SAGITTAL-PLANE MOBILITY OF THE CAT CERVICAL-SPINE

The present study was conducted to evaluate the nature of sagittal-pla ne motion across cervical vertebral joints and to identify the centers of rotation for each joint in anaesthetized cats X-rayed in a range o f head-neck postures. Relative positions of adjacent pairs of vertebra e were assessed by constructing transparent templates for each vertebr a that could be overlaid onto different X-rays, and then by digitizing the locations of three markers attached at a distance from each templ ate. The finite centers of rotation for each joint were estimated usin g a rigid-body method. The errors associated with the estimates were q uantified further by using a method in which the positions of digitize d markers were fitted to concentric circles using a least-squares appr oach. The center of rotation between the skull and C1 was located at t he cranial articular facets between the two bones. The center of rotat ion between C1 and C2 was situated near the tip of the odontoid proces s close to the site of attachment of the transverse ligaments. Centers of rotation for the other cervical vertebral joints were located in t he region of the intervertebral disc. A similar range of values was ob tained for centers of rotation when extended or flexed postures were u sed for the calculations, suggesting that the centers of rotation may not move markedly throughout a range of sagittal-plane rotations of ap proximately 90-degrees at the skull-C1 joint and about 15-30-degrees a t the other cervical joints. These results showed that all cervical jo ints rotated during sagittal-plane motion. A minimal representation of the musculoskeletal mechanics of the feline neck probably requires mu ltiple segments, each corresponding to a single vertebral bone.