= Solution
\b[The chief historical varieties are subglenoid, subcoracoid, subclavicular and posterior <shoulder dislocation>; treatment restores the <humeral head> gently, checks the <axillary nerve> and circulation, and restores useful movement.]
The <glenohumeral joint> combines a large <humeral head> with a shallow <glenoid cavity>. Its range of movement depends on the comparatively loose <joint capsule>; the <glenoid labrum>, <rotator cuff> and surrounding <muscles> provide stability. An injury can therefore lever the <humeral head> out of the <glenoid cavity> while tearing the <joint capsule> and sometimes the <glenoid labrum> or adjacent <bone>.
The historical names describe where the <humeral head> is found relative to the <scapula> and <clavicle>:
* In subglenoid <shoulder dislocation>, the <humeral head> lies below the <glenoid cavity>, toward the <axilla>. Old descriptions of displacement “downwards into the axilla” need not mean the persistently overhead arm position now called <luxatio erecta>.
* In subcoracoid <shoulder dislocation>, the <humeral head> lies in front of the <glenoid cavity>, beneath the <coracoid process>. This is the familiar anteroinferior pattern.
* In subclavicular <shoulder dislocation>, the <humeral head> has passed farther forwards and medially, beneath the <clavicle>; this is a rarer, more extensive anterior displacement.
* In posterior <shoulder dislocation>, historically also called subspinous displacement, the <humeral head> lies behind the <glenoid cavity>, toward the <scapular spine>. Modern assessment is particularly alert to this pattern after a <seizure> or electrical injury. True inferior <shoulder dislocation>, <luxatio erecta>, and exceptional superior displacement complete the directional classification; they should not be forced into the common anterior pattern.<Shoulder Dislocations: Emergency Department by the Royal Children's Hospital Melbourne>[Sections 3–4: anterior and posterior displacement and their mechanisms]{ref}
An 1867 answer would stress early recognition, relaxation of the <muscles>, and controlled traction with suitable countertraction or gentle leverage to guide the <humeral head> through the torn <joint capsule>. <Anaesthesia> made relaxation practicable. These are principles, not a reason to reproduce old forceful manoeuvres or indiscriminate pulley traction: force can produce a <fracture> or damage the <axillary artery> and <brachial plexus>.
Current assessment establishes the direction and associated <fracture>, usually with <radiography> in appropriate views. Before and after <joint reduction>, record <pulse>, <perfusion>, distal movement and sensation, including sensation over the lateral <deltoid muscle> supplied by the <axillary nerve>. A <nerve injury> accompanying <joint dislocation> makes prompt restoration of alignment especially important.<Peripheral Nerve Injury by the British Orthopaedic Association>[BOASt, response to identification of peripheral nerve injury, recommendation 5]{ref} <Joint reduction> is performed by trained clinicians with suitable <analgesia> and, when needed, <sedation> or <anaesthesia>. Repeated forceful attempts are inappropriate; irreducibility or associated complex <fracture> requires specialist management.<Dislocated shoulder by the NHS>[Treatment for a dislocated shoulder]{ref}
After <joint reduction>, reassess the <axillary nerve> and circulation and confirm alignment and relevant <fractures> with <radiography>. A temporary <sling> relieves pain, followed by progressive <physiotherapy> to restore movement and <rotator cuff> function. The balance is between recurrent instability and stiffness: prolonged immobilisation is not a universal solution. Recurrent instability, significant structural injury and persistent weakness require further assessment.<Shoulder Dislocations: Emergency Department by the Royal Children's Hospital Melbourne>[Sections 7–10: gentle reduction, repeat neurological examination, imaging and follow-up; this source specifically addresses children and adolescents]{ref}
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