To date, the diagnosis of whiplash injuries  has been very difficult and largely based on subjective, clinical  assessment. The work by Winters and Peles Multiple Muscle  Systems–Biomechanics and Movement Organization. Springer, New York  (1990) suggests that the use of finite helical axes (FHAs) in the neck  may provide an objective assessment tool for neck mobility. Thus, the  position of FHA describing head-trunk motion may allow discrimination  between normal and pathological cases such as decreased mobility in  particular cervical joints. For noisy, unsmoothed data, the FHAs must be  taken over rather than large angular intervals if the FHAs are to be  reconstructed with sufficient accuracy; in the Winters and Peles study,  these intervals were approximately 10 degrees.

In order to study the  movements’ microstructure, the present investigation uses instantaneous  helical axes (IHAs) estimated from low-pass smoothed video data. Here,  the small-step noise sensitivity of the FHA no longer applies, and  proper low-pass filtering allows estimation of the IHA even small  rotation velocity omega of the moving neck. For marker clusters mounted  on the head and trunk, technical system validation showed that the IHAs  direction dispersions were on the order of one degree, while their  position dispersions were on the order of 1 mm, for low-pass cut-off  frequencies of a few Hz (the dispersions were calculated from  omega-weighted errors, in order to account for the adverse effects of  vanishing omega).

Various simple, planar models relating the  instantaneous, 2-D centre of rotation with the geometry and kinematics  of a multi-joint neck model are derived, in order to gauge the utility  of the FHA and IHA approaches.

Some preliminary results on asymptomatic  and pathological subjects are provided, in terms of the ‘ruled surface’  formed by sampled IHAs and of their piercing points through the  mid-sagittal plane during a prescribed flexion-extension movement of the  neck.

J Biomechanics. 1994; 27(12):1415-32.

Author information: Woltring HJ, Long K, Osterbauer PJ, Fuhr AW.  Whiplash Analysis, Inc. Phoenix, AZ.