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

BACKGROUND: In order to create a well-functioning total hip arthroplasty (THA), it is important to restore femoral off-set and thus the abductor lever arm. The aim of this study was to investigate the clinical effect of increasing the abductor lever arm to and beyond the anatomical native lever arm in minimally invasive total hip arthroplasty performed through a direct anterior approach. MATERIALS AND METHODS: We compared the 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 in two groups based on whether they kept their anatomical lever arm or had an increased lever arm. The clinical outcome was assessed using hip osteoarthritis outcome score (HOOS), Harris hip score and UCLA activity score. RESULTS: Patients who kept their anatomical lever arm did not experience a significantly better clinical outcome than the patients with an increased abductor lever arm. We found no significant difference in clinical scores at any of the follow-ups during the first year after THA. CONCLUSION: The results of this study suggest that an increase in the abductor lever arm does not have major effects on the clinical outcome after THA. To avoid the potential negative effects of decreasing the lever arm, the surgeon should aim for an equal or slightly increased lever arm. Level of evidence Level 3, prospective cohort study.