Knee dislocation

Schenck KD I–V

Multiligament injury · popliteal artery

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A tibiofemoral dislocation tears at least two of the four main ligaments and threatens the popliteal artery, which is fixed above (adductor hiatus) and below (soleal arch). Many reduce spontaneously before arrival, so think of it in any multiligament injury.

Posterior knee dislocation, lateral. Arrow: the tibia lies completely behind the femoral condyles. Check the popliteal artery in every case. — Kael Duprey, MD, JD and Michelle Lin, MD, CC BY 4.0, via Wikimedia Commons.

Mechanism

High energy (road traffic) or low energy in obese patients (stepping off a kerb). Hyperextension causes anterior, a dashboard blow posterior dislocation.

Clinical findings

Reduce immediately and recheck pulses.
Ankle–brachial index in every case: below 0.9 means CT angiography; a pulseless limb goes to theatre.
Common fibular nerve (foot drop) in up to a quarter. Compartment syndrome.

Imaging

AP and lateral (look for Segond fracture, tibial spine or fibular head avulsion). MRI for the ligaments once the limb is safe.

Classification

Kennedy: By direction: anterior, posterior, medial, lateral, rotatory.
Schenck KD: I one cruciate + collateral, II both cruciates, III both cruciates + MCL (M) or posterolateral corner (L), IV all four, V with fracture; C vascular, N nerve injury.

Types shown in 3D

Anterior: The most common direction, from hyperextension. The popliteal artery is tethered above and below the knee and tears or thromboses: check pulses and the ankle–brachial index in every case; CT angiography if abnormal.
Posterior: Dashboard blow to the front of the tibia. Same vascular risk; the common fibular nerve is often stretched too.
Lateral: Valgus force: the tibia goes out sideways, with the medial collateral and both cruciates torn.

Treatment

Emergency: Reduction, splint in 20° flexion or spanning external fixator if unstable, vascular repair if needed (with fasciotomies).
Ligaments: Staged or early (within 3 weeks) reconstruction of the cruciates and repair/reconstruction of the collaterals and posterolateral corner in most active patients.

Aftercare

Long rehabilitation; stiffness and residual laxity are common.

Complications

Popliteal artery injury (amputation if missed)
Common fibular nerve palsy
Stiffness / arthrofibrosis
Residual instability
Post-traumatic arthritis