Researchers at the Indian Institute of Technology (IIT) Guwahati have developed an affordable prosthetic leg which will allow persons with disabilities (PwDs) to thrive in Indian conditions. Besides this prosthetic leg’s suitability for uneven terrain, different age groups and multiple stages of prosthesis use, it allows users to do deep squats, sit cross-legged and perform yoga.
Funding for this research came from the Ministry of Education, Government of India and the Department of Biotechnology, Government of India. Meanwhile, IIT-G researchers further collaborated with 151 Army Base Hospital, Guwahati, Tolaram Bafna Kamrup District Civil Hospital, Guwahati, Guwahati Neurological Research Centre (GNRC), and North Eastern Indira Gandhi Regional Institute of Health and Medical Sciences (NEIGHRIMS), Shillong.
The development of this prosthetic leg, which took affordability and adaptability to local locomotion needs into consideration, was led by Professor S Kanagaraj, Department of Mechanical Engineering.
In a press release issued by the institute earlier this week, Prof Kanagaraj said, “The knee joint developed by our team has a spring-assisted deep squat mechanism, which helps to use Indian toilet system more comfortably; the knee rotating mechanism helps to have cross-legged sitting; the locking mechanism helps to reduce the fear of falling of patients while walking in unknown terrain; adjustable link length in the knee helps to have either more stability or easy flexing depending on age and requirement of the patients. Overall, the knee joint is designed to meet the Indian lifestyle which other products fail to fulfil.”
Features of the prosthetic limb
Prosthetic legs developed with technology from the West ignore Indian locomotion needs, such as cross-legged sitting, deep squatting for toilet use, and exercise postures in yoga. Its advanced knee rotation mechanism facilitates cross-legged sitting and permits a significant improvement in range over traditional prosthetic knees. The deep squat mechanism helps to prevent the arrest of motion while standing up and reduce metabolic energy cost.
“To mimic the rotation capability in the developed knee joint, a compression spring-assisted mechanism is encapsulated in the knee joint which allows rotation of the lower limb concerning the hip joint. This cross-legged sitting posture helps the users to socialise in day-to-day events like during yoga practice, eating at certain social functions, etc. Additionally, a person can utilise this feature along with the flexed knee to tie shoe laces without removing the prosthetic leg,” explains Prof Kanagaraj, in a conversation with The Better India.
He adds, “The deep-squat mechanism, meanwhile, involves two-phase extension assist springs in combination with the kinematic structure (link length) of the knee joint which allows the user to sit at a deep-squat position. This spring stores energy while going into a deep squat position and releases the stored energy while the user is trying to stand up from that position. In short, assisting the user to get up, unlike other available mechanisms which only assists till sitting in a chair position and restricts after that. This mechanism is not found in any other commercially available mechanically operated knee joints.”
Also, PwDs require additional stability depending on the stage of prosthesis use. Once the amputee is used to their leg, walking on uneven terrain and staircases is difficult. To address this, researchers at IIT-G have developed a knee-locking mechanism which can be activated and deactivated by the amputee as they encounter difficult conditions.
“Consider a situation where a person with amputation has difficulty in managing stability. In this condition, knee flexion locking capability will allow the user to put weight on the prosthetic leg which does not have any flexion or bending. So, the person will be more stable. The prosthetic leg will act like a rigid crutch fitted to the residual limb. But the person has to lift (lurch) the hip to get floor clearance so that any stumbling situation can be avoided. However, this walking style is not characteristic of human gait. Proper strengthening of muscles can enable the user to walk with flexed knees after weeks of training. This flexion locking capability also allows the user to stand for a longer duration without bending the knee while avoiding the fear of falling,” he says.
This locked knee acts as a rigid stick which is most stable in several types of terrains such as gravel, staircases, ramps, etc, as the degree of freedom of the knee is arrested which increases the stability of the user at the initial stage of prosthesis usage.
Depending on the residual length of the patient’s leg, the prosthesis requirements vary. Going further, depending on the person’s age, more stability is required. For example, older patients are at a higher risk of falling. As per the patient’s needs, link length adjustability and prosthesis alignment adjuster mechanism are also provided for customisation.
Supports up to 100kg bodyweight
During physical activity, dynamic balance is key to stopping a person from falling. The solutions presented by this prosthetic leg are reduction in impact load on hard surfaces, maximisation of toe-off force and improved balance.
“While a person is walking, tendons provide essential support and stability to the foot. As an amputee is missing these tendons, shock-absorbing springs that replicate their function of storing and releasing energy are included in the dynamic ankle joint. This reduces the impact on the amputee. In addition, the human foot normally has the freedom to adjust by rotating according to the conditions. The dynamic ankle mimics this adaptability to a great extent,” explains Prof Kanagaraj.
Meanwhile, the abnormality noticed in their gait pattern of knee and foot is reduced using the Sankalp knee design and confirmed using gait and motion analysis.
“Sankalp knee (second-generation knee joint) is another knee joint developed by the team whose trials have been done on several users. Its kinematic analysis of the performance during the gait cycle (walking style of humans) showed that it matches the normal human walking pattern with minimum deviation. The abnormality was reduced by using a four-bar mechanism in the knee design. Based on the feedback obtained from the previous generation knee joints, the current third-generation knee joint is designed with added functionalities that can be suited to the Indian lifestyle,” he claims.
Abnormality in gait patterns comes from the amputation of a healthy person that removes important muscles needed for the normal gait pattern. Though a mechanical prosthesis tries to compensate for lost motion, it fails to replicate the exact motion due to the absence of energy storage and release. “The Sankalp Knee provides spring-assisted mechanisms to compensate for the energy storage and release and thus reducing the abnormality in gait pattern,” he adds.
Thanks to this, Prof Kanagaraj believes lower limb amputees will have an improved quality of life.
As per the press release, the other aspects of this solution compared with peers include:
- A four-bar injection moldable polycentric knee joint with a locking mechanism.
- Avoids arrest of motion while standing up from a deep squat position and provides extra energy during leg swing using spring-assisted extension bias mechanism (Indian Patent application number- 201931014318).
- Customisable link length can be adjusted by the prosthetist to increase the stability and ease of flexion according to patient limb length, activity, or age (Indian Patent application number- 202031017295).
- Extra stability during standing or rehabilitation activities using a manual knee flexion lock mechanism to switch from polycentric to rigid knee configuration.
- Minimising the ground force, maximising walking propulsion, and balancing while walking on an uneven terrain using dynamic ankle joint with plantar-dorsiflexion and inversion-eversion movement.
- The prosthetic leg is tested as per international standard loading conditions up to 100 kg body weight.
- Reduced weight of prosthetic leg is achieved by selecting suitable polymers, aluminium alloys and stainless steel for different components.
The release claims that after the fixation of their developed technologies amputees were able to walk with a flexed knee in between parallel bars and outside of it on the first-day rehabilitation at Gait and Motion Analysis Laboratory, IIT-Guwahati. Additionally, amputees were able to use the different functionalities of the prosthetic leg with and without any additional support in their daily life.
“We are at the final stage of the trial process where rehabilitation feedback from the users is ongoing. Depending on the user’s needs, the cost of the prosthetic leg varies from Rs 25,000 to Rs 50,000. We are in the process of discussing with a few companies for technology transfer. We are still open to discussing with anyone interested in commercialising it.” he says.
(Edited by Yoshita Rao)