A Great Joint

Want to know the secret to success? Read on…

I was just kidding to get your attention. This article is actually on the rehabilitation of the ankle joint, which is a kind of secret to success. A healthy body leads to a healthy mind, and good health always leads to success, doesn’t it?

Anyway, the ankle joint is a very important joint in the human body. It functions like a hinge joint and plays a critical role in the way we walk and in other day-to-day activities. Thus if there is any problem with this joint, it needs to be remedied quickly and effectively.

Muscle atrophy is one of the major issues to deal with when the ankle is injured or has lost its strength. Patients with muscle atrophy undergo rehabilitation exercises by applying resistive force and obstructing foot movement to strengthen the muscles and engage with their neuromuscular system.

This can be successfully accomplished by using a passive wearable ankle-foot exoskeleton. However, the existing devices in the market cannot offer bidirectional and variable resistance rehabilitation.

The existing devices do not take into consideration the bidirectional motion of the ankle. There are two motions of the ankle, namely – dorsiflexion motion, and plantar flexion motion. Dorsiflexion motion is when you lift up your foot at the ankle. Walking on the heels is an example of dorsiflexion motion. Plantar flexion motion is when you push your foot downwards at the ankle. Pressing down a car pedal or standing on your toes are examples of this type of motion.

The existing devices use helical springs, torsional springs, or lightweight pneumatic actuated muscle as the energy-storing module for the purpose of resistance rehabilitation. But these devices cannot provide bidirectional resistance unless they are used in pairs. The major drawback of these devices is that the stiffness cannot be varied without changing these elastic elements. They also do not help in strengthening of the muscles and neuromuscular recovery.

In this study, the authors Mr. Avinash S. Pramod, Ms. Poongavanam Palani, and Prof. Asokan Thondiyath from the Department of Engineering Design, Indian Institute of Technology Madras, Chennai, India, and Prof. Santhakumar Mohan from the Department of Mechanical Engineering, Indian Institute of Technology Palakkad, India, have developed a novel, low-cost, one-degree-of-freedom, wearable passive ankle-foot exoskeleton.

This exoskeleton is easy to carry and affordably priced for the general population. The mechanism is designed to mimic the human foot trajectory during plantar flexion and dorsiflexion movement. The exoskeleton helps a user who has weak muscles to carry out bidirectional resistance training exercises. The outcomes from the validation experiment showed good improvement in the energy level of the plantar flexor and dorsi flexor muscles.

This prototype can be further improved by modifying the footrest into a footwear attachment for better foot grip. It can be modified to be automatic or semi-automatic and can be used to control the stiffness, based on the user feedback and training requirements.

Prof. Giuseppe Carbone from the Department of Applied Mechanics, University of Calabria, Bari, Italy, who is also the Chair Professor, IFToMM TC on Robotics and Mechatronics, appreciated the advantages of the work done by the authors with the following comments: “This paper proposes the design and development of a passive ankle rehabilitation exoskeleton. The main novelty is the possibility of applying adjustable bidirectional resistance to meet users’ needs. This enables patients with muscle atrophy to undergo rehabilitation by daily exercising and strengthening their muscles on their own. This approach has been proven to be both cost and recovery effective.

I hope similar solutions will be available for real end-users in a near future.”

Prof. Marco Ceccarelli from LARM2-Laboratory of Robotics and Mechatronics, University of Rome, Tor Vergata, Rome, Italy, gave his analysis and the scope for future studies based on this work with the following comments: “The paper presents an interesting exoskeleton for motion assistance of human ankle. Although bulky, it shows interesting features in terms of rigid structures with proper motion actuation combining two antagonist linear actuators with a spring that has been tested in a successful prototype for only flexion and dorsiflexion movements. It can be noted that the low-cost design is suitable for home manufacturing with 3D printing of parts and using commercial components. Some future work can be suggested in making the shape and the size more adjustable and comfort for different users, together with some more sensing to monitor the outcomes of the exercise/rehabilitation usage.”   

Article by Akshay Anantharaman
Click here for the original link to the paper


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