Measurements of long-term periprosthetic bone changes around a unique composite implant.

Periprosthetic bone changes around a non-bonded composite implant were measured after 6.5 years of implantation. The implanted and unimplanted femora of three canines were cut simultaneously at 3-mm increments. Cortical bone changes at all levels were determined from contact radiographs of the sections using an image analysis system. Alternating sections were cut into 3-mm cubes. The elastic properties of the cancellous bone cubes were determined using ultrasonic techniques. The method of directed secants was used to determine the cancellous bone orientation. The proximal cortical wall thickness on the implanted side increases by an average of 30%. The cancellous bone directly adjacent to the implant was an almost continuous shell encircling the prosthesis. The periprosthetic orientation was circumferential around the implant. The elastic and shear moduli of the cancellous bone increased on the implanted side. The bone changes are currently being correlated with results from finite element calculations.