Computational Modeling of Nonlinear Behavior in Orthopaedics

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

David C. Snethen in a Senior Composition Recital

This is the program for the senior composition recital of David C. Snethen. This recital took place on March 10, 1997, in the McBeth Recital Hall in the Mabee Fine Arts Center

Creating Welcoming Environments for Workers with Disabilities: Managing Cognitive Demand

This comic is a collaboration between CeKTER and the Temple University Rehabilitation Research and Training Center on Community Living and Participation of Individuals with Psychiatric Disabilities (ACL grant #’s 90RTCP0001 & # 90RT5021). It is based on work by Gretchen Snethen, PhD, CTRS and colleagues. The comic shows and example of how workers with disabilities can be supported at work. A transcript of the comic is available here on the CeKTER website. A .png version of the comic is available below under Additional Files

Experimental Approach Embankments at Salt Fork River Bridges on US 177 and Their Initial Performance

This paper presents preliminary findings based on the initial performance evaluation of five approach embankments used in a bridge replacement project over the Salt Fork of the Arkansas River on US Highway 177 in Noble and Kay Counties, Oklahoma. The research involved instrumentation and measurement of four experimental approach embankments and one control approach embankment, all with similar dimensions. Instrumentation inc1uded total pressure cells to measure lateral earth pressure against the abutment wall, inclinometer casings to measure lateral movement of the backfill material and abutment walls, telescoping couplings on the inclinometer casings to measure settlement of the backfill and foundation, amplified liquid settlement gages for measurement of foundation settlement, and piezometers to measure pore water pressure. The four experimental backfills used were geotextile reinforced granular backfill, controlled low strength material backfill, dynamically compacted granular backfill, and flooded and vibrated granular backfill. The control section was unclassified borrow material placed at the contractor\u27s discretion as long as density requirements were met. This paper documents and presents summaries of the preliminary findings regarding initial performance and construction cost of each approach embankment