Short-Term Analysis of the Changes in the Bone Mineral Density of the Proximal Femur After Uncemented Total Hip Arthroplasty: A Prospective Study of 110 Patients

Introduction Mechanical loading continuously exposes the bone to remodeling processes. Increased load leads to a gain in bone mass, and reduced load results in a loss. After inserting a prosthesis, the proximal femur is bypassed in loading as the bodyweight shifts distally. This lack of load induces bone resorption according to Wolff’s law. To avoid this bone resorption, the implant's bending stiffness should be less than the femoral bone. Dual-energy X-ray absorptiometry (DEXA) is a well-accepted method to measure periprosthetic bone mineral density (BMD) after total hip arthroplasty (THA). Since the strength and durability of the fixation of a femoral prosthesis in cementless hip arthroplasty depend largely on the quantity and quality of the surrounding bone, preoperative and postoperative evaluation of the quantity and quality of the femoral bone is very important in the long-term prognosis of hip arthroplasty. Materials and methods A prospective study of 110 patients in the age group of 25-60 years who underwent uncemented total hip arthroplasty in our tertiary healthcare institution was performed. An uncemented, fully hydroxyapatite-coated implant from a single manufacturer was used in all the patients. All the patients were mobilized on the first post-operative day. The BMD was measured at the proximal femur and the distal tip using a DEXA scan. Gruen zones were used for calculating BMD at different anatomical locations in the femur, with particular importance to zones 1, 4, and 7. Results The pre-operative BMD in all zones measured, viz. zones 1, 4, and zone 7 of the affected side, was found to be significantly lower as compared to the BMD values on the control side (P< 0.05). The mean change in the mean BMD was calculated for all the zones and compared with each other using an unpaired t-test. The mean BMD changes were found to be significantly higher in zone 7 in comparison to both zones 1 and 4 (p<0.05). Conclusion Significant periprosthetic bone loss after uncemented THA in the femur was noted in Gruen zones 1, 4, and 7 during the first six months after THA, with the greatest bone loss in the femoral calcar area (zone 7). The lower the preoperative BMD of the patient, the greater the postoperative bone loss.