BONE MINERAL DENSITY COMPARISON USING DUAL-ENERGY X-RAY ABSORPTIOMETRY SCANS IN PATIENTS WITH BILATERAL TOTAL HIP REPLACEMENTS – A LONGITUDINAL, INTER-PROSTHESIS EVALUATION

Abstract

Introduction: Dual-energy x-ray absorptiometry (DEXA) measurement is a valuable and accurate method of assessing periprosthetic bone loss around femoral stems.

Method: The cohort was 21 patients who underwent total hip arthroplasties with double-threaded, cone-shaped, modular, femoral stems and who already had a prosthetic contralateral hip. The contralateral hip arthroplasties were Autophur fully porous coated, Exeter cemented and Charnley cemented stems. DEXA measurements were performed in the anteroposterior femoral plane using a Lunar DPXL densitometer and analysed using the Lunar Orthopaedic Software Package, Version 1.7, designed for periprosthetic measurements. The initial measurement was performed between two and four weeks after the surgery as a baseline and then repeated after three, six, 12 and 24 months. The DEXA scan results were analysed comparing the bone density of the double-threaded cone-shaped modular femoral stem side with the contralateral side in a longitudinal study.

Results: The contralateral hip bone quality remained fairly constant in keeping with the maturity of the hip arthroplasties. The insertion of the double-threaded cone-shaped modular femoral stem caused the expected initial bone loss in Gruen zones one and seven due to proximal stress-shielding. Only minor bone loss occurred distally, reflecting good fixation and load transfer of the prosthesis.