CMC Dislocations (Excluding The Thumb)

Modern Study Review (AI-Generated)

High-Yield Summary

Carpometacarpal (CMC) dislocations excluding the thumb are rare but clinically significant injuries often associated with high-energy trauma and metacarpal fractures. These injuries primarily involve the 4th and 5th CMC joints, which allow limited but important mobility for hand function. Prompt diagnosis is challenging due to subtle radiographic findings but critical to prevent chronic instability, pain, and post-traumatic arthritis. Modern management emphasizes early closed reduction and stabilization to restore alignment and preserve hand function.

Key Diagnostic Findings

Aspect	Details
Anatomy	– CMC joints are primarily gliding (arthrodial) joints except the 5th, a modified saddle joint. – 2nd and 3rd CMC joints are rigid; 4th and 5th allow 15-20° flexion. – Deep motor branch of ulnar nerve lies volar to 5th CMC near hook of hamate. – Deep palmar arterial arch lies beneath 3rd CMC joint.
Clinical Presentation	– History of trauma, often high-energy. – Swelling, pain, and deformity over dorsal hand. – Associated metacarpal fractures common. – Possible ulnar nerve symptoms if deep branch involved.
Imaging	– Standard AP, lateral, and oblique hand X-rays. – Look for loss of normal CMC joint alignment, especially dorsal displacement. – CT scan may be needed for subtle or complex injuries.
Classification	– No widely adopted formal classification system specific to non-thumb CMC dislocations. – Injury patterns often described by direction (dorsal vs volar) and associated fractures.

Current Gold Standard Treatment

Phase	Treatment Approach
Acute	– Prompt closed reduction under anesthesia. – Percutaneous K-wire fixation preferred to maintain reduction. – K-wires can be placed from metacarpal to adjacent metacarpal or into carpal bones. – Open reduction and internal fixation (ORIF) reserved for open injuries or irreducible dislocations. – Emphasis on restoring metacarpal shaft alignment and length.
Chronic (>3 weeks)	– Observation if mild incongruity and minimal symptoms. – Symptomatic arthritis treated with arthrodesis or interposition arthroplasty.

Modern Complications & Outcomes

Complication	Notes
Chronic instability	Persistent subluxation or dislocation leads to pain and functional impairment.
Post-traumatic arthritis	Common in untreated or malreduced injuries, especially at 4th and 5th CMC joints.
Ulnar nerve injury	Possible if deep motor branch is compressed or injured during trauma or surgery.
Stiffness and loss of grip strength	Due to prolonged immobilization or joint incongruity.
Outcomes	Early reduction and stable fixation correlate with improved pain relief and functional recovery.

Classic Clinical Notes