The effect of metacarpal shortening on digital flexion force.

Metacarpal shaft fractures are common injuries that frequently unite with some shortening of the metacarpal. The aim of this study was to determine the effect of metacarpal shortening on digital flexion force. The index metacarpal of six cadaveric upper limbs was incrementally shortened. The flexion force produced at the end of the finger was recorded using a small load cell. At full extension, there was no significant change in flexion force produced regardless of the amount of shortening. However, at 50% aggregate flexion the loss of force became statistically significant at a shortening of 7.5 mm or more. At full digital flexion, the loss of force became statistically significant at shortening of 5 mm or more. At increasing amounts of finger flexion, progressive metacarpal shortening produces proportionally greater loss of fingertip flexion force. From this study it appears that metacarpal shortening of up to 5 mm should give minimal loss of finger flexion force.