The three most common etiologies of metacarpal fractures are direct force (i.e. "crush" injury), axial loading ("boxer's fracture"), and torsional strain. Fractures of the 3rd and 4th metacarpals are generally stable. receiving significant support from adjacent metacarpals, interosseous muscles, and intermetacarpal ligaments. Fractures of so-called "border" metacarpals are most concerning since they are more prone tto dorsal/volar angulation, malrotation, and shortening.
Acceptable (not requiring reduction) dorsal/volar angulation depends upon which metacarpal is fractured and the location of the fracture along the shaft. The index and ring carpometacarpal (CMC) joints are relatively immobile, thus tolerating little-to-no metacarpal angulation -- generally 15Â° or less. Whereas, the CMC joints of the 4th and 5th digits have a broader range of motion, permitting up to 70Â° of fracture angulation in some cases. Additionally, proximal shaft fractures will angulate more than distal fractures.
Malrotation is an infrequent, yet significant problem. All but the slightest cases of malrotation require surgical reduction and fixation. Shortening of the metacarpal shaft generally occurs only with oblique or spiral fractures, and is not usually concerning unless it exceeds 3 mm. Additional sequelae of metacarpal fractures include loss of the MCP joint prominence (the "knuckle"), displacement of the proximal metacarpal head into the palm, and finger clawing.
Regardless of fracture characteristics, any fracture resulting in dysfunctional impairment of the hand due to neurovascular insult, malrotation, clawing, a painful palmar metacarpal head, et cetera, requires surgical correction.