INTERTROCHANTERIC CANCELLOUS BONE AS A PREDICTOR OF RSA MIGRATION OF UNCEMENTED FEMORAL STEMS

Abstract

Introduction: In postmenopausal female patients with hip osteoarthritis, osteoporosis as well as altered local trabecular bone architecture may lead to a increased migration of uncemented hip prostheses.^1,2 The aim of this study was to determine whether 3D bone architecture and mechanical properties of intertrochanteric cancellous bone in the proximal femur predict RSA migration of uncemented femoral stems.

Materials and Methods: The study population consisted of 61 female patients with primary hip osteoarthritis. Informed consent was obtained prior to any study-related procedures. The Ethical Committee approved the study protocol.

All patients underwent a total hip replacement (ABG II, Stryker) with uncemented proximally hydroxyapatite-coated femoral stem with tantalum RSA markers. Ceramicceramic bearing surfaces were used. A uniplanar type of RSA setup was applied. The RSA examinations were performed postoperatively and at 3, 6, and 12 months.

During surgery, cancellous bone biopsy was taken from the proximal femur from the site of stem implantation. The specimens were scanned with micro-CT. 3D analysis of trabecular bone geometry and BMD was performed using CTAn software. After micro-CT imaging, the trochanteric cancellous bone specimens were subjected to a destructive compression test. Maximum force and stiffness were calculated. Linear regression analysis was applied to study correlations between different parameters investigated.

Results: The patients exhibited major differences in the density and structural quality of intertrochanteric cancellous bone. Significant correlations were found between the measured biomechanical parameters and the structural parameters calculated from micro-CT data.

Unexpectedly, the quality of intertrochanteric cancellous bone did not predict RSA migration of the femoral stems. The femoral stems reached high stability within 3 months and there were no significant differences in the axial and rotational migration of the femoral stems between the patients with normal or poor quality of the intertrochanteric cancellous bone.

Discussion: The 3D bone architecture, mineral density and mechanical properties of the local intertrochanteric cancellous bone do not seem to serve as predictors of femoral stem migration. The observation suggests that the significance of cancellous bone quality for the initial stability of uncemented femoral stems has been over-emphasized.