Background: PolyWareTM software (PW) has been exclusively used in most of the polyethylene wear studies of total hip arthroplasty (THA). But, we found that PolyWareTM (PW) measurements can be significantly inaccurate and unrepeatable depending on imaging conditions or subjective manipulation choices. In this regard, this study reveals the required conditions to achieve the best accuracy and reliability of the PW measurements.
Methods: The experiment examined the dependency of PW on several measurement conditions. The X-ray images of in-vitro THA prostheses were acquired under a clinical X-ray scanning condition. A liner wear of 6.67 mm, an acetabular lateral inclination of 36.7° and an anteversion of 9.0° were simulated.
Results: Among all the imported X-ray images, those with a resolution of 1076×1076 exhibited the best standard deviation in wear measurements as small as 0.01 mm and the least occurrences of blurriness. The edge detection area specified as non-squared and off the femoral head center exhibited the most occurrence of blurriness. At the X-ray scanning moment, an eccentric placement of the femoral head center by 15 cm superior to the X-ray beam center led to an acetabular anteversion error up to 5.3°.
Conclusion: The results request researchers to observe following conditions; 1) the original Xray image be 1076×1076 squared X-ray images, 2) the edge detection area be specified as a square with edge lengths of 5 times the diameter of the femoral head centered at the femoral head center, 3) the femoral head center or acetabular center be placed as close to the center line of the X-ray beam as possible, at the X-ray scanning moment.