SENSITIVITY OF EBRA VERSUS DIRECT METHODS FOR MEASURING MIGRATION AFTER THA

We aimed to determine whether the EBRA method had greater precision and sensitivity for measuring implant migration following total hip arthroplasty (THA) than direct plain radiographic techniques using modern measuring tools. Short-term precision was evaluated in 20 subjects following THA. Consecutive, standardised radiographs of the hip were performed on the same day after repositioning. Prosthetic cup and stem migration were measured from the plain radiographs using a digital calliper following methods described by Ianotti, Malchau, Nunn, Sutherland and Wetherall, and compared to those made using EBRA. Precision was expressed as 95% confidence interval (95%CI = 1.96x Std.dev.). 10 subjects were then followed prospectively with standardised plain radiographs at baseline, 6,12 and 26 weeks after THA. Migration measurements made using EBRA were compared to those made using the most precise plain radiographic method. The 95%CI of all EBRA cup and stem measurements was ±1mm or smaller. Only the Sutherland method had a similar level of precision (95%CI ±1.11 to 1.28 mm: F-Test P>0.05; all other method comparisons with EBRA P The EBRA method is a precise method for describing implant migration in small groups of patients in the early period following THA, and manual methods lack sufficient precision to be used for this purpose.