Posterolateral Corner

The posterolateral corner (PLC) is a collective term for multiple structures within the knee joint. These include:

• Tibia
• Fibula
• Lateral Femur
• IT band
• Long and short heads of biceps femoris tendon
• LCL (otherwise known as the fibular collateral ligament)
• Popliteus tendon
• Popliteofibular ligament (PFL)
• Lateral gastrocnemius tendon

The three most important static stabilisers are the LCL, popliteus tendon and PFL as they restrict varus, external rotation and posterior translation.

From 0 to 30 degrees of flexion, the LCL is the main structure preventing varus opening of the knee (although the IT band assists). The popliteofibular ligament connects the popliteus muscle at the musculotendious junction to the posterior, medial portion of the fibular styloid and stablises the knee during external rotation.The popliteus tendon provides static and dynamic stabilisation to the knee during posterolateral rotation.

The two convex opposing surfaces (lateral femoral condyle and lateral tibial plateau) makes the posterolateral corner more unstable than the medial aspect, therefore increasing the risk of poor healing post-injury.

Specialised Tests

Varus Stress Test at 0 and 30 degrees

       Grade I - Pain but no gapping of the lateral joint space

       Grade II - Some gapping of the lateral joint space, but with a definite end point

       Grade III - Significant gapping with no definite end point.

Increased gapping at 0 degrees typically indicates a serious posterolateral injury with a high probability of cruciate ligament involvement. Lower grades at 30 degrees are more indicative of partial LCL tears, with higher grades indicating complete tears of the LCL.

Posterolateral Drawer Test - Similar to the posterior drawer test, however the foot is externally rotated to 15 degrees. While stabilising the foot, appy a posterolateral rotation to the tibia. Increased mobility indicates injury to the popliteus complex.

Figure 4 Test - Patient lies supine and flexes the knee to 90 degrees with the ankle resting on the other knee by placing the hip into external rotation. Application of a varus stress on the knee places tension particularly on the popliteus complex. When injured, there is no tension to stabilise the lateral meniscus allowing it to medially displace into the joint, reproducing the patient's symptoms at the lateral joint line.