Animation of in vitro biomechanical tests

Interdisciplinary communication of three-dimensional kinematic data arising from in vitro biomechanical tests is challenging. Complex kinematic repres entations such as the helical axes of motion (HAM) add to the challenge. Th e difficulty increases further when other quantities (i.e. load or tissue s train data) are combined with the kinematic data. The objectives of this st udy were to develop a method to graphically replay and animate in vitro bio mechanical tests including HAM data. This will allow intuitive interpretati on of kinematic and other data independent of the viewer's area of expertis e. The value of this method was verified with a biomechanical test investig ating load-sharing of the cervical spine. Three 3.0 mm aluminium spheres we re glued to each of the two vertebrae from a C2-3 segment of a human cervic al spine. Before the biomechanical tests, CT scans were made of the specime n (slice thickness= 1.0mm and slice spacing=1.5mm), The specimens were subj ected to right axial torsion moments (2.0Nm). Strain rosettes mounted to th e anterior surface of the C3 vertebral body and bilaterally beneath the fac et joints on C3 were used to estimate the force flow through the specimen. The locations of the aluminium spheres were digitised using a space pointer and the motion analysis system. Kinematics were measured using an optoelec tronic motion analysis system. HAMs were calculated to describe the specime n kinematics. The digitised aluminium sphere locations were used to match t he CT and biomechanical test data (RMS errors between the CT and experiment al points were less than 1.0mm). The biomechanical tests were "replayed" by animating reconstructed CT models in accordance with the recorded experime ntal kinematics, using custom software. The animated test replays allowed i ntuitive analysis of the kinematic data in relation to the strain data. Thi s technique improves the ability of experts from disparate backgrounds to i nterpret and discuss this type of biomechanical data. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.