Chapter 5 Conclusions and Future Directions
5.2 Related Future Directions
5.1.5 Computer Modeling and Finite Element Analysis
All new hip and knee implants must undergo wear-simulator testing in order to be
evaluated for potential clinical use. It is well recognized, however, that wear simulators
are associated with a number of limitations.17 Implants must undergo millions of wear cycles in order to produced clinically relevant results. At a cycle frequency of 1 to
1.5 Hz, this results in many weeks or months of testing. Wear simulators are also very
costly to purchase and operate. Finally, the kinematics that a wear simulator is capable of
producing are not truly representative of the walking, stair-climbing, bending, twisting,
and other motions physiologically produced in an actual patient.28 For these reasons, computer-based wear simulations have recently been developed.17-20
Figure 5.8: A step-up platform instrumented with a force plate (A) will enable the collection of knee joint kinematics, kinetics, and implant wear from patients (B).
Micro-CT can contribute to these studies in a number of ways. All simulations
utilize a 3D model of the components. As noted previously in section 6.2.3, micro-CT
can be used to reverse-engineer 3D geometries of the components, to produce an accurate
representation for the wear simulation. It has been found that the CAD models of inserts
vary from manufactured components, necessitating reverse engineering for proper wear
analysis. These reverse-engineered geometries can also be used in finite element analysis,
to study the stresses and strains around and within the implants. Finally, in order to
ensure the accuracy of the computer simulation, the results of new simulation programs
must be validated against the results from mechanical wear simulator studies, and from
components retrieved from patients. Micro-CT can be used in these studies to accurately
quantify the wear that has occurred. In an example of this, we have worked with
collaborators to compare a wear map of a retrieved tibial insert (developed through
micro-CT) to the peak contact stresses on the same tibial insert using a computer model
(Figure 5.9).
Finally, the kinematics and implant wear data acquired from the dynamic
radiography trials can also be integrated into computer models, providing accurate, Figure 5.9: For a retrieved tibial insert, a deviation map was constructed
patient-specific in vivo data that can greatly improve the utility of such simulations. Such
an integration of multiple modalities holds great potential as an exciting area of future
research, greatly decreasing the cost and time required to develop and test new joint
replacement components.
5.3 References
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