In the last decade, arthroscopic techniques for the treatment of posterior glenohumeral instability have increased [7]. Numerous published studies show high rates of good results with arthroscopic treatment [15-18].

Open surgery techniques are still used mainly for the treatment of glenoid and humeral bone defects and in corrective osteotomies in dysplasias and glenoid retroversions.

There are two options for surgical management in glenohumeral instabilities depending on the cause leading to instability: open or arthroscopic procedures that aim to repair bone defects (whether at the level of the glenoid or the humeral head) and open or arthroscopic procedures that aim to repair soft tissues and capsulolabral injuries. Obviously, some patients will require procedures on bone defects and soft tissues within the same surgical procedure [19].

There are multiple surgical techniques, both open and arthroscopic, for the treatment of posterior glenohumeral instability. When indicating a surgical technique, multiple factors have to be taken into account, such as the age of the patient, the cause of instability (traumatic or atraumatic), the severity of the injury (luxations or recurrent posterior subluxations or microinstabilities), the pattern of instability (unidirectional or multidirectional), the type of patient and his/her functional demands (athletes versus non-athletes, and more specifically, throwers) and the presence or absence of associated lesions (superior labrum anterior and posterior [SLAP], rotator cuff tears, long head biceps tendon lesions) [5, 20]. The treatment should be planned according to each case on an individual basis according to the patient characteristics and the injury type.

Open or arthroscopic surgical treatment is indicated in patients with functional limitations arising from instability and/or pain that have not improved with rehabilitation treatment.

The indications for arthroscopic treatment are recurrent posterior subluxation caused by injury of the labrum or the capsulolabral complex; recurrent posterior subluxation caused by capsuloligamentous laxity or capsular redundancy; and multidirectional instability with posterior instability as a primary component [7].

Relative contraindications of arthroscopic surgery include [7] lack of arthroscopic surgical skill on the part of the surgeon and extensive bone lesions (reverse Hill Sachs or reverse Bankart lesion) that require the use of subscapularis transfer, allograft or osteotomy. Arthroscopic surgical techniques have been described for the management of bone defects.

Poor capsulolabral tissue and previous open surgery are also relative contraindications.

The main indications for open surgery would be in cases of reverse Hill Sachs lesions or broad reverse Bankart lesions not accessible by arthroscopy.

Surgery is contraindicated in cases of habitual voluntary posterior glenohumeral instabilities and with uncooperative patients or those with underlying psychiatric disorders. Although voluntary posterior dislocation is not an absolute contraindication [9], the mental state of the patient must be taken into account before considering the surgical option due to the high rate of poor results [21].

The chronicity of the lesion, the bone quality, and the general condition of the patient must be evaluated because in cases of chronic dislocations in which the patient has minimal pain with acceptable function, low functional demands, or older age, therapeutic abstinence as the treatment of choice must be considered [22].

Although procedures for bone defects have traditionally been associated with open surgery techniques, in recent years, multiple arthroscopic surgical techniques have been described for the management of bone defects, especially for the glenoid [4, 23].

The main surgical procedures for the treatment of bone defects or abnormalities of either the humerus (mainly reverse Hill-Sachs lesions) or the glenoid (bone loss in the posterior glenoid, increased glenoid retroversion, glenoid hypoplasia) are as follows:

A. Humeral bone defects

• Non-anatomical techniques
• Anatomical techniques (disimpaction and placement of bone graft or reconstruction with allografts)
• Substitution techniques

B. Bone defects or glenoid anomalies

• Posterior bone block
• Posterior opening glenoid osteotomy
• Rotational osteotomy of the humeral neck

Anatomical techniques have better clinical results compared to non-anatomical procedures, particularly if they have been performed arthroscopically [24].

In 1952, McLaughlin [28] described the transfer of the subscapularis tendon insertion and its suture at the site of the reverse Hill-Sachs lesion to limit maximum internal rotation and to prevent engagement of the humeral defect in the posterior part of the glenoid (Fig. 2). This non-anatomic humeral defect reconstruction technique is performed by a deltopectoral approach. Different arthroscopic techniques for performing a modified McLaughlin technique have been published [29, 30]. In 1987, Neer et al.. [6] described a modification of the McLaughlin technique for the transfer of the subscapularis tendon with the lesser tuberosity (Fig. 3). The purpose of this modification is to facilitate the fixation of the subscapularis tendon, as it is a bone-bone fixation.

Fig. (2). The transfer of the subscapularis tendon insertion and its suturing at the site of the reverse Hill-Sachs lesion.

Fig. (3). The transfer of the subscapularis tendon with the lesser tuberosity.

Arthroscopic and open surgery variations are reported on the literature by plication of the subscapularis without detachment of the tendon [30, 31].

This technique effectively avoid the bone defect to engage on the glenoid rim [28].

We prefer non-anatomical techniques (McLaughlin or its modifications) for reverse Hill-Sachs lesions with impairment of the articular surface between 20% and 50%.

Another non-anatomical technique is rotational osteotomy of the proximal humerus [27, 32-34]. This technique is rarely used today due to the risk of avascular necrosis of the humeral head and osteoarthritic progression of the joint [6, 35, 36]. The rate of postoperative complications detected in a systematic review with this technique was 29%, a mean postoperative Constant score 79 and the rate of recurrence was 5,6% [37, 38].

This anatomical reconstruction technique may be useful in lesions affecting up to 50% of the humeral surface [6, 27, 38, 40-42]. Unlike the disimpaction and bone grafting technique, reconstruction of the humeral head using an allograft should be considered when there is a situation of non-viable cartilage at the fracture site. The main advantage of this technique is that it offers the greatest anatomic restoration possible of the injured area, which would facilitate the subsequent placement of an arthroplasty if necessary [22]

The allograft should be of a similar size to the defect of the damaged head; for this reason, it may be useful to perform radiographs of the contralateral side.

Using a deltopectoral approach and after reference and detachment of the subscapularis tendon, a capsulotomy is made. After reduction of the dislocation, the state of the cartilage at the lesion site is analyzed, along with the range of rotation required to cause engagement of the lesion at the site of the posterior portion of the glenoid.

The preparation of the humeral defect is performed with a small oscillating saw, preparing a defect that is measurable and homogeneous. Subsequently, graft preparation is performed, using measurements slightly above those of the prepared bed to fit the allograft under pressure on its bed (Fig. 4). The graft is then fixed with 2 Herbert-type screws. The stability of the joint rotation should be checked via internal and external rotation, and it should be verified that the allograft does not rub against the glenoid in any range of motion. One can then proceed to reinsert the subscapularis and to perform the layered closure.

Fig. (4). Reconstruction with allograft.

The reconstruction of defects of the humeral head using an allograft restores joint stability, relieves pain, and leads to long-term clinical improvement in the patient [7, 43-53].

Gerber and Lambert [19, 42] reported a Constant score of 96 at 5 years of follow up with allograft reconstruction.

Martinez et al. [43, 45-47, 50, 52, 53], reviewed 6 patients treated with allograft reconstruction of segmental defects of the humeral head. They reported that this technique has a good long-term follow-up result in 50% of the patients. Some complications are pain, instability, osteoarthrosis and collapse of the allograft.

Gerber et al. [4, 44, 54, 55], reported excellent clinical results at a mean follow-up of 10.7 years after use of this technique.

In a systematic review Longo et al. [37, 43, 53] reported a rate of postoperative complications after humeral allograft reconstruction of 74%. Mean postoperative Constat score was 76,2 and the rate of recurrence of instability was 0%.

For defects greater than 50% of the articular surface or in the case of dislocations over 6 months in duration where there is poor bone quality, some authors advocate hemiarthroplasty or total shoulder arthroplasty as a treatment of choice [6, 22, 38]. In patients of advanced age with defects of approximately 40% and with low functional demands, arthroplasty would also be indicated. Although some authors advocate total arthroplasty as a treatment of choice, others base themselves on the state of the glenoid when deciding to place a full arthroplasty instead of a hemiarthroplasty [22, 27, 33, 34]. Hawkins et al. [4, 6, 43] reported that total shoulder arthroplasty is more reliable at pain relief and restoration of function than hemiarthroplasty. Although good results are obtained with this treatment, functional outcomes in cases of instability are below those that have been treated for osteoarthritis [38]. In this case, we consider it essential to perform a computed tomography (CT) scan to assess bone stock and possible glenoid retroversion, which should be taken into account during surgery.

Gravriidilis et al. [23, 34] reviewed 12 patients with shoulder arthroplasty after posterior instability. This treatment provided good midterm results with a significant improvement in the range of motion.

Treatment of posterior glenohumeral instability through arthroplasty techniques has the highest rates of recurrence of instability compared with other surgical techniques. Longo et al. [37, 49, 56] reported a rate of recurrence of 14%. The rate of postoperative complications was 19% and the mean postoperative Constant score is 58,2. Reoperation occur in more than one-quarter of patients [38].

The main causes of glenoid defects that lead to posterior glenohumeral instability include osteochondral fractures resulting from dislocations, increased retroversion of the glenoid or glenoid hypoplasia. The main techniques for treating glenoid bone defects are posterior bone block and posterior opening osteotomy of the glenoid [7, 43, 46-53]. These procedures may also be indicated in the event of failures in the treatment of soft tissues with recurrent posterior instability [19, 50].

While classically this procedure has been performed using an open surgical technique [43, 46, 47, 50, 52, 53], in recent years, publications have described arthroscopic techniques and their results [4, 53-55].

The open procedure is performed with the patient in lateral decubitus and through a posterior incision in line with the axillary fold. After incision of the posterior deltoid, the space between the infraspinatus and the teres minor is dissected, and the capsulotomy is then performed. After decortication of the posterior edge of the glenoid, one proceeds with bone fragment osteosynthesis [43, 53]. The autograft is obtained from the iliac crest [4, 43, 52], although studies have been published in which the bone fragment is obtained from the distal clavicle [23, 54] or even from the distal tibia [49, 56, 57] (Fig. 5).

Sirveaux et al. [50, 57], published a study with the use of iliac crest bone graft and acromion pediculated bone block. No patient in this study had posterior subluxation or dislocation postoperatively, Servien et al. [53], reviewed 21 patients treated with open posterior bone block, with average follow-up of 6 years and a Constant score of 93,3. The autors concluded that the bone block procedure could be a procedure of choice in recurrent posterior instability.

Fig. (5). Posterior bone block. The autograft is obtained from the iliac crest.

Barbier [43, 58] presented a report of 8 patients treated with iliac bone block autograft in average follow-up of 3 years. The mean postoperative Constant score was 96,25. Their study showed good and satisfactory results in 80% of cases at a mean of 3 years follow-up.

In other hand, Meuffels [21, 52] presented poor long-term results of the posterior bone block procedure, with 36% of futher posterior dislocation. After 18 years osteoarthritis was present in all patients.

Schwartz et al. [54, 59] performed 19 arthroscopic posterior bone block in posterior shoulder instability. At a median follow-up of 20,5 months the overall Rowe and Walch-Duplay scores improved significantly.

Struck et al. [57, 58] reported the results after open posterior bone block at long-term and short-term. The clinical results showed no clinical difference with good to verygood overall results in the subjective and objective scores.

Treatment by posterior bone block improves posterior glenohumeral instability in both the short- and the long-term. Low rates of recurrence have been noted [57, 60].

Glenoid retroversion has been defined as an angle in the sagittal plane greater than -7° [58, 61]. Hurley et al. [21, 59, 61, 62] reported retroversion angles of -10° in patients with posterior instability in comparison to the -4° angle of the control group. To correct glenoid retroversion, a posterior opening osteotomy may be performed at the site of the glenoid through a posterior approach to the joint. The osteotomy must be 1 cm medial to the articular surface [59, 63] and parallel to it, with the aim of opening the osteotomy without breaking the anterior cortex. An iliac crest allograft can be used, and the fixation must be performed with either 4.0mm screws or a small plate in the shape of a “T”. This procedure is technically demanding and has a high complication rate [5, 58].

Hawkins et al. [24, 60], described relatively poor outcomes with a complication rate of 41%.

Norwood et al. [24, 61], reported 47% of instability after this procedure.

In addiction, coracoid impingement and anterior dislocation haven been described following posterior glenoid osteotomy [59, 61, 62, 64, 65], and inadvertent penetration of the glenohumeral joint at the time of surgery can predispose to glenohumeral artritis [5, 63, 65].

Before arthroscopic surgery, all patients should be clinically evaluated at both shoulders in supine decubitus position. The presence of anterior, posterior or inferior glenohumeral translation should be assessed when there is an initial sulcus sign greater than 2 cm or when, after repairing an instability, there is a persistent sulcus sign greater tan 1cm in external rotation.

The patient is placed in lateral decubitus at a 30⁰ posterior slope (so that the glenoid surface is parallel to the ground). The arm is placed in a traction device at 45° abduction and 20° shoulder flexion with approximately 4-5 kg of longitudinal traction (Fig. 6).

Fig. (6). The arm is placed in a traction device at 45° abduction and 20° shoulder flexion.

The first arthroscopic portal we perform is posterior, approximately 2 cm inferior and medial to the posterolateral angle of the acromion [5, 37]. Under direct view from this portal, the accessory posterior portal is located using a spinal needle at approximately 1 cm inferior and lateral to the posterolateral angle of the acromion (posterosuperior portal) or the posterolateral accessory portal or portal 7, which is located 2 cm inferior and 2 cm lateral to the posterior portal or exactly 2 cm lateral and inferior to the posterior corner of the acromion (Fig. 7). The choice of one or another portal is defined according to the best direction obtained with the spinal needle for subsequent implant placement (Fig. 8). Finally, the standard anterior and anterosuperolateral portals are made. The arthroscope is inserted into the latter portal to assess the rear and front portions of the glenohumeral joint.

Fig. (7). Posterosuperior portal and the portal 7.

Fig. (8). The choice of one or another portal is defined according to the best direction obtained with the spinal needle for subsequent implant placement.

An evaluation should be made of the dynamic stabilizers, especially the intra-articular portion of the subscapularis, the rotator cuff, and the long head of the biceps, along with the static stabilizers: the articular surfaces, the labrum and the glenohumeral ligaments, especially the posterior cord of the inferior glenohumeral ligament, which is the primary posterior stabilizer with the arm flexed and in internal rotation, and the middle and upper glenohumeral ligaments [24, 65, 66].

Arthroscopic assessment will help identify potential injuries associated with posterior instability. These injuries mainly include the following:

1. Bone lesions or defects:
   • Of the posterior glenoid.
   • Posterior Bankart bone lesion or reverse Bankart bone lesion.
   • Anterior Hill-Sachs lesion or reverse Hill-Sachs.
2. Lesions or defects of soft tissues:

• Posterior Bankart lesion
• Kim lesion, lesion of the posteroinferior labrum (Fig. 9)
• Posterior labrocapsular periosteal sleeve avulsion (POLPSA lesion)
• Bennet lesion
• Posterior humeral avulsion of the glenohumeral ligament (PHAGL lesion)
• Glenoid labrum articular disruption lesion (GLAD lesion)
• Posterior capsular redundancy or laxity
• Injury to the rotator interval
• Associated lesions: Superior labrum anterior to posterior (SLAP lesion) and Partial articular surface tendon avulsion (PASTA fracture); lesions to the upper, middle and inferior glenohumeral ligaments; and capsular redundancy.

Fig. (9A,B). Kim lesion, lesion of the posteroinferior labrum.

The most common complication is recurrence, which may be due to either a new lesion or failure of the initial intervention.

Recurrence rates of treatment of posterior instability range between 0 and 10% [68, 72].

Petrera et al. [69, 73] reported recurrence rates of arthroscopic surgery of 6% compared to 6.7% for open surgery, without finding statistically significant differences. However, other studies refer to higher recurrence rates in open (9.2%) versus arthroscopic treatment (2.9%).

Recurrence rates have decreased progressively due to improved surgical techniques, especially with the recognition of anterior Hill-Sachs lesions, as it is essential to determine the size and orientation of the lesion and the presence of engagement of the anterior Hill-Sachs lesion with the rim of the glenoid. Depending on the size and the presence or not of engagement, we must perform different surgical techniques on Hill-Sachs lesions, from subscapularis transfers alone or with bone fragments, filling bone defects with grafts, to prosthetic replacements, as have been described throughout the chapter.

Contact sport athletes have higher recurrence rates [52, 70] after arthroscopic treatment, even though we believe that arthroscopic repair in this group of patients allows us to act with greater ease and less aggressiveness in the cases of posterior capsulolabral lesions and to perform subscapularis transfers at the site of Hill-Sachs lesions.

The closure of the rotator interval has been proposed as a technique to reduce recurrence rates. Recent biomechanical studies have not shown that the arthroscopic rotator interval closure is beneficial for the treatment of posterior glenohumeral instability [26, 71].

One problem related to anatomical reconstruction techniques and posterior bone blocks in the treatment of posterior glenohumeral instability is recurrences due to reabsorption of the allograft used [57, 68].

Although avascular necrosis (AN) can occur as a result of a fracture-dislocation, AN risk increases with the degree of fracture displacement, the extent of the lesions to the tuberosities and the increase of time between the time of injury and treatment, such as in posterior inveterate dislocations [72, 74]. Immediate reduction and stable internal fixation favor the revascularization of the humeral head and decrease the risks of AN, which is why we must prevent further posterior inveterate dislocations by being very careful in the initial diagnosis.

The development of osteoarthritis is a frequent complication. Aparicio et al. [73] identified radiographic degenerative changes in most cases of their series after posterior fracture-dislocations, and Meuffels et al. [52] show a series with 100% osteoarthritic changes after the use of posterior bone block. Treatment is based on symptomatology, which does not always need to have a correlation between symptoms and radiological findings. Initially, patients may benefit from nonsurgical treatment based on rehabilitation and retraining programs or modified activity and treatment with oral anti-inflammatories and painkillers. Total shoulder arthroplasty should be indicated in patients who do not improve or worsen with nonsurgical treatment.

Shoulder stiffness is common in cases of posterior fracture-dislocations that have been delayed in the initial treatment, posttraumatic degenerative changes, deformities of the humeral head and AN [26]. Treatment of stiffness will depend on the cause that generates it; in the absence of degenerative changes or collapse of the humeral head, arthroscopic capsulotomy followed by rehabilitation therapy improves functional outcomes. When stiffness is associated with degenerative changes or collapses of the humeral head, shoulder arthroplasty should be indicated.

The stiffness after posterior instability surgery often appears as a loss of less than 10º of internal rotation, this loss may have little impact on most people but can cause major problems for throwing athletes (baseball, handball), tennis players, or swimmers.

Although rare, there are other complications associated with the treatment of posterior glenohumeral instabilities, such as infections after open reduction and internal fixation [68], and nerve lesions, particularly of the axillary and suprascapular nerves, which may be injured during open surgery [74].