Correction of Error in Two-dimensional Wear Measurements of Cemented Hip Arthroplasties

The irregularity of individual wear patterns of total hip pros- theses seen during patient followup may result partially from differences in radiographic projection of the components between radiographs. A method to adjust for this source of error would increase the value of individual wear curves. We developed and tested a method to correct for this source of error. The influence of patient position on validity of wear measurements was investigated with controlled manipulation of a cadaveric pelvis. Without correction, the error exceeded 0.2 mm if differences in cup projection were as small as 5°. When using the described correction method, cup positioning differences could be greater than 20° before introducing an error exceeding 0.2 mm. For followup of patients in clinical practice, we recommend using the correction method to enhance accuracy of the results.