| Several characterization studies and walking experiments were undertaken in an attempt to understand the functional role of prosthetic feet in walking, and the influence of footwear on that role. Characterization of several biomechanical properties of prosthetic feet and prosthetic feet with shoes was accomplished with the use of a specially-designed testing apparatus. Foot deflection, center of pressure location, damping and energy storage and return characteristics were quantified at several foot/ground orientations (analogous to walking) from heel contact to toe-off, under physiologically appropriate loading conditions. Data from fifteen prosthetic foot types show a wide range of properties, and that foot geometry and center of pressure location are as important as flexibility and energy return---probably more important---in characterizing prosthetic feet. Data from three prosthetic foot types, with and without a shoe, indicate that footwear has little influence on the foot/shoe complex at angles near midstance, but has a substantial influence at angles analogous to late stance and toe-off. The same shoe has different effects on different foot types, but generally tends to equalize the differences between them. The concept of the effective shape of the foot during walking was developed and characterized during walking experiments for six different prosthetic feet and four normal human feet. During single limb stance, feet generally have rocker-like shapes that are created in a quasi-static manner. It was found that prosthetic feet do not return energy until after opposite heel contact. The results led to the design, construction, and testing of an experimental prosthetic foot design on three unilateral trans-tibial amputees. The design allows separate modification of the shape and energy characteristics. A priori prosthetic alignment is a natural result of the foot design, and emphasizes the finding that foot shape and alignment are highly interrelated. The primary role of prosthetic feet in walking is to create a beneficial foot shape during single limb stance that promotes smooth symmetrical progression of the trunk. Flexibility in current foot designs is primarily required to create a beneficial foot shape, and secondarily to aid swinging the limb through return of elastic potential energy. |
