Meeting Abstract

54.5  Thursday, Jan. 6  Intervertebral joint kinematics during the startle response in Striped bass, Morone saxatilis NOWROOZI, B.N.*; BRAINERD, E.L.; Brown University; Brown University bryan_nowroozi@brown.edu

The vertebral column provides both stiffness and flexibility to the body to aid in locomotion in a variety of vertebrate taxa. Despite this conserved function, the morphology of vertebrae and intervertebral joints (IVJs) varies greatly across vertebrates. In ray-finned fishes, the vertebral centra are biconid hourglass-shaped structures that house the IVJ tissues both between and within their hollow cones. This amphicoelous morphology is present in all but a few actinopterygian fish species and spans diverse swimming styles. It has been suggested that these amphicoelous IVJs function as simple hydrostatic hinges, bending only in the lateral plane. Here we test this hypothesis by measuring the 3D kinematics of amphicoelous vertebrae in the striped bass during the startle response. We use X-ray Reconstruction of Moving Morphology (XROMM) to visualize the 3D motions of one caudal IVJ in three individuals. By applying a helical axis analysis to the rigid body kinematics for each reconstruction we identify the center of rotation and the neutral axis of bending. Given this center of rotation, we place joint coordinate systems accordingly to measure rotations and translations in all 6 degrees of freedom. Results show that the caudal IVJs of striped bass do not act as simple hinges. We saw substantial rotation in all three planes of motion: lateral bending, torsion, and dorsoventral bending. Lateral bending and torsional rotation angles ranged up to 20°, while dorsoventral bending ranged up to 9°. Translations along any of the three axes were generally less than 1 mm.