Investigating the Effectiveness of Off-the-shelf Orthotic Sandals

							        Investigating the Effectiveness of Off-the-shelf Orthotic Sandals on Self-selected
                                           Gait
                             Michael Koh, Alex Ong, Tarkeshwar Singh
                                      Republic Polytechnic

Abstract
The purpose of the study was to investigate the biomechanical aspects of lower limb gait
due to the use of off-the-shelf orthotic sandals. Data was collected on 14 healthy male
subjects while walking across a gait platform comprising three Kistler portable force
plates integrated and synchronized with the active marker motion capture CODA
system. Ground reaction forces (GRF), range of foot pronation and tibia rotation were
obtained. Results show that using the orthotic sandals reduces attenuates the rate of
pronation and tibial rotation. However, while foot pronation was significantly (p<.04)
reduced, tibial rotation was reduced but not significantly. With respect to GRF, there is
no difference. Overall, the orthotic sandals tested was found to be effective in reducing
rate of pronation and range of pronation. This would potentially improve gait
mechanics particularly for the lower limbs.

Key words: motion analysis, kinetics, pronation, tibial rotation, ground reaction forces

1. Introduction

Much research has been done on the use of orthotic insoles in shoes to treat heel pain or to
improve gait and sports performance [1,2,3,4]. It is reported that orthotics help to stabilize
muscle activity, reduce fatigue, and dampen the soft tissue vibration when put into the shoes
of the sportsmen [1]. Some researchers [6] have proposed that notion that the moulding of the
foot orthotics help in shock absorption by providing a larger contact area between foot and
foot orthotics. Moulded conditions means that the feet is in contact with entire forefoot and
mid-foot regions of the orthoses, thereby, supporting the medial aspect of the foot. It has been
suggested [3] that maximum foot inversion and maximum foot inversion velocity were
reduced with moulding. With respect to vertical GRF, it has been postulated that moulding
can reduce both the magnitude of the vertical impact peak force and the vertical loading rate
during the early stance phase. Some researchers claim that using foot orthoses to increase the
effects of foot mechanics during gait [4]. They showed that maximum foot eversion,
maximum foot eversion velocity, maximum tibia rotation and tibia rotation velocity can be
reduced when using orthoses.

Sandals or thongs, are one of the most common styles of leisure footwear. When walking, we
apply up to 1.5 times our body weight on the foot. Normal people spend about 6 % of their
time on foot during the day [5]. Since the feet pronates on every step we take, over pronation
may cause foot or limb injuries such as shin splints or cartilage breakdown. For instance,
swelling behind the medial malleolus as a result of poor gait dynamics can make normal
standing and walking very painful and difficult [6]. Therefore, proper cushioning is required
to reduce these impact forces and protect the one from injury.

However, there is limited research done on the use of sandals. Research that has been done on
sandals have attempted to measure falls and injury in both the elderly and the young. Other
physical activity research tended to identify the health benefits of walking for transport,
exercise. A search through an electronic database produced hardly any research that examines
or discusses how orthotic sandals can affect lower limb gait mechanics. Therefore, this study
aims to investigate how orthotic sandals influence the gait mechanics of the lower limb
during normal self-selected walking speeds.

2. Methodology

2.1 Subjects
14 male participants (Age: 32 ± 1.58 yrs; Height: 169 ± 8 cm; Weight: 70 ± 20 kg)
participated in this study. Informed voluntary consent was obtained from the participants
prior to the experimentation. The study was ethically approved by the Ministry of
Education’s Institutional Review Board for the Science Mentorship Programme. All the
participants were familiarized with both the orthotic and normal sandals 2 weeks prior to
experimentation. The participants were also informed of their right to withdraw without
prejudice at any time during the data collection process if they felt uncomfortable.

2.2 Experimental setup and data analysis

Data was collected on a gait platform comprising three Kistler portable force plates integrated
and synchronized with the active marker motion capture CODA system. Ground reaction
forces (GRF), range of foot pronation and tibia rotation were obtained.

Selected anatomical landmarks of the illiac crest, sacrum, epicondyle, greater trochanter,
lateral and medial malleolus of the ankle, medial and lateral heel and the first and fifth meta-
tarsal were used. One complete stride was chosen for analysis. These landmarks were used to
create a 6-segment model that comprised the hip, knee, ankle and toes.

The subjects walked at a self-selected speed over the gait platform for familiarization. This
was done first using normal sandals. After four trials of familiarization, data was collected.
The trial result was checked to ensure that all the markers were visible and each foot had
landed entirely on the piezoelectric force plates. Only the left leg’s heel strike and toe-off
data was analyzed because gait symmetry was assumed between the two legs. One complete
stride was recorded and the left leg data was extracted from this recorded stride. This
extracted data was filtered and smoothened. The process was repeated for the orthotic
sandals. Figure 1 shows the set up.




Figure 1. Experimental set up of force plate and motion capture.

Based on the literature reviewed, the gait parameters selected for analyses were: vertical
ground reaction force at heel strike; tibial rotation and ankle pronation angle during the gait
cycle.
3. Results and Discussion

Figure 2 shows the averaged vertical GRF in Newtons at heel strike, for the two conditions,
with (orthotic sandals) and without (normal sandals). There is no difference between the
vertical GRF experienced between the two types of sandals. This finding does not support the
notion that increasing contact area between foot and orthoses will attenuate GRF at heel
strike. It is possible that in instances where such an attenuation occurred, it was due to custom
moulded orthotics as opposed to off-the-shelf orthotics which is the current situation.

 GRF (N)




Figure 2. Mean vertical GRF (N) at heel strike for two conditions, with orthotic sandals
(with) and normal sandals (without) for n=14 male subjects.

During gait, the foot undergoes supination and pronation at different phases of gait. It was
speculated that the orthotic sandals could reduce the range of pronation. In figure 3, we
observe that the range of pronation is significantly reduced (p<.04).

                          R
                  Pronation ange
                  (0)

                                              *
                                              p<0.04




Figure 3. Range of pronation (in degrees) for two slipper conditions – orthotic (with) and
normal (without) for n=14 male subjects.
Our results also show that the mean range of tibia rotation while wearing normal sandals is
higher than the orthotic sandals by 0.12 degrees. While this may suggest that orthotic sandals
help decrease the range of tibia rotation that occurs during gait, however, the difference was
insignificant.

Figure 4 shows the graph of averaged pronation and tibial rotation in ‘with orthotics sandals’
(With) and ‘without orthotics sandals’ (Without) conditions. Each line starts from the heel
strike and ends at the instant when supination and external rotation of tibia begins. It can be
seen that the slope depicting the rate of pronation and tibial rotation is attenuated for the
orthotic condition. Our finding with regard to attenuated range of pronation and tibial rotation
is consistent with the literature.

The mechanism of tibial rotation and pronation is often used as a basis in explaining lower
limb injury. Although this mechanism remains a postulation, for now, the sandals designed to
help alleviate lower limb injury through this mechanism of reducing tibial rotation and foot
pronation does fulfill its intended design.




Figure 4. Illustration of the rate of tibial rotation and pronation for averaged ‘with’ and
‘without orthotic sandals’ conditions for n=14 male subjects.

4. Conclusions
The purpose of the study was to analyze the influence of off-the-shelf orthotic sandals
intervention on ground reaction force, pronation and tibia rotation throughout the entire
stance phase in a sample of healthy male adults. It was hypothesized that the intervention of
orthotic would have significant influence on the ground reaction force, tibia rotation and
pronation. We found that there was a significant reduction in the range of pronation as a
consequence of orthotic slipper use.
Acknowledgement
Our thanks to Koh Yu Han, and Oh Xueyan from Hwa Chong Institute for assisting in this
project as part of the science research mentoring programme of the Ministry of Education,
Singapore. Special thanks to Vasyli International from Australia, who provided the
ORTHAHEEL orthotic footwear..

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