Relation between lower extremity alignment and proximal femur anatomy. Parameters during total hip arthroplasty

SummaryBackgroundLower extremity alignment correlates with native femoral offset. Eventual impact of the change in femoral offset induced by total hip arthroplasty (THA) on lower extremity alignment has not been documented.HypothesisTHA significantly changes lower extremity alignment, and the change correlates with the change in femoral offset.Materials and methodsWe conducted a prospective study of 200 patients with primary hip osteoarthritis or avascular femoral head necrosis who underwent cementless THA. Pre-operative computed-tomography templating was performed and the femoral component was then custom-manufactured to replicate the native femoral anatomy. Mean age was 58 years (range, 28–83 years). Before and at least two years after THA, two observers who were not involved in the surgical procedures used standing antero-posterior long-leg radiographs to determine the mechanical axis of the lower-limb (hip-knee-ankle [HKA] angle), femoral offset, neck-shaft angle (NSA), and lower-limb length discrepancy (LLLD).ResultsMean values pre-operatively and at last follow-up were as follows: HKA angle, 179.2°±3.9° (range, 170.5° to 190.5°) and 177.7°±3.5°(range, 173° to 187°); LLLD, −0.7mm (range, –30mm to+25mm) and+5.1mm (range, –7mm to+21mm); NSA, 134°±7.5° (range, 100° to 124°) and 135°±4.2° (range, 124° to 146°); and femoral offset, 42±7.8mm (range, 24mm to 68mm) and 49±7.5mm (range, 33mm to 70mm). Although THA significantly altered lower-limb alignment, univariate and multivariate analyses showed no significant association between the change in HKA angle and the change in femoral offset.DiscussionLower-limb alignment was significantly affected by THA, although the HKA angle changes were small. The small impact of THA on HKA angle values may be ascribable to efforts aimed at replicating the native femoral offset during arthroplasty, as well as to the limited sample size and to potential measurement errors related to the small size of the changes. Our results suggest that, provided careful attention is directed to replicating the native femoral offset, THA in patients with limited pre-operative anatomical abnormalities may have no major impact on the biomechanical parameters of the ipsilateral knee.Level of evidenceLevel III, prospective diagnostic study