Osteoarthritis of the Hip and Uncemented Total Hip Arthroplasty : Effects of Immediate Weight Bearing on Implant Stability, Bone Mineral Density, and Body Composition

Abstract: The initial recommendation for the postoperative regime after uncemented total hip arthroplasty (THA) was 6-12 weeks of partial weight bearing (PWB) to obtain a stable implant position during bone ingrowth. In recent years patients with uncemented THA have increasingly practiced full weight bearing (FWB) after surgery, which has largely been based on clinical experience rather than on scientific evidence. The aim of this thesis was to investigate the effects of FWB versus PWB for 3 months on the stability of the implants and on bone mineral density (BMD), as well as body composition (BC) of the lower extremities.We used radiostereometric analysis (RSA) to measure implant micromotion and dual X-ray absorptiometry (DXA) to measure BMD and BC. Forty-six patients with strictly unilateral osteoarthritis of the hip (OAH) received uncemented THA. These patients were then randomized to the FWB or PWB groups and followed for 5 years.In a preoperative cross-sectional study the BMD of the hip and heel were compared between the OAH-affected side and the healthy side. The study showed an increase of BMD at the femoral neck and a decrease at the total hip and trochanter. The results of a RSA study of cup stability showed that there might be minimal movement in medial and proximal directions during the first postoperative week. These results indicate that the RSA baseline investigation of uncemented cups should be performed as early as possible after the first postoperative day. FWB had no adverse effects on the stability of the uncemented press-fit cups or the uncemented cementless Spotorno (CLS) femoral stems after a 5-year follow-up. There was no difference in periprosthetic BMD around the CLS stem regardless of the postoperative weight bearing regime. All zones around the femoral stem indicated a recovery in BMD toward baselines, except the calcar region, which showed progressive loss in BMD to -22% at 5 years post-surgery. FWB had no effect on the changes in BC after surgery.In conclusion, FWB is safe in uncemented THA in terms of stability, BMD and BC. Furthermore, THA apparently counteracts age-related changes in BC but not in BMD.