Pathology – injury to a structure in the posterolateral aspect of the knee, specifically the lateral (fibular) collateral ligament, popliteus tendon and/or popliteofibular ligament.
Presentation – posterolateral knee pain, knee instability, possible common peroneal nerve signs and symptoms.
Diagnosis – combining history with clinical tests, stress X-Rays and MRI.
Clinical tests – varus stress, dial, reverse pivot shift, external rotation recurvatum, posterolateral drawer, figure 4/frog-leg. The diagnostic ability of tests are either limited or not reported.
Treatment – isolated PLC injury may be managed without surgery. Multi-ligament injuries have better outcomes with surgery.
Where to refer – orthopaedics for onward referral to physiotherapy or surgery.
The posterolateral corner consists of 28 individual static and dynamic structures that provide stability to the back (posterior), outer (lateral) aspect of the knee (figure 1). The lateral (fibular) collateral ligament (LCL), popliteus tendon and popliteofibular ligament are considered the most important stabilisers due to the significant support they provide to this relatively unstable part of the knee (figure 2). The common peroneal nerve is intimately related the posterolateral structures and fibula as it courses down the leg.
Figure 1-2: anatomy of the posterior (left) and lateral aspect of the knee (right). With permission LaPrade et al (2007) and LaPrade & Wentorf (2002).
The LCL is the main restraint to external rotation and adduction (varus) of the tibia between 0-30° of knee flexion. The popliteus tendon provides significant resistance to external tibial rotation, while the popliteofibular ligament provides both varus and external rotation stability. Together these tissues also resist hyperextension (over-straightening) of the knee; therefore, any forceful movements into external tibial rotation, varus, hyperextension or combinations of these positions can injure the PLC structures.
In the early stages following injury, the individual may complain of pain at the posterolateral aspect of the knee and the relevant soft tissues, or their points of insertion to bone, are usually tender on palpation (poking). Numerous PLC structures, including the LCL and popliteofibular ligament, attach to the head of the fibula and may avulse (pull away) bone during injury (figure 3). Tenderness at the fibular head may indicate a knee fracture and X-ray is therefore required to confirm or exclude this diagnosis. Pain may also be present in the medial (inside) compartment due to impaction of the bones during the injury.
Figure 3: avulsion fracture of the head of the fibula.
The LCL is an extra-articular structure (located outside the joint); therefore, injury to this ligament can result in localised lateral knee swelling. However, LCL injury rarely occurs without injury to an intra-articular structure (located inside the knee joint), therefore PLC injury usually presents with swelling within the knee joint (effusion).
Injury to the PLC can result in lateral and/or posterolateral rotatory instability (PLRI), which is often described by the individual as a ‘giving way’ sensation in the knee. Patients may demonstrate a varus thrust or posterolateral hyperextension thrust when walking, where the knee ‘thrusts’ outwards or backwards and outwards respectively during the weight bearing phase on the injured side. PLRI occurs when there is excessive posterior translation and lateral rotation of the lateral tibial plateau and the individual may walk with their lower leg and foot internally rotated to avoid placing the knee in this unstable position.
Unrecognised or untreated PLC injuries place greater strain on surgically reconstructed cruciate ligaments, which subsequently increases the risk of graft failure and further knee instability. In long-standing (chronic) cases, posterolateral knee instability can place excessive loads on the medial compartment of the knee, which in turn can lead to degenerative changes and associated medial knee symptoms.
The common peroneal nerve transmits signals from the skin to the central nervous system for sensation, and signals from the central nervous system to the muscles for muscular contraction. This nerve is affected in up to 26.2% of PLC injuries, presenting as altered sensation in the first web space (between the big toe and second toe) and/or top of the foot, or weakness into ankle dorsiflexion (upwards movements), toe extension and/or ankle eversion (outwards movement of the foot) (video 1). Individuals with weakness due to common peroneal nerve injury may walk with a foot drop gait.
Video 1: sensory and motor assessment of the common peroneal nerve.
27% of PLC injuries are isolated, with most injuries occurring in combination with cruciate ligament ruptures and knee dislocations. 18% of knee dislocations involve injury to vascular structures, which can become limb or life threatening. As a priority, it is therefore important to assess for vascular injury in cases of known or suspected knee dislocations.
Clinical tests that quantify adduction (varus), posterolateral rotation of the tibia or hyperextension (recurvatum) of the knee have been recommended to assess the integrity of the PLC. For details on the diagnostic accuracy of clinical tests for PLC injury, please visit the statistics section.
Varus Stress Test
This test is performed at both 20-30° and 0° of knee flexion, assessing for lateral joint gapping/laxity and an end point (video 2).
Video 2: varus stress test at 20-30° and 0° of knee flexion.
Varus laxity at 20-30°, but not at 0°, is suggestive of an LCL injury. Varus gapping at both 20-30° and 0° suggests the other PLC structures are also injured, with likely additional involvement of a cruciate ligament.
External Rotation 'Dial' Test
This test is performed with the patient supine (on their back) or prone (on their front) and knees together. The tibia is externally rotated as far as possible with the knee at 30° and 90° of knee flexion. The amount of external tibial rotation is compared between sides at both angles, using the medial borders of the feet for reference (video 3).
Video 3: prone dial test at 30° and 90°.
A side-to-side difference of greater than 10° is considered a positive test. A test that is positive at 30° of knee flexion but negative at 90° is suggestive of a PLC injury, while a test that is positive at both 30° and 90° may suggest additional posterior cruciate ligament (PCL) injury.
The PLC and PCL work together to control external rotation of the tibia, with most resistance provided at 30° of knee flexion by the PLC; in a PLC injured knee the dial test may therefore be positive in this position. As the knee flexes (bends) further, the PCL provides more resistance to external tibial rotation. In a PLC injured knee, the amount of external tibial rotation may therefore be less at 90° when the PCL is intact, but if there is a combined PLC-PCL injury, this side-to-side difference in external rotation may remain or increase at 90°. However, the only published study that has investigated the diagnostic accuracy of the dial test found that the test can be positive at both 30° and 90° in isolated PLC injuries. Care must also be taken when interpreting the dial test as positive tests at both 30° and 90° may indicate medial knee injury often, but not always, in association with an ACL rupture.
Reverse Pivot Shift Test
This is performed with the patient supine, knee flexed to 70-80° and foot supported on the examiner’s pelvis. The foot and leg is externally rotated, an axial load is applied through the foot and a valgus force applied to the knee via the proximal fibula. The knee is then straightened, assessing for a ‘shift’ at the knee (video 4).
Video 4: reverse pivot shift test.
This test aims to sublux (partially dislocate) the lateral tibia posterolaterally, which then relocates at approximately 40° of knee flexion, constituting a positive test. A positive test indicates a PLC injury with a markedly positive test suggestive of a combined PLC-PCL injury.
It is important to note that up to 35% of normal knees will test positive during the reverse pivot shift test.
External Rotation Recurvatum Test
This test is performed with the patient lying supine. The thigh is stabilised with one hand and the heel is lifted off the bed with the other hand by pulling upwards on the big toe (video 5).
Video 5: external rotation recurvatum test.
The test is deemed positive if the heel lifts ≥3cm further off the bed when compared with the unaffected side and is suggestive of a combined PLC and anterior cruciate ligament injury.
The extra movement at the knee is caused by a combination of anterior translation, varus angulation and external rotation of the tibia.
Posterolateral Drawer Test
This test is performed with the patient supine, knee flexed to 80° and tibia externally rotated 15°. A posterolateral force is then applied to the tibia, with a finger on the posterolateral aspect of the knee assessing for laxity (video 6).
Video 6: posterolateral drawer test
Increased posterolateral laxity is suggestive of a combined PLC and PCL injury.
Figure 4 and frog-leg test manoeuvre
The figure 4 test is performed with the patient supine or sitting, with the heel on the opposite leg, hip flexed, abducted and externally rotated; the leg will look like the number 4. The LCL is palpated for side to side difference.
The frog leg test is performed in supine, knees flexed to 90° and the soles of the feet together. The examiner applies a varus stress to both knees while simultaneously palpating the posterolateral structures for side-to-side difference in joint gapping and tissue integrity. This manoeuvre can be repeated at various knee angles as required (video 7).
Video 7: figure 4 and frog leg test.
A side-to-side difference in joint gapping or tissue integrity constitutes a positive test, which is considered diagnostic of posterolateral instability.
Classification of PLC injuries
Hughston grading scale: the amount of lateral joint gapping is measured during a varus stress test at both 30° and 0° of knee flexion. An increase in gapping on the injured side is graded as follows (table 1):
Table 1: Hughston grading scale
|Increased lateral knee gapping||0-5mm||5-10mm||>10mm|
It is important to note that this scale is based on the perceived amount of gapping and the actual values, as measured with X-ray (varus stress radiographs), are less than proposed.
Fanelli grading scale: this scale grades posterolateral instability by combining the findings of the external rotation and varus stress tests (table 2).
Table 2: Fanelli classification of posterolateral instability: PFL (popliteofibular ligament), PLT (popliteus tendon), LCL (lateral collateral ligament).
|Type||External rotation||Varus stress test at 30 degrees||Injured structures|
|A||Increased||Normal||PFL and PLT|
|B||Increased||Mild increase ≈ 5mm||PFL, PLT, attenuation of LCL|
|C||Increased||10mm||PFL, PLT, LCL, lateral capsular avulsion and cruciate ligament disruption|
If PLC injury is suspected, imaging can be ordered to assist diagnosis and to guide management.
The varus stress test may be performed during X-ray (varus stress radiographs), to objectively measure the difference in lateral joint gapping between sides; the amount of lateral knee gapping increases with each additional injury to a PLC structure (LCL= 2.7mm, + PLT = 3.5mm, + PFL = 4mm).
In individuals with a PCL injury, kneeling PCL stress X-rays with a side-to-side difference of more than 12mm are suggestive of a combined PCL and PLC injury.
In long-standing presentations, a standing long leg X-ray (figure 4) can identify leg malalignment that may require correction before, or during, PLC surgery. A line drawn from the head of the femur to the ankle indicates the mechanical access of the leg. If the mechanical axis falls medial to the Fujisawa point, there will more stress on the PLC, which may increase the risk of failure following PLC surgery.
Figure 4: standing long leg X-ray showing the mechanical axis (white and blue lines) and Fujisawa point.
MRI is useful to confirm injury to PLC structures and identify associated injuries (e.g. ACL, traumatic meniscal tears). Bone bruising may be evidence in the medial compartment of the knee, particularly the anteromedial femoral condyle, due to an impact of opposing bones.
The optimal management of isolated PLC injuries is not conclusive as little evidence exists comparing the conservative (non-surgical) and surgical outcomes. Based on limited evidence, the outcomes of surgery are superior to non-surgical management in combined PLC and cruciate ligament injuries. Dislocated knees, which often involve the PLC, have been shown to have superior outcomes in function, knee stability, return to work and return to sport following surgical intervention.
Early studies suggest that Grade I-II injuries may be successfully managed without surgery but grade III injuries have persistent instability and a five-fold increased chance of developing knee osteoarthritis. More recent studies have described successful management of grade III lateral collateral injuries but this evidence is limited. The PLC is initially protected with a long lever brace and protected weight bearing (figure 5) to encourage healing. For individuals with an incomplete LCL tear, a medial unloader brace (figure 6) is recommended when returning to sporting activities. Below is an example protocol, based on expert opinion and published studies.
Figure 5: Long lever brace and protected weight bearing with crutches, medial unloader brace.
Surgical repair/reattachment of avulsed PLC structures may only be possible within three weeks of injury as after this timeframe the injured tissue may retract or die (necrose), rendering the damaged tissues irreparable. However, in these acute presentations, the failure rate for PLC repair and staged cruciate ligament reconstruction is 38%, whereas the failure rate of PLC and cruciate ligament reconstruction is 9%. Mid-substance LCL tears, or non-acute presentations, are not considered repairable, therefore surgical reconstruction may be indicated. The failure rate for PLC reconstruction in chronic (longstanding) presentations is 10%.
Various surgical techniques have been proposed; the procedure of choice is often dependent on surgeon preference and patient presentation.
Limited evidence exists regarding rehabilitation after PLC surgery; rehabilitation is often inadequately described regarding the number of sets/repetitions of exercises and criteria for progression. Below is a recommended protocol based on expert opinion.
The management of common peroneal nerve injury is dependent on the patient presentation. Most patients with an incomplete palsy (paralysis/weakness) will achieve full muscle recovery and a wait-and-see approach is therefore advocated, whereas less than 40% of patients with a complete motor palsy will regain the ability to dorsiflex at the ankle. Electromyography and nerve conduction studies may be performed to evaluate the status of the nerve and surgical intervention may be necessary if there is no evidence of recovery within 3 months of injury. During this wait-and-see period, an ankle foot orthosis (foot drop splint) and ankle range of movement exercises are required to prevent equinus deformity (stiffness resulting in an inability to dorsiflex the ankle).
Surgical intervention may involve exploration and release of the nerve from surrounding scar tissue (neurolysis) at the time of PLC repair/reconstruction, while nerve repair or nerve grafting may be considered in cases of complete nerve disruption. Based on limited evidence, the most predictable means of re-establishing antigravity dorsiflexion in persistent common peroneal nerve palsy is a posterior tibial tendon transfer.
Recovery following PLC injury is dependent on the presence or absence of additional injury, and whether surgery has been performed or not. Return to work and sporting activity is possible in most cases after combined ACL-PLC reconstruction.
Suspected or confirmed knee dislocations should be assessed and managed on an emergency basis (i.e. via A&E). Suspected PLC injury should be referred to orthopaedics for assessment and onward referral to physiotherapy or surgery, as appropriate.
Written by: Richard Norris & Daniel Massey, The Knee Resource
Reviewed by: Robert F. LaPrade, MD, PhD
Complex Knee and Sports Medicine Surgery, The Steadman Clinic
Chief Medical Officer, Steadman Philippon Research Institute
Co-Director, Sports Medicine Fellowship Program
Director, International Scholar Program
Adjunct Professor, Orthopaedic Surgery, University of Minnesota
Affiliate Faculty, College of Veterinary Medicine and Biomedical Sciences, Colorado State University
Bae JH, Choi IC, Suh SW, Lim HC, Bae TS, Nha KW, et al. Evaluation of the reliability of the dial test for posterolateral rotatory instability: a cadaveric study using an isotonic rotation machine. Arthroscopy. 2008;24(5):593-8.
Bonanzinga T, Zaffagnini S, Grassi A, Marcheggiani Muccioli GM, Neri MP, Marcacci M. Management of Combined Anterior Cruciate Ligament-Posterolateral Corner Tears: A Systematic Review. Am J Sports Med. 2014;42(6):1496-503.
Bushnell BD, Bitting SS, Crain JM, Boublik M, Schlegel TF. Treatment of magnetic resonance imaging-documented isolated grade III lateral collateral ligament injuries in National Football League athletes. Am J Sports Med. 2010;38(1):86-91.
Cooper DE. Tests for posterolateral instability of the knee in normal subjects. Results of examination under anesthesia. J Bone Joint Surg Am. 1991;73(1):30-6.
Cooper JM, McAndrews PT, LaPrade RF. Posterolateral corner injuries of the knee: anatomy, diagnosis, and treatment. Sports Med Arthrosc. 2006;14(4):213-20.
Ellera Gomes JL, Leie MA, Ramirez E, Gomes TE. Frog-Leg Test Maneuver for the Diagnosis of Injuries to the Posterolateral Corner of the Knee: A Diagnostic Accuracy Study. Clin J Sport Med. 2016;26(3):216-20.
Geeslin AG, LaPrade RF. Outcomes of treatment of acute grade-III isolated and combined posterolateral knee injuries: a prospective case series and surgical technique. J Bone Joint Surg Am. 2011;93(18):1672-83.
Geeslin AG, Moulton SG, LaPrade RF. A Systematic Review of the Outcomes of Posterolateral Corner Knee Injuries, Part 1: Surgical Treatment of Acute Injuries. Am J Sports Med. 2016;44(5):1336-42.
Gollehon DL, Torzilli PA, Warren RF. The role of the posterolateral and cruciate ligaments in the stability of the human knee. A biomechanical study. J Bone Joint Surg Am. 1987;69(2):233-42.
Grood ES, Stowers SF, Noyes FR. Limits of movement in the human knee. Effect of sectioning the posterior cruciate ligament and posterolateral structures. J Bone Joint Surg Am. 1988;70(1):88-97.
Haddad MA, Budich JM, Eckenrode BJ. Conservative management of an isolated grade iii lateral collateral ligament injury in an adolescent multi-sport athlete: a case report. Int J Sports Phys Ther. 2016;11(4):596-606.
Harner CD, Vogrin TM, Höher J, Ma CB, Woo SL. Biomechanical analysis of a posterior cruciate ligament reconstruction. Deficiency of the posterolateral structures as a cause of graft failure. Am J Sports Med. 2000;28(1):32-9.
Hughston JC, Andrews JR, Cross MJ, Moschi A. Classification of knee ligament instabilities. Part II. The lateral compartment. J Bone Joint Surg Am. 1976;58(2):173-9.
Hughston JC, Norwood LA. The posterolateral drawer test and external rotational recurvatum test for posterolateral rotatory instability of the knee. Clin Orthop Relat Res. 1980(147):82-7.
Jackman T, LaPrade RF, Pontinen T, Lender PA. Intraobserver and interobserver reliability of the kneeling technique of stress radiography for the evaluation of posterior knee laxity. Am J Sports Med. 2008;36(8):1571-6.
Jakob RP, Hassler H, Staeubli HU. Observations on rotatory instability of the lateral compartment of the knee. Experimental studies on the functional anatomy and the pathomechanism of the true and the reversed pivot shift sign. Acta Orthop Scand Suppl. 1981;191:1-32.
James EW, LaPrade CM, LaPrade RF. Anatomy and biomechanics of the lateral side of the knee and surgical implications. Sports Med Arthrosc. 2015;23(1):2-9.
Kannus P. Nonoperative treatment of grade II and III sprains of the lateral ligament compartment of the knee. Am J Sports Med. 1989;17(1):83-8.
Kim YH, Purevsuren T, Kim K, Oh KJ. Contribution of posterolateral corner structures to knee joint translational and rotational stabilities: a computational study. Proc Inst Mech Eng H. 2013;227(9):968-75.
Krukhaug Y, Mølster A, Rodt A, Strand T. Lateral ligament injuries of the knee. Knee Surg Sports Traumatol Arthrosc. 1998;6(1):21-5.
LaPrade RF, Heikes C, Bakker AJ, Jakobsen RB. The reproducibility and repeatability of varus stress radiographs in the assessment of isolated fibular collateral ligament and grade-III posterolateral knee injuries. An in vitro biomechanical study. J Bone Joint Surg Am. 2008;90(10):2069-76.
LaPrade RF, Ly TV, Griffith C. The external rotation recurvatum test revisited: reevaluation of the sagittal plane tibiofemoral relationship. Am J Sports Med. 2008;36(4):709-12.
LaPrade RF, Morgan PM, Wentorf FA, Johansen S, Engebretsen L. The anatomy of the posterior aspect of the knee. An anatomic study. J Bone Joint Surg Am. 2007;89(4):758-64.
LaPrade RF, Muench C, Wentorf F, Lewis JL. The effect of injury to the posterolateral structures of the knee on force in a posterior cruciate ligament graft: a biomechanical study. Am J Sports Med. 2002;30(2):233-8.
LaPrade RF, Resig S, Wentorf F, Lewis JL. The effects of grade III posterolateral knee complex injuries on anterior cruciate ligament graft force. A biomechanical analysis. Am J Sports Med. 1999;27(4):469-75.
LaPrade RF, Terry GC. Injuries to the posterolateral aspect of the knee. Association of anatomic injury patterns with clinical instability. Am J Sports Med. 1997;25(4):433-8.
LaPrade RF, Tso A, Wentorf FA. Force measurements on the fibular collateral ligament, popliteofibular ligament, and popliteus tendon to applied loads. Am J Sports Med. 2004;32(7):1695-701.
LaPrade RF, Wentorf F. Diagnosis and treatment of posterolateral knee injuries. Clin Orthop Relat Res. 2002(402):110-21.
LaPrade RF, Wentorf FA, Crum JA. Assessment of healing of grade III posterolateral corner injuries: an in vivo model. J Orthop Res. 2004;22(5):970-5.
Loomer RL. A test for knee posterolateral rotatory instability. Clin Orthop Relat Res. 1991(264):235-8.
Lunden JB, Bzdusek PJ, Monson JK, Malcomson KW, Laprade RF. Current concepts in the recognition and treatment of posterolateral corner injuries of the knee. J Orthop Sports Phys Ther. 2010;40(8):502-16.
Medina O, Arom GA, Yeranosian MG, Petrigliano FA, McAllister DR. Vascular and nerve injury after knee dislocation: a systematic review. Clin Orthop Relat Res. 2014;472(9):2621-9.
Moulton SG, Geeslin AG, LaPrade RF. A Systematic Review of the Outcomes of Posterolateral Corner Knee Injuries, Part 2: Surgical Treatment of Chronic Injuries. Am J Sports Med. 2016;44(6):1616-23.
Norris R, Kopkow C, McNicholas MJ. Interpretations of the dial test should be reconsidered. A diagnostic accuracy study reporting sensitivity, specificity, predictive values and likelihood ratios. Journal of ISAKOS: Joint Disorders & Orthopaedic Sports Medicine. 2018 Mar 14:jisakos-2018.
Noyes FR, Cummings JF, Grood ES, Walz-Hasselfeld KA, Wroble RR. The diagnosis of knee motion limits, subluxations, and ligament injury. Am J Sports Med. 1991;19(2):163-71.
Noyes FR, Stowers SF, Grood ES, Cummings J, VanGinkel LA. Posterior subluxations of the medial and lateral tibiofemoral compartments. An in vitro ligament sectioning study in cadaveric knees. Am J Sports Med. 1993;21(3):407-14.
Olsson O, Isacsson A, Englund M, Frobell RB. Epidemiology of intra- and peri-articular structural injuries in traumatic knee joint hemarthrosis – data from 1145 consecutive knees with subacute MRI. Osteoarthritis Cartilage. 2016;24(11):1890-7.
Peskun CJ, Whelan DB. Outcomes of operative and nonoperative treatment of multiligament knee injuries: an evidence-based review. Sports Med Arthrosc. 2011;19(2):167-73.
Ridley TJ, McCarthy MA, Bollier MJ, Wolf BR, Amendola A. The incidence and clinical outcomes of peroneal nerve injuries associated with posterolateral corner injuries of the knee. Knee Surg Sports Traumatol Arthrosc. 2017.
Rochecongar G, Plaweski S, Azar M, Demey G, Arndt J, Louis ML, et al. Management of combined anterior or posterior cruciate ligament and posterolateral corner injuries: a systematic review. Orthop Traumatol Surg Res. 2014;100(8 Suppl):S371-8.
Sanchez AR, Sugalski MT, LaPrade RF. Anatomy and biomechanics of the lateral side of the knee. Sports Med Arthrosc. 2006;14(1):2-11.
Woodmass JM, Romatowski NP, Esposito JG, Mohtadi NG, Longino PD. A systematic review of peroneal nerve palsy and recovery following traumatic knee dislocation. Knee Surg Sports Traumatol Arthrosc. 2015;23(10):2992-3002.