Both tibia and femur and their surrounding ligaments determine the passive motion of the knee joint. Under the action of the nervous system muscles together with the passive elements control the dynamics of the joint. Any injury of these elements will result in degradation of the function of the joint. Anterior cruciate ligament (ACL) is one of the important elements that contribute to the stability of the knee, not only through passive restraint of tibia anterior translation but also the proprioception feedback of dynamic control of muscles. This research contains three projects to investigate the biomechanics and neuromuscular control and adaptation of the knee joint after ACL injuries or reconstruction. The first project will develop a computer-graphics-based mathematical model of the knee joint suitable for the inclusion into a complete locomotor system model which will be useful for the calculation of the mechanical variables of the joint with special emphasis on the ACL forces and the quantification of dynamic knee stability during functional activities. The second project will analyze the gait characteristics of ACL injured and ACL reconstructed patients using the model with optoelectronic and dynamic electromyographic systems. In the first year, the main objective is to investigate the differences of gait variables and muscle activation pattern in ACL deficient and reconstructed patients during functional activities. The second year, the effects of functional knee bracing in three anatomic planes with three-dimensional motion analysis will be exam to study the long-term neuromuscular adaptations in ACL reconstructed patients. With the model developed in project 1 and neuromuscular profile found in project 3, to study the muscle-ligament interaction, adaptations and knee dynamic stability during functional activities. And the third project will examine the neuromuscular adaptation of knee muscles in these specific subjects. It aims to establish the length-tension and force-velocity relationships of quadriceps and hamstrings in ACL-D and ACL-R in the short and long term and investigate whether the voluntary activation failure is responsible for the weakness observed and the corresponding changes in the long term. The second year, we will examine the short and long term modification in reflex activity in terms of H-reflex and tendon jerk response in ACL-D and their restoration in ACL-R, and explore the possible adaptive changes in balance strategy as well as the muscle activation patterns while maintaining balance. And then hope to incorporated the results with the changes in functional performance concerning lower extremities and general mobility in final year. Results of these projects will help us understand the recovery and neuromuscular adaptation after ACL injuries. It will contribute to guide the future rehabilitation program in this particular group of patients.
