Focused examination of the medial and lateral collateral ligaments including varus and valgus stress testing, posterolateral corner assessment, and recognition of combined ligament injuries.
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.
High-Yield Exam Summary
Medial Collateral Ligament (MCL):
Lateral Collateral Ligament (LCL):
Posterolateral Corner (PLC):
MCL integrity (isolated)
Increased medial joint opening compared to opposite side
MCL injury (isolated if stable at 0°)
Ability to detect true positives
Ability to exclude false positives
Combined MCL + cruciate/capsular injury
Increased medial joint opening at full extension
Combined MCL injury with ACL, PCL, or posteromedial capsule injury
Ability to detect true positives
Ability to exclude false positives
Why Test at 0° AND 30°:
Interpretation:
Systematic Palpation:
Associated Findings:
LCL integrity
Increased lateral joint opening compared to opposite side
LCL injury
Ability to detect true positives
Ability to exclude false positives
Combined LCL + cruciate/PLC injury
Increased lateral joint opening at full extension
Combined LCL injury with cruciate or posterolateral corner injury
Ability to detect true positives
Ability to exclude false positives
Posterolateral corner injury (+/- PCL)
Greater than 10° asymmetry in external rotation
Increased at 30° only = Isolated PLC. Increased at BOTH 30° and 90° = PLC + PCL combined injury
Ability to detect true positives
Ability to exclude false positives
Posterolateral corner injury
Lateral tibial plateau rotates posteriorly more than medial side
Posterolateral corner injury
Ability to detect true positives
Ability to exclude false positives
Posterolateral rotatory instability
Clunk as lateral tibial plateau reduces from posteriorly subluxed position at 20-30° flexion
Posterolateral corner injury (opposite of ACL pivot shift)
Ability to detect true positives
Ability to exclude false positives
Posterolateral corner injury
Affected side shows more hyperextension and external rotation
Posterolateral corner injury (often with PCL)
Ability to detect true positives
Ability to exclude false positives
| grade | opening | description | stability | treatment |
|---|---|---|---|---|
| Grade I | 0-5mm | Mild sprain, fibers stretched | Stable, firm endpoint | Conservative |
| Grade II | 5-10mm | Partial tear | Some instability, endpoint present | Usually conservative |
| Grade III | greater than 10mm | Complete tear | Gross instability, no endpoint | Consider surgery (especially LCL/PLC) |
MCL + ACL ("Unhappy Triad" or O'Donoghue Triad):
LCL/PLC + PCL:
Knee Dislocation (Multiligament):
Vascular Injury Alert: Posterolateral corner injuries and knee dislocations have high risk of popliteal artery injury:
"28-year-old rugby player tackled from the side. Unable to bear weight. Immediate swelling medial knee."
| feature | mcl | lcl |
|---|---|---|
| Frequency | Much more common | Less common (higher energy) |
| Mechanism | Valgus force | Varus force |
| Associated Injuries | ACL, medial meniscus | PCL, posterolateral corner |
| Healing Potential | Excellent (conservative) | Poorer (may need surgery) |
| Surgical Indications | Rare (Grade III with instability) | More common (especially with PLC) |
| Vascular Risk | Low | Higher (with PLC injury) |
High-Yield Exam Summary