Overview
- LCL, popliteus tendon and popliteofibular ligament
- Resist varus, external rotation and posterior translation
- Rarely isolated, usually with ACL or PCL tears
- Missed PLC injury is a common cause of cruciate graft failure
- Varus stress at 0° and 30°, dial test, external rotation recurvatum and posterolateral drawer
- Common peroneal nerve injury in a significant proportion
- Early repair or reconstruction for acute grade III, osteotomy first for chronic varus
- Most commonly in association with anterior or posterior cruciate ligament injury
- Cause of failure of cruciate reconstructions
Western Health Orthopaedic Registrar presentation – Acute PLC Injuries by Dr Marc Friso
Anatomy
- Primary stabilisers are the FCL, popliteus tendon and popliteofibular ligament
- FCL is the main restraint to varus
- Popliteus and popliteofibular ligament resist external tibial rotation
- Common peroneal nerve lies posterior to biceps femoris
Classification
Hughston (varus opening)
| Grade | Varus opening |
|---|---|
| I | 0 to 5 mm |
| II | 6 to 10 mm |
| III | Over 10 mm |
Original publication Hughston JC, Andrews JR, Cross MJ, Moschi A. Classification of knee ligament instabilities. Part II. The lateral compartment. J Bone Joint Surg Am. 1976;58(2):173-9.
Fanelli
| Type | Description |
|---|---|
| A | External rotation only |
| B | Adds mild varus from partial FCL injury |
| C | Adds marked varus from complete FCL and capsular disruption |
Original publication Fanelli GC, Larson RV. Practical management of posterolateral instability of the knee. Arthroscopy. 2002;18(2 Suppl 1):1-8.
Clinical Features
- Varus opening at 30 degrees implies isolated lateral injury, at full extension added cruciate injury
- Dial test, 10 degrees or more asymmetry at 30 only in isolated PLC injury, at 30 and 90 with PCL
Investigations
- Arcuate fracture (fibular styloid avulsion) on radiographs
- Varus stress films, about 2.7 mm gap increase suggests isolated FCL, about 4 mm grade III PLC
Management
- Grade I and II, bracing and rehabilitation
- Grade III, surgery within about three weeks
- Repair alone fails more often than reconstruction
- Chronic injury in a varus knee needs HTO first
- LaPrade anatomic, two grafts reconstructing FCL, popliteus and popliteofibular ligament
- Larson fibular based, single graft, no direct popliteus reconstruction
Complications
- Peroneal nerve injury, tunnel convergence, residual laxity and stiffness
Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.