The role of femoral offset and the abductor lever arm in minimally invasive total hip arthroplasty

Abstract

When placing the components during THA the goal is to restore the optimal biomechanics of the hip. Evidence suggests that correct placement of the components plays an important role in order to prevent impingement, provide optimal conditions for the abductor muscles and minimize polyethylene wear. The aim of this study was to clarify the clinical effect of increasing the abductor lever arm in minimally invasive total hip arthroplasty. We compared the abductor lever arm of the operated hip to the lever arm of the contralateral native hip on radiographs in 148 patients following THA. The patients were divided into two groups based on whether they kept their anatomical lever arm or had an increase in the lever arm. The clinical outcome was assessed using Hip Osteoarthritis Outcome Score (HOOS), Harris Hip Score and UCLA activity score. Evaluations took place at 6 weeks, 4 months and 1 year postoperatively. Patients who kept their anatomical lever arm did not experience a significantly better clinical outcome than the patients who had an increased abductor lever arm. The results of this study suggest that an increase in the abductor lever arm does not have detrimental effects on the clinical outcome after THA. To avoid the potential negative effects of a diminished lever arm, the surgeon should aim for an equal or slightly increased lever arm.