Magnuson-Stack Procedure

The Magnuson-Stack procedure, first published by Paul B Magnuson and James K Stack in December 1943, ^{[1, 2]} is a historically important nonanatomic operation for shoulder instability. It is predicated on tightening of the subscapularis by altering the insertion site from the lesser tuberosity to a groove created lateral to the bicipital groove. This produces a “sling effect” on the humeral head. ^[3]

The advantages of the Magnuson-Stack procedure over other procedures for anterior instability of the shoulder include the ease of execution of the procedure and a lesser degree of shoulder functional limitation. ^[4] The disadvantages include the predictable loss of external rotation, in addition to not addressing any capsular or labral pathology. ^{[3, 5, 6]}

This procedure was originally indicated for patients with unidirectional anterior instability of the shoulder.

Before a Magnuson-Stack procedure is performed, it is improtant to exclude voluntary, posterior, and multidirectional instability as diagnoses. Any restriction in external rotation preoperatively would be exacerbated following this type of repair.

Because of the loss of external rotation, the applicability of the Magnuson-Stack procedure is limited. Athletes and laborers requiring a normal range of motion (ROM) in external rotation would be limited with this procedure. This also would limit use for throwers and overhead athletes.

Adequate padding is imperative in prevention of intraoperative complications. It is also important to identify the neurovascular structures in the approach to the subscapularis.

After surgical stabilization of the anterior shoulder, the main outcomes measured would be a recurrence of instability and the significance of the loss of external rotation.

In an evaluation of 19 cases in 1960, Palumbo et al identified recurrence of dislocation in 10.5% of the patients. ^[4]  Karadimas et al reported a 2% recurrence of instability, whereas Miller et al reported a 17% recurrence of instability. ^[3]

Regarding functional loss, Aamoth et al noted in 1977 that 92% of the athletes studied returned to their preoperative sport. ^[7]  They noted that 48% of the athletes had residual loss of external rotation at their side and 30% had a loss of external rotation with overhead motion. The average loss of external rotation within the athletes studied was 11º.

Palumbo et al also saw a limitation of 15-50º of external rotation in one half of their patients and a limitation of 60-80º in the other half. ^[4]  Karadimas et al noted that 11 of their 135 patients were limited by 10-30º in external rotation. ^[3]  Regan et al, comparing the Magnuson-Stack procedure with the Bristow procedure and the Putti-Platt procedure, found that the Magnuson-Stack procedure limited external rotation the least. ^[8]