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

Abstract

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. ß

Assessment of pain‐related behavior and pro‐inflammatory cytokine levels in the rat rotator cuff tear model

“…Although previous studies showed that rotator cuff repair in a rat model was sufficient to improve shoulder function using quantitative ambulatory measures, 7,14 this experiment (sharp transection followed by immediate repair) may have not accurately replicated the pathophysiology of rotator cuff tear and rotator cuff repair in clinical settings. Furthermore, in this study we only evaluated the validity of our model over a short time period (21 and 56 days after surgery).…”

Subscapularis Release in Shoulder Replacement Determines Structural Muscular Changes

“…The ratio of the cross-sectional area of the anterior versus posterior rotator cuff muscles also was calculated. This ratio corresponds to the AP force couple of the glenohumeral joint [17] if the shoulder is examined in the same position in the CT gantry before and after surgery [6]. To avoid a learning curve effect, the first 10 images were measured twice.…”

The Detrimental Effects of Systemic Ibuprofen Delivery on Tendon Healing Are Time-Dependent

“…Restoration of function after tendon damage stemming from injury, overuse, or degenerative disease is largely dependent on the reestablishment of the muscle-tendon-bone connection with minimal scarring between the tendon and its surrounding tissues [16,18]. Current clinical treatment protocols after tendon repair often include NSAIDs, chiefly for their pain-relieving effects, with a secondary indication in their limitation of inflammation [20].…”