Minimally Invasive Subscapularis Release for Internal Rotation Contracture of the Shoulder in Residual Brachial Plexus Birth Injury.

Abstract

Background: Shoulder internal rotation contracture is one of the most common problems observed in patients with residual brachial plexus birth injury^1,2. Minimally invasive subscapularis release is a simple extra-articular procedure that involves the release of the subscapularis origin from the undersurface of the scapula. This procedure addresses the contracture and has been shown to result in remodeling of the glenohumeral joint when concomitant conjoined tendon transfer is performed³.

Description: The procedure is performed with the patient in the lateral decubitus position. The procedure is initiated by elevating the medial border of the scapula by performing internal rotation and forward flexion of the arm. A 1-cm incision is made at the junction of the upper one-third and lower two-thirds of the medial border of the scapula, and space for insertion of a periosteal elevator is made with a hemostat. Sequentially, 5-mm and 10-mm periosteal elevators are inserted and are slid in a clockwise direction to release the muscle fibers from their origin on the undersurface of the scapula. After circumferential release, the internal rotators and the anterior shoulder joint capsule are stretched with gentle and progressive external rotation of the shoulder joint. A postoperative shoulder spica is applied with the shoulder in the corrected position.

Alternatives: Operative alternatives to this technique include anterior open reduction of the glenohumeral joint with release of the pectoralis and subscapularis at their humeral insertions^4,5. Arthroscopic subscapularis and anterior capsular release has also been described. Other extra-articular techniques, such as an open subscapularis slide from the lateral scapular border, have been described^6,7.

Rationale: Losing strength of internal rotation at the shoulder is the main concern when releasing the subscapularis from its insertion. Internal rotation strength is maintained following this technique because the muscle-tendon unit ratio is unchanged. Benefits of performing this technique from the medial border include easier access to the tight superomedial septae of the subscapularis and reduced likelihood of iatrogenic injury to circumflex scapular neurovascular pedicle.

Expected outcomes: Significant improvement in shoulder abduction and external rotation range (both passive and active) can be expected postoperatively. In a published series of 45 patients, the mean improvements in passive and active external rotation were 80° and 43°, respectively. Mean shoulder abduction improved from 101° preoperatively to 142° postoperatively. The aggregate 5-point Mallet Score improved from 12.8 points preoperatively to 18.5 points postoperatively. Glenohumeral remodeling can be expected in young children with Waters type-IV glenohumeral joint changes. Older pediatric patients may still have persistent internal rotation posture of the arm despite glenohumeral remodeling as a result of changes in the humeral torsion profile.

Important tips: Avoid going beyond the subscapularis ridge to prevent penetration into important neurovascular structures at the 1-o'clock and 3-o'clock positions for the right side.In patients with evidence of C7 involvement, such as weak wrist or elbow extension, postoperative immobilization should be in 40° of external rotation. These patients are at risk for developing postoperative external rotation contracture.

Acronyms and abbreviations: MISR = minimally invasive subscapularis releaseBPBI = brachial plexus birth injuryCT = computed tomographyMRI = magnetic resonance imaging.