Dissociation of bipolar components following bipolar hemiarthroplasty: A report of two different cases and review of the literature.

In elder patients, the treatment for femoral neck fracture generally involves bipolar hip hemiarthroplasty. Hip dislocation is one of the most common complications of bipolar hip hemiarthroplasty. In many studies, hemiarthroplasty dislocation frequency ranged from 1.2% to 8.4%. However, dissociation between femoral head and femoral components is an extremely rare complication in bipolar hemiarthroplasty. Component dissociation was reported following polyethylene break after Bateman bipolar hemiarthroplasty which has been used since 1985. Self-centering systems have been developed to varus positioning of femoral head within in bipolar plate. In a self-centering system, normal forces on articular surface between acetabulum and femoral head should rotate femoral head into valgus position. However, dissociation of acetabular components was also reported with self-centering systems. In the literature, the largest case series reporting dissociation between components after bipolar hemiarthroplasty was reported in 2014 by Hasegawa et al., which included seven cases. Other larger studies were reported by Uruç et al. in 2017 (5 cases) and by Georgiou et al. in 2016 (5 cases). In this study, two different cases are reported dissociation between components after bipolar hemiarthroplasty. In conclusion, dissociation between components is a rare complication following bipolar hemiarthroplasty; however, it results in revision surgery in almost all cases. As spontaneous or traumatic dissociation can occur during maneuvers of closed reduction after hip dislocation, one should be careful during closed reduction of hip dislocation.