Abstract
PurposeWe aimed to assess polyethylene liners of retrieved hips of one design of a dual mobility (DM) cup liner and two designs of femoral stems to better understand the role of femoral stem design on polyethylene impingement.MethodsThis was a case-control study involving 70 retrieved highly cross-linked polyethylene (X3) liners used with ABGII (n = 35) and Rejuvenate (n = 35) stems (Stryker). All polyethylene liners were assessed for evidence of rim deformation and the damage quantified using metrology methods.ResultsA total of 80% of polyethylene liners paired with ABGII necks had macroscopic evidence of neck impingement resulting in a raised lip whilst 23% of liners paired with Rejuvenate necks had evidence of a raised lip (p < 0.0001). The height of the raised rims of the DM cups paired with ABGII necks had a median (range) of 139 μm (72–255). The height of the raised rims of the DM cups paired with Rejuvenate necks had a median (range) of 52 μm (45–90) (p < 0.0001).ConclusionOur new findings from retrieved dual mobility bearings showed that polyethylene liner rim deformation resulting from impingement with the femoral neck occurs in early in-human function, is circumferential in distribution, and is affected by the stem neck design. We recommend the use of highly polished and non-edged neck designs when used in conjunction with DM cups.
Highlights
Joint instability continues to pose challenges to total hip arthroplasty
Our new findings from retrieved dual mobility bearings showed that polyethylene liner rim deformation resulting from impingement with the femoral neck occurs in early in-human function, is circumferential in distribution, and is affected by the stem neck design
We recommend the use of highly polished and non-edged neck designs when used in conjunction with Dual mobility (DM) cups
Summary
Joint instability continues to pose challenges to total hip arthroplasty. The incidence of dislocation is reported as 0.2% to 3% in the first year following the primary procedure, up to 7% after 25 years, and as high as 25% after revision arthroplasty [1, 2]. DM cups have a large diameter femoral head, increasing the head-neck ratio and the ‘jump distance’ needed to dislocate the ball from the acetabulum [5] resulting in improved stability [6,7,8]. DM cups are vulnerable to impingement between the femoral neck and the polyethylene liner rim, the so-called third articulation, which can cause intraprosthetic dislocation (IPD) [6, 9], defined as the dissociation of the small-diameter head retained within the liner due to loss of the retentive power of the rim, leading to surgical treatment. Clinical studies have shown that the design of the femoral neck influences the stability of DM cups [10,11,12,13] but the mechanism is not known. The objectives were to compare the polyethylene liners of two femoral stem designs for (1) visual assessment of damage and (2) quantification of deformation by means of metrology methods
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