JOA - 2026-06-19 - Journal Article
The AAHKS Clinical Research Award: Maximizing Bearing Size Markedly Reduces Dislocations in Primary Total Hip Arthroplasty.
Wang E, McCormick K, Di Gangi C, Di Pauli von Treuheim T, Meftah M, Schwarzkopf R, Hepinstall MS
Topics
Key Takeaway
Maximizing bearing diameter in primary fixed-bearing THA yielded zero dislocations in 835 patients versus a 1.0% rate in those receiving non-maximized bearings (OR 0.14 on LASSO regression, P = 0.003).
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Summary
This study asked whether fully maximizing bearing diameter (e.g., 36 mm in a 48/50-mm cup) reduces dislocation risk in primary fixed-bearing THA. Retrospective review of 8,607 patients at a single academic center from 2016–2022 used LASSO logistic regression to control for approach, liner geometry, and intraoperative technology. Zero dislocations occurred in the 835 maximized-bearing patients versus 79 dislocations (1.0%) in the remainder, with a protective OR of 0.14—substantially larger than robotic assistance (OR 0.35), lateral approach (OR 0.48), or anterior approach (OR 0.62).
Key Limitation
Only 9.8% of patients received maximized bearings, raising the possibility of unmeasured selection bias—surgeons may have preferentially maximized bearings in patients with anatomically favorable acetabula or lower baseline dislocation risk.
Original Abstract
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.