Abstract
Dear Sir,
van Velzen JM, Houdijk H, Polomski W, van Bennekom CAM. 2005. Usability of gait analysis in the alignment of trans-tibial prostheses: A clinical study. Prosthet Orth Int 29(3): 255 – 267.
The authors have conducted an excellent study of the use of gait analysis to interpret the effects of changes in alignment of leg prostheses. They have, however, repeated the error made by many analysts in Figure 6 and its caption by showing and stating that the vector of the resultant ground to foot passes through the centre of mass of the body. This is only true if the principal axes of the body remain at a constant inclination to the laboratory reference axes. If the body inclines cyclically relative to the laboratory axes it will develop cyclical angular accelerations and the body equilibrium under the action of the related inertial couples will require that the ground to body force vector be offset cyclically from the centre of mass. These angular accelerations occur in normal walking of unimpaired individuals but are of larger magnitude in the gait of amputees and other disabled persons.
Yours sincerely
John P. Paul
Bioengineering Unit
University of Strathclyde
Glasgow G4 0NW
UK