INTRODUCTION:

Optimal management of retroversion in anatomic total shoulder arthroplasty (aTSA) remains controversial and limited attention has been directed to the impact of glenoid inclination. Prior biomechanical study suggest that residual glenoid inclination generates shear stresses that may lead to early glenoid loosening. Combined biplanar glenoid deformities may complicate anatomic glenoid reconstruction and affect outcomes. The goal of this matched-cohort analysis was to assess the relationship between biplanar deformities and mid-term radiographic loosening in aTSA.

METHODS:

The study cohort was identified via an institutional repository of 337 preoperative CT scans from 2010-2017. Glenoid retroversion, inclination, and humeral head subluxation were assessed via 3D-planning software. Patients with retroversion ≥ 20˚ and inclination ≥ 10˚ who underwent aTSA with eccentric reaming and non-augmented components were matched by age, sex, retroversion, and Walch classification to patients with retroversion ≥ 20˚ only. Primary outcome was glenoid component Lazarus radiolucency score.

RESULTS:

Twenty-eight study subjects were matched to 28 controls with retroversion only. No difference in age (61.3 vs. 63.6 years, p=0.26), sex (19 [68%] vs. 19 [68%] male, p=1.0), or follow-up (6.1 vs. 6.4 years, p=0.59). Biplanar deformities had greater inclination (14.5˚ versus 5.3˚, p<0.001), retroversion (30.0˚ versus 25.6˚, p=0.01) and humeral subluxation (86.3% versus 82.1%, p=0.03). Biplanar patients had greater postoperative implant superior inclination (5.9 [4.6] vs. 3.0 [3.6] degrees, p=0.01) but similar rate of complete seating 24 [86%] vs. 24 [86%] p=1.0). At final follow-up, biplanar subjects had higher Lazarus radiolucent scores (2.4 [1.7] vs. 1.6 [1.1], p=0.03) and higher proportion of patients with glenoid radiolucency (19 [68%] vs. 11 [39%], p=0.03). No difference in complete component seating (86% versus 86%, p=0.47) or initial radiolucency grade (0.21 versus 0.29, p=0.55) on immediate postop radiographs. Biplanar patients demonstrated a greater amount of posterior subluxation at immediate postop(3.5% [1.3%] versus 1.8% [0.6%]; p=0.03) and final follow-up (7.6% [2.8%] versus 4.0% [1.8%]; p=0.04). At final radiographic follow-up, biplanar subjects had higher Lazarus radiolucent scores (2.4 [1.7] vs. 1.6 [1.1], p=0.03; ICC=0.82). Bivariate regression analysis demonstrated biplanar deformity was the only significant predictor (OR 3.3, p=0.04) of glenoid radiolucency.

CONCLUSION:

Biplanar glenoid deformity resulted in time-zero glenoid implant superior inclination and increased mid-term radiographic loosening and posterior subluxation. Attention to glenoid inclination is important for successful anatomical glenoid reconstruction. Future research is warranted to understand the long-term implications of these findings and impact of utilizing augmented implants or reverse shoulder arthroplasty to manage biplanar deformities.