ANALYSIS OF PERIPROSTHETIC TISSUE FORMATION AROUND A POROUS TITANIUM ENDOPROSTHESIS USING CT-BASED SPATIAL RECONSTRUCTION

Objective: Reformatted CT-based image data may be of use in evaluation of new bone formation around massive bone replacement implants, but t he impact of metal-induced artifacts on the accuracy of image reconstr uction is unknown. This study was designed to evaluate the accuracy an d precision of quantitative image reconstruction in the presence of a titanium implant. Materials and Methods: Model porous-coated titanium implants were harvested from 23 dogs 12 weeks after surgical implantat ion. Contiguous 1.5 mm transverse CT scans were done first with the ti tanium implant in place, then repeated after replacement of the implan t with an acrylic spacer. Microradiographs of sections cut at defined locations were used to establish gray level thresholds for image recon struction and to validate the accuracy of CT-based image data. Reforma tted image data were used to determine periprosthetic bone volume (mm( 3)) and area of interfacial contact between bone and implant (mm(2)) R esults: The CT-based data derived with either implant material had an accuracy of 83-88% and a precision coefficient of variation (CV) of 2- 4% for both volume and contact area variables. Presence of titanium di d not seriously affect the quality of images obtained, and results wer e strongly correlated with those obtained with acrylic. Conclusion: Ac curate volumetric data derived from CT-based images of periprosthetic new bone formation can be obtained in the presence of a titanium endop rosthesis. Improved demonstration of spatial relationships of bone and implant may improve postoperative evaluation.