A shoulder joint dislocation is a common upper limb injury were force is applied to the very mobile joint. It is a common dislocation after a fall and most often can be felt as a popping out of the shoulder joint. Up to 90% of shoulder joints dislocate to the front and can cause a bulge in the front part of the shoulder. This injury can repeated itself if not properly treated the first time.

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upper arm pain shoulder dislocation

Anatomy of the shoulder joint

The main joint of the shoulder is a ball and socket joint. This joint is called the glenohumeral joint where the long bone of the upper arm (humerus) forms the ball and the shoulder blade forms the socket (glenoid fossa). The head of the humerus is usually centered and aligned in the joint allowing for friction-less movement. In a shoulder dislocation the joint is forced out of the socket by outside forces.

The shoulder joint is kept stable by static stabilisers and dynamic stabilisers. The static stabilisers are structures surrounding the shoulder joint that cannot contract or move. These include the joint shape, ligaments, shoulder capsule and the labrum (a fibrous ring of tissue attached to the edge of the socket that increases the depth of the socket). The inferior glenohumeral ligament (IGHL) is the main ligament preventing a forward slide of the head of the humerus. This ligament is very important to prevent the shoulder dislocating forward.

The main dynamic stabilisers are the rotator cuff muscles with assistance from the shoulder blade muscles and the long head of the biceps. The front part of the shoulder deltoid muscle, together with the pectoral muscles and latissimus dorsi can assist in an emergency to stabilise the shoulder joint.

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What causes a shoulder joint dislocation?

A Shoulder dislocation is one of the most common traumatic sports injuries. The shoulder joint is dislocated when traumatic forces are applied to the joint usually from the back and side. The most common position to dislocate the shoulder in is when the arm is forced to turn more outwards when the arm is lifted to the side at 90 degrees. This forces the head of the humerus forward and results in the shoulder being ‘popped’ forward.

A partial dislocation (subluxation) is when the upper arm bone is only partially out of the socket. In a partial shoulder dislocation the shoulder may go back into position by itself. A full shoulder dislocation is when the ball joint is completely out of the socket. Any instability in the shoulder makes it more vulnerable to dislocations and needs less force to dislocate the joint. Falling directly onto your shoulder or taking a sudden tackle, may catch you ‘off guard’ and you may not have anticipated the sudden, massive force to your shoulder. This overwhelms the muscles which reacts too late to stabilise your shoulder joint.

Shoulder Dislocation, Dislocated shoulder joint,

Types of shoulder dislocations

Forward (anterior shoulder dislocation)

An anterior dislocation happens if the head of the humerus slides forwards and downwards towards your chest and doesn’t go back. This is by far the most frequent dislocation of the shoulder joint and is as high as 95% of all dislocations. It is primarily caused by the excessive outwards rotation and sideways lifting of the shoulder (the throwing position). In this position, the ligaments and muscles provide the least amount of support to the joint. The rotator cuff is always injured in this process as it tries and fails to stop the shoulder joint from dislocating.

When the head of the humerus is dislocated forward it will possibly damage the labrum at the front edge of the socket (Bankart lesion), there may also be a fracture of the front edge (bony Bankart lesion) and damage to the shoulder ligaments. A compression fracture of the head of the humerus at the back (Hill-Sachs’ lesion) or tearing of the labrum may occur (SLAP-lesion).

Backwards (posterior shoulder dislocation)

A posterior dislocation happens if the head of the humerus slides backwards out of the socket. This is a very uncommon dislocation which is usually caused by strong forces or impact to the front part of the shoulder. Another mechanism of injury is when you fall on an outstretch hand as when you fall from a bike. The forces required to dislocate backwards is extreme and this type of forces are seen in car accidents.

The rate of these types of dislocations is less than 2%. The strong traumatic forces often result in internal damage and other internal shoulder pathologies. Posterior dislocation are commonly present with fractures and extensive ligament damage.

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Symptoms of a dislocation

  • Swelling around the shoulder joint
  • The shoulder would have a deformed appearance (looks like it is popping out)
  • There would be numbness in the shoulder and tingling may go down the arm
  • The shoulder would be weak with painful movement
  • Bruising can be visible around the shoulder.

What does a dislocation look like?

Forward (anterior shoulder dislocation)

  1. Arm out to side, with elbow bent and turned to the head (thrower position)
  2. Shoulder deformity as rounded shape may be lost
  3. Head of humerus can be felt from the front of the shoulder
  4. All movements are painful and restricted
  5. Distorted shape under the armpit and tissue swelling at the collarbone
  6. Minor nerve injuries (peripheral)

Backwards (posterior shoulder dislocation)

  1. Arm out to side, with elbow bent and turned to the feet
  2. Shoulder may be deformed or round like opposite shoulder
  3. Head of humerus may be seen at the back of the shoulder
  4. Most movements are painful and restricted, but cannot turn shoulder in
  5. Possible pinch of the artery
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Damage to the musclenervebone, veins and arteries may occur with a dislocation. There is a possibility that with reducing (putting back into socket) the dislocation the nerve or an artery may be pinched. If the nerve is pinched it would give extreme pain, with loss of sensation and pins & needles down the arm. If the artery is pinched it will result in the hand becoming cold and pale. The pulse at the wrist can be compared to the opposite side in order to determine if there is a reduced pulse.

Diagnosis

Physiotherapists are experts in human anatomy and movement. Physiotherapist often work field side during sporting events and diagnose dislocations very easily. A clinical assessment and local observation is the starting point. A brief description of the position before the injury and the clinical assessment provide the necessary information to make a diagnosis.

Joints are tested in their ability to move freely without restriction. A joint can be moved actively (meaning you voluntarily move the joint without assistance) or passively (meaning the therapist moves it for you while you relax). The passive movement test will exclude the injury from muscles and allow as to assess the joint independently.

X-ray

We will refer you for an X-ray if a dislocation is suspected to determine the position and direction of the dislocation. It is very important to exclude fractures with the X-ray.

CT-scan

A CT-scan is recommended if a fracture was found especially around the rim of the shoulder joint. The CT scan is less expensive than an MRI scan and requires referral by a specialist.

MRI-scan

A MRI is a very expensive scan which can only be referred by a specialist and in the shoulders case this is usually by the orthopeadic surgeon. The MRI scan can show us all the soft tissues and often will be able to show us if there is any underlying shoulder pathology deep inside the joint like a labrum injury.

What else can your Shoulder pain be

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