Varus Knee Test for Lateral Collateral Ligament (LCL) Injury
The varus stress test evaluates LCL integrity by applying a varus (adduction) force to the knee, typically performed at 0° and 30° of flexion, with increased lateral joint opening indicating LCL injury. 1
Test Procedure
Patient Positioning and Technique
- Position the patient supine with the knee in slight flexion (30°) for optimal assessment 1
- Stabilize the distal femur with one hand while applying a varus (adduction) stress to the proximal tibia with the other hand 1
- Apply approximately 5 Nm of varus torque to assess lateral joint opening 2, 3
- Test at both 0° (full extension) and 30° of flexion to differentiate isolated LCL injury from combined injuries 4
Critical Technical Consideration
- Apply posterior tibial load during varus testing to avoid overestimating instability in ACL-deficient knees 2
- Without posterior tibial load, varus-valgus laxity may be falsely elevated in ACL-injured knees, as the ACL contributes approximately 30 N of restraining force at 30° flexion 2
Interpretation of Results
Grading Joint Opening
- <10° of lateral joint widening = slight instability 4
- >10° of lateral joint widening = moderate instability 4
- Frank redislocation with stress = gross instability requiring surgical fixation 4
Clinical Correlation
- Increased laxity at 30° flexion suggests isolated LCL injury 1
- Increased laxity at both 0° and 30° indicates more extensive posterolateral corner (PLC) involvement 3
- Pain around the fibular head in the figure-of-four position combined with inability to palpate the LCL suggests complete LCL disruption 5
Diagnostic Accuracy and Limitations
Test Performance
- Varus stress testing has sensitivity of 84% and specificity of 96% when performed 4-5 days post-injury (allowing acute pain and swelling to subside) 4
- Acute testing may be limited by patient guarding and pain 4
Common Pitfall
- Isolated LCL injuries may not demonstrate obvious instability on manual testing despite complete rupture 5
- In such cases, rely on patient history (forced varus mechanism), pain with palpation at fibular head, and inability to palpate the LCL 5
When to Advance to Imaging
Indications for MRI
- Clinical suspicion of LCL injury with normal or equivocal varus stress testing 5
- Suspected high-grade ligament injuries or posterolateral corner involvement 4
- MRI demonstrates 93-96% sensitivity and 100% specificity for visualizing ligamentous injuries 4
- Varus stress MRI can quantify lateral joint space opening and assess functional capacity of the PLC 3
Stress Radiography Considerations
- Varus stress radiographs have limited diagnostic value (67% accuracy) and cause pain during acute testing 4
- Stress radiography is considered obsolete and should not be used in acute settings 4
- Dynamic fluoroscopy can distinguish stages of collateral ligament injury but requires specialized equipment 4
Associated Injuries to Assess
Concurrent Ligament Damage
- ACL-deficient knees demonstrate significantly greater varus-valgus laxity than intact knees 2, 6
- Lateral knee instability correlates with positive Lachman and pivot shift tests 6
- 19.7% of ACL ruptures have concomitant posterolateral corner injuries that must not be missed 4