The World Health Organization (WHO) has estimated that 422 million adults have diabetes in 2014, in contrast to 108 million in 1980. People who had amputation because of diabetes were higher than those who had amputation caused by other factors [1].The amputees need an artificial substitute or replacement for the missing body parts in the form of prosthetic devices to restore normal functions of missing body parts and carry out regular motions [2]. The prosthetic device for transtibial amputation consists of three fundamental components which include a socket, pylon, and foot. The socket is the core component of a prosthetic device, and it is a coupling structure between the residual and artificial limb (prosthesis) [3, 4]. The socket transmits mechanical loads from the amputee body into the foot, and vice versa [5]. Thereby, socket fitting is an indicator of user’s comfort and satisfaction [6–8].
Prosthetists often customize the transtibial prosthetic socket by hand casting and modifying to fit around the stump[6–8]. This conventional socket manufacturer needs a long-time process to fabricate the socket and highlight bone and muscle areas of the stump. Therefore, prosthetists must have professional skills for the socket fabrication [3, 9]. Currently, the three-dimensional (3D) printed machine and computer-aided manufacturing (CAM) are utilized to develop the 3D printed socket model. Computer-aided design (CAD) is employed to edit and manipulate the socket design easily. Therefore, the 3D printed technique has overcome tedious conventional socket fabrication [8, 10]. An interface pressure of the 3D printed variable-impedance prosthetic socket was evaluated for a transtibial amputee at Biomechatronics Group, Massachusetts Institute of Technology (MIT) [11]. The pressure was recorded by using F-Socket transducers during the stance phase of the gait cycle. This study observed that the contact pressure at the fibula head region and tibia region was reduced during a single-leg standing in contrast to the conventional socket.
The interface pressure within the prosthetic socket can indicate the user's satisfaction and comfort with the socket.[4]. Indeed, the prosthetic socket must meet the pressure tolerance profile of the residual limb by providing a secure suspension system and superior fitting[12]. Prosthesis suspension systems play a critical role in pressure distribution around the stump. [13].The suspension systems set the stump inside the socket via a single distal pin/lock, suction, lanyard, or magnetic coupling [14, 15]. Silicon liner (pin/ lock) and suction systems are commonly used as suspension systems for transtibial prostheses. A pin/ lock liner offers excellent attachment with the residual limb [13, 16]. However, this liner could increase the interface pressure at the residual limb distal during a swing phase of gait cycle, which causes pain and skin injuries. The suction suspension system provides an excellent fitting and could minimize a quantity of pistoning within a socket as compared to the pin/lock suspension system [14, 17]. A study survey conducted by Dillingham, Pezzin [18] found that 146 amputees were not satisfied with their suspension system because they suffered from skin injuries and pain at the stump during daily activities.
Pressure in the pin/lock suspension system was evaluated via Fiber Bragg Grating during the stance phase by Al-Fakih, Arifin [19]. In this study, a simulation machine was utilized to apply load and generate ten gait cycles to mimic a human body weight and the amputee's gait cycle. Moreover, an artificial stump was built from silicon material to form the amputee’s residual limb. The authors observed that the highest values of peak pressure (kPa) of the artificial stump were recorded at the anterior middle (34.18), posterior proximal (42.25), lateral distal (53.99) and medial distal (56.06) during the stance phase. Therefore, the highest peak pressure among all values was at the medial distal region.
A new suspension system (HOLO) was established by removing the pin from the silicon liner and replacing it with a loop fastener. A velcro strap (hook) was contacted to the socket wall at the medial and lateral areas. Pressure distribution of the new suspension system (HOLO) was evaluated during a walk of 10 healthy subjects by using the F-Socket transducers (9811E) and was compared with a pin/lock suspension system[20]. The findings of this study concluded that high pressure was measured at the lateral and medial sides during the stance phase of the new suspension system (HOLO). However, the pin/lock liner has high pressure at the distal region of the stump in anterior, posterior, and medial areas during the stance phase of gait.
Pressure in Dermo and Seal-In X5 liner was evaluated during a regular walk by using
F- socket sensors in a study by Ali, Osman [21].The highest value of pressure was recorded at the anterior of the stump in Seal-In X5 liner (84.9 kPa). On the other hand, the pressure at the anterior for the Dermo liner was 60.2 kPa[21].
Furthermore, Eshraghi, Osman [22] investigated the pressure of a new magnetic suspension system and compared it with the pin/lock and seal-in suspension systems by using four F-socket transducers. In this study, the mean peak pressure at the anterior and posterior sides of the pin/lock system was higher than the anterior and posterior of the magnetic suspension system (89.89 kPa vs. 79.26 kPa (Anterior); 47.22 vs. 26.01 kPa) (posterior), respectively).
Later, a new air pneumatic suspension system (APSS) was developed at the Applied Biomechanics Laboratory in University of Malaya by Pirouzi, Osman [23]. APSS can manage the change of the residual limb size and attachment. During this study, five subjects used APSS during a normal walk to evaluate the performance and pressure distribution. The study observed that the interface pressure was reduced by using APSS. Results showed that the highest value of pressure was recorded at the anterior middle (56.43 kPa) [23]. APSS had the lowest value of pressure among all suspension systems in the anterior middle region, whereas, the APSS still had a costly silicon liner material without pins. APSS has an air bladder that is embedded inside the socket wall as an air cuff in a bladder piece. Therefore, inflation and deflation of an air bladder cannot be controlled on one side of the stump with one air bladder piece, and it can be inflated and deflated together at all sides.
The continuous change of the residual limb size or volume concentrates the pressure at a specific area of the stump[23, 24]. Consequently, the amputees suffer from injury and pain of the residual limb, which results in high-pressure distribution [25]. Issues related to the management of interface pressure which has occurred by the continuous change in the stump size, doffing, and donning of new design solutions remain unemployed despite attempts to address these problems[23]. To overcome the high interface pressure within the prosthetic socket, this study aims to redistribute an interface pressure within the 3D printed transtibial prosthetic socket and reduce the high pressure. This article developed a new pressure management system to control pressure distribution inside the 3D printed socket. The hypothesis is that this system would provide a relief in bony areas and convenient coupling at the stump muscle areas with adequate interface pressure.