By Jyoti Singh
New Delhi: Locomotor disability is a significant problem in India, with an estimated one per cent of the population suffering from it. Of them, 7.7 percent are transfemoral amputees. Transfemoral amputation also known as ‘above knee amputation’ is a surgical procedure performed to remove the lower limb above the knee joint when that limb has been severely damaged or diseased.
In order to alleviate the suffering of such people, researchers at the Indian Institute of Technology, Delhi have designed and fabricated a low-cost, and light-weight polymeric polycentric prosthetic knee joint with energy-efficient gait option.
The prosthetic is made up mainly of polymeric material through injection molding technique and is polycentric in design consisting of an upper part, a lower part with pylon adaptor, a middle bar, a side bar and connecting bolts. It weighs a mere 350 grams. The upper and lower parts are made of plastic material and the side and middle bars are made of aluminum alloy with a high strength-to-weight ratio. The side and the middle bars transfer the total weight of the body from the upper part of the knee joint to the lower part during single limb stance phase.
The prosthetic has multiple articulations with four axis points being the most common configuration. Since the four axes are connected by four linkage bars, this type of polycentric knee is also called four bar knee.
Polycentric designs offer several biomechanical advantages and, as a result, are increasingly popular. A key distinction is that the functional centre of rotation is generally located outside the knee joint, which provides inherent stability due to long leverage. In four bar knee, the instantaneous centre of rotation (ICOR) can be determined geometrically by drawing straight lines through the posterior and anterior axes. The point in space where they intersect is the instantaneous centre of rotation. “ICOR is an imaginary centre of rotation at the time of movement it rotates from extension to flexion from one place to another,” explained Prof Naresh Bhatnagar, lead researcher.
The researchers took seven years to come up with this knee joint design. It has been tested clinically at Department of Physical Medicine and Rehabilitation, Government Medical College, Thiruvananthapuram.
