Dynamic and Static Stabilization of Anterior Shoulder Instability With the Subscapular Sling Procedure

There are numerous arthroscopic techniques available to address anterior shoulder instability. Complications are various, and in pursuit of new treatment options, an alternative arthroscopic technique with less potential for complications has been developed. The novel subscapular sling with a semitendinosus graft provides both dynamic and static stability. This procedure uses a semitendinosus graft as a sling around the upper two-thirds of the subscapular tendon, attached to the anterior glenoid rim. The sling phenomenon present in the Latarjet procedure was the basis of the development. The efficacy of the subscapular sling procedure has been verified in biomechanical studies and further investigated in a clinical pilot study. The procedure can be performed without altering the anatomy of nearby structures such as the coracoid process, the conjoined tendon, and the axillary and musculocutaneous nerves. The authors propose the arthroscopic subscapular sling procedure as an alternative to existing surgical treatment options for recurrent anterior shoulder instability.

A nterior shoulder instability is a challenge both for patients and surgeons. There are many treatment options available, depending on the structures injured. 1 In cases of mere anterior soft-tissue damage, the traditional Bankart repair may be used. 2 Bonetransferring procedures are preferable in shoulders with severe glenoid bone loss and residual luxation following previous soft-tissue stabilization. [3][4][5] Both Bankart and bone-grafting procedures been known to have complications. [6][7][8][9][10][11] The potential for better treatment options led to the development of the subscapular sling with a semitendinosus (ST) graft. 12,13 Feasibility and biomechanical cadaveric studies have been performed, 12,13 and a clinical pilot study of the subscapular sling shows promising preliminary results. The purpose of this paper is to present the surgical procedures involved in the subscapular sling method with an ST graft. The ST graft is pulled through a slit in the subscapular tendon and attached to the anterior glenoid rim to replace the torn labrum. A sling is constructed around the upper two-thirds of the subscapular tendon and provides, together with the reconstruction of the labrum, both static and dynamic stabilization of the shoulder (Fig 1).

Surgical Procedure (With Video Illustration)
The surgical procedure is illustrated in Video 1. The patient is placed in the beach chair position under general anesthesia with an optional brachial plexus block. For ease of graft harvest and patient positioning, the ipsilateral knee is used when possible. The knee is draped, and local anesthesia with adrenalin is applied to avoid the use of a tourniquet. The anatomic landmarks of the shoulder are marked (Fig 2). Standard posterior portal, anterior, and anterosuperior portals are positioned with the anterior portal cranial to the superior edge of the subscapular tendon.
A diagnostic arthroscopy is performed after an external examination of the shoulder stability. The rotator cuff and in particular the subscapular tendon are inspected to rule out injuries. Furthermore, the amount of glenoid bone loss, on/off-track HilleSachs lesions, and labral and ligament ears are assessed (Fig 3).
The ST tendon is identified through a small skin incision on the proximal medial tibia and harvested with a corkscrew tendon stripper. The graft is doubled, whip stitched, and the length is measured. Additional    sutures are placed at both ends of the graft to ease the advancement into the joint and around the subscapular tendon before fixation (Fig 4). Before skin closure, a 12-gauge catheter is advanced on the medial side of the thigh along the remaining hamstrings tendon to administer ropivacaine.
Remnants of the anterior labrum are removed from the 2-to 5-o'clock position using different rasps, shaver, and radiofrequency coblation. The anterior glenoid must be cleared of soft tissue to support ingrowth of the ST graft. The anterior portion of the subscapular tendon is cleared, and the axillary nerve is identified and kept at a distance from the portals and instruments during surgery. All instrumentation is performed lateral to the conjoined tendon, thus also preserving the musculocutaneous nerve, which is not visualized. The lower anterolateral portal is created lateral to the conjoined tendon from anterior to posterior direction using an aiming guide, cannulated needle, guidewire, switching stick, and halfpipe instruments with the shoulder in 20 of external rotation (Figs 5-7 and Video 1). The aiming guide has a marking at 3 cm, allowing the surgeon to decide the proportion of the subscapular tendon to be included in the sling.
After the correct placement of the aiming guide, a long, cannulated needle is advanced into the joint and a switching stick slid carefully over it (Figs 8 and 9).
Dilators of increasing size are advanced over the switching stick and finally, a halfpipe instrument is placed through the subscapular tendon into the joint (Figs 9 and 10).
A banana knife or a coblation device is passed over the halfpipe and used to make a slit in the longitudinal direction between the lower and middle third of the subscapular tendon. This is performed with a neutral rotation of the shoulder and cutting from medial to lateral under visual control. A short switching stick or blunt round instrument is advanced on the anterior wall of the subscapular tendon through the anterosuperior portal down to the halfpipe to facilitate the placement of a pulling suture (#2) and subsequently the ST-graft (Figs 6 and 11). With the help of a grasper, the pulling suture (#2) is introduced into the joint between the glenoid and the posterior wall of the subscapular tendon from the anterosuperior portal through the slit in the subscapular tendon and back out through the anterosuperior portal (Figs 6, 12, and 13). The tendinous graft end is connected to this suture and pulled into the joint and around the subscapular tendon through the anterosuperior portal (Fig 14).
It is of immense importance to keep the shoulder in at least 20 of internal rotation at this point of the procedure to avoid impingement of the graft between the humeral head and the subscapular tendon. An external To prevent a reduction in external rotation and abduction, the arm is at this point of the procedure held in 30 of abduction and 20 of external rotation to prevent the sling being too tight. The remaining graft is cut and removed from the joint. The graft fixation is assessed and the shoulder advanced carefully into the 90/90 position to judge the stability and containment of the joint. The joint is flushed, and the portals and camera are removed. The small incisions are sutured, and the shoulder is placed in a supportive sling for 4 weeks. Patients are recommended a postoperative rehabilitation program instructed by a physiotherapist. Pendulum and limited rotational exercises are started on the first postoperative day.

Discussion
This paper presents the surgical technique of the novel subscapular ST sling. The sling supports the subscapular tendon and pulls it in a posterior direction to prevent an anterior dislocation. The ST graft replaces the lost anterior labrum and has, together with the subscapular tendon sling, both a static and dynamic stabilizing effect on the shoulder (Fig 21).
This procedure is an alternative option to other arthroscopic stabilizing procedures to treat anterior shoulder instability. After a Bankart stabilization, one third of the patients (mainly male patients younger than the age of 22 years) experience residual dislocation or do not return to their preinjury sporting level. 7,14-16 In cases of previously performed soft-tissue stabilizing with recurrence, treatment options are usually different bone grafting procedures. 17 The iliac crest bone grafting procedure and the Latarjet render good results but do have complications. 6,8,18 The subscapular sling is part of a development in recent years seeking to find a surgical technique with fewer potential complications. Such a new procedure could fill the large gap between the Bankart fixation and the more difficult and anatomy-changing bone procedures. The pursuit of new procedures may also lead to the development of better arthroscopic instruments and subsequently improve the treatment options available.   Bone grafting procedures may change the anatomy of the shoulder. They are performed by both open surgery and arthroscopically. 3,19 The proposed technique leaves the coracoid and adjacent tendons untouched and not transferred, which potentially reduces the risks of nerve injury, because portals and instrumentation are not needed medial to the conjoined tendon. A remplissage procedure could be advocated in engaging HilleSachs lesions, 20,21 but has to our knowledge not been combined with the subscapular sling. Table 1 displays the advantages and disadvantages of the subscapular sling procedure.
The drawbacks of this procedure include the use of an ST autograft, but allografts may also be an option. There are reports of reduction in flexion strength at the donor site, but sequalae are otherwise limited to postoperative pain and loss of sensation around the donor site. 22,23 Patients scheduled for this operation must be informed about the potential of pain, thrombosis, and loss of sensation. Postoperative administration of lowmolecular-weight heparin should be considered to avoid thrombosis. The long-term effects of this technique are unknown. Postoperative magnetic resonance imaging has confirmed an intact reconstructed labrum, sling, and subscapular tendon (Fig 22). The sling may nevertheless cause erosion and rupture of the subscapular tendon. Ruptures of such kind or muscle atrophy of the subscapularis have not been detected.
The graft-sling and the subscapular tendon can eventually lose firmness and strength and subsequently reduce the stability of the shoulder. Firm attachment and ingrowth of the graft on the anterior glenoid rim  are essential to achieve a negative joint pressure and suction effect. These effects may diminish if the healing is disturbed by poor graft quality and/or bone quality. The tightness of the sling is important to assess during surgery. An overconstrained sling would hinder the external rotation and may also, in the long run, induce arthritis because of the excessive pressure on the anterior part of the glenohumeral joint. Table 2 displays the indications and contraindications for this procedure. A torn subscapular tendon is an absolute contraindication because the dynamic stability of the subscapular sling is dependent on an unimpaired tendon. An elongated subscapular tendon with a partial tear may be a relative contraindication. The subscapular sling has not been tested with substantial glenoid bone loss and should in these cases be avoided until further studies have investigated its efficacy. A further development could be to use a quadriceps tendonebone graft in shoulders with severe glenoid bone loss. 24 The subscapular sling procedure with a ST graft may in future be included in the possible treatment options for patients suffering from residual anterior shoulder instability.