Abstract
Introduction: Although a variety of fixation techniques have been reported for fixation of oblique or spiral metacarpal fractures, lag screw fixation has been reported to be the most biomechanically stable method. Lag screws are inserted following over-drilling of the proximal cortex, which provides compression at the fracture site. We believe the compression provided by the Leibinger Bow system makes over-drilling unnecessary.
Methods: Twenty fresh-frozen human cadaveric metacarpal bones (index, ring and middle) were utilised. Bones were cleared of soft tissue and the proximal ends were embedded in Wood’s metal using a Teflon mould. Long oblique osteotomies were performed with a fine oscillating saw. Bones were randomly allocated to lagged and non-lagged groups. All bones were held in the Leibinger Bow and fixed with two screws at right-angles across the fracture site. The proximal cortex of the lagged specimens was over-drilled and the non-lagged specimens were not. The bones were subjected to cantilevered bending to failure in a mechanical testing machine. The axial stress was calculated from results for load to failure and the moment of inertia for each specimen.
Results: All specimens failed through the proximal screw. Analysis of variance statistical analysis revealed no significant difference in axial stress between the two groups.
Conclusions: Minute errors during over-drilling of the proximal cortex can easily lead to inadequate fixation. These data suggest that the use of the Leibinger Bow System may eliminate the need for this over-drilling. This not only shortens the procedure, but also reduces the chance of errors leading to poor fixation.
The abstracts were prepared by Professor A. J. Thurston. Correspondence should be addressed to him at the Department of Surgery, Wellington School of Medicine, PO Box 7343, Wellington South, New Zealand
