Posterior Cruciate Ligament Tear

The posterior cruciate ligament is the primary restraint to posterior tibial translation and the central stabilizer of the knee. Injuries make up 1 to 44% of acute knee ligament injuries depending on the population, and most (60 to 80%) occur with other ligament injuries. Mechanisms:

• Dashboard injury (posterior force on the flexed tibia)
• Fall on the flexed knee with the foot plantarflexed
• Hyperextension and rotational injury

Grading by posterior tibial step off relative to the femoral condyles in 90 degrees of flexion: grade I is 1 to 5 mm (step off preserved), grade II 6 to 10 mm (flush), grade III over 10 mm (tibia behind the condyle, which suggests a combined injury). Isolated grade I and II injuries generally do well, but late patellofemoral and medial compartment osteoarthritis occurs with persistent laxity. Associated injuries include posterolateral corner, medial collateral ligament, anterior cruciate ligament, meniscus and popliteal artery.

• Posterior knee pain, mild swelling (the effusion is often small because of capsular tears), and difficulty kneeling or descending stairs
• Posterior sag sign, posterior drawer test (the most sensitive test, about 90%) and a positive quadriceps active test
• Dial test at 30 degrees (increase over 10 degrees external rotation than the other side suggests posterolateral corner injury), and at both 30 and 90 degrees (posterolateral corner with the posterior cruciate)
• Reverse pivot shift and varus stress laxity
• Red flags: cool or pulseless limb (ankle brachial index below 0.9 needs CT angiography), foot drop, grade III laxity and gross instability

• Examination with the posterior drawer and sag signs. Check neurovascular status.
• Radiographs for tibial avulsion at the posterior insertion and posterior subluxation.
• Stress radiographs at 90 degrees of flexion with posterior load: side-to-side difference of 8 mm or more indicates a complete tear, and 12 mm or more suggests a combined injury.
• MRI for ligament continuity, bone bruising and associated injuries.

Differentials: anterior cruciate tear, posterolateral corner injury, tibial plateau fracture, patellar tendon rupture, meniscal injury.

Isolated grade I and II:

• Functional posterior cruciate brace for 6 weeks, with quadriceps strengthening and no hamstring resistance for 12 weeks.
• Ibuprofen 400 mg orally every 8 hours for up to 5 to 7 days with food.
• Return to sport at 6 to 12 weeks if there is no effusion and the strength deficit is under 10%.

Surgery:

• Acute avulsion fractures displaced over 2 mm: fixation.
• Grade III isolated, combined injuries and symptomatic chronic laxity: single or double bundle reconstruction or tibial inlay technique with autograft (hamstring, quadriceps) or Achilles allograft, ideally within 3 weeks for combined injuries.
• Cefazolin 2 g IV before incision (3 g if over 120 kg), and enoxaparin 40 mg SC daily for 7 to 14 days in patients at high risk of thrombosis.

Postoperative rehabilitation: non-weight-bearing in extension for 2 to 6 weeks, prone motion exercises, no resisted hamstring work for 4 months, and a return to sport at 9 to 12 months.

Complications: residual posterior laxity (common), arthrofibrosis, popliteal artery injury during tunnel drilling, graft failure, saphenous neuralgia.

Follow up at 2 weeks, 6 weeks, 3 months, 6 months and 12 months with repeat stress radiographs if laxity persists. Counsel on osteoarthritis risk.