The shoulder joint (the glenohumeral joint) is one of the most mobile joints in the human body, with both muscles and ligaments helping stabilize the joint. When understanding different types of shoulder joint instability, the following factors need be taken into account:

  • Frequency :Acute / Recurrent / Fixed (Chronic)
  • Cause:Traumatic / Atraumatic (voluntary, involuntary) / Microtraumatic / Congenital / Neuromuscular
  • Direction:Anterior / Posterior / Inferior / Multidirectional
  • Degree:Dislocation / Subluxation / Microtrauma (transient)

A complete dislocation occurs when the ball of the upper arm bone (humeral head) is all the way out of the joint socket (glenoid fossa). A common type of shoulder dislocation is anterior dislocation, where the humeral head slips forward (anterior instability), anterior to the glenoid fossa. This means the upper arm bone moved forwards and downwards. First time traumatic anterior shoulder dislocation usually happens after a severe trauma. It causes severe pain and can lead to potential complications.



Acute traumatic anterior dislocation causes:

  • Severe pain
  • Swelling
  • Weakness
  • Typical deformity

For young people, it may tear the stabilising ligaments, predisposing to recurrent instability of the shoulder joint. In older people, it may cause damage to the rotator cuff tendons, predisposing to stiffness and weakness of the shoulder joint. In elderly people, it may cause damage to the bones, for example, the greater tuberosity, anteroinferior part of the glenoid rim, or the proximal humerus.



The shoulder joint is so painful that the patient can hardly move his or her shoulder joint. Usually, he or she has to support the involved arm with the opposing hand. There is “squaring” of the shoulder joint, with prominence of the acromion.

An orthopaedic surgeon will perform a detailed examination of the shoulder joint to look for any associated injury. He or she will check for the vascular status and the neurological status of the upper limb, in particular the axillary nerve – to see if there is any active or passive range of motion of the shoulder in any plane of motion. Depending on the clinical conditions, the orthopaedic surgeon may also examine other parts of the body to look for any associated injury.

Plain anteroposterior X-ray of a shoulder joint with anterior dislocation can show the typical feature, with the humeral head being located anterior and inferior to the glenoid fossa. Associated fractures may or may not be easily detected. For this reason, the orthopaedic surgeon may need an additional imaging study, either additional views or other specific investigations such as CT scan.



An orthopaedic surgeon will reduce the ball of the upper arm bone (humerus) back into the joint socket. This process is called closed reduction. Severe pain stops almost immediately once the shoulder joint is back in place. For cases with delayed presentation (chronic dislocation), closed reduction may not be possible and require surgery with open reduction.



An orthopaedic surgeon may immobilise the shoulder in a sling or other device for several weeks following a successful closed reduction. Plenty of rest is needed. The sore area can be iced 3 to 4 times a day. Controversy exists concerning the use of immobilisation and its duration. Patients need to discuss this issue with their orthopaedic surgeon.

After the pain and swelling go down, the doctor will refer the patient to a physiotherapist for rehabilitation exercises. These can help restore the shoulder's range of motion and strengthen the muscles. Rehabilitation will begin with gentle muscle toning exercises. Later, weight training can be added.

For young people that experience recurrent shoulder instability with episodic dislocations after trivial trauma, surgery may be required to repair or tighten the torn or stretched ligaments that help hold the joint in place.