A study of injury mechanism: traumatic bilateral L4-5 facet dislocation – case report and literature review

Abstract

Introduction: Traumatic facet dislocation in the lower lumbar spine are rare, with most cases previously reported to be dislocation of lumbosacral joint (L5-S1). We present a case of young male presenting with bilateral L4-5 traumatic facet dislocation after fall injury. Possible biomechanical pathophysiology were discussed. Methodology: PubMed was searched using search terms '(L4-5 OR L4-L5) and Traumatic spondylolisthesis OR dislocation OR locked facet OR jumped facet' Results and Analysis: Four case reports were found in the PubMed English literature. Discussion and Conclusion: In the four case reports, the injuries were head-on collision motor vehicle accidents. The proposed pathophysiology was an extension-distraction force. The thoracic spine and pelvis were immobilized by seatbelt, while the remaining thoracolumbar spine swung forward by momentum. Our patient fell backwards with his upper back landing onto a metal bar which acted as a fulcrum, the spine above and below was forced backwards by gravity. As a result, the spine was forced into hyperextension, and break at its weakest point. In both scenarios, there were no direct impact force at the dislocation site, rather a hyperextension of spine occurs. Also, we have identified anatomical variants in our case which includes a more coronally aligned facet joints and the presence of L5 spina bifida. We believe that the level of injury is related to anatomical variants, and the L4-5 traumatic facet fracture dislocation and the lumbosacral dislocation should be grouped into the same disease entity.