Radiographic assessment of biomechanical parameters following hip resurfacing and cemented total hip arthroplasty

Resurfacing hip arthroplasty and total hip replacement both aim to restore anatomical parameters.Leg length and offset discrepancy can result in altered joint reaction forces, and are associated with increased wear, dislocation, and decreased patient satisfaction. This study assesses the accuracy of leg length and offset restoration after either a Birmingham Hip Resurfacing (BHR) or a cemented total hip replacement (THR).Standardised antero-posterior radiography was performed on two groups of 30 patients with unilateral primary osteoarthritis undergoing either a cemented total hip or resurfacing. The normal contra-lateral hip was used as the control. Leg length and offset were measured pre-operatively with no significant difference between the two groups.Cup offset, femoral offset, total offset and leg length of the prosthesis and normal side were measured by two observers and mean measurements were analysed by a paired t test.Leg lengths in each group did not differ significantly from the normal side, THR 0.53 mm (95% CI -2.4 to 3.4 mm) but BHR implantation did result in mean leg shortening of -1.9 mm (95% CI -4.5 mm to 0.6mm). Cup offset differed significantly from normal anatomy in both groups, as did femoral and total offset for the total hip replacement group. However, femoral offset was restored in the Birmingham resurfacing group. When the THR group was compared against the BHR group we found no difference between restoration of leg lengths (p = 0.21) and cup offset (p = 0.30) but femoral (p = 0.0063) and total offset (p = 0.03) were restored more accurately with a BHR.