Fig 1.
Heidelberg friction simulator.
Modification of a single-station simulator to allow for low friction measurements in the hip joint.
Fig 2.
Filled with diluted calf serum (protein content: 30 g/l) and temperature-controlled at 37±1°C (36 mm ceramic-on-XPE bearing, right hip).
Fig 3.
(A) Translation from the transducer origin to the head’s center. (B) Rotation around the y-axes for alignment with the taper axes.
Table 1.
Specimens for dynamic testing.
Fig 4.
Hydrostatic bearing with water supply.
Sectional view through water channels of the (ideal) bearing with fluid separated bearing surfaces.
Fig 5.
Simulator kinematics for all tested procedures.
(A) ISO 14242–1, (B) extension-flexion under static load and (C) extension-flexion with a dynamic load profile.
Fig 6.
(A) Pendulum setup with 2000 N arm weight. (B) Detail view on fulcrum. (C) Theoretical model of the physical pendulum (clockwise rotation).
Table 2.
Test matrix.
Fig 7.
Frictional torque before (x0-y0-z0) and after (x-y-z) transformation of the coordinate system to the head’s center (36 mm ceramic-on-XPE).
(A) Mx and (B) My (note that Mz remains unchanged as Δx = Δy = 0).
Fig 8.
Repeated measurements for one single sample.
Comparison of the results for each moment component after 1000 ISO cycles (A) Mx, (B) My and (C) Mz.
Fig 9.
Resultant torque measured with the hydrostatic bearing (ceramic-on-polyethylene).
(A) Without water pressure (dry). (B) Separation of bearing surfaces by water pressure (hydrostatic bearing).
Fig 10.
(A) Comparison of friction results from the physical pendulum and the extension-flexion oscillation using the hip simulator (36 mm ceramic-on-XPE). (B) Extension-flexion (hip simulator) and best fit torque amplitudes for different head sizes. (C) Oscillation angles from experimental (Pendulum) and calculated data (Best fit, 36 mm ceramic-on-XPE).
Fig 11.
Results from extension-flexion oscillation with a dynamic force profile.
(A) Frictional torque around the axis of rotation with force and motion profile (36 mm ceramic-on-XPE). (B) Min-Max torques for the investigated ceramic-on-XPE bearing sizes.
Fig 12.
Resultant frictional torque over the total testing duration of 1000 ISO cycles.
Comparison of ceramic-on-XPE bearings of 28, 36 and 40 mm nominal diameter.
Fig 13.
Results from the ‘normal gait’ kinematics according to ISO 14242–1 (x-y-z coordinate system in the head’s center).
(A) Frictional torque for ceramic-on-XPE with bearing diameters of 28, 36 and 40 mm (cycle 999). (B) Mean maximum frictional torques and standard deviations of the last three consecutive gait cycles (997–999).
Fig 14.
Isolated torque around the taper axes (Mz’, Fig 3B).
(A) Ceramic-on-XPE bearings of different head sizes (28, 36 and 40 mm). (B) Mean frictional taper torque peak-to-peak values (min-max) of three consecutive gait cycles.
Table 3.
Literature data on friction measurements on total hip replacements with polyethylene bearings.