Metacarpal Fractures: Anatomy, Injuries and Treatment-Metacarpal Shaft Fractures: The Effect of Shortening on the Extensor Tendon Mechanism

Metacarpal Shaft Fractures: The Effect of Shortening on the Extensor Tendon Mechanism

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This study aimed to determine the acceptable limits of metacarpal shaft fracture shortening in a cadaver model by assessing the extensor lag produced at the metacarpophalangeal (MCP) joint. The study used fresh-frozen cadaver hands to create metacarpal shaft fracture models and performed sequential shortening up to 10 mm. The results showed that for every 2 mm of metacarpal shortening, an average of 7° of extensor lag was produced at the MCP joint. This suggests that the MCP joint's capacity for active hyperextension may compensate for the extensor lag caused by metacarpal shortening in the clinical setting.<br /><br />Metacarpal fractures are common hand injuries, accounting for about 22% of hand fractures. The acceptable limits of fracture shortening have not been well established. Previous studies have varied in their findings and justifications for the acceptable limits of shortening, ranging from none to 6 mm or more.<br /><br />In this study, it was found that up to 6 mm of shortening produced an average extensor lag of 21° at the MCP joint. The deep transverse intermetacarpal ligament and the adjacent metacarpal bones and interosseous muscles were identified as obstacles to further shortening beyond 6 mm. The study also noted that most MCP joints exhibited baseline hyperextension of 20°, which would still allow for near-neutral extension even with the extensor lag produced by 6 mm of shortening.<br /><br />This study focused on the extensor tendon mechanism and did not assess the effect of metacarpal shortening on the flexor tendon mechanism. However, it was mentioned that relative lengthening of the flexor tendons due to metacarpal shortening should not be problematic since both the flexor and lumbrical would be relatively lengthened equally. The study concluded by stating that their current clinical approach to metacarpal shaft fractures with shortening involves obtaining reduction of rotational or angulatory deformities and considering surgical restoration of metacarpal length if adequate MCP joint extension is not achieved.<br /><br />In summary, this study found that for every 2 mm of metacarpal shortening, an average of 7° of extensor lag was produced at the MCP joint. The study also noted that most MCP joints exhibited baseline hyperextension, which would still allow for near-neutral extension even with the extensor lag produced by 6 mm of shortening. These findings suggest that the MCP joint's hyperextension capacity may compensate for the extensor lag caused by metacarpal shortening in the clinical setting.

Keywords

metacarpal shaft fracture

shortening limits

extensor lag

metacarpophalangeal joint

cadaver model

fracture models

acceptable limits

hand injuries

hyperextension capacity

clinical setting