Importance of the subscapularis muscle after total shoulder arthroplasty

Abstract

Background: The rotator cuff muscles are the main stabilizer of the glenohumeral joint. After total shoulder arthroplasty using anterior approaches, a dysfunction of the subscapularis muscle has been reported. In the present paper we tested the hypothesis that a deficient subscapularis following total shoulder arthroplasty can induce joint instability. Methods: To test this hypothesis we have developed an EMG-driven musculoskeletal model of the glenohumeral joint. The model was based on an algorithm that minimizes the difference between measured and predicted muscular activities, while satisfying the mechanical equilibrium of the glenohumeral joint. A movement of abduction in the scapular plane was simulated. We compared a normal and deficient subscapularis. Muscle forces, joint force, contact pattern and humeral head translation were evaluated. Findings: To satisfy the mechanical equilibrium, a deficient subscapularis induced a decrease of the force of the infraspinatus muscle. This force decrease was balanced by an increase of the supraspinatus and middle deltoid. As a consequence, the deficient subscapularis induced an upward migration of the humeral head, an eccentric contact pattern and higher stress within the cement. Interpretation: These results confirm the importance of the suscapularis for the long-term stability of total shoulder arthroplasty.

A semi-automated quantitative CT method for measuring rotator cuff muscle degeneration in shoulders with primary osteoarthritis

“…glenohumeral joint instability), or if subluxation is causing muscle degeneration. Muscle degeneration is associated with maximum muscle force, and muscle force is associated with glenohumeral joint stability and subluxation [25]. Conversely, scapulohumeral subluxation can be associated with loss of function, and thus muscle degeneration.…”

Ultrasound vs. MRI in the assessment of rotator cuff structure prior to shoulder arthroplasty

“…The integrity of the subscapularis tendon is therefore crucial for the long term stability of a total shoulder arthroplasty. 20 …”

The return of subscapularis strength after shoulder arthroplasty

“…24 Despite this, poor healing or rupture of a repaired subscapularis is not uncommon 14,15,22,23,28 and can be associated with weakness, instability, and pain. 1,22,29 In addition to a tendon's intrinsic ability to heal, strength recovery of a muscle-tendon unit after its surgical release may be dependent on 3 separate factors: the method by which it is detached, the method by which it is repaired, and the effect of the underlying articular degenerative or inflammatory disease process on the tendon itself. In outcomes studies, the contralateral shoulder is frequently used as a marker of ''normal'' strength and range of motion, particularly in the setting of rotator cuff tears and trauma.…”