Osteodensitometry in uncemented total hip arthroplasty using computertomography

The aim of this investigation was to evaluate a new method developed for the measurement of bone mineral density and bone remodelling phenomena after total hip arthroplasty using computer tomography. Computertomography is a radiological technique to examine bone structures in high resolution. Using an extended scale it is possible to investigate bone scans and implants with fewer metal artifacts. For osteodensitometry measurement a special software (IMPact HIP) for the analysis of the data was used. The measured parameters were the overall bone mineral density (mg Calcium-Hydroxyapatite/ml) and the cortical bone structure. A standard scan mode enable to compare the computertomography scans at follow-up. Nineteen total hip arthroplasty patients (20 hips) with a mean age of 58 years (31-70) were operated on using an uncemented titanium alloy stem with a tapered design. The periprosthetic bone was assessed using computertomography-assisted osteodensitometry two weeks and one year after surgery. We observed a decrease of the overall bone mineral density (15%) and of the cortical bone structure (20%) one year after insertion of the stem in the proximal part of the femur. The area corresponds to the Gruen zones 1 and 7. On the other hand, a decrease of mineral density of 5% for the overall bone and of 3% for the cortical bone was found at the level of the tip of the stem, which corresponds to the Gruen zones 3, 4 and 5. Computertomography-assisted osteodensitometry allows to investigate the bone remodelling after total hip arthroplasty by separating the analysis of the overall bone mineral density and of the cortical structure. The present method is a reliable tool for quality-control in total hip arthroplasty.