A new bone fixation device for human joint test rig machine

In vitro experimental tests are of great importance in human joint biomechanics. These tests allow the study of the kinetostatic and dynamic behaviour of human joints: a limb specimen is connected to a rig, controlled loads are applied, and the joint displacements are measured. Fixation of the bone to the rig is a typical problem that raises in these applications. A new fixation device is presented in this paper that features several interesting and innovative characteristics: it consists of a passive parallel mechanism that allows adjustment of the pose of the bone with respect to the rig with six degrees of freedom; if needed, the bone can be removed from the rig and repositioned exactly at the same pose during the experimental tests; all six degrees of freedom of the fixation device can be locked by acting only on two screws, thus simplifying the fixation operation; the parallel structure of the mechanism guarantees a high fixation stiffness. The complete design is presented and discussed, together with the results from the workspace and stiffness analyses of the mechanism, that are particularly important for the considered applications.