Anterior – or frontal – shoulder instability (ASI) is the most common type of shoulder instability, making up more than 80 per cent of all shoulder instability cases generally.
ASI occurs when the head of the upper arm bone (humerus) slips to the front of the shoulder joint. The severity of the injury depends on the degree of the “slip” of the bone and can be anything from a mild displacement to a true dislocation. It is generally caused by trauma but can also occur with overuse or in those with a congenital softness of the tissue surrounding the shoulder joint. In a vast majority of cases, however, it is caused by trauma, such as in a fall on an outstretched arm.
Depending on the severity of the trauma, the shoulder can be damaged in a number of ways.
Firstly, patients could suffer an injury to the ligaments which support the front part of the shoulder’s “ball and socket” joint. This is known as a Bankart lesion.
Patients could also have fractured the shallow socket in the shoulder that gently cups the head of the upper arm bone. This is known as a bony Bankart lesion. Any bone loss associated with this can increase the risk of future dislocations and requires a referral to a surgeon.
In more serious cases, ASI can result in a compression fracture of the bone at the head of the upper arm. This is known as a Hill-Sachs’ lesion. Generally, this injury also requires a surgical consult.
Rotator cuff injuries – tears in the tissues connecting muscle to the bone around the shoulder joint –, This could particularly happen for those aged over 40.
Finally, neurological and vascular weakening or injury, particularly in the main axillary nerve – which runs from the upper spine down the arm – can also be caused by ASI.
Patients with anterior shoulder instability generally present with pain and a heightened sense of fear and apprehension of further displacement.
Treatment depends on the degree of instability, patient characteristics and severity of symptoms.
Obviously, if there was any acute dislocation, the priority is to relocate the shoulder as soon as possible. In that case the patient must urgently attend the nearest hospital emergency department.
Many conditions associated with ASI require a surgical review. For example, in younger patients (particularly those less than 20-years-old) there is a higher rate of dislocation, which can cause dislocation of the shoulder again.
If there is any structural damage as a result of ASI, for example Bankart lesion or bone fracture, again a surgical opinion is necessary. Common surgeries associated with this kind of damage are known as Bankart repairs or Laterjet procedures.
However, if the patient presents with a milder dislocation, they can be treated conservatively. Initially we want to lessen the pain and inflammation, this can be done by placing the arm in a sling temporarily, using pain killers and frequent icing.
After an initial rest and recovery period, the patient can work on the gradual return to movement, proper activation and control of the shoulder muscles including the rotator cuff and shoulder girdle muscles.