Design of a Fully Passive Prosthetic KneePresented by:N. VasukrishnaUniversity college of engineering,osmania universityB.E (IV/IV), BME1005-12-731030

Introduction

Prosthesis Device to replace part of the limb or missing limb

“substitute”

Prosthetist a person skilled in prosthetics and its application.

Prosthetics: a rehabilitation science includes theory and practice of design, production of prosthesis and application

Even the passive knee joints in developed countries are too expensive to meet the requirements of amputees in the developing world.

An estimated 230,000 above-knee amputees are in need of prosthetic devices in India with a majority of them facing severe socio-economic constraints in their daily lives.

. DETERMINATION OF OPTIMAL MECHANICAL COMPONENT

Designers of prosthetic devices have used components such as springs and dampers and optimized them with the aim of replicating ideal knee moment required for walking with able-bodied kinematics

DETERMINATION OF OPTIMAL MECHANICAL COMPONENT COEFFICIENTS

Determination of optimal mechanical component coefficients for replicating able-bodied knee moment.

DESIGN OF THE MECHANISM The three axis crucial for mechanism function

shown:

The early stance flexion (ESF) axis, The knee axis, The locking axis.

Control through late-stance and swing phases:

The horizontal position of the locking axis is located such that the GRF vector moves anterior to the locking axis during mid-stance, which causes an extension moment about the locking axis.

Differential damping:

To achieve normative kinematics and to minimize metabolic energy expenditure, dampers are needed to dissipate knee power during late-stance and swing phases.

The figure shows the implementation of the differential damping system in the mechanism. The two radially spaced dampers with brake-pad components apply equal normal force (N) from both sides on part 4.

PRELIMINARY USER TRIAL:

The mechanism’s early stance locking function and late stance unlocking function was tested through early stage user-trials by subjects of our target user group: above-knee amputees in India.

Two subjects were fitted with the prototype with the help of trained prosthetists at the Jaipur-Foot clinic in Jaipur, India.

Contd…

The evaluation protocol included the 2-minute walk test.

The primary objective of the trial was to find out if the locking mechanism was functional as intended and whether that enabled a smooth stance to swing transition.

Contd…

User trials at Jaipur-foot clinic, India. (a) and (b) show the prosthesis assembly as fitted on to the subject.

Contd…

Late stance flexion after disengagement of the latch in the knee mechanism shown in (c) and (d).

DISCUSSION AND FUTURE WORK:

An important design strategy for this mechanism was using the movement of the center of pressure from foot heel region to the toe region (and the resulting change in direction of the GRF vector) as an indicator of the phase of the gait cycle.

Contd…

Polycentric knees also similarly utilize the GRF vector direction to enable late-stance flexion but do so at the cost of achieving ideal kinematics of stance-swing transition.

Polycentric knees with extremely posterior instantaneous centers of rotation make it difficult for the users to transition from stance into swing because of delayed late stance flexion.

Ideal prosthesis:

ReGENeration?

İmg 47

Conclusion:

Producing highly realistic prosthetics.

Self confidence to the patient.

REFERENCES:Guidelines for Training Personnel in Developing Countries

for Prosthetics and Orthotics services, World Health Org., 2005.

I. C. Narang, B. P. Mathur, P. Singh, and V. S. Jape “Functional capabilities of lower limb amputees”, Prosthet.Orthot. Int., vol. 8, no. 1, pp. 43-51, Apr. 1984.

Y.Narang, V.Arelekatti, A.Winter, “The effects of prosthesis inertial properties on prosthetic knee Moment and hip energetics required to achieve able-bodied kinematics”, IEEE Transactions on Neural Systems and Rehabilitation Engineering, in press.