Anatomy and relationships of the suprascapular nerve: anatomical constraints to mobilization of the supraspinatus and infraspinatus muscles in the management of massive rotator-cuff tears.
Thirty-one shoulders in eighteen cadavera were dissected to allow study of the neurovascular anatomy of the rotator cuff and to help determine the limits of mobilization of the cuff for the repair of chronic massive retracted tears. The dissection demonstrated the diameter, length, and relationships of the suprascapular nerve and its branches and made clear the dangers of extensive mobilization and advancement of the supraspinatus and infraspinatus muscles. The suprascapular nerve ran an oblique course across the supraspinatus fossa, was relatively fixed on the floor of the fossa, and was tethered underneath the transverse scapular ligament. In twenty-six (84 per cent) of the thirty-one shoulders, there were no more than two motor branches to the supraspinatus muscle, and the first was always the larger of the two. In twenty-six (84 per cent) of the thirty-one shoulders, the first motor branch originated underneath the transverse scapular ligament or just distal to it. In one shoulder (3 per cent), the first motor branch passed over the ligament. The average distance from the origin of the long tendon of the biceps to the motor branches of the supraspinatus was three centimeters. In fifteen (48 per cent) of the thirty-one shoulders, the infraspinatus muscle had three or four motor branches of the same size. The average distance from the posterior rim of the glenoid to the motor branches of the infraspinatus muscle was two centimeters. The motor branches to the supraspinatus muscle were fewer, usually smaller, and significantly shorter than those to the infraspinatus muscle. The standard anterosuperior approach allowed only one centimeter of lateral advancement of either tendon and limited the ability of the surgeon to dissect safely beyond the neurovascular pedicle. The advancement technique of Debeyre et al., or a modification of that technique, permitted lateral advancement of each muscle of as much as three centimeters and was limited by tension in the motor branches of the suprascapular nerve. In some situations, the safe limit of advancement may be even less. We concluded that lateral advancement of the rotator cuff is limited anatomically and may place the neurovascular structures at risk.