Date of Award

8-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Bioengineering

Committee Member

Melinda K. Harman, Committee Chair

Committee Member

Hai Yao, PhD

Committee Member

Guigen Zhang, PhD

Committee Member

Kyle Jeray, MD

Abstract

Total knee replacement (TKR) is one of the most common orthopaedic procedures performed in the USA and is projected to exceed 4.3 million by 2030. Although TKR surgery has a success rate of 95% at 10 years for most TKR designs, revision surgery still occurs approximately once for every ten primary TKR surgeries. Failure modes in TKR involve the interplay between implant mechanical performance and surrounding biological tissues. The orthopaedic community has turned to computational modeling as an effective tool to analyze these complex interactions and improve patient outcomes. The objective of these studies was to utilize a combined computational and experimental approach to investigate modes of TKR failure where material nonlinearity plays a significant role in the biomechanics under investigation.

A finite element (FE) model of a modular TKR taper junction was developed in order to investigate the stress environment in relation to corrosive behavior under in vivo loading conditions. Linear elastic and elastoplastic material models were defined and angular mismatch parametrically varied in order to determine the sensitivity of model predicted stresses to material model selection and taper junction geometry. It was determined that positive angle mismatches cause plastic deformation and overestimated stresses in linear elastic analyses compared to elastoplastic analyses. Calculated stresses were also strongly correlated with angle mismatch when varied ±0.25o. Model stress distributions agreed with corrosion patterns evident on retrieved modular TKR components and magnitudes corresponding with corrosive behavior in vitro.

Additionally, a series of passive FE TKR models were developed in order to investigate the intrinsic relationship between TKR component alignment, ligament tensions, and knee kinematics during intraoperative assessments. A kinematically-driven model was developed and validated with an open source dataset, and was able to discriminate clinical outcomes based on calculated ligament tensions when input in vivo kinematics. Patient-specific simulations found greater tension in lateral ligaments for poor outcome patients compared to good outcome patients, and statistically significant differences in tensions for the POL, PFL, DMCL, and ALS ligaments during mid-flexion. A force-driven model was also developed and validated with in vitro cadaver testing, and found that variation in tibial component alignment of ±15o influence intraoperative ligament tensions. However, definitive trends between TKR component alignment and ligament tension were not discerned. Nonetheless, both modeling approaches were found to be sensitive to subclinical abnormalities.

These findings suggest mechanical stress is a key contributor to taper junction corrosion and that ligament tensions are the mechanism leading to abnormal function in the passive TKR knee. These studies contributed innovative computational models that provide a foundation to advance the understanding of these complex relationships, and modeling frameworks that exemplify sound verification and validation practices.

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