Development of a pre-clinical experimental simulation model of the natural porcine knee with appropriate ligamentous constraints

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.

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

“…As shown in Fig 5, the AP displacement and TR angle output profiles under all the spring constraint conditions showed a similar shape to the intact knee, which was observed for all four knees studied. Increasing the AP spring rate from 20 N/mm to 70 N/mm caused incremental decreases in overall AP displacement ( Fig 5A) while increasing the free length from 0 mm to 4 mm caused increases in overall AP displacement ( Fig 5B), which was consistent with the findings from the porcine knee model [8]. The response of TR angle profiles to spring rate and free angle was similar to that of AP displacement (Fig 5C and 5D).…”

“…Therefore, a sample that had free motion greater than the above threshold values had a higher risk of dislocation of the femoral-tibial joint, causing knee instability and eventually damage of the cadaveric knee contact surfaces. As suggested by our previous porcine knee model [8], in addition to spring stiffness and free length, the stability of the knee…”

“…Our previous study [8] demonstrated that either increasing the free length/rotation or decreasing the spring rate would increase the AP displacement or TR angle. Therefore, for knee samples which needed larger than 4 mm or 4˚to match the profiles of AP displacement or TR angle, a reduced spring rate was applied rather than increasing the free length /rotation gap.…”

“…Our previous study showed that soft tissue variations affect the knee kinematics and tribological function of the natural porcine knee. This indicated that the soft tissue constraints would also affect the functional performance of early-stage surgical interventions, such as cartilage and meniscal repair and replacement therapies in the natural knee model [8]. Therefore, it is important to develop a method to replicate individual variations in soft tissue constraints in the natural knee simulator in order to more appropriately simulate the biomechanical environment in vivo.…”

“…For the porcine knee model, one set of AP physical springs in the sagittal plane was used to simulate the primary function of the cruciate ligaments in controlling AP motion. A displacement control profile was applied to the porcine knee model in order to control tibial motion while investigating appropriate constraints in the AP direction [8]. For the human knee model, both the sagittal and transverse planes were investigated with the aim of simulating the total soft tissue function in the knee joint.…”