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Herman J. Woltring
11-17-1989, 04:51 AM
Dear Biomch-l readers,

Among the replies received until now on my standardization query of a few days
ago, there was one with a review paper currently in print:

Goeran Selvik, Roentgen Stereophotogrammetric Analysis - A Review Article,
Acta Radiologica 31(1990), Fasc. 2.

In this paper, X is defined as the transverse axis (from the right, -, to the
left, +, of the body in the `anatomical' position), Y is the vertical axis (from
the feet, -, to the head, +), and Z is the sagittal axis (from the posterior, -,
to the anterior, +, direction). This applies equally to left, central, and
right body segments; by consequence, anatomically oriented terms such as endo-/
exorotation, ab-/adduction and medio-lateral translation in the limbs would have
opposite signs between the ipsi- and contralateral sides. As a motivation for
this choice, reference was made to M.M. Panjabi, A.A. White & R.A. Brand in the
Journal of Biomechanics 7(1974), 385 and to M. Williams & H.R. Lissner, Biome-
chanics of Human Motion, W.B. Saunders Co., Philadelphia 1962.

Furthermore, segment rotations are defined as a Cardanic convention about body-
fixed axes, in the sequence X, Y and Z from the neutral or reference attitude.
Assuming (as is the usual situation) that joint motion is defined as distal
w.r.t. proximal (in the case of the limbs, not necessarily for other parts of
the body), this results in `body-fixed' axes denoting flexion-extension in the
proximal segment and ab-/adduction in the distal segment, while endo-/exorota-
tion of the joint is defined about a `floating' axis, in the sense of Grood &
Suntay (1983). This is different from these authors' definition who chose
endo-/exorotation about a distally fixed axis, and ab-/adduction about the
`floating' axis. As indicated in a 1988 paper by Blankevoort et al. in the
Journal of Biomechanics, the numerical difference is small for typical knee
angulations. However, if one desires to standardize rotational parametriza-
tions, it might be useful to define one which can also be used for other joints
and for segment motion definitions.

Since Roentgenstereophotogrammetry is a highly advanced field of quantitative
biokinematics, its results should be carefully considered for their transfer-
ability to whole-body kinematics in gait and other forms of functional move-
ment. In the former, much interest is directed to translations as in, e.g.,
joint loosening, and less to rotations. In whole-body movement studies, it is
just the opposite, thus special attention to rotational parametrizations might
deserve even more attention than given in Selvik's work.

I would be grateful for further reactions -- Herman J. Woltring (CAMARC/NL).