What the labrum does
The shoulder is a ball-and-socket joint with a notably shallow socket, which is what allows it the range of movement it has and also what makes it the most commonly dislocated joint in the body. The labrum is a rim of cartilage around the edge of that socket. It deepens the socket, acts as an attachment point for the ligaments and capsule, and helps keep the ball centred.
When the shoulder dislocates, the labrum is commonly torn away from the bone. If it heals in a detached position, the socket is left effectively shallower and the ligaments slacker than before, and the shoulder is more likely to dislocate again. This is why recurrent instability is common after a first dislocation, particularly in younger people.
Why instability can recur after a repair
A labral repair reattaches the torn labrum and tightens the capsule, and for most people it restores stability. Some shoulders, however, become unstable again. The reasons vary and include a further significant injury, loss of bone from the rim of the socket or the ball over repeated dislocations, failure of the repair to heal, an underlying degree of generalised joint laxity, or return to a demanding contact sport.
Recurrent instability is therefore not necessarily a sign that the first operation was done poorly. It is often a reflection of how much bone and soft tissue was already lost by the time the shoulder was first repaired.
What is assessed when instability recurs
Assessment of a shoulder that has dislocated again after a repair generally involves working out the direction of instability, how much bone is missing from the socket and the humeral head, the state of the previous repair, and whether anything else has been injured at the same time. Structures commonly looked at on imaging include:
- Detachment of the labrum, most often at the front of the socket.
- The condition of the capsule and ligaments.
- The rotator cuff tendons and their attachments.
- Bone loss from the glenoid rim or an impression fracture of the humeral head.
- Bleeding and soft tissue swelling from the recent dislocation.
MRI is the usual starting point for the soft tissues, often with a CT scan where bone loss needs to be quantified. The findings determine whether a repeat soft tissue repair is appropriate or whether a bone block procedure is needed to rebuild the socket.
Related information
Our shoulder instability page explains the condition and the treatment options in more detail, and the shoulder anatomy page covers how the joint is put together. See also shoulder injuries and the rehabilitation page. To arrange an assessment, see the consultation page.