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


Frank A. Cordasco, MD, MS

Attending Orthopaedic Surgeon, Hospital for Special Surgery
Professor of Orthopaedic Surgery, Weill Cornell Medical College
Surgical Director, Ambulatory Surgery Center, Hospital for Special Surgery
Co-Medical Director, Leon Root Motion Analysis Laboratory, Hospital for Special Surgery

Bryan T. Kelly, MD

Associate Attending Orthopedic Surgeon, Hospital for Special Surgery
Sports Medicine and Shoulder Service, Hospital for Special Surgery
Assistant Professor of Orthopedic Surgery, Weill Cornell Medical College

Riley J. Williams III, MD

Associate Attending Orthopedic Surgeon, Hospital for Special Surgery
Director of the Institute for Cartilage Repair, Hospital for Special Surgery
Associate Professor of Orthopedic Surgery, Weill Cornell Medical College


Neal C. Chen, MD
Orthopaedic Sports Medicine Program, University of Michigan Health System

 

Sherry I. Backus, PT, DPT, MA
Leon Root, M.D. Motion Analysis Laboratory, Rehabilitation Department, Hospital for Special Surgery

 

James C. Otis, PhD
SHRI-CORE Orthopedic Research Labs

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.

This article appears in HSS Journal: Volume 6, Number 1.
View the full article at springerlink.com.

About the HSS Journal

HSS Journal, an academic peer-reviewed journal, is published twice a year, February and September, and features articles by internal faculty and HSS alumni that present current research and clinical work in the field of musculoskeletal medicine performed at HSS, including research articles, surgical procedures, and case reports.

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