Abstract
Introduction
Periprosthetic osteolysis following total hip arthroplasty is caused mainly by polyethylene wear particles and necessitates revision surgery at some stage even in the presence of well-fixed implants. Therefore, methods to estimate the polyethylene wear become important, with manual wear measurement methods as the main outcome measurement even in the presence of computer-assisted measurement methods on account of easy availability and simplicity in their use with reasonable accuracy. The purposes of this study were to quantify the accuracy and reproducibility of the slide presentation software method on clinical radiographs and to compare it with that of the previously described Livermore's method, and to determine the usefulness of the slide presentation software methods for highly cross linked polyethylene wear measurement.
Materials and Methods
81 hips out of 61 patients who underwent primary total hip arthroplasty between October 2000 and January 2006 were retrospectively evaluated for polyethylene wear by two independent observers using the Livermore's and the slide presentation software methods. All the hips were implanted with highly cross linked polyethylene acetabular liners with cementless acetabular components. The 28 mm sized cobalt chrome alloy femoral heads were used in all cases. The mean age of the patients was 50.8 years(range, 27–73 years), and the mean follow-up period was 6.6 years (range, 2–11 years). Paired radiographs were analyzed using the Livermore's and the slide presentation software method. For the Livermore's methods, radiographs were magnified to 200%, printed, and readings taken with digital calipers with an accuracy of 0.01 mm(Figure 1). For the slide presentation software method, we used Microsoft Office PowerPoint software(Microsoft Corp., Redmond, WA, USA) as described in a previous our study(Figure 2).
Results
The mean polyethylene wear rate in 81 hips measured by the Livermore's method was found to be 0.071±0.12 and 0.081±0.09 mm/year by observer 1 and 2 respectively. The mean polyethyelene wear rate measured by slide presentation software method was found to be equally 0.069±0.07 mm/year by observer 1 and 2. Interobserver and intraobserver variance were evaluated using Pearson correlation coefficient. Correlation coefficients for interobserver variance were 0.802 for the Livermore's method and 0.979 for the slide presentation software method. Correlation coefficient for intraobserver variance were 0.777 for the Livermore's method and 0.965 for the slide presentation software method in observer 1, 0.303 for the Livermore's method and 0.941 for the slide presentation software method. The mean time consumed in each radiographic measurement with the Livermore's method was 15.52 minutes (range, 10.67–22 minutes) as compared to 9.55 minutes (range, 5.42–13.5 minutes) measured with the slide presentation software method (p < 0.001).
Conclusion
The slide presentation software method was more accurate in serial intra-observer measurements and more reproducible in inter-observer readings for polyethylene wear than the traditional Livermore method, and was simple to use and less time consuming. Not all orthopaedic surgeons have access to CT for measuring polyethylene wear, hence the use of this type of manual method becomes a necessity on account of its easy availability and repeatability in serial measurements.
