Chronic Shoulder Instability and Dislocation
Dislocations make the shoulder joint prone to further episodes. Repeated episodes can lead to chronic shoulder instability where the laxity of the shoulder joint causes the head of the humerus to not remain consistently in its position within the joint.
Stability of the shoulder joint
| Stability | Description |
|---|---|
| Dynamic stability | Stability during movement. Provided by the rotator cuff |
| Static stability | Stability at rest. Provided by the glenoid labrum |
Anterior Shoulder Dislocation
Anterior dislocation of the head of the humerus from the glenoid cavity is the most common shoulder dislocation (96%). It is frequently seen in younger patients after acute trauma, usually in sports. A history of prior dislocation is a risk factor due to laxity of ligaments.
- Reasons why anterior shoulder dislocations are so common
- Shallow glenoid cavity
- The extraordinary range of movement of the shoulder joint
- Underlying conditions such as ligamentous laxity
- The sheer vulnerability of the joint during stressful activity of upper limb
- Mechanisms
- Indirect trauma to upper extremity with shoulder in abduction, extension, and external rotation (Most common) aka FOOSH
- Direct trauma to the posterior shoulder, anteriorly directed
- Convulsive mechanism and electrical shock
- Recurrent instability (Congenital or acquired laxity, results in dislocation with minimal trauma)
- Signs and symptoms
- Shoulder pain
- Arm held abducted and externally rotated
- Prominent head of humerous
- Notable asymmetry
- Reduced range of motion at shoulder
- Physical examination
- Assess neurovascular status
- Axillary nerve damage
- Stabilize the adducted arm and ask the patient to abduct. Palpate the deltoid muscle (motor component)
- Check for numbness over the regimental patch (skin over the proximal arm; sensory component) ****
- Axillary artery damage
- Check for radial pulse
- Investigations
- X-ray of affected shoulder: AP view + Scapular-Y (lateral) view, or axillary view
- Non-operative treatment
- Closed reduction followed by sling immobilization for 3 weeks
- NSAIDs for pain and proper healing of the ligaments
- Techniques for closed reduction
- Stimson’s technique: the patient is left prone with the arm hanging over the side of the bed. Give high analgesics. After 15 or 20 minutes the shoulder may reduce
- Hippocratic method: gently increasing traction is applied to the arm with the shoulder in slight abduction, while an assistant applies firm countertraction to the body
- Kocher’s method: The elbow is bent to 90 degrees and held close to the body; no traction should be applied. The arm is slowly rotated 75 degrees laterally, then the point of the elbow is lifted forwards, and finally the arm is rotated medially. This technique carries the risk of nerve, vessel and bone injury and is not recommended.
- Indications for operative management
- First-time dislocation in young active men
- Soft tissue interposition
- Labral injury
- Diplaced greater tuberosity fracture that remains >5mm superiorly displaced following closed reduction
- Glenoid rim fracture >5mm in size
- Operative treatment
- Arthroscopic ligamentous repair of anterior/inferior labrum (Bankart lesion)
- Shoulder immobilizer post-op for upto 3 weeks
- Complications of anterior shoulder dislocation
- Recurrent anterior dislocation
- Osseous lesions
- Hill-Sachs lesion (compression fracture of the posterolateral humeral head caused by impaction against the glenoid rim)
- Glenoid lip fracture (”Bony Bankart Lesion”)
- Greater tuberosity fracture
- Fracture of acromion or coracoid
- Post-traumatic degenerative changes
- Soft-tissue lesions
- Rotator cuff tear (older patients)
- Capsular or subscapularis tendon tear
- Vascular injury (Axillary artery)
- Nerve injury (Musculocutaneous and axillary nerves)
- Late complications
- Shoulder stiffness
- Unreduced dislocation
- Recurrent dislocation: can be predicted through the apprehension test
Associated injuries
| Injury | Description |
|---|---|
| Bankart lesion | A tear or detarchment of the anterior-inferior portion of the glenoid labrum from the glenoid rim (caused by anterior dislocation) |
| Osseus Bankart lesion | A fracture of the anterior-inferior portion of the glenoid bone in association with a Bankart lesion of the labrum |
| Reverse Bankart lesion | A tear of the posterior-inferior portion of the glenoid labrum (caused by posterior dislocation) |
| Perthes lesion | A variant of Bankart lesion where the anterior-inferior laburm is detached but remains attached to the intact peritoneum |
| Anterior Labroligamentous Periosteal Sleeve Avulsion (ALPSA) | A variant of Bankart lesiosn in which the anterior-inferior labrum is torn and medially dislpaced along with the intact periosteum |
| Glenolabral Articular Disruption (GLAD) | A superficial injury involving the anterior-inferior labrum and adjacent glenoid articular cartilage, without significant instability |
Posterior Shoulder Dislocation
Posterior dislocation of the head of the humerus from the glenoid cavity is extremely rare (2-4% of shoulder dislocations). It is easy to miss and usually results from disorganised rotator cuff muscle contraction (such as in electric shock, seizures, etc.) or from severe restraint, e.g. half-Nelson
- Mechanism
- Indirect trauma with the shoulder in adduction, flexion, and internal rotation
- Electric shock or convulsive mechanism (Contraction of big internal rotators > External rotators)
- Direct trauma applied to anterior shoulder
- Signs and symptoms
- Painful shoulder
- Arm held adducted and internally rotated and locked in that position
- Palpable mass posterior to shoulder
- Flattened anterior shoulder
- Coracoid prominence
- Investigations
- X-ray of affected shoulder (AP, scapular-Y, and axillary views): often undiagnosed with unidirectional XR
- Light bulb appearance on AP view, as the head of humerus stands somewhat away from the glenoid cavity (empty glenoid sign)
- X-ray of affected shoulder (AP, scapular-Y, and axillary views): often undiagnosed with unidirectional XR
- Treatment
- Non-operative
- Closed reduction and sling immobilisation
- Reduction is by pulling on the arm with the shoulder in adduction, then gently rotating laterally while the head is pushed forwards
- NSAIDs for pain
- Operative
- Open reduction
- Non-operative
