![]() In addition to simple fracture characteristics, the anatomical cascade of the metacarpals should play into the physician’s diagnosis. Because of the natural hyperextension at the MCP, a total of 5 to 6 mm of metacarpal height (21 to 30 degrees of extensor lag) is tolerable before detrimental effects occur. Still, for every 2 mm of metacarpal height that is lost, there are a concomitant 7 degrees of extensor lag at the MCP joint. Īs loss of metacarpal height becomes more severe, extension lag of the digit in question becomes more significant. Metacarpal-phalangeal (MCP) joints show an average of 20 degrees of hyperextension. It is also important to consider rotational and shortening deformities as well as multiple metacarpal fractures and the amount of initial displacement, as these can be indicators of unstable fractures that will necessitate operative fixation. Location is also important and is usually divided into the distal aspect being the neck or head, the shaft, and the base being the most proximal portion. ![]() Examples include transverse, oblique, spiral, displaced, or comminuted. ![]() Ĭlassification of these injuries has its basis on basic fracture characteristics. An external rotation oblique film allows for visualization of the fourth and fifth MC fractures and CMC dislocations, while an internal rotation oblique film allows for visualization of the second and third MC and CMC fracture/dislocations. Imaging of metacarpal fractures should include standard PA and lateral as well as an oblique view to further exam the ulnar-most digits. Similarly, intraarticular fractures of the metacarpal base also arise from axial loads and can lead to carpometacarpal joint arthritis. These neck fractures often result from a combination of axial load with a slight flexion moment, which causes the neck to fracture and displace volarly. Perhaps the most well-known fracture type is the so-called “boxer's fracture,” implying a fracture of the neck of the fifth metacarpal with a volar displacement that presents in 20% of all hand fractures. Oblique fractures can be seen after rotational and axial loads, while bending forces with axial loads produce a butterfly fragment with differing degrees of comminution again depending on the amount of force imparted by the injury. For metacarpal shaft fractures, direct blows to the dorsum of the hand can result in transverse fractures with varying degrees of comminution depending on the velocity of the injury. Metacarpal fractures can occur in a variety of settings, but most commonly occur as a result of direct trauma.
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