Introduction
Definition
The term multidirectional instability (MDI) was first described by Neer and Foster in their preliminary report in 1980, when they reported the results of open inferior capsular shift as a treatment for this condition. A few years later, they defined MDI as symptomatic subluxations or dislocations of the glenohumeral joint in three directions. On the basis of these studies, they concluded that patients with MDI had symptomatic laxity in anterior, posterior, and inferior directions. In 1998 Matsen et al. proposed the acronym AMBRI (Atraumatic, Multidirectional, Bilateral, good response to Rehabilitation, and sometimes requiring Inferior capsular shift) to describe this kind of instability. Although many years have passed, there is still confusion as to the definition of MDI. At present, Neer’s definition is most quoted, but other symptoms such as pathological capsular laxity, unidirectional instability with multidirectional laxity, or atraumatic laxity of anterior capsule and glenohumeral ligaments are also used to describe MDI , . Furthermore, many have traditionally equated laxity, a physical finding, with instability, a pathological condition, and thus comparative studies using strict definitions are lacking.
Classification
This lack of clarity also applies to shoulder instability classification. Even today, we do not have a generally accepted and approved system for assessing shoulder instability, thus complicating the classification of MDI. A number of new shoulder instability classification systems have been published, and typically MDI is considered to be one instability variant. , , However, there is still discrepancy in the use of the term “multidirectional” among the authors. In the United States, the International Classification of Diseases 9th Edition is considered to be the most frequently used system of instability classification, but its accuracy is still being questioned.
Etiology
The etiology and pathomechanism of MDI are still being studied and are not clearly defined. Most reports accept the presumption that this condition is multifactorial. , , In the most recent reports, connective tissue intrinsic pathophysiology is believed to play the primary role in the development of MDI. Bony anomalies are also reported as being contributory, but their contributions are less clearly defined. Some studies have reported changes in the glenoid shape and its version, , and others have reported the presence of chondrolabral lesions in patients with posteroinferior instability. , The redundancy of capsule, mainly inferiorly, is considered to be the principal pathology for MDI. Finally, dynamic stabilizers, including the rotator cuff and periscapular musculature in patients with MDI, have been reported to have aberrant firing patterns, producing atypical scapular kinematics and periscapular muscle aberrancies , that can be observed in electromyographic studies.
Diagnosis
The diagnostic workup for MDI can be very challenging. It is critical that one differentiates MDI from multidirectional laxity of the shoulder (MDL), which is also characterized by an excessive glenohumeral translation, but, unlike MDI, is asymptomatic. Chief complaints and clinical findings may differ widely among patients with MDI. Therefore the patient’s history and a very thorough clinical examination are essential for proper diagnosis and decision making. The most commonly reported problems are nonspecific pain during everyday activities and a feeling of muscle strength reduction. Patients may also complain of subluxation or dislocation incidents, but MDI more commonly presents itself as pain during shoulder function. Furthermore, most patients are unable to identify one particular traumatic event, as the onset is usually insidious and worsens with prolonged activity.
Joint laxity is a competitive advantage in many sports such as swimming and throwing events, but with prolonged use, the dynamic stabilizers of the shoulder can fatigue, moving an asymptomatic athlete with laxity to a symptomatic pathological laxity, leading to a diagnosis of MDI. , In athletes with MDL, care must be taken to ensure the dynamic stabilizers of the shoulder stay strong, to minimize this crossover from laxity to instability. Another key point in the diagnosis of MDI is to identify whether the instability is voluntary or not. The voluntary element of glenohumeral instability is rare, but the surgical treatment of these patients has a higher rate of failure, especially if they suffer from coexisting mental illness. , It is important that a distinction be made between voluntary instability that is “positional,” meaning patients can demonstrate the instability by moving their scapula and shoulder, from instability that is “volitional,” where the patient demonstrates this as a “party trick.” The former can often be corrected, whereas the latter is very difficult to treat surgically. The hallmark of MDI has traditionally been a symptomatic sulcus sign ( Fig. 28.1 ). This is a physical sign on examination which is significant for laxity, and if it reproduces the patient’s symptoms, it is consistent with instability.
Imaging Studies
Imaging can be a very helpful tool in recognizing some of the critical findings in MDI. Radiographs, the most frequently used tool, should be taken in three views (anteroposterior Grashey view, scapular Y, axillary) and may be helpful in revealing bony lesions, or glenoid morphological changes such as hypoplasia. To identify soft tissue alterations like capsular redundancy or labral lesions, magnetic resonance imaging or, if possible, magnetic resonance arthrography (MRA), is recommended. MRA allows a more accurate assessment of the extended capsule, glenohumeral joint volume, and glenohumeral ligaments by filling the joint with intraarticular contrast ( Fig. 28.2A‒C ). However, it is crucial to note that radiology findings are not specific for MDI and may be present in other conditions.
Preoperative Complications
Preoperative treatment complications can be defined as unsuccessful treatment outcomes based on incorrect diagnoses and a flawed decision-making process. One of the most typical mistakes is overlooking accompanying disorders. In the case of MDI, the most frequently misdiagnosed cases are conditions that may give a clinical presentation similar to MDI.
Generalized Joint Laxity
Generalized joint laxity, described as an increased range of joint motions, is a condition that should be given great attention owing to its high rate of coexistence with MDI. Moreover, differentiation between normal laxity and instability may be a great challenge, particularly because numerous patients with MDI have a symptomless contralateral shoulder, regardless of similar grade of laxity. It has been reported that 40% to 70% of MDI patients have generalized joint laxity. , In these patients, overstretched glenohumeral ligaments and joint capsule may predispose MDI development. Several methods have been described to diagnose generalized ligamentous laxity, although no single system of classification has emerged as the gold standard.
One of the most commonly used scales is the Beighton scale ( Table 28.1 ), which typically examines passive hyperextension of the metacarpophalangeal joint, thumb opposition to the forearm, and active elbow hyperextension and knee hyperextension. , Generalized laxity is said to be a main factor for worse results, including recurrent instability, in patients with traumatic onset of instability( Fig. 28.3 ).
| Characteristic | Score |
|---|---|
| Passive dorsiflexion of the little finger beyond 90 degrees | 1 point for each hand |
| Passive apposition of the thumb to the ipsilateral forearm | 1 point for each hand |
| Active hyperextension of the elbow beyond 10 degrees | 1 point for each hand |
| Active hyperextension of the knee beyond 10 degrees | 1 point for each hand |
| Forward flexion of the trunk with extended knees so that the palms of the hands rest flat on the floor | 1 point |
Scapular Dyskinesis
Another condition that should be considered is scapular dyskinesis (SD), which is described as a dysfunction of the scapula at both the static and dynamic level. , Many different factors can contribute to the occurrence of SD, including excessive thoracic kyphosis and increased cervical lordosis, muscle weakness, nerve injury, or rotator cuff injury. During examination, the visual observation of scapula position and motions should note both the static and dynamic positions of the scapula ( Fig. 28.4 ). Moreover, the scapular assistance test and scapular retraction test may be very helpful to assess any abnormalities in the function of the scapula. Failure to address these dynamic stabilizers is one of the main causes of failure to treat MDI. There are also some genetic disorders, such as Ehlers–Danlos syndrome , and facioscapulohumeral muscular dystrophy (FSHD), which may contribute to MDI. However, in 4% to 13% of cases, joint hypermobility is not associated with any inborn diseases. , Ehlers–Danlos syndrome is an autosomal recessive, inherited systemic connective tissue disorder. It has variable penetration, and so its clinical presentation is not always obvious. , Unrecognized connective tissue disorders correlate with worse outcomes after surgical stabilization ( Fig. 28.5 ).
Facioscapulohumeral Muscular Dystrophy
We should also consider FSHD, especially in patients reporting difficulties with over-shoulder–level activities. FSHD is a dominantly inherited dystrophy caused by deletion of D4X4 . Clinical presentation may broadly differ, but typically the earliest chief complaints are facial and shoulder weakness. In this case, family history is essential. , Identification of these confounders may have a profound effect on treatment approaches, patient counseling, and outcomes that must be considered in the optimal care of the patient with MDI.
Treatment Failure
The goal in the treatment of MDI is to reinstate the static and dynamic stability of the shoulder so that the patient will be able to do daily activities or participate in sports. Age, hand dominance, smoking, sport activity, psychiatric disease, and the patient’s expectations should be taken into account.
Conservative Treatment–Related Failure
Conservative treatment is a standard as primary care in MDI patients. It is based on rehabilitation with the aims of increasing dynamic stability and diminishing symptoms. Physiotherapy is generally prescribed for at least 6 months and concentrates on optimizing the dynamic stabilizers of the shoulder girdle, as well as patient education as to positions of risk and avoidance of activities that exacerbate their symptoms. Several studies have shown that nonsurgical therapy can be effective in between 30% and 80% of patients.
Surgical Treatment–Related Failure
Surgical treatment is recommended when conservative management fails. In such a setting, open and arthroscopic techniques may be considered. Before deciding on the surgical procedure type, a thorough assessment should be made as to the various contributions to each individual MDI case. This may require a soft tissue approach, a bony approach, or a combination of both.
Open Versus Arthroscopic Surgical Approach
Among open techniques, the open inferior capsular shift was one of the first to be described and is still commonly practiced. Arthroscopic techniques have been more recently introduced, with arthroscopic pancapsular plication as the most common technique. Reconstructive techniques, such as osteotomy of glenoid neck and labral augmentation, are far less frequent.
Open Surgery and Recurrent Instability
Open surgery has been the method of choice since Neer et al. described an open inferior capsular shift. Neer treated 40 shoulders (17 of them were followed for more than 2 years) and reported that, in one case, recurrent subluxation was observed within 7 months after operation. Since that time, several authors have also reported similar results to Neer. Four of these studies were performed in athletes ( Table 28.2 ).
| Authors | Follow-Up | Number of Treated Shoulders/ Cases | Postoperative Instability | |
|---|---|---|---|---|
| Open surgery | Neer and Foster | <2 yrs | 17 | 1/17 subluxating shoulder within 7 months |
| Pollock et al. | 5.1 yrs | 49 (36 patients-athletes) | 2/34 repaired through anterior approach began to subluxate anteroinferiorly 0/15 repaired through posterior approach had recurrent instability | |
| Cooper and Brems | 3.3 yrs | 43 | 4 shoulders developed recurrent symptomatic instability (1 patient with a postoperative history of injury) | |
| Lebar and Alexander | 2.3 yrs | 10 | 1 patient had recurrent instability and required further surgery | |
| Hamada et al. | 8.3 yrs | 34 (26 patients) | 9 shoulders had recurred instability (from 3 months to 3 years postoperative) | |
| Choi and Ogilvie-Harris | 3.5 yrs | 53 (47 patients-athletes) | 3/37 had anterior dislocation after anterior inferior capsular shift (1 anterior alone, 1 anterior and inferior, 1 in all three directions) 2/16 had dislocation after posterior inferior capsular shift (1 anteriorly and 1 posteriorly) | |
| Bak et al. | 4.5 yrs | 26 shoulders (25 patients-athletes) | 1 shoulder spontaneously redislocated and 1 had recurrent subluxation | |
| Vavken et al. | 7.5 yrs | 18 shoulders (15 patients) | 1 shoulder had recurrent instability | |
| Bigliani et al. | 4 yrs | 68 (63 patients-athletes) | 1 shoulder dislocated | |
| van Tankeren et al. | 3.3 yrs | 17 (17 patients) | 2 patients had recurrent dislocation 2 patients had subluxation |
Several modifications of open techniques have also been reported. Altchek et al. performed a modified Bankart operation in which a T-shaped incision was made in the anterior portion of the capsule, with advancement of the inferior flap superiorly and of the superior flap medially. His group consisted of 40 patients (42 shoulders) who had been injured during athletic activities and were followed for an average of 3 years. He reported four patients with episodes of postoperative instability.
Other results for the modified capsular shift were published by Marquardt et al. He treated 35 patients (38 shoulders) with T-plasty modification of an inferior capsular shift with suture anchors and reported an overall redislocation rate of 10.5% with a mean follow-up of 7.4 years.
Recurrent instability is the most commonly observed complication among open technique studies. The percentage of instability complications ranges from 1.5% to 26% of treated cases ( Table 28.2 ).
Arthroscopic Surgery
As arthroscopic techniques have developed, they have been also adopted for MDI patients. A number of papers have discussed the results of arthroscopic capsular plication or its modification. Duncan and Savoie described in 1993 results of 1 to 3 years’ follow-up after performing an arthroscopic modification of the inferior capsular shift. In terms of complications, they reported mild discomfort while swimming in one patient. Further studies have shown similar results and are included in Table 28.3 . Similar to open techniques, the most common complication of arthroscopic treatment is recurrent instability. This may be caused by oversight of accompanying lesions such as Bankart lesion or rotator cuff interval lesions. According to Schenk et al., in multidirectional instability a dysplastic glenoid, rotator cuff injury, interval injury, circumferential labral tearing, and generalized laxity contribute to high rates of recurrent instability.
| Author | Follow-Up | Number of Treated Shoulders/Cases | Postoperative Instability | |
|---|---|---|---|---|
| Arthroscopic surgery | Lyons et al. | 2.3 yrs | 27 shoulders (26 patients- athletes) | 1 patient with Ehlers–Danlos Syndrome type II developed instability |
| Duncan and Savoie | 1–3 yrs | 10 | – | |
| Baker et al. | 2.8 yrs | 43 shoulders (40 patients-athletes) | – | |
| Treacy et al. | 5 yrs | 25 (11 athletes in the group) | 3/25 had an episode of recurrent instability | |
| McIntyre et al. | 2.8 yrs | 19 (9 athletes in the group) | 1/19 had recurrent anterior subluxations | |
| Kim et al. | 4.3 yrs | 31 | 1/31 had recurrent instability | |
| Witney-Lagen et al. | 5.1 yrs | 50 | 1/50 had recurrent instability | |
| Ma et al. | 3 yrs | 23 | – | |
| Raynor et al. | 3.3 yrs | 45 shoulders (41 patients) | 7/41 experienced instability episodes postoperatively, and 3 of these underwent revision surgery | |
| Buess et al. | 2.3 yrs | 32 shoulders (31 patients) | 3/32 had symptoms of instability | |
| Voigt et al. | 3.3 yrs | 9 shoulders (8 athletes) | 3/8 patients experienced symptomatic reinstability and required reoperation | |
| Alpert et al. | 4.7 yrs | 13 | 2/13 patients had recurrent instability | |
| Hewitt et al. | 4.8 yrs | 43 shoulders (40 patients) | 3/40 patients had postoperative dislocation (all traumatic in nature) |
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