Abstract
Amputees pursue to obtain an artificial limb that suits them and adapts as close as possible to their healthy limb, especially for amputees of the lower limbs that are characterized by the necessity of performing the function of walking through the existing joints to make the amputee feel like having a healthy limb and perform its own needs. Here in this research we will address the improvement of the prosthetic limb of the amputee through the ankle joint, as a movable ankle joint was designed for the level of amputation through the ankle joint in the SolidWorks program and the data was analyzed using ANSYS to find out the extent to which the joint is able to perform plantar flexion and dorsal flexion movements and its range of motion by applying them realistically through tests conducted on the amputee when wearing the prosthetic with the hinged ankle joint and simile it with the conventional prosthetic with the fixed joint.
1 Introduction
Amputation is a surgical operation performed by the doctor to remove the limb (upper or lower) as a result of inflammation, burn, trauma or any other reason leading to amputation [1–3]. After the amputation, the patient needs to wear an artificial limb that performs the function that the natural limb used to perform. As in the amputation of the lower limbs, the patient needs an artificial limb that performs the movements required for the purpose of walking, such as the artificial limb for ankle amputation [4]. Although walking is easy for healthy people, it is difficult for a certain number of people to carry out basic movements, especially those who have undergone amputation in their lower limbs, as walking is a complex process that combines multiple functions of muscles and tendons that allow maintaining balance and stability and moving the body from one place to another [5].
The ankle joint plays an essential role in walking because of its great importance in the gait cycle, especially the plantar flexion and the dorsal flexion that occur in this joint [6–8]. As in this research, the amputation prosthesis through the ankle joint was improved by designing a movable ankle joint that performs plantar flexion and dorsiflexion movements, the basics of walking.
The primary objective of this research is to improve the functionality of lower limb prosthetics by designing a movable ankle joint that facilitates both plantar flexion and dorsiflexion. By incorporating these movements, the prosthetic will better mimic the natural gait cycle, thus enhancing the user's ability to walk and perform daily activities.
This paper contributes to the field by:
Innovative Design: Proposing a new prosthetic design that incorporates a dynamic ankle joint mechanism, enabling greater range of motion and adaptability.
Functional Analysis: Evaluating the impact of the movable ankle joint on walking efficiency, balance, and stability in users.
User-Centric Approach: Highlighting the importance of tailored prosthetic solutions that consider individual needs, ultimately aiming to improve user acceptance and psychological well-being.
Through these contributions, this research aims to bridge the gap between traditional prosthetic functionality and the complexities of natural movement, enhancing the overall rehabilitation experience for amputees.
While the researchers previously discussed the manufacture of a movable ankle joint with different manufacturing methods, it does not serve the purpose intended for the level of amputation through the ankle joint, such as the little height required for this level of amputation, as touched upon in Ventura et al. [9], where manufacturing technique was used to generate energy storing and return ankles with different stiffness levels to identify how energy storage and return properties influence lower extremity muscle activity during below-knee amputee walking. Martinez et al. [10] designed an ankle joint of a unidirectional spring that aims to store energy in dorsiflexion and release it in the movement of the soles of the feet, but it is specific for amputation below the knee, as well as with a lot of weight, and the patient faces difficulty ascending and descending stairs, sitting and standing, which must be addressed in the future.
In Cherelle et al. [11], the main challenge lies in recovering as much energy as possible from the gait, as the 3-foot prosthetic ankle simulator is an energy-saving mechanism using the principle of optimal energy distribution. But it is designed with a height that is not suitable for an amputatee through the ankle joint.
Dong et al. [12] used a five-bar spring mechanism. The new energy mechanical ankle joint is designed for below-the-knee amputation level, due to its flexibility during various special movements of the foot during walking, the most important of which are PF and DF without constraints, but in the future act of walking must be developed on different terrains. Kim et al. [13] studied muscle activity and metabolic costs for people with transtibial amputation altering muscle activity when walking with a powered prosthesis, and whether this change relates to changes in metabolic costs. Lathouwers et al. [14] aimed to evaluate the Talaris Demonstrator during daily activities by means of performance-related, physiological and subjective outcome measures. The subjective measures indicate the added value of this device, while overall task performance and intensity of effort do not differ between the Talaris Demonstrator and the current prosthesis. While Vaca et al. [15] determined how systematically varying the prosthetic foot-ankle stiffness affects standing and walking performance in persons with unilateral, transtibial amputation. The results improved our understanding about how prosthetic foot-ankle stiffness influences standing and walking in unilateral transtibial prosthesis users. It informs how variation of ankle dorsiflexion stiffness can influence key aspects of balance and gait. Vinay et al. [16] focused on developing and analyzing a Passive Ankle-Foot Prosthesis to attain 2 DOF, i.e., plantarflexion-dorsiflexion and inversion-eversion motions of a foot, such that it could mimic the behavior of a natural lost limb. They presented the integration of manual ankle stiffness modulation into the same design for dorsiflexion- plantarflexion, which can be altered by the amputee to a preferred stiffness for various ambulation requirements. Xiu et al. [17] presented a compliant passive ankle–foot prosthesis (CPAF) capable of 2-DOF rotation during locomotion. Dynamic analysis indicated that the proposed prosthesis provided good gait movement and generated sufficient ankle torque during level-ground walking, and the metabolic tests demonstrated that the configuration-4 of the compliant component could achieve the best efficiency during walking. Hameed et al. [18] had developed actuators that integrate passive and active devices to imitate the natural stride. Despite that, the current typical actuation technologies have significant limitations. They collected virtual gait. They aimed to improve the prosthetic limb for amputation through the ankle joint by providing the limb with a joint that performs the necessary foot movements for the walking process. Louessard and Bonnet [19] evaluated both the impact of the ankle stiffness and the visual system on static balance, as they proposed to investigate if the visual alteration more significantly impacts the correlation between ankle stiffness and static balance than without alteration. They confirmed that static balance decreases when ankle stiffness decreases.
2 Designed methodology of the project
All prosthetic feet commonly used for amputation level through the ankle joint provide movements in a simple manner at high cost, on the other hand, ankle joint designs for different levels of amputation are not suitable for use at the level of amputation through the ankle joint because of their heavy weight and non-cosmetic and most importantly the due to their height because at the level of amputation through the ankle joint only the foot bones are missing. Therefore, a movable ankle joint with a low height and suitable for this level of amputation was designed using the SolidWorks program to provide (planter flexion PF, dorsiflexion DF, eversion, and inversion) what is necessary for the function of walking. For analysis the ANSYS program was used to find the maximum stresses, total deformations, and the safety factors at each stage of the movement before manufacturing the required joint. Table 1 represents the characteristics that were used in the program for the proposed model.
Mechanical properties
| Bolt | Ankle joint | Foot | |
| Material | Stainless steel | Aluminum alloy | Carbon fiber |
| Tensile Ultimate Strength (MPa) | 586 | 310 | 345 |
| Tensile Yield Strength (MPa) | 207 | 280 | 230 |
| Young modulus (GPa) | 193 | 71 | 395 |
| Passion ratio | 0.31 | 0.33 | 0.2 |
Ankle Joint Design and Modelling Using SolidWorks s Software: The ankle joint was designed consisting of two pieces, one fixed to the foot and the other fixed to the socket, and they are fixed to each other by means of bolts from the sides to perform the dorsiflexion and plantar flexion movements., as illustrated in Fig. 1. Then the joint was analyzed in the ANSYS program.
Ankle joint design using SolidWorks s software, (a) Ankle joint front side, (b) Ankle joint left side, (c) Ankle joint top side, (d) Ankle joint trimetric view, (e) Assembly of ankle joint with the foot
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
A prototype of the ankle joint was designed but there were some changes that addressed some problems such as the command to perform PF, DF, INV and EV movements in an easy and useful way.
An ankle joint was manufactured from an aluminum alloy plate but failed during bending to obtain the required shape due to its hardness, as shown in Fig. 2.
Part of ankle joint design failure
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
As hown in Fig. 3, an ankle joint was designed with a slightly different idea than what was manufactured but lacking the performance of lateral movements (INV and EV) Therefore, the proposed model was found to be better than the previously mentioned models.
First ankle joint assembly proposed design
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
Numerical Analysis: numerical methods have been adopted to obtain approximate solutions to the equations which are generally difficult to obtain. Among these numerical methods, the one that approximates continuity with an infinite degree of freedom by a discrete body with a finite degree of freedom is called finite element analysis. The finite element method has become a powerful tool for the numerical solution of a wide range of engineering problems [20]. The use of ANSYS has been adopted to generate the Finite Element Model shown in Fig. 4.
Ankle joint and foot in ANSYS
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
A 13th Gen Intel(R) Core (TM) i7-13620H 2.40 GHz with 16.0 GB of RAM and 128 MB Graphic size was used in the simulation. Simulation software ANSYS and SolidWorks s can be memory-intensive, especially for large assemblies and simulations. More RAM helps in mesh refinement, transient simulations, and post-processing large data sets. While SolidWorks s benefits from dedicated workstation GPUs ANSYS mainly relies on CPU performance.
A convergence study determined the best finite element meshing for static foot ankle prosthesis structure analysis. Figure 5 shows mesh created by raising the number of elements to 467,128, nodes to 835,674, and stress enduring constant to 6.5427 MPa (Fig. 5).
Mesh convergence by workbench ANSYS
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
Experimental work includes the main tools and procedures that were used to design and manufacture the socket and ankle joint to enhanced prosthesis for ankle joint amputation. Also, with testing and evaluation of the patient's gait while wearing a movable limb containing the ankle joint (the limb that was manufactured).
Ankle Joint Manufacturing: For the purpose of implementing the design realistically and accurately, the ankle joint was manufactured by CNC machine Vector 610 from aluminum metal. The ankle joint was assembled by attaching it with screws, with the addition of springs and a piece of rubber, to be able to make the necessary movements and absorb energy (storage and waste of energy) during stance phase and push off as shown in Fig. 6.
Mechanical Test: The spring tension test (two types) to choose the best spring that must be present in the manufactured ankle joint, in order to choose the best spring. It was concluded that the most reliable spring in designing the spring connection between the two models is model No. 1. When a test was conducted on the first model, it was observed that the spring stretches steadily with a force exceeding 170 N when a tension force is applied to it. The experiment was conducted using four springs once and five springs again for the same type of spring for the purpose of strengthening as shown in Fig. 7. As for the second model of the spring, it was observed that the spring stretches at a very small rate with a force exceeding 300 N, and when the force is removed, it does not return to its original position.
Ground Reaction Force Test: The test was conducted by walking on a force plate containing three sensors for a patient amputated through the ankle joint (age 53 years), whose weight was (70 kg), who was amputated due to previous wars.
Range of Motion Test: The range of motion of the ankle joint was measured (by Goniometers), which was designed in the SolidWorks program, and the allowable range of the plantar flexion and dorsal flexion movements was determined when the patient walked with the artificial limb with the ankle joint that was manufactured.
Ankle joint parts
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
Spring tensile test
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
2.1 Proposed ankle joint
When comparing the proposed model with other manufactured models, we find that the proposed model is very simple in terms of the materials used in it, the mechanical method by which it was designed, and other important features such as light weight, a price suitable for the patient, and an aesthetic appearance, as it does not contain devices and branches that cause inconvenience to the wearer. A bolt was selected for fastening two pieces together.
The necessary values to know the efficiency of the design were calculated in the ANSYS program according to the equations below:
s. f.: safety factor
σy: stress yield (MPa)
σ: stress design (MPa)
σ: von mises stress
σx: normal stress x component σy: normal stress y component σz: normal stress z component τxy: shear stress x y
τyz: shear stress y z
τxz: shear stress x z
From Fig. 8, we find that the proposed design in this research is the most acceptable for the patient, as compared to tose of previous studies [5] and [6] which are large, heavy, and difficult to be accepted aesthetically.
The assembly of the final form of the ankle joint
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
3 Numerical and experimental evaluation
ANSYS is a software package that uses the finite element method to calculate the numerical solution to a complex problem whose solution is lengthy to calculate the equivalent stress (von-Mises), total deformation and safety factor [21]. The results of the ankle joint in the plantar flexion (toe connect) stage show that the von-Mises stress is in Fig. 9a, and the total deformation is shown in Fig. 9b, when the fixed support is the toes only. And the results of the ankle joint in the dorsiflexion (heel strike) stage, the von-Mises stress is shown in Fig. 9c, and the total deformation is shown in Fig. 9d, when the fixed support is the heel only. The maximum values of both the equivalent stress and the total deformation are shown in Table 2. The safety factor is 15 in regard to the maximum equivalent stress, which is considered safe and acceptable (Fig. 10).
Numerical results for the prosthetics foot: (a) von-Mises stress for planter flexion, (b) Total deformation for planter flexion, (c) von-Mises stress for dorsiflexion, (d) Total deformation for dorsiflexion
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
Numerical maximum values
| No | Maximum stress (MPa) | Total deformation (mm) |
| PF | 38.62 | 0.0632 |
| DF | 26.49 | 0.0574 |
Factor of safety
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
This numerical analysis indicates that as the total deformation increased, the von Mises stress values increased as well, giving the highest von Mises stress, of approximately 38 MPa, in the plantar flexion (toe-off phase).
The ground reaction forces were measured when the patient walked on the force plate once when wearing the prosthesis with the fixed ankle joint and again when the patient wore the prosthesis with the movable ankle joint as in Table 3, Figs 11 and 12.
Ground reaction force
| Fixed ankle joint prosthetic (Max. GRF) | Movable ankle joint prosthetic (Max. GRF) | ||
| Proper side | 286.57 N | Proper side | 356.19 N |
| Amputee side | 468.90 N | Amputee side | 317.14 N |
Time for fixed ankle joint prosthetic (blue curve for the healthy limb and green curve for the amputated limb)
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
GRF vs. Time for movable ankle joint prosthetic (blue curve for the healthy limb and green crve for the amputated limb)
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
The results of the GRF test illustrated that the percentage difference in forces for the sound limb from the proposed ankle joint prosthesis and the traditional prosthesis is about 10.96%, 38.88%, respectively. When the GRF test was carried out using the traditional prosthesis, there is instability in the gait, compared to the proposed ankle joint prosthesis, which is closer to the sound foot.
When measuring the range of motion of the ankle joint when the patient was walking and performing the plantar flexion and dorsal flexion movements, it was found that the range of movement of the plantar flexion is about (25°) and the range of movement of the dorsal flexion is about (20°), as shown in Fig. 13.
ROM ankle joint for the planter flexion and dorsiflexion movements
Citation: International Review of Applied Sciences and Engineering 2025; 10.1556/1848.2025.00985
4 Discussion
Numerical analysis was conducted to find out the stresses and deformations expected to occur during toe off once by making the fixing base the whole foot, when the von-Mises stress is 26.49 MPa and the total deformation is 0.057475 mm, and the other by making the fixation only at the front of the foot when the von-Mises stress is 38.62 MPa and the total deformation is 0.063299 mm.
We note from the results of test of the ground reaction force As from Table 3, Figs 11 and 12, which is the limb with a movable joint that there is a convergence in the value of the peak force reached by both the amputated and healthy parts, and this indicates the extent of the patient's comfort, balance and confidence in walking while wearing the limb with a movable ankle joint.
The results of the range of motion indicated a closeness of the values of normal ankle joint motions compared to the manufactured ankle joint and the fixed joint.
In general, the patient feels satisfied when the prosthesis is used with the movable ankle joint when wearing it for a long period of walking.
5 Conclusion and future work
This study introduced a movable ankle joint prosthesis designed for through-ankle amputees, significantly improving mobility and gait stability. Key findings include: Improvement of Ground Reaction Force GRF testing showed a 10.96% reduction in force imbalance compared to traditional prosthetics clusters, which have led to stable gait patterns. The prosthetic developed would allow for a total of 25 degrees of plantar flexion and 20 degrees of dorsiflexion, which is in line with natural movement of the ankle. Stress in the FEA model shows that the maximum for plantar flexion was 38.62 MPa (0.0633 mm of deformation), 26.49 MPa (0.0575 mm of deformation) in dorsiflexion, and safety of factor 15 availability for structure satisfaction. The patients just congratulated the improved enhancement of comfort of walking and confidence compared to the local prosthetics.
In Future Work Incorporation: Material optimization (e.g., carbon fiber or composite polymers) might reduce weight by another 15%–20% with improved durability. Energy storage and return mechanisms (e.g., spring-assisted mechanisms or with adaptive damping) may result in an overall walking efficiency improvement of 10%–15%. Smart prosthetics with sensors enabling real-time gait adjustments which increase actually balance by 20%. Conducting long-term clinical trials involving a larger and more heterogeneous population of a group of patients (of age from 20 to 60, different levels of activity).
Acknowledgment
The authors would like to thank the laboratory personnel of Prosthetics and Orthotics Engineering Department at Al-Nahrain University for their significant contribution in the improvement of the experimental work.
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