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Suspected spontaneously reduced tibiofemoral knee dislocation with multiligament injury and indirect signs of

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HardKnee InjuriesSuspected spontaneously reduced tibiofemoral knee dislocation with multiligament injury and indirect signs of vascular injuryMSRA

A 32-year-old man attends a GP-led urgent treatment centre 90 minutes after a high-speed motorcycle collision. Witnesses report that his right knee was visibly deformed immediately after the crash but appeared to straighten before ambulance arrival. Knee radiographs show no fracture and normal tibiofemoral alignment. He has a large effusion, a positive Lachman test, posterior drawer laxity and marked varus laxity at 30 degrees of flexion. He has reduced ankle dorsiflexion and reduced sensation in the first dorsal web space. The foot is warm with palpable dorsalis pedis and posterior tibial pulses; ankle-brachial pressure index is 0.96. What is the most appropriate next step?

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Correct answer: D — Arrange immediate emergency transfer for trauma, orthopaedic and vascular assessment with CT angiography

Explanation lettering: B = shown as A · A = shown as B · D = shown as C · E = shown as D · C = shown as E

This is a suspected spontaneously reduced tibiofemoral knee dislocation rather than an isolated ligament injury. The witnessed transient deformity despite normal current radiographs is the first key inference. The combined anterior, posterior and varus instability indicates a multiligament injury pattern, including cruciate and posterolateral structures. The common peroneal nerve deficit provides a further high-risk feature. Although there are no NICE-defined hard signs of vascular injury (absent pulse, continued bleeding or expanding haematoma), this patient has indirect vascular-risk signs: a mechanism consistent with knee dislocation and paraesthesia/neurological deficit. The NHS Lothian major-trauma guideline advises CT angiography as soon as possible for indirect signs and specifically identifies knee dislocation and paraesthesia as such indicators. This mandates emergency trauma-pathway transfer rather than outpatient investigation. A and B under-triage a potentially limb-threatening injury; MRI is useful later for ligament definition but must not precede vascular assessment. C is plausible because a normal ankle-brachial pressure index can support serial assessment in some protocols, but the directly applicable UK trauma guidance recommends CT angiography where indirect signs are present. D may identify arterial flow abnormalities, but CT angiography is the specified urgent imaging modality for this risk category and should be coordinated through trauma, orthopaedic and vascular services.

Reference: Vascular trauma associated with fractures/dislocations (Reviewed 1 April 2025) — https://www.rightdecisions.scot.nhs.uk/south-east-scotland-major-trauma-guidelines/generalvascularurology/vascular-trauma-associated-with-fracturesdislocations/ Fractures (complex): assessment and management, section 1.2 Vascular injury (2016; current NICE recommendations page accessed 15 August 2026) — https://www.nice.org.uk/guidance/ng37/chapter/recommendations