Retroacetabular Stress-shielding in THA

Abstract

We conducted a randomized clinical trial to compare periacetabular bone density changes after total hip arthroplasty using press-fit components with soft and hard liner materials. Bone density changes were assessed using quantitative computed tomography-assisted osteodensitometry. Twenty press-fit cups with alumina ceramic liners and 20 press-fit cups with highly cross-linked polyethylene liners were included; the nonoperated contralateral side was used as the control. Computed tomography scans were performed postoperatively and 1 year after the index operation. At the 1-year followup, we found no differences of periacetabular bone density changes between the alumina and polyethylene liner cohorts. However, we observed marked periacetabular cancellous bone density loss (up to -34%) in both cohorts. In contrast, we observed only moderate cortical bone density changes. The decrease of periacetabular cancellous bone density with retention of cortical bone density after THA suggests stress transfer to the cortical bone.

Periacetabular Bone Mineral Density Changes After Resurfacing Hip Arthroplasty Versus Conventional Total Hip Arthroplasty. A Randomized Controlled DEXA Study

“…This is in accordance with the recent report from Yahia et al [13] where similar results were found 2 years postoperative. In contrast to other studies, where a 3% to 35% decrease of cranial acetabular BMD was seen after the placement of a press-fit cup [7,9,23,26,27], we only found a significant decrease for one of the two cranial ROIs in the THA group. As confirmed in other studies we found the most rapid changes in BMD in the first 6 months after surgery, but (smaller) BMD changes still occurred until 24 months [27][28][29].…”

The influence of acetabular cup material on pelvis cortex surface strains, measured using digital image correlation

“…This study's results are corroborated by clinical DEXA scan measurements (Wright et al, 2001;Stolk et al, 2004;Laursen et al, 2007;Pitto et al, 2008;Mueller et al, 2009;Meneghini et al, 2010), cadaveric implant-bone load distribution measurements (Widmer et al, 2002) and previously published numerical predictions (Thompson et al, 2002;Manley et al, 2006) which indicated that stiffer metal cups load the superior acetabular rim cortex preferentially, whereas polymeric cups transferred load more evenly. Implant material is not the only factor; clinical evidence has shown that cemented cups produce a more natural load transfer pattern than press-fitted implants (Mueller et al, 2009).…”

“…Clinical radiographic measurements have indicated that contemporary cementless acetabular cups preferentially load the acetabular rim, and shield the central ilium from load (Wright et al, 2001;Pitto et al, 2008). This has been identified by a significant loss of bone mineral density superior to the pole of cementless cups, which stabilises after the first postoperative year (Sabo et al, 1998;Wright et al, 2001;Stolk et al, 2004;Laursen et al, 2007;Pitto et al, 2008;Meneghini et al, 2010) indicating an adaptive process. The results confirm the hypothesis, with a CFR-PEEK cup generating a smaller average increase in cortex strains, and less acetabular rim cortex strain concentration than a CoCr cup.…”

“…Therefore, conclusions can only be drawn considering the stimulus for cortical bone adaptation, but predictions of resulting cancellous adaptations may also be made. Clinical observations have informed the suggestion that increased peri-acetabular cortical load transfer may lead in turn to reduced polar cancellous load transfer (Wright et al, 2001;Pitto et al, 2008), so it can be predicted that an implant which reproduces the intact bone's cortical strain distribution more closely will also produce more physiological cancellous bone strains. A further limitation is that the study employed an in-vitro model.…”

“…Notwithstanding possible incorrect cup positioning and wear-induced osteolysis, retrieval evidence suggests that loosening may be linked to increased bearing friction late in the implant's life (Tuke et al, 2008). Maintenance of supporting bone quality would delay loosening, but reduced bone mineral density (BMD) has been measured in the periprosthetic bone near the pole of press-fit cups (Sabo et al, 1998;Wright et al, 2001;Stolk et al, 2004;Laursen et al, 2007;Pitto et al, 2008;Mueller et al, 2009;Meneghini et al, 2010), in a pattern consistent with adaptive remodelling. Periprosthetic bone deterioration may promote earlier failure, so preservation of supporting bone quality is a goal for implant designers.…”