Abstract
A robust and stratified pre-clinical natural knee model, which has the capability to more appropriately simulate the biomechanical environment in vivo, will deliver more efficient and reliable assessment of soft tissue interventions before clinical studies. In order to simulate the biomechanical function of the natural knee without the natural ligaments in place, there is a requirement to develop appropriate spring constraints for the natural knee model. Therefore, this study was to investigate the effect of spring constraints on the function and output of the natural porcine knee model, and determine the spring constraint which most closely replicated the function of the natural ligaments. Two linear compression springs with stiffnesses of 9 N/mm (spring-9) and 20 N/mm (spring-20) were set at different free lengths in the anterior-posterior (A/P) axis in a natural knee simulator. The kinematic (A/P displacement) and tribological properties (shear force) output of the simulator were compared at different spring settings. The most appropriate spring setting was determined by comparing the A/P displacement and shear force output at different spring settings with those of the all ligaments model. Spring-9 with a free length of 4 mm showed the minimal difference (-0.03±0.68 mm) in A/P displacement output and spring-20 with a free length of 5 mm showed the minimal difference (-0.10±0.73 mm) in A/P displacement output compared to the all ligament control. There was no statistical difference between the two minimal differences either in A/P displacement or in shear force (paired t-test, p = 0.58, and p = 0.68 respectively) when both spring settings matched most closely to the A/P kinematics of the intact knee. This indicated that both conditions were appropriate spring constraints settings in the A/P direction for the natural porcine knee model.
Highlights
Over eight million people in the UK suffer from osteoarthritis [1], which costs the National Health Service over £5 billion per year
Spring-9 produced higher peak values of A/P displacement compared to spring-20 when both of the springs were set at the same free length
For spring-20, the maximum A/P displacements which were most closely matched to the A/P displacement of the all ligament control were at free lengths of 5 mm and 6 mm during the swing phase of the gait cycle
Summary
Over eight million people in the UK suffer from osteoarthritis [1], which costs the National Health Service over £5 billion per year. A pre-clinical experimental simulation model of the natural porcine knee. Excellence in Medical Engineering funded by the Wellcome Trust and EPSRC, WT088908/z/09/z. John Fisher is an NIHR Senior Investigator and is supported through The EPSRC Centre for Innovative Manufacturing in Medical Devices. Simulation Solutions manufactured the natural knee joint simulator. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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