What is Multi-Directional Instability (MDI)? The shoulder is a ball and socket joint (like the hip joint) that is designed for great mobility and poor stability (unlike the hip). The shoulder is one of the most mobile joints in the body and therefore the risk for dislocation is significantly increased. Dislocations occur of the gleno-humeral (ball-and-socket) joint of the shoulder. Dislocations can either be a complete dislocation or a partial dislocation which are referred to as subluxations. A dislocation commonly leads to shoulder instability with re-dislocations and/or subluxations occurring often. Patients with isolated shoulder ligamentous laxity or generalized ligamentous laxity throughout the body often have problems. Being born with shoulder laxity does not mean that an individual will have problems necessarily, but problems do occur when these individuals attempt to participate in sports at a level that causes overuse of the shoulder girdle muscles (rotator cuff and peri-scapular muscles). In most instances these muscles can overcome the inheritant laxity; however, when they become injured or fatigued this ability is lessened and pain, decreased functional ability, and subluxations may occur. This leads to a problem commonly referred to as multi-directional instability (MDI). The diagnosis of MDI comes down to the history and physical exam primarily. X-rays tend to be normal in most MDI cases and MRIs are rarely helpful. Causes Shoulder ligament laxity – inherited Repetitive overhead shoulder activity Signs & Symptoms Acute Aching pain Occasional popping and slipping with or without pain Chronic Recurrent popping or slipping Decreased production with sports Persistent aching Weak shoulder girdle muscles Treatment Initial treatment of MDI is directed towards the reduction in pain and inflammation. This can be assisted with physical therapy to maintain normal motion while directing the greatest effort towards strengthening the muscles around the shoulder blade. If this is successful in reducing pain and restoring normal function, then a gradual return to sport is warranted. If there is no improvement, or worsening of symptoms with rest and physical therapy, surgical stabilization of the shoulder may be necessary. If unresolved or untreated, MDI can lead to arthritic wear in the long term due to the chronic instability or “slipping” of the shoulder joint.