Short communicationInertial control as novel technique for in vitro gait simulations
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.
References (18)
- et al.
Foot kinematics during walking measured using bone and surface mounted markers
J. Biomech.
(2007) - et al.
A dynamic cadaver model of the stance phase of gaitperformance characteristics and kinetic validation
Clin. Biomech.
(1998) - et al.
Gait analysis in ankle osteoarthritis and total ankle replacement
Clin. Biomech. (Bristol, Avon)
(2007) - et al.
Foot bone kinematics as measured in a cadaveric robotic gait simulator
Gait Posture
(2011) - et al.
Gait analysis after ankle arthrodesis
Gait Posture
(2000) - et al.
A robotic cadaveric gait simulator with fuzzy logic vertical ground reaction force control
IEEE Trans. Robot.
(2012) - et al.
Arthrodesis of the first metatarsophalangeal jointa robotic cadaver study of the dorsiflexion angle
J. Bone Jt. Surg.
(2010) - et al.
In vitro simulation of stance phase gait part Imodel verification
Foot Ankle Int.
(2003) - et al.
In vitro simulation of the stance phase in human gait
J. Musculoskelet. Res.
(2001)