Evaluation of a new methodology to simulate damage and wear of polyethylene hip replacements subjected to edge loading in hip simulator testing

Abstract

Wear and fatigue of polyethylene acetabular cups have been reported to play a role in the failure of total hip replacements. Hip simulator testing under a wide range of clinically relevant loading conditions is important. Edge loading of hip replacements can occur following impingement under extreme activities and can also occur during normal gait, where there is an offset deficiency and/or joint laxity. This study evaluated a hip simulator method that assessed wear and damage in polyethylene acetabular liners that were subjected to edge loading. The liners tested to evaluate the method were a currently manufactured crosslinked polyethylene acetabular liner and an aged conventional polyethylene acetabular liner. The acetabular liners were tested for 5 million standard walking cycles and following this 5 million walking cycles with edge loading. Edge loading conditions represented a separation of the centers of rotation of the femoral head and the acetabular liner during the swing phase, leading to loading of the liner rim on heel strike. Rim damage and cracking was observed in the aged conventional polyethylene liner. Steady-state wear rates assessed gravimetrically were lower under edge loading compared to standard loading. This study supports previous clinical findings that edge loading may cause rim cracking in liners, where component positioning is suboptimal or where material degradation is present. The simulation method developed has the potential to be used in the future to test the effect of aging and different levels of severity of edge loading on a range of cross-linked polyethylene materials. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 1456-1462, 2018.

Hip simulator testing of the taper‐trunnion junction and bearing surfaces of contemporary metal‐on‐cross‐linked‐polyethylene hip prostheses

“…As shown in Table , the mean volumetric wear rate of the XLPE liners, 2.74 ± 0.74 mm 3 /Mc, falls within the range of wear rates found in previous MoXLPE hip simulator studies . The surface roughness (Sa) of the articulating surface of the XLPE liners showed a significant decrease posttest ( p < 0.001).…”

“…No other in vitro MoXLPE hip simulator studies (Table II) have reported wear from the metallic femoral taper. [11][12][13][14][15][16][17][18] Metal release from the taper-trunnion junction of MoXLPE modular hip implants The CoCrMo femoral tapers (0.045 AE 0.024 mm 3 /Mc) and titanium trunnions (0.044 AE 0.003 mm 3 /Mc) showed similar volumetric wear rates in this in vitro wear test. If 1 Mc of the in vitro hip simulator test is equivalent to 1 year in vivo, 52 then the mean volumetric wear rate of the CoCrMo femoral taper (0.045 AE 0.024 mm 3 /year) and titanium trunnion (0.044 AE 0.003 mm 3 /year) falls within the range of wear rates found in previous MoP retrieval studies, which included few Corail ® components in their respective cohorts, 50,53 as shown in Table I.…”

“…These relatively unchanged roughness measurements indicate minimal damage at the articulating surfaces of the CoCrMo femoral heads. No other in vitro MoXLPE hip simulator studies (Table II) have reported wear from the metallic femoral taper …”

“…Wear at the bearing surfaces of XLPE liners As shown in Table II, the mean volumetric wear rate of the XLPE liners, 2.74 AE 0.74 mm 3 /Mc, falls within the range of wear rates found in previous MoXLPE hip simulator studies. [11][12][13][14][15][16][17][18] The surface roughness (Sa) of the articulating surface of the XLPE liners showed a significant decrease posttest (p < 0.001). This finding was supported by an elimination of the original machining marks from the bearing surfaces of the XLPE liners (see Fig.…”

“…5 Furthermore, the revision rates at 16 years for XLPE (6.4%) are lower than non-XLPE (12.4%) hip replacement procedures. 5 The wear rates of metal-oncross-linked-polyethylene (MoXLPE) bearing couples are typically less than 11 mm 3 /million cycles (Mc) [11][12][13][14][15][16][17][18] compared with metal-on-non-XLPE, which have reported wear rates ranging from 10 to 51 mm 3 /Mc. 14,19,20 Clinical trials and mid-to long-term follow-up studies of XLPE have shown significantly reduced wear, less osteolysis, and a lower risk of revision than conventional non-XLPE.…”