Human Factors & Ergonomics Design Project

Khade Grant EGRB 421 Final Project 11/30/2015

EGRB 421 Final Design Project

A Prosthetic Device Design Providing Natural Gait Movement for Patients in Full-Leg Casts

Khade Grant

11/30/2015


Abstract:

A fracture is a break in the continuity of a bone. The tibia is the most commonly fractured long bone in the body (33% of all fractures in the body). After a fracture, the leg is usually put in a cast depending on the type of tibial fracture. There are three kinds of tibial fractures: Tibial shaft fractures, tibial plateau fractures, and tibial plafond fractures. Tibial shaft fractures, which are the most common tibial fracture (93% of tibial fractures), occur between the knee and the ankle. These fractures require the leg to be put in a full-leg cast for recovery. Unsurprisingly, during recovery, mobility is an issue for those who have fractured their tibia. There are some current solutions; such as crutches, knee-scooters, or the iWalk 2.0; that have been proposed to address the mobility issue, but these fall short of providing those in full-leg casts with a natural walking motion or sufficient maneuverability. Also, the required use of hands heavily limits the activities the user can perform during movement while using many of these mobility aids. The proposed design solution consists of an electromechanical prosthetic device which consists of two titanium alloy pylons (rods) on the left and right of the injured leg. Both rods attach to a mechanical knee on each side and continue past the knees and come together to form one rod beneath the patient’s foot. The foot portion of the device has rubber on the end to promote some ankle flexion motion. The patient is supported with neoprene straps. The device consists of angular sensors and microprocessors that relate the hip flexion angle during each stage of the human gait cycle to the knee flexion angle at the corresponding stage in the gait cycle. The output signal produced from the hip flexion angle is calibrated to produce the corresponding knee flexion angle. First, anthropometric data was collected from the Center for Disease Control (CDC) for men and women to determine the required sizes and dimensions of the device. Next, the material properties for various materials were evaluated and the optimum materials were selected for use in the design. The required electrical properties of the mechanical knee were then incorporated into the physical device. After finalizing a design model, the device will undergo strength testing as well as motion testing to determine if the model is a sufficient design. The final prototype will be able to sufficiently provide normal human gait movement to people who are confined to full leg casts.


Introduction

A fracture is a break in the continuity of a bone. Fractures to the leg are a very common injury. The tibia is the most commonly fractured long bone in the body. Almost 500,000 people fracture their tibia each year, making up around 33% of all fractures in the body (Fields, 2015). These fractures are often expensive as the healthcare cost for tibial fractures range from $11,686 to $25,556 per patient depending on the location and severity of fracture (Antonova et al. 2013). After a fracture, the leg is usually put in a cast depending on the type of tibial fracture. There are three kinds of tibial fractures: Tibial shaft fractures, tibial plateau fractures, and tibial plafond fractures. Tibial shaft fractures, which are the most common tibial fracture, occur between the knee and the ankle. These fractures require the leg to be put in a full-leg cast for recovery. Tibial plateau fractures occur just below the knee joint. These require at-least a full-leg cast for recovery and are usually the worst kind of fractures as they can lead to problems such as knee arthritis even after recovery. Tibial plafond fractures occur at the bottom of the shin around the ankle joint. These fractures are perhaps the least severe, as they only require a lower leg cast.

Unsurprisingly, during recovery, mobility is a big issue for those who have fractured their tibia. There are some current solutions to address the mobility issue. These mainly include crutches, knee-scooters, and wheel chairs. These mobility aids often do not provide sufficient mobility to its users. One way to ergonomically measure the effectiveness of mobility aids is to look at if they allow its users to adequately perform the instrumental activities of daily living (IADLs) and the basic activities of daily living (BADLs). The IADLs are the complex skills required to live independently. These include: shopping, preparing meals, using the telephone, home maintenance, managing medications, driving, and managing finances: Crutches are the most common mobility aid. Crutches, however, don’t give the user a natural walking motion or sufficient maneuverability. The required use of hands heavily limits the types of activities the user can do during movement. Using current mobility aids, around two-thirds of users have significant limitations in one or more of the IADLs (NCHS, 1998). BADLs, such as walking, climbing stairs, eating, putting on clothes, and grooming are also significantly limited under the current mobility aids. Approximately one-third of the people who use mobility aid devices need assistance from another person in performing the BADLs compared to less than 1% in non-users (NCHS, 1998).

There is a need for a design that provides enhanced mobility, is hands-free during motion, and provides a natural walking motion during recovery. One recent invention, the iWALK 2.0, takes a step in the right direction. The user rests his/her knee on a pad which is attached to a mechanical leg and has a strap on the thigh to make it secure. This allows a more natural walking motion than any device currently on the market. However, there are some shortcomings. There is no flexion in the knee of the mechanical leg, so the walking motion is not natural. More importantly, since the knee must be bent in order to use the device, it can only be used by patients with lower leg casts. Only tibial plafond fractures, which make up only about 7% of tibial fractures, can be treated with a lower leg cast. This device cannot be used by 93% of the tibial fracture population.

The design solution should be a mechanical device that allows natural walking movement by providing full knee flexion and sufficient ankle flexion for patients in full-leg casts. The device should be hands-free and should allow for normal walking speeds on relatively flat surfaces. In addition to a natural walking motion, the device should provide sufficient mobility, stability, and safety to its users.

The deliverables for this device are as follows:

1. Electromechanical Hinged Knee Joint: The knee-joint will be microprocessor controlled. The microprocessor will analyze and interpret signals from knee-angle sensors and moment sensors.


It will also be controlled using position sensors in the knee using signals from an angular position sensor on the hip. The knee joint will produce the required knee flexion of the device. (Calibrated specifically to the user prior to injury, or calibrated using average gait data from a stored database obtained during testing).

2. Rotary encoder: The rotary encoder must accurately measure hip flexion angles.3. Foot structure capable of plantar/dorsi ankle flexion: The mechanical ankle will further allow for

better approximation of normal human gait movement.4. Normal human gait movement data: Data consisting of natural human gait movement, including

hip and knee flexion angles during each stage of gait movement. This data will be used to calibrate the device.

5. Final Prototype: A final prototype will be designed after various alternative designs are considered and rigorous tests are conducted.

Description of Approach and Methods

Design and Selection Criteria

The first step in the design process was to use anthropometric data to fit human lower limb dimensions to the design. This mainly included looking at anthropometric data. The product design is generally for both men and women. In order to take into account the various size differences between the population, as well as the differences between men and women, the anthropometric data measurements for the 5th, 10th, 15th, 25th, 50th, 75th, 85th, 90th, and 95th percentiles for both men and women were tabulated and used to determine the various dimensions of the design product. There were three key measurements used in this section. The first was the upper leg length in centimeters for males and females 20 years of age and older. The second key measurement was the knee height in centimeters for males and females 20 years of age and older. The last key measurement was the mid-thigh circumference in centimeters for males and females 20 years of age and older. This dimension was used for the inner circumference of the top ring of the mechanical leg that would fit around the thigh of the user. The knee height dimensions were used to determine where on the mechanical leg to place the artificial knee that would allow for rotation. This data was obtained from resources such as the Centers for Disease Control and Prevention (CDC). Additionally, it could be experimentally obtained by the designers. The following table was a sample of the measurements used.

Table 1. Anthropometric data in centimeters for relevant measures. Obtained from CDC (2008)

The anthropometric data was used to determine the lengths of the upper and lower pylons, as well as the circumference of the leg strap. The 10th, 50th, and 95th percentiles were used to determine the dimensions of three different sizes for the device. The upper pylon length was calculated using


approximately three-fourths the length of the upper leg. The lower pylon length was determined using a measurement slightly larger than the knee height measurement. The strap dimensions were determined using a measurement slightly smaller than the thigh circumference measurements. The dimensions of the device are shown in the final design section in table 3.

There were various materials that were considered for the design of the mechanical leg. For the dual-pylons, aluminum, titanium, and steel were the materials considered. Titanium (Ti-6Al-4V) was chosen as the material because it is very strong yet lightweight. The material properties of Titanium are provided below in Figure 1.

Figure 1. Material Properties of Ti-6Al-4V (ASM, 1996)

Based on the fatigue strength of 240 MPa and the Shear Strength of 550 MPa, and including a safety factor of 5 as well as designing to the 95th percentile in terms of knee height and body mass, the minimum inner radius dimension for a cylindrical pylon with an outer radius of 2 cm was determined to


be 1.61 cm. The calculations of the dimensions are shown in Appendix I. The sole of the device will be fitted with rubber to provide some natural ankle flexion during movement. A preliminary stress test was conducted on the device made of Ti-6AL-4V. The results (shown in Appendix III) confirm that the selected material is sufficient for this design.

The strapping on the upper leg is made from non-flexible vinyl lined with neoprene. Neoprene is a synthetic rubber that prevents slippage of the strap on the leg and provides sufficient breathability (Smith, 1985). Use of non-flexible vinyl prevents the strap from stretching, thus holding the patient in place.

Comparison of Solutions

Three design concepts were considered for this device. All of the designs consisted of a rotary encoder on the hip. The rotary encoder detected the angular displacement and sent the resulting signal to a circuit in the mechanical knee that produced a corresponding output signal. That output signal was used as the input to produce the desired angular rotation. The first considered design was Alternative 1. It used a single-turn potentiometer as the rotary encoder. Alternative 2 was similar to Alternative 1 except it used an optical rotary encoder in place of the single-turn potentiometer. An optical rotary encoder uses a light shining onto a photodiode through slits in metal to detect angular displacement. This rotary encoder provides a very slight increase in accuracy but a substantial increase in cost. It is also difficult to maintain because it is very sensitive to dust. Alternative 3, used an On Axis Magnetic rotary encoder. This encoder employs the use of a 2 pole neodymium magnet rotating over the center of the encoder. This encoder can be very inaccurate and was thus insufficient for use in this application. The alternative solutions were scored based on various categories. The following scoring chart was used to select the best alternative. The maximum possible scores for each category ranged from 3 (little importance) to 9 (maximum importance). The design alternative with the highest score was selected.

Table 2. Scoring Chart of Design Alternatives

Specifications (possible points) Alternative 1 Alternative 2 Alternative 3

Function (9) 9 9 9

Features (9) 9 9 8

Novelty and commercial potential (6) 6 6 6

Safety (9) 9 9 5

Human factors (9) 7 7 4

Maintenance (6) 6 4 5

Reliability (9) 8 9 4

Manufacturability (6) 5 5 5


Regulatory requirements (9) 9 9 9

Cost (6) 6 2 6

Ease of use (9) 9 8 6

Comfort (6) 5 5 5

Lifetime (3) 3 2 2

Total (96) 91 84 74

Final Design

The final design consists of two titanium alloy pylons (rods) on the left and right of the injured leg. Both rods attach to a mechanical knee on each side. The pylons continue past the mechanical knees and come together to form one rod beneath the patient’s foot. The foot portion of the device has rubber on the end to promote some ankle flexion motion. The device has multiple straps made of neoprene around the patient’s thigh for support. The device consists of sensors that relate the hip flexion angle during each stage of the human gait cycle to the knee flexion angle at the corresponding stage in the gait cycle. The final design has a rotary encoder attached to the patient’s hip. A single-turn potentiometer is used as the rotary encoder. It produces an output signal corresponding to the hip flexion angle. The mechanical knee rotates the legs of the device using gears. These gears are microprocessor controlled. The microprocessor takes an input signal produced from the single-turn potentiometer and produces an output signal that causes the gears to rotate the leg to the determined angular position. The output signal produced from the hip flexion angle is calibrated to produce the corresponding knee flexion angle. In addition to knee flexion, the design also gives the user the option to lock the mechanical knees in the anatomical position in order to allow users to climb stairs. The motion design system is only be for relatively flat surfaces. In order to account for the height difference produced by the mechanical leg, an elevated shoe is provided and should be worn by the user. During motion the device will be hands-free.

Below is a model of the final device design, as well as the device on the human leg in various stages of the gait cycle.


Figure 2. SolidWorks Model of Prosthetic Design. (a) Isometric View. (b) Frontal View. (c) Sagittal View. (d) Isometric w/ person model.

Figure 3. SolidWorks Motion Model of Prosthetic Device in Main Stages of the Human Gait Cycle

As stated in the methods, titanium alloy (Ti-6Al-4V) is the material used for the pylons, and non-flexible vinyl lined with neoprene is the strapping material for the upper leg.

The dimensions and measurements of the device components are listed below in table 3.


Table 3. Dimensions and weight of major device components (from 50th percentile)

Length

(cm)Outer Radius

(cm)Inner Radius

(cm)Weight

(lbs)Upper Pylon 38 1.5 0.875 1.73Lower Pylon 54.1 1.5 0.875 2.46Foot

Section 8 N/A N/A 1.54Straps 50 N/A N/A 0.5

The total weight of the device is estimated to be 10.5 lbs. The determination/calculation of the dimensions and weight of the major components are shown in Appendix I. A materials parts list is also shown in Appendix I. The strap is sufficient to hold the weight of a male in the 95 th percentile. The minimum surface area of the strap was determined using the weight and the ultimate stress of skin. The ultimate stress of skin is around 20 MPa (Gallagher, 2012). The area of the straps was over 800 times the minimum required area. The calculations are shown in Appendix I. Since the cross-sectional area of the thigh increases with height, the non-flexible vinyl straps won’t slip up the thigh when an upward reaction force is applied to it during walking.

The initial design drawings are shown in Appendix II. The drawings consist of the frontal and lateral view in the anatomical position, and the lateral view of the device in the middle of the gait cycle.

Electrical Properties

The device consists of a sensor placed on the hip. The sensor placed on the hip will be a rotary encoder (angular position sensor). There are various types of angular position sensors that could be used, but for this application a single turn potentiometer (resistive rotary encoder) should be sufficient.


Figure 4. Single turn potentiometer (Webster, 2009)

A single turn potentiometer consists of a stationary resistive and power element and a movable wiper. It uses the concept of voltage division to produce varying output voltages as a wiper moves along the resistor. Using voltage division, the output voltage Vo produced from a constant input voltage Vi is given by:

V o=R2

R1+R2×V i=

R2Rtotal

×V i.

As the wiper turns counter-clockwise R2 decreases and the output voltage decreases proportionally. For the single-turn potentiometer the power and resistive element will remain stationary as it will be attached to the hip of the patient. The wiper will be directly controlled by the movement of the femur. Thus as the hip flexes or extends during movement, the wiper will rotate and produce a corresponding voltage change. Therefore, each hip flexion angle will have a corresponding output voltage.

During the human gait cycle, hip flexion angles correspond to knee flexion angles. For example, in healthy individuals, when 70% of the gait cycle is complete, the hip flexion angle is approximately 12°. This corresponds to a knee flexion angle of 64°. The corresponding hip and knee flexion angles are shown in Figure 5.


Figure 5. Trajectories of hip and knee angles during human gait cycle (Colombo et al., 2000)

The voltage produced from a hip flexion angle would cause the mechanical knee to rotate to the corresponding knee flexion angle.

Sample Calculation: Vi = 20mV. At 0° hip flexion the wiper is at 180°. Thus R2 = Rtotal/2. This implies 0° hip flexion corresponds to V0 = 10mV.

At 12° hip flexion, the wiper is at 192°. Thus R2 = 192360

×R total. V o=

192360

×R total

Rtotal×20mV=10.67mV .

10.67mV will then be calibrated to produce a knee flexion angle of 64°.

The mechanical knee consists of a microchip circuit, an analog to digital (A/D) converter, a digital to analog (D/A) converter, a microprocessor, an electric stepping motor, and gears. The microchip circuit will transfer the electric energy produced by the single-turn potentiometer to the A/D converter. Varying hip flexion angles will produce voltages (and thus current) at varying amplitudes. The varying amount of electric energy produced will be passed to the A/D converter. The signal will then be converted to a digital signal. This signal will then be passed to the microprocessor which will process the digital data according to the preprogrammed instructions given to it. The microprocessor will then output a digital signal to the D/A converter which will produce and pass an electric signal to the electric


stepping motor. The specific electric signal from the D/A converter will cause the electric stepping motor to provide the mechanical energy necessary to rotate the gears to an absolute angle. The mechanical legs which are attached to the mechanical knee will thus be forced to rotate to that angle.

The electric signal produced by a specific hip flexion angle will be converted into a specific digital signal corresponding to the inputted electric signal. The microprocessor will be preprogrammed to convert that digital signal to a new digital signal that will correspond to the absolute angle rotation in the mechanical knee. The new digital signal will be converted to an electric signal (by the D/A converter) of the magnitude required to cause the electric stepping motor to produce a rotation of the gears in the mechanical knee to the absolute angular position desired. The signal processing flowchart in the mechanical knee is shown in figure 6.

Figure 6. Signal Processing Flowchart of Mechanical Knee

In order to ensure the knee flexes to the appropriate angle and to prevent over-rotation, one of the gears will contain a High-Resolution Magnetostrictive Position Sensor. These are position sensors produced by MTS and uses the same technology as the MTS testing systems used in Dr. Wayne’s Biomechanics Lab. The inside of the mechanical knee will have these position sensors as well located at various angular positions. The position sensor on the gear will remain activated, but only the position sensors around the inside of the mechanical knee at the correct angular knee positon (corresponding to the hip angular position) will be activated. When two activated position sensors come in contact, the rotation stops at that position.


The microprocessor will allow the calibration of the mechanical knee to be very robust. A microprocessor is a programmable device that accepts digital data as input, processes that data according to preprogrammed instructions stored in its memory, and outputs digital data. A computer program will need to be written in the future for the microprocessor to produce the required electric signal. The program will have to relate the electric signal produced by hip flexion to a corresponding signal that produces the required absolute angle rotation. Since a 12° hip flexion angle produces 10.67mV, and assuming an electric signal of 15mV applied to the electric stepping motor will cause a rotation to the 64° position, the following sample code shown in Figure 7 could be used.

Figure 7. Sample Code for microprocessor

One potential problem is the fact that some hip flexion angles occur twice in the gait cycle, and thus have two different corresponding knee flexion angles. This problem is solved by adding an additional wiper (offset 90° clockwise from the first wiper), a differentiator, another microprocessor, A/D and D/A converter, and a single-pole double-throw (SPDT) switch. Since hip flexion angles only occur once when the hip is flexing, and then again when the hip extends, the voltage produced from the first wiper can be used when the hip is flexing, and the voltage produced from the second wiper (produces different values because of the 90° offset) can be used when the hip is extending. While the

hip is flexing, the output voltage would be increasing. Thus the differentiator (i=C× dvdt ) would

produce a positive current. When the microprocessor receives a positive current signal it will cause the switch to connect to the first wiper. However, when the hip is extending, and a negative current is produced from the differentiator, the microprocessor will cause the switch to connect to the second wiper. The signal processing flowchart for the entire device is shown below in figure 8:


Figure 8. Signal Processing Flowchart for Entire Device

Testing/Evaluation Methods

The device will undergo two major testing methods: strength testing and motion testing; as well as post-production evaluation.

Strength Testing: The methods required for testing pylon strength before use are compressive loading and bending tests. These tests will consist of applying normal and cyclic compressive loads, as well as bending loads to the device until failure to determine the maximum loads the device can bear. Furthermore, before the design can be used in the market, it must first undergo trials by healthy human subjects. These tests will consist of performing walking movements at various speeds; namely, walking at 60% normal walking speed, walking at normal walking speed (5.0 km/h or 3.1 mph), and a brisk


walking pace at around 9.0 km/h. During testing, the pylons will be fitted with piezoelectric polymeric films (polyvinylidene fluoride). These films are thin, lightweight and pliant. They will be placed in the longitudinal and circumferential directions on the pylons during the tests in order to measure strain. Furthermore, a preliminary compression test (results shown in Appendix III) was conducted on the SolidWorks model.

Motion Testing: The motion produced by the device will be evaluated using motion analysis tools provided by ©Vicon Motion Systems Ltd. First, the human subjects will be tracked moving at the three varying speeds without wearing the device. The data obtained will serve as the control. Next, the human subjects will be tracked while performing the same walking movements while wearing the device. The data obtained will then be compared to the control data using various motion analysis techniques such as spatial analysis and fourier analysis to determine how closely the device approximates human gait movement. Also, the number and degree of lateral and forward/backward compensatory movements produced during walking with and without the device will be compared and analyzed to determine stability. The amount and degree of arm abduction (a movement used by humans for stability) will also be analyzed and compared to arm movement during normal walking. Subjective measurements will also be collected by asking the users to rate the comfort, stability, and mobility of the device on a 1(worst) – 10(best) scale.

Post-Production Evaluation: After the device enters the market, customer feedback will be collected specifically for the categories of comfort, safety, mobility, and ease of use. Customer feedback will also be collected in terms of the percentage of users that experience limitations in performing one or more of the IADLs and the BADLs. This percentage will be compared to the percentage of users that experience significant limitations while using other traditional mobility aids. Customer feedback on any additional comments or concerns that customers may have will also be collected.

Summary

There are some potential limitations associated with the proposed design solution. One limitation is mobility during walking up and down stairs. The device is designed to produce natural walking motion on relatively flat surfaces, not for climbing stairs. Thus, a future improvement for this device would be to add a mobility feature that allows the user to naturally move up and down stairs. This could possibly be done by adding a separate stair-climbing mode that the user can select. This mode would calibrate hip flexion angles to knee flexion angles while walking up and down stairs. Another potential limitation is the weight of the device. Although the weight of the device is only estimated to be around 10.5 pounds, and the user won’t need to constantly lift the full weight; the weight of the device could still make it slightly cumbersome to move after walking for extended periods of time. The cost of the device is also another potential limitation. Thus, a future improvement for this device would be to conduct further material research and select a lighter and cheaper, yet sufficiently strong, material. A new “super-steel” alloy that is supposedly as strong as titanium but ten times as cheap and also lighter is being developed in South Korea (Crew, 2015). The material is an alloy consisting of steel, aluminum, and a small amount of nickel. The added nickel is the key ingredient in this new material.

In conclusion, tibial fractures are the most common long bone fractures in the body, making up around 33% of all fractures in the body. The majority of tibial fracture (93%) require a full leg cast. Various designs are on the market that provide patients in lower leg casts with sufficient mobility. However, there is a significant need for a mobility aid suitable for the 93% of the tibial fracture population who are not able to benefit from the current designs. The proposed design provides people


recovering from tibial fractures with a hands-free device that allows for a natural walking motion by providing knee flexion. The design solution consists of a mechanical prosthetic leg apparatus which provides knee flexion through a mechanical knee. The device consists of angular sensors and microprocessors that relate the hip flexion angle during each stage of the human gait cycle to the knee flexion angle at the corresponding stage in the gait cycle. The output signal produced from the hip flexion angle is calibrated to produce the corresponding knee flexion angle. This hands-free device provides people with tibial fractures who are subjected to rehabilitation in full-leg casts with the ability to move naturally.


References

[1] Fields, Karl B. “Tibial Shaft Fractures in Adults.” UptoDate. Sep 29. 2015. Web Nov 29. 2015

[2] Antonova, E., et al. “Tibia Shaft Fractures: Costly Burden on Nonunions.” BioMed Central. Jan 26. 2013. Web Nov 29. 2015

[3] National Center for Health Statistics. “National Health Interview Survey on Disability.” Centers for Disease Control and Prevention. Jul. 1998. Web Nov 30. 2015

[4] Margaret, A., et al. “Anthropometric Reference Data for Children and Adults: United States, 2003-2006.” Centers for Disease Control and Prevention. Oct 22. 2008. Web Nov 2. 2015

[5] Matweb LLC. “Titanium Ti-6AL-4V (Grade 5), Annealed.” Aerospace Specification Metals Inc. May 1996. Web Nov 3. 2015

[6] Simth, J. “The Ten-Year Invention: Neoprene and Du Pont Research.” Technology and Culture. Jan. 1985. Web Nov 30. 2015

[7] Gallagher, A.J. “Dynamic Tensile Properties of Human Skin.” International Research Council on the Biomechanics of Impact. Sep. 2012. Web Nov 30. 2015

[8] Webster, J. “Medical Instrumentation: Application and Design.” John Wiley & Sons, Inc. Feb 2009. Print.

[9] Colombo, G., et al. “Treadmill Training of Paraplegic Patients Using a Robotic Orthosis.” Journal of Rehabilitation Research & Development. Dec. 2000. Web Nov 29. 2015

[10] Crew, Bec. “New ‘Super-Steel’ Alloy is as Strong as Titanium, but 10 Times Cheaper.” Science Alert. Feb 6. 2015. Web Nov 30. 2015


Appendix I – Calculation/Validation of Dimensions and Materials List

Supplementary Figure 1. Calculation/Validation of Dimensions and Material Parts List


Appendix I (continued)

Supplementary Figure 2. Calculation/Validation of Dimensions


Appendix II – Initial Drawings

Supplementary Figure 3. Initial Drawings. (a) Frontal View. (b) Sagittal View. (c) Sagittal View during Gait Cycle


Appendix III – Preliminary Test Results

Compression Test Results

Name Type Min MaxStress1 VON: von Mises Stress 0 N/m^2

Node: 504552.45758e+006 N/m^2Node: 83321

iKhade-Static 1-Stress-Stress1Supplementary Figure 4. Compression Test Results: Stress Analysis

Appendix III (continued)


Name Type Min MaxDisplacement1 URES: Resultant Displacement 0 mm

Node: 504550.00288903 mmNode: 80672

iKhade-Static 1-Displacement-Displacement1Supplementary Figure 5. Compression Test Results: Deformation Analysis


Appendix III (continued)

Name Type Min MaxStrain1 ESTRN: Equivalent Strain 0

Element: 294141.75294e-005 Element: 54094

iKhade-Static 1-Strain-Strain1Supplementary Figure 6. Compression Test Results: Strain Analysis

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