Biomechanics of the Cervical Spine
Degenerative changes in the cervical spine are known to decrease mobility, necessitating knowledge on normal ranges of motion (ROM) in this spinal region to measure restricted motion. Numerous studies have reported the normal ROM of the cervical spine in the past, yet improved technology continually allows researchers to investigate this topic with more certainty.
In vivo experiments, or those that are performed inside of a living body, may be limited by the motivation of the subject; skin slippage of measuring instruments; and accidental self-loading by a subject. In vitro models - those taken outside of the natural model - allow for a more controlled research environment.
This in vitro study utilized 16 full cervical spine specimens that were dissected to eliminate any non-ligamentous tissue. The authors wished to determine the biomechanical properties of the cervical spine using load-displacement curves. Movements of axial rotation, lateral bending, and flexion-extension were generated with a specially designed loading fixture, and ROM was calculated with stereophotogrammetry.
Results: Primary motions were associated with rotation and translation motions. Regarding flexion-extension, a maximum flexion of 12.3 degrees was measured at C1-C2, and the maximum extension was 20.2 degrees at C0-C1. During axial moment loading, rotation was greatest (56.7 degrees) at C1-C2; during lateral bending, average ROM for all vertebral levels was 7.9 degrees.
This study is relevant to the clinician examining cervical spine motions in three dimensions to understand the effects of trauma and degenerative diseases in the spine.
Panjabi MM, Crisco JJ, Vasavada A, et al. Mechanical properties of the human cervical spine as shown by three-dimensional load-displacement curves. Spine
2001:26(24), pp. 2692-2700.