This document presents the design of a knee mechanism for prosthetic limbs to help replicate able-bodied knee moments. The mechanism uses springs, dampers, and other components optimized through determining optimal mechanical coefficients. Preliminary user trials with two subjects in India found the locking mechanism was functional for smooth stance to swing transitions as evaluated through a 2-minute walk test. Future work will focus on further improving the kinematics of stance-swing transition. The goal is to produce highly realistic prosthetics that improve patient confidence.

1. Presented by:
N. Vasukrishna
University college of engineering,
osmania university
B.E (IV/IV), BME
1005-12-731030

2. 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

3.  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.

4.  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

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

7. DESIGN OF THE MECHANISM
The three axis crucial for mechanism function shown:
 The early stance flexion (ESF) axis,
 The knee axis,
 The locking axis.

13. 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.

14. 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.

15. 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.

16. 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.

17. 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.

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

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

20. 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.

21. 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.

22. Ideal prosthesis:

23. ReGENeration?
İmg 47

24. Conclusion:
Producing highly realistic prosthetics.
Self confidence to the patient.

25. 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.