A new methodology for subject-specific finite element (FE) modeling of the tibiofemoral (TF) joint based on in vivo computed tomography (CT), magnetic resonance imaging (MRI), and dynamic stereo-radiography (DSX) data is presented. Two techniques to incorporate in vivo skeletal kinematics as FE boundary conditions were implemented and compared: one used MRI-measured tibiofemoral kinematics in a non-weight-bearing supine position and allowed five degrees of freedom at the joint in response to an axially applied force; the other used DSX-measured tibiofemoral kinematics in a weight-bearing standing position and permitted only axial translation in response to the same force. The model-predicted cartilage-cartilage contact areas were examined against ‘benchmarks’ from a novel in situ contact area analysis (ISCAA) in which the intersection volume between non-deformed femoral and tibial cartilage was characterized to determine the contact. The results showed that the DSX-based model predicted contact areas in close alignment with the benchmarks, and outperformed the MRI-based model. The importance of accurate, task-specific skeletal kinematics in subject-specific FE modeling and the necessity of subject-specific verification are discussed.
A study of the effects of partial meniscectomy on the intra-articular contact mechanics was then conducted as an illustration of application of the verified models. A musculoskeletal dynamic model was used to generate the knee joint forces as boundary conditions for the above developed FE models. Thus, a sequence of quasi-static position-dependent FE models was developed for a series of time points throughout a decline walking task. These time points include heel-strike and in increments of 0.05 seconds up to 0.30 seconds, and additionally, the time points of the two peak compressive joint force values for each knee. Several factors were observed to measure the effects on intra-articular contact mechanics. The greatest maximum compressive stress was recorded in the partially meniscectomized compartment or in the opposite compartment of the contralateral knee throughout all time points. The significance of the application of the FE models for evaluation of the biomechanical effects of meniscectomy is demonstrated, and the importance of simultaneously observing joint kinematics and intra-articular contact mechanics at more than one time point during a dynamic task is discussed
