Metacarpal #’s Excluding the Thumb
The two radial metacarpals form the fixed, stable longitudinal axis, while the 4th and 5th are mobile. The bases are firmly adherent to the carpometacarpal joint, with minimal motion of the 2nd and 3rd, and 15-25o of flexion and extension of the 4th and 5th. The dorsal surface is the tensile surface, while the volar is the compressive surface.
Metacarpal Head Fractures
– if possible, these should be anatomically reduced and fixed with small K-wires or AO minifragment screws. It is not clear what constitutes ï¿½satisfactoryï¿½ reduction.
– if severely comminuted, consider external fixation to achieve length.
Metacarpal Neck Fractures
These are very common, particularly of the 5th. Virtually all present with volar angulation. The amount of acceptable angulation depends on the metacarpal injured. The 2nd and 3rd are less mobile, and therefore tolerate less angulation than the 4th and 5th. Generally speaking, these are easy to reduce by flexing the MCP to 90o, and pushing dorsally on the proximal phalanx. What is not so clear, is whether this reduction can be maintained with cast/external immobilization. Various devices have been advocated, in particular, the Galveston brace in which the MCP is flexed to 90o, but the PIP and DIP joints are allowed to move.
The authors of the Rockwood and Green chapter suggest that even if the fracture is reduced, the splint will likely not hold it reduced and residual angulation is inevitable with a dorsal prominence on the hand. If this is unacceptable to the patient, they fix them with K-wires. This is admittedly a bit nihilistic of an approach, and the authors also state that for the significantly angulated, they will often try reduction and splinting, with the hope that this will reduce, but not eliminate, the ultimate angular deformity. As a blanket statement, they say that a flexion deformity of greater than 40o is ï¿½severeï¿½ and is associated with pseudoclawing which would be functionally suboptimal. Pseudoclawing (I think) is caused by the intrinsics being stretched out over the flexed metacarpal head, so that the MCP joint gets extended by the extensors, while the DIP and IP joints are flexed down by the unopposed FDP and FDS tendons.
5th Metacarpal – accept up to 30o of angulation (This number varies amongst authors from 20 to 50.) Most authors accept up to 30o, because this is about what the CMC joint is capable of.
4th Metacarpal – accept up to 20o of angulation, also because this is about what the CMC joint is capable of.
2nd and 3rd Metacarpal – accept up to 10o of angulation.
– beyond the acceptable degrees of angulation, these should be fixed with K-wires (0.045).
Metacarpal Shaft Fractures
These can be transverse, spiral/oblique, or comminuted. In general, the border metacarpals are less stable than the central two metacarpals (3 and 4), as the former have more intrinsic support from the intrinsics and transverse metacarpal ligament.
Jupiterï¿½s book indicates that 5o of malrotation leads to 1.5 cm of digital overlap, suggesting that ANY rotational deformity should be corrected. They indicate that 3-4 mm of shortening is acceptable, but beyond 4 mm, malrotation often occurs. The Rockwood and Green authors indicate that ï¿½at least 5 mm of shortening and probably up to 10 mm can be accepted without loss of function if there is no angulation or rotational alignmentï¿½.
– again, minimal angulation of the 2nd and 3rd is acceptable, being the stable metacarpals. Jupiter suggests that up to 10o of dorsal angulation is acceptable in the 2nd and 3rd metacarpals, while 20o is acceptable in the 4th and 5th. No rotation is acceptable.
– if, after closed reduction, the angulation is acceptable and the rotation is correct, treat with a volar/dorsal slab with the MCPï¿½s held in about 60-70o of flexion.
– if not acceptable, ORIF with K-wires, plates, cerclage wires. Consider K-wiring to an adjacent metacarpal.