Surgical treatment of chronic posterior fracture-dislocations of the shoulder by transfer of the subscapularis tendon

J.C. FEROUSSIS[1], I.K. TRIANTAFILLOPOULOS[2], P. DALLAS[1], A. ZOGRAFIDIS[1], N. KONSTANTINOU[1], A. PAPASPILIOPOULOS[1]
[1] 17th Orthopaedic Department, Asklepeion Voula Hospital
[2] 21st Orthopaedic Department, Medical School, University of Athens

ABSTRACT
We evaluated the results of treatment in six patients with chronic locked posterior dislocation of the glenohumeral joint associated with an anteromedial humeral head defect involving 20% to 40% of the articular surface. Patients sustained open reduction and transfer of the subscapularis tendon to the defect, according to McLaughlin's technique. The average length of follow up was three and a half years. Four patients, with a dislocation less than three months, had excellent results demonstrating little or no pain, almost full range of motion and no functional restriction in the activities of daily living. The remaining two patients, with dislocation more than three months, had good results demonstrating slight restriction of motion and mild functional disability. All patients had normal muscle strength and the Constant score was above 80%. At three months, patients could perform all activities except strenuous manual labour. At six months, patients returned to unrestricted full activity. McLaughlin's technique reliably decreases pain and significantly improves range of motion and level of function, restoring the stability of the glenohumeral joint.

Key words: Chronic posterior glenohumeral fracture-dislocation, subscapularis muscle transfer.

INTRODUCTION
Posterior shoulder dislocation is a relatively uncommon event, with an incidence of 1% to 4% of all shoulder dislocations. Because of the infrequency of this condition, the diagnosis is often missed, with significant consequences to the patient[12]. Symptoms may be confused with a shoulder contusion or rotator cuff injury. Significant complications such as chronic posterior dislocation and degenerative disease of the shoulder can occur if the diagnosis is missed[11].
The diagnosis and management of chronic, locked, posterior fracture-dislocations of the glenohumeral joint remain a challenge for the treating physician. Treatment consisted of closed reduction and immobilization, McLaughlin's procedure by subscapularis muscle transfer, hemiarthroplasty, total shoulder arthroplasty, open reduction with internal fixation, arthroplastic resection, and arthrodesis[8]. In our study, we advocated open reduction of the glenohumeral joint and the McLaughlin's procedure for the treatment of chronic locked posterior shoulder dislocation with head defect of less than 40% of the articular surface and we evaluated the results and the final outcome of this procedure.

MATERIAL AND METHOD
Six consecutive patients who had missed, locked, posterior fracture-dislocation of the glenohumeral joint, were treated with open reduction and transfer of the subscapularis tendon to the defect, according to McLaughlin's technique[9,10]. There were four men and two women from twenty-five to fifty-two years of age. Motor vehicle accident was the cause of the injury in all cases.
Patients were complaining for shoulder pain and restriction of movements. Complete elimination of external rotation was noticed in all cases. Furthermore, prominence of the acromion and posterior shoulder bulging were also detected.
The interval from injury to diagnosis was six weeks to six months. Four patients had a locked dislocation for a period less than three months and two patients for a period more than three months (figure 1). An axillary radiograph and a computed tomography scan, which demonstrated the approximate size of the impression defect, confirmed diagnosis (figure 2)[13]. In all cases, the defect of the humeral head involved 20% to 40% of the articular surface. In one case, an associated subcapital fracture of the humerus was present. Unsuccessful closed reduction was attempted in two cases.

SURGICAL TECHNIQUE
Under general anaesthesia, patient was placed in the beach-chair position with the head of the bed elevated approximately 30 degrees. The anterior deltopectoral approach was used and developed from its origin, superiorly at the clavicle, to its distal extend, at the insertion of the pectoralis major. Rotator cuff interval was identified following the landmarks of the upper end of the bicipital groove and the anterosuperior edge of the glenoid. The subscapularis tendon was identified and carefully dissected from the lesser tuberosity with a small piece of bone. An effort was made to keep the inferior aspect of the subscapularis tendon, for the protection of the axillary nerve that passes just below the most inferior edge of the tendon. Tendon was dissected using an electro-cutting instrument. The goal of the osteotomy of the small piece of bone was not to fill the whole defect but to achieve a better fixation of the sutures. Osteotomy was performed with a sharp osteotome without disturbing the bicipital groove and the subscapularis was tagged with a No1 Mersilene suture and retracted medially. Extensive soft tissue release both to the anterior and to the posterior aspect of the shoulder was then performed. During mobilization, axillary nerve damage risk both to the anterior as well as to the posterior aspect of the shoulder was taken into consideration. With slight external rotation and gentle traction in 90 degrees of flexion, dislocation was reduced. A Bristow elevator was inserted and used as a lever taking great care not to damage the humeral head. At that point, the humeral head and the joint were visualized and the remaining articular cartilage was carefully inspected to assess the degree of degenerative changes. The defect was then prepared to expose a bleeding bony surface that would facilitate healing of both the subscapularis tendon and the bone fragment. Finally, the subscapularis tendon was transferred into the defect as close to the articular cartilage as possible in a way to achieve a buttress effect. The tendon was fixed in place using trans-osseous sutures or Mitek anchors. After completion of the transfer, stability of the glenohumeral joint was accessed. Closure was begun by assessing the rotator interval followed by the closure of the deltopectoral interval.
In two cases, dislocations were more than three months old, and extensive soft tissue release led to relative instability. In those cases, a Kirschner wire was used to stabilize the joint for ten days until the soft tissues healed (figure 3). In one case, with a six-weeks-old associated subcapital fracture, the fracture was mobilized and a fixation plate was used (figure 4). All patients were immobilized postoperatively for a period of three to six weeks with the arm at the side and in neutral rotation.

1. 2.
Figure 1. Six-months-old posterior fracture-dislocation of the right shoulder.
Figure 2. Computed tomography confirming an old posterior fracture-dislocation of the right shoulder and determining the size of the humeral head defect.

REHABILITATION
Prior to discharge, at the first or second postoperative day, additional radiographs were obtained to confirm the position of the humeral head at the glenoid (figures 5,6). The arm was immobilized in a neutral rotation by a special cast. The duration of immobilization ranged from four to six weeks. At that period, patient was allowed free movement of the hand and wrist and was instructed to perform deltoid isometrics. At the completion of the immobilization period, the cast was removed and a sling was placed for additional two weeks. At this period, the patient was allowed active motion of the elbow, wrist and hands. When the sling was discontinued, patients were instructed to use the upper extremity for activities of daily living. Internal rotation exercises were restricted for three months. Gentle stretching exercises were added at ten weeks and resistive strengthening exercises at twelve weeks.

3.
Figure 3. Postoperative x-ray showing the provisional stabilization of the unstable gleno-humeral joint with a k-wire.

4. 5.
Figure 4. A six-weeks-old associated subcapital fracture of the humerus, treated with plate fixation.
Figure 5. Postoperative x-ray confirming the reduction of the gleno-humeral joint. A special brace keeps the humerus in neutral rotation.

RESULTS
The average length of follow up was three and a half years. Stability was restored and maintained in all cases. Four patients reported little or no pain. They regained almost full range of motion and no functional restriction in the activities of daily living (Figure 7). The results considered being excellent. Constant score was above 90%[4]. The remaining two patients, with unreduced dislocation more than three months, had slight restriction of motion, mild functional disability and the results considered good (figure 8). Constant score was above 80%. All patients had good muscle strength. No patient developed avascular necrosis of the head but one had signs of mild arthrosis of the joint.
At three months, patients could perform all activities except strenuous manual labour. At six months, patients returned to unrestricted full activity.

6.
Figure 6. Postoperative x-ray confirming the reduction of the gleno-humeral joint. Mitek anchors have been used for the subscapularis tendon transfer.

7.
Figure 7. Range of motion in a woman with a less than 3-months-old posterior dislocation of the right shoulder, six months after surgery.

8.
Figure 8. Range of motion in a man with a more than 3-months-old posterior dislocation of the right shoulder, six months after surgery.

DISCUSSION
Posterior glenohumeral dislocations may result in anteromedial head impression fractures referred as reverse Hill-Sachs defects. The bony defect can become a factor causing recurrent instability. When this occurs, operative management is often directed at correcting the anteromedial humeral head defect.
Chronic, missed, locked, posterior fracture-dislocations of the shoulder raise a difficult problem for treatment, especially in young patients. Surgical options depend on the etiology of the dislocation, the chronicity of the dislocation, the age of the patient, and the determination of the size of the humeral head defect. Therefore, preoperative planning is very important.
A careful assessment of the etiology of the posterior dislocation of the glenohumeral joint is of great importance. An underlying seizure disorder is often present1. This will require a neurologist's consultation in order to control seizures and avoid additional episodes during the postoperative period, and to identify any treatable etiology of the seizure disorder. Other causes of the posterior shoulder dislocation involve motor-vehicle accidents, alcohol-related injuries or electroshock[6].
Chronicity should also be assessed preoperatively. Firstly, will indicate the chance of achieving a successful closed reduction. Secondly, it will provide some indication of the difficulty of achieving an open reduction, and thirdly, it will indicate the status of the remaining articular cartilage. Checchia and co-authors, annualised the surgical outcome of fifty-six shoulders treated with several methods during a mean follow-up of three years. They found good and excellent results in those cases that were treated up to two years of the lesion and fair to poor results in those patients treated after two years of the lesion[2]. In our series, patients with posterior dislocation unreduced for a period less than three months had better results than those with a dislocation unreduced for a period more than three months.
The most important aspect of the examination is the determination of the size of the humeral head defect. The size of the defect, expressed as a percentage of the humeral head articular surface, is the key factor in determining treatment. It is calculated radiographically, including standard trauma series and axillary lateral view as well as the computed tomography. The size of the anteromedial defects can be quite variable. In chronic cases, the size of the defect is larger than in acute posterior dislocations that are reduced properly. This is due to two causes: first, multiple episodes of posterior dislocation, even if reduced properly, can result in a larger defect. Second, prolonged contact between the posterior glenoid and the humeral head, as occurs in chronic unreduced dislocations and the following physiotherapy to achieve range of motion when the diagnosis is missed, may result in defects that encompass a significant portion of the humeral head.
In acute dislocations, defects of less than 20% will not probably contribute to recurrent instability. However, in chronic dislocations, a defect of even this size may require subscapularis transfer at the time of open reduction. Defects of 20% to 45% are usually found in association with chronic dislocations. Following open reduction of these injuries, a subscapularis transfer (McLaughlin's procedure) or a lesser tuberosity transfer (modified McLaughlin's procedure) will be required to maintain stability. An alternative is the rotational osteotomy of the humerus for restoring the glenohumeral congruity. Keppler and co-authors, advocated the rotational osteotomy of the humerus in ten patients with locked posterior dislocation of the shoulder and a humeral head defect involving 20% to 40% of the articular surface. The final outcome was not very encouraging since six patients had good-excellent results, two patients had fair results and two patients demonstrated poor results[7]. The disadvantage of this technique compared to subscapularis transfer is the use of hardware.
In cases that the humeral head defect is greater than 45% of the articular surface or there is a significant deterioration of the remaining articular cartilage of the humeral head or the glenoid, prosthetic replacement is preferred. Cheng and co-workers advocated total shoulder arthroplasty of seven shoulders in five patients who had locked posterior dislocation of the glenohumeral joint[3]. They reported that the American Shoulder and Elbow Surgeons' Shoulder score improved significantly from 20.1 before surgery to 55.6 after surgery (p=0.018). Gerber and colleagues managed four patients with chronic locked posterior dislocation of the glenohumeral joint associated with a defect of the humeral head greater than 40% of the articular surface with reconstruction of the shape of the humeral head with use of an allogeneic segment of the femoral head[5]. Three patients demonstrated satisfactory results and restored stability for an average period of six years. The fourth patient developed secondary avascular necrosis of the remaining portion of the humeral head.
McLaughlin's procedure is defined as a transfer of the subscapularis tendon into an anteromedial humeral head defect that resulted from either an acute or a chronic posterior glenohumeral dislocation[9,10]. Modified McLaughlin procedure consists of a transfer of the lesser tuberosity with the subscapularis attached, into the anteromedial humeral head defect. McLaughlin technique is indicated in small humeral head defects, up to 25%, in which the soft tissue alone is sufficient to fill the defect. Modified McLaughlin technique, is indicated in larger defects, 25% to 45%, with the subscapularis attached adequately to fill the bony defect and prevent recurrent instability. Our technique of utilizing a small bone piece instead of the whole lesser trochanter has some advantages when compared to McLaughlin and modified McLaughlin technique. In comparison with the McLaughlin technique, the advantage is the use of the small bone, which is large enough to stabilize the sutures passed through the transferred tendon. In comparison with the modified McLaughlin technique, osteotomy of a larger amount of the lesser tuberosity may result in compromise of the most medial aspect of the bicipital groove causing mal-tracking and subluxation of the biceps tendon, necessitating tenodesis. The small amount of bone taken in our series prevents problems of biceps tendon subluxation that could result from disruption of the medial insertion of the transverse humeral ligament.
We conclude that in chronic locked posterior dislocations associated with an anteromedial defect between 20% and 40% of the articular surface, open reduction and subscapularis tendon transfer is the treatment of choice. McLaughlin's technique reliably decreases pain and significantly improves range of motion and level of function, restoring the stability of the glenohumeral joint. If extensive damage to the articular surfaces of the humerus and glenoid are observed, involving more than 40% of the articular surface, shoulder arthroplasty is indicated but the results are related to the integrity of the rotator cuff. In these cases, derotation osteotomy can be used as an alternative but the critical factor is the condition of the articular cartilage of the humeral head and the glenoid.

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