Oral Presentation NZAPS and ANZSOPS Joint Scientific Meeting

Biomechanical Comparison of Locked Unicortical and Unlocked Bicortical Plate Fixation in Metacarpal Shaft Fractures in a Human Cadaveric Model (640)

Febe Minogue 1 , Wolfgang Heiss-Dunlop 1
  1. Middlemore Hospital, Auckland, AUCKLAND, New Zealand

Locking plate fixation is widely used in large long bone fixation and are now available for small "long" bones in the hand. One potential advantage in using unicortical locked fixation in metacarpals rather than bicortical unlocked fixation, would be less chance of damage to flexor tendons, and reducing the irritation from proud screws among other reasons.

Our aims were to compare fixation strength of unicortical locked plate fixation with bicortical non-locked fixation in human cadaveric model, by assessing strength under cyclical loading conditions and load to failure (LTF).  

16 matched pairs of embalmed and refrigerated human cadaveric metacarpals were allocated to either a locking or unlocked group, then had a transverse osteotomy made. Fractures were stabilised with 2.0mm self-tapping locking or cortical screws . These were loaded with cantilever testing using a 100N cell on an Instron, cyclically loading them at 1000 repititions of 30N and 50N. If there was no visible failure of the fixation from cyclical loading they were then loaded to failure with a 1kN cell. 

There was a significant difference (p=0.03) between average LTF for bicortical non-locking of 186.34N and unicortical locking of 151.39. However, the two groups had a satisfactory biomechanilcal comparison under cyclical loading. This could be a useful adjunct to standard plating technique.