CT-ASSISTED OSTEODENSITOMETRY AFTER TOTAL HIP REPLACEMENT WITH AN UNCEMENTED TAPER-DESIGN STEM: 6-YEAR-FOLLOW-UP

Abstract

Introduction: The aim of this study was to analyze the periprosthetic bone remodeling of the femoral component after implantation of an uncemented taper-design stem using CT-assisted osteodensitometry. This method allows accurate three-dimensional evaluation of cortical and cancellous bone with high resolution.

Material and methods: We followed 21 consecutive Patients with osteoarthritis who received primary total hip replacement using 21 uncemented three-dimensionally shaped taper stems (TiAl6V4-Cerafit, Ceraver, France). CT-evaluation was performed 2 weeks, 1 and 6 years post-op. Bone mineral density (BMD) [mg/ml] was determined separately for both cortical and cancellous bone using a special software.

Results: Mean decrease of cortical BMD in the proximal (metaphyseal) area 6 years post-op was −25%, (1 year post-op −15%). Only slight changes of BMD were observed in the distal (diaphyseal) area. Cancellous BMD decreased progressively from −26% 1 year post-op to −49% 6 years after index operation in the proximal area. Cortical bone density loss was lower and non-progressive at the diaphysis (Ø −7% 1 year, −9% 6 years post-OP) and the distal region (Ø −6% 1 year, −4% 6 years post-OP) of the stem. All stems showed no signs of loosening on plain radiography and good clinical results according to the Harris hip score.

Conclusion: Computertomography assisted osteoden-sitometry is the only method which allows discrimination between periprosthetic cortical and cancellous bone density changes in vivo. The analyzed uncemented stem is anchored at the diaphysis and distal region. Due to the changed biomechanical loading after stem implantation, progressive proximal cancellous bone density loss was measured for the first time in vivo. Its role in the pathogenesis of implant loosening is still unknown and needs to be further elucidated.