- 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.
M. Gurland.
Hand Clin. Vol 8. 1992. p 733-744.
