IMPACT EXPERIMENTS IN ORTHOPEDIC BIOMECHANICS

INTRODUCTION: A better understanding of the fracture mechanism, kinematics of the anatomic structure and tissue tolerances can improve clinical prognosis and the design of anthropomorphic test devices. In this study an impact apparatus was designed to do experiments in-vitro on three areas of orthopedic biomechanics, on either hard or soft tissue. This study included three topics: cervical vertebra fractures, Achilles tendon injuries and calcaneal fractures under impact loading. For practical reasons immature bovine and mature porcine specimens, especially the latter, have been the most popular ones used as the model for in-vitro or in-vivo mechanical studies [1,2]. Most studies have classified spinal fractures and dislocations based on radiographic information in order to understand the fracture patterns and instabilities produced by cervical spinal fractures [3,4]. We have attempted to produce clinically-relevant fractures under high speed impact using porcine cervical vertebrae to analyze the mechanical responses of bones and discs in both fractured and non-fractured specimens. Musculotendinous strain injuries have been cited in clinical medicine as among the most common injuries. In recent years many studies have been done examining muscle strain injuries [5,6,7]. Usually they used MTS with slower deformation rates from quasi-static to 50 cm/sec, in contrast to real life injuries, which are usually sudden and fast. Therefore the purpose of this study was to cause high speed Achilles tendon strain injuries and to examine the biomechanical, functional, and structural changes associated with muscle-tendon trauma. A number of different techniques have been described for internal fixation of calcaneal fractures [8,9,10]. Although the stability of the fixation is an important factor in maintaining the position of the reduction, it is not known what fixation strength is necessary to achieve bone union with satisfactory alignment and the biomechanical behavior of these techniques. However, little has been reported for intra-articular fractures of the calcaneus. In this study, we compared the fixation strength of two types of fixation methods, namely lateral buttress plating with or without a longitudinal transfixing screw. Based on this information, a better method of internal fixation for calcaneal fractures could be selected for clinical use.