Fig 1.
Left: inferior part, right: superior part. The small deepening on the inferior part (on the top left in this picture) marks the posterior side.
Fig 2.
Schematic representation of the bearing geometry parameters.
Left: sagittal cross section, right: coronal cross section.
Fig 3.
Universal Joint Simulator used for testing of the TDR bearing.
Upper image (A): Testing arrangement. The silicone gaiter is fixed to the polyoxymethylene fixtures. The coordinate system refers to the sample, the rotations can be understood based on that and from the mechanical setups rotation axes. Lower images (B): Computer Aided Design renderings of the custom fixtures for the universal joint simulator with a test sample in place. Assembly view (left), sagittal (centre) and coronal (right) cross sections. The grey parts are made from stainless steel; the light grey parts are made from polyoxymethylene. The silicone gaiter is not shown for clarity. The ceramic samples are shown in pink. The sphere centre of the superior part of the bearing is in the centre of rotation of the simulator in all three axes.
Table 1.
Test profiles used for investigation of the optimized ceramic bearing in vitro in a simulator.
Fig 4.
Load- and motion profile for the test profile: three coupled rotations under sinusoidal load.
It is based on the wear test standard ISO18192 for cervical TDRs.
Table 2.
Geometric values. Mean values refer to all six samples used in the tests though some tests only used five of them.
Table 3.
Main results of testing.
Fig 5.
Friction loop of the flexion/extension test (above) and lateral bending test (below).
The movement cycle starts at the bottom centre of the loop. The flexion movement profile starts with flexion (positive rotation), while the lateral bending movement profile starts with bending to the right side (dexter) (positive rotation). The movement direction is indicated by the arrows. In the flexion/extension test data, it can be seen, that when the movement direction changes and the movement into the new direction starts, higher friction (static friction) is measured, then in the central part of the loop (dynamic friction). The datapoints between the blue vertical lines were included in the evaluation of the dynamic friction. The green circles show where static friction could be evaluated. Such friction hysteresis loops are also used in studies on fretting wear, Fantetti et al. give a detailed description of these loops [26]. S = Sample.
Fig 6.
Axial rotation torque over axial rotation in the axial rotation test.
The movement cycle starts at the bottom centre of the loop and then moves toward positive rotation initially (the inferior part of the simulator rotated to the right side thereby simulating axial rotation to the left). The arrows indicate the movement direction.
Fig 7.
Mean friction factor over the course of the test cycle, during three coupled rotations under sinusoidal load.
S = Sample.