- 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.