Restoration of anterior-posterior rotator cuff force balance improves shoulder function in a rat model of chronic massive tears

• Published in: Journal of orthopaedic research Vol. 29; no. 7; pp. 1028 - 1033
• Main Authors: Hsu, Jason E., Reuther, Katherine E., Sarver, Joseph J., Lee, Chang Soo, Thomas, Stephen J., Glaser, David L., Soslowsky, Louis J.
• Format: Journal Article
• Language: English
• Published: Hoboken Wiley Subscription Services, Inc., A Wiley Company 01-07-2011
• Subjects: animal model; Animals; Biomechanical Phenomena - physiology; Chronic Disease; Disease Models, Animal; force couple; Forelimb - physiology; Gait - physiology; glenohumeral kinematics; Muscle, Skeletal - physiology; Orthopedic Procedures - methods; partial repair; Range of Motion, Articular - physiology; Rats; Rats, Sprague-Dawley; Recovery of Function - physiology; rotator cuff; Rotator Cuff - physiology; Rotator Cuff - surgery; Rotator Cuff Injuries; Shoulder Joint - injuries; Shoulder Joint - physiology; Shoulder Joint - surgery
• ISSN: 0736-0266; 1554-527X
• DOI: 10.1002/jor.21361

The rotator cuff musculature imparts dynamic stability to the glenohumeral joint. In particular, the balance between the subscapularis anteriorly and the infraspinatus posteriorly, often referred to as the rotator cuff “force couple,” is critical for concavity compression and concentric rotation of the humeral head. Restoration of this anterior–posterior force balance after chronic, massive rotator cuff tears may allow for deltoid compensation, but no in vivo studies have quantitatively demonstrated an improvement in shoulder function. Our goal was to determine if restoring this balance of forces improves shoulder function after two‐tendon rotator cuff tears in a rat model. Forty‐eight rats underwent detachment of the supraspinatus and infraspinatus. After four weeks, rats were randomly assigned to three groups: no repair, infraspinatus repair, and two‐tendon repair. Quantitative ambulatory measures including medial/lateral forces, braking, propulsion, and step width were significantly different between the infraspinatus and no repair group and similar between the infraspinatus and two‐tendon repair groups at almost all time points. These results suggest that repairing the infraspinatus back to its insertion site without repair of the supraspinatus can improve shoulder function to a level similar to repairing both the infraspinatus and supraspinatus tendons. Clinically, a partial repair of the posterior cuff after a two‐tendon tear may be sufficient to restore adequate function. An in vivo model system for two‐tendon repair of massive rotator cuff tears is presented. © 2011 Orthopaedic Research Society Published by Wiley Periodicals, Inc. J Orthop Res 29: 1028–1033, 2011