Influence of cup orientation on the wear performance of metal-on-metal hip replacements

Abstract

There are a number of factors that determine the overall outcome of total hip replacement (THR) surgery, some of which appear to be related to the surgical procedure. In particular, the inclination angle at which the acetabular component is placed has been reported to influence the long-term successful performance of THR. The present study assessed the influence of cup orientation on the wear of 40 mm diameter metal-on-metal (MoM) hip bearings tested in a hip simulator. The bearings had a mean radial clearance of 150 microm; the cups oriented at 35 degrees, 50 degrees, and 60 degrees to the horizontal were loaded for up to 6 x 10(6) cycles. In each test the wear rates during the run-in phase were higher than in the steady state phase; the wear rates during the run-in phase were not significantly different for each cup orientation. However, at cup angles of 50 degrees and 60 degrees, the steady state wear rates were 0.69 mm3/ 10(6) cycles and 1.7 mm3/10(6) cycles respectively, significantly higher than at 35 degrees (0.24 mm3/10(6) cycles). The results indicated that larger cup inclination angles not only move the position of the wear scar but also, more significantly in MoM bearings, increase the wear rates and total wear volume generated.

New Insights into Wear and Biological Effects of Metal-on-Metal Bearings

“…It is also speculated that the implantation of the acetabular component in excessive anteversion and/or abduction may destabilize the layer and lead to excessive wear. This agrees with clinical observation 27 and experimental hip wear testing 28 . Hence, a better understanding of the kinetics of the tribomaterial formation and removal at the hip joint could be crucial for improved clinical outcome.…”

Acetabular Cups in 60 mm Metal-on-Metal Bearings Subjected to Dynamic Edge-Loading with 70° Peak-Inclination in 10-Million Cycle Simulator Study

“…At 5 Mc in the Inverted study, the corresponding cup wear ratios were BAW = 95% and STD = 70%, these satisfying hypothesis 4. Prior steep-cup studies did not provide individual head and cup wear-rates [53,55], so there were no other comparisons at 5 Mc duration. Given these examples of MOM wear variations, we are of the opinion that such "MOM outliers" should be included as part of the overall assessment.…”

“…The radiographic presentation of steeply-inclined cups has frequently been criticized, many studies citing "edge loading" as major evidence for adverse MOM wear in patients [21,22,24,27,[29][30][31]49]. It is therefore interesting that three very different simulator studies of edge-loaded cups [53,55,60] produced MOM wear-rates elevated compared to control data (Table 1) but still within the range (0.5 to 2 mm 3 /Mc) considered typical of many MOM simulator studies [65]. In prior 3rd-body wear studies with CoCr and Ti6Al4V particulates, wear-rates > 3 mm 3 /Mc turned the MOM lubricants black [66].…”

“…The internationally accepted methodology shows the cup mounted above the femoral head (Figure 2), thereby simulating the "Anatomic" hip configuration as viewed on patient radiographs (Figure 1) [43]. The stipulated test inclination for the cup ( Wear studies with large-diameter MOM bearings followed standard simulator guidelines ( Figure 2) with some preferring to use a 35° cup inclination [46][47][48][49][50][51][52][53][54][55]. Resulting wear-rates appeared acceptably low at 0.5 to 0.8 mm 3 per million load cycles (Mc).…”

Reply to Letter to Editor: THA with the ABG I Prosthesis at 15 Years: Excellent Survival with Minimal Osteolysis

“…Numerous reports mirror Dr. Gallo's experience of poor outcomes with this implant. Unfortunately we cannot offer additional insight regarding reasons why our results are better than those previously published.There is increasing evidence in relation to hard bearing surfaces that surgical technique and correct cup placement are more important than previously thought [1,3]. It seems likely that these factors plus cup diameter/polyethylene thickness and polyethylene quality also will influence outcomes in other prostheses using conventional bearings.…”