Subscapularis-Sparing Anatomic Total Shoulder Arthroplasty



Subscapularis-Sparing Anatomic Total Shoulder Arthroplasty


Robert K. Fullick, MD

Christoph H. G. Fuchs, MD



INTRODUCTION

Surgery of the glenohumeral joint may be accomplished through multiple approaches. The deltopectoral, anterolateral, transacromial, and posterior approaches have all been described in the literature. The deltopectoral approach is the most commonly used approach in anatomic total shoulder arthroplasty (ATSA). This approach traditionally has required violating the subscapularis tendon by means of either tenotomy, tendon peel, or lesser tuberosity osteotomy. Anatomic repair and healing of subscapularis is critical to restore stability and adequate function following ATSA.1 Postoperative subscapularis dysfunction, fatty atrophy, and incomplete or failed healing are commonly reported in the literature and can result in pain, poor function, instability, and early failure requiring revision surgery. A multitude of different techniques for repairing the subscapularis after tenotomy, peel, and lesser tuberosity osteotomy (LTO) have been developed2,3,4,5,6,7,8,9,10,11,12 in order to improve postoperative subscapularis function. However, subscapularis dysfunction whether from partial or complete failure, weakness, or fatty atrophy continues to be an issue. Armstrong13 used ultrasound to evaluate 30 patients following tenotomy for total shoulder arthroplasty (TSA) and found a 13% failure rate of their repair. Jackson found a 47% rate of subscapularis tenotomy repair failure on ultrasound examination in 15 patients and that these patients had significantly worse disabilities of the arm, shoulder, and hand (DASH) scores.14 Miller found an abnormal lift-off and belly-press tests in 67% of patients.15 Gerber found that 37 patients treated with LTO and repair during TSA had 100% healing of the osteotomy but only 89% had a normal belly-press test and 75% had a normal lift-off test.16 Fatty infiltration was also noted to progress by one-stage in 24%, two stages in 15%, and three stages in 6% and was associated with poorer outcomes.16 These findings were supported by Qureshi who found in a retrospective review of 30 patients following LTO that 40% of patients had an abnormal belly-press examination and 17% were unable to tuck their shirt in behind their back.17 In a randomized, controlled trial of LTO versus subscapularis peel in shoulder arthroplasty, Laapner found no significant difference in functional outcomes.8 Miller reported a 5.8% revision rate after total shoulder replacement (TSR) due to subscapularis repair failure in a study of 119 patients.18 Due to these shortcomings, which persist despite numerous modifications of subscapularis management during ATSA, attention has recently been directed toward developing and modifying new approaches, which either minimize or completely avoid traumatizing the subscapularis tendon (VIDEO 20.1).1,19,20,21,22


ANATOMY

Pertinent anatomy to understand and implement the approaches described in this chapter includes a detailed knowledge of the rotator interval, the subscapularis muscle, and the axillary nerve. Neer first named the triangular space between the subscapularis, the supraspinatus, and the coracoid as the “rotator interval.”23 The interval is bordered medially by the base of the coracoid process, superiorly by the anterior border of the supraspinatus, and inferiorly by the upper border of the subscapularis. Contents of the rotator interval include the superior and middle glenohumeral ligaments (SGHL and MGHL), the long head of the biceps tendon (LHBT), glenohumeral joint capsule, and the extra-articular coracohumeral ligament.24 The rotator interval is an average of 414 mm2. in area. The capsule at the superior border of the subscapularis tendon at the glenoid is extremely thin, measuring only about 0.06 mm in thickness.25

The subscapularis muscle arises from the subscapularis fossa of the anterior scapula and is the most powerful rotator cuff muscle.5 It constitutes 53% of all rotator cuff musculature, more than the other three parts of the rotator cuff combined26 and constitutes the anterior portion of the transverse force couple that balances the glenohumeral joint. The upper two-thirds are tendinous and insert on the lesser tuberosity of the humerus. The lower one-third is muscular and inserts on the humeral metaphysis.27 It is innervated by the upper (C5-C6) and lower (C5-7) subscapular nerves, which Checchia et al reported enter the muscle as close as 1 cm medial to the glenoid rim.28 The axillary nerve is located 32.8 mm below the lower border of the subscapularis before it enters the quadrilateral space29 but
can move more proximally into the operative field with shoulder manipulation such as arm abduction, which tensions the nerve.







SUPEROLATERAL SUBSCAPULARIS-SPARING ROTATOR INTERVAL APPROACH

While some surgeons have been using a superior approach for reverse total shoulder arthroplasty (RTSA) for some time,30 Lafosse was the first to describe a rotator interval technique for ATSA.19 Designed to preserve the subscapularis, the approach consists of an anterolateral incision that angles down the lateral arm and utilizes a deltoid split and rotator interval approach to access the proximal humerus and glenoid (FIGURES 20.1 and 20.2). He reported acceptable results in his published case series of 17 patients. However, several technical difficulties led him to abandon the technique. Commonly encountered problems included suboptimal inferior osteophyte resection (8/17 patients), difficulties judging head size (5/17 heads were deemed too small), and anatomic neck cuts that were either too proximal or distal (6/17). The technique also risked deltoid complications including dehiscence and potential anterior deltoid denervation. While these difficulties led Lafosse to develop a new technique, his superolateral rotator interval approach has been further utilized and refined by other surgeons including Adkison.20

Adkison modified the Lafosse subscapularis-sparing (SSS) superior approach via the rotator interval by changing the incision to a saber incision, which, in his opinion, not only allowed easier access to the proximal humerus but also made the approach extensile. He also had specialized instruments created, including special cutting blocks and angled drills and reamers, which allowed him to adopt the approach for almost all ATSAs. The subscapularis sparing approach was not utilized in cases with significant glenoid deformity or glenoid medialization. In these situations, a standard deltopectoral approach should be utilized.


TECHNIQUE

The patient is positioned in the beach chair position with a 45° incline and a folded sheet behind the ipsilateral scapula. Carefully position the patient at the edge of the bed to allow unrestricted shoulder extension. A 7 cm straight saber incision is made halfway between the anterolateral acromial margin and acromioclavicular joint (FIGURE 20.3). Gelpi retractors are placed, and skin flaps are developed medially to the acromioclavicular joint and anterolaterally to expose the demarcation between the anterior and middle deltoid raphe. Stimulating the muscle with an electrocautery device can help identify this division in the deltoid. The deltoid is subperiosteally elevated off the anterior acromion
from the deltoid split approximately 1 cm medially. The deltoid is split distally, taking care not to extend past 3 to 4 cm distal to the acromion to minimize the risk of axillary nerve injury (FIGURE 20.4). A stay suture can be placed at the inferior margin of the split to minimize risk of propagation. The axillary nerve can be palpated through the deltoid split on the underside of the deltoid
muscle to confirm its location. Two blunt modified Kolbel self-retaining retractors are then inserted into the deltoid split, and subdeltoid adhesions are released digitally or with a Langenbeck elevator. The shoulder is then externally rotated to help identify the LHBT and define the borders of the rotator interval. The rotator interval tissue is incised starting from 5 mm posterior the biceps tendon, dividing the coracohumeral ligament, and exiting the shoulder joint anteriorly down to the upper border of the subscapularis tendon. Next, the arcuate artery is cauterized in the bicipital groove. The biceps tendon is tenotomized from its labral anchor and tenodesed at the transverse ligament. A biceps tenolysis may be done distal to the tenodesis to help ensure proper tension of the tendon. The rotator interval tissue is then incised posteriorly from the subscapularis upper edge back to the glenoid, creating a triangular flap of tissue that remains attached to the supraspinatus (FIGURE 20.5). The rotator interval tissue flap is tucked under the supraspinatus to protect it and allow for later closure at the conclusion of the procedure. The blunt modified Kolbel retractor is then placed into the rotator interval between the supraspinatus and subscapularis. A Darrach retractor may be inserted superiorly under the supraspinatus tendon to identify the insertion of the tendon. A second Darrach retractor may be inserted under the subscapularis to complete exposure. The humeral head cut is marked from the articular margin of the subscapularis to the supraspinatus articular margin with an electrocautery.





















The medullary canal is opened with a rongeur posterior to the biceps tendon, approximately 5 mm from the supraspinatus insertion and at the highest point of the humeral head. An intramedullary guide is inserted into the humerus and is oriented such that the slotted portion is placed into the gap between the supraspinatus and subscapularis (FIGURE 20.6). The cutting guide is pinned into position after appropriate placement is confirmed. The osteotomy is performed through the 132.5° neck-shaft angle cutting guide with an oscillating safety saw. Care should be taken not to damage the rotator cuff anteriorly or posteriorly and to protect critical medial and inferior neurovascular structures. After the resection is completed, it may sometimes be necessary to remove the head in two separate pieces. A curved osteotome and curette are used to free and remove the medial osteophytes. Adequate osteophyte removal may be confirmed by comparing the removed bone to the preoperative plan and by sliding an instrument back and forth along the medial calcar. During the learning curve for this approach, it may be helpful to use intraoperative fluoroscopy to confirm adequate osteophyte removal.

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Jun 23, 2022 | Posted by in ORTHOPEDIC | Comments Off on Subscapularis-Sparing Anatomic Total Shoulder Arthroplasty
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