MR Imaging of Cyclically Loaded Articular Cartilage

Principal Investigator: Nicholas J. Giori, MD, PhD

Objective: In this project, we successfully imaged articular cartilage in an intact joint under physiologic dynamic loading conditions. The goal was to be able to compare the deformation of articular cartilage that is loaded normally and with the deformation of articular cartilage that is loaded in a way that will lead to osteoarthritis. This can help us to understand how a specific mechanical stimulus leads to osteoarthritis, and can eventually lead to improved treatments for osteoarthritis.

Milestones

• Development of device for loading the joint in the scanner
• Static tests
• Dynamic tests

Work Accomplished: An MRI compatible device that can apply static and dynamic physiologic loads to a sheep knee in a 4.7 T MRI scanner was built and tested. Static and dynamic tests have been conducted. We found that the nominal compressive strain on tibial articular cartilage under the meniscus when the knee joint is axially loaded is nearly uniform, but when the meniscus is removed, joint contact area decreases by 60% and the peak nominal strain increases by 13%. A similar pattern occurs after cyclic loading. Interestingly, our cyclic loading tests revealed that the articular cartilage recovery time after loading is markedly prolonged following meniscectomy, probably due to strain dependent permeability of the articular cartilage. Increased nominal strains and prolonged desiccation of articular cartilage following meniscectomy are possible factors in the development of osteoarthritis. We are planning follow-up experiments to investigate several hypotheses that have been generated by this work.

Outcome: This study has helped us understand the complex, time dependent material behavior of articular cartilage in a whole knee joint that is subjected to physiologic mechanical loading. The material behavior of the articular cartilage that is subjected to osteoarthritis-inducing loading is dramatically different than normal articular cartilage material behavior. This gives us further insight into the mechanical factors that cause osteoarthritis.

Funding Source: Whitaker Foundation