Shoulder Instability

The shoulder is the commonest large joint in the body to dislocate. It occurs most frequently in young people and is more common in males than females.

There are a number of factors which contribute to the stability of the shoulder. The bony socket of the shoulder (glenoid) which is part of the shoulder blade (scapula) is very shallow and the head or ball of the arm bone (humeral head) is large in comparison to the size of the socket. These features allow the joint to have a large range of movement but make it unstable as the head is not ‘contained’ within the socket due to its shallowness. To provide stability, the socket is deepened by a ring of soft tissue cartilage around the rim of the socket, called the labrum which is like the rim of a saucer or shallow dish. The capsule or lining of the joint is thickened in areas forming specific ligaments which act as ‘check reins’ to prevent excessive movement when the shoulder is in certain different positions.

If the ball of the shoulder displaces completely out of the socket so that there is no contact between the two surfaces this is known as a dislocation. If the ball partially displaces out of the socket but there is still some contact this is known as a subluxation. When there is a tendency for the shoulder to dislocate or subluxate on more than one occasion this is known as recurrent instability.

If any of these structures are “torn” for example following a tackle or fall playing sport the shoulder can become unstable. This is known as “traumatic instability”. In addition the muscles of the shoulder act as the most important “dynamic” stabiliser of the shoulder and work in a specific fashion to co-ordinate shoulder movements whilst maintaining the position of the humeral head on the centre of the glenoid socket . If this pattern of movement is ‘upset’ then again the shoulder can become unstable and this is known as “atraumatic instability” as this is not caused by any specific injury or traumatic event.  It is possible to have instability that is a spectrum of combination of the two types. 

Traumatic Instability

This is where the shoulder dislocates following a traumatic incident e.g. a fall or tackle playing sport. It usually dislocates with the arm stretched backwards and outwards similar to the position of a driver reaching for their seat belt. It usually dislocates out of the front of the shoulder (anteriorly) and rarely out of the back (posteriorly).

When a traumatic force is applied to the shoulder causing it to dislocate the labrum will be torn off the front of the socket (glenoid) and the ligaments can lose their tension and therefore not function correctly. Occasionally the capsule of the shoulder joint can also detach from the undersurface of the humeral head. The dislocation generally has to be reduced under sedation in an A & E department. In approximately 2/3rds of patients when the shoulder is relocated the rim or labrum does not reattach to the correct position on the front of the bony socket so that a structural defect then exists which leaves the shoulder at risk of re-dislocating. This structural defect is called a ‘Bankart lesion’, named after the surgeon who first described it.

In young patients it is common to suffer repeated dislocations of the shoulder. A further dislocation occurs in up to 90% of patients under 30 years of age and can have a significant impact on the ability to return to pre-injury sporting activities. Patients who plan to return to contact sports, who are young (<30years) or participate in sports involving forced overhead activity are at the highest risk of further dislocation. If patients have surgery to stabilise their shoulder then the risk of further dislocation is reduced significantly to approximately 10%. Recent studies have also shown that patient satisfaction rates and return to pre-injury sporting level are higher if the shoulder is stabilised with an operation. However, one must weigh this up against the risks of having an operation, undergoing the post-operative rehabilitation and having time off work and sport following surgery.

Occasionally, when the shoulder dislocates it not only detaches the labrum from the glenoid but also knocks a segment of bone off the front of the socket which is known as a ‘bony Bankart lesion’. This makes the socket narrower and the shoulder even more likely to dislocate in the future when the patient returns to their normal activities.

If the patient is at high risk of dislocating again and wishes to consider surgery then there are a number of options. If only the soft tissue around the socket, ie the labrum, is damaged then a keyhole (arthroscopic) repair can be performed (see Arthroscopic Stabilisation). If there is a significant amount of bone loss from the glenoid then it is more advisable to perform a Laterjet procedure (see Laterjet Operation) whereby part of the shoulder blade known as the coracoid bone is detached and inserted on to the front of the socket to replace the lost bone area at the front of the socket. A tendon called the Conjoint tendon is left attached to the coracoid bone block and this further aids the stability of the joint by acting as a sling at the front the shoulder to prevent further dislocation.  

Treatment after first time dislocation

Once a patient has had their shoulder relocated back into the socket then they are given a sling to rest the shoulder for a period of time. My recommendation is to use the sling for comfort and when the patient feels able to gently start moving their shoulder then they can do so. I do not recommend that a patient keeps there arm in a sling for a number of weeks and I think it is preferable to start gentle mobilisation exercises under the supervision of a physiotherapist. Once the patient has regained a full range of movement in the shoulder and the same strength as the other side then the patient can try to return to their normal recreational activities. It will take several weeks before patients are able to attempt this.

If the patient wishes to discuss reducing the chance of the shoulder dislocating again then an appointment to discuss the available treatment options is recommended.

Atraumatic Instability

This is where the shoulder dislocates or more commonly subluxates (partial dislocation) with minimal force. It is most common in young female patients. There are a number of factors that contribute to this condition including joint laxity and loss of the normal synchronised pattern of movement of the muscles around the shoulder joint. People that have 'lax' joints, can often hyper-extend their knees and elbows and can get the palms of both hands onto the floor with their legs straight with ease. Whilst this joint laxity is normal for these people and something they have always had, the instability often arises when there is a change in how the muscles around the shoulder are interacting with each other or a change in posture/ position of the arm. Often the arm will subluxate out of the joint simply by lifting the arm above shoulder height and it is far more common for the shoulder to subluxate out of the back of the socket (posterior instability) than in traumatic instability. This is because the strong muscles around the shoulder joint are not working in the correct order causing them to pull the shoulder out of joint with active movement in a particular direction.

The main treatment for this is physiotherapy although the physiotherapist will need to be specialised in treating patients with this condition (we can give recommendations). The physiotherapist will look at the way in which the muscles and shoulder joint are moving as well as the patient’s posture. The phsyiotherapist will aim to train the patient to re-sequence the muscles in order to prevent further dislocations. The patient has to be motivated and willing to undergo this treatment which takes several months. The treatment can be very frustrating in the early stages as it takes lots of patience and application to reactivate these muscles which may have been ‘dormant’ for many months or even years.

There is virtually no place for surgery to treat this condition and surgery should not automatically be considered an alternative solution if physiotherapy fails!