PCL / MCL / LCL Injuries

Injuries to the posterior cruciate (PCL), medial collateral (MCL) and lateral collateral (LCL) ligaments are less common than ACL injuries, apart from the MCL, which is the most commonly injured knee ligament.

• •MCL: valgus mechanism; most isolated injuries heal without surgery
• •PCL: posterior force on the flexed tibia (dashboard injury); most isolated injuries are managed without surgery
• •LCL: rarely injured alone, usually part of a posterolateral corner (PLC) injury, which must not be missed because untreated PLC injury is a recognised cause of cruciate graft failure

Injury to more than 1 ligament may mean the knee has dislocated and needs urgent vascular assessment.

PCL, often described as the strongest knee ligament:

• •Runs from the lateral aspect of the medial femoral condyle to the posterior tibia
• •The larger anterolateral bundle, tight in flexion, is the primary restraint to posterior tibial translation; the posteromedial bundle tightens in extension
• •The meniscofemoral ligaments of Humphry (anterior) and Wrisberg (posterior) run alongside it from the lateral meniscus
• •Mechanism: a dashboard blow to the flexed proximal tibia, hyperflexion or hyperextension

MCL:

• •The superficial MCL, from the medial femoral epicondyle to the proximal medial tibia, is the primary valgus restraint
• •The deep MCL attaches to the capsule and medial meniscus, hence the frequent MCL and medial meniscus pairing
• •A distal tibial avulsion can displace over the pes anserinus (a Stener-like lesion) and lowers the threshold for surgery

LCL and PLC:

• •The LCL runs from the lateral femoral epicondyle to the fibular head, with no lateral meniscus attachment, and is the primary varus restraint
• •With the popliteus tendon and popliteofibular ligament it forms the PLC, which resists varus, external rotation and posterior translation of the lateral tibia
• •Mechanism: varus, or hyperextension with varus

Collateral grading:

• •Grade I: stretch, firm end-point
• •Grade II: partial tear, end-point present but more laxity
• •Grade III: complete tear, no end-point