ACL Tear - Clinical

Disclaimer: This page is intended for licensed healthcare professionals and students in clinical training. It is an educational reference only and does not constitute clinical advice, diagnosis, or a treatment protocol for any individual patient. Clinical decisions should always be made within the context of a full patient evaluation and within the scope of the clinician's license and training.

 

This page references peer-reviewed literature current as of the most recent available evidence. The Bridge Physical Therapy is a USA-based clinical and educational resource.

Anatomy & Structural Overview

  • The anterior cruciate ligament (ACL) is an intra-articular, extrasynovial ligament of the knee joint. It originates from the posteromedial aspect of the lateral femoral condyle and courses anteromedially to insert on the anterior tibial plateau, medial to the anterior horn of the lateral meniscus. [1] The ACL is composed of two primary functional bundles: the anteromedial (AM) bundle, which is taut in knee flexion and primarily resists anterior tibial translation, and the posterolateral (PL) bundle, which is taut in knee extension and contributes to rotational stability. [2]
  • Mean ACL length is approximately 32–38 mm with a cross-sectional area of approximately 44–60 mm², though significant morphological variation exists across sex, body habitus, and tibial slope geometry. [3] The ligament receives its vascular supply primarily from the middle genicular artery, a branch of the popliteal artery, which contributes to the ligament's limited intrinsic healing capacity following complete rupture. [4]
  • The ACL is richly innervated with mechanoreceptors — Ruffini endings, Pacinian corpuscles, and free nerve endings — that contribute to proprioceptive afferent signaling at the knee. [5] This neurosensory function has direct clinical relevance: ACL disruption produces measurable deficits in joint position sense and neuromuscular control that persist beyond structural healing and must be addressed explicitly in rehabilitation. [6]
  • Clinical relevance: A thorough understanding of bundle-specific anatomy informs the interpretation of special test findings and guides rehabilitation sequencing. AM bundle insufficiency is associated with increased anterior translation (positive Lachman, anterior drawer), while combined AM and PL bundle insufficiency is associated with rotational instability (positive pivot shift). [2]

 

References

[1] Duthon VB, Barea C, Abrassart S, Fasel JH, Fritschy D, Ménétrey J. Anatomy of the anterior cruciate ligament. Knee Surg Sports Traumatol Arthrosc. 2006;14(3):204–213.

[2] Zantop T, Petersen W, Sekiya JK, Musahl V, Fu FH. Anterior cruciate ligament anatomy and function relating to anatomical reconstruction. Knee Surg Sports Traumatol Arthrosc. 2006;14(10):982–992.

[3] Anderson AF, Dome DC, Gautam S, Awh MH, Rennirt GW. Correlation of anthropometric measurements, strength, anterior cruciate ligament size, and intercondylar notch characteristics to sex differences in anterior cruciate ligament tear rates. Am J Sports Med. 2001;29(1):58–66.

[4] Arnoczky SP, Rubin RM, Marshall JL. Microvasculature of the cruciate ligaments and its response to injury. J Bone Joint Surg Am. 1979;61(8):1221–1229.

[5] Denti M, Monteleone M, Berardi A, Panni AS. Anterior cruciate ligament mechanoreceptors: histologic studies on lesions and reconstruction. Clin Orthop Relat Res. 1994;308:29–32.

[6] Grooms DR, Page SJ, Onate JA. Brain activation for knee movement in individuals with anterior cruciate ligament reconstruction: proof-of-concept for neural re-education re-injury risk. J Athl Train. 2015;50(6):685–688.

Mechanism of Injury & Pathomechanics

  • Mechanism of Injury
  • The majority of ACL tears — estimated at 70–80% — occur via noncontact mechanisms. [7] The canonical noncontact injury pattern involves a rapid deceleration, cutting, or landing task during which the knee is positioned near full extension, in valgus collapse, with internal tibial rotation and an anteriorly directed ground reaction force vector. [8] This loading combination produces high tensile stress within the ACL, particularly the AM bundle, that exceeds ligament failure threshold.
  • Contact mechanisms, accounting for the remaining 20–30% of injuries, most commonly involve a direct blow to the lateral aspect of the knee producing forced valgus and external tibial rotation — the classic "clip" mechanism in American football. [7]
  • Sex-Based Injury Risk
  • Female athletes demonstrate ACL injury rates 2–8 times higher than male athletes participating in the same sports. [9] Proposed contributing factors include: narrower intercondylar notch dimensions, smaller absolute ACL cross-sectional area, greater knee valgus during dynamic tasks, reduced hamstring co-activation patterns, hormonal influences on ligament laxity, and differences in neuromuscular recruitment strategies. [9, 10] No single factor has been established as causally dominant, and the current evidence supports a multifactorial model. Importantly, modifiable neuromuscular factors are the primary targets of ACL injury prevention programs such as PEP, FIFA 11+, and the KIPP protocol. [10]
  • Concomitant Injuries
  • Isolated ACL tears are less common than combined injuries. The clinician should maintain high suspicion for:
  • Meniscal tears: Present in approximately 50% of acute ACL injuries, rising to over 70% in chronic ACL-deficient knees. [11] Lateral meniscus tears are more common acutely; medial meniscus tears predominate in chronic cases.
  • Bone contusions: MRI demonstrates lateral compartment bone bruising (lateral femoral condyle and posterior lateral tibial plateau) in up to 80% of acute ACL tears, reflecting the pivot-shift mechanism. [12]
  • Medial collateral ligament (MCL) sprain: The classic "unhappy triad" of ACL, MCL, and meniscal injury — though true simultaneous involvement of all three is less common than historically described.
  • Posterolateral corner (PLC) injury: Underdiagnosed and clinically significant; combined ACL and PLC injuries alter rotational kinematics in ways that must be addressed surgically before or concurrent with ACL reconstruction.

 

References

[7] Boden BP, Dean GS, Feagin JA Jr, Garrett WE Jr. Mechanisms of anterior cruciate ligament injury. Orthopedics. 2000;23(6):573–578.

[8] Hewett TE, Myer GD, Ford KR, et al. Biomechanical measures of neuromuscular control and valgus loading of the knee predict anterior cruciate ligament injury risk in female athletes. Am J Sports Med. 2005;33(4):492–501.

[9] Prodromos CC, Han Y, Rogowski J, Joyce B, Shi K. A meta-analysis of the incidence of anterior cruciate ligament tears as a function of gender, sport, and a knee injury-reduction regimen. Arthroscopy. 2007;23(12):1320–1325.

[10] Myklebust G, Bahr R. Return to play guidelines after anterior cruciate ligament surgery. Br J Sports Med. 2005;39(3):127–131.

[11] Shelbourne KD, Nitz P. Accelerated rehabilitation after anterior cruciate ligament reconstruction. Am J Sports Med. 1990;18(3):292–299.

[12] Sanders TG, Medynski MA, Feller JF, Lawhorn KW. Bone contusion patterns of the knee at MR imaging: footprint of the mechanism of injury. Radiographics. 2000;20(Suppl 1):S135–S151.

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Clinical Presentation & Subjective Examination

  • Mechanism History
  • The subjective examination of a suspected ACL injury should begin with a precise mechanism history. The clinician should establish whether the injury was contact or noncontact, the position of the limb at time of injury, the playing surface, footwear, and whether the patient was aware of the injury event or was struck from behind. A noncontact deceleration or cutting mechanism in a young athlete with immediate effusion and inability to continue play carries a very high pre-test probability for ACL involvement and should drive the objective examination accordingly.
  • Cardinal Subjective Features
  • The following subjective findings are commonly reported and clinically relevant when considered in aggregate. No single feature is pathognomonic.
  • Audible or perceived "pop": Reported in approximately 50–70% of ACL tears. [13] The pop reflects sudden tensile failure of the ligament. Its absence does not rule out a complete tear; its presence significantly raises clinical suspicion particularly in the context of a noncontact mechanism.
  • Immediate effusion: Hemarthrosis developing within 2–4 hours of injury is the hallmark of acute ACL disruption. This distinguishes ACL tears from most meniscal injuries, which produce slower-developing effusion over 12–24 hours. [14] In any patient presenting with acute traumatic hemarthrosis of the knee, the clinician should consider ACL tear as the primary diagnosis until proven otherwise. Studies demonstrate ACL injury is the cause of acute hemarthrosis in approximately 70% of cases. [14]
  • Inability to continue activity: The majority of patients with complete ACL tears are unable to return to play immediately following the injury event. This is not universal — partial tears and high-pain-tolerance athletes may attempt to continue — but immediate cessation of play is a meaningful historical feature.
  • Giving way or instability: In the subacute and chronic phases, patients frequently report episodes of the knee "giving out" during cutting, pivoting, or descending stairs. This reflects functional rotational instability from loss of the ACL's role as a primary restraint to anterior tibial translation and a secondary restraint to internal tibial rotation. [15] Quantifying frequency and context of giving way episodes informs surgical vs. conservative decision-making.
  • Pain: Acute ACL tears produce significant pain at the time of injury, though pain often diminishes rapidly as hemarthrosis develops and soft tissue swelling limits further motion. Clinicians should not use pain reduction as a sign of injury resolution in the acute phase.
  • Subjective Examination Framework
  • A structured subjective examination for suspected ACL injury should capture the following domains:
  • Activity level and functional demands: Use the Tegner Activity Scale [16] to establish pre-injury activity level. This directly informs the surgical vs. conservative discussion — a level 9–10 athlete (competitive pivoting sport) has fundamentally different risk-benefit considerations than a level 4 recreational cyclist.
  • Patient goals and timeline: Return-to-sport timeline, upcoming competitive events, occupational demands, and patient preference for surgical vs. non-surgical management are all relevant to the shared decision-making process and should be documented.
  • Prior knee history: Contralateral ACL injury, prior ipsilateral knee surgery, and history of ligamentous laxity or hypermobility syndrome alter both injury risk interpretation and rehabilitation expectations.
  • Psychosocial screening: Fear of reinjury, kinesiophobia, and psychological readiness are independent predictors of return-to-sport success following ACL reconstruction. [17] Brief validated screening using the ACL-RSI (ACL Return to Sport after Injury scale) or Tampa Scale of Kinesiophobia should be introduced early — not reserved for the end of rehabilitation.

 

References — Cinical Presentation & Subjective Examination

[13] Majewski M, Susanne H, Klaus S. Epidemiology of athletic knee injuries: a 10-year study. Knee. 2006;13(3):184–188.

[14] Noyes FR, Bassett RW, Grood ES, Butler DL. Arthroscopy in acute traumatic hemarthrosis of the knee. Incidence of anterior cruciate tears and other injuries. J Bone Joint Surg Am. 1980;62(5):687–695.

[15] Andriacchi TP, Dyrby CO. Interactions between kinematics and loading during walking for the normal and ACL deficient knee. J Biomech. 2005;38(2):293–298.

[16] Tegner Y, Lysholm J. Rating systems in the evaluation of knee ligament injuries. Clin Orthop Relat Res. 1985;198:43–49.

[17] Ardern CL, Taylor NF, Feller JA, Webster KE. Fifty-five per cent return to competitive sport following anterior cruciate ligament reconstruction surgery: an updated systematic review and meta-analysis including aspects of physical functioning and contextual factors. Br J Sports Med. 2014;48(21):1543–1552.

Special Tests: Detail and Clinical Application

  • The following section provides clinical context for each test represented in Diagram 2 above. Sensitivity and specificity values are drawn from the Benjaminse et al. systematic review and meta-analysis unless otherwise noted. [18]
  • Lachman Test
  • The Lachman test is the most diagnostically accurate single clinical test for ACL integrity and is considered the gold standard physical examination maneuver. [18] It is performed with the patient supine, the knee positioned at 20–30 degrees of flexion — a position that relaxes the posterior capsule and isolates the ACL as the primary restraint to anterior tibial translation.
  • The clinician stabilizes the distal femur with one hand while applying an anteriorly directed force to the proximal tibia with the other. A positive test is characterized by excessive anterior tibial translation relative to the contralateral limb and, critically, by the quality of the endpoint. A soft or absent endpoint is more diagnostically significant than the absolute magnitude of translation. [19]
  • Pooled sensitivity is 0.85 (95% CI: 0.72–0.93) and specificity 0.94, yielding a positive likelihood ratio of approximately 14.2. [18] This places a positive Lachman in the range of a large and clinically meaningful shift in post-test probability.
  • Clinical considerations: The Lachman test is less reliable in acutely injured knees with significant hamstring guarding, large effusion, or in patients with large thighs where the examiner has difficulty stabilizing the femur. The prone Lachman (Rocher modification) or use of a roll under the distal femur can assist in these cases. Examiner experience significantly influences accuracy. [19]
  • Anterior Drawer Test
  • The anterior drawer test is performed with the hip at 45 degrees of flexion and the knee at 90 degrees of flexion, with the examiner seated on the patient's foot. Anterior force is applied to the proximal tibia with both hands. At 90 degrees of flexion, the posterior capsule and secondary restraints become more engaged, reducing the ACL's relative contribution to the test result. This accounts for the test's substantially lower sensitivity (0.55; 95% CI: 0.37–0.72) compared to the Lachman. [18]
  • The anterior drawer retains reasonable specificity (0.92) and remains part of the standard examination, but a negative anterior drawer in isolation should not be used to rule out ACL injury. Its primary value in the current era is as a complementary maneuver and for chronic ACL insufficiency assessment where guarding is reduced.
  • Pivot Shift Test
  • The pivot shift test assesses rotational instability — specifically, the subluxation and sudden reduction of the lateral tibial plateau that occurs in ACL-deficient knees during a valgus and internal rotation loading pattern. [20] It is performed by applying a valgus stress and internal rotation torque to the tibia while moving the knee from extension into flexion. A clunk or shift felt at approximately 20–30 degrees of flexion constitutes a positive test.
  • The pivot shift is highly specific (0.98) but has poor sensitivity in the awake patient (0.24), primarily due to patient apprehension and voluntary hamstring guarding. [18] Under anesthesia, sensitivity rises substantially to 0.70–0.98 depending on grading method. [20] The pivot shift is graded 0–3 (0 = negative, 1 = glide, 2 = clunk, 3 = gross) and grade correlates with the degree of rotational instability, which has implications for surgical graft selection and postoperative outcomes.
  • Clinical significance: A positive pivot shift in the clinical setting, despite its lower sensitivity, is highly specific and confirms functionally significant rotational instability. Its presence may influence the decision toward surgical reconstruction even when other tests are equivocal.
  • Combined Testing Strategy
  • No single special test should be used in isolation to confirm or exclude ACL injury. The combination of a positive Lachman and positive pivot shift yields post-test probability approaching 95% in populations with moderate-to-high pre-test probability. [18] The clinical examination should always be interpreted in the context of the mechanism history, effusion pattern, and functional complaints.

 

References

[18] Benjaminse A, Gokeler A, van der Schans CP. Clinical diagnosis of an anterior cruciate ligament rupture: a meta-analysis. J Orthop Sports Phys Ther. 2006;36(5):267–288.

[19] Katz JW, Fingeroth RJ. The diagnostic accuracy of ruptures of the anterior cruciate ligament comparing the Lachman test, the anterior drawer sign, and the pivot shift test in acute and chronic knee injuries. Am J Sports Med. 1986;14(1):88–91.

[20] Galway HR, MacIntosh DL. The lateral pivot shift: a symptom and sign of anterior cruciate ligament insufficiency. Clin Orthop Relat Res. 1980;147:45–50.

Section 5 — Differential Diagnosis

The following conditions must be considered in any patient presenting with acute knee injury, effusion, or instability. Clinical differentiation relies on the integration of mechanism, effusion characteristics, special test findings, and where appropriate, advanced imaging

Differential Diagnosis

The following conditions must be considered in any patient presenting with acute knee injury, effusion, or instability. Clinical differentiation relies on the integration of mechanism, effusion characteristics, special test findings, and where appropriate, advanced imaging.

DDx Summary Table

 

 

 

 

 

ConditionKey distinguishing featuresPrimary differentiating testsImaging of choice

ACL tear (complete)Acute hemarthrosis, pop, noncontact mechanism, positive Lachman/pivot shiftLachman, pivot shift, anterior drawerMRI (sensitivity >90%)

ACL tear (partial)Partial effusion, less instability, intact endpoint on LachmanLachman endpoint quality, KT-1000 arthrometryMRI — may underestimate partial tears

PCL tearPosterior sag sign, posterior drawer positive, dashboard mechanismPosterior drawer, posterior sag (Godfrey), quadriceps active testMRI

Meniscal tear (isolated)Joint line tenderness, delayed effusion (12–24 hrs), McMurray/Thessaly positiveMcMurray, Thessaly, joint line palpationMRI (sensitivity 0.87 medial, 0.79 lateral)

MCL sprainValgus stress pain and laxity, medial joint line and ligament tenderness, contact mechanismValgus stress test (0 and 30 deg), palpationStress X-ray, MRI if grade unclear

Posterolateral corner injuryVarus instability, external rotation asymmetry, dial test positiveDial test (30 and 90 deg), varus stress, reverse pivot shiftMRI — often requires experienced reader

Patella dislocation / relocationLateral apprehension, medial retinaculum tenderness, mechanism of valgus/twistingPatellar apprehension test, J-sign, medial retinaculum palpationX-ray (rule out osteochondral fx), MRI

Osteochondral fractureOften concurrent with ACL or patellar dislocation, loose body sensationImaging essential — clinical exam unreliable in isolationX-ray + MRI

Proximal tibiofibular joint injuryLateral knee pain, fibular head tenderness, uncommon but misdiagnosedPalpation, anteroposterior fibular head stressX-ray, MRI if uncertain

DDx Prose Supplement

ACL versus PCL: The mechanism is the most immediately useful differentiating feature. PCL injuries classically result from a posteriorly directed force to the proximal tibia with the knee flexed — the dashboard mechanism in motor vehicle accidents, or a fall onto a flexed knee with the foot plantarflexed. The posterior sag sign (visual posterior drop of the tibia relative to the femur at 90 degrees of flexion) and a positive posterior drawer are the PCL equivalents of the Lachman and anterior drawer. Critically, an apparent positive anterior drawer in a PCL-deficient knee may represent the tibia returning from a posteriorly subluxed position to neutral — not true anterior translation — a phenomenon that can lead to misdiagnosis of ACL injury. [21] The quadriceps active test (active quadriceps contraction in the posterior drawer position) will reduce a PCL-deficient tibia anteriorly, helping confirm PCL involvement.

ACL versus isolated meniscal tear: Effusion timing is the most practical initial differentiator. Hemarthrosis within 2–4 hours strongly favors ACL or osteochondral injury. A more gradual effusion over 12–24 hours, combined with mechanical symptoms (locking, catching), joint line tenderness, and positive McMurray or Thessaly tests in the absence of instability testing findings, points toward isolated meniscal pathology. However, concomitant ACL and meniscal injury is common (approximately 50% of acute ACL tears involve concurrent meniscal damage [11]), and the absence of instability signs does not eliminate the need to assess meniscal integrity in an ACL-confirmed case.

ACL versus posterolateral corner (PLC): Combined ACL and PLC injury is one of the most consequential diagnostic oversights in knee trauma, as failure to address PLC instability surgically before or concurrent with ACL reconstruction leads to high graft failure rates. [22] The dial test is the key differentiating maneuver: external rotation asymmetry greater than 10 degrees at 30 degrees of knee flexion (with normalization at 90 degrees) indicates isolated PLC injury; asymmetry persisting at both 30 and 90 degrees suggests combined PLC and PCL involvement. Varus stress testing at 0 and 30 degrees of flexion completes the PLC assessment. Any patient with a confirmed ACL tear and significant lateral-sided pain or mechanism should be screened for PLC injury before surgical planning.

ACL versus patellar dislocation: Both injuries can present acutely with hemarthrosis, a perceived pop, and an inability to continue activity. The mechanism — typically a valgus and external rotation force with quadriceps contraction, or a direct lateral blow — differs from the typical ACL noncontact deceleration pattern. Medial retinaculum tenderness and a positive patellar apprehension sign differentiate patellar dislocation. MRI demonstrating medial patellofemoral ligament (MPFL) disruption and a lateral femoral condyle bone bruise (the classic kissing lesion of patellar dislocation) confirms the diagnosis and rules out concurrent osteochondral fracture.

 

References

[21] Rubinstein RA Jr, Shelbourne KD, McCarroll JR, VanMeter CD, Rettig AC. The accuracy of the clinical examination in the setting of posterior cruciate ligament injuries. Am J Sports Med. 1994;22(4):550–557.

[22] LaPrade RF, Wentorf FA, Olson EJ, Carlson CS. An in vitro biomechanical study of the effect of lateral knee bracing on knee stability. Am J Sports Med. 1999;27(3):363–372.

Condition:

ACL Tear (Complete)

Key Distinguishing Features:

Acute hemiarhtorsis, pop, noncontact mechanism, positive Lachman/pivot shift

Primary Differentiating Tests:

Lachman, pivot shift, anterior drawer

Imaging of Choice:

MRI (sensitivity >90%)

Condition:

ACL Tear (partial)

Key Distinguishing Features:

Partial effusion, less instability, interact endpoint on Lachman

Primary Differentiating Tests:

Lachman endpoint quality, KT-1000 arthometry

Imaging of Choice:

MRI - may underestimate partial tears

Condition:

PCL Tear

Key Distinguishing Features:

Posterior sag sign, posterior drawer positive, dashboard mechanism

Primary Differentiating Tests:

Posterior drawer, posterior sag (Godfrey), quadriceps active test

Imaging of Choice:

MRI

Condition:

Meniscal Tear (Incomplete)

Key Distinguishing Features:

Joint line tenderness, delayed effusion (12–24 hrs), McMurray/Thessaly positive

Primary Differentiating Tests:

McMurray, Thessaly, joint line palpation

Imaging of Choice:

MRI (sensitivity 0.87 medial, 0.79 lateral)

Condition:

MCL sprain

Key Distinguishing Features

Primary Differentiating Tests

Imaging of Choice

Condition

Key Distinguishing Features

Primary Differentiating Tests

Imaging of Choice

Condition

Key Distinguishing Features

Primary Differentiating Tests

Imaging of Choice

Condition

Key Distinguishing Features

Primary Differentiating Tests

Imaging of Choice

Condition

Key Distinguishing Features

Primary Differentiating Tests

Imaging of Choice

Condition

Key Distinguishing Features

Primary Differentiating Tests

Imaging of Choice

ACL versus PCL: The mechanism is the most immediately useful differentiating feature. PCL injuries classically result from a posteriorly directed force to the proximal tibia with the knee flexed — the dashboard mechanism in motor vehicle accidents, or a fall onto a flexed knee with the foot plantarflexed. The posterior sag sign (visual posterior drop of the tibia relative to the femur at 90 degrees of flexion) and a positive posterior drawer are the PCL equivalents of the Lachman and anterior drawer. Critically, an apparent positive anterior drawer in a PCL-deficient knee may represent the tibia returning from a posteriorly subluxed position to neutral — not true anterior translation — a phenomenon that can lead to misdiagnosis of ACL injury. [21] The quadriceps active test (active quadriceps contraction in the posterior drawer position) will reduce a PCL-deficient tibia anteriorly, helping confirm PCL involvement.

 

ACL versus isolated meniscal tear: Effusion timing is the most practical initial differentiator. Hemarthrosis within 2–4 hours strongly favors ACL or osteochondral injury. A more gradual effusion over 12–24 hours, combined with mechanical symptoms (locking, catching), joint line tenderness, and positive McMurray or Thessaly tests in the absence of instability testing findings, points toward isolated meniscal pathology. However, concomitant ACL and meniscal injury is common (approximately 50% of acute ACL tears involve concurrent meniscal damage [11]), and the absence of instability signs does not eliminate the need to assess meniscal integrity in an ACL-confirmed case.

 

ACL versus posterolateral corner (PLC): Combined ACL and PLC injury is one of the most consequential diagnostic oversights in knee trauma, as failure to address PLC instability surgically before or concurrent with ACL reconstruction leads to high graft failure rates. [22] The dial test is the key differentiating maneuver: external rotation asymmetry greater than 10 degrees at 30 degrees of knee flexion (with normalization at 90 degrees) indicates isolated PLC injury; asymmetry persisting at both 30 and 90 degrees suggests combined PLC and PCL involvement. Varus stress testing at 0 and 30 degrees of flexion completes the PLC assessment. Any patient with a confirmed ACL tear and significant lateral-sided pain or mechanism should be screened for PLC injury before surgical planning.

 

ACL versus patellar dislocation: Both injuries can present acutely with hemarthrosis, a perceived pop, and an inability to continue activity.

The mechanism — typically a valgus and external rotation force with quadriceps contraction, or a direct lateral blow — differs from the typical ACL noncontact deceleration pattern. Medial retinaculum tenderness and a positive patellar apprehension sign differentiate patellar dislocation. MRI demonstrating medial patellofemoral ligament (MPFL) disruption and a lateral femoral condyle bone bruise (the classic kissing lesion of patellar dislocation) confirms the diagnosis and rules out concurrent osteochondral fracture.

 

References

[21] Rubinstein RA Jr, Shelbourne KD, McCarroll JR, VanMeter CD, Rettig AC. The accuracy of the clinical examination in the setting of posterior cruciate ligament injuries. Am J Sports Med. 1994;22(4):550–557.

[22] LaPrade RF, Wentorf FA, Olson EJ, Carlson CS. An in vitro biomechanical study of the effect of lateral knee bracing on knee stability. Am J Sports Med. 1999;27(3):363–372.