Introduction

Knee dislocation results in a high risk of vascular injury due to the relatively fixed position of the popliteal artery. Given that 50% of knee dislocations may reduce spontaneously prior to hospital, clinicians need to have a high index of suspicion to avoid missing an ischaemic limb in a multi-ligament knee injury (MLKI). Some authors recommend an evidence based protocol for vascular assessment but this requires correctly identifying a transient dislocation that has been reduced. The aim of this study was to identify predictors of vascular injury in MLKI and create a protocol for vascular assessment in the emergency department to avoid missed ischaemia in these patients.

Methods

A prospective database of multi-ligament knee injuries (MLKIs) in a level 1 major trauma centre was reviewed from 2019 - 2023. Multi-ligament knee injury was defined as disruption of at least two of the four major knee ligaments comprising the ACL, PCL, MCL (posteromedial corner) and LCL (posterolateral corner). Digital records and MRI reports were assessed to include demographics, mechanism of injury, assessment of vascular status of limb, treatment and outcome.

Results

73 knees were included (40 KDI, 4 KDII, 25 KDIII, 2 KDIV, and 2 KDV). 34 knees were high-energy mechanisms. 25 knees were sports injuries.
The rate of vascular injury in this cohort was 7% (5/73). The rate of common peroneal nerve injury was 16% (12/73). Of the 5 patients that had a vascular injury, 4 presented dislocated to the emergency department and the other gave a clear history of transient dislocation and reduction on the sporting field. All 5 patients with a vascular injury were Schenk IIIL classification involving both cruciate ligaments and the posterolateral corner.
44 knees within the original cohort met the criteria of either presenting dislocated (21), having a clear history of dislocation with spontaneous reduction (20) and/or presenting with CPN palsy (12). The rate of vascular injury in this subgroup was 11% (5/44). 48% (21/44) underwent CT Angiography as part of initial assessment. 30% (18/44) underwent delayed CT Angiography (mean 5 days, range 1-11 days). In the group of transient dislocations that were not dislocated on presentation, only 7% (2/23) underwent CT Angiogram as part of their initial assessment. One patient who underwent delayed CT Angiogram at 7 days had a vascular injury requiring vascular bypass and fasciotomies. In the 29 MLKIs that did not meet these three criteria there were no vascular injuries.

Discussion

Our study suggests the patients most at risk of vascular injury are those presenting dislocated or with a clear history of transient dislocation in association with a lateral sided injury/foot drop. We have implemented a protocol in our unit to identify these patients in the emergency department and fast track them to CT angiography. Patients not meeting the above criteria who subsequently have confirmed MLKI on MRI or clinical examination will have ABPIs and serial vascular assessment performed.