Implant positioning in total hip arthroplasty: influence of horizontal and vertical offset on functionality of prosthetic hip joint.

Abstract

To analyze the effect of implant position measured in terms of offset on patient reported outcomes (PRO) following hip arthroplasty (THA). A total of 243 patients of the total hip replacement who had a one year follow-up were included in the study. Standard both hips radiograph was used to asses post-surgery implant position in terms of horizontal offset and vertical offset, and correlated with functional outcome which was evaluated as change in PRO. i.e., Harris hip score (HHS) post-op. With center of hip rotation as reference, horizontal offset was calculated as sum of distance, of centre, from proximal femoral shaft axis and a vertical line through ipsilateral teardrop, and vertical offset as limb length discrepancy. Post-op patients were classified into three groups depending on the measurement of horizontal offset of the operated hip. The patients having operated hip horizontal offset within 5mm of the normal hip were grouped as restored offset (RO); those having shorter or higher offset by more than 5mm compared to normal hip were labeled as decreased (DO) or increased offset (IO) group respectively. The groups were further subdivided into suboptimal and optimal function groups based on HHS, and among these groups, limb length discrepancy was evaluated. Post follow-up mean HHS (78.23 ± 9.96) improved significantly in all three groups (p < 0.0001). The difference in post-operative HHS among DO, RO, and IO groups was significant, with their averages being 72.5 ± 4.7, 82.1 ± 6.5, and 75.2 ± 4.8 respectively (p = .01). Limb length discrepancy was significantly more common in patients with suboptimal functional scores in all three groups. This study concluded that both horizontal offset and vertical offset should be reconstructed in patients operated with unilateral THR due to hip pathology, since both factor demonstrated a comparable additive effect on clinical outcome.