Prepared for the
12th Annual Upper Cervical Spine Conference

Edward F. Owens, Jr. MS, DC
Life College, Marietta, GA

An appreciation for the character and magnitudes of spinal intersegmental motion is an important part of the chiropractor's education. While there is literature available based on cadaver studies that describes the representative motions of individual joints, it is difficult for most students to gain an appreciation of that motion. Cineradiography provides a global view of skeletal motion, however, it is still difficult to distinguish specific intersegmental motion. Also, the results of computerized kinematic and dynamic models of the spine have been difficult to visualize because of the lack of high resolution three-dimensional graphic models to demonstrate them.

To render spinal kinematics more accessible to students and practitioners, a computerized spinal animation project is underway at Life College. Graphical design and animation software (3D Studio, Autodesk, Inc.), running on an MS-DOS compatible computer ( 486-DX2-66) is being used to stage and manipulate high resolution digitized vertebrae (Viewpoint DataLabs, Orem, Utah).

An animation is developed by positioning the modeled vertebrae in a "scene", complete with simulated lighting and cameras to provide a perspective view. A bone-like surface material is applied to the model to give it a realistic appearance. The motion of each vertebra in an animation is carefully programmed to simulate real motion. The general ranges of motion were taken from the literature (White AA, Panjabi MM: The basic kinematics of the human spine. Spine 3:12, 1978), but the particular characteristics of the motion were developed by applying two general skeletal motion criteria:

  1. Bones cannot pass through each other,
  2. Synovial joint surfaces should stay in uniform contact as they glide on each other.
Applying these criteria makes possible the investigation of the specific character of spinal motion, such as instantaneous axis of rotation. In the case of Atlas-Axis movement, for example, it was found that the atlas needed to translate posteriorward during extension so that the anterior arch stayed in uniform contact with the dens. Also, when two synovial joints were involved in a motion, it was possible to locate the center of motion by finding the intersection of perpendicular bisectors to the joint surfaces. The detail of movement in the animations is sufficient to demonstrate complex coupled motions, such as lateral flexion and rotation. Animations have also been carried out to show the effects of lack of coupling and displacement of the axis of motion of the vertebrae.

To date, a series of animations has been developed that demonstrates the motion of the cervical spine in flexion/extension, lateral flexion and rotation. Global, whole neck movements have been simulated along with specific representative intersegmental movements. Animations can be viewed on video tape for classroom presentations or downloaded via the Internet for private use. These animations have already been used in motion palpation and technique classes at Life College to demonstrate spinal anatomy and kinematics.