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Carpometacarpal Fracture Dislocation



- See: Metacarpal Extra-articular Base Frx

- Discussion:
    - relatively mobile ring and little CMC joints are more susecptible to dislocation than the immobile index and long rays;
    - fifth CMC is the most frequently injured;
    - pertinent anatomy:
         - ring and little metacarpals articulate w/ distal articular surface of hamate;
         - little metacarpal articulation:
         - is a cancave-convex saddle joint analogous of thumb CMC joint;
         - flexion extension arc of 20-30 deg;
         - rotatory motion assists w/ little finger to thumb opposition;
         - ring metacarpal: 10-15 deg of mobility;
         - index and long metacarpal articulation allow minimal motion;
    - mechanism of frx of little CMC:
         - stability of CMC joint derives from articulation w/ carpal bones,
         - convex bases metacarpals are displaced dorsally losing stability of articulation and causing extrinsic tendon power to be unbalanced;
         - ECU is a deforming force since it inserts onto base of 5th metacarpal;
         - overpull of ECU along w/ interposition of capsule may complicate reduction;
         - most common presentation is the dorsal avulsion frx of metacarpal base;


- Exam:
    - swelling, tenderness, and crepitation over CMC joints;
    - beaware of compartment syndrome;
    - deep motor branch of ulnar nerve:
          - passes adjacent to hook of hamate & can be traumatized;
          - nerve lies just volar to little CMC w/ deep palmar arch below long CMC;


- Radiographs:
    - three views are required: AP, lateral & oblique views:
          - 30 deg oblique view w/ supination: accentuates index CMC;
          - 30 deg oblique view w/ pronation: accentuats fifth CMC;
    - types of frx:
          - epibasal;
          - two part (reverse Bennet);
          - three part;
          - comminuted with impaction;


- Reduction:
    - displaced epibasal & two part frxs dislocations are readily reduced using longitudinal traction on 5th metacarpal followed by manual pressure on the base of the metacarpal;

- Treatment:
    - these frx dislocations are usually unstable frx & require operative fixation;
    - once reduced stabilize joint w/ two 0.45 inch K wires;
    - one pin should be directed across metacarpo-hamate joint & other into the base of the fourth metacarpal;
    - hence, K wires are placed into the fifth and fourth metacarpals;
    - leave K wires in for 6-8 weeks



Carpometacarpal dislocations. Long-term follow-up.

Multiple carpometacarpal dislocations. A review of four cases.

Carpal bone dislocations: an analysis of twenty cases with relative emphasis on the role of crushing mechanisms.

Arthroplasty of the basal joint of the thumb. Long-term follow-up after ligament reconstruction with tendon interposition.

Carpometacarpal joint injuries of the fingers.