Lower-extremity prosthetics

Since one of the goals of lower extremity prosthetics is to replace function, much attention is given to the restoration of gait or ambulation. While some argue that optimal gait for a lower extremity amputee need not be symmetric, symmetry in ambulation is cosmetic. As such, the prosthetist and physical therapists attempt to restore normal, symmetric gait—given constraints such as Joint contractures, weak hip/knee musculature, poor balance, and the potential need for an assistive device. 

In terms of recent innovations, it is worth acknowl ging advances in lower extremity prosthetics with respect to suspension. Historic suspension mechanisms such as hip and waist belts and fork straps and supracondylar cuffs for transfemoral and transtibial amputees, respectively, have been largely replaced by suction. Suction has been induced using neoprene suspension sleeves, TES belts, and shuttle-locking mechanisms. 

Since the design of the prosthesis varies with amputation level, prosthetic design will be reviewed for the aforementioned lower extremity amputation levels. Since the primary levels of lower extremity amputation are transtibial (54 percent") and transfemoral (33 percent"), the prostheses for these amputation levels will be presented in greater detail. 

Prosthetic Feet. With the exception of partial foot amputees, the prostheses for all lower extremity amputees require a prosthetic foot. The prescription criteria for these feet take into consideration the amputation level, residual limb length, subject activity level, cosmetic needs, and the weight of the individual. Prosthetic feet range from the SACK (solid ankle cushioned heel) foot, which is relatively simple and inexpensive, to dynamic-response or energy-storing feet that are more complicated and considerably more costly. Note that prosthetic feet are often foot and ankle complexes. As such, prosthetic feet may replace plantarflexion/dorsiflexion, pronation/supination, and inversion/eversion. Prosthetic feet are typically categorized in terms of the function(s) they provide or replace and whether or not they are articulated. 

Several groups have used computer models of the residual limb to investigate the residual limb-prosthetic socket interface. Many investigators have also used finite-element modeling of the residual limb and the prosthetic socket of lower extremity amputees to investigate residual limb-prosthetic socket biomechanics and to estimate the interface stress distribution (for review, see refs. 38, 46, and 47). 

Sabolich Research and Development (Oklahoma City, Okla.) recently has developed commercial systems for the upper and lower extremities that attempt to supplement sensation lost by amputation. Their Sense of Feel leg provides sensory feedback to the residu limb. Output from force transducers in the sole of the foot is transmitted to the residual limb via electrodes in the prosthetic socket. The amplitude of the tingling sensation is proportional to the force measured at the foot, thereby providing direct feedback to the amputee regarding the relative loading of the forefoot versus the heel. Such information is hypothesized to improve lower extremity balance. Clinical trials are currently underway. 

Klute GK, Berge JS, Orendurff MS et al. (2006) Prosthetic intervention effects on activity of lower-extremity amputees. Arch Hiys Med Rehabil 87(5) 717-722. 

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