Patent Publication Number: US-11026814-B2

Title: Pivot-flex foot

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of the filing date of international PCT Application No. PCT/US2017/036480, filed Jun. 8, 2017 that in turn claims priority to U.S. Provisional Patent Application Ser. No. 62/347,415, filed Jun. 8, 2016, which are hereby incorporated by reference in their entirety. 
    
    
     GOVERNMENT RIGHTS 
     This invention was made with government support under Grant Nos. A9243C and I01 RX002456, awarded by the Department of Veterans Affairs. The government has certain rights in the invention. 
    
    
     BACKGROUND 
     Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
     Amputees are prone to pain and injury caused by loads applied to the residual limb through the prosthetic socket, as well as through compensatory gait adaptations. One source of pain and discomfort is epidermoid cysts which occur where the skin of the residual limb rubs against the brim of the socket. These cysts often develop over years of prosthesis use, and can become painful enough to prevent use of the prosthesis. These and other skin problems are attributed to the shear stress and humidity seen by the skin of the residual limb of lower-limb prosthesis users. Shear stress has been shown to cause blisters, and is a primary cause of callosities and trophic ulcers. A major source of shear stress on the residual limb of amputees is transverse-plane torque. Transverse-plane torque is a normal part of walking in non-amputees and increases in the inside leg of a turn. Turning steps compose a large fraction of the steps of daily living. In non-amputees, transverse-plane torque is transmitted from the ground to the trunk through the bones and muscles of the leg. In amputees, the torque is transmitted from the prosthetic socket to the skin of the residual limb. Amputees experience less transverse-plane torque during walking than non-amputees, due to compensatory gait patterns. Prosthetic legs for trans-tibial amputees typically consist of a prosthetic foot which is connected by a rigid pylon to the socket which interfaces with the residual limb. Because rotation is not allowed between the foot and the socket, any rotation between the foot and the knee must occur at the knee or between the residual limb and the socket. Thus, amputees must either adopt a compensatory gait pattern with reduced transverse-plane rotation or accept sliding between the residual limb and the socket. 
     In addition to skin problems at the interface between the residual limb and the socket, prosthesis users also suffer from increased rates of musculoskeletal problems such as osteoarthritis and chronic back pain compared with non-amputees. Improving prosthesis comfort during walking could lead to a more symmetric weight distribution and decreased risk of osteoarthritis. 
     While the human ankle contains a complex set of joints that allows rotation in each of the sagittal, coronal, and transverse planes, conventional prosthetic feet are typically designed to provide rotation in the sagittal plane only. Split toe or other multiaxial feet can provide some coronal-plane motion. A transverse rotation adapter can be added in series with the prosthesis pylon. While transverse rotation adapters increase transverse-plane rotation and decrease peak joint torques in the transverse plane rotation, their stiffness cannot be adjusted by the user and if excessively compliant may reduce amputee dynamic stability. Therefore, an improved prosthesis to couple the sagittal plane motion to the transverse plane may be desired. 
     SUMMARY 
     Example devices described herein allow adaptation of a prosthetic foot in the medial-lateral direction, including pronation and supination of the prosthetic foot. The device described herein may mimic the functions of a normal foot by coupling a rotation of prosthetic foot with respect to the sagittal plane to a rotation of the prosthetic foot with respect to the transverse plane. The disclosed devices may improve walking, running, and other forms of bipedal motion for people with prosthetic feet. In particular, the disclosed devices may allow for reduced transverse-plane torque in the residual limb of the user. The disclosed devices may further help improve the gait of the user, thereby reducing musculoskeletal problems of the user. Robotic prostheses may also benefit from the mechanical adaptations of the invention to make them more versatile and functional. 
     Thus, in one aspect, a prosthetic device is provided including (a) an ankle component, (b) a foot component coupled to the ankle component, wherein the foot component has a longitudinal length extending at least partially along a sagittal plane of a user when the prosthetic device is in use, wherein the foot component has a thickness extending at least partially along a transverse plane of a user when the prosthetic device is in use, and (c) a coupling mechanism positioned between the foot component and the ankle component, wherein the coupling mechanism couples a rotation of the foot component with respect to the sagittal plane to a rotation of the foot component with respect to the transverse plane. 
     These as well as other aspects, advantages, and alternatives, will become apparent to those of ordinary skill in the art by reading the following detailed description, with reference where appropriate to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cross-section view of an example cantilever leaf spring with a vertical force at the toe, according to an example embodiment. 
         FIG. 2  is a transverse cross-sectional view of a cantilever leaf spring aligned with the sagittal plane, according to an example embodiment. 
         FIG. 3  is a transverse cross-sectional view of a cantilever leaf spring misaligned with the sagittal plane, according to an example embodiment. 
         FIG. 4  is a perspective view of an example prosthetic foot, according to an example embodiment. 
         FIG. 5  is a perspective view of another example prosthetic foot, according to an example embodiment. 
         FIG. 6  is a side cross-section view of a lower cantilever leaf spring and an upper cantilever leaf spring of the prosthetic foot of  FIG. 5 , according to an example embodiment. 
         FIG. 7  is a front view of the example prosthetic foot of  FIG. 5 , according to an example embodiment. 
         FIG. 8  is a top view of an example cosmetic foot shell, according to an example embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Example methods and systems are described herein. It should be understood that the words “example,” “exemplary,” and “illustrative” are used herein to mean “serving as an example, instance, or illustration.” Any embodiment or feature described herein as being an “example,” being “exemplary,” or being “illustrative” is not necessarily to be construed as preferred or advantageous over other embodiments or features. The example embodiments described herein are not meant to be limiting. It will be readily understood that the aspects of the present disclosure, as generally described herein, and illustrated in the figures, can be arranged, substituted, combined, separated, and designed in a wide variety of different configurations, all of which are explicitly contemplated herein. 
     Furthermore, the particular arrangements shown in the Figures should not be viewed as limiting. It should be understood that other embodiments may include more or less of each element shown in a given Figure. Further, some of the illustrated elements may be combined or omitted. Yet further, an example embodiment may include elements that are not illustrated in the Figures. 
     As used herein, with respect to measurements, “about” means+/−5%. 
     As used herein, “sagittal plane” means a plane that is parallel to a length of a prosthetic foot, dividing the prosthetic foot into left and right portions. 
     As used herein, “coronal plane” means a plane that is perpendicular to a length of a prosthetic foot, dividing the prosthetic foot into back and front portions. 
     As used herein, “transverse plane” means a plane that is parallel to a width of a prosthetic foot, dividing the prosthetic foot into top and bottom portions. 
     As used herein, “coupling ratio” means a ratio between rotation of the prosthetic foot in the sagittal plane to rotation of the prosthetic foot in the transverse plane. For example, if a rotation of three degrees in the sagittal plane causes a rotation of one degree in the transverse plane, then the prosthetic foot has a coupling ratio of 3:1. 
     The human ankle is a complex mechanism that does not behave like a simple hinge. Instead, rotations in each of the sagittal, coronal, and transverse planes are allowed and coupled together. In particular, the axis of rotation of the talocrural joint during ankle dorsiflexion is inclined downwards and laterally relative to horizontal, and the rotation ranges from 10 to 26 degrees among individuals. This rotation couples dorsiflexion with internal rotation of the shank relative to the foot, a feature which is not replicated in traditional prosthetic feet and ankles. The device described herein may mimic the functions of a normal foot by coupling a rotation of prosthetic foot with respect to the sagittal plane to a rotation of the prosthetic foot with respect to the transverse plane, as described in more detail with reference to the figures below. The disclosed devices may improve walking, running, and other forms of bipedal motion for people with prosthetic feet. 
     Modern prosthetic feet are typically composed of a carbon-fiber composite cantilever leaf spring (called the keel) enclosed in a cosmetic silicone foot shell. The cosmetic foot shell is very flexible and the mechanical behavior of the foot is determined by the shape of the composite leaf spring. The typical keel has a non-uniform rectangular cross-section with a large width-to-thickness ratio ranging from 2:1 to 10:1. Because the cantilever leaf spring is much more flexible in the sagittal plane than in the other planes, the rotation of the foot is effectively confined to the sagittal plane.  FIG. 1  shows a schematic representation of the sagittal-plane rotation of an example cantilever leaf spring. Because the stiffness of the cantilever leaf spring is distributed, there is no single axis of rotation. Instead, the effective axis of rotation moves forward during the gait cycle as the center of pressure progresses from the heel to the toe. Additionally, many keels are split along the sagittal plane. This allows differential deflection between the medial and lateral cantilever leaf springs, which emulates coronal-plane rotation. However, this does not translate to a rotation with respect to the transverse plane. 
     A cantilever leaf spring can provide coupling between flexure in the sagittal and transverse planes by tailoring the cross-section of the cantilever leaf spring. This can be seen by considering a rectangular cross-section subject to a bending moment M y  in the sagittal plane. If the principal moments of inertia are aligned with the sagittal plane moment as shown in the transverse cross-sectional view of the cantilever leaf spring in  FIG. 2 , the deflection of the beam obeys: 
                           ∂   2     ⁢     w   z         ∂     x   2         =       M   y       EI   zz         ,           ∂   2     ⁢     w   y         ∂     x   2         =       -       M   z       EI   yy         =   0               (   1   )               
where E is the modulus of elasticity of the material, w y  and w z  are the deflections in they and z directions, respectively, and I yy  and I zz  are the second moments of area of the cross-section.
 
     If the transverse cross-section of the cantilever leaf spring is rotated as in  FIG. 3 , a sagittal plane bending moment results in deflections in both they and z directions: 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     The ratio of the deflections is: 
     
       
         
           
             
               
                 
                   
                     
                       
                         
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     For a rectangular cross-section, 
                 Izz   Iyy     =       t   2       w   2         ,         
where t is the thickness and w is the width of the cross-section. If the rotation angle is constant and the thickness is small relative to the width, then
 
               Izz   Iyy     ⪡     1   ⁢           ⁢   and   ⁢           ⁢       w   y       w   z         ≈       tan   ⁡     (   θ   )       .           
Thus, coupling between sagittal-plane and transverse-plane rotation can be achieved in a cantilever beam with a rectangular cross-section if the cross-section is misaligned with the sagittal plane.
 
     Thus, in a first aspect,  FIG. 4  illustrates an example prosthetic device  100  in accordance with one embodiment of the invention. As shown in  FIG. 4 , the prosthetic device  100  may include an ankle component  102 , and a foot component  104  coupled to the ankle component  102 . The ankle component  102  and the foot component may be unitary components, or they may be separate components that are coupled together. The foot component  104  has a longitudinal length  106  extending at least partially along a sagittal plane of a user when the prosthetic device  100  is in use. In addition, the foot component  104  has a thickness  108  extending at least partially along a transverse plane of a user when the prosthetic device  100  is in use. The prosthetic device  100  may also include a coupling mechanism  110  positioned between the foot component  104  and the ankle component  102 . The coupling mechanism  110  couples a rotation of the foot component  104  with respect to the sagittal plane to a rotation of the foot component  104  with respect to the transverse plane. A coupling ratio of the rotation of the foot component  104  with respect to the sagittal plane to the rotation of the foot component  104  with respect to the transverse plane ranges from about 2:1 to about 6:1. The coupling mechanism  110  is configured to cause the foot component  104  to rotate away from a midline of the user when the prosthetic device  100  is in use. 
     The coupling mechanism  110  may take a variety of forms. In one example, as shown in  FIG. 4 , the coupling mechanism  110  comprises a hinge  112  positioned between the ankle component  102  and the foot component  104 . As shown in  FIG. 4 , the hinge  112  is positioned at an offset angle with respect to the sagittal plane of a user. The offset angle of the hinge  112  ranges from about 5 degrees to about 30 degrees. As such, the hinge  112  causes the foot component  104  to move up and down as well as in and out, thereby coupling a rotation of the foot component  104  with respect to the sagittal plane to a rotation of the foot component  104  with respect to the transverse plane. The hinge  112  may further include a torsion spring  114  configured to bias the hinge  112  to a closed position. 
     In another example, as shown in  FIG. 5 , the foot component  104  comprises a lower cantilever leaf spring  116 . In such an embodiment, the coupling mechanism  110  comprises one or more upper cantilever leaf springs  118  each having a transverse cross-section defined by a width extending at least partially along a coronal plane of a user when in use and a thickness extending at least partially along the transverse plane of a user when in use.  FIG. 6  illustrates a side cross-section view of the lower cantilever leaf spring  116  and an upper cantilever leaf spring of the one or more upper cantilever leaf springs  118 . The transverse cross-section of the one or more upper cantilever leaf springs  118  may take a variety of forms. 
     In general, the transverse cross-section of the one or more upper cantilever leaf springs  118  may be any shape as long as (i) the stiffness in the coronal plane and the transverse plane are much different (e.g., the one or more upper cantilever leaf springs  118  are much stiffer in one direction than in the other direction), and (ii) the minor principal axis of the one or more upper cantilever leaf springs  118  is misaligned with the sagittal plane. In one example, the transverse cross-section is L-shaped. In another example, the transverse cross-section is triangular-shaped. 
     In yet another example, as shown in  FIGS. 5-7 , the transverse cross-section is rectangular-shaped. In such an example, a ratio of the width to the thickness of the one or more upper cantilever leaf springs may range from about 2:1 to about 20:1. As shown in  FIG. 7 , the transverse cross-section of the one or more upper cantilever leaf springs  118  are each misaligned with the sagittal plane by a rotation angle such that if the foot component  104  is subjected to a bending moment along the sagittal plane, the sagittal plane bending moment will simultaneously deflect the foot component  104  along both the sagittal plane and the transverse plane. The rotation angle of the one or more upper cantilever leaf springs  118  with respect to the sagittal plane may range from about 0 degrees to about 30 degrees. In one example, the rotation angle is constant along the longitudinal length of the foot component. In another example, the rotation angle varies along the longitudinal length of the foot component. 
     In one embodiment, as shown in  FIG. 5 , the lower cantilever leaf spring  116  is coupled to a first end  120  of the one or more upper cantilever leaf springs  118 , and the ankle component  102  is coupled to a second end  122  of the one or more upper cantilever leaf springs  118 . Further, as shown in  FIG. 5 , the first end  120  of the one or more upper cantilever leaf springs  118  may be coupled to the lower cantilever leaf spring  116  via a mechanical fastener  124 . The mechanical fastener  124  may comprise a nut and bolt, a screw, or a rivet, as non-limiting examples. Other mechanical fasteners are possible as well. In another embodiment, an adhesive may be used to secure the first end  120  of the one or more upper cantilever leaf springs  118  to the lower cantilever leaf spring  116 . In another embodiment, the one or more upper cantilever leaf springs  118  and the lower cantilever leaf springs  116  may be manufactured as one continuous piece, such that the first end  120  of the one or more upper cantilever leaf springs  118  is secured to the lower cantilever leaf spring  116  during manufacturing. 
     In one embodiment, as shown in  FIG. 5  and  FIG. 7 , the ankle component  102  is coupled to the second end  122  of the one or more upper cantilever leaf springs  118  via a bracket  126 . The bracket  126  may include an upper portion  128  removably coupled to a lower portion  130 . The upper portion  128  and the lower portion  130  may each include one or more angled cutouts  132  configured to receive the one or more upper cantilever leaf springs  118  at the rotation angle. As such, the bracket  126  may help maintain the rotation angle of the one or more upper cantilever leaf springs  118  such that the transverse cross-section of the one or more upper cantilever leaf springs  118  are each misaligned with the sagittal plane. 
     In one example, the one or more upper cantilever leaf springs  118  comprises a single leaf spring. In another example, the one or more upper cantilever leaf springs  118  comprises a plurality of leaf springs, such as three or four leaf springs. In yet another example, as shown in  FIGS. 5 and 7 , the one or more upper cantilever leaf springs  118  comprises two leaf springs  118 A,  118 B. In such an example, as shown in  FIG. 7 , each of the two leaf springs  118 A,  118 B are misaligned with the sagittal plane by the rotation angle. 
     In another example, as shown in  FIG. 5 , the prosthetic foot  100  may further include an elastomer material  134  positioned between the lower cantilever leaf spring  116  and the one or more upper cantilever leaf springs  118 . The elastomer material  134  may comprise a foam material, rubber, neoprene, or silicone, as non-limiting examples. The elastomer material  134  may provide a cushioning and dampening between the lower cantilever leaf spring  116  and the one or more upper cantilever leaf springs  118 . 
     In another embodiment, as shown in  FIGS. 5 and 7 , the prosthetic device  100  may include one or more wedges  136  coupled to a bottom surface  138  of the lower cantilever leaf spring  116 . In one particular example, as shown in  FIG. 5 , the one or more wedges  136  comprise a toe wedge  136 A positioned under a front portion of the lower cantilever leaf spring  116  and a heel wedge  136 B positioned under a rear portion of the lower cantilever leaf spring  116 . In another example, the one or more wedges  136  comprises a single wedge extending a length of the foot component  104 . As shown in  FIG. 7 , a lateral border  142  of the foot component  104  may be lower than a medial border  144  of the foot component  104 . As such, the one or more wedges  136  may be shaped and angled such that a bottom surface  140  of the one or more wedges  136  is parallel to a ground surface when in use. The one or more wedges  136  are configured to distribute the load from the foot component  104  to the ground surface. 
     The lower cantilever leaf spring  116  may comprise a first material, the one or more upper cantilever leaf springs  118  may comprise a second material, and the one or more wedges  136  may comprise a third material that is different than the first material and the second material. In one example, the first material is the same as the second material such that the lower cantilever leaf spring  116  and the one or more upper cantilever leaf springs  118  comprise the same material. In another example, the first material is different than the second material such that the lower cantilever leaf spring  116  and the one or more upper cantilever leaf springs  118  comprise different materials. In one example, the first material of the lower cantilever leaf spring  116  comprises a stiffer material than the second material of the one or more upper cantilever leaf springs  118 . In another example, the first material of the lower cantilever leaf spring  116  comprises a more compliant material than the second material of the one or more upper cantilever leaf springs  118 . 
     The first material may comprise carbon fiber, carbon fiber composite, high density nylon material, steel, aluminum, fiberglass, or a sandwich panel with carbon fiber or fiberglass outer layers around a foam, honeycomb, or balsa core. The second material may comprise carbon fiber, carbon fiber composite, high density nylon material, steel, aluminum, fiberglass, or a sandwich panel with carbon fiber or fiberglass outer layers around a foam, honeycomb, or balsa core. The third material may comprise nylon, ABS, PLA, poylethylene, carbon fiber, or a fiberglass composite. 
     As shown in  FIG. 5 , the prosthetic device  100  may further include a pyramid adapter  146  coupled to the ankle component  102 . The pyramid adapter  146  is configured to be coupled to a prosthetic limb of a user. Further, as shown in  FIG. 8 , the prosthetic device  100  may further include a cosmetic foot shell  148  configured and arranged for disposing over at least a portion of the foot component  104 . The cosmetic foot shell  148  may include a cavity  150  into which the foot component  104  may be positioned. 
     It should be understood that arrangements described herein are for purposes of example only. As such, those skilled in the art will appreciate that other arrangements and other elements (e.g. machines, interfaces, functions, orders, and groupings of functions, etc.) can be used instead, and some elements may be omitted altogether according to the desired results. Further, many of the elements that are described are functional entities that may be implemented as discrete or distributed components or in conjunction with other components, in any suitable combination and location, or other structural elements described as independent structures may be combined. 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope being indicated by the following claims, along with the full scope of equivalents to which such claims are entitled. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.