Dislocation or instability of the Gleno-Humeral Joint (Shoulder)
The Gleno-Humeral Joint has the largest range of movement of any joint in the body. In order to allow this range of movement the degree of stability of the joint is sacrificed. The bony socket (Glenoid) is small and relatively flat only made slightly cup shaped by the cartilage and a ring of soft tissue termed the labrum (lip). There is a greater reliance on the ligaments and muscles to prevent it coming out of joint or dislocating. If any of these structures are damaged or do not work properly the shoulder can become unstable or dislocate.
Instability or dislocations can occur as a consequence of a number of issues.
Traumatic.
A typical dislocation is a consequence of marked force applied to the arm, with the hand away from the body and in extension, as if starting to make an overarm throw or pitch. There is typically damage to the restraining structures. This usually involves a tear of the labrum (lip of the socket) and the capsule (lining of the joint) with possible bony damage to both the socket and the humeral head (ball).
The shoulder can be unstable or dislocate in any direction. The ball typically comes out of the front of the socket and lies in front or in front and below the shoulder. Dislocations where the shoulder comes out posteriorly (backwards) are uncommon and are typically associated with a seizure (fit) or electrocution.
Atraumatic.
Atraumatic dislocations or instability are typically a consequence of an underlying laxity of the soft tissue constraints or an abnormality of the shape of the Glenoid (socket).
Muscule patterning (muscle imbalance).
The muscles around the shoulder normally act to maintain the Gleno-Humeral Joint in place. Under certain circumstances they can contract abnormally acting to dislocate the Joint rather than keep it located.
Although the most common that the predominant cause of instability is traumatic damage it is common for there to be a combination of issues. In addition, the predominate type of instability may change with time.
Traumatic dislocations or instability:
Signs and symptoms:
Dislocation.
Typically there is an episode when the shoulder comes out of joint. This is associated with pain and deformity of the shoulder. It is often painful to move the arm at all and it is usually kept by the side. The normal curve of the shoulder is lost and the acromion is felt as a prominence with a fullness often felt anteriorly (at the front). The joint often needs to be reduced under medical supervision in the hospital. The dislocation may reduce spontaneously or may reduce when the arm is repositioned.
Dead arm.
There may not be a complete dislocation. Occasionally the arm may be injured sufficiently to damage the restraining structures but without the shoulder coming completely out of joint. There may be pain felt throughout the whole arm and the arm may feel ‘lame’ for a time.
Ongoing instability.
The shoulder may dislocate again or do so repeatedly. The joint may feel as if it is going to come out if the arm is placed in certain positions, so called apprehension. There may be pain rather than a sensation of instability with certain movements.
Diagnosis:
The diagnosis may be clear from the history and examination. Further imaging is usually undertaken to confirm the diagnosis and plan treatment.
X Rays (plain radiographs). These are important to diagnose a dislocation and to identify associated injuries as well as confirming the shoulder is back in joint.
Magnetic Resonance Imaging Arthrogram (MRI-A). This involves the injection of a contrast into the joint before the examination. This improves the detail of the exam and allows the identification of damage to the labrum as well as possible damage to other structures such as the rotator cuff tendons.
Computerised Tomography (CT scan) with or without contrast. This scan allows the imaging of the bony structures including potential damage to the socket. If an injection of contrast is used it can be used in the place of an Magnetic Resonance Imaging Arthrogram (MRI-A) to visualise damaged soft tissues and labrum.
Initial treatment:
Reduction.
The dislocated shoulder should be reduced as soon as is safely possible. Some people such as team physiotherapists may have been trained to reduce the shoulder at the side of the pitch. If there is no one available to reduce the shoulder then the patient should be taken to an emergency department.
The shoulder is typically X Rayed to exclude associated injuries. Painkillers and sedation or Entonox (Gas and Air) are often given to allow the shoulder to be reduced comfortably. The shoulder is typically much more comfortable once it is reduced back into the correct position. X Rays should be taken to confirm the reduction and check for any associated injuries. Very occasionally the shoulder can not be reduced without a General Anaesthetic (being fully asleep).
Immobilisation.
There is some evidence that the risk of re-dislocation is reduced by immobilising the arm in external rotation (a hand shake position). Immobilisation in this position is difficult and poorly tolerated and the benefit is not marked. As a consequence it is usual to immobilise the arm in a broad arm sling or Polysling for up to 3 weeks.
Rehabilitation can be commenced as soon as this is comfortable.
Further treatment.
Once the shoulder has dislocated the risk of further dislocations increases. The degree of increased risk depends on a number of factors including; the amount of structural damage to the joint, the activities undertaken (eg: contact sports), the age and gender of the individual. In certain situations the risk of a further dislocation may be as high as 80%.
It is reasonable to consider surgical stabilisation after the first dislocation in certain circumsatnces. The alternative is to pursue rehabilitation allowing the shoulder to strengthen and become more comfortable avoiding at risk activities.
If the shoulder continues to dislocate or feels unstable it may be necessary to consider surgical intervention.
Surgical Stabilisation.
If the shoulder continues to be symptomatic and either dislocates or feels like it will dislocate again surgery may be necessary. The type of surgery will depend on the structural damage, which needs to be corrected. If the damage is largely soft tissue affecting the labrum and capsule then this can usually be addressed with a soft tissue procedure typically undertaken arthroscopically (keyhole). If the damage is principally to the bone of the glenoid or humeral head or both then it may be necessary to address this with a coracoid transfer operation or Latarjet.
Atraumatic instability:
Atraumatic dislocations or instability are typically a consequence of an underlying laxity of the soft tissue constraints or an abnormality of the shape of the Glenoid (socket). Patients are often very supple or double jointed. There may be an association with minor repetitive injury or trauma.
The signs and symptoms may be the same as for a traumatic dislocation or there may a pain or discomfort within the shoulder which may be vague and undefined. There may be a perceived looseness within the shoulder rather than frank instability or dislocations.
If the shoulder is dislocates then the immediate treatment is the same as in traumatic shoulder dislocation. The mainstay of treatment is rehabilitation from a specialist shoulder physiotherapist. This rehabilitation may focus initially away from the shoulder on the core abdominal muscles and buttocks on which the scapula-thoracic function depends. The shoulder will not be optimally stable unless the scapulo-thoracic function is optimal.
If the shoulder remains stable the surgical intervention may be necessary. This is typically in the form of an arthroscopic (keyhole) procedure which tightens lax tissue as well as addressing any structural damage
Shoulder stabilisation –capsular shift.
Muscule patterning (muscle imbalance).
The muscles around the shoulder normally act to maintain the Gleno-Humeral Joint in place. Under certain circumstances they can contract abnormally acting to dislocate the Joint rather than keep it located. This is the least common form of instability but its contribution to instability may subtle and may be missed.
Treatment is in the form of specific specialist rehabilitation to retrain the muscles to contract appropriately. Surgical intervention may exacerbate the abnormal muscle patterning.
