So that the mechanical design can really be considered an "orthopedic device", two studies were carried out to see if there was a correspondence between what was done and what was described by Insall (86) as "a specific biomechanical condition in consequence of which the instantaneous center of rotation must fall on the perpendicular of the point of contact between articular surfaces "

The same Insall claims that this does not happen when the knee does not have the ability to perform a correct physiological motion, or "when the knee is applied an ... orthopedic device which forces the articular movement in a unnatural direction".

 Of the two works below the first highlights the symmetry between the articular path of the knee proceeds from radiogram to precise angles and a monoplanar model in plastic animated by a joint with variable center of rotation. The precise overlap between the path of the radiological profile and those of the model, highlights a marked similarity between the two trajectories, similarity from which is also deductible the overlap of the instantaneous center of rotation and its consequent perpendicularity with respect to the articular surfaces.

The second study, instead, was set on the analysis of  tractions to which cruciate ligaments are subject during flexion-extension, to verify a possible forcing "in an unnatural direction" of the articular heads.