Multidirectional Shoulder Instability (MDI)

Understanding Multidirectional Shoulder Instability (MDI)

In multidirectional instability (MDI), the shoulder is loose in more than one direction, typically forward, backward and downward. Unlike most dislocations, MDI usually develops without a single major injury. The capsule, the envelope of ligaments around the joint, is larger and looser than normal, often in people with generally flexible joints or after repetitive overhead sports such as swimming, gymnastics and volleyball ^[1].

Patients describe pain, fatigue, a sense that the shoulder is loose or "slips out," and sometimes numbness or tingling down the arm with certain positions. Symptoms often affect both shoulders.

Rehabilitation is the foundation of treatment: a structured program to strengthen the rotator cuff and shoulder blade muscles and improve control of the joint helps most patients ^{[1, 2]}. When instability continues despite a dedicated program, surgery tightens the capsule on all sides. The inferior capsular shift described by Neer and Foster reduces the redundant capsule and remains the basis for today's open and arthroscopic capsular plication techniques ^{[1, 2]}.

Causes & Risk Factors

• A naturally loose (redundant) joint capsule
• Generalized joint hypermobility
• Repetitive overhead sports such as swimming, gymnastics and volleyball
• Weakness or poor control of the rotator cuff and shoulder blade muscles

Symptoms

Common signs and symptoms of Multidirectional Instability include:

• Pain and fatigue with overhead or carrying activities
• A feeling that the shoulder is loose or slips out
• Clicking or clunking
• Numbness or tingling down the arm in certain positions
• Symptoms in both shoulders

Treatment Options

Treatment for Multidirectional Instability depends on the severity of your condition and may include:

• A structured rehabilitation program (the first and most important treatment)
• Activity modification
• Arthroscopic capsular plication
• Open inferior capsular shift

References

1. Neer CS 2nd, Foster CR. Inferior capsular shift for involuntary inferior and multidirectional instability of the shoulder. A preliminary report. J Bone Joint Surg Am. 1980;62(6):897-908. pubmed.ncbi.nlm.nih.gov/7430177/
2. Gaskill TR, Taylor DC, Millett PJ. Management of multidirectional instability of the shoulder. J Am Acad Orthop Surg. 2011;19(12):758-67. doi.org/10.5435/00124635-201112000-00006