The shoulder joint is a ball and socket joint. View anatomy detail.
The ball is large in comparison to the socket which is small shallow and vertical. This anatomical arrangement gives the shoulder a fantastic range of movement allowing the person to position their hand. Unfortunately this is not a very stable design. A number of other structures other than the bones help to keep the shoulder joint in position.
Shoulder stability is governed by both static and dynamic factors.
- The ligaments and the joint capsule, which hold the bones together
- The glenoid labrum, which is a rim of cartilage around the edge of the socket that helps to deepen the socket.
- Muscles around the shoulder are vital in dynamically maintaining the correct position of the ball and socket when the arm is moving.
What are the symptoms of instability?
Shoulder dislocation is when all continuity between the ball and socket joint is lost. The shoulder may dislocate immediately after an injury, if so there is sudden severe shoulder pain, and the shoulder contour may look abnormal. Pain may refer down the arm and the arm can sometimes feel numb or tingly. These acute dislocations sometimes spontaneously reduce on their own but may require reduction by a professional for example at the local Hospital Emergency Department.
In patients with chronic instability the shoulder may recurrently dislocate or partially dislocate known as a subluxation. This may be felt as the shoulder slipping or sliding or as though it is about to come out of joint.
Are their different types of instability?
Shoulder instability is best described by probable cause of the instability.
The widely used classification developed by I. L. Bayley from the Royal National Orthopaedic Hospital can be helpful in understanding shoulder instability. This suggests that there are three different poles that characterize the different types of shoulder instability. Between these polar differences overlap of symptoms and aetiology can occur.
Traumatic Structural instability:
This is most commonly the result of an acute shoulder dislocation in the young athlete. A significant traumatic event occurs to the shoulder such as in a rugby or football tackle, or in fall skiing. The shoulder ball most commonly dislocates anteriorly, and subsequent recrrent anterior instability symptoms occur because there has been a traumatic injury to the structure of the shoulder joint. This structural damage is most commonly in the form of damage to the glenoid labrum, (Bankart lesion) and to the back of the humeral head (Hill Sachs lesion).
Atruamatic Non Structural instability:
This is most commonly seen in the young patient who gradually develops progressive shoulder instability. The shoulder may dislocate or sublux in a number of directions. No structural abnormality can be found in the shoulder and the cause of instability is due to poor coordination of the muscles around the shoulder “muscle patterning”. This often best treated with specialist physiotherapy and surgery is very rarely indicated.
Atraumatic Structural instability:
This again is common in the younger patient who has no clear history of trauma and develops progressive instability, the underlying cause is most commonly a muscle patterning problem but a structural abnormality in the shoulder may develop due to the recurrent instability.
Laxity does not mean that a shoulder will be unstable! Some patients have lax or loose joints. Patients with joint laxity may not have any symptoms at all.
What investigations may be done?
X Rays of the shoulder are frequently performed to assess the bony anatomy of the shoulder. MRI scanning and in particular MRI Arthrography when some dye is placed in the joint just before the MRI scan can be very helpful at identifying structural abnormalites within the shoulder.
What are the treatment options?
The treatment depends a great deal on the symptoms and cause of the shoulder instability. There are both non operative and operative treatment options. Most patients respond well to physiotherapy especially in the muscle patterning group of patients, surgery is only very rarely indicated in this group.
Stabilisation surgery is most frequently offered to the group of patients with recurrent traumatic structural instability.
The aim of this surgery is to repair the damaged structures in the shoulder in order to improve the symptoms of instability. The exact type of surgery will be discussed in detail with you but is most frequently in the form of either an arthroscopic key hole or open anterior stabilization of the shoulder. (link to about your operation)
We follow the British Elbow and Shoulder Society and British Orthopaedic Association Pathway for the management of traumatic anterior instability of the shoulder (link to article)