Abstract
Background
Osteoarthritis (OA) is a degenerative, chronic disease of the articular cartilage that affects more than 150 million people [1]. In the knee, OA can begin as either isolated medial OA or isolated lateral OA. Previous research [2,3] shows medial OA and lateral OA have characteristic cartilage lesion locations and progression patterns as well as flexion angles associated with lesion development, indicating strong involvement of mechanical factors in disease initiation. Therefore, it is important to investigate these mechanical factors. Previous studies combined data sets (geometry, motion, load) from separate sources. The aim of the current work was to use a consistent multi-modal approach.
Method
A finite element (FE) model of a healthy knee in full extension was created using magnetic resonance imaging (MRI) and motion analysis data from the same subject (female, 24 yrs). MRI data was obtained using a 3T MRI scanner (Philips Medical Systems/Achieva). Surface geometries of the tibia, femur, and associated cartilage were then semi-automatically segmented and processed (Mimics 12.5; Geomagic Studio 11; SolidWorks 2009). Motion data was collected at 100 Hz (Vicon 612) during level walking and subsequently applied to a lower limb model (AnyBody Version 3.0) to calculate muscle forces. Both sets of data were then combined to create a subject-specific FE model (ANSYS 11.0) which was solved to determine relative contact areas, pressures, and deformations in the medial and lateral tibiofemoral compartments.
Results
Contact area in the medial tibiofemoral compartment was approximately twice as large as in the lateral compartment. Medially, tibiofemoral contact occurred anteriorly and centrally; maximum cartilage deformation also occurred in these regions. Laterally, contact occurred centrally in both the anterior-posterior and medial-lateral directions with maximum deformation gradients occurring anteriorly and posteriorly. Overall, cartilage deformation was larger in the medial (1.73 mm) than in the lateral compartment (1.50 mm). Contact pressure was also larger medially (111 kN) than laterally (83 kN) with equal pressure gradients extending in all directions from the centre of medial tibiofemoral contact but concentrated posterior to the lateral compartment's contact area.
Discussion
The current results match previous literature. Contact areas for tibiofemoral cartilage at full extension correlate well with lesion locations described in medial OA, commonly associated with small flexion angles. Concentrated pressure gradient locations also agree with cartilage lesion progression directions cited in the literature. Future work will involve creating more subject-specific models and including higher flexion angles.
J Boyd was funded by the Clarendon Fund, National Science Foundation and Whitaker International Fellowship.
