The role of greater tuberosity healing in reverse shoulder arthroplasty: a finite element analysis

Background: The lack of greater tuberosity (GT) healing in proximal humerus fractures has been negatively correlated with outcomes for hemiarthroplasty; however, there is still debate regarding the effects of GT healing in reverse shoulder arthroplasty (RSA). Our goal was to examine the effects of GT healing using a kinematic finite element analysis (FEA) model. Material and Methods: Computer-aided design models of a medialized glenoid with a lateralized humerus (MGLH) RSA design were uploaded into an FEA shoulder model in 2 different configurations: healed greater tuberosity (HGT) and nonunion greater tuberosity (NGT). Deltoid muscle forces and joint reaction forces (JRFs) on the shoulder were calculated during abduction (ABD), forward flexion (FF), and external rotation (ER). Results: Force magnitude of the anterior, middle, and posterior deltoid muscle as well as JRFs modeled in both GT scenarios were similar for ABD (muscle forces P = .91, P = .75, P = .71, respectively; arid JRF P = .93) and for FF (muscle forces P = .89, P = .83, P = .99, respectively; and JRF P = .90). For ER, the force magnitude between 2 GT settings showed statistically significant differences (HGT: 931 N vs. NGT: 6.13 N) (P < .001). Likewise, during ER, JRFs were different, and the NGT group showed a steep drop in JRF after 10 degrees of ER (HGT: 28.4 N vs. NGT: 18.38 N) (P < .001). Conclusion: GT healing does not seem to impact RSA biomechanics during abduction or forward flexion; however, it does affect biomechanics during external rotation. Overall orthopedic surgeons can expect good results for patients after RSA even with poor GT healing. (C) 2019 Published by Elsevier Inc. on behalf of Journal of Shoulder and Elbow Surgery Board of Trustees.