Collateral-ligament injury — Rapid

Synopsis

Localise medial and lateral ligament injury, detect multiligament, peroneal-nerve and vascular threats, use stress examination and MRI coherently, protect healing without stiffness, and identify patterns needing repair or reconstruction.

Identify mechanism and exact tenderness: MCL spans medial femur to tibia; LCL runs lateral femur to fibular head and lateral injury demands peroneal-nerve examination.
Apply valgus and varus stress at about 30 degrees to isolate collaterals and in extension to screen capsule and cruciates, but do not stress a possible fracture or unreduced dislocation.
Grade laxity by endpoint and opening, compare the other knee and repeat when guarding settles; pain without opening differs from complete functional disruption.
Obtain radiographs for trauma, avulsion and alignment. MRI maps ligament location, cruciates, corners, menisci and cartilage when severity or combined injury changes treatment.
Most isolated grade I and II MCL injuries and many grade III MCL injuries use a hinged brace when needed, early range, weight bearing as tolerated and progressive rehabilitation.
LCL and posterolateral injury, persistent valgus opening in extension, multiligament injury, displaced avulsion, entrapment or failed healing need early specialist surgical planning.
Rehabilitation restores full extension, flexion, quadriceps and hip strength and single-leg control while progressively reducing the brace; prolonged cast immobilisation is harmful.
Return to contact or cutting activity requires pain-free full motion, no effusion, a stable endpoint and task-specific strength and control, not elapsed time alone.

Key red flags

Gross laxity in more than one plane, high-energy mechanism or transient deformity requires knee-dislocation vascular surveillance even with present pulses.

Foot drop, weak eversion or first-web-space sensory loss with lateral injury suggests common peroneal nerve involvement and needs serial documentation and specialist review.

Tense swelling, disproportionate pain or passive-stretch pain suggests compartment syndrome and requires emergency assessment.

Focal bony tenderness, inability to bear weight or avulsion on radiograph may represent plateau fracture, fibular-head injury or a skeletally immature avulsion rather than a simple sprain.

Investigation priorities

Immediate neurovascular examinationFirst step

Detect arterial and common peroneal injury.

First-line trauma radiographsFirst line

Identify fracture, avulsion and alignment.

Management branches

ThreatExclude dislocation and vascular injury

High-energy mechanism, gross laxity, deformity, neurological change or perfusion concern is present.

Reduce deformity, immobilise and document vascular and nerve function before and after intervention.
Measure perfusion and obtain urgent CT angiography and vascular input when abnormal or equivocal.
Image fractures and map all ligaments and corners after limb safety is addressed.
Refer to an experienced multiligament knee team for repair, reconstruction and rehabilitation planning.

Key medicines

Topical or short oral NSAIDUse a licensed topical NSAID at the product frequency or one oral NSAID at the lowest effective adult dose for the shortest period that enables motion, adding gastroprotection when an oral regimen and individual risk require it.Review gastrointestinal, renal, hepatic and cardiovascular disease, blood pressure, pregnancy, anticoagulants and concurrent NSAIDs; worsening instability, nerve change or vascular symptoms require reassessment rather than more analgesia.

Thromboprophylaxis for selected immobilised patientsUse the current local lower-limb immobilisation regimen only after formal venous-thromboembolism and bleeding assessment, prescribing the exact agent, dose, start and stop dates if risk outweighs harm.Renal function, pregnancy, body weight, prior thrombosis, bleeding and existing anticoagulation change choice; early safe movement remains important and calf or chest symptoms require urgent assessment.

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