PCL / MCL / LCL Injuries

PCL: dashboard mechanism or hyperflexion/extension, with posterior knee pain and an effusion that is often less dramatic than ACL injury. Symptoms are typically vague - difficulty with deceleration and descending stairs - rather than dramatic giving way. The posterior sag sign (Godfrey test - patient supine, hips and knees flexed to 90 degrees) is the most important first step; a posteriorly subluxed tibia produces a false-positive anterior drawer (pseudo-Lachman). The posterior drawer test is graded by the relationship of the medial tibial plateau to the medial femoral condyle - Grade III (tibia posterior to the condyle) suggests combined PCL + PLC or another associated injury. The dial test must be performed whenever PCL injury is suspected.

MCL: valgus mechanism, immediate well-localised medial knee pain, and tenderness along the MCL from medial femoral epicondyle to proximal medial tibia. The valgus stress test is the key diagnostic manoeuvre - test at 30 degrees of flexion (isolates the MCL) and at 0 degrees of full extension. Increased laxity at 30 degrees only indicates an isolated MCL injury; valgus laxity at 0 degrees suggests posteromedial or cruciate involvement and changes the pathway. Always assess the ACL because MCL + ACL is one of the most common combined patterns.

LCL and PLC: varus mechanism, lateral knee pain, and tenderness from the lateral femoral epicondyle to the fibular head. Apply varus stress at 30 and 0 degrees. The dial test interprets external-rotation asymmetry: increased at 30 degrees alone = PLC; increased at both 30 and 90 degrees = combined PCL + PLC. Always check the common peroneal nerve (dorsiflexion, eversion, dorsal foot sensation) and always assess the PCL. MRI should always be performed when acute PLC is suspected.

Plain radiographs (AP, lateral, with or without stress views) are first-line, looking for fracture, avulsion fragments (PCL tibial avulsion, fibular head avulsion - the arcuate sign for PLC, Segond fracture flagging ACL injury), joint subluxation, and the Pellegrini-Stieda lesion (post-traumatic calcification at the medial femoral epicondyle from chronic MCL injury).

MRI is the investigation of choice for confirming ligament injury, grading severity, and assessing associated structures. MRI should always be performed when acute PLC injury is suspected, as PLC injuries are commonly missed clinically.

Urgent CT angiography is indicated if there is any concern about popliteal artery injury in multi-ligament injury or knee dislocation - hard signs of vascular injury, an ABPI less than 0.9, or persistent doubt after clinical assessment. Ultrasound has a limited role for primary ligament assessment.

MCL: isolated Grade I and II are managed non-operatively - hinged knee brace, weight-bearing as tolerated, early range of motion, and progressive rehabilitation. Return to sport is approximately 2-4 weeks for Grade I and 4-8 weeks for Grade II. Isolated Grade III is usually non-operative initially and heals with bracing and rehabilitation over 8-12 weeks, but some patterns warrant earlier surgical consideration: severe distal tibial avulsions, intra-articular entrapment, large bony avulsions, anteromedial rotatory instability, and marked valgus alignment. MCL + ACL is managed by treating the MCL non-operatively first, then delaying ACL reconstruction until the MCL has healed and range of motion is restored (typically 6-8 weeks).

PCL: isolated Grade I and II are managed non-operatively with quadriceps-focused rehabilitation; a dynamic PCL brace providing anterior tibial support is increasingly used. Isolated Grade III, displaced tibial avulsion, and combined injuries usually require surgical consideration, with PCL reconstruction typically performed with allograft.

LCL and PLC: low-grade PLC sprains may be treated non-operatively. Significant posterolateral instability (Grade III PLC or combined cruciate) usually requires early surgical management, ideally within 2-3 weeks - PLC injuries do not heal reliably non-operatively and untreated PLC is a leading cause of cruciate graft failure. PLC must be addressed at the same time as or before any cruciate reconstruction.

Multi-ligament injury or knee dislocation is a neurovascular emergency: serial monitoring of pulses and ABPI, urgent vascular workup if any concern, and staged ligament reconstruction by a specialist knee team.

MCL (non-operative): hinged knee brace, early range of motion, quadriceps activation, weight-bearing as tolerated for 0-2 weeks; progressive ROM with quadriceps, hamstring, and closed-chain strengthening plus proprioception over 2-6 weeks; functional loading and running over 6-12 weeks. Return to sport is criteria-based - full range, no medial laxity on stress, and quadriceps strength at least 90% of the contralateral side.

PCL (non-operative): quadriceps-dominant rehabilitation is the key principle because the quadriceps pull the tibia anteriorly and counteract posterior sag. Avoid isolated hamstring loading early - it worsens sag. The initial 0-4 weeks emphasises a dynamic PCL brace where available, weight-bearing as tolerated, full extension as the priority, and quadriceps activation (quad sets, straight leg raises). Progressive 4-12 weeks introduces quadriceps strengthening with closed-chain hamstring co-contraction, cycling, swimming, and proprioception. Sport-specific drills and running follow from 12 weeks when criteria are met.

Post-operative (PCL reconstruction, PLC repair or reconstruction): protocols are surgeon-dependent. Progression is slower than ACL reconstruction, with return to sport typically 9-12 months for combined injuries.

• •BOA Best Practice: ACL and multi-ligament knee injuries - Recommends prompt assessment and specialist referral for any suspected combined or multi-ligament injury, with neurovascular assessment mandatory.
• •Stannard et al. (2005, JBJS Am) - Acute PLC repair within 2-3 weeks gives substantially better outcomes than delayed reconstruction; untreated PLC is a leading cause of ACL graft failure.
• •Wijdicks et al. (2010, AJSM) - Most isolated MCL injuries heal non-operatively with a hinged brace and graduated rehabilitation; severe distal Grade III patterns may need surgical consideration.
• •Pierce et al. (2013, AJSM) - Isolated PCL injuries do well with quadriceps-focused rehabilitation and dynamic PCL bracing; combined injuries usually require surgery.
• •NICE CKS: Knee pain assessment - Provides red-flag triggers for emergency referral and multi-ligament workup.

• •MCL is the most commonly injured knee ligament, and most isolated tears (including most Grade III) heal non-operatively. Valgus laxity at 0 degrees suggests injury beyond the sMCL alone (posteromedial corner or cruciate).
• •PCL = dashboard mechanism, primary restraint to posterior tibial translation. The meniscofemoral ligaments of Humphry (anterior) and Wrisberg (posterior) are PCL accessories - exam favourites.
• •Always check the posterior sag first - a posteriorly subluxed tibia produces a false-positive anterior drawer (pseudo-Lachman) and can mislead you into diagnosing an ACL injury.
• •Isolated LCL injury is rare; any significant lateral-sided injury should prompt formal PLC assessment, with MRI mandatory in suspected acute PLC because missed PLC is a leading cause of ACL graft failure.
• •Multi-ligament knee injury may represent a knee dislocation - check pulses and ABPI. Normal findings do not exclude intimal injury, so serial observation is mandatory.
• •Pellegrini-Stieda lesion = calcification at the medial femoral epicondyle from old MCL injury; arcuate sign = fibular head avulsion indicating PLC injury.