Prosthetic foot with variable medial/lateral stiffness

A prosthetic foot includes an elongated foot member, extending between a toe section positioned at a toe location of a natural foot and a heel section positioned at a heel location of a natural foot. The elongated foot member also extends through an elevated arch section positioned between the toe section and heel section at an approximate arch location of a natural foot. An arch block is disposed below the elongated foot member under the elevated arch section. The arch block is sized and shaped to substantially fill a space or volume under the arch section. The arch block has geometric and physical properties that facilitate medial to lateral rotation to the prosthetic foot.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a prosthetic foot with multiaxial rotation.

2. Related Art

Many individuals have lost a limb for various reasons including war, accident, or disease. In most instances these individuals are not only able to live relatively normal lives, but physically active lives as well. Oftentimes, these individuals are aided in their everyday lives by a prosthetic limb. The objective of prosthesis is to provide an artificial limb that simulates the function and natural feel of the replaced limb.

With respect to prosthetic feet, the development of a functional and natural artificial foot has been limited by material and imagination. Many designs have attempted to copy the anatomy of the foot or simulate its actions by replacing the bones and muscle with various mechanical simulation by replacing the entire foot with an energy storage element such as a spring. As the user steps onto the foot, the user's weight compresses the spring. As the user moves forward, the user's weight comes off the foot and the energy stored in the spring is used to propel the user forward.

Almost all of the past designs have focused on the major aspect of the prosthetic foot movement of the ankle or foot as it relates to walking or running. Few designs consider the lateral, or side to side rotation of the foot when the foot is used on varied or uneven terrain. It will be appreciated that the forefoot and heel of a natural foot rotates with a medial to lateral roll-over to accommodate variations in terrain. Most artificial feet of previous designs usually incorporate a unitary foot that is incapable of such movement.

Some designs have attempted to mimic the lateral rotation of the forefoot of a natural foot by splitting the forefoot region of the artificial foot longitudinally from the toe toward the heel, thereby effectively creating one or more “toes” on the prosthetic foot. This design is problematic, however, because the split creates at least two forefoot regions that can bend independent from one another and can result in an unnatural, out of balance feel to the user.

SUMMARY OF THE INVENTION

It has been recognized that it would be advantageous to develop a prosthetic foot with a variable stiffness arch block for providing smooth and steady multi-axial rotation laterally across the forefoot and heel regions of the foot to allow the wearer to maneuver uneven terrain. Additionally, it has been recognized that it would be advantageous to develop a prosthetic foot with a variable stiffness arch block for providing smooth and steady multi-axial rotation to assist with a natural medial to lateral roll-over of the prosthetic foot in response to uneven terrain.

In one aspect, the present invention provides for a prosthetic foot including an elongated foot member, extending between a toe section positioned at a toe location of a natural foot and a heel section positioned at a heel location of a natural foot. The elongated foot member also extends through an elevated arch section positioned between the toe section and heel section at a approximate arch location of a natural foot. An arch block is disposed below the elongated foot member under the elevated arch section. The arch block is sized and shaped to substantially fill a space or volume under the arch section. The arch block has geometric and physical properties that facilitate medial to lateral rotation to the prosthetic foot.

In another aspect, the arch block can have at least a medial portion and a lateral portion. The lateral portion can have a stiffness different than a stiffness of the medial portion. For example, the lateral portion can have a stiffness greater than a stiffness of the medial portion in order to provide a relatively softer instep and a relatively stiffer out-step. The stiffness of the medial and lateral portions can also vary between a forward and rearward section of the arch block.

DETAILED DESCRIPTION

The present invention relates generally to a prosthetic foot with variable medial to lateral stiffness to provide for multiaxial medial to lateral rotation. The foot can have a resilient elongated foot member extending in an arcuate shape between a toe end and a heel end with an elevated attachment section between the toe end and the heel end. The attachment section can be elevated above the toe end and heel end and can form an arch with an arch space disposed below the elongate foot member. The attachment section can be attached to the stump of an amputee. An elastic arch block can be disposed below the elongate foot member in the arch space. The arch block can have geometric and physical properties that allow medial to lateral rotation of the prosthetic foot.

As illustrated inFIGS. 1-3, a prosthetic foot, indicated generally at10, is shown in accordance with an embodiment of the present invention. The prosthetic foot10can include a resilient elongate foot member20, an elastic arch block50disposed under the elongate foot member, and an attachment device80for coupling the prosthetic foot to the stump of an amputee.

The resilient elongate foot member20can extend between a toe section22positioned at a toe location of a natural foot and a heel section24positioned at a heel location of a natural foot. The elongate foot member20can extend through an arcuate and elevated arch section26positioned between the toe section and heel section. The elongate foot member20can be formed of metal, composite, or plastic material, including for example, aluminum, Delrin®, fiberglass, carbon fiber in a resin matrix, polyurethane, polyethylene, and the like.

The elongate foot member20can be resilient member that can be displaced under loads applied when the user walks on the foot10and return to an original un-displaced shape when the loads are removed. Additionally, the elongate foot member20can form an energy storing leaf spring36. In this way, the elongate foot member20can store energy as the leaf spring36is displaced when the user steps down on the foot10and return the stored energy to the user when the user lifts up the foot.

The elastic arch section26can be disposed at the approximate arch location of a natural foot. The arch section can also include an upper attachment section28configured to attach to the stump of an amputee. The attachment section28can be on the arch section in a rearward position that corresponds to the approximate location of an ankle of a natural foot. An attachment device,80, as known in the art, can be coupled to the attachment section and can facilitate coupling of the prosthetic foot to the stump of an amputee.

The arch block50can be disposed below the elongated foot member20under the elevated arch section26. The arch block50can be sized and shaped to substantially fill the space or volume under the arch section. The arch block50can be formed from the same materials used in the elongated foot member20. The arch block can also be formed of fiberglass, plastic, carbon epoxy, aluminum, metal, wood, and the like. Additionally, the arch block50can be formed of an elastic material such that as the arch block is compressed under loads applied as the user walks on the foot, the arch block elastically returns to an original, uncompressed shape when the loads are removed.

The arch block50can also have geometric and physical properties that allow and facilitate medial to lateral rotation of the prosthetic foot10when a rotational load is applied to the foot. For example, the arch block50can include an angled toe end52and an angled heel end54that extend between a medial side56and a lateral side58of the arch block. The toe end52and heel end54can be angled at a non-perpendicular, oblique angle with respect to a longitudinal axis, indicated generally at70, and at a nonparallel, oblique angle with respect to a transverse axis, indicated generally at72, of the foot member of the prosthetic foot. Specifically, the intersection60of the toe end52with the medial side56can be positioned closer to the attachment section28, arch section26, or heel section24than the intersection62of the toe end52with the lateral side58. Similarly, the intersection64of the heel end54at the medial side56can be positioned farther from the attachment section28, arch section26, or heel section24than the intersection66of the heel end54with the lateral side58. In this way, the toe end52and heel end54can be angled at an oblique angle with respect to both the longitudinal axis70and transverse axis72of the foot member20.

It will be appreciated that the toe end52and heel end54can have a variety of angles with respect to one another in order to achieve various rotational configurations of the prosthetic foot10. Thus, in one aspect, the angle of the toe end52and the angle of the heel end54can be similar so that the toe end is parallel to the heel end, as shown inFIGS. 1-3. In another aspect, the toe end can be angled and the heel end can be perpendicular to the longitudinal axis of the prosthetic foot so as to enable rotation of the forefoot region of the prosthetic foot while limiting rotation of the heel. In yet another aspect, the toe end can be perpendicular to the longitudinal axis of the prosthetic foot and the heel end can be angled so as to enable rotation of the heel region of the prosthetic foot while limiting rotation of the forefoot region. Other angular relationships between the toe end and heel end of the arch block as known to those of skill in the art can be used to selectively increase or decrease medial to lateral roll-over of the prosthetic foot.

The arch block50can also have physical or material properties that can facilitate medial to lateral rotation of the prosthetic foot10. For example, as shown inFIGS. 4-5, a prosthetic foot100is shown in accordance with another embodiment of the present invention. The prosthetic foot100can be similar in many respects to the prosthetic foot10described above and shown inFIGS. 1-3and can include an elongate foot member20with an attachment device80. Additionally, the prosthetic foot100can have an arch block150awith at least a medial portion174and a lateral portion176.

The lateral portion174and the medial portion176can each have a different stiffness so as to provide a laterally variable stiffness across the arch block150. Thus, in one aspect, the lateral portion176can have a stiffness greater than the stiffness of the medial portion174to provide a relatively softer instep and a relatively stiffer out-step. Additionally, the arch block150bcan have an intermediate portion178between the medial and lateral portions. The intermediate portion178can have a greater stiffness than the medial and lateral portions.

Additionally, the arch block150can include a polymer material that can extend substantially the length of the medial portion174, the lateral portion176and the intermediate portion178. Accordingly, the polymer material of the intermediate portion178can have a greater durometer than the polymer material of the medial portion174and the polymer material of the lateral portion176, and polymer material of the lateral portion can have a greater durometer than the polymer material of the medial portion. In this way, the stiffness of the polymer material can facilitate a relatively softer instep and a relatively stiffer out-step.

Advantageously, having a softer instep and stiffer out-step, as provided by the arch block50or150allows the prosthetic foot to smoothly rotate and twist about multiple longitudinal axes of the elongate foot member20in response to variation or uneven surfaces in the terrain. This results in a smooth and steady multi-axial rotation of the elongate foot member that can assist the wearer maintain balance and maneuver over uneven terrain by providing a natural medial to lateral roll-over of a prosthetic foot.

As illustrated inFIG. 6, a prosthetic foot200is shown in accordance with another embodiment of the present invention. The prosthetic foot200can be similar in many respects to the prosthetic foot10and100described above and shown inFIGS. 1-5and can include an elongate foot member20with an attachment device80. Additionally, the foot200can include an arch block250having a forward section280and a rearward section282.

The stiffness of the forward section280can be different than the stiffness of the rearward section282. Thus, in one aspect, the forward section280can have a greater stiffness than the rearward section282to provide a softer heel-strike motion during a step. In another aspect, the forward section280can have a softer stiffness than the rearward section282so as to provide a softer toe off motion during a step.

In the case where the arch block250has medial, intermediate and/or lateral portions174,176, and178, the stiffness of the forward section280and rearward section282can also vary with the medial to lateral portions of the arch block. Thus, in one aspect, the forward section276aof the lateral portion176can have a greater stiffness than the rearward section276bof the lateral portion, and the rearward section274bof the medial portion can have a greater stiffness than the forward section274aof the medial portion174so as to facilitate a medial to lateral rotation of the prosthetic foot200in a generally medial-toe to lateral-heel direction.

In another aspect, the rearward section276bof the lateral portion176can have a greater stiffness than the forward section276aof the lateral portion, and the forward section274aof the medial portion174can have a greater stiffness than the rearward section274bof the medial portion174so as to facilitate a medial to lateral rotation of the prosthetic foot200in a generally medial-heel to lateral-toe direction.

Advantageously, having a variable stiffness longitudinally along the length of the foot as well as laterally across the width of the foot, as provided by the prosthetic foot200, allows the foot to smoothly rotate and twist about multiple longitudinal and lateral axes of the foot plate in response to variation or uneven surfaces in the terrain and also in response to dynamic movement of the foot by the user during strenuous physical activity. This smooth and steady multi-axial rotation of the foot can assist the wearer in maintaining balance and maneuvering over uneven terrain and during strenuous activity, such as running or hiking, by providing a natural medial to lateral roll-over of a prosthetic foot.

As illustrated inFIG. 7, a prosthetic foot300is shown in accordance with another embodiment of the present invention. The prosthetic foot300can be similar in many respects to the prosthetic feet10,100and200described above and shown inFIGS. 1-6and can include an elongate foot member20with an attachment device80. Additionally, the foot300can include an arch block350having an upper portion380and a lower portion382.

Advantageously, the upper portion380and the lower portion382can have different material properties from one another in order to facilitate multiaxial rotation of the prosthetic foot with respect to the attachment device80coupled to the attachment section28. For example, the upper portion380can have a different stiffness or hardness than the lower section382so that the applied loads between the arch block350and the elongated foot member20can be at least partially absorbed in the softer upper portion.

It will be appreciated that combinations of the various prosthetic feet10,100,200and300described herein can be combined in accordance with the principles and concepts of the present invention. For example, the foot300shown inFIG. 7having an arch block with different upper and lower sections can be combined with the foot200shown inFIG. 6having an arch block with different lateral sections. Such a foot may have different sections extending both laterally across the arch block and vertically across the arch block.

As illustrated inFIG. 8, a prosthetic foot400is shown in accordance with another embodiment of the present invention. The prosthetic foot400can be similar in many respects to the prosthetic feet10,100,200and300described above and shown inFIGS. 1-7and can include an elongate foot member20with an attachment device80and an arch block50. Additionally, the foot400can include an elastomeric bushing410disposed between the elongated foot member20and the arch block50. The elastomeric bushing410can facilitate multiaxial rotation of the arch block50with respect to the elongated foot member20, or multiaxial rotation of the elongated foot member20with respect to the arch block50. In one aspect, the elastomeric bushing410can be a rubber o-ring. In another aspect, the elastomeric bushing410can be a polymeric washer. It will be appreciated that other elastomeric materials and geometric configurations can be used for the elastomeric bushing, as known in the art. For example, the elastomeric bushing410can be an o-ring with a uniform wall thickness, a cylindrical washer with a uniform wall thickness, a cylinder with uneven wall thickness or length from front to back or side to side, an o-ring with uneven wall thickness from front to back or side to side, and an assembly with stiffer or softer materials from front to back or side to side. Additionally, the elastomeric bushing can include the elastomeric bushing a layer of elastomeric material, a strip of elastomeric material, a grid of elastomeric material, and overlapping strips of elastomeric material as described in greater detail below.

As illustrated inFIG. 9, a prosthetic foot500is shown in accordance with another embodiment of the present invention. The prosthetic foot500can be similar in many respects to the prosthetic feet described above and shown inFIGS. 1-8and can include an elongate foot member20with an attachment device80and an arch block50. Additionally, the foot500can include strips510of elastomeric material disposed between the elongated foot member20and the arch block50. The elastomeric strips510can facilitate multiaxial rotation of the arch block50with respect to the elongated foot member20, or multiaxial rotation of the elongated foot member20with respect to the arch block50.

In one aspect, the prosthetic foot500can have a plurality of elastomeric strips510disposed laterally across a top surface550of the arch block50, and each of the elastomeric strips510can have a different stiffness so as to facilitate lateral movement of the foot with respect to the elongate foot member20. In another aspect, the prosthetic foot500can have a plurality of elastomeric strips disposed longitudinally across the top surface550of the arch block to facilitate longitudinal movement of the foot with respect to the elongate foot member20. Additionally, lateral and longitudinal elastomeric strips510can be combined on the top surface to facilitate multiaxial rotation of the arch block50with respect to the elongated foot member20.

It will be appreciated that various combinations of the geometric features and physical properties of the prosthetic foot can be made so as to configure the prosthetic foot for a particular application. For example, in one embodiment, the prosthetic foot may have an arch block only having angled toe or heel ends. As another example, the prosthetic foot may have an arch block with both angled toe and heel ends, and also with medial and lateral portions having differing stiffness. As yet another example, the prosthetic foot can include angled toe and heel ends, medial and lateral portions with variable lateral stiffness, and forward and rearward sections with variable lateral stiffness. Thus, the prosthetic foot of the present invention can advantageously be customized to accommodate a desired medial to lateral rotation or roll over.