Disassembly of Components of a Monoblock Bipolar Hip Prosthesis Following Dislocation: A Case Report and Review on “Bottle Opener Effect”

INTRODUCTION: Bipolar hemiarthroplasty has been reliable and successful treatment for geriatric patients following neck of femur fractures. Dissociation/disassembly of bipolar prosthesis is a rare complication in which separation of outer head from inner head leads to failure of prosthesis and needs revision surgery. The disassembly though commonly seen after years of primary surgery as a result of polyethylene wear leading to fixed varus position of outer head but it can happen in an acute setting anytime in immediate or late post-operative period following posterior dislocation with closed reduction attempt. We describe a rare case of disassembly of monoblock (non-modular) bipolar prosthesis following attempt of closed reduction for posterior dislocation of the prosthesis. CASE REPORT: The patient was a 70-year-old male with 3 weeks prior bipolar hemiarthroplasty of hip joint, presented with posterior dislocation. While manipulation during closed reduction maneuvers, the outer head got locked behind acetabulum and component dissociation happened through bottle opener phenomena. The patient managed with revision surgery in the form of bipolar extraction and revision with total hip joint prosthesis. CONCLUSION: Disassembly of bipolar prosthesis is a rare and unforeseen complication which obviates for revision surgery. A modular bipolar prosthesis can be reassembled or can be managed with shell, liner, and head exchange with retention of femoral stem but it is impossible to reassemble a non-modular bipolar due to its characteristic locking mechanism. It is vital to look for proper orientation and stability of components, integrity of abductor mechanism and short external rotators, and restoration of horizontal and vertical offsets during revision.