ROENTGENOGRAPHIC DENSITOMETRY OF BONE ADJACENT TO A FEMORAL PROSTHESIS

A digital imaging method was developed to quantitate the stress-relate d changes in roentgenographic bone density after total hip arthroplast y. A technique termed ''histogram-directed equalization'' was used to compensate for differences in postimaging data caused by the effects o f variable quality obtained from ten patients. Quantitative change due to variation in delivered energy was decreased by 7% for roentgenogra ms obtained with a 2 kVp variation and 31% for roentgenograms obtained with a 4 kVp variation. The method allowed the authors to accurately describe the changes observed on annual postoperative roentgenograms o btained over the past decade. The utility of the method was demonstrat ed in 15 of the senior author's long-term cases treated with fully por ous-coated implants. These cases were divided into two groups based on the diameter of the prosthetic stem implanted in each case. Five pati ents were grouped with small-diameter stems and ten with large-diamete r stems. Both groups showed substantial decrease in roentgenographic b one density (from 11% to 28%) in the medial and lateral proximal regio ns. The large-diameter group had an overall larger decrease in roentge nographic bone density at two and five years. Roentgenographic bone re modeling changes were most pronounced in the first two years. Changes between two and five years progressed at a slower rate. The results al so confirmed the predicted effect of stem diameter on bone remodeling patterns.