Aim of the FluoKin Project
The three-dimensional movement of joints is the result of a very complex interaction between physics (gravitation,
acceleration, inertia), active muscle forces and passive constraints (joint surfaces, ligaments, menisci). [1, 2]
The specific combination of these parameters for the different joints still remains to be determined. Mathematical
models try to replicate the true situation, based on anatomical studies [3, 4], a realistic picture is still not available.
The traditional movement analysis is based on the tracking of surface markers attached to the object of interest. Most of
the time the markers are attached to the skin and are thought to represent the underlying skeletal anatomy. With the help
of high-frequency videography the target of the markers can easily be captured and using dedicated software the 2D or
even 3D position of the markers in space can be calculated automatically. With all skin based markers, skin movement
artifacts are a problem. Skin movement over the underlying skeleton results in a mismatch between the marker position and
the true position of the bony protuberance defined by the marker. These errors can be in the range of centimeters  and
are more pronounced when the animal is moving fast or when there are acceleration or deceleration forces, such as at time
of heel strike or lift of.[5, 6]
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For the study of stifle kinematics in the light of a torn cranial cruciate ligament, the
pathological movements, which is predominately cranio-caudal instability, has to be expected in the range of 10 to 15 mm.
With a skin based error of about 1 to 2 centimeters in that region, it becomes clear that skin based markers systems may
fail at detecting these subtle movements. Eventhough it is possible to compensate some of the skin movement
errors [8, 9], the resulting error especially for abduction/adduction as well as endo- and exorotation still remains
significant. One solution would be intraosseous fixation of K-wires, with the markers on their tip.[11, 12] This would
allow rigid fixation oft he markers to the underlying bone. However, because of the invasiveness of the method, broad
application is not possible. With the installation of a biplanar fluroscopic high speed unit at the Veterinary Faculty of Leipzig, precise estimation
of 2D and 3D kinamtics will be possible. Fluoroscopic cinematography allows a precision of <1 mm und <1°.
The inconvenient aspect of using radiation can be limited by thorough application of all measure of safety. Our project
is special in that respect, that we aim at investigating small (rat, cat, mouse) and large objects (horses, cows) using
the same equipment. This is why a dedicated prototype is currently in construction, allowing for the most versatile
application of fluoroscopic cinematography possible.
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