Development of a system for in vitro neck muscle force replication in whole cervical spine experiments

Study Design. An in vitro biomechanical study. Objectives. To develop and evaluate a new in vitro whole cervical spine mod el that provides to the specimen, in vivo-like mechanical characteristics. Summary of Background Data. In vitro studies of kinematics, kinetics, and t rauma using isolated spine specimens (head-T1 vertebra) have usually applie d upward force to the head, resulting in tensile spine forces, contrary to the physiological compressive forces present in vivo. Further, the in vitro load-displacement curves have never been compared with the corresponding i n vivo data. Methods. A novel muscle force replication (MFR) system is presented. It con sists of a set of compressive forces applied to the various vertebrae and o cciput of a whole cervical spine specimen. Two protocols, with and without MFR, were evaluated using standardized flexibility testing. Ranges of motio n (ROM) and load-displacement curves were documented, and contrasted with s imilar in vivo data. Results. Results for the MFR were found to be similar to the in vivo measur ements, with respect to the intersegmental and whole neck motions as well a s the load-displacement curves, thus validating the MFR approach. Conclusions. The new model advances the in vitro testing, which uses whole cervical spine specimens.