View Full Version : 4 bar linkage models for in vitro spinal flexion

02-04-1998, 07:28 AM
We are currently working on a project which involves studying
in vitro spinal motion unit kinematics. What we are looking for is a
method to fix the vertebra such that they move through the natural
rotation and translational movements.

So far we have investigated the possibility of fixing a four-bar
linkage to the vertebra. Four-bar linkages have the capability of
mimicing rotation and translation and have the advantages of easy and
affordable construction. We have run into problems with the methods for
synthesizing the linkage lengths to mimic the measured spinal kinematics.
Most methods date back to the 1950's and use either graphical or simple
optimization techniques but are designed to replicate the motion of a
point rather than a rigid body. We have tried to employ Freudenstein's
method in particular (F. Freudenstein, ASME Transactions 1955) but have
found that too many variables must be assumed before any calculations can
be made and the predicted results are not physically appropriate. Any
suggestions for alternative methods of determining linkage lengths or
entirely different methods of reproducing the natural rotation of the
vertebral bodies would be appreciated.

Trish Bellchamber
University of Guelph
Department of Physics