A model based rehabilitation protocol after cartilage lesions based on mechanical loading of the knee joint.

Articular cartilage defects of the knee joint are commonly caused by trauma during sports activities. Cartilage has low self-repair and regenerative capabilities, partially due to its avascular nature, the low intrinsic density of chondrocytes, and the low turnover of the extracellular matrix. If left untreated, cartilage injuries are a major risk factor for further cartilage degeneration and eventually osteoarthritis. Therefore, the ability to regenerate native joint cartilage is an important challenge. Besides the development of cartilage repair procedures, the rehabilitation process after the repair treatment is of great importance. In the development of a safe and effective rehabilitation protocol aversivemechanical load of the repair tissue, in particular shear forces duringpeak loading, must be limited. To achieve this, mechanical loading of cartilage tissue needs to be quantified during functional activities including relevant rehabilitation exercises.
Local cartilage loading of the tibiofemoral joint can be determined using multi-scale modeling, in which musculoskeletal and finite element models are linked. The musculoskeletal model generates an estimation of the kinematics, muscle activation and strength and joint contact forces during movement based on 3D marker data, ground reaction forces and EMG. Subsequently, the finite element model uses these results to calculate the mechanical loading of cartilage at the tissue level.
Dynamic knee simulator experiments will give the exact position and load of the joint during predefined movements; this will be used for the kinematic validation of the model.  The mechanical load, deformations and strains, on the cartilage tissue will be validated with displacement encoded MRI. In addition, the experimental data sets will also be used for the optimization of specific model parameters, in particular material characteristics and boundary conditions. A sensitivity analysis of the model parameters e.g. lesion characteristics, kinematics and neuromuscular coordination, will identify theconfidence boundaries of the model and the most sensitive model parameters.
The distribution of mechanical loading of the cartilage tissue during existing rehabilitation exercises will be evaluated using the multi-scale models developed during the previous parts of the project. Rehabilitation exercises will be selected in which the mechanical load onthe cartilage tissue is optimally distributed over the contact surface to improve the rehabilitation after cartilage lesions.