Key to these functions is the “ball and socket”, or the head of the humerus/arm bone sitting nicely in the nook or socket of the glenoid– a shallow socket of the scapula/shoulder blade. All held together by ligaments, tendons, cartilage, and muscles which help to prevent the humerus head from slipping out of the shallow glenoid.

Shoulder instability occurs when the ligaments are loose and hence unable to hold the joints together, rendering them unstable. While shoulder dislocation occurs when the head of the humerus comes out of the glenoid cavity. Having shoulder instability can often lead to shoulder dislocation and vice versa.

Shoulder instability can be categorised into 3 groups, these are:

• Anterior instability: the most common type of shoulder instability and is usually the result of a shoulder dislocation or subluxation.
• Posterior instability: usually occurs due to a traumatic injury or rapid muscle contractions.
• Multidirectional instability: due to a genetic predisposition to loose joints or in individuals commonly referred to as being “double jointed”.

• Injury: injury can cause your ligaments and muscles to become overstretched or torn. This causes them to be loose and unable to hold the humerus head in the glenoid cavity.
• Overuse: with time, your ligaments and muscles can become too loose and overstretched due to repetitive movement.
• Genetics: some people are born with loose joints. Shoulder instability/dislocation can occur in these individuals without any injury, overuse, or trauma to the joint. 

Individuals with shoulder instability/dislocation are usually grouped into two categories: shoulder instability/dislocation due to post-traumatic shoulder injury (caused by injury or overuse) or shoulder instability/dislocation due to congenital causes (loose joints).

General symptoms of shoulder instability include:

• Popping or locking of the shoulder joint
• Feeling like your shoulder is stuck in a certain position
• Shoulder pain
• Loose shoulder joints
• Muscle weakness and reduced strength in the affected shoulder

• Sports/hobbies: participating in contact sports or hobbies that require repetitive movements can increase your risk of shoulder dislocation/subluxation which in turn causes shoulder instability. 
• Having loose joints: being genetically predisposed to loose joints or developing loose joints due to repetitive movements such as swimming, increases your risk of having shoulder instability/dislocation. 
• Seizures: individuals with seizure disorders such as epilepsy are at an increased risk of developing shoulder instability/dislocation. 

• Physical examination: your orthopaedic specialist will check your shoulder for areas of tenderness, range of motion, and strength. 
• X-rays: an x-ray will be performed to check for the possibility of other disorders of the shoulder.

Magnetic resonance imaging (MRI) and/or computed tomography scan (CT-scan): MRIs and CT-scans are performed to examine your bones and tissues.

Treatment options include:

• Medication and rest: painkillers and a cold compress will be prescribed to alleviate any pain or inflammation associated with your shoulder instability/dislocation.
• Physiotherapy: physiotherapy involves the use of therapeutic and gentle exercises to improve muscle strength and improve shoulder stability/dislocation.
• Surgery: for severe or repeated cases of shoulder instability/dislocation.