The shoulder is designed for a great degree of motion in all planes. This mobility comes at the cost of stability as the shoulder is the most commonly dislocated joint in the body. Static (capsule, ligaments) and dynamic (muscles) stabilisers maintains stability and keep the humeral head centred in the glenoid.
Anterior displacement accounts for 97% of recurrent dislocations. Most often these are traumatic and occur when the arm is abducted, extended and externally rotated (throwing position). Posterior dislocations are more rare and occur with seizures, shock, and falls on a flexed, adducted arm (arm tucked in).
The patient’s history and a physical examination should try to illicit the following features:
1) History of trauma causing dislocation
2) First time vs. repeat dislocation
3) One shoulder or both?
4) Are there any other joints with significant laxity?
5) Can they voluntarily sublux?
6) Are there signs of laxity on physical exam?
- Is there mobility of the head of the humerus in the glenoid (load shift test)?
- Is there inferior displacement of the head of the humerus (sulcus sign)?
- Is there pain or sensation of subluxation with posterior forced when the arm is inabduction to 90 degrees with elbow in flexion to 90 (anterior apprehension test)?
A shoulder X-ray trauma series can show if there are bony defects to the glenoid (i.e. bony Bankart) or humeral head (Hill-Sachs). A MR arthrogram can show defects in the glenoid labrum.
Patients can be divided into two groups depending on features above.
1) TUBS (Traumatic, Unidirectional, Bankart, Surgery): As per the acronym there is often a defect that requires surgical management depending on the level of play and disability. A trial of immobilization and therapy can be a good first step, but there is a high rate of recurrent subluxation especially in the young athlete.
2) MDI (Muldirectional Instability) or AMBRI (Atraumatic, Multidirectional, Bilateral, Rehab, Inferior Capsular Shift Surgery if failed rehab): These are very common in young athletes. Think of these athletes as those with “loose ligaments”. Rehabilitation consists of strengthening of dynamic stabilizers (rotator cuff and periscapular musculature). These don’t tend to respond well to surgery, as it temporarily tightens those ligaments but they tend to “re-stretch”.
Article written by: David White, BSc, MSc, MD, CCFP