Knee Collateral Ligament Examination
The collateral ligament examination requires systematic varus and valgus stress testing at both 0° and 30° flexion. Examiners expect you to understand why 30° testing isolates the collaterals, recognize the posterolateral corner (PLC), and identify combined injuries.
Quick Reference One-Pager
MCL Testing
- Valgus stress at 0° and 30°
- Laxity at 30° only = isolated MCL
- Laxity at 0° = MCL + ACL/PCL or capsular injury
- Palpate along MCL course
LCL/PLC Testing
- Varus stress at 0° and 30°
- Dial test at 30° and 90°
- Posterolateral drawer
- Reverse pivot shift
Grading
- Grade I: 0-5mm (mild sprain, stable)
- Grade II: 5-10mm (moderate, partial tear)
- Grade III: greater than 10mm (complete tear)
Key Points
- 30° flexion unlocks the knee (isolates collaterals)
- 0° positive = combined injury
- Always compare with opposite side
Anatomy
Key Anatomy
Medial Collateral Ligament (MCL):
- Origin: Medial femoral epicondyle
- Insertion: Medial tibial metaphysis (4-5cm below joint line)
- Superficial MCL: Primary valgus restraint
- Deep MCL: Attached to medial meniscus
- Resists valgus stress and external rotation
Lateral Collateral Ligament (LCL):
- Origin: Lateral femoral epicondyle
- Insertion: Fibular head
- Cord-like structure (distinct from lateral capsule)
- Resists varus stress
Posterolateral Corner (PLC):
- LCL + Popliteus tendon + Popliteofibular ligament
- Resists varus, external rotation, and posterior translation
- Often injured with PCL
MCL Examination
Special test
Valgus Stress Test at 30° Flexion
MCL integrity (isolated)
Technique
- 1Patient supine, knee flexed 30°
- 2One hand stabilizes lateral thigh, other holds ankle/foot
- 3Apply valgus (abduction) force to the knee
- 4Assess medial joint opening and compare to opposite side
Positive Sign
Increased medial joint opening compared to opposite side
Indicates
MCL injury (isolated if stable at 0°)
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Special test
Valgus Stress Test at 0° (Full Extension)
Combined MCL + cruciate/capsular injury
Technique
- 1Patient supine, knee fully extended (locked)
- 2Apply valgus force as above
- 3Assess medial joint opening
Positive Sign
Increased medial joint opening at full extension
Indicates
Combined MCL injury with ACL, PCL, or posteromedial capsule injury
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Why Test at 0° AND 30°:
- At 0° (full extension): Knee is "locked" - cruciates, capsule, and collaterals all contribute to stability
- At 30° flexion: Knee is "unlocked" - cruciates are relaxed, collateral is the primary restraint
Interpretation:
- Laxity at 30° only = Isolated MCL injury
- Laxity at BOTH 0° and 30° = Combined injury (MCL + cruciate/capsule)
MCL Palpation
Systematic Palpation:
- Femoral origin: Medial epicondyle (most common site of injury)
- Mid-substance: Along medial joint line
- Tibial insertion: 4-5cm below joint line on medial tibia
Associated Findings:
- Swelling over medial aspect
- Ecchymosis (bruising) in acute injuries
- Point tenderness at site of tear
LCL Examination
Special test
Varus Stress Test at 30° Flexion
LCL integrity
Technique
- 1Patient supine, knee flexed 30°
- 2One hand stabilizes medial thigh, other holds ankle
- 3Apply varus (adduction) force to the knee
- 4Assess lateral joint opening
Positive Sign
Increased lateral joint opening compared to opposite side
Indicates
LCL injury
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Special test
Varus Stress Test at 0° (Full Extension)
Combined LCL + cruciate/PLC injury
Technique
- 1Patient supine, knee fully extended
- 2Apply varus force
- 3Assess lateral joint opening
Positive Sign
Increased lateral joint opening at full extension
Indicates
Combined LCL injury with cruciate or posterolateral corner injury
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Posterolateral Corner (PLC) Examination
Special test
Dial Test (External Rotation Test)
Posterolateral corner injury (+/- PCL)
Technique
- 1Patient prone, both knees flexed to 30° then 90°
- 2Examiner externally rotates both feet simultaneously
- 3Compare tibial external rotation between sides
- 4Measure at 30° and 90°
Positive Sign
Greater than 10° asymmetry in external rotation
Indicates
Increased at 30° only = Isolated PLC. Increased at BOTH 30° and 90° = PLC + PCL combined injury
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Special test
Posterolateral Drawer Test
Posterolateral corner injury
Technique
- 1Patient supine, knee flexed 80°, foot externally rotated 15°
- 2Apply posterior force to proximal tibia
- 3Observe lateral tibial plateau
Positive Sign
Lateral tibial plateau rotates posteriorly more than medial side
Indicates
Posterolateral corner injury
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Special test
Reverse Pivot Shift
Posterolateral rotatory instability
Technique
- 1Patient supine, knee flexed 70-80°
- 2Apply valgus force and external rotation
- 3Extend the knee slowly
Positive Sign
Clunk as lateral tibial plateau reduces from posteriorly subluxed position at 20-30° flexion
Indicates
Posterolateral corner injury (opposite of ACL pivot shift)
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Special test
External Rotation Recurvatum Test
Posterolateral corner injury
Technique
- 1Patient supine, legs straight
- 2Lift both legs by great toes
- 3Compare knee hyperextension and tibial external rotation
Positive Sign
Affected side shows more hyperextension and external rotation
Indicates
Posterolateral corner injury (often with PCL)
Diagnostic Accuracy
Ability to detect true positives
Ability to exclude false positives
Grading System
- opening
- 0-5mm
- description
- Mild sprain, fibers stretched
- stability
- Stable, firm endpoint
- treatment
- Conservative
- opening
- 5-10mm
- description
- Partial tear
- stability
- Some instability, endpoint present
- treatment
- Usually conservative
- opening
- greater than 10mm
- description
- Complete tear
- stability
- Gross instability, no endpoint
- treatment
- Consider surgery (especially LCL/PLC)
Combined Injury Patterns
Important Combinations
MCL + ACL ("Unhappy Triad" or O'Donoghue Triad):
- Classic: MCL + ACL + medial meniscus
- Modern data: MCL + ACL + LATERAL meniscus more common
- Valgus contact mechanism (e.g., football tackle)
LCL/PLC + PCL:
- Most common combined lateral injury
- High energy (dashboard injury, hyperextension)
- Dial test positive at 30° AND 90°
- Always assess vascular status (popliteal artery)
Knee Dislocation (Multiligament):
- By definition: ACL + PCL injured (minimum)
- Often includes collaterals
- MUST assess vascular status - CT angiography
- Reduction if still dislocated
Vascular Injury Alert: Posterolateral corner injuries and knee dislocations have high risk of popliteal artery injury:
- Always check distal pulses
- ABI (Ankle-Brachial Index) if any concern
- CT angiography for multiligament injuries
- Even if pulses present, intimal injury possible
Summary Presentation
“28-year-old rugby player tackled from the side. Unable to bear weight. Immediate swelling medial knee.”
MCL vs LCL Injury Comparison
- mcl
- Much more common
- lcl
- Less common (higher energy)
- mcl
- Valgus force
- lcl
- Varus force
- mcl
- ACL, medial meniscus
- lcl
- PCL, posterolateral corner
- mcl
- Excellent (conservative)
- lcl
- Poorer (may need surgery)
- mcl
- Rare (Grade III with instability)
- lcl
- More common (especially with PLC)
- mcl
- Low
- lcl
- Higher (with PLC injury)
Examiner Tips
Do
- Test at BOTH 0° and 30° flexion
- Explain why you test at both angles
- Grade the laxity and describe endpoint
- Compare with opposite side
- Assess for combined injuries (cruciates, PLC)
Don't
- Only test at one angle
- Forget the dial test for PLC
- Miss vascular assessment in severe injuries
- Confuse MCL femoral and tibial attachments
- Forget that medial tenderness can be meniscal