INTERPRETATION OF DIGITAL MIGRATION ANALY SIS OF UNCEMENTED PM-TOTAL HIP PROSTHESES

Purpose: Aim of this study was the validation of a digital measurement device for hip implants. Methods: From 43 patients with a minimum of four subsequent roentgenograms 246 roentgenograms of PM-shafts (an ave rage 5.72/shaft) and 142 roentgenograms of PM-cups (an average 6.45/cu p) were digitized on a DiagnostiX 2048 basis station (Pace Systems, Ge rmany). Modified Sutherland/Nunn methods were chosen for measuring pur poses. Regression analysis was done and the results were correlated to implant loosening. Results: Concerning the total vertical migration o f the cup there is a significant (p < 0.04) difference between the loo sened components (6.02 +/- 2.59 mm) and the fixed cups (2.26 +/- 2.89 mm). The average annual vertical migration rate of the stem shows a hi ghly significant difference (p < 0.007) when comparing loosened stems (0.82 +/- 0.43 mm, total migration 4.78 +/- 2.59 mm) and fixed ones (0 .20 +/- 0.54 mm, total migration 1.72 +/- 3.02 mm) Conclusions: Using the regression analysis and a sufficient number of pictures the system allows us to give migration values that make loosening likely. Howeve r for the single implant an individual prognosis of loosening is not p ossible.