[The accuracy of palpation from orientation points for the navigated implantation of knee prostheses].
OBJECTIVE
Cinematic and pointing procedures are used for non-image based navigated implantation during total knee replacement. Pointing procedures require an exact knowledge of the landmarks. In this anatomical study, landmarks are defined and repeatedly referenced. Precision and reproducibility are evaluated by means of an inter- and an intra-observer study. The axes of the femur and tibia are calculated using the landmarks.


METHODS
The specific landmarks of 30 femurs and 27 tibias were palpated by three surgeons and digitised by means of a photogrammetric system, as used intra-operatively. The recorded data were statistically evaluated.


RESULTS
The specific landmarks can be referenced with great precision. The vectors that influence the implant position show a mean femoral deviation of 0.9 mm and a mean tibial deviation of 1.0 mm. The repeating accuracy of every observer was 1.5 mm femoral and 1.0 mm tibial. The calculated long axes at the femur and tibia thus reach a precision of 0.1 degrees (min.-max.: 0-0.9 degrees) at the femur and 0.2 degrees (.0-1.1 degrees) at the tibia. The short axes at the distal femur and proximal tibia exhibit an average deviation of from 0.7 degrees to 1.9 degrees (0-11.3 degrees).


CONCLUSIONS
Long axes (mechanical axes) can be determined exactly but the precision of the short axes (rotational axes) is unsatisfactory, although palpation of landmarks was accurate. Therefore, palpation of more than one rotational axis at the femur and tibia is mandatory and should be visualized on the monitor during surgery.
Orthopädisches Spital Gersthof, Vienna, Austria. reinhard_fuiko@hotmail.com
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Fuiko
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Kotten
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Zettl
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Ritschl
D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation*; D001696:Biomechanical Phenomena / Q000706:statistics & numerical data; D003196:Computer Graphics / Q000295:instrumentation; D001330:Electronic Data Processing / Q000295:instrumentation; D004867:Equipment Design; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000295:instrumentation*; D021621:Imaging, Three-Dimensional / Q000295:instrumentation*; D007719:Knee Joint; D008432:Mathematical Computing; D015588:Observer Variation; D010173:Palpation / Q000706:statistics & numerical data*; D010780:Photogrammetry / Q000295:instrumentation*; D015203:Reproducibility of Results; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*