Date of Award

8-2014

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Bioengineering

Committee Member

Martine LaBerge, PhD, Committee Chair

Committee Member

John DesJardins, PhD, Co-Committee Chair

Committee Member

Hai Yao, PhD

Committee Member

Lonny Thompson, PhD

Committee Member

Frank Voss, MD

Abstract

Nowadays, instances of anterior knee pain and patellar fracture are more and more widely considered as significant complications following total knee replacement (TKR). The inability to freely flex/extend the knee after surgery has a critical influence on patients’ daily activities, which is one of the most common mechanical indications for TKR revisions. An overtly thick or thin patellar component selected intraoperatively in TKR surgery may cause postoperative complications, including excessive quadriceps tendon force, patellofemoral joint reaction force, and joint pain in TKR patients during knee joint motion.

The objective of the current study was to evaluate the effect of varying patellar component thickness on patellar kinematics and patellofemoral joint function following TKR. Majorly, this project consisted of three parts: (a) combined computational and experimental exploration of knee joint alignment and tibiofemoral joint mechanics; (b) computational investigation of patellofemoral joint contact pressure and quadriceps tendon force; (c) comprehensive assessment of patellar kinematics and patellofemoral joint function utilizing in-vitro cadaveric testing.

Within the first section, a 3D computational finite element (FE) model was developed based on the Stanmore knee joint simulator outputs and experimentally validated to optimize the tibiofemoral rotational alignment for appropriate patellar tracking and reduced tibiofemoral contact pressure.

Secondly, by further enhancing the computational simulation, a 3D knee joint model with was established using realistic anatomical geometry, material property and intraoperatively kinematic/kinetic boundary conditions. A commercially available TKR system was inserted in the FEA model. Quadriceps tendon force and patellofemoral contact pressure at multiple patellar thickness levels were computationally predicted and thus their variation pattern along with patellar thickness change was derived.

Thirdly, a cadaver study was conducted to comprehensively assess the biomechanical influence of patellar thickness change on patellar kinematics and patellofemoral joint function of three different thickness levels using a customized UHMWPE pressure sensor with advanced mapping capability.

Overall, the combined computational and experimental studies revealed that increase of the patellar thickness contributes to extra patellar lateral tilt, lateral shift and patellar flexion during knee joint motion. Also, the thicker patella leads to lower quadriceps tendon force at lower knee flexion angles, but higher force magnitudes at deep flexion angles. Thinner patella is believed to be associated with excessive quadriceps tendon force during knee extension, but the thickness reduction benefits patellofemoral joint function by decreasing peak patellofemoral contact pressure.

This study focused on the patellofemoral joint as a major cause of TKR failure. A direct outcome of this study was the development of an intraoperative predictive reference for practitioners in selecting the appropriate patellar component thickness to mitigate clinical failure. Novel methods and technologies utilized in the current study can be expected to advance the state of the art in real-time contact pressure measurement for congruous surfaces, advanced modeling of the complex knee bearing system as well biological tissues, and in-vitro testing solution for investigation of knee joint biomechanics.

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