In recent years, the number of young athletes engaged in sport focused and year round training has continued to increase. Overhead sports, such as swimming, throwing, and racquet sports place significant demands on the shoulder and can lead to MDI, or multidirectional shoulder instability. This is especially prevalent in young athletes, where developing anatomy and characteristic soft tissue laxity both contribute to the risk of instability.
MDI was described by Neer and Foster in 1980 and is characterized as involuntary subluxation in any combination of anterior, inferior, and posterior directions. The etiology of MDI may be due to a number of factors, including repetitive overhead activites, traumatic and recurrent dislocations, ligamentous laxity, muscular imbalance and weakness, or scapulothoracic dyskinesia. Most often, repetitive overhead activities, such as the wide extreme motions in swimming, cause micro-damage to the static stabilizers of the shoulder, leading to MDI. This is differentiated from acute, traumatic shoulder dislocations which have a extremely high recurrence rate in immature patients. Glenohumeral joint stability is supported by bony anatomy, the joint capsule, labrum, glenohumeral ligaments, long head of the biceps, the rotator cuff, and periscapular muscles.
Patients with multidirectional instability often complain of vague pain and are able to describe positions of apprehension or subluxation. They may note numbness or tingling in the affected arm reproduced with certain activities, such as carry a heavy load or sport specific motions, such as a butterfly stroke. MDI can occur bilaterally, and both shoulders of athletes should always be examined for comparison. Up to 75% of MDI patients have generalized ligamentous laxity that is noted with signs such as hyperextension of the elbows and knees, hyperextension of the MCP joints, and the ability to abduct the thumb to forearm. A careful history and focused, specific physical exam are essential to make the correct diagnosis and determine the most effective treatment.
The majority of atraumatic MDI can be treated non-operatively. Emphasis is placed on initial pain control and moves to activity modification and rehabilitation. A well coordinated physical therapy program consisting of shoulder proprioception, rotator cuff and periscapular strengthening, and scapulothoracic synchrony is critical to return an MDI athlete back to their sport with shoulder stability and confidence.
If an athlete with MDI fails 6 months of non-operative management or has more severe instability affecting daily activities, surgical management may become necessary to attain the level of shoulder stability necessary for sport.