OTA 1997 Posters - Foot & Ankle Fractures

Biomechanical Testing of Sustentacular Screw Placement in a New Experimental Model of Calcaneal Fractures

Andrew R. Jones, MD, PhD, Patrick P. Lin, MD, Simon Roe, BVSc, PhD, Matthew Kay, BS, C. Frank Abrams, PhD

University of North Carolina; NC State University, Wake AHEC, Raleigh, North Carolina, USA

Purpose: The purpose of this study was to determine whether the sustenculum screws, which are used to fix the central fragment in displaced articular calcaneus fractures, should be incorporated into the lateral plate construct. This study therefore investigates further the use of lateral plate fixation methods for calcaneus fractures. Many different techniques of internal fixation have been described. The study of these fractures has been limited in part by the lack of a suitable laboratory model. In this study, a new cadaveric model of calcaneal fractures was developed, employing a combination of osteotomies and impaction. The model consistently reproduced a central fragment comminuted intra-articular calcaneus fracture, and was used to examine this one aspect of internal fixation.

Methods: Six pairs of cadaver legs were used, and each pair was randomly divided between two experimental groups. In Group A (Screws Out), the posterior facet screws were outside of the plate, and in Group B (Screws In), the screws were incorporated into the plate. The strength of the reconstructed calcaneii were evaluated by axial loading the limb through the tibia using a mechanical testing device (Instron).

Results/Conclusions: Stiffness and energy to failure were significantly greater and Bohler's angle significantly greater in Group B (Screws In). There were no intra-articular screws in the subtalar joint found during dissections following testing. It was concluded that the position of the articular fragment of comminuted calcaneal fractures will be maintained at higher loads when the screws in the posterior facet are incorporated into the lateral plate. The model of calcaneal fractures described in this study may be suitable for examining other aspects of fixation.