The shoulder joint and instability
The shoulder joint (glenohumeral joint) is stabilised by the shoulder labrum, capsule and surrounding muscles. It is a ball and socket joint. The labrum is a cartilage-like ring surrounding the glenoid (socket) deepening it. At the top of the ring (12 O’Clock) position it gives origin to the long head of biceps tendon that runs through the shoulder joint before exiting into the upper arm. A tear of the labrum at the biceps origin is called a SLAP tear. A tear of the labrum in the front of the shoulder (3 O’ clock position and below) in which it is pulled of its attachment to the bone is called a Bankart Lesion. The capsule consists of a group of ligaments that connect the humerus (upper arm bone) to the glenoid (socket). Stretching with laxity or tearing of the labrum and/or ligaments increases the risk of instability of the shoulder which may result in pain, subluxation or dislocation.
What is shoulder instability?
Instability is the feeling of pain and/or the shoulder not feeling right as it dislocates or subluxes. With subluxation the joint moves more than it should do such that some of it is still in contact so it has not popped completely out of place. With a dislocation the joint “pops” completely out of place. Commonly dislocations occur out in the front (anterior) although they can occur out in the back (posterior) or out in the bottom (inferior – luxatio erecta).
How does instability occur?
This may occur as a result of trauma such as a fall or tackle causing the shoulder to dislocate. The force results in the labrum being torn off the glenoid and often a small compression injury or “dent” in the humeral head often referred to as a Hill-Sachs lesion. First time traumatic dislocations often present in A&E and may require reducing followed by a period of immobilisation and a sling. In higher energy dislocations a small rim of bone may break off (fracture) with the labrum rendering the joint even more unstable. If left untreated in the long-term they can result in further episodes of dislocation or subluxations and degenerative changes or “wear and tear” of the joint.
In some patients with a high degree of flexibility (generalised hypermobility) the joint is already be lax and may suffer with subluxations or dislocations with minimal trauma. Occasionally patents dislocate their shoulders without any trauma and voluntarily without pain. This group of patients usually benefit from physiotherapy for “abnormal muscle patterning” because their muscle groups are not working in a coordinated manner.
How do patients with shoulder instability present?
Patients may give a history of a traumatic event such as a fall with the arm up and out such as in a rugby tackle or holding onto something as they fall e.g. the bannister to prevent a fall downstairs. Initially the shoulder will appear deformed with severe pain before the shoulder is relocated (reduced) which may occur on the “field”, on route to the A&E department or in the hospital. Sometimes patients present with numbness on the outer side of their upper arm. Rarely a significant nerve injury may occur where they lose part or complete function of their arm.
How is shoulder instability diagnosed?
Diagnosis is made by taking an accurate history and a physical examination. Particular emphasis is placed on the mechanism of injury. An X-ray and/or MRI scan may be requested. Sometimes a special scan in which dye (contrast) is injected into the joint called a CT arthrogram or MR arthrogram is requested to exclude certain types of lesions.
How is shoulder instability treated? Surgical VS Non-Surgical management
Treatment depends on a number of factors including the type of instability, the structures injured, the age of the patient and the level and type of activity a patient wishes to return to. All cases of shoulder instability will benefit from a course of physiotherapy tailored to their type of instability.
With traumatic dislocations surgery may be required to help stabilise the joint. Most stabilisation procedures are performed arthroscopically (keyhole surgery) but in circumstances may require an open procedure (larger incision). Depending on the structures involved – an arthroscopic stabilisation will involve reattaching the detached and torn labrum (and sometimes bone rim fragment) onto the glenoid socket using special stitches. Post-operatively the patients’ shoulder is immobilised in a sling and then started on a special physiotherapy rehabilitation programme with a specialist shoulder physiotherapist and under the supervision of the surgeon.