Articles

Biomechanical Analysis of Transtibial Prosthesis Designed for Runners

Emin Taner ELMAS^1*, Servet KAYA^2
*1Assistant Professor Dr., Vocational School of Higher Education for Technical Sciences, Division of Motor Vehicles and Transportation Technologies, Department of Automotive Technology, Iğdır University, Turkey & Graduate School of Natural and Applied Sciences - Major Science Department of Bioengineering and Bio-Sciences, Iğdır University, Turkey.
²Ph.D. Student, Graduate School of Natural and Applied Sciences - Major Science Department of Bioengineering and Biosciences, Iğdır University, Turkey.

Article Info

Received Date: 05 February 2025, Accepted Date: 12 February 2025, Published Date: 14 February 2025

*Corresponding author: Emin Taner ELMAS, Assistant Professor Dr., Vocational School of Higher Education for Technical Sciences, Division of Motor Vehicles and Transportation Technologies, Department of Automotive Technology, Iğdır University, Turkey & Graduate School of Natural and Applied Sciences - Major Science Department of Bioengineering and Bio-Sciences, Iğdır University, Turkey.
Citation: Emin Taner E, Servet K. (2025). Biomechanical Analysis of Transtibial Prosthesis Designed for Runners. Biomedical and Clinical Research Journal, 1(2); DOI: http;/02.2025/BCRJ/007.
Copyright: © 2025 Emin Taner ELMAS. This is an open-access article distributed under the terms of the Creative Commons Attribution 4. 0 international License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

This article explains the “Biomechanical Analysis of Transtibial Prosthesis Designed for Runners”. The study has been realized within the scope of a Ph.D. lesson which is lectured by Asst. Prof. Dr. Emin Taner ELMAS. The name of this Ph.D. lesson is “Medical Engineering and Advanced Biomechanics” and taught at the Major Science Department of Bioengineering and Biosciences at Iğdır University, Turkey. Servet KAYA is a Ph.D. student, and he is one of the students taking this course. This article has been prepared within the scope of this Ph.D. lecture, as a part of the final exam project of Servet KAYA. [1, 63].

Keywords: medical technique; medical engineering; biomechanics; biomechanical analysis; bioengineering; prosthesis; transtibial prosthesis.

Introduction

When body parts and functions are damaged, they are either regenerated or renewed. Although regeneration is always something we want more, it is usually not possible. In such cases, the damaged body part is transplanted with the help of a donor or replaced with artificial parts [8].

Orthopedics treats disorders of the musculoskeletal system. While an artificial organ is not replaced in orthopedics, implants can be used to assist existing organs. The history of prosthetics and orthopedics dates back to ancient times and is a rapidly developing multidisciplinary field of science and technology today. To give an example from history, Tabaketenmut, the daughter of a priest in ancient Egypt who lived between 950-710 BC, had an artificial toe. This finger prosthesis was found in archaeological excavations and shows traces of use. Prosthetics that have developed from the past to the present are being developed with the latest developments in advanced material science, microelectronics and bioengineering, and solutions are being sought for current problems [8].

Vascular diseases such as diabetes are at the top of the list of causes of lower extremity amputation. Landmines, high-vehicle accidents and natural disasters such as earthquakes are also among the other causes. In amputee rehabilitation, the production of devices suitable for individuals to regain physical abilities is an important goal. A prosthesis or artificial limb is such a device that aims to replace the loss of a limb in addition to cosmetic and functional benefits for the amputee. Lower extremity prostheses are obtained by combining several parts such as the socket, handle, ankle and foot. The socket is the structure that creates the harmony and connection between the amputee's stump and the prosthesis. Since each amputee's stump is unique, the design and placement of the socket is the most difficult and delicate part. In lower extremity amputees, the socket irritates the person and prevents them from adapting to the prosthesis. According to surveys, the fact that more than half of the amputees complain of pain confirms this [2].

Method, Findings and Discussion:

Prosthetics designed for transtibial amputations have a socket on top that fits the stump. In the middle, there is a calf that connects the socket to the foot. The prosthetic foot and ankle on the bottom perform many important functions such as shock absorption during walking, stability during weight bearing, and smooth progression of the limb during walking. In addition, durability and structural stability are vital for lower extremity prosthetics [8].

Lower extremity prosthetics are generally used to restore the appearance of individuals with limb amputations and to restore the lost function of the extremity. While the number and variety of lower extremity prosthetics are increasing, their quality is also increasing. The prosthetic socket design determines the quality of the prosthesis in terms of fit, as it provides a connection between the stump and the prosthesis. Since body weight and inertial force will be carried by the soft tissues around the stump, which are not very suitable for carrying loads, pain or skin damage may occur in this area [1]. Lower extremity prostheses have undergone a great development and change, from primitive wooden wedge legs to today's electronically controlled prostheses. Recent scientific developments have led to increased prosthetic socket compatibility, modern prosthetic knee mechanisms, more functional prosthetic feet, and advanced production techniques such as three-dimensional printers. With the change in living standards, expectations such as functionality, reliability, comfort, and cosmetics from prostheses have also increased [9].

Development of Carbon Fiber Prostheses: The SACH foot (Ohio Willow Wood, Ohio, USA), invented in the late 1950s, did not change much until the early 1980s. Until then, the carbon fiber part, which was used mostly in aviation because it was a light, flexible, and durable material, was used to facilitate amputees' participation in sports activities. As the body transfers weight to this spring-like structure, the foot compresses and energy is stored. As the weight transfer is withdrawn, the carbon fiber returns to its original shape and recovers the energy stored during compression. This foot was named the "flex foot" because of its spring-like mechanism, developed by Össur, based in Reykjavik, Iceland, and provided a "push-off force" not seen in other prosthetic feet at the time [6]. The carbon fiber-reinforced Flex foot was first used in elite sports at the 1988 Paralympic Games [7]. Today, elite sprinters and jumpers generally prefer carbon fiber prosthetics.

This increase in prosthesis variety and quality has increased competition in sports. Studies are ongoing to achieve better results. The current literature describes how running-specific pretzels and running speed affect the biomechanics of athletes with bilateral transtibial amputations. One study examined the effects of prosthesis stiffness, height, and speed on biomechanics during treadmill running in five athletes with bilateral transtibial amputations. Prosthesis stiffness, height, and running speed each affected biomechanics. Specifically, athletes with stiffer prostheses exhibited higher peak and stance mean vertical GRFs, increased overall leg stiffness, decreased ground contact time, and increased stride frequency. Prosthesis height was inversely related to stride frequency. Running speed was inversely related to leg stiffness. Furthermore, at higher running speeds, the effects of prosthesis stiffness and height on biomechanics decreased and remained unchanged, respectively. Thus, prosthesis stiffness, rather than height, affected distance running performance more than sprint performance in athletes with bilateral transtibial amputations [4]. In another study comparing Re-Flex VSP (carbon fiber compression spring prosthesis) with FF and SACH foot, Re-Flex VSP was shown to have a positive effect on energy cost, efficiency and relative exercise intensity compared to other prosthetic foot types during walking and running [5].

Material Analysis of Transtibial Prostheses and Transtibial Prostheses Designed for Runners:

In the study conducted by Abbas et al., various composite materials were compared in detail to optimize below-knee prosthetic sockets. Extensible and fatigue tests provided valuable information about the mechanical properties of each group. Yield stress, ultimate stress and modulus of elasticity (E) in the Perlon group were determined as 10.216 MPa, 38.046 MPa and 1.14 GPa, respectively. However, the carbon fiber group showed significantly improved mechanical properties with modulus of elasticity (E) of 2.55 GPa, yield stress of 90.23 MPa and ultimate stress of 103.177 MPa. Finally, the glass fiber group showed an elastic modulus (E) of 1.17 GPa, a yield stress of 31.862 MPa, and an ultimate tensile of 42.934 MPa. The results showed the significant effect of carbon fiber on material performance. Carbon fiber exhibited better fatigue resistance than perlon, suggesting that carbon fiber-based sockets had a longer lifespan. Interestingly, ambient temperature was used for all tests. The interface pressure study revealed that the side (560 kPa) and the back (564 kPa) had the highest values ​​recorded. This indicates that the pressure was distributed evenly across the tissue and away from bony parts, increasing patient comfort and being compatible with the dynamics of the suspension and the comfort of the user while walking [11].

Theoretically, a compressed elastic spring will return all of its potential energy as work when released. This is called the elastic potential energy of the spring. Although this is theoretically the case, friction and heat and/or sound in the spring cause energy loss, reducing efficiency. This is called viscoelasticity [13].

Strength Analysis of Transtibial Prostheses Designed for Runners:

Finite element analysis (FEA) has been identified as a useful tool for determining the stress and strain behavior of lower extremity prostheses. This article focuses on finite element analysis for the evaluation of the structural behavior of the Sure-flex™ prosthetic foot and other load-bearing components. In this study, the highest von Mises stresses were found in the foot-pylon connection component at the foot end. The highest peak stress occurred at the posterior adjustment screw with 216MPa and the maximum stress occurred at the neck of the male pyramid with 156MPa [9].

Sports prostheses made of carbon fiber composite materials allow amputees to return to sports activities without compromising their health. The study presents the use of optical fiber Bragg gratings (FBG) embedded in a carbon fiber reinforced polymer transtibial prosthesis to create a prosthesis that can evaluate the user's gait and the performance of the prosthesis itself. Static tests showed that the prosthesis had a mechanical strength under a load of 1,206.21 N. This load value corresponds to twice the mass of the volunteer participating in the test. No damage was observed in the prosthesis structure in this range. In this study, where temperature changes were also measured, it was shown that carbon fiber material was a suitable choice for prostheses [12].

In the study conducted to develop a reliable prosthetic running blade made of carbon fiber, the performance of the running blades was evaluated with mechanical tests and finite element numerical modeling. As a result of the evaluation, it was understood that these blades have high load carrying and shock absorption capacity and it was confirmed that they could be suitable for sports like running. Tensile test showed that the composite material exhibited a linear elastic behavior up to a stress of 0.075 mm/mm. In addition, stress concentration areas and fracture points were detected within the wing structure. In addition, numerical results revealed that the maximum deflection that the wing could reach was 29.60 mm. The kinetic energy loss during the impact showed a decrease of 8.5% [21]. In addition, the high fatigue strength of the material enables long-term use. According to these results, carbon fiber prostheses can withstand static loads without deformation while carrying the user's weight.

Thermodynamic Analysis of Transtibial Prostheses Designed for Runners:

The heat loss of prostheses designed for runners can also be calculated with the following formula used to calculate the heat loss of materials.

(dQ / dt)_cond = α_cond (A / L) ΔT

According to this equation, heat loss increases with increasing thermal conductivity of the materials, increasing area and increasing temperature difference [8].

In the study conducted by Galvao et al. [12], in addition to the high performance of sports prostheses made of carbon fiber composite materials in mechanical tests, a temperature sensor was characterized and used to control temperature changes in long-term tests. The sensitivity of the temperature sensor used for temperature compensation is 10.3 pm/°C and the average expanded uncertainty is equal to 10 pm, corresponding to 1°C. These findings are consistent with the results of other studies [22]. Carbon fiber has low thermal conductivity, so it is not affected by temperature fluctuations. In addition, the friction heat generated in the prosthesis does not accumulate due to the low heat dissipation properties of carbon fibre.

Mechanical Analysis of Transtibial Prostheses Designed for Runners:

Since the biomechanics of the human body change after amputation, step length asymmetry, which is seen as longer steps on the prosthetic limb, has been reported in unilateral transtibial amputees while sprinting in the long jump approach [18]. This is an attempt to compensate for the absence of the limb. In this study, amputees with the largest step length asymmetry at the beginning of the approach run, i.e. at a slower running speed, tended to increase running speed by increasing the sound limb step length. The prosthetic limb step length remained constant. In this way, the amputee aims to finish the race in a shorter time. This situation is seen to decrease the step length symmetry at higher running speeds.

The knee [19] and hip [19], [20] of the amputee limb flexed more than the sound limb at foot contact. During stance phase, the prosthetic ankle and residual knee range of motion are limited and angular velocity is reduced [19], resulting in limited prosthetic limb plantar flexor moments [16], [19]. During push-off, the residual knee is flexed more and the hip is less extended than the intact limb [19], [20]. This more upright limb position on the prosthetic limb may be an attempt to reduce loading on this limb [20], and reduced prosthetic limb vertical ground reaction forces [20], knee extensor moment [16], [20], and horizontal braking and propulsive forces [20] have been reported during running compared to the intact limb and healthy individuals. This reduced loading will limit the likelihood of knee collapse, either as a result of reduced knee extensor muscle strength or perhaps as a result of reduced reliance on the residual knee joint as a result of reduced proprioceptive feedback [20]. The body continues to walk by relying on this. It is unknown whether increased knee flexion in the prosthetic limb can be reduced by training the knee extensor muscles, but this increased knee flexion is also seen in elite transtibial amputee long jumpers who must have strong knee extensors to jump the required distances. The reduced load around the knee is compensated for by increasing the hip extensor moment on the amputee side to help maintain an upright posture during support [16], [20]. Therefore, amputee running asymmetry issues may be due not only to the function of the prosthesis but also to reduced proprioception and the need to limit load on the amputee side knee [6].

Carbon fiber prostheses mimic the biomechanical properties of the human leg. This supports a natural walking and running motion. Carbon fiber prostheses improve balance by optimizing the center of gravity relative to the user. Proper energy return and shock absorbing effect reduce stress on the joints and muscles.

Energy Balance of Transtibial Prostheses Designed for Runners:

Since energy losses such as friction and heat occur in the springs, efficiency is never 100%. The less energy loss, the more efficiency [6].

Carbon fiber prostheses are much lighter in weight than a human limb, while amputees spend similar energy as able-bodied individuals while running [6].

The ankle is like a linear spring during the plantar flexion phase of normal walking and a non-linear spring during the dorsiflexion phase. It produces work during powerful plantar flexion such as running or jumping and absorbs less negative work during the controlled plantar flexion and dorsiflexion phases. Ankle torque, work and stiffness constantly change according to parameters such as the person's walking speed, load weight and ground slope. [10], According to studies, the human ankle produces more work than other joints in the lower extremity [13], [15], [16].

Mechanical energy can be calculated in different ways, so care should be taken when comparing results. Energy is defined as the capacity to do work. If a carbon fibre foot is modelled as a simple spring, the work done to compress the spring can be calculated by integrating a force-displacement curve [13]. The energy efficiency of the Modular III (Össur, Reykjavik, Iceland) has been reported to be 95% energy efficient by calculating it in this way [14]. Studies have also shown that reducing prosthesis stiffness reduces the metabolic energy requirements for running in athletes with bilateral transtibial amputations [3].

Conclusion

This article describes “Biomechanical Analysis of Transtibial Prostheses Designed for Runners”. The study in question was carried out within the scope of a doctoral course given by Asst. Prof. Dr. Emin Taner ELMAS. The name of this doctoral course is “Medical Engineering and Advanced Biomechanics” and it is given in the Department of Bioengineering and Bio-Sciences at Iğdır University. Servet KAYA is a student of this doctoral course and this article is within the scope of his work carried out as part of his final exam project [1, 63].