The conceptual design of 4BSF was proven by investigating the ICR and GRF movements during the stance-phase. The performances of 4BSF and Conventional 4-bar polycentric knee were evaluated by stance-phase knee flexion angle and foot to ground angle.
From the experimental result, the walking simulation from VIsual3D is shown in Fig. 6. the ICR of 4BSF was in the initial position during the heel strike (Fig. 6a) and in the same position as the conceptual design in Fig. 2a. After that, the ICR moved to the bottom of the prosthetic knee during the loading response (Fig. 6b), like in Fig. 2a, which knee mechanism rotated to stance phase knee flexion because of the flexion moment. Then, GRF shifted to the front of the ICR during mid-stance and terminal stance (Fig. 6c) to extend the knee mechanism in the same result as Fig. 2b. Later, ICR moved back to its initial position during toe-off (Fig. 6d) in order to prepare for the swing phase, the same as in Fig. 2c. Finally, the 4BSF mechanism rotated to swing-phase knee flexion (Fig. 6e), similar to Fig. 2c. The results shown that the position of the ICR and GRF vector of conceptual design and experimental results are consistent.
Figure 6The ICR position and GRF vector of experimental results (a) heel strike, (b) loading response, (c) mid-stance & terminal stance, (d) toe-off, (e) swing.
Full size image
The knee angle data is shown in Fig. 7a. Each data was captured three times, and all three trials were processed. The averaged data with the corresponding standard deviation for the important phases of gait is presented in Table 1. The conventional 4-bar prosthetic knee could not perform a knee flexion throughout the stance phase. On the other hand, the knee angle of the 4BSF started from zero degrees to ensure the person with an amputation’s stability and confidence. The maximum knee flexion angle of the high, medium, and low stance-phase spring stiffness was 5.9°, 8.6°, and 10.2°, respectively. Then, the knee angle returned to 0° at the terminal stance to be ready for the swing phase. When the front and rear bars of the 4BSF mechanism are parallel, the ICR position is located very high and behind the GRF, resulting in increased stability of the mechanism. The period of the front and rear bar going parallel is very short. The participant did not report conscious awareness of this transition. The participant’s comments indicated that walking with the 4BSF felt safer as they did not feel pushed backwards.
Figure 7(a) Mean prosthetic knee angle for walking trials as a percentage of gait cycles31, (b) Mean prosthetic foot-to-ground angle for walking trials as a percentage of the gait cycle.
Full size image
Table 1 Knee angle in different conditions with standard deviation.Full size table
According to Fig. 7a, the stance-phase spring stiffness of 4BSF can be adjusted to the maximum knee flexion angle during stance phases between low, medium, and high settings. However, the magnitude of the maximum stance-phase knee flexion angle depends on the stance-phase spring stiffness. When using a high stance-phase spring stiffness, the resistance to knee flexion increases, resulting in a lower magnitude of maximum stance-phase knee flexion angle. On the other hand, using a low stance-phase spring stiffness results in lower resistance to knee flexion and a higher magnitude of maximum stance-phase knee flexion angle.
The transition from the stance phase to the swing phase of the conventional 4-bar was slower than the 4BSF because of the difference in the initial ICR position between each mechanism, as shown in Fig. 8a. At toe-off, the GRF initially acts in front of the ICR positions of both the 4BSF and conventional 4-bar mechanisms, as indicated by the grey line. Subsequently, the GRF passes the initial ICR of the 4BSF (as shown by the red line) before reaching the initial ICR of the conventional 4-bar (as shown by the green line). This enables a faster transition to the swing phase in the 4BSF as compared to the conventional 4-bar polycentric knee. Therefore, the knee flexion angle profile of the 4BSF was closer to the profile of able-bodied gait than the conventional 4-bar.
Figure 8(a) The comparison of initial ICR between the 4BSF and the conventional 4-bar knee, (b) Comparison of gait analysis between able-bodied, conventional 4-bar, and 4BSF.
Full size image
Figure 7b shows that the early and longer duration time of foot flat gave more stance phase stability. The foot of the able-bodied gait tended to enter the foot flat at 5% until 45% of the gait cycle. On the other hand, the foot of the conventional 4-bar tended to enter the foot flat at 30% to 41% of the gait cycle. In comparison, the foot of the 4BSF tended to enter the foot flat at 21% until 35% (high stiffness), 14% until 35% (medium stiffness), and 14% until 35% (low stiffness) of the gait cycle.
As analyzed in Fig. 8b, the gait cycle was simulated at equal hip angles with three conditions. The able-bodied has stance phase knee flexion and ankle joint. The conventional 4-bar has neither stance phase knee flexion nor ankle joint, and the 4BSF only has stance phase knee flexion. The results of the simulation were used to explain the experimental results28.
According to Fig. 8b, the foot of an able-bodied gait was the fastest to enter the flat foot because it had a knee joint for the stance-phase knee flexion and an ankle joint for plantar flexion. It contrasts with people with amputations in developing countries who use both conventional 4-bar knee and SACH foot without knee and ankle flexion angles. As a result, their feet entered the flat foot slower than able-bodied gait, resulting in lower stability during early stance due to a lack of a stable base of support25,26,27. Although the foot of the 4BSF entered the flat foot slower than the able-bodied did, it entered the flat foot faster than a conventional 4-bar polycentric knee (Ottobock 3R20) 9%, 16%, and 16% of the gait cycle for high, medium, and low stance-phase spring stiffness, respectively.
In summary, Table 2 presents an overview of the design specifications. The prototype 4BSF was in accordance with the design specification.
Table 2 Evaluation of the prosthetic knee design specification compared to the prototype.Full size table
With high quality products and considerate service, we will work together with you to enhance your business and improve the efficiency. Please don't hesitate to contact us to get more details of single axis prosthetic knee.