Initial Workup for Suspected Posterior Cruciate Ligament (PCL) Injury
The initial workup for a suspected PCL injury should include radiographs (X-rays) as the first imaging modality, followed by MRI if clinical suspicion remains high despite normal radiographs. 1
Clinical Evaluation
History
- Mechanism of injury:
- Timing of injury (acute vs. chronic)
- Associated symptoms:
- Posterior knee pain
- Instability with activities, especially descending stairs
- Difficulty with deceleration activities
Physical Examination
Key diagnostic tests:
- Posterior sag sign - most characteristic finding; apparent disappearance of tibial tubercle when knee is flexed to 90° due to gravity-assisted posterior displacement 2
- Posterior drawer test - performed at 90° knee flexion; positive when tibia can be pushed posteriorly relative to femur 3
- Quadriceps active test - patient actively contracts quadriceps with knee flexed at 90°; positive when tibia anteriorly translates from a posteriorly sagged position 3
- Reverse pivot shift test - for posterolateral instability
Assess for associated injuries:
- Collateral ligament stability (varus/valgus stress tests)
- Anterior cruciate ligament integrity (Lachman test)
- Meniscal tears (McMurray test)
- Posterolateral corner integrity
Imaging Protocol
First-Line Imaging
- Plain radiographs (minimum of two views: anteroposterior and lateral) 1
- To rule out fractures, particularly tibial avulsion fractures
- To assess for joint effusion
- To evaluate for malalignment
- To identify associated bony injuries
Second-Line Imaging
- MRI without contrast - gold standard for PCL evaluation 1, 3
- Near 100% sensitivity for PCL tears
- Can identify:
- Complete vs. partial tears
- Location of tear (mid-substance vs. avulsion)
- Associated injuries (meniscal tears, other ligament injuries, bone contusions)
- Chronic changes
Stress Radiographs (optional)
- Posterior stress views can quantify the degree of posterior tibial translation
- Useful for grading PCL injuries:
- Grade I: 0-5 mm of posterior translation
- Grade II: 5-10 mm of posterior translation
- Grade III: >10 mm of posterior translation
Arthroscopic Evaluation
If surgical intervention is being considered, arthroscopic evaluation provides definitive diagnosis 3:
- "Floppy ACL sign" - ACL appears lax due to posterior tibial subluxation
- Posteromedial "drive-through" sign
- Direct visualization of PCL tear
Grading System
- Grade I: Partial tear with minimal laxity
- Grade II: Partial tear with increased posterior laxity but firm endpoint
- Grade III: Complete tear with significant posterior laxity and no endpoint
- Grade IV: Combined PCL tear with other ligamentous injuries
Important Considerations
- PCL tears are often missed in the acute setting due to subtle clinical findings
- Always distinguish between isolated PCL injuries and multi-ligament injuries, as treatment approaches differ significantly
- In acute injuries, examination may be limited by pain and swelling; consider re-evaluation after 1-2 weeks
- PCL injuries commonly occur with other ligamentous injuries (especially posterolateral corner injuries), which must be identified for proper treatment planning
Common Pitfalls to Avoid
- Failing to perform a complete knee examination that includes PCL-specific tests
- Misinterpreting a positive posterior drawer test as an ACL insufficiency
- Relying solely on MRI without correlating with clinical examination findings
- Missing associated injuries, particularly posterolateral corner injuries
- Overlooking tibial avulsion fractures that may require surgical fixation
By following this systematic approach to PCL injury evaluation, clinicians can accurately diagnose the injury and determine the appropriate treatment strategy based on injury severity and associated pathology.