19.1 Introduction

Multidirectional instability (MDI) of the shoulder is a diagnosis that continues to defy specific or standardized criteria. Neer and Foster first coined the term and they are widely recognized for bringing it widespread clinical attention. In 1980, they defined MDI as anterior and posterior instability associated with involuntary inferior subluxation or dislocation. ¹ Others then described it as instability in two or three directions. ² And, shortly thereafter, Matsen divided shoulder instability into two subtypes: (1) traumatic and unidirectional, containing a Bankart lesion and which is treated surgically (TUBS) and (2) atraumatic, multidirectional, and bilateral, which responds to rehabilitation but may require an inferior capsular shift for surgical treatment (AMBRI). ³ These categories are helpful for general classification, but it is important not to over-simplify and thus potentially underdiagnose multidirectional shoulder instability. For example, patients with true MDI commonly present with only unilateral symptoms, may only present following a traumatic event to the shoulder, and some do have intra-articular lesions. Such discrepancies in definition make determination of its true prevalence and comparison of clinical and research studies difficult. ⁴

The etiology of MDI is multifactorial, and theories focus on anatomic, biochemical, and neuromuscular abnormalities and their interplay. The characteristic pathologic entity of MDI is increased capsular redundancy. It may be acquired, or be due to a systemic disease, such as Ehlers–Danlos, osteogenesis imperfecta, Marfan’s syndrome, facioscapulohumeral dystrophy, or benign hypermobility syndrome. The capsular tissue of shoulders with MDI has qualitative and quantitative differences in the collagen when compared with controls. However, as the majority of patients with MDI do not have symptoms from birth, a component of MDI must be developed. Excessive capsular volume alone is not significant enough to cause symptoms. Acquired capsular laxity and symptomatic instability may be due to several pathologic pathways. Repeated minor injuries to the joint capsule, repetitive microtrauma during sport-specific activities, particularly overhead throwing, or work, can develop into global laxity and symptomatic instability in more than one direction, with or without labral injury. Alternatively, an isolated macrotrauma event can cause a significant circumferential injury to the capsulolabral complex, supportive structures, resulting in symptoms; this single event can be relatively minor but a “tipping point” in patients with baseline hyperlaxity.

Historically, treatment for MDI included a prolonged course of physical therapy, and, if patients failed, open inferior capsular shift. However, arthroscopic procedures are increasingly widespread and show comparable results to open procedures. Given the varied presentations of patients with MDI, from macrotrauma to repetitive microtrauma or minor injury accumulation to hyperlaxity with atraumatic but pathologic instability, it is necessary for surgeons to best identify patients who may benefit from arthroscopic interventions.

19.2 Clinical Presentation and History

Patients with MDI commonly present with complaints of vague pain without specific onset, and more rarely of instability. Patients may report degrees of painful “loose” shoulders, including the sensation of popping, clicking, grinding, pain with throwing, lifting overhead, or sleeping. In patients who present with painful or symptomatic hyperlaxity, the amount of laxity is not usually significantly different from their contralateral side; differentiating between normal laxity and instability can be intricate and requires a high level of clinical suspicion.

Cofield and Irving presented four questions to address in the workup of MDI: (1) What is the relationship to trauma? (2) Does the patient intentionally cause the instability? (3) What is the degree of instability? (4) What is the direction of instability? A single traumatic event can be responsible for tipping a patient with hyperlaxity into symptomatic instability. ⁵ This is particularly true if one includes repetitive use or other loss of the dynamic stabilizers in the definition of a “trauma.” ⁶ Patients younger than 40 years with history of failed surgery for unidirectional instability should be reevaluated for MDI. ²

Specific complaints can help provide clues as to the direction of symptomatic instability and begin to direct treatment options. Inferior instability can cause pain, numbness, and tingling, elicited particularly with carrying heavy objects; these are secondary to traction on the brachial plexus. Anterior instability causes symptoms in the classic position of abduction and external rotation. Posterior instability evokes symptoms with posterior loading with the humerus in flexion and internal rotation, such as football blocking, bench pressing, or simply pushing open a door.

The ability to voluntarily dislocate by selective muscle contraction has been associated with emotional disorders, secondary gain, and surgical failure. In contrast, patients with voluntary dislocation and underlying involuntary instability who can reproduce their symptoms but choose to avoid provocative positions generally respond well to surgical stabilization. A third category of voluntary instability consists of patients who experience instability with an unconscious or behavioral ticlike muscle spasm, which is best treated with biofeedback techniques.

A full medical and family history should include questions regarding other examples of ligamentous laxity, such as frequent ankle sprains or patellar dislocations or family members with similar complaints or diagnosis of a collagen disorder.

19.3 Physical Examination

The physical examination is the most important tool for making a diagnosis of MDI. A complete examination of the joint’s static and dynamic stabilizers starts with inspection of the shoulder musculature and evaluation of scapular kinematics. Any atrophy, scapular winging, or dyskinesia, particularly during symptomatic motions, is important to note. Deltoid and rotator cuff strength are assessed.

Patients with MDI have generalized ligamentous laxity in up to 75% of cases. ¹ Historically, the Beighton scale has been used to evaluate joint hyperlaxity. Knee, elbow, thumb, and metacarpophalangeal hyperextension on each side and the patient’s ability to place their hands on the floor while standing with straight knees are evaluated. Further evidence of a collagen disorder includes skin hyperelasticity, scarring in skin folds, keloid formation, and scar widening. At times, their shoulder complaints may be the initial presentation of a patient’s underlying systemic disorder. It is necessary to recognize a collagen disorder, as they are strongly associated with poor results following surgical stabilization.

The sulcus sign has been considered the sine qua non of MDI since its original description by Neer and Foster. ¹ The sulcus is a skin dimple that appears distal to the lateral acromion when caudal traction is applied to the arm in abduction and adduction, and its persistence with both internal and external rotation. Inferior humeral head displacement greater than 2 cm from the acromion is thought to be evidence of considerable laxity. A sulcus that persists in adduction-external rotation suggests rotator interval insufficiency, and one in abduction with internal or external rotation indicates inferior laxity. ^{1 , 2} Of course, this finding is only abnormal if it reproduces the patient’s symptoms. ^{2 , 3}

Provocative testing for symptomatic instability in specific directions is essential. The load-and-shift test can assess anterior or posterior instability. For inferior instability, Gagey and Gagey’s hyperabduction test can be useful. ⁷ Laxity of the inferior glenohumeral ligament is indicated by passive abduction past 105 degrees; normal controls had a mean passive abduction of ≤ 90 degrees. As is true with all MDI testings, only positions provoking symptoms are truly positive findings. A positive sulcus sign and load-and-shift test have shown a high positive predictive value for MDI. Testing that produces apprehension has been shown to be more reliable in confirming true instability than the production of pain.