Foot prosthesis and method of making same

A foot prosthesis comprising an elongate composite main member having a leg section and a toe section with one end of the leg section adapted to be connected to an amputation socket and the other end smoothly curving forwardly through an ankle section into the toe section and extending to a toe end, and a heel member extending from the toe end rearwardly generally along the toe section and then diverging from the toe section and extending to a heel tip. The main member and heel member are preferably of one piece construction with continuous fibers of the composite material extending through the main member and around the toe tip and through the heel member. A resilient material, such as rubber, is bonded between the toe section and heel member where the two are generally adjacent and the properties of the resilient material may be made adjustable by the wearer where the toe section and heel member diverge. In making the prosthesis, the uncured composite material is layed up with uncured rubber in desired position and the two materials cured together. It is preferred that the prosthesis device be removably attachable to an amputation socket by means of an aligned recess in the amputation socket which securely accepts the upper end of the leg portion of the main member.

BACKGROUND OF THE INVENTION 
1. Field: 
The invention is in the field of foot prosthesis which attach to an 
amputation socket and provide an artificial leg and foot to a wearer. 
2. State of the Art: 
There are a number of different foot and leg prosthetic devices currently 
in use. The primary goal of these devices is to extend an amputated leg to 
the ground so as to support the wearer while upright. The earliest prior 
art was merely a peg secured to the amputation which provides minimal 
mobility to the wearer. Later, a foot was added to the bottom of the peg. 
An example of a more modern basic foot prosethsis known as the "Sach Foot" 
is a carved wooden foot with an aluminum strut attaching the foot to the 
amputation socket. Additional improvements made to the basic device by way 
of ankle hinges or ball joints, improve mobility but the overall 
prosthesis remains rigid and heavy and as such remains uncomfortable to 
the wearer. Recent studies indicate such rigid systems contribute to 
premature hip deterioration due to severe axial loads transmitted to the 
wearer's hip joint. 
Recent improvements to foot prosthesis configurations utilize modern 
composite material technology to impart energy storage and release during 
use. Examples of these are the so called "Seattle Foot," which is a molded 
plastics foot and the prosthesis shown in U.S. Pat. No. 4,547,913, known 
as the Flex-Foot, which provides a composite strut and foot configuration. 
The spring like action imparted by the materials used results in 
additional mobility and comfort to the wearer. However, such prior art 
retains certain design characteristics which limit its potential 
usefulness and prevent ideal optimization possible with modern high 
performance composite materials. All known devices within this group are 
made up of individual components that must be fastened together, be it the 
heel-to-foot or the foot-to-connecting leg extension. These joints must be 
rigidly constructed so as to be strong enough to withstand the 
concentrated loads transmitted through them. The result is that local 
stiffness occurs which interferes with smooth, even flexing of the 
components during the wearer's stride. Even with the rigidly constructed 
joints, these devices are prone to fatigue and fracture at the joints thus 
placing the wearer at risk of injury. 
In addition, composite materials exhibit poor bearing strength where 
fasteners penetrate the construction. The accumulative wear and erosion of 
structural material surrounding fasteners result in loss of position or 
support of attached components after a period of continual use. The 
fastening of the heel to the ankle portion of the foot as in U.S. Pat. No. 
4,547,913 occurs at the highly stressed ankle zone. To prevent fracture, 
the buildup of materials required for strength makes attractive cosmetic 
finishing of the ankle area difficult. 
With currently known prosthesis, the prosthesis is fitted directly to the 
amputation socket and once the prosthesis is attached to the socket, it 
cannot be removed. Any change of prosthesis requires a complete change of 
the amputation socket along with the prosthesis. The fitting of the 
prosthesis to the amputation socket requires careful alignment and 
adjustment and is thus expensive. With current prosthesis, each prosthesis 
must be separately fitted and secured to its own amputation socket. 
Because of this, many prosthesis wearers cannot afford a variety of 
prosthesis such as one for sporting activities, one for normal walking, 
and one for dress wear. Since different characteristics are desirable for 
prosthesis for different uses, it would be desirable for a wearer to be 
able to easily adjust the characteristics of a prosthesis for an intended 
use or to be able easily change prosthesis for the intended use. 
Presently, if a user engages occasionally in vigorous sports activities, 
his prosthesis has to be strong enough to withstand such activity. 
However, a prosthesis designed for active sports is generally stiffer than 
that required for normal walking, is uncomfortable for normal walking, and 
generally unsuitable for use with fashion footwear. However, a softer, 
more complaint prosthesis for normal wear generally cannot take the forces 
applied during vigorous sports activity. There is currently no prosthesis 
which provides a means for the wearer to adjust the characteristics of the 
prosthesis, and it is difficult to change the prosthesis each time an 
activity changes. 
SUMMARY OF THE INVENTION 
According to the invention, a foot prosthesis provides a more natural feel 
and maintains more uniform and controllable flexibility than prior art 
prosthesis through a unitary composite construction from attachment to the 
amputation socket through the ankle area and extending to the toe section 
of the prosthesis. The heel member preferably is a unitary continuous 
extension of the prosthesis from the tip of the toe rearwardly back along 
a portion of the toe section and then to the heel tip with a resilient 
material secured between the heel member and adjacent portion of the toe 
member. An attachment means is secured to the amputation socket so that 
different prosthesis may be easily attached or removed as desired by the 
wearer. 
In a preferred embodiment of the invention, the prosthesis is molded by 
positioning continuous fibers, embedded in an epoxy resin matrix, along 
the vertical length of the leg section of the prosthesis, through the 
ankle area, across the top of the foot to the toe, and then sharply back 
to the heel tip to form a one piece composite structure without separate 
sections fastened together. Where the heel member extends back from the 
tip of the toe section, the heel and toe sections are sustantially 
adjacent and a resilient material such as a rubber pad is integrally 
molded into the structure between the heel member and the toe section 
along this area of adjacency. The rubber pad imparts flexibility and an 
integrity to the device along it s heel-to-foot junction to better handle 
and absorb heel side or torque loads which may be applied at the heel or 
axially along the leg section. The rubber pad also provides energy 
dampening and increased comfort to the wearer. In one embodiment, the 
rubber pad is made adjustable near its end where the toe and heel sections 
begin to diverge by means of providing an opening in the rubber pad and 
removable plugs of varying resilient properties which fit into the opening 
to thereby vary the properties of the rubber pad in that area and to 
effectively shift the fulcrum point of the heel. This results in a change 
of effective heel length and results in an adjustment of heel stiffness to 
optimize the performance and comfort of the prosthesis for varying 
activities. 
The construction described provides a prosthesis with more dynamic 
performance that closely simulates the complex muscular-skeletal heel and 
ankle performance. 
The attachment means secured to the amputation socket is specially fitted 
for the user and provides an aligned recess for receiving the top of the 
prosthesis. When the prosthesis is inserted into the receiving recess, it 
is securely held in the preset alignment with the amputation socket. In 
this way, a single fitting can be made to fit and align the receiving 
recess properly with the amputation socket and several prosthesis provided 
to fit into the recess. Thus, the expensive fitting process is done once 
and additional fitting for each separate prosthesis are avoided. 
In making the prosthesis, the main member and heel member are both layed up 
of uncured composite material and uncured rubber is inserted into the area 
desired between the generally adjacent portions of the toe section and 
heel member. The composite material and uncured rubber are then cured 
together.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT 
As shown in FIGS. 1 and 2, a prosthesis of the invention includes a 
composite main member 10 having a leg section 12, an ankle section 14 and 
a toe section 16 extending to a toe tip 18. A heel member 20 extends from 
toe tip 18 backwardly to heel tip 22 with the forward portion of heel 
member 20 extending along and generally adjacent to toe section 16 until 
toe section 16 turns upwardly toward ankle section 14 at which point toe 
section 16 and heel member 20 diverge. Main member 10 is of single piece 
composite construction and preferably member 20 is constructed as a 
continuation of main member 10 so that the leg section 12, ankle section 
14, toe section 16 and heel member 20 are formed as a single piece. This 
eliminates any mechanical fastening or binding together of separate 
components and provides a uniform flexure sequence for the device. Main 
member 10 and heel member 20 are constructed of either carbon, fiberglass, 
or aramid continuous fibers in an epoxy resin which surrounds and 
escapsulates the individual fibers. One or more of the fiber types may be 
utilized alone or together in the construction of the device, each 
imparting its own unique properties of strength, stiffness, toughness, and 
density to achieve the desired overall performance characteristics of the 
device. The continuous filaments extend uninterrupted from the top of leg 
portion 12 downwardly through the ankle section 14, across the top of the 
foot or toe portion 16 to the toe tip 18 and then rearward through the 
heel member to heel tip 22. 
A resilient material 24, such as a flexible rubber, is adhered between the 
adjacent portions of the toe section 16 and heel member 20. As shown, this 
material extends from the inside of toe tip 18 back to the area where the 
toe section and heel members diverge. The resilient material 24 
substantially maintains the relative positions of the upper and lower 
portions of the more rigid composite parts. Being much softer than the 
composite material, it allow deflection of the composite material without 
substantial interference and yet, under torsional load, has the strength 
to prevent the composite components from separating. Under load, the 
composite components tend to flex in opposite directions relative to each 
other. The resilient interface will elongate but retain the bond between 
the parts. Additionally, the resilient material forms a fulcrum point from 
which the cantilevered heel will deflect. This fulcrum point will be in 
the area indicated by 26 where the resilient material ends and from which 
the heel member extends backwardly to heel tip 22, but varies with the 
characteristics of the resilient material in that area. With the resilient 
material, the heel member may be secured at toe tip 18 so as to remain 
quite flexible. Without the resilient material, the same securement would 
provide a heel member too flexible to perform satisfactorily. Without the 
resilient material, the joint between the toe tip and heel and the heel 
member itself would have to be much more rigid. The resilient material 
also provides some degree of cushioning to the device upon heel impact. 
In the basic construction of the prosthesis, the composite material is 
finish trimmed so as to closely duplicate the natural foot bottom pattern 
as shown in FIG. 4. The forward foot portion may be shaped by grinding to 
satisfy left or right foot configuration requirements, however, the toe 
portion 18 remains untouched so as to protect the continuous fibers which 
pass through this area. The heel stiffness, or support capability, is a 
function of the heel member's width, thickness, and distance of the heel 
tip 22 from the point of departure 26 from the resilient material. 
Optimally, the heel stiffness should be sufficient to allow the wearer to 
walk without his or her shoulder on the side the prosthesis is worn 
dropping significantly. Shoulder drop is an indication of insufficient 
heel support. For athletic use, where more severe heel impact occurs, a 
stiffer heel is desired than for casual use. 
With the present invention, since the heel stiffness is dependent to some 
degree upon the properties of the resilient material where the toe section 
and heel members diverge, i.e., area 26, in addition to the construction 
of the heel member itself, i.e., the thickness, width, and material used 
for the heel member, the heel stiffness can be made adjustable to some 
degree by making the properties of the resilient material at area 26 
adjustable. 
For this purpose, as shown in FIGS. 6 and 7, a cavity 28 may be molded into 
the rear portion of the resilient material which is adapted to receive a 
removable plug 30. As shown in FIG. 7, the receiving cavity 28 may be 
molded with shoulders 32 at each end which, since they are formed of the 
resilient material, may be stretched to allow plug 30 to be placed in or 
removed from cavity 28. When plug 28 is in place, the shoulders 32 will 
hold it in place so it does not fall out during normal use of the 
prosthesis. By having several plugs 30 of varying properties, such as 
varying hardness, the heel stiffness of the prosthesis may be varyed by 
merely changing the plug. Thus, the properties of the prosthesis may be 
changed for different activities without having to remove the prosthesis 
and change to an entirely different prosthesis with the desired different 
properties. 
The embodiment in FIG. 6 shows a round plug, and this is presently 
preferred because it is the most easily fabricated configuration. However, 
various other configuration could be used duch as a wedge or an oval 
shape. Variations in plug shape effect the amount of heel stiffness change 
that will occur when plugs of different properties are inserted. 
While various composite construction techniques may be used in forming the 
prosthesis of the invention, a presently preferred construction is shown 
in FIG. 3. The central core 48 consists of fiberglass or carbon filaments 
embedded in an epoxy resin which during construction is in a highly 
viscous or tacky condition. The state of the art procedure for forming the 
composite structure is to lay up layers of preformed sheets of the fiber 
and resin which are cut from supply rolls. This "prepreg", or resin 
preimpregnated fiber, is commercially available from various suppliers. 
The ratio of resin to fiber, i.e., resin content, is carefully controlled 
by the supplier to specifications provided by the prosthesis manufacturer. 
Tight controls during the preparation of this "prepreg" material assure 
reproducible prosthesis results. The central core of the prosthesis device 
of FIG. 3 may also contain a small amount of continuous aramid fibers 
which, due to their tough nature, will retain the components in their 
relative structural position should the device be damaged. The central 
core 48 is sandwiched front and back by layers of carbon fiber composite 
50, similar in form to the fiberglass materials previously described. 
Although the orientation of the fibers, i.e., the direction of the fibers 
relative to the long axis of the device, may be varied in infinite 
combinations to satisfy specific performance requirements, for the layers 
described so far, a generally lengthwise orientation has been found from 
analysis and testing to work best. 
The application of an additional outside layer 52 of diagonally oriented 
fibers, such as fibers set at forty-five degrees to the length axis of the 
device, has been found by testing and analysis to be effective in 
providing torsional stiffness control and stability to the device. It is 
preferred that these outer fibers completely encircle the inner fibers, as 
shown, although the outside layer could be provided on just the front and 
back sides of the member. 
The resiliant material, which binds the composite toe section and heel 
member is formed by laying up thin sheets of uncured "green" natural 
rubber upon each other in a stack, preferably each ply end offset from the 
others so as to create a tapered thickness as shown in FIG. 1. With the 
composite material and rubber in desired position, the device is cured. 
This is generally done by placing the device, in this state called a 
laminate, in a forming mold and placing the forming mold into an oven or 
autoclave and heating it in a vacuum environment to cause a molecular 
reaction within the resin. The result is a hardening of the resin which 
stabilizes the fibers thus allowing each fiber to remain positioned as 
desired, to best transmit applied load in a springlike or elastic state. 
When cured at the same time as the composite prepreg, the rubber material 
and the resin material will adhere well to each other and the individual 
plys of rubber material will reform into one homogeneous elastomeric mass. 
The cavity 28 in the rubber material is created during the fabrication 
process by applying uncured sheet rubber around a metal tooling plug and 
curing together with the rest of the foot material. After cure, the plug 
is removed leaving the desired cavity in the rubber. 
While the top of the leg portion 12 of the prosthesis may be secured to an 
amputation socket 60 in any known manner, it is perferred that it be 
removably secured to the amputation socket so that the prosthesis may be 
easily removed from the socket and replaced with a similar prosthesis of 
different properties, when desired by the wearer. The end portion 62 of 
the upper part of leg section 12 is inserted and bonded to an inner sleeve 
64 using an elastomeric adhesive 66. The end portion 62 of the device may 
be shortened, or spacers 68 may be inserted into the sleeve 64, to adjust 
foot height prior to bonding. This bonded assembly is then removably 
inserted in tight fitting relationship in a receiving recess formed by 
outer housing 70 and is held in such recess by friction and/or a fastener 
72 joining sleeve 64 and housing 70. The materials for the housing 70 and 
sleeve 64 may be molded plastic or metal which exhibit good strength, 
abrasion resistance and toughness. The special mounting avoids penetration 
of large fasteners through the structural composite prosthesis. 
Installation of housing 70 with prosthesis secured thereto to amputation 
socket 60 is accomplished using standard alignment devices common to most 
prosthetist's laboratories. Specifically, the prosthesis assembly, 
including the housing mounting plate 70, is attached to a standard 
alignment tool, not shown, through the mounting holes 72, FIG. 5, using 
screw fasteners. The alignment tool is located between housing 70 and 
amputation socket 60 in the area indicated as 74, FIG. 1. After the 
angular and lateral positioning is done in normal manner, the alignment 
tool is removed and replaced permanently with an overwrap of composite 
material 76 which, after cure, rigidly positions the attachment housing 70 
to the amputation socket 60 as shown in FIGS. 1 and 2. 
Some modern lightweight alignment devices presently available commercially 
are designed to remain permanently is position between housing 70 and 
socket 60 after positioning takes place. In such instance, composite 
material 76 may be wrapped over such alignment device to provide 
reinforcement for the mounting during active sports use. 
With any composite prosthesis device, toe impact caused by contact within 
footwear or "stubbing" the uncovered foot can cause accelerated 
degradation of the composite materials. Such degradation is resisted in 
the invention by the preferred toe formation wherein the composite fibers 
do not terminate at the tip of the toe, but extend as continuous fibers 
back to the heel. This gives superior resistance to ply separation which 
is a problem in the prior art where the fully trimmed toe area edge 
exposes the full ply lamination. 
An alternate method employed to achieve protection at the toe is to slip 
fit a tough, molded plastic cap over the toe end. The plastic cap may be 
similar to caps commonly used on snow skis. Molded left or right-hand caps 
could also aid in development of a limited selection of "universal" foot 
configurations if such an approach were taken for production. 
On devices subjected to rigorous impact and abrasion during use as in 
athletics, rock climbing, etc, the invention can be manufactured with a 
molded plastic shell 80, FIG. 8, formed to the appropriate foot contour 
directly on the device. This molding process surrounding the one piece 
laminate protects the construction from abrasive damage and is 
considerably more resistant to tearing or separation than cosmetic foam 
adhesive bonded builups typical of prior art. 
Other or further finishing of the prosthesis of the present invention to 
cosmetically improve the aesthetics when worn in public is done in any 
presently known manner, such as by use of premolded or preshaped foam or 
rubber, or of flexible foam blocks affixed to the device by adhesive and 
shaped by sanding tools to match the natural limb. FIGS. 1 and 2 
illustrate with phantom lines a typical finished configuration. 
The prosthesis foot of the present invention has been fabricated in the 
embodiments of FIGS. 1 and 6. Both embodiments were fitted to a 
recreationally active amputee and subjected to rigorous use in athletic 
sports and daily use. The present invention was described by the wearer as 
functioning very well, having uniform stiffness transition throughout the 
walking and running gait. Other prior art of the energy storage/release 
type were described by comparison as being too stiff in the toe or ankle 
where attachment fasteners were installed. During the previous three 
years, the subject wearer had broken 6 prosthesis of the prior art energy 
storage type all at the heel attachment to the ankle. 
An alternate embodiment of the prosthesis of the invention is shown in FIG. 
9. The leg section 82 of this embodiment is tubular in cross section. This 
configuration enables a very narrow width while exceeding the strength and 
stiffness properties possible with rectangular or square constructions of 
the same sectional area. The circular section also fits well into the 
receiving recess of housing 70 to maintaining interchangeability. In the 
embodiment of FIG. 9, the toe section 84 transitions to the alternate leg 
section 82 through the ankle area 86, as shown. 
The invention also includes the method of producing a foot prosthesis by 
laying up the main member and heel member in uncured composite material 
and filling in the area between the toe section of the main member and the 
heel section, where the two are generally adjacent, with uncured rubber, 
such as green natural rubber, and then curing the composite and rubber 
material together to achieve a good bond between the composite material 
and the rubber. The rubber is preferably inserted and built up by layers 
of thin sheets of the rubber stacked on one another to fill in the desired 
area. 
Whereas this invention is here illustrated and described with specific 
reference to embodiments thereof presently contemplated as the best mode 
of carrying out such invention in actual practice, it is to be understood 
that various changes may be made in adapting the invention to different 
embodiments without departing from the broader inventive concepts 
disclosed herein and comprehended by the claims that follow.