Page 262 - Handbook of Biomechatronics

256 Georgios A. Bertos and Evangelos G. Papadopoulos

excessive stance-phase knee flexion angles in the sound limb of transtibial
amputees during gait, which was speculated to be a compensatory mecha-
nism for dynamic deficiencies of the prosthetic side. This may have increased
the energy expenditure of walking because of the increased muscular effort
by the knee.
Mooney et al. (1995) examined the differences in the ground reaction
forces and moments of force during gait between the sound and residual
limbs of a transtibial amputee using the Flex Foot’s Re-Flex vertical shock
pylon (VSP) as designed, and with the shock-absorber immobilized; they
observed minimal differences between the two testing conditions.
One notable advancement in the area of the shock absorbing legs is the
J-leg. It is produced in Canada in very small quantities but has received some
positive feedback from the transfemoral (TF) amputees who have tried it.
Basically, it includes a spring in the shank, along with a standard locking
knee. The knee is locked in extension during the whole gait cycle. When
the person wants to sit down, he/she manually unlocks the knee. The floor
clearance is facilitated by the design of the foot, which can be considered an
end-point “peg-leg.” Also, the end-point foot device freely rotates
360degrees in the transverse plane, which facilitates circumduction of the
leg. The spring stiffness is constant, but there different springs are available
depending on the body weight. This is an inexpensive leg compared with
the new computerized knees of the market. Thus, it might be a good choice
for developing economies. However, there is lack of scientific literature on
this product. The disadvantage of this leg might be that its appearance is not
very cosmetic; but perhaps function is more important than cosmesis.
At the old Leg Laboratory and now Biomechatronics Group of Medial
Lab of Massachusetts Institute of Technology, Hugh Herr (2006) has
developed an auto-adaptive knee prosthesis for transfemoral amputees,
€
the Rheo-Knee marketed by Ossur (Fig. 9). External knee prostheses should
move naturally at all locomotory speeds and should perform equally well for
all amputees. Using state-of-the-art prosthetic knee technology, a prosthetist
must preprogram knee damping values until a knee is comfortable and safe to
use. The knee prosthesis should automatically adapt to the amputee without
preprogrammed information of any kind from either amputee or prosthetist.
With this technology, knee damping is modulated about a single rotary axis
using a combination of magnetorheological and frictional effects, and only
local sensing of axial force, sagittal plane torque, and knee position are used
as control inputs. Early stance damping is automatically adjusted by the con-
troller, using sensory information measured when a patient first walks on