Abstract
The mechanism of traumatic amputation (TA) from explosive blast has traditionally been considered to be a combination of blast wave induced bone injury – primary blast - followed by limb avulsion from the blast wind – tertiary blast. This results in a transosseous TA, with through joint amputations considered to be extremely rare. Data from previous conflicts has also suggested that this injury is frequently associated with a non-survivable primary blast lung injury (PBLI), further linking the extremity injury to the primary blast wave. However, our current experience in the Middle East would suggest that both the mechanism of TA and the link with fatal primary blast exposure need to be reconsidered. The aim of this study was to analyse the injury profile of the current cohort of TA fatalities to further investigate the underlying blast injury mechanism and to allow hypotheses on injury mechanisms to be developed for further analysis.
With the permission of the coroners, 121 post-mortem CT (PMCT) scans of UK Armed Forces personnel who died following an IED blast were analysed. All orthopaedic injuries were identified, classified and the anatomical level of any associated soft tissue injury noted. PMCT evidence of PBLI was used as a marker of significant primary blast exposure.
75/121 (62%) sustained at least 1 TA, with 138 TAs seen in total. 31/138 (22%) were through joints, with through knee amputations most common (23/31, 74%). Only 7/31(23%) through joint amputations had an associated fracture proximal to and contiguous with the amputation site. The soft tissue injury profile of through joint and transosseous TAs were not significantly different (p=0.569). When fatality location was considered (i.e. mounted or dismounted), no overall relationship between PBLI and TA was evident. The two pathologies were not seen to consistently occur concurrently, as has been previously reported.
The accepted mechanism for traumatic amputation following explosive blast does not adequately explain the significant number of through joint TAs presented here. The previously reported link between TA and PBLI in fatalities was not supported by this analysis of modern combat blast fatalities. Lack of an associated fracture with the majority of through joint TAs in conjunction with a lesser contribution of primary blast may implicate flail and periarticular soft tissue failure as a potential injury mechanism. Analysis of through joint TA incidence and associated injuries in survivors is now indicated. Case studies within the fatality dataset may facilitate generation of injury mechanism hypotheses. To further investigate the injury mechanism, work is required to understand osseous, ligamentous and other soft tissue behaviour and failure at high strain rates. This should allow characterisation and modeling of these injuries and inform mitigation strategies.
