PROSTHETIC FOOT HAVING CURVED ANKLE SECTION

Abstract

A prosthetic foot characterized by a foot portion and an ankle portion. The foot portion and ankle portion may be fabricated from polymer impregnated and encapsulated laminates, including such laminates as carbon fibers and/or fiberglass or synthetic fibers such as Kevlar. The ankle portion may include an upper end positioned near or below about the location of a natural human ankle joint, a lower end, and an elongated intermediate section at least a portion of which curves downward and forward between the upper end and the lower end. The foot portion may be curved and have a heel section, an arch section and a toe section. The foot portion may be connected to a lower attachment section of the ankle portion, with at least the heel section of the foot portion extending rearwardly from the lower attachment section and below the upper end of the ankle portion.

Description

Brief Description of Drawings

[0021] FIG. 1 is a side elevation view of a portion of a prosthesis constructed in accordance with the teachings of the invention;

[0022] FIG. 2 is a partially sectional plan view, taken along line 2--2 of FIG. 1;

[0023] FIG. 3 is a front elevation view, taken along line 3--3 of FIG. 2; and

[0024] FIG. 4 is a partially sectional side elevation view, taken along line 4--4 of FIG. 2.

[0025] FIG. 5 is a side elevation view of a portion of an alternative embodiment of a prosthesis constructed in accordance with the teachings of the invention;

[0026] FIG. 6 is a partially sectional plan view, taken along line 6--6 of FIG. 5;

[0027] FIG. 7 is a front elevation view, taken along line 7--7 of FIG. 6;

[0028] FIG. 8 is a partially sectional side elevation view, taken along line 8--8 of FIG. 6; and

[0029] FIG. 9 is a side elevation view of a portion of an alternative embodiment of a prosthesis.

Detailed Description of Preferred Embodiments of the Invention

[0030] Referring to the drawings, and particularly to FIGS. 1 and 2 thereof, I show a foot prosthesis 10 constructed in accordance with the teachings of the invention and including a foot portion 12 and an ankle portion 14 operatively and demountably connected to each other by bolt and nut combinations 16 associated with loadtransmitting metallic plates 17. If indicated, the foot and ankle portions can be permanently secured to each other, as by epoxy adhesive, an intermediate resilient member, or the like.

[0031] The ankle portion 14 of the prosthesis 10 includes a substantially rigid upper attachment section 18, FIG. 4, a curvilinear ankle section 20, and a lower attachment section 22. The sections 18, 20, and 22 of the ankle portion 14 are formed integrally with one another and simultaneously by a plurality of Juxtaposed, shaped laminae embedded in a hardened, flexible polymer.

[0032] The attachment section 18 has a rearward surface 58, as shown in FIG. 4, and a forward surface substantially parallel thereto. The attachment section 18 is substantially rigid and capable of sustaining torsional, impact and other loads impressed thereupon by the foot portion 12 and ankle portion 14 of the prosthesis 10. In addition, the inherent rigidity of the attachment section 18 prevents it from being distorted in any way and causes the effective transmission of the aforesaid loads imposed thereupon to a suitable ancillary prosthetic pylon 30, through a pylon coupling 32, constructed of graphite or some other appropriately strong material.

[0033] The pylon coupling 32 incorporates a split sleeve 34 which surrounds the attachment section 18, an auxiliary ankle member 50 (if any, as more thoroughly described below), and the prosthetic pylon 30. Tab members 36 are provided at the split in sleeve 34, and said tab members are provided with two centrally located openings 38, FIG. 4, adapted to accommodate bolt and nut combinations 40. The bolt and nut combinations 40 can be tightened to cause the pylon coupling 32 to grip and cause a frictional engagement of the attachment section 18, the auxiliary ankle member 50, if any, and the prosthetic pylon 30.

[0034] The pylon coupling 32 further includes gripping means 42, shown in the preferred embodiment as angular projections located on the internal surface of the coupling 32 in the interstices between the ancillary prosthetic pylon 30 and the attachment section 18 or the auxiliary ankle member 50, if any. Gripping means 42 are so sized and shaped as to provide additional surface contact and improve the aforementioned frictional engagement between the coupling 32, the pylon 30, and the attachment section 18 or the auxiliary ankle member 50 if present.

[0035] As shown in the drawings of the preferred embodiment, the tab members 36 associated with the split in the coupling 32 are adjacent the front of the prosthetic pylon 30, but those skilled in the art will understand that the aforementioned split and the tab members 36 associated therewith may alternatively be oriented toward the side or rear of the prosthetic foot 10, and still be within the scope of the present invention.

[0036] As previously mentioned, an auxiliary ankle member 50 can be utilized to decrease the flexibility of the ankle portion 14. The auxiliary ankle 50 is formed from fibrous laminates of the same character as the various portions of the prosthesis 10. In the preferred embodiment, the auxiliary ankle 50 incorporates an attachment section 44 which is mounted inside the coupling 32, between the ancillary pylon 30 and the attachment section 18 of the ankle portion 14. The auxiliary ankle 50 is secured in operative relationship with the curvilinear ankle section 20 of ankle portion 14 through the aforementioned assembly of the coupling 32, which retains the various components in the aforesaid operative relationship. On its end opposite the attachment section 44, ankle member 50 has a tapered section 46 which provides a varying flexibility along the length of the ankle member 50 and also lessens the likelihood that the ankle member 50 will be undesirably snagged or restrained in its cooperative relationship with ankle portion 14 and the cosmetic cover of the prosthesis, more thoroughly discussed below. In alterative embodiments, as will be understood by those skilled in the art, such tapering is not required in order to practice the invention, and accordingly, the ankle member 50 can be provided with a relatively uniform thickness along the length thereof.

[0037] In the preferred embodiment, the auxiliary ankle member 50 is secured against the internal radius of the curvilinear ankle section 20, so that the anticipated upward deflection of a toe section 24 of the foot portion 12, as more thoroughly described below, will eventually cause deformation of the auxiliary ankle 50 as well as deformation of the ankle section 20, effectively combining the deformation resistance and energy storage characteristics of the auxiliary ankle member 50 with those of the ankle section 20. Alternative embodiments would include securing the auxiliary ankle 50 to the rearward surface 58 of the attachment section 18 and further securing the auxiliary ankle tapered section 46 to an under surface 62 of the ankle section 20 in order to achieve the aforedescribed desired combination of the deformation resistance and energy storage characteristics of the auxiliary ankle member 50 with those of the ankle section 20.

[0038] The auxiliary ankle member 50 can be provided with different numbers of laminates to make it more or less compliant to loads transmitted through the ankle section 20. Consequently, when confronted with various anomalies in an amputee, such as overweight or excess activity levels, the basic structure of the ankle portion 14, and more particularly the ankle section 20, can be materially modified to provide ankle portion action which is precisely adjusted to the needs of the amputee. Moreover, a variety of auxiliary ankle members 50 can be made available to an amputee, allowing the flexibility of the prosthesis to be adjusted on the basis of the particular activity which the amputee is undertaking.

[0039] As previously mentioned, a cosmetic cover, not shown, can be provided to shroud the prosthesis 10 after the optimum assemblage of the foot and ankle portions 12 and 14 and any auxiliary ankle member 50 has been accomplished. Unlike prior art constructions, however, the cosmetic cover, which may be formed of low-density formed polymer, is not required to serve any ancillary shock-absorbing or other stress-isolating function since all of the loads imposed upon the prosthesis can be absorbed, transmitted and reasserted in a manner to be described in greater detail below.

[0040] The bolt and nut combinations 16, in conjunction with the load-distributing metallic plates 17, serve to secure the ankle portion 14 in operative relationship with the foot portion 12 of the prosthesis 10, as best shown in FIGS. 1-2 of the drawings. The aforesaid mode of affixation facilitates the assembly or dismounting of selected ankle portions 14 in operative relationship with selected foot portions 12 of the prosthesis 10, thus permitting a wide range of different sizes and stress load response characteristics to be related to each other to accomplish the optimum functional correspondence between the foot and ankle portions 12 and 14 to accommodate to the maximum extent the needs of the wearer of the prosthesis, and, also, to provide for a proper mating of the prosthesis 10 with a selected, ancillary pylon 30 or the like.

[0041] The foot portion 12, as best shown in FIG. 1 of the drawings, includes a toe section 24, an arch section 26, and a heel section 28 which has its rearward extremity 56 extending beyond the extreme rearward surface 58 of the ankle portion attachment section 18 of the prosthesis 10. Mating bores, not shown, in the arch section 26 of the foot portion 12 and the ankle portion 14 receive the respective bolt and nut combinations 16 to provide for the aforesaid facility in assembling and disassembling of the foot and ankle portions 12 and 14. In the preferred embodiment, the various sections of the foot portion 12 are all constructed without the necessity of tapering of the thickness thereof, although those skilled in the art will understand that the invention is not limited to such non-tapering construction.

[0042] Interposed between the under surface 62 of the ankle section 20 of the ankle portion 14 and an upper surface 64 of the heel section 28 is a resilient, spring action function block 70 of wedge-shaped configuration to determine the lever arm of the heel section 28 and isolate the under surface 62 of the ankle section 20 and the upper surface 64 of the heel section 28 from each other. The function block 70 may be fabricated from a wide variety of resilient materials, including natural and synthetic rubbers, or the like.

[0043] Similarly, a second spring action function block 72 of like shape and construction can be interposed between an under surface 74 of the lower attachment section 22 of the ankle portion 14 and an upper surface 76 of the toe section 24 to determine the lever arm of the toe section 24 and isolate the under surface 74 of the lower attachment section 22 and the upper surface 76 of the toe section 24 from each other.

[0044] The materials from which the foot portion 12 and ankle portion 14 and the auxiliary ankle 50 are fabricated must be such as to provide an energy-storing, resilient, spring-like effect. This is necessary because each engagement of the prosthesis 10 with an adjacent surface impresses compression, torsional and other loads upon the prosthesis 10 which must be stored within the prosthesis and then, dependent upon the stride of the wearer, be reimpressed upon said surface to achieve a natural stride conforming, ideally, in all respects to the stride of the unimpaired limb of the wearer of the prosthesis 10.

[0045] The foot and ankle portions 12 and 14 and the auxiliary ankle 50 of the prosthesis are preferably molded as unitary components and are carefully formed to provide for uniform absorption of stress imposed thereupon. The configuration of both portions 12 and 14 is of utmost importance and the laminates and the polymer or polymers from which the portions 12 and 14 are fabricated must be resilient and capable of absorbing the compressive, torsional and other stresses referred to hereinabove and of restoring the stored energy created by such stresses, in a natural manner, to the impacted surface which originally imposed such stresses upon the prosthesis 10.

[0046] It has been found that there is a limited number of polymers capable of sustaining the significant stresses and repetitive loads imposed upon the prosthesis 10, particularly in the light of the countless numbers of cycles to which the prosthesis 10 is subjected during normal, everyday use.

[0047] At present, the best materials for the prosthesis are a composite of high-strength graphite fiber in a high-toughness epoxy thermosetting resin system. There are several reasons for this: (1) high strength; (2) stiffness to weight ratio of graphite as compared to other materials; (3) the almost complete return of input or stored energy; (4) light weight; (5) high fatigue strength; and (6) minimal creep. As an alternative material, fiberglass/epoxy is a fair choice, but it is not as good as graphite because of lower fatigue strength and higher density. Kevlar is even less acceptable due to poor compression and shear strength, although it is the lowest density of those mentioned.

[0048] An important aspect of the polymers and laminates referred to hereinabove is that they are characterized by needed, but not excessive, flexural deflection under load, which characteristic permits the shock-absorption stress loading of the prosthesis 10 while maintaining sufficient stability to prevent the collapse of the foot and ankle portions 12 and 14 and the ankle member 50 of the prosthesis 10 while loads are imposed thereupon.

[0049] To achieve the relatively thin construction of the foot and ankle portions 12 and 14 and the auxiliary ankle member 50 of the prosthesis 10, the aforesaid polymers are utilized in conjunction with various laminating materials. Various types of fibrous laminae can be utilized to achieve the continuum required by the design of the foot and ankle portions 12 and 14 and the ankle member 50 to complement the stress-absorbing and storing characteristics of the polymers in which said fibrous laminae are embedded.

[0050] Of course, there is a wide variety of fibrous reinforcements in the form of laminae available at the present time, including such inorganic fibers as glass or carbon fibers. These inorganic fibers are customarily provided in tape or sheet form and can be readily superimposed in the mold to permit them to be encapsulated in the selected polymer.

[0051] Obviously, the number of superimposed laminae and the lengths thereof, together with the thickness of the encapsulating polymer, determine the stress characteristics of the resultant foot and ankle portions 12 and 14 and the ankle member 50 and, correspondingly, determine the total weight of the prosthesis 10. As will be apparent from the discussion hereinbelow, the individual foot and ankle portions 12 and 14 and ankle member 50 are designed to specifically accommodate individuals having different foot sizes, different weights and different strides and the individual design of the foot and ankle portions 12 and 14 and the ankle member 50 provides for matching, to an extent previously unknown in the art, the natural characteristics of the wearer's uninjured limb.

[0052] Furthermore, the function blocks 70 and 72 can be provided in different sizes and in materials having different compression characteristics so that the respective lever arms and the corresponding deflections of the heel section 28 and the toe section 24 may be increased or decreased.

[0053] As previously mentioned, the ankle section 20 is formed integrally with the upper attachment section 18 and said attachment section constitutes the upper extremity of the ankle section 20, while the initiation of the lower attachment section 22 of the ankle portion 12 constitutes the lower extremity of the ankle section 20. The configuration of the ankle section 20, in conjunction with the auxiliary ankle member 50, is the means whereby compressive loads imposed during impingement of the foot and ankle portions 12 and 14 upon an adjacent surface are absorbed and subsequently reimposed upon said surface The ankle portion 20 and the auxiliary ankle member 50 are so designed that they function, substantially, as an ankle joint to permit pivoting of the foot portion 12 thereabout in a manner analogous to the manner in which the normal foot pivots about the normal ankle joint on an axis transversely of said ankle joint.

[0054] The radii of curvature of the ankle section 20 and any auxiliary ankle member 50 correspond to provide for the inherent resilience and deflection of the foot portion 12 while inhibiting undesired, excessive collapse of the ankle section 20.

[0055] It will be noted that the arch section 26 of the foot portion 12 is substantially rigid and that the initial deflection of the heel section 28 occurs immediately adjacent the rearward extremity 56 of said heel section, terminating immediately adjacent the function block 70. Obviously, a greater length or less resilient function block 70 reduces the lever arm of the heel section 28 of the foot portion 12 and correspondingly reduces the modulus of deflection of said ankle section, while a smaller length or more resilient function block 70 increases the lever arm and correspondingly increases the deflection of the heel section 28 under load. The length of the second function block 72 likewise affects the lever arm and deflection of the toe section 24 of the foot portion 12.

[0056] The toe section 24 and heel section 28 can be provided in different lengths to correspond to the size of the foot of the wearer of the prosthesis 10. When such different lengths are provided, corresponding reduction or increase in the number of laminae and thickness of taper of the respective toe section 24 and heel section 28 can be made to provide for the proper flexure of said toe and ankle sections. It should also be noted that, even with the shortest heel section 28, the rearward extremity 56 thereof projects beyond the rearward surface 58 of the ankle portion 14. Consequently, the stabilizing and stress-absorption characteristics of the heel section 28 of the prosthesis 10 are always maintained.

[0057] In an alternative embodiment, shown in FIGS. 5-8, a toe section 82 can be incorporated into an ankle portion 80, and a heel portion 84 can be permanently or detachably associated therewith to practice certain aspects of the invention. Except for the toe section 82 being attached to the ankle portion 80 rather than the heel portion 84, the alternative embodiment of FIGS. 5-8 is constructed and functions similarly to the preferred embodiment described above. An auxiliary ankle member 86, similar in configuration and function to ankle member 50 in the preferred embodiment, may be utilized to achieve the benefits associated with ankle member 50 in the preferred embodiment. FIGS. 5-8 further show an alternative embodiment of a coupling 90 suitable for joining the ankle portion 80, the auxiliary ankle member 86, and the pylon 30 in operative engagement. Those skilled in the art will understand that many alternative embodiments of the coupling can be constructed and practiced interchangeably in connection with the many alternative embodiments of the rest of the invention.

[0058] The ankle portion 80 of the alternative embodiment of the prosthesis includes a substantially rigid attachment section 92, a curvilinear ankle section 94, an arch section 96 and a toe section 82. The sections 92, 94, 96 and 82 of the ankle portion 80 are formed integrally with one another and simultaneously by the incorporation of a plurality of laminae embedded in a hardened, flexible polymer.

[0059] The attachment section 92 incorporates two centrally-located openings 88, FIG. 8. The attachment section 92 is substantially rigid and capable of sustaining torsional, impact and other loads impressed thereupon by the ankle portion 80 and heel portion 84 of the prosthesis. In addition, the inherent rigidity of the attachment section 92 causes the effective transmission of the aforesaid loads imposed thereupon to a suitable ancillary prosthetic pylon 30, by bolt and nut combinations 98 assembled through openings 88 to a pylon coupling 90. A screw 100 or other suitable attachment means secures the ancillary pylon 30 in the coupling 90.

[0060] In the particular alternative embodiment of FIGS. 5-8, the auxiliary ankle 86 is mounted between coupling 90 and ankle portion 80, and is secured in operative relationship with the ankle portion ankle section 94 through the us of centrally-located openings in an attachment section 102 of the ankle member 86, which openings are substantially aligned with openings 88 of the ankle portion attachment section 92. Bolt and nut combinations 98 retain the various components in the aforesaid operative relationship. Alternative embodiments would include securing the auxiliary ankle 86 to the rearward surface of the attachment section 92 a described above for the preferred embodiment.

[0061] In this alternative embodiment, bolt and nut combinations 104 similar to the combinations 16 in the preferred embodiment, in conjunction with the load-distributing metallic plates 106 similar to the plates 17 in the preferred embodiment, serve to secure the heel portion 84 in operative relationship with the ankle portion 80 of the prosthesis, as best shown in FIGS. 5-6 of the drawings. The aforesaid mode of affixation facilitates the assembly or dismounting of selected heel portions 84 in operative relationship with selected ankle portions 80, thus permitting a wide range of different sizes and stress load response characteristics to be related to each other to accomplish the optimum functional correspondence between the ankle and heel portions 80 and 84.

[0062] It will, of course, be obvious to those skilled in the art that, with respect to any embodiment of the invention, the fibrous reinforcements in the form of laminae plies encapsulated in the prosthesis may be fayed or tapered to accomplish a gradual transition as the number of plies is reduced in any area of the foot or ankle portions.

[0063] Moreover, if a relatively lightweight individual partakes in sports or other activities which subject the prosthesis 10 to greater loads, an ankle or foot portion 14 or 12 will be fitted which will accommodate for those greater loads.

[0064] The ankle section 20 of the ankle portion 1 deflects under load and the auxiliary ankle member 50 similarly deflects. Additionally, the toe and heel sections 24 and 28 of the foot portion 12 deflect under such load. Therefore, when subjected to vertical compression loads, the ankle section 20, the auxiliary ankle member 50, and the toe and heel sections 24 and 28 absorb such loads.

[0065] Consequently, there is no stress concentration, either in the impact phase when the adjacent surface is initially contacted by the wearer of the prosthesis 10, or when return of the accumulated forces stored in the prosthesis 10 is accomplished.

[0066] The curvature of the toe section 24 provides for maximum accommodation of said section during surface contact in both the impact and delivery phases of the prosthesis 10. Similar considerations apply to the curvature of the heel section 28 of the foot portion 12 of the prosthesis 10. It will be noted that the arcuate, parabolic curvatures of the toe and heel sections 24 and 28 of the foot portion 12 provide for relatively extended lever arms which achieve stability and, also, stress storage and stress reaction.

[0067] The preferred method of manufacturing the foot and ankle portions 12 and 14 and the auxiliary ankle member 50 of the prosthesis 10 is by a thermosetting molding process including the utilization of molds having properly shaped and sized cavities. The cavities are designed to receive the requisite number of laminates and the proper volume of polymer.

[0068] Unlike prior art unitary devices, the fitting of the prosthesis 10 involves the judicious adjustment of the prosthesis by the proper combination of foot and ankle portions 12 and 14 and auxiliary ankle member 50, respectively. It also involves the selection of the properly designed ancillary pylon 30 which can be secured by means of the coupling 32 to the attachment section 18 of the ankle portion 14. Only when the proper correlation between the foot portion 12, ankle portion 14, auxiliary ankle member 50, and ancillary pylon 30 has been accomplished, can the cosmetic shroud, not shown, be installed upon the assembled, respective portions of the prosthesis 10.

[0069] By the prosthesis of my invention I provide a foot which can be carefully matched to the weight, stride and physical characteristics of the wearer. This is accomplished by carefully balancing the respective physical characteristics of the foot portion 12, the ankle portion 14, the auxiliary ankle member 50, and the various sections thereof.

[0070] Moreover, the assembled prosthesis is far lighter in weight than prior art prostheses since the inherent design and structure of the prosthesis, the materials used and the careful calculation of stress factors of the components of the prosthesis permit fine-tuning of the prosthesis to the needs of the wearer thereof.

Claims

1. 34. A prosthetic foot, comprising:

2. 35. The prosthetic foot of Claim 34, wherein the foot portion is connected to the lower attachment section of the ankle portion with an adhesive.

3. 36. The prosthetic foot of Claim 34, wherein each of the ankle portion and the foot portion is fabricated from superimposed laminates maintained in operative relationship by an encapsulating polymer.

4. 37. The prosthetic foot of Claim 34, wherein at least a portion of the elongated intermediate section is vertically oriented.

5. 38. The prosthetic foot of Claim 34, wherein the upper end of the ankle portion is positioned at about the location of a natural human ankle joint.

6. 39. A prosthetic foot, comprising:

7. 40. The prosthetic foot of Claim 39, wherein each of the first support member and the second support member has a substantially rectangular transverse cross-section.

8. 41. The prosthetic foot of Claim 39, wherein at least a portion of the elongated intermediate section curves downward and forward between the upper end and the lower attachment section.

9. 42. The prosthetic foot of Claim 39, wherein the second support member is curved.

10. 43. The prosthetic foot of Claim 41, wherein the second support member includes an arch section forward of the heel section.

11. 44. The prosthetic foot of Claim 39, wherein the second support member includes a toe section terminating at the forward extremity of the second support member.

12. 45. The prosthetic foot of Claim 44, wherein the toe section terminates at the forward extremity of the second support member at about the location of natural human toes.

13. 46. The prosthetic foot of Claim 44, wherein the toe section extends forwardly from the lower attachment section.

14. 47. The prosthetic foot of Claim 39, wherein the first support member and the second support member are adhesively bonded to one another.

15. 48. The prosthetic foot of Claim 39, wherein at least a portion of the first support member is substantially vertically oriented.

16. 49. The prosthetic foot of Claim 39, wherein the upper end is substantially vertically oriented.

17. 50. The prosthetic foot of Claim 39, wherein the first support member terminates in a toe section at about the location of natural human toes.

18. 51. The prosthetic foot of Claim 39, wherein the first support member is tapered between the upper end and the lower attachment section.

19. 52. The prosthetic foot of Claim 39, wherein the second support member is tapered toward the rearward extremity.

20. 53. The prosthetic foot of Claim 39, wherein the upper end of the first support member is positioned at about the location of a natural human ankle joint.

21. 54. A prosthetic foot, comprising:

22. 55. The prosthetic foot of Claim 54, wherein each of the ankle portion and the foot portion has a substantially rectangular transverse cross-section.

23. 56. The prosthetic foot of Claim 54, wherein the foot portion includes an arch section forward of the heel section.

24. 57. The prosthetic foot of Claim 54, wherein the ankle portion and the foot portion are adhesively bonded to one another.

25. 58. The prosthetic foot of Claim 54, wherein the ankle portion is tapered between the upper attachment section and the lower attachment section.

26. 59. The prosthetic foot of Claim 54, wherein the foot portion is tapered toward the rearward extremity.

27. 60. The prosthetic foot of Claim 54, wherein the elongated intermediate ankle section includes at least a portion that curves downward and forward.

28. 61. A prosthetic foot, comprising:

29. 62. The prosthetic foot of Claim 61, wherein each of the ankle portion and the foot portion has a substantially rectangular transverse cross-section.

30. 63. The prosthetic foot of Claim 61, wherein said foot portion is curved.

31. 64. The prosthetic foot of Claim 63, wherein said foot portion includes an arch section between the toe section and the heel section, said foot portion contacting said under surface of said ankle portion along at least a portion of said arch section.

32. 65. The prosthetic foot of Claim 61, wherein the ankle portion and the foot portion are adhesively bonded to one another.

33. 66. The prosthetic foot of Claim 61, wherein the elongated intermediate ankle section includes at least a portion that curves downward and forward.

34. 67. The prosthetic foot of Claim 61, wherein the toe section terminates at a forward extremity of the foot portion at about the location of natural human toes.