The AAHKS Clinical Research Award: Maximizing Bearing Size Markedly Reduces Dislocations in Primary Total Hip Arthroplasty.

BACKGROUND: Modern polyethylene allows larger bearings in fixed-bearing total hip arthroplasty (THA), but any stability benefits of fully maximizing bearing diameter (e.g., 36-millimeter (mm) in 48/50-mm cups) are not well-established. We hypothesized that maximizing bearing diameter reduces odds of dislocation in primary fixed-bearing THA.

METHODS: We retrospectively reviewed all patients who underwent fixed-bearing THA at a large, urban, academic institution between 2016 and 2022. We noted cases receiving the largest bearing available from any manufacturer for the acetabular diameter: 28 mm in 40/42 mm, 32 mm in 44/46-, 36- in 48/50-, or 40- in 52/54/56 mm. Larger cups were excluded because proportionately larger bearings were unavailable. Multivariate analyses using least-absolute-shrinkage-and-selection-operator (LASSO) logistic regression were performed to explore the association between maximized bearing diameter and dislocation risk while controlling for confounders.

RESULTS: Bearing diameter was maximized in 835 (9.8%) of 8,607 patients, whereas 7,309 (84.9%) received the second-largest bearing available. There were 79 dislocations (0.9% overall); none occurred with maximized bearing diameters (P = 0.003). On univariate analyses, dislocation risk also varied with intraoperative technology use, surgical approach, and liner geometry (P = 0.017, P = 0.008, P = 0.007, respectively). In LASSO regression including these variables, maximized bearing diameters heavily protected against dislocation (odds ratio (OR) = 0.14). Robotic surgery (OR = 0.35), computer-navigation (OR = 0.90), lateral (OR = 0.48), and anterior (OR = 0.62) approaches were also protective. Lipped (OR = 1.2) and offset (OR = 1.4) liners, commonly used with posterior approaches and non-maximized bearing diameters, were associated with slightly higher odds of dislocation. Subanalysis of 4,185 patients who underwent posterior approach THA using non-maximized bearings revealed that liner geometry did not impact dislocation odds within this subgroup.

CONCLUSION: Fully maximizing bearing diameter markedly reduced dislocation odds in primary fixed-bearing THA. The magnitude of this effect was substantially larger compared to other variables under surgeon control.