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

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.

Rotator cuff tear arthropathy.

Rotator cuff tear arthropathy represents a spectrum of shoulder pathology characterized by rotator cuff insufficiency, diminished acromiohumeral distance with impingement syndromes, and arthritic changes of the glenohumeral joint. Additional features may include subdeltoid effusion, humeral head erosion, and acetabularization of the acromion. Although the progression of rotator cuff tears seems to play a role in the development of cuff tear arthropathy, information is lacking regarding the natural progression of rotator cuff tears to cuff tear arthropathy. Controversy remains about the role of basic calcium phosphate crystals in the development of cuff tear arthropathy. Nonsurgical management is the first line of treatment in most patients. Traditionally, surgical management of rotator cuff tear arthropathy has been disappointing because of the development of complications long-term and poor patient satisfaction with functional outcomes. Recent studies, however, report promising experience with reverse ball-and-socket arthroplasty.