Purpose of the study: Bearing wear debris from total hip arthroplasty (THA) appears to be the main cause of prosthetic loosening. RSA is the most accurate for measuring THA wear. It is the gold standard but remains difficult to use in routine practice. We therefore developed a computer-assisted method for measuring wear on plain x-rays. The purpose of this work was to determine the accuracy and reproducibility of MPH Wear 4 for measuring bearing wear.

Material and methods: The accuracy of measurements were assessed on several types of new implants or implants worn by movement simulators. X-rays of these implants were taken after implantation using a phantom simulating soft tissue and radiographic deformation. Accuracy was defined as the difference between the measurement produced by the computer-assisted tool and the reference metrology. Reproducibility was studied on ten x-rays of THA in ten patients (five men and five women, mean age 77.9 ± 4.4 years). Intraobserver reproducibility was studied with ten successive measurements on the same image by the same observer. Interobserver reproducibility was studied with a series of ten measurements on ten different images by two observers.

Results: The accuracy of the method was 0.09 mm on average (range 0.06–0.13 mm). The standard deviation giving the intraobserver reproducibility was 0.005 (i.e. 5.96% of the mean value). The standard deviation giving the interobserver reproducibility was 0.02.

Discussion: The methods used for determining the accuracy of a wear measurement system are poorly defined in the literature. It is thus difficult to compare different measurement methods. It can be considered that methods displaying an accuracy less than or equal to the mean annual polyethylene wear can be retained since they can easily identify significant wear (from the third year on). Our method is easily applied in routine practice, retrospectively if needed, offering an adapted accuracy and good reproducibility. However, this method is currently applied to cemented acetabular implants. The software is currently being adapted for study of implant migration and metal-backed implants.