Instability has two distinct origins. A traumatic instability due to joint laxity is common in the younger age group without a history of trauma. This is associated with being ‘double-jointed’ and can be associated with other areas of instability such as the knee cap dislocating. Whilst surgery can be undertaken for this problem it is best treated conservatively with specialised physiotherapy which rebalances muscle strength.
Traumatic instability, as the name suggests, comes following a traumatic event where the shoulder dislocates or partially dislocates (subluxes). It can de defined by the direction in which the shoulder moves out of the joint. The most common is an anterior dislocation. As the shoulder comes out of the joint the cup (glenoid) becomes damaged at the edge (a Bankart lesion) stretching the lining of the joint (the capsule). If the head of the humerus is formally dislocated it sits on the edge of the cup and an indentation in the head is formed (the Hill-Sachs lesion). The opposite occurs if the dislocation is posterior i.e. backwards. If the shoulder dislocates upwards (superiorly) it damages the upper part of the cup and biceps tendon (a SLAP lesion). Varying degrees of these injuries produce the symptoms of the joint coming out of place (instability).
Diagram of Bankart and Hill-Sachs lesion
Once the joint is reduced the hallmark of treatment is physiotherapy to strengthen the muscles surrounding the joint. This is sometimes sufficient to give stability back to the joint. Of course this stability is very dependant on what is expected of the joint related to activities and hobbies.
The progress following a dislocation is best monitored by physical examination. We often leave scans for a little while as this is best done by injecting dye into the joint and this requires the soft tissues to heal. When you are reviewed it will be apparent how unstable the joint is and you will see any progress of this improving stability on serial examinations.
Diagram of Anterior Apprehension Testing
The imaging will quantify the amount of damage and its exact location, which will help plan surgery if this is required. The risk of recurrence is higher in younger patients, in particular if they undertake contact sports. It will also show other lesions such as a SLAP lesion. The latter is often predictable from the mechanism and by persisting instability which is typically painful.
Diagram of MRI of Bankart lesion and Hill-Sachs lesion
There is enough evidence to show that resting in a sling from a first time dislocation does not reduce the risk of dislocation later on. There was a vogue for doing acute arthroscopic procedures but in general it is better to allow things to settle down, rehabilitate and monitor instability over time. We will discuss your progress and plan a sensible approach to treatment. It is not unreasonable after a first-time dislocation to go back to sporting activities and see if instability persists. We must always remember that a further significant event will dislocate even a reconstructed shoulder.
If surgery is required the mainstay now is to undertake arthroscopic repair. This is a day case procedure under a general anaesthetic. but requires quite extensive rehabilitation. You are usually in a sling for 4 to 6 weeks. Following this it is hard work with your physiotherapist for a further 3 to 4 months. We do not allow contact sports for six months. The surgery effectively removes the movement of apprehension. This is something that can be predicted pre-surgery when you are examined. There are some small risks of infection and clots. Sometimes a frozen shoulder can occur. The success rate is in the order of 80 to 90% depending on functional levels required and the sports you undertake.
More involved procedure involving bony blocks are sometime required but only rarely. Open procedures are often reserved for failed arthroscopic procedures.
Diagram of Arthroscopic image of a Bankart repair