Shoulder

instability

Normal anatomy of the shoulder

The shoulder is made up of three bones: The upper arm bone (humerus), the shoulder blade (scapula), and the collarbone (clavicle).

The shoulder is a ball-and-socket joint: the ball, or head, of the humerus fits into a shallow socket (glenoid) in your shoulder blade.

The glenoid is surrounded by a rim of cartilage called the labrum. The labrum helps to deepen the socket and provide stability to the humeral head. There are three ligaments which run in the front and back of the joint and the entire joint is surrounded by a fibrous capsule.

The rotator cuff is a group of four muscles that come together as tendons to form a covering around the head of the humerus. The rotator cuff attaches the humerus to the shoulder blade and helps to lift and rotate your arm. The rotator cuff also helps to secure the humeral head within the shoulder socket.
There is a lubricating sac called a bursa between the rotator cuff and the bone on top of your shoulder (acromion). The bursa allows the rotator cuff tendons to glide freely when you move your arm.

The shoulder is the most mobile joint in the body, it is also the most frequent joint to be dislocated. A first time dislocation usually occurs from a traumatic injury such as a fall, rugby tackle or motorcycle / bicycle accident. The most common dislocation is anterior where the humeral head moves forwards out of the socket and towards the chest. A posterior dislocation is less common and may result from an epileptic seizure.
At the time of a dislocation the humeral head will tear the rim of labrum cartilage off the front of the glenoid socket (known as a Bankart Lesion) and stretch / partially tear the ligaments and capsule in the front of the joint. It may also break a small piece of bone off the front of the glenoid socket (Bony Bankart) or cause a small impaction fracture in the head of the humerus (Hillsachs Lesion).
These injuries which occur at the time of initial dislocation make the shoulder more unstable and the risk of re-dislocation increases significantly with each subsequent dislocation.

Some patients may experience partial dislocations where the head of the humerus comes partially out of the joint but goes back in without any orthopaedic intervention. This can occur if a patient has naturally loose ligaments and joint capsule – such as gymnasts,
ballerinas and some swimmers.

Imaging tests

In order to identify and assess the extent of all the damaged structures within the shoulder joint after a dislocation, an Xray, CT scan and an MRI may be done.

  • Xray / CT – used to assess the bones of the joint to look for fractures
  • MRI – used to assess the soft issues such as the cartilage labrum, ligaments and joint capsule

Risk of re-dislocation:

The risk of having another shoulder dislocation on the same shoulder depends on:

  • Age – The younger you are, the more chance that you will dislocate again. If you are under the age of 30 years you have a risk of approximately 70-80% that you will dislocate the same shoulder again
  • Choice of sport – Contact sports have a much higher re-dislocation rate than noncontact sports. Contact sports include – rugby, football/soccer, surfing, kiteboarding, skiing etc.
  • Racquet sports – such as tennis and squash may also increase your risk of redislocation
  • Number of dislocations – each time you dislocate your shoulder you increase the instability of the joint and it becomes easier to re-dislocate.
  • Associated injuries – injuries to the shoulder, which occur at the time of dislocation,
    such as a labrum tear or an impaction fracture of the humeral head will make your joint more unstable and easier to re-dislocate.

Non-surgical treatment

The risk of having another shoulder dislocation on the same shoulder depends on:

  • Rest – I recommend wearing a sling 24 hours a day for the first 2-3 weeks while the ligaments and torn capsule are healing
  • Activity modification – Avoid activities that cause a feeling of apprehension that the shoulder may dislocate. This position of your shoulder when your hand is on top of your head is the typical position which will give a feeling that the shoulder is about to dislocate
  • Non steroidal anti-inflammatory medication – Medication such as Voltaren and Naproxen can reduce pain and inflammation around the shoulder.
  • Physiotherapy – Specific exercises under the guidance of a physiotherapist can restore movement and strengthen your shoulder. Strengthening the rotator cuff muscles that support your shoulder can relieve pain and prevent further instability

Surgical management

The decision to choose surgical management over non-surgical management should depend on factors such as your age, number of dislocations, associated injuries in the shoulder and desired level of activity you wish to return to.

For more information please read the booklet below