Carpometacarpal Fracture Dislocation
- See: Metacarpal Extra-articular Base Frx
- 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;
- 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;
- 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:
- two part (reverse Bennet);
- three part;
- comminuted with impaction;
- 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;
- 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.
Original Text by Clifford R. Wheeless, III, MD.
Last updated by Data Trace Staff on Thursday, October 4, 2012 2:45 pm