Thumb Metacarpal #’s
Metacarpal Shaft Fractures
– uncommon, owing to the strength of cortical bone – most of the force is transmitted to the base.
– when they do occur, displacement is common with dorsal angulation due to the strong volar pull of the thenar muscles and FPL
– most can be treated with closed reduction then thumb spica cast
– K-wire if you deem it to be too unstable (whatever that means) – neither Jupiter or Rockwood and Green indicate what is acceptable alignment. If you consider it like the other metacarpals, it is more mobile than all the rest, but itï¿½s function is more critically important.
– rarely is ORIF needed.
Metacarpal Base Fractures
– Classified by Green and Oï¿½Brien
I. Bennettï¿½s fracture (intra-articular, single fragment)
II. Rolandoï¿½s fracture (intra-articular, comminuted)
IIIA. Transverse base fractures (extra-articular)
Oblique base fractures (extra-articular)
IV. Salter II injury in children
Bennettï¿½s Fractures (Green-Oï¿½Brien I)
– the base of the metacarpal is pulled radially and dorsally by the force of abductor pollicis longus, the thenar muscles, and FPL. The adductor pollicis tends to lever the base into abduction, but Jupiter suggests that this is an overestimated effect. The volar, ulnar lip of the base is held down by the strong volar anterior oblique ligament.
– there are many proponents of closed reduction and casting – this fails to hold the fragment, but the supporters suggest that the end result is not bad.
– more reliable treatment is closed reduction and percutaneous fixation – the reduction is by traction, adduction, and a dorsally applied, volarly directed force applied to the base to approximate it with the volar, ulnar lip fragment. This is then secured with two K-wires – either to the trapezium, or to the second metacarpal.
– what constitutes an ï¿½acceptableï¿½ reduction remains unresolved – aim for 2 mm gap or less.
Rolandoï¿½s Fracture (Green-Oï¿½Brien II)
– originally described as having, in addition to the volar lip fragment, a large dorsal fragment.
– depends on severity of comminution
– ORIF if large fragments exist that might accept fixation
– external fixation or simple casting with early motion if severely comminuted
Extra-Articular Fractures (Green-Oï¿½Brien IIIA, IIIB, IV)
– thankfully, the most frequent fracture of the metacarpal base.
– closed reduction and thumb spica casting is usually sufficient; ï¿½One should resist the temptation to overtreat these extra-articular fractures.ï¿½ The Rockwood and Green authors suggest the up to 30o of angulation is well tolerated.
– percutaneous pinning may be required for the long oblique fractures (have a tendency to shorten).
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