HSS Journal

, Volume 6, Issue 1, pp 30–36 | Cite as

Subacromial Injection Improves Deltoid Firing in Subjects with Large Rotator Cuff Tears

  • Frank A. Cordasco
  • Neal C. Chen
  • Sherry I. Backus
  • Bryan T. Kelly
  • Riley J. WilliamsIII
  • James C. Otis
 

Abstract

Previous studies demonstrate that scapulohumeral mechanics improve after subacromial injection. However, it is unclear how injection affects muscle firing. Forty-one subjects with two-tendon rotator cuff tears and 23 volunteer subjects with normal rotator cuffs documented by ultrasonography were examined. Electromyographic activity from 12 muscles was collected during ten functional tasks. Nine symptomatic subjects with rotator cuff tears underwent subacromial injection of anesthetic and underwent repeat electromyographic examination. Subjects with rotator cuff tears demonstrate global electromyographic differences when compared to normal controls. Asymptomatic subjects with rotator cuff tears had significantly increased anterior deltoid firing when compared to symptomatic counterparts during forward shoulder elevation. After subacromial injection, symptomatic subjects demonstrate increased anterior deltoid firing. Previous in vitro and in vivo studies have suggested that pain leads to deltoid inhibition and that subacromial injection leads to improved deltoid firing and, subsequently, improved shoulder function. This study provides direct evidence that subacromial injection improves deltoid firing in symptomatic subjects with rotator cuff tears. These findings reinforce the concept that deltoid inhibition resulting from pain is an important component of the motor disability associated with rotator cuff tears.

Keywords

rotator cuff injuries intra-articular injection local anesthetics electromyography biomechanics shoulder joint muscle tendon injuries pain adult human 

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Copyright information

© Hospital for Special Surgery 2009

Authors and Affiliations

  • Frank A. Cordasco
    • 4
  • Neal C. Chen
    • 1
  • Sherry I. Backus
    • 2
  • Bryan T. Kelly
    • 4
  • Riley J. WilliamsIII
    • 4
  • James C. Otis
    • 3
  1. 1.Orthopaedic Sports Medicine Program, University of Michigan Health SystemAnn ArborUSA
  2. 2.Leon Root, M.D. Motion Analysis LaboratoryRehabilitation Department, Hospital for Special SurgeryNew YorkUSA
  3. 3.SHRI-CORE Orthopedic Research LabsSun City WestUSA
  4. 4.Sports Medicine and Shoulder Service, Department of Orthopaedic SurgeryHospital for Special SurgeryNew YorkUSA

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