Multidirectional shoulder instability

Multidirectional shoulder instability is characterized by recurrent atraumatic instability of the glenohumeral joint due to a lax joint capsule.

Terminology

Also known as AMBRII - atraumatic, multidirectional, bilateral, responds to rehabilitation, inferior capsular shift, and interval closure .

Epidemiology

It is more common in young female patients less than 30 years of age.

Pathology 

Multidirectional instability is due to congenital laxity of the joint capsule. It is atraumatic and commonly bilateral. Poor coordination of the rotator cuff muscles contributes to the worsening of laxity. In some cases, it may have ​psychiatric cause with subjective symptoms that are not relieved by surgery. There is a positive family history in a minority of cases with genetic abnormal collagen production or cross-linking; e.g. Marfan or Ehlers-Danlos syndrome.

Radiographic features

Usually, there is no abnormality of the labrum, ligaments or tendons nor evidence of previous shoulder dislocation. However, gradually the longterm subluxation results in labral injury and rotator cuff impingement.

Some of the possible radiologic findings are:

• glenoid hypoplasia
• glenoid retroversion
• small labrum  
• generalized joint laxity 

Treatment and prognosis

Treatment is mainly rehabilitation; if surgery required then tightening of the inferior capsule and rotator interval may prove helpful.