Dr Graeme MacDougal

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Shoulder Instability

The term shoulder instability refers to a condition where the shoulder joint (the glenohumeral joint) has a tendency to ”sublux” or dislocate.

The pathology is more commonly seen in the younger age group and is often seen as a result of sporting or traumatic injuries.
SLAP and labral tear

Combined SLAP and anterior labral tear

SLAP repair

Completed SLAP repair


The glenohumeral joint or true shoulder joint is a ball and socket joint, the humeral head (or ball) being significantly larger than the socket, which is a relatively flat, plate shape.

The 2 surfaces by themselves are not very stable.

The stability of the glenohumeral joint is increased by a circular material called labrum which elevates the edge of the socket to a more saucer shape, which fits the diameter of the humeral head (ball). It essentially doubles the depth of the socket.

In addition the capsule of the joint has thickenings called the capsulolabral ligaments, and these ligaments run between the humerus and the labrum.

The capsular ligaments are not particularly strong but contain a large number of stretch receptors, which during shoulder movement send messages to the local muscles initiating reflex muscle action. Also messages are sent to the central nervous system (the brain) for coordination of biomechanical actions such as throwing and swimming, which require high level joint position sense. The labrum and the capsular ligaments are called “static stabilisers”.

Dynamic control of the shoulder glenohumeral joint is by the local muscles, in particular the rotator cuff, and also the muscles attaching to the shoulder blade (scapula). This muscle coordination for particular actions occurs in a coordinated fashion.


With any dislocation, which can occur in the anterior (front), posterior (back) or inferior (below), occurs when the joint comes out of normal position, i.e. the humeral head comes out of alignment with the socket.

When this is a brief event we often term this “subluxation” however if a “dislocation” occurs and is not able to go back into position or “reduce”, admission to a casualty unit is a common scenario.

The term “instability” includes both subluxation and dislocation, and commonly the symptoms are related to pain, a feeling of giving way, dead arm or you may just feel apprehensive about placing your arm during the throwing action or catching, or reaching or swimming.


Each individual person has a degree of flexibility in the building blocks of the soft tissues called collagen.

Some people will have a very stretchy collagen are termed “ligamentously lax”. They may be prone to dislocation in all different directions or a combination of directions, and this is called “multidirectional instability”.

The majority of patients do not suffer from this condition and the dislocation episodes that occur (most commonly anterior), are usually related to traumatic events.

Tearing or displacement of the capsule and labrum often results in a loss of joint position sense and loss of tension in the capsule, and leads to recurrent instability events, and indeed in patients under 25 years of age this may be in the order of 80% chance of recurrence with contact sports.

When a piece of bone is shaved off the front of the glenoid (socket on the scapula), this piece of bone may be referred to as a “bony bankart” and as the piece gets larger it may also be referred to as a “glenoid fracture”. These particular injuries are extremely likely to cause recurrent instability if not corrected, and usually require surgical intervention.

When the humeral head dislocates across the front of the glenoid it is common for a compression fracture to occur at the back of the head of the humerus, and this is called a “Hill-Sachs lesion”.

This will be commonly seen on X-ray reports.


As with all orthopaedic pathologies, a thorough history, clinical examination and radiological imaging including X-rays, CT plus or minus MRI are used to confirm the diagnosis and direction of instability episodes. It is important for the surgeon or treating physician to identify the most important facets of the individual’s instability and pattern.

It should be noted that as patients who dislocate their shoulders get older, the incidence of rotator cuff tear increases, and this pathology needs to be excluded with both clinical and radiological investigations.

A rotator cuff tear cannot be diagnosed on a plain x-ray.

It is recommended that any patient over 50 years of age at a minimum have an ultrasound or better still an MRI following a shoulder dislocation to exclude the possibility of rotator cuff pathology.


Treatment for shoulder instability includes initial rehabilitation and after collection of all relevant data, a decision should be made on what is appropriate for the individual patient in the long term.

For younger patients who do not play a lot of sports a rehabilitation programme may be satisfactory, but in those who are actively involved in sports, particularly throwing sports or those sports likely to induce contact trauma, it is probable that recurrent episodes of instability will occur.

This is problematic as the more frequently the shoulder is dislocated the more likely one is to get bony changes, increased ligamentous laxity and labral displacement with a deformation of the joint cartilage surface. This can lead to arthritis in the longer term.

With the advent of arthroscopic procedures the tendency towards early intervention for shoulder instability should be considered.

Arthroscopy for the majority of soft tissue injuries (capsulolabral injury) can restore the normal anatomy and tension in the joint and prevent shoulder dislocation in 90% of patients.

Those conditions where small bony bankart lesions are present may be treated arthroscopically and those who have larger bone lesions, particularly if from recurrent and multiple episodes of instability, may need to consider augmenting the front of the glenoid with a bone grafting procedure, or an acute internal fixation of the fracture.

The selection of appropriate treatment for your individual condition requires a thorough and accurate assessment by a trained practitioner.


Shoulder instability is a common condition in the active sports population which requires a thorough and early assessment when it occurs.

The best options for management of shoulder instability patterns can be discussed with your treating practitioner.

Should non-operative treatments not prevent recurrent dislocation, surgical intervention has a high success rate in preventing re-dislocation.
  Any surgical or invasive procedure carries risks. Should you wish to discuss your shoulder instability with Dr MacDougal, please make an appointment to do so in order that your individual treatment needs can be prescribed for your particular situation.

Graeme MacDougal Shoulder and Elbow Surgeon