MANUAL MINORS
A metacarpophalangeal (MCP) joint dislocation of the thumb occurs when the joint surfaces of the metacarpal and the first phalanx separate. It is typically caused by forced hyperextension or abduction, such as from a fall onto the thumb or direct trauma. The dislocation can be complete or incomplete and may involve damage to the collateral ligaments.
Diagnosis
Diagnosis is based on the observation of visible deformity, intense pain, inability to move the thumb, and possible swelling. X-rays are essential to confirm the dislocation, assess the position of the joint displacement, and rule out associated fractures.
Differential Diagnosis
Condition | Key Differences |
|---|---|
Bennett fracture-dislocation | Intra-articular fracture at the base of the first metacarpal with displacement of a bone fragment. |
Ulnar collateral ligament sprain | Localised pain without bone displacement on X-rays, possible joint instability. |
Thumb subluxation | Partial joint displacement, with less visible deformity. |
Thumb interphalangeal dislocation | Affects the joint between the phalanges, not the MCP joint, with deformity in a different area of the thumb. |
Emergency Management
Immediate immobilisation of the thumb in its deformed position, avoiding any forceful manipulation that could worsen the injury.
Administration of analgesics and anti-inflammatories to control pain.
Closed reduction of the dislocation under local anaesthesia or sedation, using specific manoeuvres to correctly reposition the joint.
Post-reduction X-rays to confirm successful alignment of the joint.
Immobilisation with a splint or cast, keeping the thumb in slight flexion to protect the ligaments and the reduced joint.
Definitive Treatment
For uncomplicated dislocations, immobilisation with a splint or cast for 3-4 weeks is usually sufficient. In cases of instability, severe ligament damage, or inability to achieve a closed reduction, surgical intervention may be required to repair the ligaments and stabilise the joint. Post-immobilisation rehabilitation with physical therapy is essential to restore thumb mobility, strength, and stability.
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