Results

Table 1: Muscle force and relative difference to control

Fig. 2: Muscle force during stance phase for a) m .tibialis posterior; b) m. tibialis anterior; c) m. peroneus and d) m. gluteus medius. The grey shaded area represents loading response.

A simulation to describe the effects of in-shoe orthoses

Dr Gunther Paul, Chris Bishop, Mike Arakilo, Dr Dominic Thewlis. University of South Australia, Adelaide, South Australia.

email: gunther.paul@unisa.edu.au

IntroductionIn-shoe foot orthoses are commonly prescribed by podiatrists to help correct biomechanical abnormalities of the lower limb. The goal of in-shoe orthoses is to reduce the loading forces acting on the lower limb in order to allow for proper rehabilitation, to prevent new injuries occurring and to promote more efficient dynamic gait patterns. Research aiming to analyse the effects of orthoses on knee, hip and pelvis kinematics has shown little effect [1]. Thus in view of the minimal effect of orthoses on joints proximal to the foot, orthoses may have additional effects on the functional tissues of the lower limbs.

The aim of this study was to simulate the effect of in-shoe foot orthoses through the manipulation of ground reaction force components.

Methods• Steady state walking trial• Three-dimensional (3-D) motion data captured using• 8-camera VICON MX F40 system at 120Hz• Defined a custom modified VICON Plug-in Gait model markerset including 22 markers in order to register kinematics of thefoot and ankle accurately

• Force data sampled using 2 Kistler force plates at 2000Hz• Joint kinematics and moments modeled from raw kinematicdata in VICON Bodybuilder

• Developed a dynamic musculoskeletal model in AnyBody (Anybody Technology)(Fig 1.)

Fig. 1: The AnyBody musculoskeletal model

• The reaction forces acting on m. tibialis posterior, m. tibialis anterior, m. peroneus, and m. gluteus medius were calculated by the model using a Min-Max recruitment solver [2]

• The original lateral force (Fy) data was multiplied by 1.5 based on medial-lateral GRF differences reported in [1] to represent the effects of medial wedging. The Fy data was also divided by 2 [1] to represent the effect of lateral wedging

• The components CoP:X and CoP:Y were displaced by 20mm in both the medial and lateral direction to represent the estimated effect of medial and lateral wedging on the CoP

Condition

Loading responseTP TA Per GM

Force (N) % diff

Force (N) % diff

Force (N) % diff

Force (N) % diff

No Intervention 131 381 148 44Lat Wedge 75 -42.7 472 23.9 110 -25.7 41 -6.8Med Wedge 200 52.7 488 28.1 227 53.4 66 50

Stance phase (between loading response and toe off)

Condition

TP TA Per GMForce (N) % diff

Force (N) % diff

Force (N) % diff

Force (N) % diff

No Intervention 843 210 958 108Lat Wedge 764 -9.4 86 -59 869 -9.3 99 -8.3Med Wedge 913 8.3 108 -48.6 1038 8.4 111 2.8

ConclusionOur manipulation of the data set appears to be a realistic simulation of the effect of in-shoe orthoses on the muscle force in m. tibialis posterior, m. tibialis anterior, m.  peroneus, and m. gluteus medius during both the rearfoot loading response and stance phase of the gait cycle. The simulation identified changes in muscle force that we might clinically expect to find with the use of in-shoe foot orthoses, e.g. that peak muscle force was reduced by lateral wedging. The ability of muscles to adapt to changes in medial-lateral force and the displacement of the COP when using in-shoe orthoses was shown.

References[1] Nester,C., van der Linden,M., Bowker,P., 2003. Effect of foot orthoses on the kinematics and kinetics of normal walking gait. Gait & Posture 17(2), 180-187[2] Arakilo,M., Thewlis,D., Paul,G., Rasmussen,J., 2009. Simulation of Ankle Joint Forces to Optimise Total Ankle Replacement Design. 7th Australasian Biomechanics Conference. Gold Coast, Australia.

AcknowledgementErgolab is supported by AutoCRC and DTED.