Koh Inoue

Novel knee joint mechanism of transfemoral prosthesis for stair ascent

The stability of a transfemoral prosthesis when walking on flat ground has been established by recent advances in knee joint mechanisms and their control methods. It is, however, difficult for users of a transfemoral prosthesis to ascend stairs. This difficulty is mainly due to insufficient generation of extension moment around the knee joint of the prosthesis to lift the body to the next step on the staircase and prevent any unexpected flexion of the knee joint in the stance phase. Only a prosthesis with an actuator has facilitated stair ascent using a step-over-step gait (1 foot is placed per step). However, its use has issues associated with the durability, cost, maintenance, and usage environment. Therefore, the purpose of this research is to develop a novel knee joint mechanism for a prosthesis that generates an extension moment around the knee joint in the stance phase during stair ascent, without the use of any actuators. The proposed mechanism is based on the knowledge that the ground reaction force increases during the stance phase when the knee flexion occurs. Stair ascent experiments with the prosthesis showed that the proposed prosthesis can realize stair ascent without any undesirable knee flexion. In addition, the prosthesis is able to generate a positive knee joint moment power in the stance phase even without any power source.

A passive transfemoral prosthesis with movable ankle for stair ascent

Stair ascent is still a difficult task for transfemoral prosthesis users. So far, a passive knee joint unit for transfemoral prosthesis developed in our previous study achieved stair ascending without handrails or any other assistance devices. However, the experimental results with the simulated socket showed that the users faced difficulty in using the knee joint at the beginning of the load response phase. In addition, large moment power of the prosthetic sides hip joint in the stance phase was required, leading to a significant imbalance of power consumption between the intact and prosthetic sides. Therefore, the purpose of the present study was to develop a passive transfemoral prosthesis for stair ascent, which had a knee extension function associated with a movable ankle joint during the stance phase in order to change the admissible force region. Experimental results by nonamputated participants with the simulated socket demonstrated that ascending was achieved in the step-over-step manner without any assistive device. In addition, it was shown that the hip joint moment power reduced to equalize the joint moment powers in both sides.

Effects of foot placement on the lower extremity in the swing phase during stair ascending: Implications for transfemoral prostheses

Stair ascending, especially step-over-step gait, is a difficult motor task for people with transfemoral amputation. Although many types prosthetic knees have been developed to attempt such locomotion, finding alternative methods is also important. The purposes of the present study were to (a) elucidate the effects of foot placement, as part of stair ascending strategies, on the lower extremity motion of able-bodied subjects and (b) investigate the effectiveness of these strategies on transfemoral prosthetic leg swinging during stair ascending in a computer simulation. In the experiment, 2 different foot placement strategies on a step were conducted with able-bodied subjects: the full-foot contact (FFC) and half-foot contact (HFC) strategies. HFC made the toe trajectory straighter, mainly owing to the knee joint motion. The joint moments at the hip and knee were smaller in the HFC condition than the FFC condition. These results suggest that HFC causes the leg swing to have more inertial motion than FFC and demonstrate the applicability of the HFC condition for transfemoral prostheses without any actuators. In the computer simulation based on the results of the first experiment, various inertial properties of a transfemoral prosthesis were examined to accomplish leg swing without tripping. Only in the HFC condition specific inertial properties allowed the prosthesis to avoid colliding with the stairs. These simulation results suggest that with natural motion, transfemoral prostheses without assistive devices could allow successful leg swing for step-over-step gait with the HFC condition and appropriate inertial properties.

Effects of functional range of knee extension for transfemoral prosthesis on stair ascent motion.

We previously proposed a passive mechanism as the link knee joint unit (LKJ) for a transfemoral prosthesis for stair ascent. The prototype allowed the experimental subjects to ascend stairs without the use of a handrail. In the present study, we modified the LKJ unit and developed further two designs of the LKJ unit. One has full knee extension function during the prosthetic stance phase (condition 1). The other design mechanically trades off the functional range of knee extension against stability of the LKJ unit (condition 3). In the stair ascent experiment with six able-bodied subjects, all subjects succeeded in ascending stairs with the three LKJ conditions without the use of a handrail. No difference was found in joint angels and joint moments of the intact and prosthetic legs among all LKJ conditions. However, subjective assessment for ease of LKJ extension during stair ascent showed that the participants felt easier to extend the LKJ unit in the condition 1 and 2 than the condition 3. It is suggested that the condition 1 or 2 is appropriate for prosthesis users who can ascend stairs with the LKJ unit. For prosthesis users who are not familiar with the LKJ unit, the condition 3 would be useful to learn how to use it.

A control method for transfemoral prosthetic knees in level walking and stair ascending based on thigh angular motion

Regaining the locomotive ability is necessary to maintain the activities of daily living in lower extremity amputees. Recently, the stability of the gait and multifunctionality of transfemoral prosthetic knees have drastically improved with the use of microprocessor-controlled knees, such as Genium ® (Otto Bock, GmbH). However, these knees, which also include products from other companies, are very expensive. Therefore, the purpose of the present study was to develop a control method for transfemoral prosthetic knees in order to perform level walking and stairs ascending safely, with fewer sensors or simpler procedures. First, we analyzed the gait of an intact subject and therefore we proposed a control algorithm for prosthetic knees with only thigh angular kinematics. Then, an evaluation experiment on the prototype knee, in which the proposed algorithm was implemented, was conducted. As a result, the participant successfully performed level walking, stairs ascending and transition between the two types of gait. The functions of the prosthetic knee changed automatically using the proposed algorithm with thigh angular kinematics. Then, the reliability of the algorithm was checked with a database of gait analyses. The results showed that the algorithm was applicable to 99.8 % of the population.

Development of a passive knee mechanism that realizes level walk and stair ascent functions for transfemoral prosthesis

Passive mechanisms have been well developed to realize the safe level walk for transfemoral prosthesis users, preventing unintended knee flexion during prosthetic stance phase. However, for stair ascent, a mechanism had not existed for a long time. We previously developed the knee joint unit whose mechanism realized prosthetic knee extension using load or external force on the knee joint unit itself. Although the level walk and stair ascent functions have been accomplished with different mechanisms, these functions should be combined into one mechanism for the prosthetic knee to contribute to regaining locomotion capacities. Therefore, the purpose of the present study was to develop a passive knee mechanism that realized both functions. We proposed a passive mechanism combining the pre-existing mechanisms. The proposed knee was designed to function as a four-link mechanism that prevented unintended knee flexion during level walking. For stair ascending, it was designed to extend the knee, using load on the prosthetic leg when the prosthetic leg contacted a step of the staircase with the knee flexed. The gait experiment with the proposed knee on a transfemoral prosthesis showed successful level walking, stair ascending, and their transition without any assistive device such as the use of a handrail. According to the experimental results, the functions worked and switched appropriately during the transition from level walk to stair ascent, depending on gait conditions without manual handling.

2P1-J09 A Passive Transfemoral Prosthesis with Movable Ankle for Stair Ascent

Stair ascent is still a difficult task for transfemoral prosthesis users. So far, a passive knee joint unit for transfemoral prosthesis developed in our previous study achieved stair ascending without handrails or any other assistance devices. However, the experimental results with the simulated socket showed that the users faced difficulty in using the knee joint at the beginning of the load response phase. In addition, large moment power of the prosthetic sides hip joint in the stance phase was required, leading to a significant imbalance of power consumption between the intact and prosthetic sides. Therefore, the purpose of the present study was to develop a passive transfemoral prosthesis for stair ascent, which had a knee extension function associated with a movable ankle joint during the stance phase in order to change the admissible force region. Experimental results by nonamputated participants with the simulated socket demonstrated that ascending was achieved in the step-over-step manner without any assistive device. In addition, it was shown that the hip joint moment power reduced to equalize the joint moment powers in both sides.

Effects of inertial properties of transfemoral prosthesis on leg swing motion during stair ascent

Stair ascent, especially the step-over-step gait, is a difficult motor task for people with transfemoral amputation. Our previous study demonstrated the effects of foot placement on the leg swing of able-bodied subjects. The study examined stair ascent with full-foot contact (FFC) and half-foot contact (HFC) as ambulation strategies. The results suggested that HFC causes the leg swing to have a greater inertial motion than FFC, as well as the applicability of the stair ascent strategy for transfemoral amputees with transfemoral prostheses without a motorized prosthetic knee joint. The present study investigated the effects of the inertial properties of a transfemoral prosthesis on leg motion during the stair ascent swing phase in simulation trials. The joint moment at the hip became smaller than that of an able-bodied subject. The peak values of the horizontal and vertical components of the joint reaction force were approximately the same as those of an able-bodied subject. These results suggest that a transfemoral prosthesis leg swing can be achieved with similar or smaller kinetic demand at the hip joint when half-foot contact on the stair steps is used as a stair ascent strategy. The mass had the largest effect of the inertial properties on the variability of the simulated kinetic parameters. The results of the present study may enhance prosthesis design with regard to the inertial properties and usability.