Benefits of thin‐shelled acetabular components for metal‐on‐metal hip resurfacing arthroplasty

Abstract

ABSTRACT:The theoretical advantage of using thinner acetabular components in hip resurfacing has not yet been clinically verified. Our purpose was to test the hypothesis of bone conservation and assess the effects of using a thinner acetabular component on hip biomechanics and clinical outcome. We compared the bone conservation, biomechanical results, and functional outcomes between hips in 35 patients who received bilateral metal-on-metal resurfacing arthroplasties with acetabular components of 5 mm thickness on one side and 3.5 mm thickness on the other. Acetabular abduction angle and acetabular anteversion were measured using Ein-Bild-Röentgen-Analysis software. Medial acetabular wall thickness and position of the hip center of rotation were measured using Image J software. The change in position of the hip center of rotation was minimal and did not reach significance. Thin-shelled components showed greater bone conservation on the acetabular side measured by an increase in the medial acetabular wall thickness. Bone conservation on the femoral side was achieved as well with thin shells. Range of motion, pain scores, and complication rates were comparable. No appreciable difference was found in bone-cup radiographic appearance between the two types of components. These data suggest that patients can experience good clinical outcomes for resurfacing with either thin or thick-shelled acetabular components. However, thin-shelled components preserve acetabular bone stock and allow the use of a larger femoral component. The use of thinner acetabular components is an improvement in bone conservation for a hip resurfacing design.

Asymptomatic prospective and retrospective cohorts with metal‐on‐metal hip arthroplasty indicate acquired lymphocyte reactivity varies with metal ion levels on a group basis

“…16,17 Contact patch to rim (CPR) distance was calculated using the mean position of the articular contact patch to the cup rim with the patient in standing weight-bearing position. 18 EBRA is not well established for measuring version angles for large diameter MoM hips.…”

“…All post-op radiographs were analyzed as previously described where cup abduction angle and anteversion angle were calculated with use of Einzel-Bild-Roentgen-Analysis cup software (EBRA-CUP Digital; University of Innsbruck, Innsbruck, Austria). 16,17 Contact patch to rim (CPR) distance was calculated using the mean position of the articular contact patch to the cup rim with the patient in standing weight-bearing position. 18 EBRA is not well-established for measuring version angles for large diameter MoM hips.…”

Acetabular Component Thickness Does Not Affect Mid-term Clinical Results in Hip Resurfacing

“…The advantage of using a thinner acetabular shell in hip resurfacing is the ability to conserve bone stock on the acetabular or the femoral side, or both [19]. However, it is necessary to verify that mid-to long-term safety and efficacy of such devices are at least as good as those of the original components before their use can be generalized.…”

“…The coverage of the femoral head by the socket was the same for both types of acetabular components and varied with femoral component size from 159°for a 36-mm head to 163°for a 54-mm head. Although the 5-mm thick socket had a constant thickness, the 3.5-mm socket was designed with greater thickness at the dome (4.7 mm) compared with the rim (3.5 mm) to maintain the same resistance to deformation during interference impaction as the thicker acetabular shell [19]. The gain in volume for a 3.5-mm thick cup of average size (48 mm inside diameter) is 1.2 mm 3 when compared with a 5-mm thick component.…”

“…After 6 years of implantation of a standard 5-mm thick porouscoated acetabular component, thinner shells (3.5 mm) were introduced in our series. The benefits of the thinner components in terms of bone conservations have been reported [19], but the effect of acetabular cup thickness on the clinical results of hip resurfacing have not been studied.…”