Magnuson-Stack Procedure 

Updated: Dec 02, 2019
Author: Elizabeth Dulaney-Cripe, MD; Chief Editor: Erik D Schraga, MD 

Overview

Background

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]

Indications

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

Contraindications

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.

Technical Considerations

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 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.

Outcomes

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 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 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 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]

 

Periprocedural Care

Patient Preparation

Anesthesia

General anesthesia is used for this procedure.

Positioning

The patient is positioned supine in a beach chair position. The room should be arranged as to allow the arm to be fully abducted and externally rotated throughout the procedure.

 

Technique

Approach Considerations

The following description of the Magnuson-Stack procedure is directly based on the original paper by Magnuson and Stack.[1]  In general, the subscapularis is approached through a deltopectoral interval. The insertion of the subscapularis is identified and detached with a bone block. This is then attached to a groove lateral to the bicipital groove at the greater tuberosity of the humerus.[6]

Magnuson-Stack Procedure

Make an incision at the junction of the anterior and medial third of the deltoid, extending from the acromion down. Expose the anterior surface of the capsule (see the image below).

Anterior shoulder. Anterior shoulder.

Externally rotate the arm and identify the subscapularis muscle. Pull the subscapularis tendon tight, and incise the subscapularis muscle from the musculotendinous junction to its attachment along the anterior lip of the bicipital groove. Insert a chisel along the distal side of the attachment medial to the lip of the bicipital groove (see the image below).

Use of a chisel to detach the subscapularis. Use of a chisel to detach the subscapularis.

Lift the tendinous attachment with a wedge of bone, and reflect it medially to expose the head of the humerus and the anterior edge of the humerus (see the image below).

Elevation of the subscapularis with a bone block. Elevation of the subscapularis with a bone block.

Inspect the head of the glenoid and the head of the humerus (see the image below).

Inspection of the anterior shoulder and glenoid. Inspection of the anterior shoulder and glenoid.

Internally rotate the arm and stretch the subscapularis tendon across the bicipital groove to the greater tuberosity. Manipulate the arm. The ideal placement allows 50% external rotation.

Drive a sharp, thin-bladed chisel parallel to the long axis of the bone. Move the chisel back and forth laterally to spread the cancellous bone and leave a wedge-shaped gutter, into which the bone attached to the subscapularis tendon is forced (see the image below).

Creation of a wedge on the lateral side of the bic Creation of a wedge on the lateral side of the bicipital groove.

Suture the tendon with doubled 00 chromic catgut suture; repeat the sutures on both sides of the wedge. Tack down the lower border of the subscapularis muscle with interrupted sutures far enough under the head of the humerus to allow the muscle and capsular tendon to have a firm grip around the head (see the image below).

Sutured subscapularis with bone block to the creat Sutured subscapularis with bone block to the created wedge lateral to the bicipital groove.

Postoperative Care

Immobilization is necessary immediately following the surgery and is continued for 3-6 weeks.[4, 7] Rehabilitation follows immobilization, but external rotation is limited for 4-6 weeks following surgery.[4]

Complications

Complications that are possible with this procedure include loss of functional abilities due to a significant loss of external rotation, recurrence of instability, and neurovascular injury. A recurrence of instability is seen in patients who regain normal external rotation.[5]

Ahmad et al mentioned that an anterior repair, such as the Magnuson-Stack procedure, would alter the loading of the glenohumeral joint.[9] This alteration in loading increases the loading along the posterior aspect of the joint, with the potential to create an abnormal posteroinferior humeral head subluxation. This would result in increased wear along the posterior aspect of the glenoid, likely leading to secondary osteoarthritis.