Orthopaedics

12-16-1998, 01:58 AM

Hello all!

I am a graduate student at The University of Texas Southwestern Medical

Center at Dallas working on a telemetry 6 DOF spatial linkage device for

knee joint assessment, and I am using the screw axis theory to determine a

joint coordinate system. The procedure involves placing the device on a

subject's limb and having them flex and extend a few degrees to estimate the

flexion/extension screw axis and then internally/externally rotate a few

degrees with the limb at 90 degrees of flexion to estimate the

internal/external rotaion screw axis. Then by taking the cross product of

the F/E and I/E axes, I should be able to compute the varus/valgus axis.

The problem is that the F/E axis and the I/E axis are described in terms of

direction cosines and a point on each axis. When I take the cross product

of the F/E and I/E axes, I get the V/V axis, which in theory is

perpendicular to the F/E and I/E axes, but I cannot find a point on the V/V

axis in order to fully describe a vector which describes that axis.

I could really use the help of those researchers who have extensive

experience in the mathematics of spatial linkage devices.

If anyone has any information about this, any insight on my problem, or a

very good reference article, I would really appreciate it.

____________________________________________

Ericka F. Calton

Graduate Student in Biomedical Engineering

Motion and Performance Laboratory

Baylor University Medical Center at Dallas

214.820.6300 (fax:214.820.1988)

e-mail: orthop@baylordallas.edu

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I am a graduate student at The University of Texas Southwestern Medical

Center at Dallas working on a telemetry 6 DOF spatial linkage device for

knee joint assessment, and I am using the screw axis theory to determine a

joint coordinate system. The procedure involves placing the device on a

subject's limb and having them flex and extend a few degrees to estimate the

flexion/extension screw axis and then internally/externally rotate a few

degrees with the limb at 90 degrees of flexion to estimate the

internal/external rotaion screw axis. Then by taking the cross product of

the F/E and I/E axes, I should be able to compute the varus/valgus axis.

The problem is that the F/E axis and the I/E axis are described in terms of

direction cosines and a point on each axis. When I take the cross product

of the F/E and I/E axes, I get the V/V axis, which in theory is

perpendicular to the F/E and I/E axes, but I cannot find a point on the V/V

axis in order to fully describe a vector which describes that axis.

I could really use the help of those researchers who have extensive

experience in the mathematics of spatial linkage devices.

If anyone has any information about this, any insight on my problem, or a

very good reference article, I would really appreciate it.

____________________________________________

Ericka F. Calton

Graduate Student in Biomedical Engineering

Motion and Performance Laboratory

Baylor University Medical Center at Dallas

214.820.6300 (fax:214.820.1988)

e-mail: orthop@baylordallas.edu

---------------------------------------------------------------

To unsubscribe send SIGNOFF BIOMCH-L to LISTSERV@nic.surfnet.nl

For information and archives: http://isb.ri.ccf.org/biomch-l

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