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Friction in orthopaedic zirconia taper assemblies
W Macdonald1, A Aspenberg, C M Jacobsson
1Department of Biomaterials/Handicap Research, Institute for Surgical Sciences, University of Gothenburg, Sweden.
Summary
This study tested zirconia ceramic heads and titanium taper trunnion junctions. Higher test loads significantly increased torque resistance, crucial for hip implant stability.
Area of Science:
- Biomaterials Science
- Orthopedic Engineering
- Tribology
Background:
- The junction between femoral head and stem is critical for hip implant longevity.
- Understanding the torsional stability of zirconia ceramic heads on titanium taper trunnions is essential for preventing adverse outcomes.
- Existing friction coefficient data may not accurately reflect real-world conditions for these specific materials.
Purpose of the Study:
- To evaluate the torque resistance of zirconia ceramic heads/titanium taper trunnion junctions under physiological conditions.
- To determine the influence of assembly force, test load, and head length on torsional stability.
- To calculate and compare coefficients of friction from torque and axial loading tests.
Main Methods:
- Twelve modified 32 mm diameter zirconia ceramic heads on titanium taper trunnion junctions were tested per ISO 7206-9:1994(E).
- Torque resistance was measured under varying assembly forces and vertical test loads (1 kN and 4 kN).
- Push-on/pull-off tests were conducted to calculate coefficients of friction under axial loading.
Main Results:
- Mean torque resistances were 8.9 N m at 1 kN and 15 N m at 4 kN test load.
- Failure torques were significantly dependent on test load (beta = 0.77; P < 0.001), with assembly force and head length having minor influence.
- Coefficients of friction for torsional stability ranged from 0.06 to >1.0, while axial loading yielded 0.16-0.31, correlating with taper angle and material.
- Torque testing exhibited greater variability than push-on/pull-off tests.
Conclusions:
- Test load is the primary factor influencing the torsional stability of zirconia ceramic heads/titanium taper trunnion junctions.
- Coefficients of friction derived from torque testing differ significantly from those used in typical stress analyses.
- These findings highlight the need for revised friction coefficient values in biomechanical models for hip implant design and analysis.