Volumetric measurement of periprosthetic bone remodeling: prospective 5 years follow-up after cemented total hip arthroplasty

Introduction

Periprosthetic bone remodeling after total hip arthroplasty (THA) is a well recognized phenomenon. Many authors have published osteodensitometric data with DEXA analysis. This study based on computerized tomography (CT).

Materials and methods

The objective of the current project is to collect prospective volumetric bone density data with a clinical CT study in six patients after cemented THA (titanium alloy stem). The follow-up time is 5 years. A data set of about 100,000 bone voxels for each femur was collected. Bone density was observed by dint of an osteodensitometric computer program. The median results were shown in seven regions of interest (ROI) around the prosthesis stem, according to Gruen.

Results

The statistical analysis of the six cases after 60 months with respect to the postoperative control demonstrated a significantly lower density in ROI 2 (−125.5HU, P = 0.014), ROI 3 (−116.7HU, P = 0.023), ROI 4 (−54.5HU, P = 0.023), ROI 5 (−90.9HU, P = 0.014) and ROI 6 (−104.9HU, P = 0.014). Maximum density decrease was observed in ROI 2 and 3. The statistical analysis of the six cases after 60 months with respect to the 24 months control demonstrated a significantly lower density in ROI 2 (−62.6HU, P = 0.014), ROI 5 (−62.9HU, P = 0.023). There was a density decrease in ROI 3, 4, 6, 7 which was not significant and a slight increase in ROI 1.

Conclusion

To our knowledge, this is the first collection of fully prospective 5 years 3D periprosthetic density data. The CT method used in the study presented here measures three-dimensionally, while the frequently used DEXA (dual X-ray absorptiometry) method measures two-dimensionally. The data are also unique as they are suitable for direct patient-specific 3D finite element meshing and biomechanical calculation. They can be graphically post-processed in order to obtain cross-sectional or 3D displays of density patterns.