The shoulder is a ball and socket joint. A dislocation is when the ball comes out of the socket.
The ball (the head of the humerus) is relatively large compared to its socket (the glenoid – part of the shoulder blade). The ball and socket have been compared to a golf ball sitting on a tee in that there is little inherent stability from the bony structures. The shoulder relies on the surrounding ligaments and muscles to keep it stable. For a shoulder to dislocate it almost always has to tear one of these supporting structures. Most commonly this is the labrum – a ring of fibrous cartilage which surrounds the socket thereby deepening it. Other structures which may be damaged include the rotator cuff, glenohumeral ligaments and the bony surfaces themselves. Damaging these structures makes the shoulder easier to dislocate the next time.
The aim of treatment is to prevent shoulder dislocations becoming a recurrent problem and thus reduce the risk of future arthritis. It is well established that the number of times a shoulder has dislocated directly correlates with the risk of later shoulder arthritis. Whether surgery is recommend depends on:
Age: a 19 year old who dislocates their shoulder for the first time has a 90% chance of redislocating with non-operative management (physiotherapy). A 44 year old who dislocates for the first time has a redislocation rate of 10-20%
Activity level: Contact athletes are prone to redislocation. Water sports enthusiasts (surfers particularly) need to consider the consequences of trying to swim with a dislocated shoulder.
Recurrent dislocators: If the shoulder is dislocating repeatedly and easily then it is time to have surgery.
Surgery involves re-attaching the torn labrum and/or ligaments to their correct position on the rim of the glenoid. This is done with arthroscopic “keyhole” surgery. Sometimes over the course of many dislocations the bone of the socket itself has worn away. In this case re-attaching the ligaments and labrum is unlikely to be successful and the worn bone needs to be restored. There are many ways to restore this bone. My preference is to perform a “Laterjet” procedure where a small amount of bone at the front of the shoulder blade (the corocoid) is transferred to the rim of the socket (glenoid).
Following surgery the arm is kept in a sling for 6 weeks to allow the repair to heal. A graded physiotherapy program is then commenced to restore movement and strength to the shoulder.
Risks of shoulder stabilisation surgery include:
- Stiffness: after 6 weeks in a sling most patients have some stiffness. This usually resolves with physiotherapy. Rarely the stiffness may become a “frozen shoulder” which will almost always still resolve – but over a longer period of time
- Recurrence of dislocation: Surgery greatly reduces the risk of re-dislocation but not to zero. For a younger, contact sport playing male the risk of re-dislocation is about 15%. Without surgery it is 90%.
- Arthritis: The smooth hyaline cartilage of the joint itself can be damaged by dislocations. Surgery does not reverse this damage.
- Infection, nerve or blood vessel damage: all very rare complications.