Osteodensitometry in uncemented total hip arthroplasty using computertomography

The aim of this investigation was to evaluate a new method developed for th e measurement of bone mineral density and bone remodelling phenomena after total hip arthroplasty using computer tomography. Computertomography is a r adiological technique to examine bone structures in high resolution. Using an extended scale it is possible to investigate bone scans and implants wit h fewer metal artifacts. For osteodensitometry measurement a special software (IMPact HIP) for the a nalysis of the data was used. The measured parameters were the overall bone mineral density (mg Calcium-Hydroxyapatite/ml) and the cortical bone struc ture. A standard scan mode enable to compare the computertomography scans a t follow-up. Nineteen total hip arthroplasty patients (20 hips) with a mean age of 58 ye ars (31-70) were operated on using an uncemented titanium alloy stem with a tapered design. The periprosthetic bone was assessed using computertomogra phy-assisted osteodensitometry two weeks and one year after surgery. We obs erved a decrease of the overall bone mineral density (15 %) and of the cort ical bone structure (20 %) one year after insertion of the stem in the prox imal 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 s tem which corresponds to the Gruen zones 3, 4 and 5. Computertomography-assisted osteodensitometry allows to investigate the bon e remodelling after total hip arthroplasty by separating the analysis of th e overall bone mineral density and of the cortical structure. The present m ethod is a reliable tool for quality-control in total hip arthroplasty.