Shape analysis of the cervical spinous process.

Most textbooks describe the bifid spinous process as a shape associated with the typical cervical vertebra. Somewhere later they may acknowledge that cervical vertebrae are not always bifid, and that its appearance may be asymmetric. A high incidence of bifid cervical spinous processes may be a human characteristic, but because of known racial/geographic variation it may not be a very good one. Rarely can one find a satisfactory explanation of the functional or developmental basis for this shape variation. This article explores the distinctive shape of the cervical spinous process. Analysis is based upon the spinous processes of the third through seventh cervical vertebrae from fifty individuals. Shape differences were evaluated using the techniques of geometric morphometrics. Statistical comparisons were based upon 1000 permutations of a MANOVA based analysis. Significant shape differences were identified among the cervical vertebrae. However, post hoc analysis failed to identify significant differences between the C3 and C4 and between the C4 and C5 spinous process shapes. Primary shape differences were due to the depth of the bifid separation and the length of the process. Vertebrae with shorter spinous processes tended to display a more pronounced bifid condition. Combined observations from this and several other investigations suggest that a combination of variation in the spinalis cervicis muscle and behavioral patterns associated with cervical load may provide the best explanation for the shape variation in the cervical spinous process. Clin. Anat. 30:894-900, 2017. © 2017 Wiley Periodicals, Inc.