Computational assessment of constraint in total knee replacement

Area of Science:

• Biomedical Engineering
• Orthopedic Biomechanics

Background:

• Total knee replacement (TKR) component constraint is crucial for passive joint stability post-surgery.
• Existing experimental methods for assessing anterior-posterior (AP) and internal-external (IE) rotational constraint follow ASTM F1223-05 standards.
• Variability in testing protocols and machine design can affect constraint measurements.

Purpose of the Study:

• To develop and validate a dynamic computer simulation for assessing AP and IE rotational constraint of TKR components.
• To evaluate the impact of secondary degrees of freedom on constraint testing.
• To investigate the sensitivity of constraint predictions to joint location and allowed motions.

Main Methods:

• A dynamic computer simulation of a posterior-substituting TKR was created using manufacturer CAD data.
• A rigid-body-spring-model formulation was employed for implant contact analysis.
• Simulations were validated against experimental data, incorporating testing frame compliance.

Main Results:

• The computer simulation accurately predicted constraint forces, comparable to experimental values when testing frame compliance was modeled.
• The simulation revealed that predicted component constraint is sensitive to varus-valgus joint location and the selection of allowed secondary motions.
• The study highlighted ambiguities in the ASTM standard regarding secondary motion accommodation in testing machines.

Conclusions:

• Computational prediction of TKR implant constraint offers a viable method to expedite design cycles.
• This simulation approach allows for objective comparisons between different TKR components.
• Refined simulation models can improve the understanding and standardization of TKR constraint testing.