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The AAHKS Clinical Research Award: Maximizing Bearing Size Markedly Reduces Dislocations in Primary Total Hip
Eric Wang1, Kyle McCormick1, Catherine Di Gangi1
1Department of Orthopedic Surgery, NYU Langone Health, New-York, New York.
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 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 least-absolute-shrinkage-and-selection-operator 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 nonmaximized bearing diameters, were associated with slightly higher odds of dislocation. Subanalysis of 4,185 patients who underwent posterior approach THA using nonmaximized bearings revealed that liner geometry did not impact dislocation odds within this subgroup.
Conclusions:
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.
