34.1 Goals of Procedure

Locked posterior shoulder dislocations are uncommon and often misdiagnosed. Overall, posterior shoulder instability accounts for approximately 3% of all shoulder dislocations with a reported prevalence of 1.1 per 100,000 per year. ¹ The general causes include epileptic seizures, high-energy trauma, electric shock, or electroconvulsive therapy. In the case of involuntary muscle contraction, the strong internal rotators of the shoulder such as the latissimus dorsi, pectoralis major, subscapularis, and teres major overpower the weak external rotators and drive the humeral head posteriorly.

During a posterior dislocation event, the shoulder is typically axially loaded with the arm in a forward elevated, adducted, and internally rotated position. As the humeral head impacts on the posterior aspect of the glenoid, an osteochondral impression fracture (also termed encoche fracture or reverse Hill–Sachs lesion) is produced. ² If the shoulder is not reduced acutely, the impression fracture can enlarge due to the grinding effects of rotational shoulder movements. A secondary deformity within the humeral head articular cartilage may also develop with prolonged dislocation. Additionally during the acute dislocation event, an injury may also occur within the posterior stabilizers of the shoulder including capsulolabral tears/avulsions, glenoid rim fractures, or rotator cuff tears.

After sustaining a posterior dislocation, patients will present with their arm held in an adducted/internally rotated position. The patient will complain of loss of motion, particularly external rotation; on examination, there may be a prominence of the coracoid process anteriorly limited to no external rotation due to the humeral head being fixed on the posterior glenoid rim. Initial radiographic evaluation includes a true anteroposterior (AP) view of the shoulder, scapular Y view, and an axillary view. If the patient’s pain and limited abduction do not allow for a standard axillary lateral, a modified axillary view, apical oblique view, or a Velpeau view may need to be considered. An axillary view is essential for the diagnosis of a posterior dislocation, as the standard AP view may appear normal ( Fig. 34.1 ). A CT scan of the shoulder with glenoid subtraction and 3D reconstruction of the humeral head is also helpful to evaluate the size and location of the humeral head defect. The CT scan is also useful in detecting any potential occult anatomical/surgical neck fractures of the humerus. An MRI should also be considered to evaluate for possible rotator cuff tears and/or injury to the ligamentous soft-tissue restraints of the posterior shoulder.

When evaluating treatment options for a posterior dislocation of the shoulder, the clinician should consider the age/demands of the patient, the size of the humeral head defect, associated pathology, and the duration of the dislocation. ³ Nonoperative treatment can be considered for elderly patients with low demands, patients with multiple medical comorbidities, or patients with unstable epilepsy. For acute shoulder dislocations, one that has occurred within 3 weeks of the traumatic event, a closed reduction can usually be successfully performed in patients with smaller humeral head defects. If the dislocation has been present for greater than 3 weeks, a successful closed reduction may be more difficult to perform and a potential open/arthroscopically assisted reduction may need to be considered. Overall, the degree of posterior shoulder instability after a successful reduction is determined by the size of the anterior humeral defect and the associated capsulolabral injury.

If the shoulder is stable after a successful closed reduction, continued closed treatment in an abduction sling in neutral rotation for 6 weeks can be considered. If, however, the shoulder is unstable after a successful closed reduction, the clinician should assess and quantify the relevant bony lesion of the humeral head. ³ In cases without a significant reverse Hill–Sachs lesion, isolated treatment of the posterior labral pathology can be performed for the unstable shoulder. For patients with associated fractures of either the surgical neck or greater tuberosity, these fractures should be considered separately and addressed directly. When the bone defect of the Hill–Sachs lesion is greater than 45%, biologic reconstruction techniques utilizing an allograft to fill the segmental defect and restore the sphericity of the humeral head should be considered for young/active patients. Elderly or low-demand patients with these large humeral head defects (> 45%) may be ideal candidates for a primary joint replacement. In patients with humeral head defects less than 40% and instability after a posterior shoulder dislocation, operative stabilization with a McLaughlin or modified McLaughlin is considered the gold standard. Disimpaction bone grafting or autologous bone graft procedures such as osteochondral transplantation can be considered in addition to the soft tissue–based stabilization of the humeral defect for lesions measuring 20 to 40%.

34.2 Advantages

In a small case series, McLaughlin outlined his original technique for treating chronic locked posterior dislocations by a split in the subscapularis tendon close to its insertion with subsequent open reduction and filling the tendon into the reverse Hill–Sachs lesion. ⁴ The subscapularis tendon was then secured to the humerus through transosseous tunnels. Neer subsequently modified this technique with an osteotomy of the lesser tuberosity and transfer of the subscapularis-tendon-bone unit into the reverse Hill–Sachs lesion. ³ As a consequence of these nonanatomic techniques, there is a significant loss in internal rotation motion and strength. Additionally, the shoulder anatomy is distorted, which can complicate any future arthroplasty-based procedures. Less invasive arthroscopic modifications have been more recently described in which the attachment of the subscapularis tendon to the lesser tuberosity is maintained while insetting it into the bony defect. ¹ This converts the reverse Hill–Sachs lesion into an extra-articular defect. While this modification is less invasive, it can still lead to deficits with internal rotation and alters the direction of force transmission/working length of the subscapularis tendon. A subsequent modification of this arthroscopic technique initially described by Duey et al utilizes the middle glenohumeral ligament (MGHL) instead of the subscapularis at the lesser tuberosity to fill the reverse Hill–Sachs lesion. ¹ While the use of the MGHL may still result in a slight loss of internal rotation, the anatomy, force vector, and function of the subscapularis are not altered. This chapter will highlight the modified McLaughlin procedure with the use of the MGHL to treat instability after a posterior shoulder dislocation.

34.3 Indications

As previously noted, reverse Hill–Sachs lesions are common after a posterior shoulder dislocation and the location/size remain the most important factors in determining treatment options. The modified McLaughlin procedure can be utilized to treat humeral defects measuring 20 to 40%. It is important to note, however, that these nonanatomic techniques are less successful when the humeral defect occupies 33 to 50% of the articular surface. ³ In cases with larger lesions, the soft tissue–based modified McLaughlin procedure can be combined with an osteochondral transplantation. For lesions greater than 45%, allograft- or arthroplasty-based procedures may need to be considered.

34.4 Contraindications

The main contraindication for the use of an isolated modified McLaughlin procedure to treat recurrent instability after a posterior shoulder dislocation is a larger reverse Hill–Sachs lesion, greater than 45%. A relative contraindication for the use of the MGHL is mainly related to certain anatomical variations in which the ligament does not have a normal size or consistency. In these cases, the subscapularis tendon can be utilized instead and inset into the humeral head defect arthroscopically. Nonoperative treatment should be considered for elderly patients with low demands and patients with unstable epilepsy or multiple medical comorbidities/advanced dementia.