Signed Grood-Suntay / ISB joint angles from segment frames

Computes the three signed clinical joint angles - flexion/extension, ab/adduction and internal/external rotation - from a proximal and a distal anatomical segment frame, following the Grood-Suntay joint coordinate system (the basis of the ISB recommendations). The flexion axis is the proximal medio-lateral (Z) axis, the rotation axis is the distal long (Y) axis, and the ab/adduction axis is the floating axis perpendicular to both. This is equivalent to a Z-X-Y Cardan decomposition of the relative rotation \(R = R_p^\top R_d\); because it is sequence-dependent, the flexion angle is extracted first and the rotation last.

Usage

groodSuntayAngles(proximal, distal, degrees = TRUE)

Arguments

proximal, distal

n x 3 x 3 arrays of per-frame segment axes (columns X = antero-posterior, Y = long, Z = medio-lateral), as returned by jointCoordinateSystem.

degrees

Logical; return degrees (default) or radians.

Value

A numeric n x 3 matrix with columns flexion, abduction and rotation.

References

Grood ES, Suntay WJ (1983). "A joint coordinate system for the clinical description of three-dimensional motions: application to the knee." J Biomech Eng, 105(2), 136-144.

See also

jointCoordinateSystem(), calculateJointAngles()