Optimized Design and Testing of Kids Ankle Foot Orthosis. A Case Study

Technical Report, 2019

13 Pages, Grade: 10.00










Ankle foot orthosis (AFO) are externally applied device that a reused to support as well as control the foot and ankle joint of patients having foot deformity. Foot drop is caused by a deficiency in the ankle joint in which results in the weakness of ankle and toe dorsiflexion. This research proposes a new approach to design and performance evaluation of AFO fabrication that utilizes modeling, simulation and analysis software (like Open Sim, Ansys Work bench & Solid work) and additive manufacturing technologies to customize the fit form to an individual. By implementing a carbon fibre strut at ankle joint the design will result in a stronger, more comfortable, more flexible AFO that can adaptively constrain ankle movement for various different activities. GAIT Analysis was performed on six patients having foot drop, from the emotion analysis system in the GAIT lab. The data from the GAIT lab was then imported into the Open Sim to create a biomechanics simulation to extract the joint angle and joint moments. These value of ankle angle and moment with & without AFO was compared with normal value. The results show a considerable effect of the use of the AFO by drop foot patients in terms of ankle angle and ankle moments. Furthermore, the muscular analysis in terms of activation and forces also suggest that the dorsiflexors are assisted by the AFO during GAIT and the activation of the plantarflexion are considerably less during the lifting of the foot of the ground.

Keywords: Ankle Foot Orthosis, Human Gait, Optimization Techniques, Teguchi Method


Ankle Foot Orthoses (AFOs) are orthoses that use the lower leg joint, the entire or part of the foot. AFOs are proposed to control improvement, cure bending or perhaps change for shortcoming. AFOs can be outlined out with adequate mechanical lever arms to control the lower leg complex unmistakably and to influence the knee joint round about [1]. AFOs are after a short time the most widely utilized orthoses in the India, addressing 26% of clinical practice by guaranteed orthotist, twofold that of some other sort of orthosis. There are many sorts of AFOs, which may move in their biomechanical setup ( searched for mechanical compel frameworks, any joint or elucidation, game-plan and degree of advancement), materials and parts[2].

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Figure 1.1: Dorsiflexion and Plantar flexion of the foot

To see how AFOs function, we should first manage two standard demand that happen at the lower leg joint "dorsiflexion" and "plantar flexion" appeared in Figure 1.1 [3]. Plantar flexion is the change the lower leg joint makes when the toes point jumping. Dorsiflexion is the progress the lower leg joint makes when the foot focuses upward. This change needs to happen when the foot tumbles off the land with the target that the patient does not clear up their toes. Patients with draft dependably have a halfway or complete inadequacy of the muscles that dorsiflexion the foot at the lower leg joint[4-5]. Whatever sorts of orthoses are recommended or fitted, they share diverse general structure shows and attempt give a couple or most of the parts underneath:

i. Rear foot quality
ii. Mid-forefoot quality
iii. Shaped underside plates to help foot alteration (tone decrease)
iv. Consolation of good standing position with comparable weight bearing on the two feet.

Numerous patients with step variation from the norm are determined to have drop foot issue. One of the basic treatment approaches toward a drop foot is lower leg foot orthosis (AFO)[6-8]. Despite the fact that, there has been a significant decent advance in outlining AFOs, however small size, wearable gadget is needed that can resolve drop foot, successfully.

By and large, AFOs can be classified in two gatherings as takes after:

i. Passive, which have settled and explained joints,
ii. Active, which have dynamic actuators.

In any case, one can include another gathering of AFOs as semi-dynamic gadgets. Since created latent AFOs were not completely accommodating for some drop foot patients, dynamic AFOs (AAFOs) were produced offering full controllable assistive gadget[9-12]. Be that as it may, current AAFOs have different impediments to get into market, for example,

i. impractical estimate,
ii. heavy weight, and
iii. high electrical power require.

Drop foot patients are a gathering of patients with lower leg issue that have ability for plantar flexion and experience the ill effects of absence of dorsiflexion. Along these lines, drop foot patients require an AFO which can improv lower leg dorsiflexion[13].


Drop foot is a motor deficiency caused by total or partial central paralysis of the muscles innervated by the common peroneal nerve, i.e. the anterior tibial muscle and the peroneal group . Stroke is an often cause of drop foot . However, many other causes are reported for spinal cord injury that results in drop foot . Drop foot effects gait, considerably. A healthy gait or a normal walking pattern depends on biomechanical and nervous system features . Stability and specific metabolic energy expenditure are properties of a healthy gait[14-17] . Drop foot can cause unstable and higher energy expenditure gait. Several researchers have performed comprehensive biomechanical measurements to analyse gait patterns for basic understanding and rehabilitation purposes . Drop foot effects kinematics, kinetics, power, energy and stability of gait. Speed of waling has reported as the simplest methods to diagnose ankle disorder. It should be noted that an abnormal gait caused by drop foot might also cause Thus, treatment of this disorder is necessary to restore stability and other features of a normal gait[18-20].

Despite a healthy subject, a drop foot patient cannot accomplish dorsiflexion, properly. As it will be discussed, abnormality in dorsiflexion also affects other parts of gait and characteristics of other joints such as knee and hip. Thus, the main purpose of drop foot treatment is to provide enough dorsiflexion assistance so that patient can achieve a normal gait pattern. It is clear that a dorsiflexor controls stability when the first contact of foot occurs until flat foot. Furthermore, a dorsiflexor controls stability in swing phase. Dorsiflexor performance effects overall gait dynamics; and thus, affects energy and power throughout the gait cycle [21-25].


There are kinds of Ankle Foot Orthotics in India. As their functions, they can be Classified into two key types-static AFO and Dynamic AFO.


Static AFO is a strict or flexible device, which has the upstanding part behind the human’s calf and a part under foot. The function of static AFO is to support patients, such as after stroke patients, who have a weakness of lower-extremity muscles and fix their ankle in a particular position. As noted, the rigid one means the material of AFO is rigid, but having small deformation. It helps patients control the ankle movement, abduction and adduction of the forefoot and stabilize the subtalar joint[26-30]. Similarly, the flexible AFO mean the material of AFO is flexible, able to have largely deformation as shown in Figure 1.2. It helps assist the dorsiflexion of patient’s ankle.

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Figure 1.2: Static AFO. (a) Rigid (b) Flexible


A dynamic AFO is an athletic, which delivers a similar shape to the static one, but free of ankle dorsiflexion. Dynamic AFO facilitates patients’ ankle movement close to healthy people, and it also makes patients’ ankle joint stable during movement[31-35]. Ankle joint hinge can be adjusted to tight or loose, depending on the recovery level of patients as shown in Figure 1.3.

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Figure 1.3: Dynamic AFO with free of ankle dorsiflexion and restrict to planar flexion


Statistical significance is a method to test whether result of a data set is statistically significant. This test provides a p-value, representing the probability of significant of result. In general, a p-value should be of 5 % or lower for consideration the significant result, depending on the field of study.

To determine whether a result is statistically significant, two methods were used to check the result.

a) Analysis of variance(ANOVA)
b) Orthogonal Array


Orthogonal Array testing is a discovery testing strategy that is an orderly,statistical method for software testing. It isutilizedwhenthequantityofcontributionstothesystemisgenerallylittle, yet too enormous to even think about allowing for comprehensive testing of each conceivable contribution to the system. Orthogonal array tells about which parameter is optimized for design.

Once the degrees of freedom are known, next step, selecting the orthogonal array is very easy task. The number of treatment condition is equal to the number of rows in the orthogonal array and must be equal to or greater than the degree of freedom. Table 7.6 shows the orthogonal arrays that are available OA9. In this research the problem is of three factors at three level and the degree of freedom is 8 as shown in Table 7.5, then the next available orthogonal array for three level is OA9.


Taguchi Orthogonal Array Design L9(3**3)

Factors: 3

Runs: 9

Columns of L9(3**4) Array

Table 1: Response Table for Signal to Noise Ratios for Strut Smaller is better

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Table 2: Response Table for Means

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Table 3: OA9 Layout with Experimental Results for Strut

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The response table is shown in Table 2 & 3 for S/N and mean y, along with the maximum difference between the levels. A better evaluation of the factors and their level can be seen in the response graph given in Figure 1.4-1.5.ForfactorA,width,level1isobviouslythebestone for S/N; for factor B, thickness, level 1 is obviously the best one for S/N; for factor C, height, level 3 is obviously the best one forS/N.

A summary of results is shown in Table 7.6, it includes design dimensions or assembly efforts aswellasinformationonthenoisetosignalratio.Forfactora,strutwidth,level1wasselected; for factor B, level 1 was selected; for factor C, height of strut, level 3 was selected for provide higher torque when applied low force as well as low cost. It should be noted that these factors and their levels are least sensitive to the three-noise factor; therefore, we have a robust design.

Hence, the optimum condition of input process parameters is A1B1C3. Then the predicted equation was:

The theoretical optimized value under the optimum condition is given by:

ὴopt= m + (mA1 – m) + (mB1 – m) + (Mc3– m) (1)

Where misthe overall mean of SN ratio data,mA1ist the mean of SN ratio data for factor A at level1and mB1 is the mean of SN data for factor B at level1and mC3 is the mean of SN ratio data for factor C at level 3. After some calculation, get the mean of the values.

m = - 22.30, mA1 = - 20.96, mB1 = - 16.504, mC3 = - 21.66

After putting the corresponding values of means in equation 7.1, ὴopt=14.524

The corresponding values of torque is given by

yopt2 = 10^(-ὴopt/10) (2)

Hence, yopt= 5.32 N-m

Since, this combination of input parameters did not exist in the orthogonal array. The average value of torque obtained at this experiment was 5.32N-m which is very close to the theoretical value predicted by Taguchi analysis (5.32<6.088).

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Figure 1.4: Main Effect Plot for SN Ratio

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Figure 1.5: Main Effect Plot for Means


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Optimized Design and Testing of Kids Ankle Foot Orthosis. A Case Study
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ISBN (eBook)
ISBN (Book)
optimized, design, testing, kids, ankle, foot, orthosis, case, study
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Dr. Harish Kumar Banga (Author)Parveen Kalra (Author)R.M. Belokar (Author)Rajesh Kumar (Author)Prashant Kumar (Author), 2019, Optimized Design and Testing of Kids Ankle Foot Orthosis. A Case Study, Munich, GRIN Verlag, https://www.grin.com/document/507068


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