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Dear all,
I wonder if the following observation is relevant to the discussion
triggered, before Christmas, by Dr Chris Kirtley "Calculation of 2D Angles ('CAST' problem)".
I use a VICON 460 with PlugInGait. Recently, from an hemiplegic patient with
a fixed equinus of 40° and a dynamic equinus of about 60-65° (combined
plantar flexion of ankle and mid foot joints), the range of computed plantar
flexion was 45° to 60° when the tibial torsion was estimated by the
software.
These values were compatible with the video recordings.
BUT when the clinically measured tibial torsion (25° external) was forced in the
computation of the static trial, (entered as -25 + zeroing the "shank offset value" computed in the "subject measurement", the computed ankle angle on the equinus side became a DORSI FLEXION ranging
from 115° to 130°....... However, on the normal side the ankle angle remains within a
normal range. These strange results and unrealistic angle values appear
every time a significant equinus is present. Is it an
effect of the gimbals lock phenomenon? Or just a bug in the software?
As usual all the answers will be compiled and posted.
yves
Yves Blanc Ph.D.
Laboratoire de cinésiologie
Hôpital Cantonal Universitaire
1211 GENEVE 14. CH
tél; XX 41 22/3727 827
fax: XX 41 22/37 27 799
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I wonder if the following observation is relevant to the discussion
triggered, before Christmas, by Dr Chris Kirtley "Calculation of 2D Angles ('CAST' problem)".
I use a VICON 460 with PlugInGait. Recently, from an hemiplegic patient with
a fixed equinus of 40° and a dynamic equinus of about 60-65° (combined
plantar flexion of ankle and mid foot joints), the range of computed plantar
flexion was 45° to 60° when the tibial torsion was estimated by the
software.
These values were compatible with the video recordings.
BUT when the clinically measured tibial torsion (25° external) was forced in the
computation of the static trial, (entered as -25 + zeroing the "shank offset value" computed in the "subject measurement", the computed ankle angle on the equinus side became a DORSI FLEXION ranging
from 115° to 130°....... However, on the normal side the ankle angle remains within a
normal range. These strange results and unrealistic angle values appear
every time a significant equinus is present. Is it an
effect of the gimbals lock phenomenon? Or just a bug in the software?
As usual all the answers will be compiled and posted.
yves
Yves Blanc Ph.D.
Laboratoire de cinésiologie
Hôpital Cantonal Universitaire
1211 GENEVE 14. CH
tél; XX 41 22/3727 827
fax: XX 41 22/37 27 799
---------------------------------------------------------------
To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl
For information and archives: http://isb.ri.ccf.org/biomch-l
---------------------------------------------------------------