The role of pectoralis major and latissimus dorsi muscles in a biomechanical model of massive rotator cuff tear

• Published in: Journal of shoulder and elbow surgery 2014-08, Vol.23 (8), p.1136-1142
• Main Authors: Campbell, Sean T., BS, Ecklund, Kier J., MD, Chu, Eileen H., MD, McGarry, Michelle H., MS, Gupta, Ranjan, MD, Lee, Thay Q., PhD
• Format: Article
• Language: English
• Subjects: acromiohumeral pressure; Acromion - physiopathology; Aged; Aged, 80 and over; Biomechanical Phenomena; Cadaver; Humans; Humeral Head - physiopathology; Joint Diseases - physiopathology; latissimus dorsi; Male; Massive rotator cuff tear; Orthopedics; pectoralis major; Pectoralis Muscles - physiopathology; Pectoralis Muscles - surgery; Rotator Cuff - physiopathology; Rotator Cuff Injuries; rotator cuff tear arthropathy; Shoulder - physiopathology; Shoulder Injuries; Shoulder Joint - injuries; Shoulder Joint - physiopathology; Superficial Back Muscles - physiopathology; Superficial Back Muscles - surgery
• ISSN: 1058-2746; 1532-6500
• DOI: 10.1016/j.jse.2013.11.030

Background Superior migration of the humeral head after massive rotator cuff tear (mRCT) is thought to lead to cuff tear arthropathy. Previous biomechanical studies have demonstrated the ability of the pectoralis major and latissimus dorsi (PM/LD) muscles to resist this migration. This study examined the role of PM/LD muscles on glenohumeral joint forces and acromiohumeral contact pressures in a mRCT model. Methods Six cadaveric shoulders were tested using a custom shoulder-testing system. Muscle insertions of the rotator cuff, deltoid, and PM/LD were preserved and used for muscle loading. Specimens were tested in 3 different humeral rotation positions at 0° abduction and 2 rotation positions at 60° abduction. Testing was performed for intact specimens, after supraspinatus removal, and after supraspinatus/infraspinatus/teres minor removal. PM/LD were loaded or unloaded to determine their effect. Humeral head kinematics, glenohumeral joint forces, and acromiohumeral contact area and pressure were measured. Results For the mRCT condition at 0° abduction, unloading the PM/LD resulted in superior shift of the humeral head. Acromiohumeral contact pressures were undetectable when the PM/LD were loaded but increased significantly after PM/LD unloading. After mRCT, superior joint forces were increased and compressive forces were decreased compared with intact; loading the PM/LD resolved these abnormal forces in some testing conditions. Conclusion In mRCT, the PM and LD muscles are effective in improving glenohumeral kinematics and reducing acromiohumeral pressures. Strengthening or neuromuscular training of this musculature, or both, may delay the progression to cuff tear arthropathy.