A discussion about the diagnosis and management of multidirectional instability (MDI) requires a review of the distinction between glenohumeral joint laxity and instability. Laxity is asymptomatic, passive translation of the humeral head as determined on clinical examination. Instability is a pathologic condition whereby pain or discomfort is attributable to excessive translation of the humeral head during active motion. These terms are not synonymous, as a patient may have laxity in more than one direction without any symptoms or experience symptoms (i.e., instability) only in one direction.

The concept of MDI was first described in 1980 by Neer and Foster (1). In this classic report, a cohort of patients with either failed surgery for instability or uncertainty in diagnosis was identified. All patients had pathologic inferior glenohumeral joint laxity combined with anterior or posterior instability, or both. These patients were treated successfully with an open inferior capsular shift, which eliminated capsular redundancy by selective capsular release and imbrication. Since this original report, there have been multiple permutations of the definition of MDI. Open and arthroscopic techniques have emerged that are designed to eliminate pathologic laxity of the glenohumeral joint without sacrificing motion. This chapter reviews our approach to the clinical evaluation and treatment of patients with MDI. To make the diagnosis of MDI, the patient must have symptomatic, involuntary subluxation, or dislocation in more than one direction.

The diagnosis and management of MDI is challenging. Part of the difficulty in diagnosing patients with MDI comes from the inconsistent definitions in the literature (2,3). Instability can be defined as subluxation or dislocation and voluntary or involuntary. Matsen popularized the acronyms TUBS (traumatic, unilateral, Bankart, surgery) and AMBRII (atraumatic, multidirectional, bilateral, rehabilitation, inferior capsular shift interval closure) to divide instability patterns into two groups (4). This segregation represents two ends of a spectrum of pathology, but it is evident that patients may experience characteristics of both of these patterns of instability. For example, a patient with multidirectional laxity may experience a traumatic anterior dislocation with a Bankart lesion.

The classification of MDI has also divided patients into groups based on whether they have voluntary or involuntary instability. It is essential to ascertain whether the patient can subluxate or dislocate his or her shoulder voluntarily. Voluntary dislocators may have a psychiatric disorder or secondary gain at the root of their instability. Habitual dislocators have instability episodes attributable to muscular imbalance. These patients often do poorly with surgical intervention. Positional dislocators are aware of activities or arm positions that will reproduce their symptoms, but will avoid these positions because the feeling is uncomfortable or painful. Involuntary subluxators are not able to reproduce their symptoms and may represent the best indication for surgical intervention if nonoperative treatment fails.

The diagnosis of MDI relies heavily upon a precise patient history and clinical examination. MDI patients are often athletic and may participate in sports that involve strenuous shoulder activity, such as swimming, gymnastics, weightlifting, or overhead sports. These patients may be aware of instability as a cause of their symptoms, or they may complain of pain or mechanical symptoms (grinding, popping, clicking) with activities. These symptoms are often experienced in the midrange positions of glenohumeral motion, such as those that occur with activities of daily living. We have seen patients who have pain anteriorly over the coracoid with secondary impingement, scapular dyskinesia, and pectoralis minor contracture, so-called SICK Scapula syndrome (5). The condition is bilateral in approximately 20% of cases, but symptoms in both shoulders may
not occur simultaneously. Thus, it is important to inquire about a history of similar symptoms in either shoulder in the past. The position of the shoulder at the time of symptom onset provides clues as to the pattern of instability that is present. Pain that occurs with the arm in a forward flexed, adducted, and internally rotated position (such as during push-ups, bench pressing, etc.) suggests posterior instability. Competitive athletes may not report pain with these maneuvers, but we have observed some patients who describe the affected arm lagging behind the well arm with bench pressing. Pain with the arm overhead is usually indicative of anterior pathology. Patients with inferior instability may notice pain or paresthesias when carrying heavy objects with the arm at the side, as the unstable shoulder allows downward traction on the brachial plexus.

The physical examination of the shoulder begins with a general cervical spine evaluation. Proper examination of the shoulder requires that the entire shoulder and periscapular muscles be exposed. We start our examination of the shoulder from the back, inspecting for any evidence of atrophy or asymmetry in scapular position and motion. Many patients will exhibit pseudowinging of the scapula or will have malpositioning of the scapula with a protracted appearance when viewed from posterior as they go through a full arc of motion. Active and passive ranges of motion are evaluated. Anterior and posterior load-shift tests determine laxity in their respective directions. They are graded as 1+, to glenoid rim; 2+, over glenoid rim with spontaneous reduction; 3+, glenohumeral dislocation requiring manipulation to reduce. To perform this test, the arm is abducted to 90 degrees and a gentle axial load is applied to center the humeral head within the glenoid. The scapula is stabilized and anterior and posterior translation is assessed. Anterior laxity becomes more apparent if and when the examiner attempts to translate the humeral head in an anterior-inferior direction. Provocative tests such as the apprehension-relocation tests also assess anterior instability. Posterior laxity is also evaluated by positioning the arm in forward flexion, adduction, and internal rotation and applying a force directed posteriorly. It is important to flex the arm enough so that the humeral head does not impinge against the spine of the scapula because this can mask posterior translation. Inferior instability is determined by the sulcus sign. With the arm at the patient’s side, downward traction is applied to the arm. In the presence of inferior capsular laxity, a dimple will form in the region between the humeral head and the lateral acromion. In a normal shoulder, this dimple disappears with maximal external rotation of the arm. A pathologic sulcus sign is one that does not diminish with humeral external rotation and signifies an incompetent rotator interval. The literature has shown a wide range of normal variants of shoulder laxity. It is not uncommon to be able to subluxate a shoulder over the glenoid rim, particularly with the examination under anesthesia. Thus, it is crucial that these clinical examination findings correlate with the patients’ symptoms. Lastly, the examiner should look for other signs of generalized ligamentous laxity. These include passive elbow hyperextension, thumb to forearm apposition, metacarpophalangeal joint extension beyond 90 degrees, and the ability to flex from the standing position and place the palms on the floor.

Plain radiographs should be inspected for evidence of bony defects in the glenoid or humeral head. In many instances for the patient with MDI, these studies are normal. If there is any suspicion for bone loss from the history, physical examination, or plain radiographs, then a CT scan will define the anatomy of these lesions best. Our current indications for CT scanning include a history of dislocation requiring reduction, recurrent dislocation, apprehension at low abduction angles, recurrent dislocation following minimal provocation (e.g., washing hair), and instability at low abduction angles (e.g., reaching in front of body). Magnetic resonance imaging with intra-articular gadolinium in a patient with MDI will show a capacious inferior capsular pouch. An abduction external rotation MRI will show laxity of the inferior glenohumeral ligament. Injuries to the glenoid labrum are less common in MDI than in cases of unidirectional instability.