CASE 56

By: Dr. Subramaniyan Ramanathan MD, Dr. Mahmoud Alheidous and Dr. Nizar Al-Nakshabandi. MD, FRCPC.

HISTORY: 25-year-old male with soccer injury.

What are your findings?

What is the differential diagnosis?

What are the causes?

FINDINGS:

There is tear of the anterior cruciate ligament, torn arcuate ligament, fibulopopliteal ligament is completely ruptured. And retraction of the anterior extension of the biceps femoris tendon.

DIAGNOSIS:

Posterior lateral corner injury of the knee.

PEARLS AND DISCUSSION:

The 4 structures of the posterolateral ligamentous complex are:

• Lateral (fibular) collateral ligament.

• Popliteus muscle.

• Popliteofibular ligament.

• Biceps femoris tendon.

The mechanism of injury is thought to be a direct blow to the anteromedial proximal tibia directed posterolaterally with knee in full extension. Combination of varus force with a posteriorly directed blow to the proximal tibia with the knee flexed. It is important to recognize this injury as it is the most common identifiable cause for failed ACL reconstruction surgery. Failure to address posterolateral instability will lead to development of osteoarthritis. Reconstruction of the posterolateral structures is performed in the acute setting. Because MRI is performed in knee injury, the radiologist should be familiar with the normal and abnormal appearance of posterolateral corner structures on MRI and suggests the diagnosis of posterolateral corner injury. Visualization of complete tears involving 2 or more structures of the posterolateral corner on MRI in particular the popliteus musculo-tendinous unit, the fibular collateral ligament, or the posterior lateral joint capsule should strongly suggest posterolateral rotatory instability.

Classification:

Grade I (0-5 mm of lateral opening and minimal ligament disruption).

Grade II (5-10 mm of lateral opening and moderate ligament disruption).

Grade III (> 10 mm of lateral opening and severe ligament disruption and no endpoint).

Treatment is by operative and postoperative approaches.

The nonoperative procedure is by immobilizing the knee in full extension with protected weightbearing for 2 weeks.

Operative is by PCL repair, PCL reconstruction, PCL repair reconstruction and with ACL construction.

Complications include arthrofibrosis, missed PCL injury, and peroneal nerve injury in up to 30% of cases.

FURTHER READING:

1. Emily N. Vinson, Nancy Major and Clyde Helms. The posterolateral corner of knee. AJR. 2008; 190: 449-458.

2. BakerCL, Norwood LA, Hughston JC. Acute posterolateral instability. Jbone Joint Surg Am 1983; 65:614

3. Chen FS, Rokito As, Pitman MI, Acute and chronic posterolateral corner rotatatory instability of knee. J Acad Orthop Surg 2000; 8:97-110.