Assessment of femoral component migration in total hip arthroplasty: digital measurements compared to RSA.

The aim of this study was to determine the accuracy of the software system "Düsseldorf Migration Analysis - Femoral Component Analysis" (DMA-FCA) in measuring stem migration in total hip arthroplasty (THA) on digitised anteroposterior radiographs of the pelvis. Bony and implant landmarks on two consecutive radiographs were used for measurements of subsidence and varus-valgus tilt. The accuracy of the method was determined by reference to radiostereometric measurements (RSA). Using specific comparability limits, comparability analysis of radiographs with respect to femoral positioning is possible with DMA. DMA-FCA and RSA measurements were performed after cementless THR in a population of 60 patients aged 38 to 69 years. With a Cronbach's alpha-index of 0.89 and 0.99 for subsidence and 0.90 and 0.98 for classic varus-valgus-tilt, the intraobserver and interobserver reliability for the DMA-FCA-method was calculated as good. Using RSA as reference method, the accuracy of DMA-FCA was calculated to be 2.51 mm for subsidence and 2.49 degrees for varus-valgus-tilt (95% confidence interval). Without comparison to RSA, DMA measured 1.94 mm for subsidence and 2.35 degrees for varus-valgus-tilt. Based on a comparison with RSA, our results show lower accuracy for DMA-FCA than for EBRA-FCA, but DMA-FCA is easier to use in everyday clinical practice. It is hoped that the use of digital measuring methods such as DMA will become standard for long-term observation and will be integrated into clinical routine in the context of quality assurance of THR.