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,Anita Ignatius,Steffen Hacker,Andreas M Seitz,Sebastian I Wolf,Stefan Van Drongelen,Lutz Dürselen

doi:10.3389/fbioe.2019.00244

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.

Highlights

For biomechanical in vitro investigations of human knee joint specimens, different types of knee joint simulators have been introduced
The target force of the M. vastus medialis increased within 120 ms to 480 N, whereas the simulated muscle force was ∼10% lower with a delay of 60 ms (R = 0.85)
It could be shown that this simulator is able to apply rapid movements of 145◦/s in combination with physiological muscle force simulation to knee joint specimens that led to realistic ground reaction forces

Summary

Introduction

For biomechanical in vitro investigations of human knee joint specimens, different types of knee joint simulators have been introduced. A distinction can be made between horizontal knee joint simulators, vertical simulators, so-called Oxford-Rigs, and simulators driven by a robotic arm. The Oxford-Rig (Kumagai et al, 2002; Lo et al, 2008) is characterized by an upright and vertical fixation of the knee joint as well as a hip- and an ankle-joint assembly (Zavatsky, 1997). The hip-joint assembly can be moved vertically, thereby providing flexion and extension to the knee joint. As a variation of the Oxford-Rig design, there are impact simulators mimicking impacts on the knee joint using falling weights (Withrow et al, 2006; Kiapour et al, 2016)

Objectives

Methods

Results

Conclusion