Wear analysis of failed acetabular polyethylene

Abstract

There are many methods for analysing wear volume in failed polyethylene acetabular components. We compared a radiological technique with three recognised ex vivo methods of measurement. We tested 18 ultra-high-molecular-weight polyethylene acetabular components revised for wear and aseptic loosening, of which 13 had pre-revision radiographs, from which the wear volume was calculated based upon the linear wear. We used a shadowgraph technique on silicone casts of all of the retrievals and a coordinate measuring method on the components directly. For these techniques, the wear vector was calculated for each component and the wear volume extrapolated using mathematical equations. The volumetric wear was also measured directly using a fluid-displacement method. The results of each technique were compared. The series had high wear volumes (mean 1385 mm(3); 730 to 1850) and high wear rates (mean 205 mm(3)/year; 92 to 363). There were wide variations in the measurements of wear volume between the radiological and the other techniques. Radiograph-derived wear volume correlated poorly with that of the fluid-displacement method, co-ordinate measuring method and shadowgraph methods, becoming less accurate as the wear increased. The mean overestimation in radiological wear volume was 47.7% of the fluid-displacement method wear volume. Fluid-displacement method, coordinate measuring method and shadowgraph determinations of wear volume were all better than that of the radiograph-derived linear measurements since they took into account the direction of wear. However, only radiological techniques can be used in vivo and remain useful for monitoring linear wear in the clinical setting. Interpretation of radiological measurements of acetabular wear must be done judiciously in the clinical setting. In vitro laboratory techniques, in particular the fluid-displacement method, remain the most accurate and reliable methods of assessing the wear of acetabular polyethylene.

Risk factors for accelerated polyethylene wear and osteolysis in ABG I total hip arthroplasty

“…The reasons for these results are not clear, but at least partially may lie in the radiographic origin of wear measurement used in these studies. These radiographic measurements may be less sensitive in detecting wear than in vitro measurements [30].…”

Constrained Cups Appear Incapable of Meeting the Demands of Revision THA

“…3). The fluid displacement method has been used in previous retrieval studies and has been shown to be accurate and reproducible in formal validation trials [13,25,37]. Annual volumetric wear rates were calculated from the measured volume between the head and the liner and the duration of implantation.…”

Tribological interactions of modern biomaterials used in total hip arthroplasty (THA)

“…To evaluate the wear, the worn profi le is compared with the profi le of a control (Cunningham et al , 2007). In addition to its easiness, the shadowgraph technique is suitable for the analysis of acetabular cup retrievals and allows for the estimation of wear where gravimetric assessment is not possible (Chuter et al , 2007).…”