Purpose: Insertion of the femoral stem during total hip arthroplasty provokes a bridge between the proximal femoral forces leading to well-documented bone resorption. A review of the literature concerning the behaviour of the contralateral femur and the spine reveals conflicting data. Some authors report variable bone mineral density of the lumbar spine while the contralateral neck, studied with non-cemented prostheseis in all cases, shows a significant fall in bone density. All patients in these studies needed an unloading period to achieve definitive fixation of the hip prosthesis. The purpose of this study was to assess bone behaviour in the contralateral femur and the lumbar spine after unilateral cemented total hip arthroplasty with immediate postoperative weight bearing.

Material and methods: The study series included 52 patients who underwent unilateral cemented total hip arthroplasty for degenerative hip disease. All were followed with standard x-rays and DPX of the contra-lateral hip and the lumbar spine. These examinations were performed one month before surgery then on D8, M3, M6, one year and two years. Bone mineral density (BMD) was measured in the femoral neck cortical and the L2–L4 trabecularlar bone. Patients were verticalised and encouraged to walk with full weight bearing on the average on day 3 to 4 after surgery.

Results: DPX did not demonstrate any significant decrease in BMD in any of the patients included in this study, neither in the lumbar spine nor in the contralat-eral femoral neck.

Discussion: Several studies in the literature point out the difficulty in recovering bone mass lost after a period of immobilisation or unloading. This bone loss could reach 10% of the bone mass even for short periods of unloading. Furthermore, minimal bone loss, to the order of 2.5% could accelerate the transformation of osteopenia into osteoporosis and increase the risk of fractures. The importance of minimising periods of unloading in older patients is thus evident.