Shoulder instability is a relatively common condition seen in orthopaedic and sports medicine settings. The shoulder joint is inherently predisposed to instability because of its bony architecture: like a golf ball on a tee. The incidence of traumatic shoulder instability is 1.7% in the general population. Other shoulder conditions, including labral tears and capsulitis, also play a role in predicting recurrent instability. Clinicians should conceptualise six clinically important considerations when managing shoulder instability.
The structure of the shoulder allows for large arc movements, more so than the hip for instance, but this increase in mobility also inherently leads to a risk of inherent shoulder instability, which can results from traumatic shoulder dislocation. The most common type of shoulder instability is anterior dislocation, accounting for over 90% of all shoulder dislocations. Men, contact athletes and enlisted persons are particularly at risk of shoulder dislocation.
The shoulder relies on complex interaction between inert and contractile structures that aim to provide constant feedback for optimal joint centration (keeping the joint centred) and performance. Structures providing this stability include the congruency of the shoulder joint with the head of the humerus bone (arm bone) and glenoid fossa (shallow socket) of the scapula (shoulder blade), the glenoid labrum, ligaments surrounding the joints, the shoulder capsule, and the rotator cuff and other surrounding musculature such as the biceps brachii. Compromising these structures increases the risk of shoulder dislocation.
Six clinical considerations for managing shoulder instability
There is a wide range of symptomatic shoulder instabilities: from subtle recurrent medical subluxations to traumatic full dislocation with neurovascular compromise. Therefore every case should be patient-centred and tailored to the specific needs of that patient at that point in time. There are six important clinical considerations when conceptualising a rehabilitation program:
- Chronicity of shoulder instability. When did the shoulder instability begin? Pathological shoulder instability may be due to acute (0-3 days), subacute (3-21 days) or chronic (>3 weeks) and the timeframe of dislocation will greatly affect the goals of management. Following a traumatic dislocation, the patients will usually present with considerable tissue damage, muscle spasm, pain and apprehension. Rehabilitation for this patient would begin with controlled range of motion, reduction of muscle spasm and guarding and pain relief with medication. Conversely, a patient presenting with atraumatic instability often presents with a history of repetitive injuries and some symptomatic complaints. There is often a sensation of laxity or inability to perform specific tasks. Rehabilitation for a patient like this would focus on early proprioception training (unconscious perception of movement and spatial orientation), neuromuscular control and strengthening exercises to improve dynamic shoulder stability.
- Severity of shoulder instability. A subtle medical subluxation is very different to a full dislocation with neurovascular compromise. Similarly, instability in one plane of movement compared to multiplane, or gross, instability are also clinically different. Furthermore, a dislocation is a complete separation of the joint surfaces and will require specific relocation to relocate the joint.
- Concomitant pathology. Considering other tissues that may have been affected by the instability and condition of the tissue. Injury to the anterior glenoid capsulolabral complex commonly occurs during a traumatic injury, which can result in anterior Bankart or Hill Sach’s bony lesions. These lesions present in approximately 80% of dislocations. Other tissues that can be affected are the brachial plexus (collection of nerves exiting the spine that innervate the arm) and the superior labrum.
- Direction of instability. Anterior shoulder instability is the most common traumatic type of instability, with 95% seen in all traumatic shoulder instabilities. However, the direction of displacement is dependent on the mechanism of injury and the individual.
- Neuromuscular control. Injury of the neurovascular bundle of the shoulder and arm could result in serious medical complications. Furthermore, the humeral head may not centre itself within the glenoid fossa, thereby compromising the surrounding stabilising tissues. Patients with poor neuromuscular control may also have excessive humeral head migration with the potential for re-injury.
- Pre-injury activity level. If the patient is an athlete who frequently performs overhead activities, such as seen in tennis or baseball, then rehabilitation should include sport-specific dynamic stabilising and neuromuscular control exercises, and plyometric exercises in the overhead position once full, pain free shoulder range and adequate strength has been achieved.