A preliminary modelling study on the equine cervical spine with inverse kinematics at walk

Abstract

The motion of the atlanto-occipital, cervical vertebral and cervicothoracic joints play an important role in equestrian sports and they are also common sites for lesions limiting performance in horses. To calculate inverse kinematics based on cervical vertebral motion and to develop a model close to the measured neck movements. Measurements were recorded in 6 horses without neck pain. Reflective markers were placed on both cristae facialis, both sides of cervical vertebra 1, 3 and 6 on the withers and hooves. The neck model was reconstructed from CT scans of the osseus structures and was developed in SIMM (Software for Interactive Musculoskeletal Modelling). Inverse kinematics calculation was done in OpenSim. Three degrees of freedom: Flexion-extension (FE), axial rotation (AR) and lateral bending (LB) were considered. The simulated motion was generated from the recorded motion of the skin markers. The differences in angular range of motion (ROM) of the joints were analysed using paired sample t tests. From the model, the smallest FE ROM was in the C5-C6 joint (2° ± 1°) and the largest was in the C3-C4 joint (11° ± 5°). The smallest AR ROM was in the C5-C6 joint (2° ± 1°) and largest AR ROM was in the atlantoaxial joint (7° ± 2°). The smallest LB ROM was in the C5-C6 joint (2° ± 1°) and the largest LB ROM was in the cervicothoracic joint (18° ± 5°). There were significant differences between the ROM of joints in 51 of 168 comparisons (P < 0.05). The result of the motion of each joint gives an insight into the biomechanics of the equine neck. The small FE ROM at C5-C6 illustrates the pathogenetical relevance of the model for the development of osteoarthritis. The calculated data also provides a source for inverse dynamics.