DISLOCATION OF THE SHOULDER
This is the commonest joint in the human body to dislocate. It occurs more commonly in adults, and is rare in children. Anterior dislocation is far more common than posterior dislocation.
Shoulder instability: This is a broad term used for shoulder problems, where head of the humerus is not stable in the glenoid. In the former, the patient may present with just pain within the shoulder, more on using the shoulder. Pain occurs due to stretching of the capsule, as the head ‘moves out’ in some direction without actually dislocating.
The instability may be in one direction (unidirectional) or more (bidirectional). It may be in multiple directions – anterior, inferior, posterior, where it is called multi-directional instability (MDI).
MECHANISM: A fall on an out-stretched hand with the shoulder abducted and externally rotated, is the common mechanism of injury. Occasionally, it results from an immediate force pushing the humerus head out of the glenoid fossa . A posterior dislocation may result from a direct blow on the front of the shoulder, driving the head backwards.
PATHOANATOMY: Classification: Dislocations of the shoulder may be of the following types:
Anterior dislocation: In this injury, the head of the humerus comes out of the glenoid cavity and lies anteriorly. It may be further classified into three subtypes depending on the position of the dislocated head.
• Preglenoid: the top lies ahead of the glenoid.
• Subcoracoid: the top lies below the coracoid process. Most common type of dislocation.
• Subclavicular: The head lies below the clavicle.
Posterior dislocation: during this injury, the top of the humerus involves lie posteriorly, behind the glenoid.
• Luxatio erecta (inferior dislocation): this is often a rare type, where the top involves dwell the subglenoid position.
Pathological changes: The following pathological changes occur in the commoner, anterior dislocation.
Bankart’s lesion: Dislocation causes stripping of the glenoidal labrum along with the periosteum from the antero-inferior surface of the glenoid and scapular neck. The head thus involves dwell front of the scapular neck, within the pouch thereby created. In severe injuries, it may be avulsion of a piece of bone from antero-inferior glenoid rim, called bony Bankart lesion.
Hill-Sachs lesion: This is a depression on the humeral head in its postero-lateral quadrant, caused by impingement by the anterior edge of the glenoid on the head as it dislocates. Rounding off of the anterior glenoid rim occurs in chronic cases because the head dislocates repeatedly over it. There may be associated injuries: like fracture of greater tuberosity, rotator-cuff tear, chondral damage etc.
Essentials of Diagnosis:
• Anterior dislocation is most common, then posterior (50:1)
• Anterior dislocation occurs with the arm abducted and externally rotated; posterior, with the arm flexed and internally rotated.
• Posterior dislocation is less painful than anterior. On physical exam, anterior dislocation produces “fullness” anteriorly and inferiorly; posterior dislocation produces fullness in back, and the coracoid is more prominent.
• Obtain orthogonal radiographic views (very important, especially with posterior dislocations, to avoid missing the diagnosis); scapular “Y” view, axillary view, and AP and “West Point” views permit visualization of occult fractures.
- Fracture-dislocation of the humerus.
- Multidirectional instability.
COMPLICATIONS: Complications are often divided into early and late.
Early complications: Injury to the axillary nerve may occur resulting in paralysis of the deltoid muscle, with a small area of anaesthesia over the lateral aspect of the shoulder. The diagnosis is confirmed by asking the patient to try to abduct the shoulder. Though shoulder abduction may not be possible because of pain, one can feel the absence of contraction of the deltoid. Treatment is conservative, and the prognosis is good.
Late complications: The shoulder is the commonest joint to undergo recurrent dislocation. This results from the following causes: (i) anatomically unstable joint e.g., in Marfan’s syndrome;
(ii) inadequate healing after the first dislocation, or (iii) an epileptic patient.
Closed reduction is indicated, with appropriate sedation and analgesia; gentle traction in line with the arm, using some internal and external rotation with appropriate countertraction, generally reduces the dislocation.
Bankart’s operation: The glenoid labrum and capsule are re-attached to the front of the glenoid rim. This is a technically demanding procedure, but has become simpler with the use of special fixation devices called anchors.
Putti-Platt operation: Double-breasting of the subscapularis tendon is performed in order to prevent external rotation and abduction, thereby preventing recurrences.
Immobilization for a short period (1–2 wk) to resolve pain for patients >50 y and for 3–4 wk for younger patients is indicated; the correct length of immobilization and position of immobilization have not been determined. Recurrent dislocation can be treated arthroscopically in many cases.