Specialty Update: What’s New in Shoulder and Elbow Surgery (2003)
Shoulder Rotator Cuff Basic Science Several studies have employed sophisticated animal models to investigate rotator cuff repair and healing. Coleman reported on a chronic rotator cuff injury and repair model involving sheep. Infraspinatus contractile forces and histological findings were evaluated at various times following either immediate or delayed tendon repair. Longer delays to repair led to greater decreases in force and more modest recovery following repair. Muscle biopsies confirmed progressive fatty infiltration that was partially reversed after tendon repair in the group with a six-week delay before repair but not in the group with an eighteen-week delay before repair. This model has important implications regarding the recovery of strength following the repair of chronic rotator cuff tears. Rodeo presented a study on growth factor-enhanced rotator cuff tendon-bone healing in a sheep model.
Histological analysis demonstrated greater new-bone and fibrovascular tissue formation in the treated animals. A substantial increase in attachment strength was noted in the treated animals at twelve weeks. The study demonstrates the ability of a growth factor to influence changes at the tendon-bone interface. MacGilivray evaluated the augmentation of rotator cuff repairs with a bioabsorbable scaffold in a goat model. Biomechanical testing showed no significant improvement in load to failure when a tendon defect was covered with a polylactic acid patch. The inability of the patch to enhance repair strength was thought to result from shielding of the patch from direct load by the repair. Halder used a cadaveric model to identify the characteristics of rotator cuff tears that were responsible for loss of strength. Detachment of one-third and two-thirds of the supraspinatus tendon affected force transmission by the rotator cuff only slightly, while detachment of the whole tendon resulted in greater reductions in force transmission.
Simulated muscle retraction also led to reductions in force transmission. Side-to-side repair of defects involving one third and two thirds of the tendon restored near-normal force transmission. These results echoed the clinical observation that patients with small rotator cuff tears may present without a loss of strength. Furthermore, side-to-side repair of otherwise irreparable defects may help to restore the integrity of the rotator cable. Chronic rotator cuff tears are often accompanied by muscle atrophy, fatty infiltration, and retraction, which may decrease overall muscle volume. Apreleva determined the reliability and validity of magnetic resonance imaging in the assessment of rotator cuff muscle volume in a study of cadaveric shoulders. Magnetic resonance imaging scans were made and the supraspinatus, infraspinatus-teres minor, and subscapularis muscle volumes were then computed with use of three-dimensional image-analysis software. Muscle volumes were confirmed with use of water displacement after dissection. The muscle volumes measured with use of the two methods were found to correlate highly, suggesting that magnetic resonance imaging may hold promise for the preoperative as... (download full pdf article)
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