Radiographic evidence of migration of the femoral stem component after THA is the most important diagnostic sign of femoral implant loosening. Early detection of stem subsidence may help in deciding to perform revision surgery before severe bone destruction has occurred, at a moment when standard clinical and radiological follow-up may still be reassuring.

The aim of this study was to identify the most appropriate bone and prosthetic landmarks to study subsidence and to determine the accuracy of the Imagika® method as compared to the ‘gold standard’ EBRA-FCA® software.

256 THA in 242 patients (102 men, 140 women) with a median age of 63.8 years (range: 36–85) received 4 different cementless or cemented prosthetic stem designs. They were followed for 10.6 years (range: 6–16). CLS® stems were used in 56 patients, MS-30® in 76, Elite® in 50 and Osteal® in 74.

4 specific analysis models were created in the Imagika® software in order to evaluate several possible landmarks on the proximal femur and on the stem, and to evaluate the possibility of using a correction factor to improve the comparability of successive x-rays taken under non standardised conditions. The most accurate prosthetic landmarks were the prosthesis shoulder in CLS® and MS-30® stems and the lateral aspect of the collar in Elite® and Osteal® stems. The best bone landmark was the top of the greater trochanter in all cases.

For the whole series, the annual linear subsidence rates were 0.049+/−0.014 mm with EBRA-FCA® and 0.052+/−0.012 mm with Imagika® respectively (P = 9E-7). Migration values in the 4 different groups were respectively 0.06 +/− 0.01 mm/yr and 0.05 +/− 0.01 mm/yr in the CLS® group (P = 4.6E-6), 0.02 +/− 0.002 mm/yr and 0.06 +/− 0.09 mm/yr in the MS-30® group (P = 6.8E-4), 0.06 +/− 0.002 mm/yr and 0.04 +/− 0.003 mm/yr in the Elite® group (P = 4.2E-5), and 0.05 +/− 0.005 mm/yr and 0.06 +/− 0.004 mm/yr in the Osteal® group (P = 7.4E-7). The different prosthetic designs did not show significant differences concerning migration values when studied according both methods.

Thanks to a correction factor, the Imagika® method uses all the radiographs when EBRA-FCA® rejects incomparable radiographs.

The Imagika® method is more users friendly and provides excellent reliability thanks to an automatic edge detection device.

Since no significant difference was observed between EBRA-FCA® and Imagika® methods whatever the prosthetic stem design studied, our results authorise us to apply these analysis models within the Imagika® software to all THAs to follow their radiographic evolution and to possibly predict the clinical evolution.