Elsevier

Journal of Biomechanics

Volume 48, Issue 2, 21 January 2015, Pages 392-395
Journal of Biomechanics

Short communication
Inertial control as novel technique for in vitro gait simulations

https://doi.org/10.1016/j.jbiomech.2014.11.044Get rights and content

Abstract

In vitro gait simulations are a preferential platform to study new intervention techniques or surgical procedures as they allow studying the isolated effect of surgical interventions. Commonly, simulations are performed by applying pre-defined setpoints for the kinetics and kinematics on all degrees of freedom (DOFs) of the cadaveric specimen. This however limits the applicability of the experiment to simulations for which pre-defined kinematics and kinetics can be measured in vivo. In this study we introduce inertial control as a new methodology for gait simulations that omits the need for pre-defined setpoints for the externally applied vertical ground reaction force (vGRF) and therefore allows the effect of interventions to be reflected upon it. Gait simulations of stance (1 s) were performed in 10 cadaveric specimens under three clinically relevant conditions: native ankle, total ankle prosthesis (TAP) and total ankle prosthesis plus triple arthrodesis (TAP+TA). In the native ankle, simulated vGRF was compared against the vGRF measured in vivo in 15 healthy volunteers and high correlations were found (R2=0.956, slope of regression line S=1.004). In TAP and TAP+TA, vGRF changed, therefore confirming the sensitivity of the method to kinematic constrains imposed with surgery. Inertial control can replicate in vivo kinetic conditions and allows investigating the isolated effect of surgical interventions on kinematic as well as kinetics.

Introduction

When studying surgical interventions on the foot, in vitro gait simulations allow isolating the effect of surgery on the resulting kinematics and kinetics (Bayomy et al., 2010, Suckel et al., 2007, Valderrabano et al., 2003, Weber et al., 2012). This is highly relevant as it is known from literature (Thomas et al., 2006, Wu et al., 2000, Valderrabano et al., 2007) that factors such as time since operation, pain, and muscle training, can influence the measured kinematics and kinetics in patients. Therefore, the isolated effect of a surgical intervention cannot be studied in vivo.

During current in vitro gait simulations, input set points derived from a control group are applied in all degrees of freedom (DOFs) of the specimen. These set-points are in the form of either tibial kinematics (Aubin et al., 2012, Noble et al., 2010, Sharkey and Hamel, 1998) or a combination of tibial kinematics and vGRF (Hurschler et al., 2003, Nester et al., 2007). This, however, limits the applicability to simulations where it is of interest to impose pre-defined kinematics and kinetics measured in vivo, e.g. when studying bone kinematics during normal gait. When however, the sole effect of an intervention on the kinematics or kinetics is studied, this approach cannot be used. The simulation is over-constrained and it does not allow the effect of the specific intervention to be reflected in the kinematics and kinetics as they are imposed and not measured.

To overcome this limitation, we present a new technique that alleviates the need for a predefined set-point for the vertical tibial kinematics or vGRF during in vitro gait simulations, which leaves one flexible DOF for the effect of the interventions to be reflected upon. To demonstrate the applicability of the technique, gait simulations were performed in intact cadaveric foot specimens and the resulting vGRF was evaluated. To motivate its clinical relevance, vGRF was also evaluated during gait simulations with identical input parameters but after applying a total ankle prosthesis (TAP) and total ankle prosthesis plus triple arthrodesis (TAP+TA) locking the hindfoot motion of the specimen.

Section snippets

Methods

The inertial control approach is applied on a custom built CGS that manipulates the sagittal plane tibial kinematics of cadaveric foot specimens (Fig. 1). Even though the remaining 3 DOFs are constrained, previous validation studies (Peeters et al., 2013, Natsakis et al., 2012) demonstrated that the CGS is able to reconstruct kinematics similar to those measured in vivo. To account for the effect of plantarflexion and the resulting up and downwards translation of the knee axis, a supporting

Results

The normalised signals of the (vGRF) obtained from the in vitro simulations and in vivo gait analysis, are presented in Fig. 4. Timing of the significant differences is indicated using an asterisk (). For the intact ankle, significant differences in vGRF of the intact in vivo and intact in vitro data are primarily found during the first 10% and between 80% and 90% of stance phase. Only isolated differences from 62% to 90% are found between the intact in vitro and TAP in vitro measurements.

Discussion

Reproducing physiologic gait in cadaveric specimens poses many challenges and several research groups have developed custom built cadaveric gait simulators trying to address them (Whittaker et al., 2011, Noble et al., 2010, Nester et al., 2007, Sharkey and Hamel, 1998, Hurschler et al., 2003, Kim et al., 2001). In several designs, physiologic tibial kinematics must be applied, coupled with adequate force production to the different tendon actuators. These input variables must be synchronised

Conflict of interest statement

The authors have no conflicts of interest to report.

Acknowledgments

This work was funded by the Chair Berghmans–Dereymaeker, the Research Foundation Flanders and the Agency for Innovation by Science and Technology in Flanders (IWT). The authors would like to thank Pieter Spaepen (KU Leuven, Campus Groep T, Belgium) for his valuable feedback during the development of this methodology.

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