The shoulder is a ball-and-socket joint, where the head of the humerus (upper arm bone) and glenoid (socket) of the scapula (shoulder blade) join together.
It is kept in place by groups of ligaments and muscles for stability.
The shoulder joint has good mobility in all directions, but this makes the joint vulnerable to instability issues.
Shoulder instability arises when the tissues surrounding the joint (ligaments and muscles) are unable to properly support the head of the humerus securely within its socket.
This instability may be associated with chronic pain and can lead to:
When the humeral head has been displaced out of the glenoid, the shoulder is said to be dislocated.
The dislocation may tear the tendons, ligaments or labrum (ring of cartilage attached to the rim of the socket) of the shoulder joint. It may occasionally be accompanied with a fracture, depending on the severity of injury / trauma.
This is a partial shoulder dislocation, when the humeral head is partially moved out of the socket. The humeral head may briefly pop out and return back into the socket automatically.
Common Symptoms of Shoulder Instability
- A persistent feeling of the shoulder being loose / “dangling” / not in its position
- Pain or a “clunk” sound in certain positions
- Repeated incidence of shoulder giving way in specific activities or arm position
- Pins & needles, numbness or weakness through the arm to the hand (if the nerve is affected)
Types of Instability
- Anterior Instability
This is the most common form of shoulder instability where the humeral head is shifted towards the front. It often occurs either from dislocation or subluxation from acute trauma in overhead sport motion (e.g. tennis, baseball).
- Posterior Instability
The humeral head is shifted backwards. This occurs less frequently. It often occurs from a trauma fall in outstretched arm or a direct forceful blow to the front of shoulder (e.g. car accident).
- Multidirectional Instability
The humeral head can be shifted out of the socket in any direction. This is usually a chronic problem and often due to genetic factors (e.g. groups of people who are very flexible, i.e hypermobile). They are best managed with a thorough shoulder rehabilitation program (Watson et al. 2018) unless a extensive tear in the labral, tendon or ligament has taken place for possible surgery.
- Born being hypermobile
- Acute trauma events (e.g. sports injury, fall)
- Micro trauma events where the shoulder structures are stressed / weakened from overuse or repetitive overhead movements (e.g. throwing sports, manual work)
- Previous history of shoulder injury or dislocation where some structures in the shoulder were torn or healed too “loosely”
- Avoid / reduce / modify painful activities
- Sling to rest and immobilize the shoulder (for severe pain and traumatic dislocation)
- Non-steroidal anti-inflammatory drugs (NSAIDs) for pain control and inflammation
- Physiotherapy for active pain relief and recovery, restoration of range of motion, strengthening and return to daily activities.
Physiotherapy and Rehabilitation
- Pain reduction and inflammation control using modalities and manual therapy
- Improve postural, rotator cuff and scapular (shoulder blade) muscle strength and mobility and restore shoulder function with rehabilitative program (Bateman et al. 2015, Watson et al. 2018)
If the shoulder does not respond to conservative approaches and rehabilitation; there are repeated episodes of dislocation or subluxation; or there is an associated labral tear or fracture, surgery may be required.