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German Society of Biomechanics (DGfB) Young Investigator Award 2019: Proof-of-Concept of a Novel Knee Joint Simulator Allowing Rapid Motions at Physiological Muscle and Ground Reaction Forces

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German Society of Biomechanics (DGfB) Young Investigator Award 2019: Proof-of-Concept of a Novel Knee Joint Simulator Allowing Rapid Motions at Physiological Muscle and Ground Reaction Forces

Florian Schall et al. Front Bioeng Biotechnol.

Abstract

The in vitro determination of realistic loads acting in knee ligaments, articular cartilage, menisci and their attachments during daily activities require the creation of physiological muscle forces, ground reaction force and unconstrained kinematics. However, no in vitro test setup is currently available that is able to simulate such physiological loads during squatting and jump landing exercises. Therefore, a novel knee joint simulator allowing such physiological loads in combination with realistic, rapid movements is presented. To gain realistic joint positions and muscle forces serving as input parameters for the simulator, a combined in vivo motion analysis and inverse dynamics (MAID) study was undertaken with 11 volunteers performing squatting and jump landing exercises. Subsequently, an in vitro study using nine human knee joint specimens was conducted to prove the functionality of the simulator. To do so, slow squatting without muscle force simulation representing quasi-static loading conditions and slow squatting and jump landing with physiological muscle force simulation were carried out. During all tests ground reaction force, tibiofemoral contact pressure, and tibial rotation characteristics were simultaneously recorded. The simulated muscle forces obtained were in good correlation (0.48 ≤ R ≤ 0.92) with those from the in vivo MAID study. The resulting vertical ground reaction force showed a correlation of R = 0.93. On the basis of the target parameters of ground reaction force, tibiofemoral contact pressure and tibial rotation, it could be concluded that the knee joint load was loaded physiologically. Therefore, this is the first in vitro knee joint simulator allowing squatting and jump landing exercises in combination with physiological muscle forces that finally result in realistic ground reaction forces and physiological joint loading conditions.

Keywords: biomechanics; contact pressure; in vitro; knee; muscle forces; rapid movement; simulator.

Figures

Figure 1
Figure 1
Knee joint simulator with a knee joint model fixed between the hip- and ankle-joint assemblies, crosshead for vertical hip displacement and pneumatic actuators for muscle force simulation.
Figure 2
Figure 2
Control of the dynamic knee joint simulator with a real-time system, Festo configuration tool for parameterisation, control of the pneumatic and electrical actuators, registration of force sensors and LabVIEW and LabVIEW real-time applications.
Figure 3
Figure 3
(A) Muscle force simulation of the quadriceps muscle using a threaded rod, steel cable, component with steel hooks and a ferrule. (B) Muscle force simulation of the hamstring and gastrocnemius muscles using threaded rods, dowels and steel cables. (C) Specimen fixed in the dynamic knee joint simulator with cylindrical metal pots, uniaxial load cells for measuring muscle forces, pressure-sensitive foil for measuring the tibiofemoral contact pressure and coordinate systems with optical markers for measuring the kinematics.
Figure 4
Figure 4
Muscle force simulation—comparison between the actual (mean values) and target muscle forces (gained in MAID study) as a function of the motion cycle (duration: 540 ms) during jump landing for M. vastus lateralis, M. vastus medialis, M. vastus intermedius/M. rectus femoris, M. biceps femoris, M. semitendinosus/M. semimembranosus, M. gastrocnemius medialis and M. gastrocnemius lateralis (n = 9).
Figure 5
Figure 5
Vertical ground reaction force—comparison between the actual (mean value, blue line) with standard deviation (envelope curve, light blue lines) and target ground reaction forces (measured during MAID study, green line) as a function of the motion cycle (duration: 540 ms) (n = 9).
Figure 6
Figure 6
Mean and peak contact pressure (mean ± SD) in the medial and lateral compartments for slow squat without muscle force simulation, slow squat with muscle force simulation and a jump landing exercise. *p ≤ 0.05 (n = 9).
Figure 7
Figure 7
Exemplary external tibial rotation as a function of the knee flexion angle during slow squat with muscle force simulation.

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