Development of a specimen-specific in vitro pre-clinical simulation model of the human cadaveric knee with appropriate soft tissue constraints

A human cadaveric specimen-specific knee model with appropriate soft tissue constraints was developed to appropriately simulate the biomechanical environment in the human knee, in order to pre-clinically evaluate the biomechanical and tribological performance of soft tissue interventions. Four human cadaveric knees were studied in a natural knee simulator under force control conditions in the anterior posterior (AP) and tibial rotation (TR) axes, using virtual springs to replicate the function of soft tissues. The most appropriate spring constraints for each knee were determined by comparing the kinematic outputs in terms of AP displacement and TR angle of the human knee with all the soft tissues intact, to the same knee with all the soft tissues resected and replaced with virtual spring constraints (spring rate and free length/degree). The virtual spring conditions that showed the least difference in the AP displacement and TR angle outputs compared to the intact knee were considered to be the most appropriate spring conditions for each knee. The resulting AP displacement and TR angle profiles under the appropriate virtual spring conditions all showed similar shapes to the individual intact knee for each donor. This indicated that the application of the combination of virtual AP and TR springs with appropriate free lengths/degrees was successful in simulating the natural human knee soft tissue function. Each human knee joint had different kinematics as a result of variations in anatomy and soft tissue laxity. The most appropriate AP spring rate for the four human knees varied from 20 to 55 N/mm and the TR spring rate varied from 0.3 to 1.0 Nm/degrees. Consequently, the most appropriate spring condition for each knee was unique and required specific combinations of spring rate and free length/degree in each of the two axes.