Shoulder Instability

Shoulder instability is the perceived or true loss of the glenohumeral joint congruity. This is commonly a shoulder dislocation. 

In some settings this includes shoulder subluxation, positional instability or severe muscle imbalance leading to lack of normal shoulder function. 

This is a separate issue from arthroplasty related instability

The pathology is varied for instability of the shoulder. The shoulder will dislocate when the forces to sublux or dislocate the joint are larger than the restraining forces. The dislocation forces can be normal muscle tone, abnormal muscle tone or activation or hyper-physiologic forces (as in some sports or accidents). The restraining forces are combined with bony anatomy, labrum (cartilage that supports shoulder joint) capsule and ligaments, muscle tone, shoulder positioning and the force/load  being carried.

This approach allows the breakdown to look at tailoring treatment to the pathology in question, but most often, treating multiple areas at once is employed,

Mutlple causes of shoulder instability.

Traumatic:

• traumatic anterior dislocation - sports, rugby, accidents
• Posterior dislocations - often seizures or electrical shock related.

Non traumatic:

• ligamentous laxity, such as Downs Syndrome, Ehlers Danlos and other generalised ligamentous laxity syndromes
• Glenoid or humeral abnormalities - such as glenoid growth arrest/ dysplasias
• Severe muscle imbalance - weak or increased tone - cerebral palsy, paralysis, child hood brachial plexus injuries.
• Voluntary or habitual shoulder dislocations

Common complications of ongoing shoulder instability are pain, lack of function, possible brachial plexus (nerves from spine to supply the arm) palsy and arthritis.

The main goal of treatment is to improve the stability of the shoulder to slow the progression of arthritis and prevent ongoing dislocations, whilst allowing to function at your desired level.

Management is tailored to each individual, their pathology, their treatment thus far, their goals and the extent of their condition.

Dr Drynan uses the well known French designed shoulder Instability Severity Index Score (ISIS) to assist in managing patients. Combining this with Hovelius et al classic 1982 paper estimating the natural history of shoulder instability for age, examination findings, investigation results and patient goals a targeted treatment can arranged.

Initial treatment from a traumatic shoulder dislocation is to be reduced, placed in a sling for no longer than 3 weeks. The patient would benefit from a medical review at that stage, ensure no plexus injury, no associated fracture, and over all stability assessment, then physiotherapy initiation.

Physiotherapy is recommended for shoulder instability. As the whole proximal girdle is included in shoulder positioning, and a risk factor for instability, assisting in muscle balance about the shoulder to enhance the stabilising forces and reduce the dislocation forces. Dr Drynan routinely refer  stabilisation patients to physiotherapy.

Surgery:

Surgical options include reattaching the labrum (cartilage rim) to the glenoid, tightening the capsule and ligaments to stabilise the shoulder, reattaching capsule to the humerus, moving part of the rotator cuff muscles to stop the shoulder dislocating, placing a bone block on the glenoid at the area the shoulder is dislocating to improve stability. In the elderly and severe recurrent setting other options exist.

The outcomes for shoulder instability are varied as the operations, pathology, rehabilitation and recovery vary. Pooled results from a systematic review of literature published 2017, showed the Latarjet procedure (moving a piece of bone to the glenoid) has a 2.7% chance of re-dislocation, and a Bankart repair (placing the labrum back to the glenoid) has a 15% change of re-dislocation. These results are to be interpreted with your condition, options available to you and your goals for treatment, Dr Drynan will go through this with you.

Regarding arthritis prevention, the best prevention is to decrease the number of dislocations or re-dislocations. There are similar radiographic outcomes following both procedures.