Muscle atrophy and fatty infiltration of the rotator cuff muscles, particularly of the infraspinatus, play a significant role in determining functional outcome after cuff repair. Tear size appears to have the most influential effect on repair integrity. A successful repair did not lead to improvement or reversal of muscle degeneration and a failed repair resulted in significantly more progression. In general, healed repairs demonstrated minimal progression. These findings suggest that repairs should be performed, if possible, before more significant deterioration in the cuff musculature in order to optimize outcomes, and that understanding the degree of muscle atrophy and fatty infiltration before surgery can help guide patient expectations.

The increase in national rates of rotator cuff repair over the last decade has been dramatic, particularly for arthroscopic assisted repair.

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Forty-four patients, ranging in age from 17 to 57 years (average, 32), were evaluated an average of 4 years (range, 2 to 9) after surgical reconstruction for Allman-Tossy Grade III acromioclavicular dislocations. Twenty-seven patients underwent repair for acute injuries (< 3 weeks after injury) and 17 patients underwent reconstructions for chronic injuries (> 3 weeks). Coracoclavicular fixation with heavy nonabsorbable sutures was used to correct superior displacement in all cases. In addition, transfer of the coracoacromial ligament to the distal clavicle was performed in 15 of the 27 early repairs and 17 of the 17 late reconstructions. Overall, 26 of 27 (96%) early repairs and 13 of 17 (77%) late reconstructions achieved satisfactory results. There was a trend for better results and return to sports or heavy labor with early repairs; however, this was not statistically significant (P = 0.065). When the results of early repairs were compared with those of late reconstructions performed more than 3 months after injury, the results of the shoulders undergoing early repair were significantly better (P < 0.01). Overall, 39 of 44 (89%) patients achieved a satisfactory result. Surgical reconstruction for acromioclavicular dislocation provides reliable results including use of the arm for sports or repetitive work.

Summary:The tensile properties of the inferior glenohumeral ligament have been determined in 16 freshly frozen cadaver shoulders. The inferior glenohumeral ligament was divided into three anatomical regions: a superior band, an anterior axillary pouch, and a posterior axillary pouch. This yielded 48 hone-ligament-bone specimens; which were tested to failure in uniaxial tension. The superior hand was consistently the thickest region, averaging 2.79 mm. The thickness of the inferior glenohumeral ligament decreased from antero-superiorly to postero-inferiorly. The resting length of all three anatomical regions was not statistically different. Total specimen strain to hilure for all bone-ligament-bone specimens averaged 27%. Variations occurred between the three regions, with the anterior pouch specimens failing at a higher strain (34%) thar, those from the superior band (24%) or the posterior pouch (23%). Strain to failure for the ligament midsubstance (11%) was found to be significantly less than that for the entire specimen (27%). Thus, larger strain must occur near the insertion sites of the inferior glenohumeral ligament. Stress at failure was found to be nearly identical for the three regions of the ligament, averaging 5.5 MPa. These values are lower than those reported for other soft tissues, such as the anterior cruciate ligament and patellar tendon. The anterior pouch was found to be less stiff than the other two regions, perhaps suggesting that it is composed of more highly crimped collagen fibers. Three failure sites were seen for the inferior glenohumeral ligament: the glenoid insertion (40%), the ligament substance (35%). and the humeral insertion (25%). In addition, significant capsular stretching occurred before failure, regardless of the failure mode. Key Words: Ligament-Biomechanics-Inferior glenohumeral ligament-Material testing-Instability-Shoulder.Recurrent anterior glenohumeral instability (dislocation or subluxation) is a common clinical problem that can often lead to significant disability. Maintaining glenohumeral stability is a complex phenomenon that depends on the interaction of dynamic muscular forces and static capsulo-ligamentous restraints. Many investigators have at-

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Nine fresh-frozen, human cadaveric shoulders were elevated in the scapular plane in two different humeral rotations by applying forces along action lines of rotator cuff and deltoid muscles. Stereophotogrammetry determined possible regions of subacromial contact using a proximity criterion; radiographs measured acromiohumeral interval and position of greater tuberosity. Contact starts at the anterolateral edge of the acromion at 0 degrees of elevation; it shifts medially with arm elevation. On the humeral surface, contact shifts from proximal to distal on the supraspinatus tendon with arm elevation. When external rotation is decreased, distal and posterior shift in contact is noted. Acromial undersurface and rotator cuff tendons are in closest proximity between 60 degrees and 120 degrees of elevation; contact was consistently more pronounced for Type III acromions. Mean acromiohumeral interval was 11.1 mm at 0 degrees of elevation and decreased to 5.7 mm at 90 degrees, when greater tuberosity was closest to the acromion. Radiographs show bone-to-bone relationship; stereophotogrammetry assesses contact on soft tissues of the subacromial space. Contact centers on the supraspinatus insertion, suggesting altered excursion of the greater tuberosity may initially damage this rotator cuff region. Conditions limiting external rotation or elevation may also increase rotator cuff compression. Marked increase in contact with Type III acromions supports the role of anterior acromioplasty when clinically indicated, usually in older patients with primary impingement.