Introduction and Aims: The purpose of this study was to validate in a clinical series a method to measure femoral component migration in surface arthroplasty based on the principles of EBRA-FCA.

Method: The first 400 hybrid MMSA in 355 patients have an average of 3.5 years follow-up (range two to six years). The average age was 48 years, 73% were men and 35% had secondary osteoarthritis. All patients were evaluated prospectively at three months and then yearly. We reviewed the x-rays of 26 hips that had undergone metal-on-metal resurfacing using EBRA-FCA. Minimum follow-up was 3.5 years. Group 1was free of any clinical or radiographic signs of loosening (17 hips); group 2 had failed from femoral component aseptic loosening (nine hips). Mean age for the whole group was 50.7 years (28–67). Sixty-six percent were male and 63% were operated for osteoarthritis. We recorded migrations of 2mm or greater and the time to initiation of migration.

Results: Group 2 showed significantly greater migration than group 1, respectively: 4.57 mm versus 1.62mm for centre of the head (p=0.005), 4.51mm versus 1.05mm for stem tip (p=0.001). Initial migration was significantly sooner in group 2 versus group 1: 19 months versus 29.2 months (p=0.030). In group 2, the average time to first migration detected with EBRA-FCA was significantly less than time to first clinical symptoms: 19 months versus 29.5 months (p=0.003). More importantly, the time to detection of significant migration was shorter than the time to detection of the first metaphyseal stem radiolucency: 19 months versus 24.3 months (p=0.028).

Conclusion: EBRA-FCA represents a reliable tool to measure migration of femoral component, which may become essential in the assessment of the clinical performance of MMSA. It is best used in large clinical series with standardised x-ray technique and limiting the number of observers.