The precise reconstruction of the center of rotation in total hip arthroplasty after femoral neck fractures - a clinically crucial challenge

Abstract

In past experiments based on 3-D models, medialization of the center of rotation (COR) in total hip arthroplasty (THA) with unilateral hip dysplasia showed a negative influence on the muscle strength of the abductors and the reaction force of the hip joint. The COR displacement was referenced to the healthy non-dysplastic hip and the results therefore might contradict given paradigms, where reduced hip loading forces are claimed to increase functional outcomes. The aim of this study was a clinical evaluation of the COR placement towards the patient’s recovery with respect to daily living ability and mobility using der Barthel index and the Parker mobility score (PMS). 110 patients who underwent THA after a femoral neck fracture between January 2019 and January 2021 were retrospectively evaluated towards their Barthel index on discharge (N = 68). 47 Patients were available for a follow up interview and were interviewed for the Barthel index and Parker Mobility Score (PMS) 6 and 12 months after surgery. COR medialization, superior COR displacement and especially the combination of both (superomedialization) leads to reduced mobility while inferior displacement leads to increased pain. According to our results we recommend an exact vertical COR-restoration, while horizontal medial displacement needs to be avoided.