Abstract:
A multi-axis prosthetic ankle includes a bottom component connected to a prosthetic foot, a lower leg connection component connected to a prosthetic lower leg, an elastomeric material securely connecting the bottom component with the lower leg connection component, and a mechanical device suspended in the elastomeric material. The mechanical device is formed of a first bracket connected to the bottom component and a second bracket connected to the lower leg connection component. The first and second brackets interlockingly float in the elastomeric material, and are not in direct contact with one another, thereby permitting relative movement of the bottom component and the lower leg connection component by deformation of the elastomeric material. At least one mechanical stop is positioned to prevent the relative angular movement of the ankle from deforming the elastomeric material beyond the elastic limit thereof.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates generally to prosthetic devices, and more particularly to a multi-axis prosthetic ankle joint.  
           [0003]    2. Discussion of the Background  
           [0004]    A prosthetic ankle is a component which connects a prosthetic foot with a prosthetic lower leg. For smooth walking, especially, across uneven ground, it is important for the ankle to be designed for a full range of foot motion with respect to the lower leg prosthesis. Most prosthetic ankles currently on the market are modular in design and do not provide optimally controlled multi-axis motion. Often the prosthetic ankle has such a low stiffness that it effectively reduces any functional capabilities of the attached prosthetic foot, resulting in a choppy, unnatural and uncomfortable gait. Some ankles require adjustments to the assembly in order to achieve the desired function.  
           [0005]    A full range of motion may be accomplished by the use of multiple axes of rotation in the ankle joint. However, conventional prosthetic ankle joints that provide multi-axis motion tend to require extensive maintenance including the replacement of parts in order to function properly. This is because the conventional ankle joint designs require elastic members to slide in contact with either a rigid surface, which is typically metallic, or another elastic surface. This surface-to-surface sliding motion is the primary cause of material breakdown.  
         SUMMARY OF THE INVENTION  
         [0006]    It is therefore an object of the present invention to provide a multi-axis prosthetic ankle joint which does not suffer from the shortcomings of the prior art.  
           [0007]    According to a feature of the invention as set forth in the claims, a multi-axis prosthetic ankle comprises a bottom component adapted to be connected to a prosthetic foot, a lower leg connection component adapted to be connected to a prosthetic lower leg, an elastomeric material securely connecting the bottom component with the lower leg connection component, and a mechanical device suspended in the elastomeric material. The mechanical device comprises a first rigid element connected to the bottom component but not to the lower leg connection component, and a second rigid element connected to the lower leg connection component but not to the bottom component. The first and second elements interlockingly float in the elastomeric material, and are not in direct contact with one another, so as to permit relative movement of the bottom component and the lower leg connection component by deformation of the elastomeric material.  
           [0008]    By “interlockingly float” it is meant that the first and second elements are suspended in the elastomeric material in close relation to one another, but do not contact one another except through the intermediary of the elastomeric material. Since the deformation of the elastic material permits multi-axis relative movement of the bottom component and the lower leg connection component, including translational movement, the ankle joint of the invention can simulate natural ankle motion by providing plantar flexion, dorsi flexion, inversion, eversion, translation and internal/external rotational movement. Such motion is optimally controlled by the multi-axis deformation of the elastic material, without sacrificing the energy return of the prosthetic foot. Further, since the components of the mechanical device are bonded to, and encased by, the elastomeric material, the ankle has the ability to absorb and damp both rotational and linear impacts.  
           [0009]    Since there is no surface-to-surface sliding motion within the ankle, the material breakdown which might otherwise occur due to surface-to-surface sliding motion is reduced or eliminated.  
           [0010]    As force is applied to the ankle, the ankle moves in rotation and translation with a fluid motion by deforming the rubber medium. According to a further feature of the invention, at least one mechanical stop is positioned to prevent the relative angular movement of the ankle from deforming the elastic material beyond the elastic limit thereof. Since the deformation of the elastomeric material is thus always kept within the elastic limit, any tendency of breakdown in the elastomeric material is further reduced.  
           [0011]    According to a further feature of the invention, the mechanical device comprises a generally U-shaped first part connected to the bottom component so as to define a first aperture, and a generally U-shaped second part connected to the lower leg connection component so as to define a second aperture. The first part floatingly extends through the second aperture, and the second part floatingly extends through the first aperture.  
           [0012]    According to yet a further feature of the invention, a multi-axis prosthetic ankle comprises a bottom component adapted to be connected to a prosthetic foot, a lower leg connection component adapted to be connected to a prosthetic lower leg, an elastomeric material securely connecting the bottom component with the lower leg connection component, and mechanical means for limiting a deformation of the elastic material. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:  
         [0014]    [0014]FIG. 1 is a top plan view of an embodiment of a multi-axis prosthetic ankle according to the invention, showing the encasing elastomeric material in phantom lines;  
         [0015]    [0015]FIG. 2 is a front elevation view of the multi-axis prosthetic ankle of FIG. 1;  
         [0016]    [0016]FIG. 3 is a side elevation view of the multi-axis prosthetic ankle of FIG. 1;  
         [0017]    [0017]FIG. 4 is a top plan view of the lower leg connection component of the embodiment of FIG. 1;  
         [0018]    [0018]FIG. 5 is a front elevation view of the lower leg connection component of FIG. 4;  
         [0019]    [0019]FIG. 6 is a front elevation view of the bracket mounted to the lower leg connection component in FIG. 1;  
         [0020]    [0020]FIG. 7 is a top plan view of the bottom component of the embodiment of FIG. 1;  
         [0021]    [0021]FIG. 8 is a sectional view taken along lines VIII-VIII of FIG. 7; and  
         [0022]    [0022]FIG. 9 is a sectional view of taken along lines IX-IX of FIG. 1. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    Referring now to the attached figures which illustrate a non-limiting embodiment of a multi-axis prosthetic ankle according to the invention, and more particularly to FIGS. 1 through 3 which, for clarity of illustration, show the elastomeric casing in phantom lines to reveal the encased components of the mechanical device (rigid mechanical means), the main components of the multi-axis prosthetic ankle are the bottom component  10 , the lower leg connection component  20 , the mechanical device  30  (rigid mechanical means) and the elastomeric casing  40  bonded to the bottom component and the lower leg connection component, and floatingly encasing the elements of the mechanical device.  
         [0024]    Referring more particularly to FIGS. 7 and 8, the bottom component  10  comprises a generally circular disk like base  12 , and a first “U” shaped bracket  14  (first rigid element) projecting perpendicularly upwardly from the base. The first bracket  14  extends generally diametrically on the base and defines a slot like first aperture  16  having respective top and bottom surfaces  16   a  and  16   b.  The base  12  and first bracket  14  are preferably integrally formed from a rigid material such as stainless steel, but could be formed of any other rigid material such as titanium, aluminum or rigid plastic. The base  12  preferably includes a threaded center hole  18  to accept a bolt for the securement of the bottom component  10  to a prosthetic foot.  
         [0025]    The lower leg connection component  20  also has a generally circular disk like base  22 , and has a pyramid part  24  projecting perpendicularly upward from a central portion of the upper surface of the base  22  for connection of the ankle joint to a lower leg prosthesis. The pyramid part  24  may be of a generally conventional design. The lower leg connection component  20  is also preferably integrally formed of stainless steel, but can also be formed of other rigid materials including titanium, aluminum or rigid plastic. A lower portion  26  of the pyramid part  24  may be circular to accept a separate aluminum snap on dome  28 .  
         [0026]    A second bracket  31  (second rigid element) is mounted to the lower surface of the base  22 , for example by bolts  32  passing through bolt holes  34  in the base  22  and the legs of the second bracket. The second bracket  31  is also “U” shaped to define a slot like second aperture  36  having, when mounted to the base  22 , respective top and bottom surfaces  36   a  and  36   b.  Moreover, a shim  38  may be positioned between one leg of the bracket  31  and the bottom of the base  22 , as will be explained below. To this end, one of the legs  31   a  of the second bracket  31  is shorter than the other. The bracket  31  is preferably formed of aluminum alloy, but can be formed of other rigid materials, including stainless steel, titanium or a hard plastic.  
         [0027]    During assembly of the multi-axis prosthetic ankle, the second bracket  31  is interlockingly positioned within the slot like aperture  16  of the first bracket  14  to form the mechanical device  30 , after which the second bracket  31  is bolted to the lower surface of the base  22  of the lower leg connection component  20  via the bolts  32  and the shim  38 . At this time, a shim  38  of a proper thickness is selected on the basis described below, and is positioned between the end of the shorter one of the legs of the second bracket  31  and the lower surface of the base  22 . As will be readily understood by those skilled in the art, the shim has a through hole for the bolt  32 , and the legs  31   a  and  31   b  of the second bracket  31  have respective threaded through holes  31   c  and  31   d.  The resulting assembly is generally shown in FIGS.  1 - 3 .  
         [0028]    Subsequently, the assembly of the bottom component  10 , lower leg connection component  20  and the second bracket  31  is placed within a mold (not shown). At this time, the assembly of the lower leg connection component  20  and second bracket  31  is held in a slightly elevated position so that the surfaces  36   a  and  36   b  of the second aperture  36  do not contact either of the surfaces  16   a  or  16   b  of the first bracket  14 . Instead, the second bracket  31  is held so as to float without contact with the first bracket  14 . While the ankle components are held in this condition, rubber is injected into the mold and permitted to harden. The rubber is preferably a thermoset rubber polymer having a high resistance and memory under cyclical loading. Examples are butyl rubber, ethylene-propylene rubber, neoprene rubber, nitrile rubber, polybutadiene rubber, polyisoprene rubber, stereo rubber, styrene-butadiene rubber, natural rubber or a combination of two or more of these rubbers.  
         [0029]    The polymer rubber (elastomeric material) thereby encases and bonds to the bottom component  10 , the lower leg connection component  20  and the mechanical device  30  composed of the interlocking brackets  14  and  31 . The rigid components are thus fused together with the polymer rubber to form a flexible assembly. This allows for a smooth transition through the entire gait cycle, from heel strike, through midstance to toe off. As can be seen from FIG. 9, the interlocking brackets  14  and  31  do not contact one another but instead are floatingly bonded through the intermediary of the intervening rubber material  42  of the casing  40 . The peripheral surfaces of the bases  12  and  22  of the bottom component and the lower leg connection component, respectively, have annular concave recesses  12   a  and  22   a  at their circumferential peripheries. These annular recesses improve the grip of the rubber material bonded to the components  10  and  20 .  
         [0030]    The snap on dome  28  is then mounted to the pyramid part  24 , and the ankle assembly is incorporated into a lower leg prosthesis in a conventional manner.  
         [0031]    During walking, relative motion (translation and multi-axis rotation) between the bottom component  10  mounted to the foot prosthesis, and the lower leg connection component  20  mounted to the lower leg prosthesis is permitted by the elastic deformation of the rubber material of the casing  40 . The motion is thus polycentric and multi-axial with no fixed center of rotation or translation. Moreover, there is no surface to surface contact of the rigid parts  14  and  31  of the mechanical device  30 , and so the material breakdown which could otherwise occur due to surface rubbing is minimized or avoided. The rubber material of the casing  40  also absorbs impact energies and so acts as a vibration dampening device.  
         [0032]    The casing may optionally include a protruding enlargement  60  at the posterior part of the ankle. The tendon  60  serves to stiffen the ankle when the toe is loaded.  
         [0033]    By selecting a shim  38  of the proper thickness, one can control the thickness of the rubber material  42  in the spaces which separate the brackets  14  and  30 . One can thereby control the compliance of the joint depending upon the expected loads, which can be anticipated by the weight and general physical activity level of the intended user. This done by selecting a shim  38  providing a desired height “H” for the aperture  36  which allows a predetermined spacing between the brackets, and by the selection of the hardness of the rubber material of the casing  40 . A shore hardness A of between 70 and 99 is usually selected for adults, whereas a shore hardness A of between 50 and 70 is usually selected for children. For easy reference, the snap on dome  28  can be color coded to the rubber hardness.  
         [0034]    The angular degree of rotational motion between the bottom component  10  and the lower leg connection component  20  is limited by stops. In the preferred embodiment, the stops take the form of a limit of the compression of the rubber material of the casing due to the turning of the interlocking brackets  14  and  31 . That is, by selecting a proper shim for providing a desired height “H” for the aperture  36 , one also selects the resulting thickness of the rubber material present between the brackets, e.g., the intervening rubber material at  42 . As the ankle pivots during walking, the rigid surfaces of the brackets  14  and  31  approach one another while compressing the intervening rubber material of the casing. The resistance of the rubber material to further compression increases as the ankle pivots. When this resistance equals the turning load on the ankle, the rubber material acts as a fixed stop against further rotation. Since the expected load on the ankle and the compression resistance of the rubber material are known, one skilled in the art can select a shim for a desired height “H” to permit a predetermined rotation stop for the ankle. Of course, other forms of the rigid stops could instead be used.  
         [0035]    The ankle according to the invention has a higher load range of increasing moment of resistance, compared to prior art ankles which flatten out over lower load ranges. Preferable angles of movement permitted by the stops are as follows:  
         [0036]    Internal/External rotation: ±11° to 15°.  
         [0037]    Plantar flexion: 13° to 15°.  
         [0038]    Dorsi flexion: 13° to 15°.  
         [0039]    Inversion/Eversion: ±5° to 10°.  
         [0040]    Anterior/Posterior translation: ±0.10 to 0.375 inches.  
         [0041]    Medial/Lateral translation: ±0.05 to 0.250 inches.  
         [0042]    Vertical displacement: 0.030 to 0.375 inches.  
         [0043]    Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described herein.