthroscopic typing comparison (outpatient examination) showed Lachman +2 (anterior translation >5 mm or no firm endpoint) in 99% of complete tears and in only 32.6% of all types of partial tear; pivot shift +2 or +3 in 86.4% of complete tears and 23.6% of partial tears; conversely, pivot shift 0 or +1 in 76.4% of partial tears and only 13.5% of complete tears[13]. In the same team's concurrent 177 cases from Grenoble and Lyon (examined both in clinic and under anesthesia, taking the higher grade), pivot shift +2 or +3 identified complete tear with sensitivity 82.2% and specificity 87%[15]. Among these tests the pivot shift has the highest discriminative power, but examination cannot separate the subtypes of partial tear (AM retained, PL retained, healed to the PCL)[13][15].
Examination under anesthesia can reveal a pivot shift masked by muscle guarding when the patient is awake: material cited by DeFranco gives awake pivot-shift sensitivity of 24% and under-anesthesia sensitivity of 92%[6]; the French Arthroscopy Society called the pivot shift under anesthesia the principal global test of residual-bundle functional status[4]; all grades in Kocher's pediatric series were obtained under anesthesia[16]; Sonnery-Cottet's 2009 series listed absence of examination under anesthesia as a limitation of its own[17].
2.3 Instrumented Laxity
The value of instrumented measurement is that it yields a number that can be compared at follow-up; its drawback is that each instrument, each flexion angle, and each applied force has its own reading and the readings are not interchangeable.
Dejour used Telos stress radiographs (15 kg) to measure the side-to-side difference in medial-plateau anterior translation: complete tear 9.1 ± 3.4 mm, all types of partial tear 5.2 ± 2.9 mm; by residual-bundle function, functional partial tear 4.4 ± 2.4 mm (median 4 mm) and nonfunctional 7.0 ± 2.5 mm (median 6 mm)[13]. Three combinations followed: pivot shift 0 or +1 and side-to-side difference <4 mm identified a functional remnant with sensitivity 0.76 and specificity 0.90; positive pivot shift and side-to-side difference 4–9 mm identified a nonfunctional remnant with sensitivity 0.56 and specificity 0.92; positive pivot shift and side-to-side difference >9 mm identified complete tear with sensitivity 0.88 and specificity 0.96[13]. These three combinations judge whether a patient already planned for surgery currently has a functional remnant; the study did not follow whether they predict later complete tear[13]. The same school's 177-case results were similar (Telos 15 kg at 20° of flexion; Rolimeter measured both in clinic and under anesthesia, taking the maximum): Telos side-to-side difference was 7.4 ± 4.3 mm for complete tear and 4.0 ± 3.3 mm for partial tear; Telos >5 mm plus pivot shift +2 or +3 identified complete tear with sensitivity 88% and specificity 94.6%. Telos side-to-side difference rose stepwise with pivot-shift grade—1.2 mm, 4.3 mm, 7.3 mm, and 10.4 mm for grades 0, +1, +2, and +3—whereas Rolimeter showed no correlation with pivot-shift grade[15]. These thresholds come from one school, one instrument, and one applied force, all in patients already decided upon for surgery; with other instruments or loading conditions, only the numerical range can be referenced, not used as diagnostic cutoffs.
Rolimeter's 4 mm is often treated as a partial-tear criterion. The Lyon team's 2019 nonoperative cohort used "Rolimeter side-to-side difference ≤4 mm and negative pivot shift" as one inclusion criterion; entrants had a mean side-to-side difference of 2.6 mm (0–4 mm), with 11 exactly at 4 mm[18]. In that study this figure was an inclusion criterion, not a diagnostic cutoff; the same team's 2009 surgical series used ≤6 mm plus a delayed firm endpoint to suggest partial tear, with means of 4.8 mm in the partial-tear group and 7.5 mm in the complete-tear group[17]. The chief problem with the KT-1000 is false negatives: material cited by Sonnery-Cottet and Colombet shows a 50% false-negative rate for the KT-1000, equally among complete tears[7].
GNRB data must distinguish inventor reports from independent validation. The inventors reported that a side-to-side difference of 1.5 mm at 134 N identified partial tear with sensitivity 80% and specificity 87%, but 14 of their 24 partial-tear cases were lax scarred ligaments; the Methods state a loading range of 0–250 N, ROC analysis used 134 N, and the Abstract's wording on force is unclear[19]. Rouen's independent study tested this threshold in 157 arthroscopy patients of various indications: for arthroscopic AM- or PL-retained partial tears, Telos, Lerat, and GNRB side-to-side differences at every force level from 89 to 250 N did not differ from those of normal ligaments (at GNRB 250 N: normal 0.93 mm, the two partial-tear types 1.08 mm and 1.03 mm, healed to PCL 1.45 mm, complete tear 4.23 mm), so ROC analysis excluded the partial-tear group outright[20]. A Paris series of 139 cases gave a cutoff between complete and partial tear: 2.5 mm at GNRB 250 N, sensitivity 84%, specificity 81%, AUC 0.89, but 30 of that study's 42 partial tears were enrolled because low laxity was a condition for nonoperative treatment, so the threshold carries circular reasoning, which the authors themselves list as the main bias[21]. Taken together, the three studies make a clear point: instruments can separate complete tears from knees whose fibers still restrain anterior translation, but cannot separate a functional partial tear from a normal knee.
Instrumented readings have two uses in clinical decisions. First, combined with the pivot shift before surgery: a negative pivot shift and a small side-to-side difference usually mean the remnant is still functional. Second, during nonoperative treatment, repeat measurement on the same instrument under the same conditions; change in the reading matters more than a single absolute value.
2.4 MRI Interpretation of Tear Extent and Bundle Identity
MRI reliably shows ligament injury and the status of the menisci and cartilage, but it is unreliable for distinguishing partial from complete tear and for identifying which bundle is involved. Data from 1.0–1.5 T scanners in the 1990s already made this plain: on blinded reading, the proportion of arthroscopically confirmed partial tears called abnormal was 62%, versus 94% for complete tears; only 19% of partial tears were correctly classified, versus 90% of complete tears[22]; three readers' sensitivity for partial tear was 0.40–0.75 (Abstract values; the lowest of six readings in Table 1 was 0.35) and specificity 0.62–0.89[23]; clinical MRI reports identified only 1 of 9 arthroscopic partial tears, calling 5 normal and 3 complete tears[24]. Three-tesla imaging has not changed the picture: an Antwerp prospective study of 172 cases reported sensitivity 77% and specificity 97% for partial tear, with 5 of 40 tears (13%) misclassified between complete and partial, and acute hematoma causing stable partial tears to be misread as complete[25]; the same team, reviewing 51 arthroscopically confirmed partial tears, found MRI called them partial tears in only 20%–47%, complete tears in 16%–23%, mucoid degeneration in 12%–27%, and normal in 18%–23%, with kappa between two readers of 0.48–0.56 and localization to a specific bundle in only 6%[26]. In Dejour's 300 cases, MRI showing fiber absence or severe distortion was present in 96% of complete tears and 73% of all types of partial tear, a difference that was not statistically significant, and MRI could not localize to the AM or PL bundle[13]. Sonnery-Cottet's 2009 review of preoperative MRI in 174 cases failed to identify a single partial tear[17]. In Kocher's pediatric series, radiologists read 32/45 arthroscopically confirmed partial tears as partial tears, another 10 as complete tears, and 3 as no ligament injury, for sensitivity 71%[16].
MRI does have value in two respects. The first is bundle-by-bundle judgment of whether a remnant exists: Seoul 1.5 T imaging including an oblique coronal sequence read AM-bundle status with 91% accuracy and PL-bundle status with 78%, but MRI within 6 weeks of injury tended to overestimate PL injury[5]; another group in the same city reported coronal reading of remnant presence with sensitivity about 75%–80% and specificity about 95%[27]. The second is reframing the reading task: a Chicago series of 238 cases divided axial images into six categories and changed the reading target from partial versus complete tear to stable versus unstable, grouping normal ligaments with stable partial tears and unstable partial tears with complete tears, yielding sensitivity 100% and specificity 96%; the "isolated bundle sign" (only a single fiber bundle far smaller than normal along the ligament course) was present in 6 cases, all unstable partial or complete tears[28]. That study had only 8 unstable partial tears, so the exact figures should not be transplanted, but stratifying imaging by functional stability better matches the needs of treatment decisions.
Author's view and practice: after an MRI report of "partial tear," the next step in assessing residual-bundle function is physical examination, examination under anesthesia, or instrumented measurement—not another MRI. The most useful MRI information at this point is the status of the menisci and cartilage, which determines whether early arthroscopic surgery is needed and also shapes what will be found at later surgery if the condition progresses. Early post-injury MRI overestimates injury because of hematoma, especially in the PL bundle[5][25].
2.5 Arthroscopic Exploration and Probe Assessment
Arthroscopic exploration is the final criterion, but what it judges is whether fibers are present and under tension, not whether they will tear later. The French Arthroscopy Society practice is first to observe morphology, confirm that both the tibial and femoral ends of the residual fibers lie within the anatomic insertions, then tension the fibers in the Cabot (figure-of-4) position and test resistance with a probe[4]. Dejour classified residual fibers as "functional" (resisting further elongation under probe traction) or "nonfunctional" (able to be elongated markedly)[13]. The AM bundle is explored at 70°–90° of flexion and the PL bundle in the figure-of-4 position; from a standard anterolateral portal the PL bundle is hidden behind the AM bundle, and isolated PL tears are easily missed[11][12][17]. Petersen particularly notes one easy misjudgment: at 90° of flexion the PL bundle is normally lax, and laxity is not equivalent to tear—tightening in extension indicates that it is intact[11].
Proportions among arthroscopic findings reflect how common partial tears are. In Sonnery-Cottet's 2009 consecutive series of 174 reconstructions, partial tears accounted for 21.2% (37 cases), of which PL tears were 8.6% (15) and AM tears 12.6% (22); all 15 PL tears were at the femoral insertion[17]. In Dejour's 300 cases, partial tears accounted for 41%, with PL retained 22%, AM retained 7%, and healed to the PCL 12%[13]. In a Pittsburgh series of 121 cases operated within 120 days of injury, both bundles were completely torn in 75% and one bundle in 25%; the PL bundle showed no tear in only 12%, the AM bundle was intact in none, and in 44% the two bundles tore at different sites[29]. In Ochi's Hiroshima series of 169 cases, 17 (10%) met criteria for augmentation reconstruction (AM 13, PL 4)[30]. All these proportions come from surgical populations rather than injury populations and, depending on each center's requirements for a "functional bundle," range from 7% to 41%.
Arthroscopy also reveals a group that needs separate handling: the stump healed to the PCL, looking like a continuous ligament. This type accounted for 23% of the French Arthroscopy Society's 418 cases, with good mechanical quality in only 13%[4]; in Dejour's material its stress-view laxity lay between complete tear and true bundle retention, which the authors interpreted as pseudostability[13]. A San Diego series of 48 complete-tear reconstructions mapped scar morphology to mechanics: stump scar to the PCL 38%, to the notch roof 8%, to the lateral wall of the notch 12%, and no identifiable ligament tissue 42%; after stump resection, KT anterior translation increased by 1.3 mm, 3.4 mm, 4.3 mm, and −0.2 mm, respectively—only scar that crossed the joint to the femur made a measurable contribution to anterior stability[31]. That study's subjects were a complete-tear population, and later Hiroshima investigators noted that unrecognized partial tears may have been mixed in[32].
2.6 Change in the Remnant Over Time
The remnant changes with time. Histologic staging of the stump after complete tear provides background: the first weeks after injury are an inflammatory phase; 3–8 weeks see regeneration of the epiligament; 8–20 weeks are a proliferative phase with cellular and vascular density peaking at 16–20 weeks; and remodeling matures at 1–2 years. In 23 specimens at no time point was there tissue bridging the two ends; a synovial layer containing contractile cells formed on the stump surface, which the authors thought might contribute to stump retraction[33]. These specimens came from complete-tear reconstruction patients and cannot be applied directly to the uninjured bundle in a partial tear, but they explain Sonnery-Cottet's 2009 arthroscopic findings: the torn PL bundle retracted toward the tibia over time, the degree of retraction correlating with the interval from injury to surgery; three cases operated within weeks of injury had mild extension loss, and at arthroscopy the torn bundle was seen to impinge on the notch roof in extension—the mechanism the authors proposed for a cyclops-like picture after partial tear[17]. Stumps adherent to the PCL still contained Ruffini and Pacini mechanoreceptors 4 months to 3.5 years after injury (Results: 12/12 cases; the Abstract says 15 cases and the table lists 12—see Section 9.1), whereas free mushroom-like stumps had almost none[34]. The rationale that "preserving the remnant may help proprioception" rests on this evidence, which likewise comes from a complete-tear population.
Nakamae (Hiroshima, 2010) used navigation to measure laxity before and after remnant resection intraoperatively; the population was complete tears (stumps bridging the PCL or notch, 30 cases)—an adjacent population: in those operated within one year of injury, 30° anterior laxity increased by 2.22 mm after remnant resection, versus only 0.17 mm beyond one year (P < .01); the remnant made no measurable contribution to rotational stability[32]. The KT-2000 side-to-side differences reported in the same study are useful for reference: PL partial tear 3.28 ± 1.77 mm, AM partial tear 2.97 ± 1.14 mm, and three types of complete tear 5.69–6.77 mm[32].
Time also affects the pivot shift. Preoperative data from the French Arthroscopy Society's 168 AM-bundle reconstructions showed that pivot-shift grade correlated with laxity (P < 0.04) and worsened as the interval from injury to surgery lengthened; the authors inferred that rotational laxity deteriorates over time[35]. On that inference, the same knee can be stable on examination one month after injury and show a positive pivot shift a year later without contradiction.
Table 1. Preoperative tests of residual-bundle function and their decision thresholds
| Test | Suggests a functional remnant | Suggests a nonfunctional remnant or complete tear | Source and limits |
|---|---|---|---|
| Lachman | Firm, delayed endpoint; +1 | No firm endpoint; +2 (99% of complete tears)[13] | 300 surgical cases; subtypes of partial tear not separable |
| Pivot-shift test | 0 or +1 (76.4% of partial tears; outpatient examination)[13] | +2 or +3 (86.4% of complete tears)[13]; sensitivity 82.2%, specificity 87% (higher of outpatient and under-anesthesia grades)[15] | Awake sensitivity 24%, under anesthesia 92%[6]; the two study populations may overlap |
| Telos stress view (15 kg) | Side-to-side difference <4 mm plus pivot shift 0/+1: sensitivity 0.76, specificity 0.90[13] | 4–9 mm plus positive pivot shift suggests nonfunctional remnant (sensitivity 0.56, specificity 0.92)[13]; >9 mm plus positive pivot shift: sensitivity 0.88, specificity 0.96[13]; >5 mm plus pivot shift +2/+3: sensitivity 88%, specificity 94.6%[15] | Same school, same applied force, all patients planned for surgery; judges present function, not followed for prediction of progression |
| Rolimeter | ≤4 mm and negative pivot shift (nonoperative cohort inclusion criterion)[18]; <6 mm plus delayed firm endpoint[17] | Complete tear 7.5 mm (median 7 mm)[17] | Readings in 1 mm increments; no correlation with pivot-shift grade[15][36] |
| GNRB | At 250 N, partial tear 1.0–1.1 mm, no different from normal 0.93 mm[20] | At 250 N, ≥2.5 mm favors complete tear (sensitivity 84%, specificity 81%)[21]; complete tear 4.23 mm[20] | Inventors' 1.5 mm / 134 N threshold not reproduced by independent work[19][20] |
| KT-1000 / KT-2000 | Side-to-side difference ≤3 mm and negative pivot shift[6]; partial tear 2.97–3.28 mm[32] | ≥5 mm is one of Noyes' criteria for functional insufficiency[2]; complete tear 5.69–6.77 mm[32] | False-negative rate up to 50%[7]; cadaveric single-bundle section increased translation by only 1.3 mm[14] |
| MRI | Continuous ligament, elliptical axial cross section[28] | Fiber absence or cloud-like mass (96% of complete tears)[13]; isolated-bundle sign, posterior displacement of the posterior horn of the lateral meniscus[22][28] | 51-case retrospective series called partial tear in only 20%–47%, kappa 0.48–0.56, bundle localization 6%[26]; prospective sensitivity 77%[25], pediatric series 71%[16]; early hematoma overestimates[5][25] |
| Arthroscopic probe (figure-of-4) | Insertions anatomic, resistance to traction[4][13] | Can be elongated; healed to the PCL (good quality in only 13%)[4] | Judges present tension, not future tear |
3. Natural History of Nonoperative Treatment
Table 2 summarizes eight original natural-history studies and the French Arthroscopy Society systematic review. Population definitions, follow-up length, and outcome criteria differ among studies; these figures should not be pooled and can be read only by population.
Table 2. Natural-history studies of nonoperative treatment for partial ACL tear
| Study | Population and confirmation | N | Follow-up | Progression or functional insufficiency | Reconstruction during follow-up | Return to preinjury sport level | Caveats |
|---|---|---|---|---|---|---|---|
| Sandberg 1987[37] | Acute hemarthrosis, stable under anesthesia, arthroscopically confirmed ~7 days after injury; interstitial hemorrhage 15, AM 4, PL 10; untreated | 29 | Mean 36 months (12–60) | Unstable signs in 18/29; positive pivot shift 3/29, all in the PL group | Not reported | All maintained sports activity | Half were interstitial hemorrhage only; 4 reinjured patients were excluded |
| Fruensgaard 1989[38] | Examination under anesthesia plus arthroscopy within 2 weeks; ≥1/3 of fibers tense under the probe; plaster 6 weeks | 41 | Mean 17 months (12–22) | Static anterior instability 21/41, of whom 14 had a positive pivot shift; Stryker 30-lb anterior translation: unstable group injured knee 8.4 mm, contralateral 4.7 mm; stable group injured knee 4.5 mm (absolute translation, not side-to-side difference) | 0 | Unstable group Tegner 6.9→4.8; stable group 6.1→5.8 | At least 18 cases involved the MCL (14 partial, 1 with partial PCL injury, 3 complete tears sutured)—not an isolated population |
| Noyes 1989[2] | Arthroscopic confirmation within 6 weeks; ≤75% tear, remnant resisting anterior translation, negative pivot shift | 32 (84% of 38 followed) | Mean 67 months (24–110) | 12/32 (38%); ≤1/4: 2/17; 1/2: 4/8; 3/4: 6/7 | 2 reconstructions; another 2 had repeat arthroscopy showing absent ligament | Same level without problems: functional group 20%, insufficient group 0 | Meniscal tear at index arthroscopy in 53%; most first reinjuries after 2 years, but authors could not tell whether insufficiency preceded or followed reinjury |
| Buckley 1989[39] | Arthroscopic 10%–75% tear within 6 weeks, laxity ≤5 mm, negative pivot shift, no other ligament injury | 25 | Mean 49 months (8–88) | Symptoms in 84%; giving way in 52% (7 only during cutting sports) | 2/25 (8%) | 44% | Military population; partial meniscectomy in 52%; tear proportion unrelated to scores |
| Bak 1997[40] | Arthroscopic confirmation within 4 weeks; ≤75%, remnant under tension, no concomitant injury | 56 | Median 5.3 years (2.0–12.7) | 6/56 (11%) progressed and reconstructed in the first year; loose definition 23%; of 34 examined, negative pivot shift 56%, Stryker ≤2 mm 71%, maximum 4.5 mm | 11% | Of 34 with activity grading, 10 (~30%) kept preinjury level; cutting sports 27→8 | Telephone follow-up only in 16; activity decline may mask ligament insufficiency |
| Messner 1999[41] | Arthroscopic confirmation within 10 days; ≤50% injury, anterior drawer under anesthesia ≤1+; all had concomitant MCL/meniscus/fracture injuries; 3 single-bundle sutures | 22 | Mean 20 years (18–25) | At 20 years, positive Lachman 10/21, positive pivot shift 1/21 | 0 during observation | Tegner 7→5; 5 still at preinjury level | Osteoarthritis grade 2–3 in 4/21; all had concomitant injury and 3 had a bundle sutured—cannot represent >50% tears |
| Kocher 2002[16] | ≤17 years; Lachman/pivot shift grade A or B under anesthesia; arthroscopically confirmed; 27 open physis, 18 closed; 9 with grade II MCL sprain | 45 | Mean 6.1 years (2.3–11.6) | Reconstruction 14/45 (31%); >50%: 9/17; PL-predominant: 10/20; pivot shift grade B: 5/5 | 31% | Not reported | Source of the recommendation not to reconstruct first when bone age ≤14 years |
| Fayard 2019[18] | <30 years, regularly active, delayed but firm Lachman endpoint, Rolimeter ≤4 mm, negative pivot shift, MRI without meniscal or cartilage injury; no arthroscopy | 41 | Mean 43 months (24–96) | 16/41 (39%), mean 20 months; ≤20 years OR 5.19; pivoting contact sport OR 6.29 | 13 already reconstructed, 3 awaiting surgery | Whole cohort 44%; ≤20 years 25% | Meniscal injury found in 8 of the 16 who progressed; authors acknowledge some entrants may already have been complete tears |
| French Arthroscopy Society systematic review 2012[3] | 12 studies of arthroscopically confirmed 25%–75% tears, 1976–1997 | Review reports 436 (sum of cases in the two tables 386) | Mean 5.2 years (1–15) | Review-reported values: clinical insufficiency 40.9% (11%–78%); positive pivot shift 26.3% | 8.1% (0–21%) | Review reports 52% (21%–60%); tables also show 79% and 100% | Pooling method not stated; totals cannot be verified; transcription of primary data erroneous; osteoarthritis not assessed |
Noyes' 1989 prospective cohort is the starting point for understanding natural history. Of 38 acute, arthroscopically confirmed, pivot-shift–negative partial tears with disruption of no more than 75%, 32 (84%) completed a mean 67 months (24–110 months) of follow-up; ages were 14–38 years, and 24 trained 4–7 days per week. Twelve knees (38%) progressed to functionally complete tears, judged by a positive pivot shift and/or a KT-1000 side-to-side difference of 5 mm or more. Three factors related to progression: arthroscopic tear proportion (≤1/4: 2 of 17 progressed, about 12%; 1/2: 4 of 8, 50%; 3/4: 6 of 7, 86%); already mildly increased anterior translation at first presentation (increase of one grade: 10/19 progressed; equal to the uninjured side: 2/13); and further twisting injury with giving way during follow-up (reinjury: 11/18 progressed; no reinjury: 1/14). Reinjury rates were 29% for quarter tears, 75% for half tears, and 100% for three-quarter tears; most first reinjuries occurred two years or more after the index injury; the insufficient group averaged 2.2 reinjuries and the functionally retained group 0.85; the authors stated that they could not determine whether insufficiency preceded or followed reinjury. Knees that did not progress were not entirely normal either: about half had symptoms and functional limitation during competitive or vigorous sport; both groups reduced their training intensity markedly, and 58% of the insufficient group and 20% of the functionally retained group continued to train with moderate or greater problems[2].
Thirty years later, the Lyon team narrowed the study population to those most intent on returning to sport: 41 patients under 30 years who trained regularly, had a delayed but firm Lachman endpoint, Rolimeter side-to-side difference ≤4 mm, negative pivot shift, and MRI without meniscal or cartilage injury, all managed first nonoperatively. At a mean follow-up of 43 months (24–96 months), 16 (39%) progressed to complete tear at a mean of 20 months (6–43 months); 12 were related to sport trauma (10 in pivoting contact sports). The odds ratio for progression was 5.19 for those ≤20 years (P = .037) and 6.29 for return to pivoting contact sport (95% CI 1.36–38.03; P = .026); the study detected no association of sex, initial Rolimeter laxity, or psychological readiness score with progression (the pivot shift was negative in all at entry, so it could not be assessed). Of the 16 who progressed, meniscal injury was found in 8 (13 already reconstructed, 3 awaiting surgery), including 4 medial meniscal ramp lesions. Among the 25 who did not progress, at final follow-up Tegner fell from 7.0 to 5.9 and IKDC from 96.0 to 85.7 (scores available in 23–24); only 18 of the whole cohort (44%) returned to their preinjury sport level, and only 5/20 (25%) of those ≤20 years; the proportion among nonprogressors alone was not reported[18]. The authors also noted that some entrants may already have been complete tears underestimated by examination and MRI[18].
In the three decades between these two studies, Danish and Swedish cohorts pointed in two different directions. Of 56 Copenhagen cases arthroscopically confirmed within 4 weeks with no concomitant injury, 6 (11%) progressed to complete tear and reconstruction within the first year; among the remaining 50 at a median 5.3 years, median Lysholm was 86 and 62% were good or excellent, with Tegner falling from 7 to 5. Of 34 with activity grading, only 10 (~30%) kept their preinjury activity level, and participation in cutting sports fell from 27 to 8; of the same 34 on examination, the pivot shift was negative in 56%, with glide in 13 and clunk in 2, and Stryker side-to-side difference was within 2 mm in 71% with a maximum of 4.5 mm[40]. The authors' reading was that those who abandoned high-load sport had good knee function, while the decline in activity itself may have masked ligament insufficiency[40]. Linköping's 22 cases provide the longest follow-up. These knees had arthroscopic injury ≤50% and anterior drawer under anesthesia of at most 1+; all had concomitant injuries (MCL, medial meniscus, tibial-spine fracture, and others; 9 underwent MCL repair and 3 single-bundle suture); 19 ACLs were not operated and 3 had single-bundle reattachment. At 20 years (18–25 years), none underwent ACL reconstruction during observation; median Lysholm was 96, positive pivot shift 1/21, positive Lachman 10/21. Of 21 radiographs, 4 showed grade 2–3 osteoarthritis, the most severe in a patient with severe MCL injury, meniscectomy, and continued high-level sport[41]. These data show that initially stable knees with injury of no more than half the ligament that actively reduced their sport level can go 20 years without reconstruction; that conclusion cannot be extended to tears of more than half or to knees with anterior translation already present at first presentation, nor extrapolated to mean lifelong freedom from reconstruction.
Two early studies offer different angles. Malmö's 29 cases were the earliest arthroscopic cohort, all untreated; after a mean of 3 years, 18 had unstable examination signs, but only 3 had a positive pivot shift—all in the PL-injury group (3/10)—and 3 of the 5 who complained of instability were precisely these 3; functional scores in all three groups were 94–96, and all maintained sports activity[37]. Horsens' 41 cases followed for 17 months showed static anterior instability in 21, with a positive pivot shift in 14; the unstable group's injured-knee Stryker 30-lb translation was 8.4 mm and the contralateral 4.7 mm, versus 4.5 mm in the stable group's injured knee; Tegner in the unstable group fell from 6.9 to 4.8; neither arthroscopic injury extent nor initial examination predicted which knees would become unstable[38]. Oakland Naval Hospital's 25 cases pointed the other way: tear proportion was unrelated to outcome (score 84 for ≤30%, 80 for >30%); 84% had symptoms at follow-up, but only 2 (8%) underwent reconstruction[39]. Neither Horsens nor Oakland was an isolated partial-tear population (Horsens had at least 18 MCL injuries; Oakland had partial meniscectomy in 52%), showing how "progression rates" move with population composition.
The French Arthroscopy Society's 2012 systematic review placed together 12 arthroscopically confirmed nonoperative studies from 1976–1997 (9 Level IV, 3 Level III; reported total 436 cases; mean age 28.6 years; mean follow-up 5.2 years): preoperative Lachman was positive in a mean of 49.7%, and the pivot shift was uniformly negative in the 5 studies that reported it; at follow-up, 40.9% (11%–78%) of knees were clinically ACL-insufficient, Lachman positive in 47.6%, pivot shift positive in 26.3% (5%–51%), pain reported in 54.3%, mean Lysholm 88.4, return to preinjury sport level 52% (21%–60%), reconstruction during follow-up 8.1% (0–21%), and secondary meniscectomy 7.2%[3]. The authors' conclusions included two points: those who limited their sport had good mid-term results, but a positive pivot shift appeared in a quarter of knees and progressing knees had more pain; for pivoting athletes, the surgical indication is the same as for complete tear[3].
Data note. The sum of the 12 studies in the review's two tables is 386, yet the text writes 436; a simple average of the insufficiency proportions by study is about 37.9% and does not yield the text's 40.9%; return to sport is written as 21%–60%, yet the tables include 79% and 100%; the review does not state its pooling method. Transcription of primary studies also disagrees with the originals in several places: Buckley's pain proportion of 64% is recorded as an insufficiency proportion and 25 cases as 21; Fruensgaard's 21 static instabilities are recorded as 21 positive pivot shifts; Bak's Lachman proportions and Noyes' reconstruction counts also disagree with the originals. The pooled values above can therefore be treated only as the review's reported values; numbers in Table 2 and in the body of this chapter follow the original cohorts[3].
These studies are from earlier decades, when reconstruction indications were stricter than today; the 8.1% reconstruction rate reflects the surgical threshold of that time, not of the present.
Pediatric and adolescent data come from Kocher's 2002 prospective cohort: 45 patients under 17 years with acute hemarthrosis, MRI signal change, Lachman and pivot shift grade A or B under anesthesia, and arthroscopically confirmed partial tears, all managed first without reconstruction, mean follow-up 6.1 years (2.3–11.6 years); 27 of 45 had open physes and 18 closed, 17 had 20 meniscal tears, and 9 had a grade II MCL sprain—neither a purely open-physis nor a purely isolated-injury population. Fourteen (31%) underwent reconstruction for instability and reinjury at a mean of 13.5 months after injury; all showed midsubstance complete tear at reconstruction. On univariate analysis, reconstruction rates were 53% (9/17) for tears >50% versus 18% (5/28) for ≤50%, 50% (10/20) for PL-predominant versus 16% (4/25) for AM-predominant, and 100% (5/5) for pivot-shift grade B versus 23% (9/40) for grade A; those reconstructed were older in both chronologic and bone age than those not; multivariate analysis left only tear >50% (P = .02) and PL predominance (P = .049); survival analysis identified older bone age, tear >50%, and PL predominance as time-dependent risk factors. Among the 31 not reconstructed, those with tear >50% or PL predominance had lower Lysholm, satisfaction, and Cincinnati scores[16]. The authors' recommendations were: bone age 14 years or under with a normal or near-normal examination—do not reconstruct first; ages 15–17—consider reconstruction; if arthroscopy has been done, recommend reconstruction for tear >50% or PL predominance[16]. Physeal status was not a significant factor in this cohort; the authors thought this might reflect inadequate power for a dichotomous variable[16].
First, the proportion progressing to complete tear in young active populations is around 30%–40%, whether in 1980s arthroscopic cohorts or 2010s MRI-plus-examination cohorts; Linköping-type cohorts that were initially stable, had injury of no more than half, and limited their sport had no reconstructions in 20 years, yet 4 of 8 half-tear knees in Noyes' cohort still progressed, so low risk cannot be judged from tear proportion alone. Second, progression concentrates in the young, those in pivoting sports, those with large tear proportions, and those with PL involvement; those with quarter tears or less who do not play pivoting sports progress less. Third, timing of progression has no regular pattern: Copenhagen's 6 all occurred in the first year, Lyon's mean was 20 months with the latest at 43 months, and most first reinjuries in Noyes' cohort came after two years, so a normal three-month revisit does not mean progression will not occur later—follow-up should continue beyond return to sport. Fourth, return to preinjury sport level in these cohorts is usually 30%–50%; activity level also falls among nonprogressors, residual pain is common, and populations with good functional scores are often those who actively lowered their sport level. Fifth, when progression occurs, meniscal injury may already be present in up to half—the principal cost of waiting.
4. Nonoperative Protocol, Follow-up Visits, and Signals That Change the Plan
4.1 Rehabilitation Protocol
There are no controlled studies of nonoperative protocols for partial tear. The Lyon team's standard protocol is: crutches and weight-bearing for the first 6 weeks without a brace, restoring range of motion and progressive quadriceps strength; from 6 weeks to 3 months, strengthen the quadriceps and hamstrings and introduce neuromuscular training; after 3 months allow nonpivoting sport, and after 4 months pivoting sport[18]. Noyes' "4-4-4-4" protocol of that era divided four 4-week blocks, with partial weight-bearing for the first 4 weeks and gradual return to sport within 16 weeks, avoiding terminal-extension resistance in the 0°–30° flexion range; after comparison the author found no benefit of plaster immobilization over splinting with early motion[2]. DeFranco and Bach used neither immobilization nor bracing and noted that there is no evidence bracing prevents progression of partial tear to complete tear[6]. In the ACL Study Group questionnaire, among surgeons choosing nonoperative care, 75% did not restrict weight-bearing and 59% used no brace; for return-to-sport clearance, 87% relied on functional testing, 40% on time since injury, 33% on side-to-side laxity difference, and 26% on imaging; of those using time, 56% chose 3 months after injury and 22% chose 4–6 months; for specific functional-test items, 87.8% used performance tests, 77% assessed strength, 76% assessed swelling, and 52% required a painless Lachman[1].
Two bodies of material on nonoperative care of complete tears can be borrowed, but their populations had KT-1000 side-to-side differences ≥3 mm and were complete tears. Delaware's screening protocol, applied about 4 weeks after injury once swelling had resolved and range of motion had returned, used four pass criteria: overall knee function score ≥60%, no more than one episode of giving way since injury, activities-of-daily-living scale ≥80%, and 6-meter timed single-leg hop reaching 80% of the uninjured side; 42% of 93 passed, and of 28 who passed and chose nonoperative care, 22 (79%) returned to their preinjury level that season without giving way; outcomes in those who failed screening were not followed[42]. A 5-week progressive training program from Oslo and Delaware included 10 supervised sessions: 3–4 sets of 6–8 repetitions of maximal-effort strength exercises, single-leg hop plyometrics, balance training, and 10 perturbation sessions. Applied to 100 complete tears within 90 days of injury, absolute quadriceps torque on the injured side rose 8.2%–11.1%, hopping 5.5%–9.5%, and subjective IKDC from 69.7 to 77.2. Adverse events occurred in 4/98 (about 4.1%; the original writes 3.9%), all swelling and pain after plyometrics; no one had giving way during training, and 1 had giving way on a crossover hop test after the program ended[43]. The Panther consensus (23 experts voting, evidence mainly from general ACL injury) provides a framework equally applicable to partial tear: first a period of progressive rehabilitation to improve dysfunction, then a decision on surgery (100% agreement); those still unstable in desired activities after rehabilitation are referred for surgery (100%); surgery is preferred for those wishing to return to jumping, cutting, and pivoting sports, whereas those who perform only straight-line activity may accept nonoperative care (both 100%); the consensus cites Fayard's 39% progression rate and half with meniscal injury as supporting evidence for "refer for surgery if still unstable after rehabilitation," but did not vote separately on partial tear[44].
4.2 Follow-up Visits and Signals That Change the Plan
Sonnery-Cottet and Colombet's flow chart divides patients with a positive Lachman but firm endpoint and MRI signs of ligament injury into three groups: those with side-to-side laxity difference <4 mm and a negative pivot shift receive nonoperative care, with examination and laxity rechecked every 3 months; those with difference <4 mm but a positive pivot shift undergo surgery if very young, if meniscal injury is extensive, or if sport demand is high, and otherwise are observed with follow-up first; those with difference >4 mm who work in high-risk occupations or play pivoting sports undergo surgery, with technique chosen by arthroscopic findings; during nonoperative care, conversion to surgery occurs once the difference exceeds 4 mm and/or the pivot shift becomes positive[7].
Data note. The body of that review disagrees with its flow chart: the text writes the second group as "side-to-side difference <4 mm, with or without locking," and says groups 2 and 3 both undergo surgery; Fig. 10 of the flow chart, however, keeps a first-observe branch for the second group. This chapter follows the flow chart, because it connects with the authors' own "every-3-months revisit" plan[7].
The value of this algorithm is not the specific 4 mm figure but that it specifies what to recheck, how often, and what result triggers a change. Noyes recommended longer follow-up: every 6 months for 5 years after injury in active patients, because reinjury often comes after two years[2].
Author's view and practice: a firm Lachman endpoint, negative pivot shift or only a slight glide, no further giving way since injury, and no regular pivoting contact sport allow deferred surgery; those who wish to return to ball sports but are willing to rehabilitate for three months and then reassess may also be observed first. The three-month revisit assesses four items: no pain and no recurrent swelling; normal range of motion; no worsening of Lachman or pivot shift; and ipsilateral strength, single-leg hop, and deceleration–cutting tests at target. Three months is only the start of assessment; those who do not meet test targets continue training. Meanwhile, any further twisting injury or giving way warrants immediate return, without waiting for three months. Any of the following four situations warrants earlier reassessment and a revised plan. Three of them indicate that the remnant is already insufficient to maintain stability, and most who still wish to return to ball sports should accept reconstruction: conversion of the pivot shift from negative to positive; a clear increase in the side-to-side laxity difference measured on the same instrument under the same conditions; and inability, after three months of training, to resume target sport because of instability. The fourth is new meniscal symptoms: these require prompt clarification of meniscal and remnant status but do not themselves prove that the remnant has failed—the Copenhagen cohort included knees with new meniscal injury whose ACL had not retorn at arthroscopy[40].
The single new piece of information most likely to change the plan is, in clinic, examination under anesthesia plus instrumented measurement, and in the operating room, remnant tension under the probe. Repeat MRI can assess the menisci and cartilage but cannot assess residual-bundle function.
5. Surgery I: Selective Single-Bundle Reconstruction with Remnant Preservation
5.1 Rationale and Conditions for Remnant Preservation
Four reasons are given for preserving the remnant: residual fibers share load early in graft healing; residual tissue's blood supply and synovium favor graft incorporation; mechanoreceptors in the remnant may preserve proprioception; and the intact bundle is a reference for tunnel placement[4][12][45]. These reasons are biologically plausible, but the French Arthroscopy Society in 2010 also stated that studies comparing "preservation of an effective remnant" with "preservation of an ineffective remnant" are lacking, and whether these theoretical advantages translate into better clinical outcomes is unproven[4].
Centers agree on the intraoperative conditions for retaining the remnant: both the tibial and femoral ends of the other bundle lie within the anatomic insertions, the course is normal, and there is tension under the probe; a lax, scarred remnant, one healed to the PCL forming a false continuity, or one that obscures the femoral insertion and interferes with tunnel placement is cleared, and standard reconstruction is performed instead[4][7][12]. Quantification of this requirement differs by center: Hiroshima requires that the remnant connect femur to tibia rather than to the PCL and exceed one third of normal diameter[30][46]; Seoul requires anatomic femorotibial bridging, thickness greater than 50% of one bundle, and elongation under probe traction of less than 5 mm[27]; Pujol's randomized study made "arthroscopic visualization of a PL bundle with intact insertions" the final inclusion criterion and excluded all preoperative suspects who did not meet it at arthroscopy[47].
5.2 Results
Table 3. Selective single-bundle reconstruction with remnant preservation: principal studies
| Study | Design and population | N | Follow-up | Laxity | Function | Complications and failure |
|---|---|---|---|---|---|---|
| French Arthroscopy Society 2012[35] | 11-center retrospective; AM reconstruction preserving PL; preoperative pivot shift positive or marked 41%; 10 with grade II+ cartilage injury | 168 | 26 months | 5.5→1.1 mm | IKDC 63.7→90.5; objective A/B 92% | Cyclops lysis 9; failure 5 (3%); residual pain 13% |
| Pujol 2012[47] | Multicenter randomized; selective AM reconstruction vs standard single-bundle reconstruction | 29 vs 25 | 1 year | 1.24 vs 1.87 mm (P = 0.03) | IKDC 86.2 vs 85.7; Lysholm 90.9 vs 91.8 | Cyclops lysis 1; power <80% |
| Demirağ 2012[48] | Single-center randomized (intraoperative randomization); arthroscopic remnant bridging femur–tibia, integrity >half; PL torn, AM intact; remnant-preserving augmentation vs remnant-clearing transtibial single-bundle reconstruction | 20 vs 20 | 24.3 months | No instrumented measurement; final Lachman and pivot shift no difference | IKDC and Lysholm improvement no difference (both ~86 postoperatively) | Cyclops 1 (augmentation group); grade 1 arthrofibrosis 7 each; less tibial-tunnel enlargement in augmentation group; injury-to-surgery 2.3 vs 8 months |
| Sonnery-Cottet 2010[49] | Single-surgeon series; of 256 cases, 14% had good PL tension in figure-of-4 | 36 (33 assessed) | 24 months | 4.8→0.8 mm | Objective IKDC A 73%, B 24% | Cyclops lysis 2 (both 8 mm grafts, large remnants); traumatic rupture 1; suspected "wrong-bundle" 1 |
| Adachi 2000[50] | Nonrandomized comparison; chronic ACL insufficiency with bridging remnant (diameter 1/3–1/2), Lachman 100% positive; augmentation group 9 with MCL injury | 40 vs 40 | 3.2 years | 5.3→0.7 mm vs 6.0→1.8 mm (P < 0.05) | Lysholm 94.8 vs 93.8; position-sense error 0.7° vs 1.7° | Only 40 of 57 analyzed; position sense without preoperative values |
| Ochi 2009[51] | Case series; mix of single-bundle partial tears and cross-healed remnants | 45 | 2.9 years | KT-2000 3.4→0.5 mm | Lysholm median 75→100 | Failure not reported |
| Nakamae 2014[46] | Nonrandomized three groups, all with second-look arthroscopy; augmentation group lower preoperative laxity (3.6 vs 5.2/5.4 mm) | 73 vs 82 double-bundle, 61 single-bundle | 29 months | 0.4 vs 0.9 vs 1.3 mm (vs single-bundle P = 0.013) | Lysholm and pivot shift no difference; good synovial coverage 82% vs 61%/62% | Reinjured patients already excluded before analysis |
| Buda 2006[52] | Case series; Lachman ≤1+, pivot shift ≤trace, one healthy bundle at arthroscopy | 47 | 5 years | KT-2000 0–3 mm in 41/47 | IKDC good/excellent 95.7%; Tegner 6.8→6.1 | No rerupture; reoperation 4 (hardware removal 2, lateral release 1, meniscus 1) |
| Serrano-Fernandez 2010[53] | Case series; over-the-top semitendinosus; includes 1 with MCL injury | 24 | Median 6.2 years | KT-1000 difference ≤2 mm | IKDC A 16, B 6; Tegner 7→6 | No rerupture; peroneal palsy 1 (recovered) |
| Yoon 2009[27] | Retrospective three groups; preoperative Lachman ≥2 in 85%–88%; authors acknowledge not pure partial tears | 40 AM augmentation, 42 PL augmentation vs 82 reconstruction | 2 years | 2.24, 2.15 vs 1.87 mm (no difference) | IKDC A 60%, 52% vs 61% | Failure not reported |
| Sonnery-Cottet 2013[54] | Single-surgeon series; isolated PL reconstruction preserving AM remnant; preoperative pivot shift all positive | 39 (35 with MRI) | 24.2 months | Rolimeter 5→1.5 mm | Subjective IKDC 43.5→89.9; objective A 34, B 5 | 1 traumatic graft rupture at 18 months excluded from analysis; no cyclops on MRI |
The French Arthroscopy Society's 2012 multicenter retrospective series is the largest: 11 centers, 2006–2010, 168 AM reconstructions preserving the PL bundle, age 30 years (14–58), injury-to-surgery 3 months (0–68), follow-up 26 months (12–59). Preoperatively, 83% had instability and 48% pain; Lachman positive with delayed firm endpoint 66%; pivot-shift glide 40%, positive 30%, marked 11%, negative 19%; mean side-to-side laxity difference 5.7 mm (arthrometer) or 5.3 mm (Telos). Postoperatively, subjective IKDC rose from 63.7 to 90.5, Lysholm from 80 to 95.5, objective IKDC A or B 92%, side-to-side laxity difference from 5.5 mm to 1.1 mm (P < 0.00001), and postoperative pivot shift showed glide in 4 and was positive in 1. The costs were residual pain in 13%, related to postoperative extension loss; 9 cyclops syndromes requiring repeat arthroscopic lysis, related to graft type and more common with conventional-diameter patellar-tendon grafts; and 5 (3%) graft failures[35]. The authors therefore stressed that graft diameter should be smaller than in conventional reconstruction to avoid excess tissue in the notch[35]. The study had no control group and did not assess whether the preserved PL bundle was truly functional postoperatively; 41% already had a positive or marked pivot shift preoperatively, and arthroscopy also found grade II or higher cartilage injury in 10 (untreated in 8, drilled in 1, osteochondral transplant in 1)—not a population of examination-stable isolated partial tears[35].
The same society's multicenter randomized study: 54 patients with delayed but firm Lachman endpoint, MRI consistent with partial tear, and arthroscopically confirmed intact PL insertions were randomized to selective AM reconstruction preserving the PL (29) or standard single-bundle anatomic reconstruction (25), with 1-year follow-up. Subjective IKDC rose from 55.8 and 56.8 to 86.2 and 85.7, Lysholm from 69.9 and 71.1 to 90.9 and 91.8, with no differences; Rolimeter side-to-side difference fell from 5.0 and 5.1 mm to 1.24 and 1.87 mm (P = 0.03); IKDC A or B 89.6% vs 84% and negative pivot shift 82.8% vs 72%, neither different; 1 selective-group patient underwent cyclops lysis at 3 months. The authors stated that sample size left power below 80%, follow-up was only 1 year, and whether an approximately 1 mm difference has long-term meaning is hard to predict[47]. Jenny's commentary noted that the Rolimeter reads in 1 mm increments with 0.5 mm reading uncertainty, and with operator variation a between-group difference of 0.6–0.7 mm falls within measurement error[36]; Pujol's reply was that measurement error under blinded randomization enters both groups' variance equally and cannot, by a single instrument's error alone, negate a statistically significant between-group difference, while whether 0.7 mm is perceptible to patients or clinically meaningful is a separate question[55]. This chapter's author holds that both sides have a point: the difference is statistically established, but its clinical and long-term meaning remains unsettled.
Data note. That randomized study's pre-inclusion criterion writes "negative pivot shift," yet the baseline table at enrollment shows a negative pivot shift in only 6/54 (11%), with glide in 61% and positive in 26%; the original does not explain this inconsistency[47]. Separately, Sonnery-Cottet and Colombet's 2016 review, summarizing this study, reverses the two group sizes (writing resection 29 and preservation 25; the original is preservation 29 and standard reconstruction 25) and mentions that at least at 2-year follow-up the side-to-side difference of 1.6 mm vs 1.1 mm was no longer statistically different; that 2-year result appears only in the review's summary, and this chapter has not seen a formal follow-up paper[7].
The second randomized study is a single-center series from Bursa, Turkey: 40 patients (36 men, 4 women; mean age 30 years) with preoperative examination and MRI suspicious for partial tear and arthroscopic confirmation of a remnant bridging femur to tibia with integrity greater than half (torn portion PL, intact portion AM) were randomized intraoperatively to remnant-preserving augmentation or remnant-clearing transtibial single-bundle reconstruction, 20 each, all with hamstring tendons, mean follow-up 24.3 months (21–28). The two groups did not differ in magnitude of IKDC or Lysholm improvement, final Lachman or pivot shift, range of motion, or satisfaction; 1 cyclops in the augmentation group needed second-look resection, and each group had 7 grade-1 arthrofibroses; tibial-tunnel enlargement was significantly less in the augmentation group (P = 0.001), with a smaller femoral difference (P = 0.03). The study had no instrumented measurement; the Methods state that patients with rotational instability were excluded, yet the tables still list preoperative pivot-shift grades 2 and 3; injury-to-surgery intervals differed greatly (augmentation 2.3 months, standard 8 months); sample size was set for 80% power without stating which outcome[48]. The study adds evidence of no difference in subjective scores but does not answer whether remnant preservation yields better stability.
Data note. The Results paragraph of that paper writes that the augmentation group's tibial tunnel "enlarged by only 18 mm"; by its Table II (7.50→7.68 mm) this should be 0.18 mm—a typographical error. Table I's group headers are missing in the PDF; this chapter therefore does not cite that table's group figures[48].
The same team's earlier series of 36 AM reconstructions came from the 14% of 256 consecutive reconstructions with good PL tension in the figure-of-4 position; at mean 24 months, Rolimeter fell from 4.8 mm to 0.8 mm, objective IKDC was A in 73% and B in 24%, and 2 underwent lysis at 4 and 13 months for persistent extension loss—both with 8 mm grafts and large intraoperative remnants; another patient at 2 years had a markedly positive pivot shift with a side-to-side difference of only 1 mm, which the authors speculated reflected preoperative misidentification of residual fibers as the PL bundle, warning surgeons against "reconstructing the wrong bundle"[49]. Preoperatively, 61% of this group had a markedly positive pivot shift—again not an examination-stable population[49].
The Hiroshima series was the earliest to report that augmentation outperformed standard reconstruction. Adachi's 2000 augmentation indication was chronic ACL insufficiency with a remnant bridging femur to tibia, diameter one third to one half of normal, and a femoral attachment slightly anterior; preoperative Lachman was positive in all and pivot shift in 93.3%; 40 augmentations versus 40 contemporaneous standard reconstructions: KT-2000 side-to-side difference fell from 5.3 ± 2.6 mm to 0.7 ± 1.8 mm in the augmentation group and from 6.0 ± 2.4 mm to 1.8 ± 2.1 mm in the standard group, joint-position-sense error 0.7° versus 1.7° (both P < 0.05), Lysholm no different; only 40 of 57 entered analysis, and position sense had no preoperative values[50]. Ochi's 2009 series of 45 (37 AM, 8 PL reconstructions) mixed single-bundle partial tears with "cross-healed" remnants; KT-2000 fell from 3.4 mm to 0.5 mm, position-sense error from 1.6° to 0.3°, Lysholm median from 75 to 100, with no controls and failure not reported[51]. Nakamae's 2014 three-group comparison all had second-look arthroscopy: postoperative KT-2000 was 0.4 mm in 73 augmentations, 0.9 mm in anatomic double-bundle, and 1.3 mm in anatomic single-bundle (versus single-bundle P = 0.013; versus double-bundle no difference); pivot shift and Lysholm did not differ; good synovial coverage of the graft was 82% versus 61% and 62%; but preoperative laxity in the augmentation group was 3.6 mm, clearly lower than the other groups' 5.2 and 5.4 mm, reinjured patients had already been excluded before analysis, and the authors acknowledged that a more stable knee preoperatively being more stable postoperatively is unsurprising[46].
Italian and Spanish series come closest to the classic examination-stable definition. Rizzoli's 47 chronic partial tears (Lachman 0 or 1+, pivot shift negative or only trace, one healthy bundle at arthroscopy, unable to resume sport after 8–12 weeks of rehabilitation) used over-the-top augmentation with distally based semitendinosus–gracilis; at 5 years there were no reruptures, IKDC A 31, B 14, C 2, Tegner from 6.8 to 6.1, KT-2000 30-lb side-to-side difference 0–3 mm in 41/47, and reoperation in 4 (hardware removal 2, lateral patellar release 1, meniscus 1)[52]; another series of 28 from the same team with MRI follow-up showed that the preserved remnant remained identifiable in 79% of knees, and graft continuity with normal signal correlated with clinical outcome[56]. Málaga's 24 cases at median 6.2 years had no reruptures, IKDC A 16, B 6, Tegner from 7 to 6, and 15 returned to their prior sport level[53]. These series have no controls and no preoperative instrumented values.
Contrary controlled data come from a Korean three-group comparison and from later systematic reviews. In Seoul's 164-case three-group comparison, AM augmentation (40), PL augmentation (42), and standard reconstruction (82) had postoperative KT-1000 of 2.24, 2.15, and 1.87 mm, with no differences in IKDC or pivot shift; the authors themselves wrote that preoperative Lachman ≥2 accounted for 85%–88% of entrants, that the preserved remnant was not an intact single bundle, and that "pure partial tears are rare"[27]. A 2014 systematic review included only 13 studies with a standard-reconstruction control (6 selective single-bundle reconstructions for partial tear, 6 remnant preservation or tensioning for complete tear, 1 unspecified): remnant-preservation groups showed an advantage in KT-1000/2000 laxity in only 2/9, Lachman in 1/8, pivot shift in 0/8, and objective IKDC in 0/5; included studies did not find significantly increased cyclops or motion loss, which is not the same as proving that risk does not increase; both studies assessing tunnel enlargement showed less tibial-tunnel enlargement in the remnant-preservation group, among them Zhang's randomized study of remnant preservation in complete tears (an adjacent population), with tibial-tunnel diameter at 24 months 12.9 versus 13.9 mm and enlargement 25.7% versus 34.0%, and no difference in functional scores or KT-1000[57]; the conclusion was not to use the technique routinely and to confine it to clinical trials[58]. Another 2014 systematic review included 10 surgical studies of partial tear, among them suture repair with bone-marrow stimulation (Gobbi 2009), thermal shrinkage, and a diagnostic identification series—not all selective augmentations; only 2 (Adachi, Yoon) had standard-reconstruction controls, mean methodological scores were in the low 60s, and the conclusion was that evidence is too weak and the augmentation technique too demanding for routine clinical use[59]. Sonnery-Cottet and Colombet's 2016 literature review pooled 17 studies and 3 meta-analyses then available: 805 partial reconstructions in all, only 5 with a remnant-resecting standard-reconstruction control, only 2 exceeding 50 cases; isolated PL reconstruction accounted for 145 (the review writes 20%; by 805 cases the figure is about 18%). The review found only one dedicated series of that technique—Lyon's 39 with clinical and MRI follow-up. Of 741 consecutive reconstructions, 44 (6%) had isolated PL reconstruction; after excluding 4 contralateral knee ligament operations and 1 traumatic graft rupture at 18 months, 39 were followed for 24.2 months: subjective IKDC rose from 43.5 to 89.9, objective IKDC A in 34 and B in 5, Rolimeter side-to-side difference from 5 mm to 1.5 mm; MRI in 35 showed continuous grafts in all and no cyclops. All these patients had positive Lachman and pivot shift preoperatively, and the authors wrote that the 5 with pivot-shift grades 2–3 could not, by definition, be counted as partial tears[54]. Of the review's 5 controlled studies, only 1 showed significantly lower laxity than conventional reconstruction; the remaining scores did not differ; for complications, cyclops with extension loss was 9/168 (5.3%) in the largest series, related to thick grafts especially patellar tendon; and the rerupture rate in the largest series was 3%[7].
5.3 Technical Costs
The remnant can obscure the femoral insertion. Siebold and Fu note that the AM femoral insertion at 90° of flexion is hidden behind the PL bundle, and anatomic placement often requires drilling through a low anteromedial portal at 130° of flexion; the PL tibial tunnel lies behind the AM insertion and is harder to drill[12]. Hiroshima authors write that the preserved remnant obscures the tibial footprint, and placing a Kirschner wire at the intended position depends on arthroscopic experience[30][51]. Sonnery-Cottet and Colombet choose outside-in femoral tunneling because vision at 90° of flexion is good, the drill does not pass through the notch, and remnant clearing is minimized; the graft is only a three- or four-strand folded semitendinosus, diameter not exceeding 8 mm, to avoid excess fibrous tissue in the notch causing cyclops[7]. These technical details show that remnant-preserving surgery depends more than standard reconstruction on the surgeon's familiarity with insertion anatomy, and that there is a risk of mistaking residual fibers for an intact bundle and reconstructing the wrong bundle[49].
Author's view and practice: the value of selective reconstruction is that it preserves native tissue in suitable cases, and postoperative laxity and functional scores can be expected to match those of standard reconstruction; whether long-term results are superior to standard anatomic reconstruction is unsettled. Suitable cases are knees in which the other bundle's insertions are intact at arthroscopy and there is tension under the probe; when the remnant is lax or already scarred, it need not be preserved for preservation's sake. Graft thickness should be chosen according to the space left by the remnant, not carried over from conventional reconstruction diameters.
6. Surgery II: Primary Repair
Primary repair sutures the torn ends back to the insertion without harvesting a tendon. Direct repair data for partial tears are scarce; most evidence comes from complete-tear populations.
Direct partial-tear repair data included in this chapter come from two research lines. The first is pulley-technique repair reported by Liao and Zhang of the Chinese PLA General Hospital in 2020: of 183 surgically treated ACL injuries in 2014–2016, 23 (13%) were proximal partial tears with good stump tissue quality (only mild interstitial tearing, able to hold suture), all repaired; 21 were followed for a mean of 36 months (25–49 months), with 2 lost. All entrants had clinical instability preoperatively (abnormal anterior drawer and/or Lachman); 13/21 had a positive preoperative anterior drawer and 8/21 a positive Lachman; age 32 years (17–56), 16 men and 5 women, injury-to-surgery 24 days (10–87 days); injury mechanism was sport (including military training) in 17, traffic accident in 3, and a fall in 1; the original does not report the number of military personnel and explicitly describes a 56-year-old nonmilitary woman. At final follow-up, anterior drawer and Lachman were negative in 20 and anterior drawer was 1+ in 1; Lysholm rose from 71 ± 9 to 94 ± 6, subjective IKDC from 64 ± 10 to 86 ± 11, and Tegner 6.3 versus 6.1 with no difference; one 20-year-old soldier removed his brace himself at 1 month and returned to military training, then reruptured at 2 months in an obstacle race. Limitations listed by the authors include no control, unblinded assessors and patients, stability assessed only by manual testing without KT-1000, and short follow-up; they state explicitly that the technique should not be promoted until directly compared with reconstruction[60].
The second line comes from Gobbi's group in Milan, with a different approach: torn fibers are sutured back to residual ligament with absorbable suture, then microfracture-style bone-marrow stimulation is performed at the femoral insertion; for type III injuries in which both bundles are elongated but not torn, the Methods section states that only bone-marrow stimulation without suture is performed (yet the appendix case-by-case table registers 1 of these as suture plus bone-marrow stimulation—main text and appendix disagree). The 2009 report is this line's early result: 26 athletes among 99 acute ACL injuries, ages 14–40 years (inclusion criterion written as under 40 years; Table 1 has 1 case aged 40), operated within 4 weeks of injury, with arthroscopically confirmed proximal incomplete tears (partial AM 14, partial PL 2, both bundles partial 10). At 25.3 months (17–38 months), Rolimeter side-to-side difference fell from 3.5 mm to 1.3 mm, and none reached 3 mm at final follow-up; the main text reports pivot shift negative in 23, positive in 2, and glide in 1 (appendix registers negative 23, positive 3); objective IKDC A in 23/26; 5 (19%) did not return to their preinjury sport level[61]. The 2018 long-term report expanded the same line to 50 partial tears with symptomatic instability from 2004–2012 (including part of the 2009 cohort; the two reports' numbers cannot be added), all operated within 4 weeks of injury, mean follow-up 10.2 years (5.3–14.3 years): 6 lost, 44 traceable, of whom 12 (27%) underwent reconstruction for secondary ACL insufficiency (11 with clear reinjury, 1 without trauma); Kaplan–Meier survival was 80.2% at 5 years and 72.7% at 10 years; among 43 with scores, final subjective IKDC averaged 90.4 and Lysholm 96.2—these means include the most recent scores before reconstruction in those who failed, not the results of nonfailures alone; those with secondary failure were younger at surgery (23.6 versus 31.7 years) and had larger side-to-side differences about 2 years postoperatively (3.4 versus 0.9 mm)[62]. This line's technique differs from Liao's pulley-anchor method and cannot be pooled as an effect estimate for one treatment; both are single-surgeon uncontrolled series, and Papalia's review listed the 2009 report as the only repair series among surgical studies of partial tear[59].
The 2024 Chinese expert consensus, in Recommendation 8, states that primary repair may be used for partial injury in athletes, military personnel, and other high-demand groups, on the grounds that partial injury in this population often involves impaired stump blood supply, may progress to complete tear, and usually responds poorly to nonoperative care; it takes a cautious stance toward primary repair of complete tears (agreement 92.7%)[63]. The supporting material cited by the consensus is precisely the 23-case series above[63].
Data note. The consensus's summary of that study disagrees with the original in three places: it writes "23 military personnel," whereas the original does not report the number of military personnel and explicitly includes nonmilitary patients; it writes "IKDC score rose from (71 ± 9) to (94 ± 6)," figures that in the original are Lysholm scores, the original IKDC being 64 ± 10 to 86 ± 11; and it does not state that 2 of 23 were lost and 21 completed follow-up[60][63].
The consensus's remaining recommendations apply equally to partial tear: MRI for initial assessment of location, arthroscopy for final judgment of stump quality (Recommendation 4, 100%); prefer proximal injuries (Recommendation 5, 96.4%); acute repair within 3 weeks of injury is feasible, nonacute timing is debated (Recommendation 6, 92.7%); short- to mid-term outcomes of suture-anchor repair, internal-brace augmentation, and bridge-enhanced repair are similar to reconstruction, and mechanically augmented internal bracing is preferred for young or overweight patients, those with concomitant meniscal or cartilage injury, and those with high activity demand (Recommendation 9, 90.9%); the consensus itself states that these studies have small samples and short follow-up and that no best technique is clearly recommended[63].
The remaining repair material comes from complete-tear populations, mostly proximal tears—adjacent populations; tear location, physeal status, and timing of surgery are not uniform across studies. The HSS algorithm places clear limits on repair indications: repair only when the distal stump is at least 90% of ligament length and tissue quality is good; the authors also state explicitly that partially torn knees are usually stable, that the purpose of selective single-bundle augmentation is to prevent complete tear, and that this is a different matter from repairing or reconstructing an unstable complete tear[64]; their first 11 proximal-avulsion repairs came from 5.7% of 190 ACL operations in 2008–2012, mean injury-to-surgery 39 days (10–93 days), mean follow-up 41 months, failure in 1, and KT-1000 <3 mm in 7 of 8 measurable cases[65]. Berlin's prospective nonrandomized comparison found only 41 eligible proximal avulsions among 420 operations; anchor repair (20) versus single-bundle reconstruction (20) at 28 months showed KT-1000 1.95 versus 1.15 mm and no IKDC difference, but failure was 3/20 (15%) in the repair group versus 0/20 in reconstruction, and reoperation 20% versus 0%[66]. The Dutch randomized trial compared dynamically augmented suture repair with all-inside semitendinosus reconstruction in patients aged 18–30 years with Tegner 5–10 who could be operated within 3 weeks of acute complete tear; inclusion was not screened by tear location, and of 24 repairs, 20 were proximal, 3 midsubstance, and 1 distal; actual surgery time was a median of 13 days for repair and 47 days for reconstruction. At 2 years, median subjective IKDC was 95.4 versus 94.3, judged noninferior; rerupture 2/23 versus 4/21; nonrevision reoperation 5 versus 3[67]. At 5 years, IKDC was 90.2 versus 96.6; the lower bound of the repair group's confidence interval (75.9) fell outside the noninferiority margin of 86.6 while the upper bound exceeded the reconstruction group's median, and the authors' conclusion changed to "inconclusive"; clinical failure was 5/24 versus 6/22, and reoperations other than ACL revision 9/24 versus 4/20 (the two outcome types cannot be added); the authors also cautioned against use in young active patients[68]. A systematic review of 13 studies and 1101 cases reported approximately 2-year failure rates for proximal-tear repair which, by the authors' formal 2020 corrigendum, were nonaugmented 10/74 (13.5%), statically augmented 4/69 (5.8%), and dynamically augmented 106/958 (11.1%); reoperation after dynamic augmentation was 10% and hardware removal 29%; evidence level IV, and the authors put their conclusion in the title: appears safe, but higher-level evidence is needed[69][70].
Data note. That review's original Abstract writes 9/74 (10%) and 6/69 (7%), while the body and tables write 9% and 6%. The authors then published a formal corrigendum stating that after excluding previously included conference abstracts, the failure counts and proportions had not been correctly updated, correcting them to 10/74, 4/69, and 106/958; that corrigendum appeared online in September 2020 and was assigned to a 2022 volume/issue, and is not the same as the 2019 first correction that only revised the methodological scoring table. This chapter follows the corrigendum[69][70].
The randomized trial of bridge-enhanced repair enrolled patients aged 13–35 years (median 17) with closed physes and acute midsubstance complete tears within 45 days of injury—it cannot be used to support repair in those with open physes: at 2 years, IKDC 88.9 versus 84.8 and KT-1000 1.61 versus 1.77 mm both met noninferiority; hamstring strength index 98.2% versus 63.2%; ipsilateral repeat ACL surgery 9/64 (14.1%) versus 2/35 (5.7%)[71].
The signal of high repair failure in adolescents also comes from complete-tear populations. Gagliardi 2019 compared suture-augmented repair in 22 patients aged 7–18 years with quadriceps-tendon reconstruction in 157; repair inclusion required proximal femoral avulsion (Sherman type I), healthy tissue able to hold suture, and length sufficient to return to the insertion without a gap; the repair group was younger (13.9 versus 15.7 years) and had a higher open-physis proportion (68.2% versus 42.0%). Cumulative failure within 3 years was 48.8% (95% CI 28.9%–73.1%) after repair versus 4.7% (95% CI 2.1%–10.3%) after reconstruction; the hazard ratio after adjustment for age, sex, body-mass index, and injury-to-surgery time was 10.66 (Results 95% CI 3.45–32.92; Abstract writes 3.41–32.92); the study detected no independent association of age at surgery with failure (P = .16); among nonfailures, IKDC, Lysholm, range of motion, and return to sport did not differ[72]. This is a single-surgeon nonrandomized cohort with only 22 repairs; what it shows is the early failure risk of repair for adolescent proximal complete tears and cannot be converted directly into a failure rate for partial-tear repair, but when deciding whether to repair a partial tear in an adolescent athlete with open physes, this evidence must not be overlooked.
Data note. The Chinese consensus's summary of this study writes "failure rate 48.8%, 10.66 times the reconstruction group's 4.7%" and on that basis "the younger the age, the higher the failure risk." The original's 10.66 is a hazard ratio after adjustment for sex, age, body-mass index, and injury-to-surgery time, not the ratio of the two percentages (48.8 divided by 4.7 is about 10.4); the original detected no association of age with failure (P = .16) and does not support "younger age, higher risk." This chapter follows the original wording[63][72].
Two further sets of material cited by the consensus point in the same direction: repair failure 37% under age 22, 4.2% at 22–35 years, and 3.2% over 35; failure after repair in 46 military personnel 26.1%, with higher failure risk in those required to participate in competitive sport (OR = 7, P = 0.015)[63].
Author's view and practice: the partial tear suited to repair is a proximal tear with good stump quality, a short time since injury, and a patient whose demand is high yet who is unwilling to accept tendon harvest and bone tunnels. Patients should be told preoperatively that direct evidence for this technique consists of only two single-center uncontrolled research lines, and that in the longer-followed line about one quarter underwent reconstruction for secondary instability at ten years; salvage after repair failure is primary reconstruction, not revision. For adolescents with open physes, the signal of high repair failure is strong enough that the author does not treat repair as a routine option for partial tear.
7. Special Populations
7.1 Children and Adolescents with Open Physes
The proportion of partial tears in children is not low: in pediatric series cited by Kocher, 22%–53% of midsubstance ACL injuries were partial tears, and 96% of his own 45 cases were proximal tears[16]. Decision-making still rests on Kocher's proposed tear proportion, bundle identity, and pivot-shift grade under anesthesia, plus bone age; but only 27 of these 45 had open physes, and the 31% reconstruction rate comes from a mixed-physeal cohort. Bone age 14 years or under with a normal or near-normal examination allows deferred reconstruction, because the proportion needing reconstruction in this group is relatively low; ages 15–17, tear >50%, and PL predominance carry high risk of progression and poor function[16]. That cohort's "do not reconstruct first" protocol included 6 weeks in a hinged brace limiting terminal extension, 6–8 weeks of toe-touch weight-bearing, and return to sport after 3 months in a functional brace—different from current practice[16]. The Chinese consensus's stance on proximal-injury repair in those with open physes is that "efficacy remains debated," and it recommends deciding among nonoperative care, repair, and reconstruction according to growth, ligament status, compliance, and preference (Recommendation 7, 98.2%)[63].
7.2 High-Demand Athletes and Military Personnel
This population has the highest progression risk and is also the most willing to accept surgery. In the Lyon cohort, the odds ratio for progression among those returning to pivoting contact sport was 6.29[18]; 24 of Noyes' 32 trained 4–7 days per week, and reinjury occurred in level-I sport in 33% and level-II in 39%[2]; of 34 Copenhagen cases with activity grading, continued participation in cutting sports fell from 27 to 8, and that study's authors wrote that "cutting and pivoting sports can be resumed, at the cost of knee stability"[40]. Sonnery-Cottet and Colombet list "high-risk occupation or pivoting sport with side-to-side difference >4 mm" directly as a surgical group[7]. Military repair material cited by the consensus is discussed in Section 6; the original did not report the number of military personnel. This chapter's author holds that for this population the cost of waiting is meniscal injury at reinjury, and the benefit is sparing some from unnecessary surgery; explaining Fayard's data and involving the patient in the choice is more appropriate than applying any single rule.
8. Differential Diagnosis and Prioritization When MRI Reports a "Partial Tear"
A knee whose MRI report reads "partial tear" may belong to any of the five situations in Table 4.
Table 4. Criteria for judging each situation when MRI reports a "partial tear"
| Situation | Findings supporting this situation | Findings lowering its likelihood | Information most likely to change the judgment next |
|---|---|---|---|
| Functional remnant; rehabilitation first is reasonable | Firm Lachman endpoint; negative pivot shift or glide; small side-to-side difference on the same instrument; no further giving way since injury; no pivoting contact sport; injury of no more than half | Pivot shift ≥+2; Telos (15 kg) side-to-side difference >5 mm; giving way already present | Pivot shift and same-instrument remeasurement at three months; any episode of giving way |
| Remnant present but functionally insufficient | Positive pivot shift plus Telos (15 kg) side-to-side difference 4–9 mm (Dejour's combination for identifying a currently nonfunctional remnant in surgical candidates—not a progression predictor); giving way already present since injury; ≤20 years and returned to pivoting contact sport; arthroscopic tear >half or PL-predominant | None of the above | Examination under anesthesia plus stress radiographs or arthrometer |
| False continuity from stump healed to the PCL | Continuous fibers on MRI; examination like a complete tear; laxity between the two | Tension under the probe and insertions anatomic | Probe; such stumps are generally not worth preserving |
| Isolated PL tear (uncommon) | Anterior drawer and Lachman nearly normal; positive pivot shift; symptoms only with cutting; MRI often fails to identify | Predominantly anterior instability | Exploration in figure-of-4; easily missed through a standard anterolateral portal |
| Early post-injury extension loss (uncommon) | Weeks after injury; passive extension loss; torn bundle impinging on the notch roof | Normal range of motion | Arthroscopic clearing of the impinging torn bundle |
The first situation is a functional remnant. Such knees begin with rehabilitation and are reassessed at three months; progression may occur in the first year or only after a reinjury two or more years later, so follow-up should continue beyond return to sport.
The second situation is a remnant that is present but functionally insufficient, shown by: a positive pivot shift and Telos 15 kg side-to-side difference of 4–9 mm (Dejour used this combination to identify whether surgical candidates currently have a functional remnant; it has not been followed to test prediction of complete tear); giving way already present since injury; or belonging to the high-risk group shown by the Lyon cohort (≤20 years, pivoting contact sport). The combination of pivot shift with laxity, and giving way after injury, show that the remnant is already insufficient to maintain stability; youth and pivoting contact sport are factors associated with progression in the cohorts. The cost of waiting is meniscal injury, and most who still wish to play ball sports should accept surgery—this is the author's judgment based on symptoms and sport demand, not a direct conclusion of any single study.
The third situation is false continuity from a stump healed to the PCL: MRI appears to show continuous fibers, yet examination resembles a complete tear, and laxity lies between the two[4][13]. Such knees are managed as complete tears, and the arthroscopic stump is generally not worth preserving.
The fourth situation is uncommon but real: isolated PL tear. Anterior drawer and Lachman are nearly normal, the pivot shift is positive, and symptoms appear only with cutting; MRI often fails to identify it, and it is easily missed through a standard anterolateral portal, requiring exploration in the figure-of-4 position[11][12][17]. It accounted for 8.6% of a surgical population[17], and in the Malmö cohort it was precisely the PL-injured knees that showed a positive pivot shift and complaints of instability[37].
The fifth situation is also uncommon: early post-injury extension loss. The torn bundle embeds in the notch roof with a cyclops-like picture, seen by Sonnery-Cottet in 2009 in 3 cases operated within weeks of injury[17].
Which new piece of information is most likely to change the judgment depends on the current decision stage. When examination and MRI conflict, it is examination under anesthesia plus stress radiographs or an arthrometer; when reinjury occurs during nonoperative care, it is rechecking the pivot shift and same-instrument laxity; when surgery is decided but the technique is not yet chosen, it is remnant tension under the probe—obtainable only at arthroscopy, but diagnostic arthroscopy need not be arranged solely for that purpose.
9. Evidence Notes
Natural-history material rests chiefly on five cohorts—Noyes 1989, Bak 1997, Messner 1999, Kocher 2002, Fayard 2019—and the French Arthroscopy Society's 2012 systematic review; diagnostic material on Dejour's 2013 series of 300, Panisset's 2012 series of 177, and the two Antwerp MRI studies; surgical material on the French Arthroscopy Society's 2012 retrospective series of 168 and randomized study of 54, supplemented by the Turkish randomized study of 40. The two randomized studies (Pujol 2012, Demirağ 2012) both compared two reconstructions for partial tear with 1–2 years of follow-up; no randomized study has compared nonoperative care with surgery for partial tear. Denominators for progression proportions come from differently defined populations; progression has been judged by arthroscopy in some, by pivot shift and KT-1000 in others, and by MRI in still others—this chapter does not pool these figures. All odds ratios and percentages are observational associations. Diagnostic thresholds mostly come from populations already decided upon for surgery; cohorts that include nonoperatively treated patients (30 of Paris's 42 partial tears were nonsurgical) use laxity as an inclusion criterion and carry circular reasoning without independent validation. Long-term osteoarthritis data in partial-tear populations consist only of Linköping's 21 cases (all with concomitant injuries)[41] and the 15% degeneration at 8 years cited by the French Arthroscopy Society[4]. Dedicated material on PL tears is scarce: one 15-case arthroscopic identification series[17] and one 39-case isolated PL reconstruction series[54]. Several studies from Lyon, Grenoble, and the French Arthroscopy Society come from the same school; Dejour 2013 and Panisset 2012 populations very probably overlap, and this chapter does not treat them as mutually independent confirmation. Biologic agents, intraligamentous injection, and similar augmentation methods are outside this chapter's scope.
9.1 Data Discrepancies in the Source Literature
The following sources contain internal data inconsistencies or transcription errors.
| Source | Problem in the original or in a summary of it | Reading points |
|---|---|---|
| 2024 Chinese expert consensus summarizing Liao 2020[60][63] | Writes Lysholm 71 ± 9 → 94 ± 6 as IKDC; writes "23 military personnel," whereas the original does not report military numbers and explicitly includes nonmilitary patients; does not state that 2 were lost | Follow the original: Lysholm 71→94, IKDC 64→86, 21 completed follow-up |
| 2024 Chinese expert consensus summarizing Gagliardi 2019[63][72] | Writes the adjusted hazard ratio 10.66 as a multiple of two percentages; writes "younger age, higher failure risk" | Follow the original: adjusted hazard ratio; the study detected no association of age with failure (P = .16) |
| Sonnery-Cottet and Colombet 2016 summarizing Pujol 2012[7][47] | Reverses the two group sizes (writes resection 29, preservation 25); 2-year results appear only in the review's summary | Follow the original 29 vs 25; mark 2-year results as a summary |
| Sonnery-Cottet and Colombet 2016[7] | Three-group classification in the text disagrees with the flow chart: the text says groups 2 and 3 both undergo surgery; the flow chart keeps a first-observe branch for group 2 | Follow the flow chart and note it |
| Pujol 2012 systematic review[3] | Text total 436; sum of 12 studies in the two tables 386; mean insufficiency by table does not yield 40.9%; return-to-sport range 21%–60% disagrees with table values of 79% and 100%; transcription of Buckley, Fruensgaard, Bak, and Noyes disagrees with the originals | Mark pooled values as review-reported; Table 2 follows the original cohorts |
| Pujol 2012 randomized study[47] | Pre-inclusion criterion writes "negative pivot shift"; baseline table shows negative pivot shift in only 6/54 | Record as an unexplained inconsistency in the original; figures follow the table |
| Noyes 1989[2] | Table I marks progression in 11 cases; text 12 | Follow the text 12/32; the unmarked case is inferred to be case 28 (KT-1000 difference 7.25 mm), not confirmed by the authors |
| Fayard 2019[18] | Table 4 has confidence intervals and P values but no OR column; Results sentence says nonprogressors had higher preinjury Tegner, yet Table 3 shows 7.0 vs 7.9 | OR from the text; Tegner from Table 3 |
| Papalia 2014[59] | Table 5 swaps Buda 2006 and Buda 2008 results; text total 634 differs from Table 1 sum 594 by 40 (Adachi's control group not listed in the table) | Do not cite that table's Buda data or total |
| Hu 2014[58] summarizing Zhang 2014[57] | Text attributes a significant Lachman advantage to Adachi; Table 4 to Naylor; Table 5 reverses Zhang's two groups' 24-month tibial-tunnel diameters (original: remnant-preservation 12.9 ± 1.0 mm, clearing 13.9 ± 1.3 mm), though the Discussion's direction is correct | Cite only Hu's counts; tunnel figures from Zhang's original |
| Gobbi 2009[61] | Methods state type III injuries receive only bone-marrow stimulation without suture, yet the appendix case-by-case table registers case 16 as suture plus bone-marrow stimulation; inclusion criterion writes under 40 years, Table 1 case 15 is 40; preoperative Rolimeter side-to-side difference written as 3.7 ± 1.0 mm in one place in the text, 3.5 ± 0.7 mm in Abstract and appendix summary; final pivot shift main text 23/2/1, appendix 23 negative / 3 positive | Technique written as "bone-marrow stimulation with or without suture"; age 14–40 years; laxity 3.5 mm; pivot shift noted as main-text report |
| Gobbi 2018[62] | Table 3 lists 12 secondary failures (type I 9, II 1, III 2); Table 4 header also writes n = 12, yet percentages are 73%, 9%, 18%, which do not match 9/12, 1/12, 2/12 (close to calculation on 11 cases, reason not stated); Appendix Table A3 Marx means for two augmentation methods (10.5, 10.0) are both below A1's overall mean 10.8—the two tables' means are incompatible, reason not stated | Cite only 12/44 and overall scores, not type percentages |
| Achtnich 2016[66] | Unclear whether 20 clinical-table cases, 21 enrolled, or MRI 18+3 are the analysis set | Follow the original: failure 3/20, reoperation 20% |
| Hoogeslag 2022[68] | Table 3 row for return to preinjury Tegner percentages (35.0%, 39.1%) do not match footnote denominators (23, 20) | Do not cite that row |
| Gagliardi 2019[72] | Hazard-ratio 95% CI lower bound Abstract 3.41, Results 3.45 | Follow Results; note the difference |
| van der List 2020[69][70] | Original Abstract and body failure rates disagree; authors published a formal 2020 corrigendum | Follow corrigendum: 13.5%, 5.8%, 11.1% |
| Panisset 2012[15] | Results paragraph miswrites same-group figures from two instruments as between-group contrasts (7.4/5.3, 4.0/2.6) | Follow Table 2 |
| Beldame 2012[20] | Results paragraph writes 89–200 N; Methods, tables, and ROC description are 89–250 N | Follow tables: 250 N |
| Robert 2009[19] | Abstract unclear on loading force: Methods write 0–250 N; ROC analysis at 134 N | Note the analysis force |
| Georgoulis 2001[34] | PCL-adherent group Abstract 15 cases, Results 12; Table 1 has 16 rows (12 plus 4), total 17 disagrees with 16 | Follow Results: 12/12 |
| Umans 1995[23] | Abstract sensitivity lower bound 0.40; Table 1 six readings lowest 0.35 | List both |
| Eitzen 2010[43] | 4/98 written as 3.9% (actually about 4.1%) | List both |
| Demirağ 2012[48] | Results "18 mm" should be 0.18 mm; Table I group headers missing | Do not cite that figure or the group numbers |
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