Page 261 - Handbook of Biomechatronics

Lower-Limb Prosthetics 255

5 ADVANCES IN COMMERCIALLY AVAILABLE LOWER-
LIMB PROSTHETICS
5.1 Advances in Shock Absorption Prosthetic Legs
Shock absorption in amputee walking is an important component. Leeuwen
et al. (1990) recognized that the absence of the necessary shock absorption in
transtibial prostheses might cause proximal joint disease. They claimed that
the shock transmitted during prosthetic gait should not be different than the
shock transmitted during normal gait. The effectiveness of the cushioned
heel as a shock absorber led to its continued use in most prosthetic foot
designs (Perry et al., 1997). Edelstein (1988) suggested that all commercially
available prosthetic feet provide some degree of shock absorption. The solid
ankle cushion heel (SACH) foot has a cushioned heel, which is compressed
during heel strike and provides shock absorption, simulating the normal
plantar flexion movement of the foot during early stance (Lehmann et al.,
1993a,b). Pitkin (1995) has investigated a rolling-joint prosthetic foot/ankle
mechanism, which is claimed to incorporate shock absorption, balance, and
dorsiflexion functions.
Davies and Holcomb (2001) found significant differences in the heel
strike acceleration and heel strike transient amplitude between the prosthetic
and the sound side. Poor attenuation in one knee leads to changes in the
walking pattern. Amputees have been shown (nonconclusively) to have
greater incidence of osteoarthritis than nonamputees; those with trans-
femoral amputations are three times more likely to exhibit this condition
at the hip than a transtibial amputee (Kulkarni et al., 1998). Gitter et al.
(1991) compared the gaits of five able-bodied subjects to the gaits of five
unilateral transtibial amputees walking with three different feet. They found
that regardless of prosthetic foot type, there was a loss of the shock absorp-
tion function of the prosthetic-side knee during loading response. Wirta
et al. (1991) compared five ankle-foot devices, and found that transtibial
amputees preferred walking with those that developed less shock and had
greater damping at heel contact. Van Jaarsveld et al. (1990a,b) supported
the idea that the reduction of peak accelerations during heel strike was an
important aspect of the prosthesis functionality in transtibial amputees.
Lehmann et al. (1993a,b) assumed that the shock-absorbing characteristics
of prosthetic foot designs are a measure of comfort during gait, and found
that the SACH foot attenuated the higher frequency components of accel-
eration more than the Seattle ankle/lite foot. Snyder et al. (1995) observed