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Prosthetic foot

  • US 5,139,525 A
  • Filed: 12/23/1991
  • Issued: 08/18/1992
  • Est. Priority Date: 07/31/1989
  • Status: Expired due to Term
First Claim
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1. In a foot prosthesis including a hollow cosmesis, a spring means fastened in the cosmesis and extending in a longitudinal direction of the cosmesis for storing energy on heel strike and releasing energy on toe-off, an ankle joint connected to the foot cosmesis and a leg adapter for connecting the foot prosthesis to a leg connected to the ankle joint, the improvement comprising:

  • said spring means comprising a forward lower portion extending generally parallel with the lower portion of the foot cosmesis and anchored in the forward lower portion of the foot cosmesis, a rearwardly located hook portion including a lower section connected to the lower portion and an upwardly and forwardly extending bent hook section including an upper terminal section connected to and extending forwardly from the forwardly bent section so as to lie above said lower section;

    a snubbing means for transmitting load from the leg adapter to the spring means via the ankle joint, said snubbing means secured to the upper terminal section of the spring means;

    said hook portion having a concave curved inner surface having a first geometric contour and said snubbing means having a convex curved outer surface having a second geometric contour smaller than the curvature of said hook portion, said snubbing means disposed within said hook portion with said snubbing means convex outer surface extending along said hook portion concave inner surface over a limited portion of said snubber outer surface so as to leave a free length of said hook portion not engaging the snubbing means;

    said snubbing means connected to the upper terminal section of the spring such that a lower portion of said convex curved outer surface is normally spaced above the forward lower portion of the spring means when the foot prosthesis is unloaded vertically, and such that forward pivotal motion of the leg adapter relative to the foot cosmesis causes the inner surface of the hook portion to progressively wrap around the outer surface of the snubber means to effectively foreshorten the effective length of the primary spring means and to thereby vary the spring rate of the spring means;

    whereby increasing forward pivotal motion of the leg prosthesis produces a progressively increasing spring rate producing a progressively higher force resisting such forward pivotal motion.

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