title: Effect of lateralized design on muscle and joint reaction forces for reverse shoulder arthroplasty.
abstract: BACKGROUND
  Manufacturers of reverse shoulder arthroplasty (RSA) implants have recently designed innovative implants to optimize performance in rotator cuff-deficient shoulders. These advancements are not without tradeoffs and can have negative biomechanical effects. The objective of this study was to develop an integrated finite element analysis-kinematic model to compare the muscle forces and joint reaction forces (JRFs) of 3 different RSA designs.
  
  
  METHODS
  A kinematic model of a normal shoulder joint was adapted from the Delft model and integrated with the well-validated OpenSim shoulder model. Static optimizations then allowed for calculation of the individual muscle forces, moment arms, and JRFs relative to net joint moments. Three-dimensional computer models of 3 RSA designs-humeral lateralized design (HLD), glenoid lateralized design, and Grammont design-were integrated, and parametric studies were performed.
  
  
  RESULTS
  Overall, there were decreases in deltoid and rotator cuff muscle forces for all 3 RSA designs. These decreases were greatest in the middle deltoid of the HLD model for abduction and flexion and in the rotator cuff muscles under both internal rotation and external rotation. The JRFs in abduction and flexion decreased similarly for all RSA designs compared with the normal shoulder model, with the greatest decrease seen in the HLD model.
  
  
  CONCLUSIONS
  These findings demonstrate that the design characteristics implicit in these modified RSA prostheses result in mechanical differences most prominently seen in the deltoid muscle and overall JRFs. Further research using this novel integrated model can help guide continued optimization of RSA design and clinical outcomes.
authors.affiliation: Department of Aerospace and Mechanical Engineering, Western Michigan University, Kalamazoo, MI, USA.
authors.forename: William
authors.initials: W
authors.lastname: Liou
authors.affiliation: Department of Aerospace and Mechanical Engineering, Western Michigan University, Kalamazoo, MI, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Department of Orthopaedic Surgery, Wayne State University School of Medicine, Taylor, MI, USA.
authors.forename: Graysen R
authors.initials: GR
authors.lastname: Petersen-Fitts
authors.affiliation: Department of Orthopaedic Surgery, Wayne State University School of Medicine, Taylor, MI, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Lombardo
authors.affiliation: Department of Orthopaedic Surgery, Wayne State University School of Medicine, Taylor, MI, USA.
authors.forename: Sasha
authors.initials: S
authors.lastname: Stine
authors.affiliation: Department of Orthopaedic Surgery, Wayne State University School of Medicine, Taylor, MI, USA. Electronic address: sabes001@gmail.com.
authors.forename: Vani J
authors.initials: VJ
authors.lastname: Sabesan
mesh_terms: D000072228:Arthroplasty, Replacement, Shoulder / Q000379:methods; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D057645:Deltoid Muscle / Q000503:physiopathology*; D020342:Finite Element Analysis; D006801:Humans; D008962:Models, Theoretical; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D012399:Rotation; D017006:Rotator Cuff / Q000503:physiopathology*; D012785:Shoulder Joint / Q000601:surgery; D000072227:Shoulder Prosthesis
keywords: RSA implant design; Reverse shoulder arthroplasty; finite element analysis; humeral lateralized design; kinematic model; shoulder biomechanics