Abstract:
Disclosed herein are flexible prosthetic components that are designed to be snap-fit to bone of a patient. The prosthetic components each have an outer articular surface and an inner bone contacting surface opposing the outer articular surface. The bone contacting surface has an anterior surface and an opposing posterior surface configured to contact corresponding anterior and posterior surfaces of the patient&#39;s bone. At least one of the anterior and posterior surfaces includes one or more protrusions extending outwardly therefrom. The anterior and posterior surfaces of the prosthetic components may flex toward and away from one another such that the one or more protrusions may snap-fit into corresponding recesses in the bone. The bone of the patient may be resected to include planar surfaces or resurfaced to include a curved surface corresponding to the respective bone contacting surface of the prosthetic components.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to prosthetic components and surgical methods for artificial joint replacement, and in particular relates to flexible prosthetic components that can be snap-fit onto resected bone. 
       BACKGROUND OF THE INVENTION 
       [0002]    Joint replacement surgery to remove and replace arthritic or dysfunctional joint surfaces with orthopedic prosthesis is widespread today. Hip and knee replacement operations are among the most commonly performed operations in the U.S. Knee replacement surgery can involve one or more damaged knee surfaces. Total knee arthroplasty (“TKA”) is used to treat various forms of knee arthropathies, and is performed by removing and replacing all damaged articulating surfaces of the knee with a prosthetic component. Generally, TKA includes one or more of the following steps: a) removal of damaged cartilage along with a small amount of bone from the tibia and femur, b) replacement of damaged bone surfaces with metal components, and replacement of cartilage with medical grade plastic, c) resurfacing of the underside of the patella with a plastic disk, and d) inserting a piece of smooth, medical grade plastic between the metal parts to facilitate ease of movement. 
         [0003]    Many different types of articulating material combinations are used to make prosthetic components. One of the more commonly used combinations includes a metal femoral surface articulating against a polymer tibia and patella surface. After implantation, the friction these components are subjected to may lead to metal erosion. Metal ions and debris released at the area of the implant can lead to complications such as osteolysis. Build-up of metal debris in soft body tissue can cause metallosis. Although poisoning from metallosis is rare, metal-on-metal implants containing cobalt-chromium alloys are known to cause arthroprosthetic cobaltism, which is an established health condition. 
         [0004]    Stress shielding by stiff metal prosthetic implants can lead to bone resorption. Stress shielding is a mechanical phenomenon that occurs in prosthetic composites of stiff and flexible materials. In its natural state, a femur carries load by itself. However, when provided with a stiff metal implant, the femur is subject to reduced stress, hence stress shielded. Clinical patient series and animal experiments have shown that reduce stress loading can lead to bone loss. Changes in bone morphology have been linked to the effect of stress shielding and a subsequent adaptive remodeling process. 
         [0005]    Stiff metal prosthesis are generally implanted to bone by long anchor pins and secured by using bone cement such as polymethylmethacrylate compositions, for example. Aseptic loosening of the bone cement surface, i.e., failure of the bond between an implant and bone in the absence of infection, has been observed in many cases. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    The present invention is for novel flexible prosthetic components and methods of securing these flexible prosthetic components to resected bone. The flexible prosthetic components disclosed herein have an outer articular surface and a bone contacting surface with one or more protrusions extending outwardly. The elasticity of the flexible prosthetic components in conjunction with fabricated protrusions will enable these prosthetic components to be slipped over and snap-fit around resected bone. 
         [0007]    “Snap-fit” as used herein is a fixation method, whereby the elasticity of the flexible prosthetic is used to securely anchor prosthetic on resected bone by interlocking protrusions with corresponding recesses in resected bone. The flexible prosthetic components, which are smaller in their neutral state than the recipient bone, can be elastically deformed by the application of an external force by hand or special equipment to position the protrusions to align with corresponding recesses made in resected bone. Immediately upon removal of this external force, the deformed prosthetic will wrap around resected bone forcing protrusions to mate with recesses. Compressive forces of the flexible prosthetic acting on resected bone and stress induced by the interlocking fit between protrusions and recesses will result in secure mechanical retention. 
         [0008]    Snap-fitting flexible prosthetic components on resected bone will simplify joint replacement surgery by eliminating or substantially reducing the need for bone cement. Interlocking components, i.e., protrusions and recesses, will facilitate in precise positioning of prosthetic on bone. Biocompatible flexible polymers used in making flexible prosthetic components will reduce or eliminate complications induced by commonly used metallic prosthetic components such as the release of metal ions and metallosis. Flexible polymers are inherently more flexible than their metal counterparts and will allow for natural loading on replaced joints. This will reduce bone stress shielding and consequently lead to less bone resorption. 
         [0009]    A first aspect of the present invention is a flexible prosthetic component comprising of an outer annular surface, opposing bone contacting surfaces with one or more protrusions and recesses. 
         [0010]    In one embodiment according to this first aspect of the present invention, the opposing bone contacting surfaces are parallel to each other and perpendicular to a distal surface. The sagittal distance between the opposing bone contacting surfaces is less than the corresponding bone dimension. The anterior and posterior bone contacting surfaces have multiple protrusions extending outward and parallel to the distal surface. Protrusions are fabricated to mate with corresponding recesses cut in resected bone. 
         [0011]    In another embodiment according to the first aspect of this invention, the proximal ends of the opposing bone contacting surfaces are angled inwards and set at acute angles to a distal surface. The sagittal distance between the proximal ends of the opposing bone contacting surfaces is less than the corresponding bone dimension. The anterior and posterior bone contacting surfaces have multiple protrusions extending outward and parallel to the distal surface. Protrusions are fabricated to mate with corresponding recesses cut in resected bone. 
         [0012]    In yet another embodiment of this first aspect, the opposing bone contacting surfaces are parallel to each other and perpendicular to a distal surface. The sagittal distance between the opposing bone contacting surfaces is less than the corresponding bone dimension. The anterior and posterior bone contacting surfaces have multiple protrusions extending outwardly and inferiorly towards a longitudinal axis. Protrusions are fabricated to mate with corresponding recesses cut in resected bone. The angled protrusions will ratchet into corresponding recesses in this embodiment and strengthen the interlocking of flexible prosthetic to resected bone. 
         [0013]    In still yet another embodiment of this first aspect, an anterior bone contacting surface is obtusely angled to a distal surface and a posterior bone contacting surface is perpendicular to the distal surface. All interior bone contacting surfaces have multiple protrusions and recesses to mate with corresponding features in resected bone. 
         [0014]    In still yet another embodiment of this first aspect, the bone contacting surface is a curved articular surface. The flexible prosthetic component in this embodiment is of substantially uniform thickness to snap-fit over a resurfaced distal femoral. 
         [0015]    A second aspect of the present invention is a method for securing a flexible prosthesis component having an articular surface and an opposing surface to resected bone. The method comprises the steps of preparing protrusions and recesses in resected bone that correspond to protrusions and recesses in flexible prosthetic, inserting the protrusions at least partially into recesses, and applying force to the articular surface to deform flexible prosthetic to snap-fit the protrusions into recesses around resected bone upon release of external force. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]    A more complete appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed description in which reference is made to the accompanying drawings in which: 
           [0017]      FIG. 1  is a perspective view of one embodiment of a flexible prosthetic component of the present invention. 
           [0018]      FIG. 2  is a side elevation view of the flexible prosthetic component of  FIG. 1 . 
           [0019]      FIG. 3  is a top plan view of the flexible prosthetic component of  FIG. 1 . 
           [0020]      FIGS. 4A-C  are side elevation views of the flexible prosthetic component of  FIG. 1  showing the sequential steps to secure the flexible prosthetic component to resected bone. 
           [0021]      FIG. 5  is a side elevation view of another embodiment of a flexible prosthetic component. 
           [0022]      FIG. 6  is a side elevation view of yet another embodiment of a flexible prosthetic component. 
           [0023]      FIG. 7  is a perspective view of a still yet another embodiment of a flexible prosthetic component. 
           [0024]      FIG. 8  is side elevation view of the flexible prosthetic component of  FIG. 7 . 
           [0025]      FIG. 9  is a perspective view of a still yet another embodiment of a flexible prosthetic component. 
           [0026]      FIG. 10  is a side elevation view of the flexible prosthetic component of  FIG. 9 . 
           [0027]      FIGS. 11A and 11B  are side elevation views of the flexible prosthetic component of  FIG. 9  showing the sequential steps to secure the flexible prosthetic component to resurfaced bone. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Referring to  FIGS. 1-3 , there is shown an embodiment of a flexible prosthetic component depicting a distal femoral component  100 . Femoral component  100  has an outer articular surface  104  and an opposing inner bone contacting surface  105 . Outer articular surface  104  includes an articular condyle surface having a pair of laterally spaced-apart articular posterior condyle surfaces. The outer articular surface is curved to correspond to the convex curvature of a femoral condyle prior to any degeneration or wear thereof. An articular posterior medial condyle surface  116  and an articular posterior lateral condyle surface  120  are separated by a cut-out for the intercondylar notch  112 . 
         [0029]    The inner bone contacting surface  105  opposing the outer articular surface  104  comprises an anterior surface  122 , an anterior chamfer surface  106 , a distal surface  108 , a posterior chamfer surface  114 , a posterior medial condyle surface  118 , and a posterior lateral condyle surface  124 . A longitudinal axis L 1 , shown in  FIG. 2 , is perpendicular to distal surface  108  and parallel to a longitudinal axis L 2  of anterior surface  122  and a longitudinal axis L 3  of posterior surfaces  114 ,  118 . 
         [0030]    Distal surface  108  has two laterally spaced-apart securing posts  110  to aid in the fixation of femoral component  100  to resected bone  10 . Protrusions  102  are present on anterior surface  122 , and protrusions  126  are present on posterior lateral condyle surface  124  and posterior medial condyle surface  118 . These protrusions extend outwardly along axis L 4  for the anterior surface and along axis L 5  for the posterior lateral condyle surface. 
         [0031]      FIGS. 4A-4C  show several side elevation views of sequential steps to snap-fit distal femoral component  100  to resected bone  10 .  FIG. 4A  shows a first step in which an apex surface  127  located between articular surface  104  and bone contacting surface  105  contacts an anterior chamfer resected surface on resected bone  10  and is slid in a proximal direction such that at least some of the protrusions on posterior condyle surface  126  and securing posts  110  on the distal surface  108  are at least partially inserted into corresponding recesses or negative engagements  128  and recess  138  cut in resected femur  10 . This step secures the posterior lateral condyle surface  124  and distal surface  108  with resected femur  10  by an interference fit. 
         [0032]      FIG. 4B  shows another step, in which application of an external force by hand or specialized instrument elastically deforms flexible femoral component  100  to snap-fit around resected femur  10 . As shown in side elevation view of  FIG. 4A , the distance between longitudinal axis L 2  and L 3  of femoral component  100  in a neutral position about a sagittal plane is less than the corresponding dimension of the resected bone  10 . The flexible femoral component  100  must consequently be elastically deformed by the application of an external force to wrap around the resected bone  10 . Elastic deformation includes material elongation of femoral component  100  and counterclockwise rotations of longitudinal distal surface axis L 6  to meet a longitudinal distal resection axis L 6 ′ and axis L 2  to L 2 ′. This elastic deformation will align protrusions on anterior surface  102  to engagement features  128  on resected femur, such that these mating parts will snap-fit to anchor distal femoral component  100  to resected bone  10 . 
         [0033]      FIG. 4C  shows the snap-fitted distal femoral component  100  around the resected bone  10 . When the external elastic deformation force is removed, compressive forces acting around the distal femoral component  100  will anchor it to the resected bone  10 . In addition to the compressive force created by the flexible distal femoral component  100 , the interlocking of engagement features on resected bone  10  with protrusions on posterior surface  126  and protrusions on anterior surface  102  will induce stress on the mating parts and result in a stronger bond. 
         [0034]      FIG. 5  shows a side elevation of another embodiment of a flexible prosthetic component depicting a distal femoral component  200 . Femoral component  200  has an outer articular surface  204  and an opposing inner bone contacting surface  205 . Outer articular surface  204  includes an articular condyle surface having a pair of laterally spaced-apart articular posterior condyle surfaces. The outer articular surface is curved to correspond to the convex curvature of the femoral condyle prior to any degeneration or wear thereof. An articular posterior medial condyle surface and an articular posterior lateral condyle surface  220  are separated by a cut-out for the intercondylar notch. 
         [0035]    The inner bone contacting surface  205  opposing the outer articular surface  204  comprises an anterior surface  222 , an anterior chamfer surface  206 , a distal surface  208 , a posterior chamfer surface  214 , a posterior medial condyle surface, and a posterior lateral condyle surface  224 . The inner anterior and posterior surfaces are separated by distal surface  208 . Longitudinal axis L 1  is perpendicular to distal surface  208 . 
         [0036]    Distal surface  208  has two laterally spaced-apart securing posts  210  to aid in the fixation of the femoral component  200  to resected bone  10 . Protrusions  202  are present on anterior surface  222 , and protrusions  226  are present on posterior lateral condyle surface  224  and posterior medial condyle surface. 
         [0037]    Anterior surface  222 , posterior medial condyle surface, and posterior lateral condyle surfaces  224  are set at acute angles with respect to the distal surface  208 . This configuration increases the compressive forces acting on the inner bone contacting surfaces resulting in a tighter bond between the femoral component  200  and the resected bone  10 . Procedure to snap-fit femoral component  200  is similar to steps outlined in  FIG. 4A-4C . 
         [0038]      FIG. 6  shows a side elevation of a yet another embodiment of a flexible prosthetic component depicting a distal femoral component  300 . Femoral component  300  has an outer articular surface  304  and an opposing inner bone contacting surface  305 . Outer articular surface  304  includes an articular condyle surface having a pair of laterally spaced-apart articular posterior condyle surfaces. The outer articular surface is curved to correspond to the convex curvature of the femoral condyle prior to any degeneration or wear thereof. An articular posterior medial condyle surface and an articular posterior lateral condyle surface  320  are separated by a cut-out for the intercondylar notch. 
         [0039]    The inner bone contacting surface  305  opposing the outer articular surface  304  comprises an anterior surface  322 , an anterior chamfer surface  306 , a distal surface  308 , a posterior chamfer surface  314 , a posterior medial condyle surface, and a posterior lateral condyle surface  324 . Longitudinal axis L 1  is perpendicular to distal surface  308  and parallel to longitudinal axis of anterior surface L 2  and longitudinal axis of posterior condyle surface L 3 . 
         [0040]    Distal surface  308  has two laterally spaced-apart securing posts  310  to aid in the fixation of femoral component  300  to resected bone  10 . Protrusions  302  are present on anterior surface  322 , and protrusions  326  are present on posterior lateral condyle surface  324  and posterior medial condyle surface. Protrusions extend outwardly and inferiorly along axis L 8  for the anterior surface and along axis L 9  for the posterior lateral condyle surface. When angled protrusions are inserted into matching corresponding recesses in resected bone  10 , this mating provides an additional degree of constraint by interlocking prosthesis to bone and thereby negating forces acting directly perpendicular to the anterior or posterior surfaces of femoral component  300 . Procedure to snap-fit distal femoral component  300  is similar to steps outlined in  FIG. 4A-4C . 
         [0041]      FIGS. 7 and 8  show a still yet another embodiment of a flexible prosthetic component depicting a distal femoral component  400 . Femoral component  400  has an outer articular surface  404  and an opposing inner bone contacting surface  405 . Outer articular surface  404  includes an articular condyle surface having a pair of laterally spaced-apart articular posterior condyle surfaces. The outer articular surface is curved to correspond to the convex curvature of a femoral condyle prior to any degeneration or wear thereof. An articular posterior medial condyle surface  416  and an articular posterior lateral condyle surface  420  are separated by a cut-out for the intercondylar notch  412 . 
         [0042]    The inner bone contacting surface  405  opposing the outside articular surface  404  comprises an anterior surface  422 , an anterior chamfer surface  406 , a distal surface  408 , a posterior chamfer surface  414 , a posterior medial condyle surface  418 , and a posterior lateral condyle surface  424 . The inner anterior and posterior surfaces are separated by a distal surface  408 . Longitudinal axis L 1  is perpendicular to distal surface  408  and parallel to longitudinal axis of the posterior condyle surface L 3 . Longitudinal axis L 2  of the inner anterior surface is set at an obtuse angle to longitudinal axis of distal surface L 6 . 
         [0043]    All five interior prosthetic surfaces have positive  402  and negative features  426  to aid in the fixation of the femoral component  400  to resected bone  10 . Protrusions  402  extending outwardly along axis L 4  are present on anterior surface  422 . Procedure to snap-fit distal femoral component  400  is similar to steps outlined in  FIG. 4A-4C . Protrusion and recess features may also include those prepared so as to allow for a rotation about a single pivot point or different pivot points between the prosthetic component and the resected bone as described in U.S. Pat. Pub. No. 2012/0330429, the disclosure of which is hereby incorporated by reference herein. 
         [0044]      FIGS. 9 and 10  show another embodiment of a flexible prosthetic component. Distal femoral component  500  has an outer articular surface  504  and an opposing inner bone contacting surface  505 . In this embodiment, the inner bone contacting surface  505  is curved to correspond to the convex curvature of an osteoporotic bone or a resurfaced distal femur. Outer articular surface  504  includes an articular condyle surface having a pair of laterally spaced-apart articular posterior condyle surfaces. The outer articular surface is curved to correspond to the convex curvature of the distal femur prior to any degeneration, wear and/or resection thereof. An articular posterior medial condyle surface  516  and an articular posterior lateral condyle surface  520  are separated by a cut-out for the intercondylar notch  512 . 
         [0045]    The inner curved bone contacting surface  505  has positive features  502 ,  526  on the respective anterior and posterior surfaces thereof. The distal femoral component  500  is substantially of uniform thickness such separated by the inner bone contacting surface  505  and the outer articular surface  504 . Uniform thickness of the distal femoral component  500  allows for minimal bone removal by femoral resurfacing to snap-fit femoral component over resurfaced bone and to repair the articular surface of the distal femur. 
         [0046]      FIGS. 11A and 11B  show side elevation views illustrating sequential steps of one method to snap-fit distal femoral component  500  to resurfaced bone  20  having an articular surface  538 . Articular surface  538  may be an osteoporotic bone surface being an irregularly shaped convex surface. In some embodiments, inner bone contacting surface  505  may be shaped to conform to articular surface  538  whether it be a native bone surface that has been at least partially degenerated or resurfaced using standard or robotic instrumentation.  FIG. 11A  shows a first step in which an apex surface  527  located between the outer articular surface  504  and the bone contacting surface  505  of femoral component  500  contacts an anterior surface of the resurfaced bone  20  such that at least some of the protrusions  502  on the anterior surface of the femoral component  500  are at least partially inserted into corresponding recesses or negative engagements  530  in the resurfaced bone  20 . This step preferably secures the anterior surface of the femoral component  500  to the anterior surface of the resurfaced bone  20  by an interference fit. 
         [0047]      FIG. 11B  shows another step, in which application of an external force by hand or specialized instrument elastically deforms the flexible femoral component  500  to snap-fit around the posterior surface of the resurfaced femur  20 . The bone contacting inner surface area of the femoral component  500 , in a neutral position, is slightly smaller than the recipient resurfaced bone  20 . The flexible femoral component  500  must consequently be elastically deformed by sliding and stretching the femoral component by the application of an external force to wrap around the resurfaced bone such that protrusions  526  on the posterior surface of the femoral component  500  snap-fit with the corresponding recesses  528  on the resurfaced bone  20 . The femoral component  500  of this embodiment is made of substantially uniform thickness to allow for minimal bone removal during bone resurfacing. In other embodiments, the thickness of a flexible prosthetic may be varied to compensate for femoral degeneration. Bone resections, including resurfacing to implant a flexible femoral component  500  to a resected distal femur may include dynamic trialing methods described in U.S. Pat. Pub. No. 2015/0057758, the disclosure of which is hereby incorporated by reference herein. 
         [0048]    Flexible snap-fit prosthetics can be made using suitable biocompatible polymers such as polyetherehterketone (“PEEK”). Thin metal constructs can also be used. Material flexibility, rigidity, and strength are key factors for material selection to achieve functionality and benefits described herein. 
         [0049]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.