Abstract
The use of plates and screws for the treatment of certain metacarpal fractures is well established. Securing plates with bicortical screws has been considered an accepted practice. However, no study has questioned this.
This study biomechanically assessed the use of bicortical versus unicortical screws in metacarpal plating. Eighteen fresh frozen cadaveric metacarpals were subject to midshaft transverse osteotomies and randomly divided into two groups. Using dorsally applied Leibinger 2.3mm 4 hole plates, one group was secured using 6mm unicortical screws, while the second group had bicortical screws. Metacarpals were tested to failure using a four point bending protocol in an apex dorsal direction on a servo-hydraulic testing machine with a 1kN load cell. Load to failure, rigidity, and mechanism of failure were all assessed.
Each group had three samples that did not fail after a 900 N load was applied. Of those that failed, the mean load to failure was 596N and 541 N for the unicortical and bicortical groups respectively. These loads are well in excess of those experienced by the in-vivo metacarpal. The rigidity was 446N/mm and 458N/mm of the uni-cortical and bicortical groups respectively. Fracture at the screw/bone interface was the cause of failure in all that failed, with screw pullout not occurring in any.
This study suggests that there may be no biomechanical advantage in using bicortical screws when plating metacarpal fractures. Adopting a unicortical plating method simplifies the operation, and avoids potential complications associated with overdrilling and oversized screws.
Correspondence should be addressed to the editorial secretary: Associate Professor Jean-Claude Theis, Department of Orthopaedic Surgery, Dunedin Hospital, Private Bag 1921, Dunedin, New Zealand.
