Biomechanics of a collum-fixated short stem in total hip arthroplasty

Background: Biomechanical reconstruction of the hip significantly impacts the clinical outcome and implant survival. Our knowledge is limited of the ability of neck-stabilised prostheses to restore hip biomechanics. We hypothesised that hip biomechanics, specifically leg length and global offset (GO), may be restored to an acceptable range using the PrimorisTM stem. Methods and material: In this retrospective study, we analysed 152 patients who underwent total hip replacement (THA) using the short collum-fixated stem PrimorisTM. The primary outcomes were hip parameters measured by x-ray following THA using the PrimorisTM stem. After surgery, the biomechanical parameters used were measured at the arthroplasty and the native contralateral side of the same x-ray. The X-rays were taken one year after the patient's surgery. 1. GO. 2. Leg length discrepancy (LLD). 3. Neck shaft angle (NSA). Results: We recorded an average GO of -3.4 mm (standard deviation (SD) 7.2) and an average LLD of +3.8 mm (SD 6.4). Furthermore, we registered an average 14-degree NSA increase (SD 7.4). Conclusion: The PrimorisTM neck-stabilised stem enabled hip anatomy restoration to a favourable range with respect to GO and LLD as the average difference fell within +/- 5 mm. However, the stem tended to be implanted in valgus.