Radiology in Primary Care Sports and Exercise Medicine
August 6, 2020
Ulnar Nerve Entrapment
February 22, 2021

Posterolateral Corner Injuries

Posterolateral Corner Injuries


18M Elite Level Field Lacrosse player presents with 2 year history of right lateral knee pain. Initially, injury was sustained when hit from the left side, with this right leg planted resulting in the large varus force. A pop was felt, he was removed from the game, and swelling developed a few hours later. He underwent rehabilitation, without further imaging, for suspected IT Band tear. He presents to clinic with ongoing lateral knee pain, worse with sprinting and change of direction. Expresses ongoing instability with change of direction, and catching at terminal flexion portion of squat. 


The posterolateral corner (PLC) of the knee is commonly referred to as “the dark side of the knee”, due to the fact that little was known about its specific anatomy, biomechanics, and management options. Thankfully, our knowledge around these topics has greatly expanded with numerous studies confirming the PLC’s structure and validating biomechanical reconstructive techniques. The incidence of posterolateral knee injuries among patients presenting with an acute hemarthrosis of the knee injury has been reported as 9.1%3

28% of PLC injuries occur in isolation, with the vast majority associated with ACL or PCL injuries. If a PLC injury is missed or left untreated, it may compromise the integrity of an ACL or PCL surgical reconstruction. This would subsequently lead to altered knee biomechanics and early degenerative changes. 

In order to identify PLC injuries, a high index of suspicion is needed in conjunction with a thorough history and physical examination. 


Three Static Stabilizers:

1.Lateral Collateral Ligament (LCL)

  • Primary varus stabilizer of the knee

2.Popliteus Tendon (PLT)

  • The most anterior insertion of the PLC structure
  • Tendon becomes intra-articular as it courses deep to the LCL

3.Popliteofibular Ligament (PFL)

Secondary Stabilizers:

These structures assist in static and dynamic stabilization and are listed from deep to superficial: 

  • Lateral capsular thickening consisting of the meniscofemoral and meniscotibial ligaments
  • Coronary ligament
  • Sural triceps (lateral gastrocnemius, medial gastrocnemius, and soleus)
  • Fabellofibular ligament
  • Long head of biceps femoris
  • IT band

Figure 1: Anatomy of the Posterolateral Corner1


Main function: 

  • Primary restraint against varus forces
  • Limits posterolateral rotation of the tibia on the femur
  • In cruciate ligament deficient knees:
    • Provides anterior and posterior stabilization of the tibia 

Secondary function:

  • Internal rotation (PLT)
  • Anteroposterior tibial translation

History and Physical Examination: 


  • Sudden, traumatic onset
  • Mechanism of Injury:
    • Posterolateral directed force to the anteromedial knee (varus force)
    • Hyperextension (contact or non-contact)
    • External rotation twisting injury
    • Non-contact varus 
    • Knee dislocation
  • Commonly associated with ACL or PCL tears
  • Symptoms: 
    • Pain, ecchymosis, swelling
    • Side-to-side instability
    • Difficulty walking on uneven ground or up/down stairs
    • Paresthesias in common peroneal nerve distribution 
      • One third of PLC injures have peroneal nerve damage

Physical Examination: 

    • Inspection:
      • Standing Varus Alignment or Hyperextension
      • Varus Thrust gait
      • ?Bruising on anterior aspect of tibia
      • Posterior knee ecchymosis or swelling
    • Palpation:
      • Localized to the lateral and posterolateral aspect of the knee
      • Place patient in ‘Figure 4 position’ to more easily identify and palpate the lateral structures of the knee (LCL, lateral meniscus, biceps femoris tendon, IT Band, etc.
    • Special Tests: 
      • Consider injury chronicity when interpreting findings. 


  • Varus Stress Test:


        • Perform at 0° and 20-30° of flexion
        • Laxity at 20-30°, without laxity at 0° = isolated LCL injury
        • Laxity at 20-30°, with laxity at 0°  = LCL, PLC, and cruciate ligament injury


  • Dial Test


      • Measures ER of the tibia relative to the femur
      • Patient placed in prone (or supine) position, with knees flexed at 30° and then 90°
      • Tibia is externally rotated and compared to the contralateral side
      • >10° difference at 30° flexion, without difference at 90° = isolated PLC injury
      • >10° difference at 30° and at 90° = combined PLC and PCL injury
      • Important: Dial test is NOT pathognomonic for PLC injury2

Figure 2: Dial test: Patient prone and the knees flexed to a) 90° and b) 30°. Note: increased external rotation of the right leg compared to the left. Consistent with PLC & PCL injury


  • Posterolateral Rotatory Drawer Test


      • Addition of rotation to the posterior drawer test
        • Tibia is placed in external rotation with posterior directed force at the anterior tibial tuberosity
      • Compare amount of translation with rotation vs. posterior drawer in neutral position


  • Reverse Pivot Shift


      • Essential component to PLC Exam
      • Technique:
        • Patient supine with knee flexed at 90° → joint line palpated → valgus load to knee → external rotation force to tibia → slowly extend knee
      • Positive test = reduction of subluxed lateral tibial plateau at 35-40° of flexion
      • Why? IT Band changes from knee flexor to knee extender
      • PPV: 68%, NPV: 89%
      • Comparison to contralateral the knee is essential. Positive in 35% of uninjured knees


  • External Rotation Recurvatum Test


      • Technique:
        • Patient supine → knee extended → grasp first toe → lift leg off table while stabilizing anterior distal femur to the table with opposite hand
        • Compare height of heel to contralateral side
      • Poor sensitivity: 10% of 134 PLC injuries
      • However, positive predicted combined ACL/PLC injuries


  • Neurovascular Exam


    • Particular attention to integrity of common peroneal nerve as can be injured in up to 15% of cases


  • Radiograph
    • Acute injury
      • may see avulsion fracture of the fibula (arcuate fracture) or femoral condyle
      • Can be negative
    • Chronic injury 
      • Standing long-leg AP alignment
      • Assess for malalignment that may need to be corrected with biplanar osteotomy (before or at the time of PLC reconstruction
    • Bilateral Varus Stress Views
      • Performed at 20° flexion
      • Distance between most distal aspect of the lateral femoral condyle and the corresponding tibial plateau
      • Side-to-side difference 2.7-4mm = isolated LCL
      • Side-to-side difference > 4mm = PLC injury
      • Pre and post-operative views are helpful to objectively assess PLC reconstruction stability2

Figure 3: Arcuate Fracture

Figure 4: Stress radiographs

  • MRI
    • Look for injuries to PLC structures
    • In acute injuries: 
      • bone marrow edema to medial femoral condyle and medial tibial plateau
    • Coronal oblique thin slice through fibular head is the best view for PLC structures 
    • Chronic multiligamentous injuries
      • Less reliable and accurate
      • Previously torn ligaments, may appear morphologically intact yet physiologically incompetent 
  • Other
    • Vascular studies if concerns for vascular injury or ABI <0.9
    • EMG/NCS if concerns for neurological dysfunction


  • International consensus that current classifications systems are too vague/complicated
  • Updated system needed.  


  • Significant heterogeneity amongst international consensus. 
  • Non-operative:
    • Indications
      • Grade I PLC injuries
      • Grade II isolated midsubstance injury
    • Hinged knee brace locked in extension x 4 weeks
    • Progressive rehabilitation and quadriceps strengthening
    • Return to sport: 8 weeks
  • Operative:
    • Acute injuries should be addressed within 2-3 weeks of injury
    • PLC repair: 
      • isolated acute Grade II PLC avulsion injuries
    • PLC hybrid reconstruction and repair: 
      • Grade III midsubstance
      • Avulsion injury with poor tissue or repair not possible
      • Rehabilitation
        • hinged knee brace, NWB x 6 weeks
        • range of motion protocols differ 
          • some advocate for passive ROM immediately 0-90°
          • others immobilize for 2 weeks, then begin motion
        • at 6 weeks, begin weight bearing and closed-chain strengthening
        • return to activities / sports in approximately 6 to 9 months
      • outcomes
        • Improved outcomes compared to nonoperative treatment
        • repair has higher failure rate than reconstruction
        • improved outcomes with early treatment
        • anatomic reconstruction restores rotatory stability, but not all varus stability on stress testing
    • PLC reconstruction, +/- ACL reconstruction, +/- PCL reconstruction, +/- High tibial osteotomy
      • Acute and chronic combined ligamentous injuries
      • Rehabilitation
        • Postoperatively immobilize and protected weight bear x 4 weeks make 
        • Passive ROM at 4 weeks 
        • Avoid active hamstring exercises to not stress PLC 
        • Full active extension is allowed
      • Prognosis
        • Less revision and better outcomes than ligament repair
        • ACL reconstruction + PLC repair 33% achieved IKDC grade A or B compared to 88% of patients who underwent ACL + PLC reconstruction


  • Regardless of surgical technique the following principles should be applied: 
    •  Sequential staged rehabilitation protocol: range of motion → muscular endurance → strength → power
    • Immediate post-op protocol: Knee brace x 6 wks, early ROM (day 1)
    • RTP: Isolated PLC reconstruction NOT before 9 months and based on functional tests
    • PLC injuries rarely occur in isolation so post-operative rehabilitation protocols are based on the concomitant injuries.


Author:  Dr. Alessandro Francella (PR ND Nov 10,2020)


  1. Chahla, J., et al. (2016). “Posterolateral Corner of the Knee: Current Concepts.” Arch Bone Jt Surg 4(2): 97-103.
  2. Chahla, J., et al. (2019). “Posterolateral corner of the knee: an expert consensus statement on diagnosis, classification, treatment, and rehabilitation.” Knee Surgery, Sports Traumatology, Arthroscopy 27(8): 2520-2529.
  3. Devitt, B. M. and D. B. Whelan (2015). “Physical examination and imaging of the lateral collateral ligament and posterolateral corner of the knee.” Sports Medicine & Arthroscopy Review 23(1): 10-16.
  4. Basseet A. Posterolateral Corner Injury.