title: Electromyographic analysis of reverse total shoulder arthroplasties.
abstract: BACKGROUND
  Understanding how reverse total shoulder arthroplasty (RTSA) affects muscle activation may help refine it. This study evaluated deltoid and upper trapezius activity during shoulder abduction, flexion, and external rotation in RTSA recipients.
  
  
  METHODS
  Fifty individuals were recruited for this study: 33 were ≥6 months postunilateral RSTA, and 17 comprised our control group. Control individuals easily performed all functional tasks and had no history of shoulder pathology or pain. RTSA participants were divided into 3 groups according to implant design. Participants performed weighted and unweighted abduction in the coronal plane, forward flexion in the sagittal plane, and unweighted external rotation. Electromyography activation of the anterior, lateral, and posterior aspects of the deltoid and the upper trapezius muscles was recorded bilaterally. Motion capture using passive reflective markers quantified 3-dimensional motions of both shoulders.
  
  
  RESULTS
  During abduction and flexion, deltoid and upper trapezius activity was significantly increased in RTSA shoulders. Posterior deltoid activation was highest in shoulders with the medial glenosphere/lateral humerus implant. Medial glenosphere/medial humerus shoulders were most similar to the control group's anterior, lateral, and posterior deltoid muscle activation during weighted flexion.
  
  
  CONCLUSIONS
  RTSA increases muscle activation compared with normal shoulders. RTSA often restores stability and motion but not normal deltoid or upper trapezius activation. Increased muscle activation in shoulders with RTSA suggests less efficiency. RTSAs with lateral or medial glenosphere centers of rotation had mostly similar muscle activation. Average posterior deltoid activation did not exceed 20% of maximal voluntary isometric contraction for any group during unweighted external rotation, and differences between groups were <5% maximal voluntary isometric contraction.
authors: Department of Orthopaedics & Rehabilitation, University of Florida, Gainesville, FL, USA.
authors: David
authors: D
authors: Walker
authors: Department of Orthopaedics & Rehabilitation, University of Florida, Gainesville, FL, USA. Electronic address: wrightw@ortho.ufl.edu.
authors: Thomas W
authors: TW
authors: Wright
authors: Department of Orthopaedics & Rehabilitation, University of Florida, Gainesville, FL, USA.
authors: Scott A
authors: SA
authors: Banks
authors: Department of Orthopaedics & Rehabilitation, University of Florida, Gainesville, FL, USA.
authors: Aimee M
authors: AM
authors: Struk
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D001132:Arm; D019643:Arthroplasty, Replacement; D004576:Electromyography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009119:Muscle Contraction / Q000502:physiology; D018482:Muscle, Skeletal / Q000503:physiopathology*; D016059:Range of Motion, Articular; D012399:Rotation; D012782:Shoulder / Q000503:physiopathology* / Q000601:surgery
keywords: Basic Science; Electromyography; Reverse total shoulder arthroplasty; implant design; muscle function; physical therapy; rehabilitation; surgical technique