Abstract
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/°. 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.
Highlights
Knee osteoarthritis affects 4.71 million people in the UK and this number is expected to double by 2035 due to an ageing and increasingly obese population [1]
The results indicated that each individual human knee joint specimen had different knee kinematics as a result of variations in anatomy and soft tissue laxity
Our previous study [8] demonstrated the effect of anterior posterior (AP) spring constraints on the kinematic outputs in the porcine knee simulation model, which showed that increasing the free length caused an increase in the AP displacement and increasing the spring rate caused a decrease in the AP displacement
Summary
Knee osteoarthritis affects 4.71 million people in the UK and this number is expected to double by 2035 due to an ageing and increasingly obese population [1]. We previously developed a novel pre-clinical simulation model of the natural whole porcine knee joint, which has been successfully applied to the assessment of the tribological performance of osteochondral grafts in the knee joint [6,7,8]. The refined porcine knee model [8] was shown to successfully simulate the natural porcine knee ligament function by constraining the anterior posterior (AP) motion using physical compressive springs. The results highlighted the influence of input parameters of spring constraints (spring rate and free length) on the outputs of the natural porcine knee model including knee kinematics and tribological function. For the porcine model, which had low biological variability due to consistency in key parameters such as knee dimensions and anatomy due to sourcing tissue from pigs of the same breed, age and sex, the kinematic outputs across replicates showed low variability. The porcine model is, not a specimen-specific model and average spring conditions enabled the simulation of ligament function for all samples studied
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