Abstract:
A prosthetic for use in an interphalangeal joint including a body portion and a weave portion. The body portion may be manufactured from a hydrogel material. The body portion includes an pair of stems and an intermediate section located in between the two stems. The intermediate section includes a recess allowing for flexing of the body portion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/888,841, filed Feb. 8, 2007, the entire disclosure of which is incorporated by reference herein. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to the field of joint replacement. Specifically, the present invention relates to a joint prosthesis for proximal interphalangeal joints. 
     2. Description of the Related Art 
     The replacement of damaged or diseased joints in the human body has been known for some time. Devices utilized to replace natural joint structures generally mimic natural movement of the joint. In addition, such devices are often configured to provide for a natural “at rest” position similar to that of the natural joint. 
     Known proximal interphalangeal joint prosthetics typically employ two stems or arms with an intermediate pivoting structure. In some devices, the entire prosthetic is manufactured from a single elastomer material or from metal alloy. 
     SUMMARY 
     The present invention relates to a prosthetic used to replace a damaged joint, such as a pivotal interphalangeal joint, for example. The prosthetic may include a body portion and an outer weave portion. The body portion may include an intermediate portion and a pair of stems connected to, and extending from, the intermediate portion. 
     The body portion may be formed from a hydrogel material, which may expand upon absorption of water. In addition, the outer weave portion may include a plurality of layers including a polymer layer and a metal layer. The polymer layer may be located intermediate the metal layer. 
     The intermediate portion may include a recess, which may be formed in the palmar side of the intermediate portion. 
     In one form thereof, the present invention provides a prosthetic used to replace a damaged joint including a body portion including an intermediate portion and a pair of stems connected to the intermediate portion; and an outer weave encompassing the body portion. 
     In another form, the present invention provides a prosthetic used to replace a damaged joint including a body portion including an intermediate portion and a pair of stems connected to the intermediate portion; wherein the body portion is formed from hydrogel. 
     In another form, the present invention provides a prosthetic used to replace a damaged joint including a body portion formed from a hydrogel material and including a pair of interconnected stems; and an outer weave at least partially encompassing at least one of the stems. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above-mentioned and other features and advantages of this invention, and the manner of attaining them, will become more apparent and the invention itself will be better understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of a prosthetic device embodying the present invention; 
         FIG. 2  is a perspective view of the prosthetic device of  FIG. 1  with a portion of the outer weave omitted for illustrative purposes; 
         FIG. 3  is a side view of a body portion of the prosthetic device, illustrating exemplary ranges of motion thereof from a substantially non-flexed or neutral position shown in solid lines; 
         FIG. 4  is a side view of the body portion depicted in  FIG. 3  in a flexed position; and 
         FIGS. 5-7  are side views of a finger illustrating an exemplary surgical method of implanting the prosthetic of  FIG. 1 . 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION 
       FIGS. 1 and 2  depict different views of a joint prosthetic, generally indicated by numeral  2 , representing an exemplary embodiment of the present invention. Prosthetic  2  includes a body portion  4  and a cover or weave portion  6  encompassing body portion  4 . In  FIG. 2 , a portion of weave portion  6  has been omitted in order to illustrate body portion  4  with respect to weave portion  6 . The depicted embodiment of prosthetic  2  is configured to be utilized in the proximal interphalangeal (PIP) joint of a human finger  30 , as shown in  FIG. 7 . 
     With reference to  FIGS. 3 and 4 , body portion  4  includes a first stem  8 , a second stem  10  and an intermediate portion  12 . Stems  8 ,  10  and the intermediate portion  12  may be formed with a unitary one-piece construction. In the present embodiment, body portion  4  may be formed from any suitable hydrogel material. 
     A hydrogel is a network of polymer chains that are water-soluble but made insoluble through physical and/or chemical crosslinks. These materials are sometimes found as a colloidal gel in which water is the dispersion medium. Hydrogels are generally formed from natural or synthetic polymers. Hydrogels may be classified as “superabsorbent” and may contain over 99% water, by weight. In addition, hydrogels may have the ability to swell due to water absorption. Hydrogels may also possess a degree of flexibility very similar to natural tissue, due to their significant water content. Suitable hydrogels include hyaluronic acid, polypropylene fumarate, and Poly(ethylene glycol)-co-polylactide, methyl cellulose, and carboxy methyl cellulose. 
     In general, the stems  8 ,  10  are sized and configured to be received within intramedullary recesses or bores of adjacent bones. For example, in the exemplary implantation depicted in  FIG. 7 , the first stem  8  is sized and configured to be received into a bore  42  of the middle phalanges  34  of the finger  30 . Similarly, the second stem  10  is sized and configured to be received into a bore  44  of the proximal phalanges  36  of finger  30 . 
     Intermediate portion  12  is configured to provide flexion motion between the first stem  8  and the second stem  10 . With reference again to  FIGS. 1 through 4 , intermediate portion  12  includes a first surface  14  and a second surface  16 . In the depicted embodiment, first surface  14  is substantially planar while second surface  16  includes a concave area or recess generally indicated by numeral  18 . 
     In the present embodiment, the concave area  18  is located on the palmar side of the prosthetic  2  and includes a bending portion defined by arcuate surface  20 . Arcuate surface  20  extends medial-laterally. 
     Second surface  16  also includes two flanges  22 ,  24 . The flanges extend in the palmar direction on opposite sides of arcuate surface  20 . As depicted in the figures, the flanges  22 ,  24  travel toward each other during flexion movement. The flanges  22 ,  24  are configured to engage during flexion movement in order to inhibit over-flexion, as shown in  FIG. 4 . 
     For illustrative purposes, the first stem  8  defines a central axis, generally indicated by numeral  26 , which extends longitudinally through the center of first stem  8 . Similarly, second stem  10  defines a central axis, generally indicated by numeral  28 , which extends longitudinally through the center of second stem  10 . When in a neutral or rest position depicted in solid lines in  FIG. 3 , the first stem  8  extends at a slight angle with respect to the second stem  10 . Accordingly, in the rest position, the first stem  8  and the second stem  10  do not extend along a straight line, rather, axis  26  and axis  28  are positioned at an angle of approximately 15° with respect to each other when the prosthetic  2  is “at rest” or under no significant external forces, or stress. The at rest angle may be any angle suitable for a given usage of prosthetic  2 . 
     With reference specifically to  FIGS. 3 and 4 , the intermediate portion  12  allows for infinite flexion motion to any position intermediate the positions depicted in phantom in  FIG. 3 . As shown in  FIG. 3 , in the depicted embodiment, intermediate portion  12  may allow for infinite flexing between about 0° and about 108° as defined by the axes  26 ,  28 .  FIG. 4  depicts the prosthetic  2  in a flexion position. 
     The slight angle defined by the axes  26 ,  28  generally conforms to the naturally-biased position of the phalanges  34 ,  36 , which generally extend at angles ranging from about 10° to about 50°, depending on the location of the joint. For example, the natural bias of the PIP in a typical index finger differs from the natural bias of a PIP in a ring finger. Those possessing ordinary skill in the art may readily determine a suitable angle to accommodate the natural bias of any extremity at rest. 
     It should be noted that the normally biased attitude of the two stems  8 ,  10  is at an angle that accommodates the natural bias in the joints. Thus, the bias of the prosthetic  2  will not tend to force a finger in which the prosthetic  2  is implanted into an unnatural straight position or an unnatural overly bent position. 
     With reference still to  FIGS. 1 and 2 , in the present embodiment, weave portion  6  may comprise multiple braided layers of suitable material. For example, in the embodiment depicted in  FIG. 2 , weave portion  6  may include an outer metal layer  7  and a polymer  9 . The polymer layer  9  may be arranged intermediate the hydrogel surface of body  4  and the outer metal layer  7  of the weave  6 . The inclusion of the polymer layer  9  of the weave  6  reduces the potential for the outer metal layer  7  to damage the hydrogel surface of body  4 . If necessary, additional layers of material may be utilized intermediate the hydrogel surface of body portion  4  and the outer metal layer  7  of weave portion  6  to further reduce the potential for damage to body portion  4 . 
     Weave portion  6  may be formed in any suitable manner, such as by way of braiding, for example, and may be interconnected to body portion  4  in any known manner. For example, weave portion  6  may be woven around body portion  4  by way of insert braiding. Also, weave portion  6  may be woven in any suitable manner that restricts the motion of the prosthetic  2  in order to ensure the prosthetic does not flex in a direction incompatible with the normal direction of flexion of a joint. In addition, the formation of the weave portion  6  may constrain the motion of the prosthetic to that of a normal joint. 
       FIGS. 5 through 7  depict the various stages of an exemplary surgical method for implanting prosthetic  2  in a PIP joint.  FIG. 5  depicts a finger  30  including distal phalanges  32 , middle phalanges  34 , proximal phalanges  36 , and a natural PIP joint  38 . In an exemplary method of implantation of prosthetic  2 , a gradual curving dorsal incision may be made over the PIP joint  38 . Through suitable dissection, skin flaps (not shown) may be gently elevated in order to expose a portion of the extensor tendon mechanism (not shown). An additional incision may be made intermediate the central tendon (not shown) and the lateral band (not shown) on the opposite side of finger  30 . The dorsal capsule (not shown) may then be incised in order to expose the PIP joint  38 . 
     After suitable incision and preparation has been accomplished, a surgeon may remove the natural PIP joint  38 . In particular, the central tendon (not shown) may be protected with retractors (not shown) while a micro-oscillating saw (not shown) is used to resects the proximal phalanges  36  at a position that results in the removal of the PIP joint  38 . A rongeur (not shown) may also be utilized to remove spurs from the middle phalanges  36  thereby flattening out the middle phalanges. 
     As depicted in  FIG. 6 , the removal of the PIP joint  38  results in void  40  having a size predetermined to receive prosthetic  2 . The surgeon may remove additional bone structure on the proximal phalanges  36  and the middle phalanges  34 , as necessary, such that void  40  is large enough to receive the intermediate member  12  of the prosthetic  2 . 
     The surgeon may then create a start hole (not shown) in the exposed intramedullary tissue of the remainder of the middle phalanges  34  using a known instrument (not shown) such as a reamer or a sharp awl. The surgeon thereafter removes the intramedullary tissue in order to create a bore  42  in the middle phalanges  34  configured to receive first stem  8  of prosthetic  2 . The surgeon may employ a series of sequentially sized broaches (not shown) with the final size corresponding to that of first stem  8 . The surgeon may prepare the proximal phalanges  36  in a similar manner thereby resulting in bore  44 . 
     The surgeon may optionally attempt a trial fit of the prosthetic  2 . The trial fit may result in additional sizing or shaping of the bores  42 ,  44 . In addition, the trial fit may determine if additional portions of the proximal phalanges  36  or the middle phalanges  34  should be removed. Furthermore, the trial fit may be used to determine if a different sized prosthetic  2  is required. A correctly sized prosthetic  2  should seal well against the middle phalanges  34  and the proximal phalanges  36  and be stable. 
     The surgeon may then insert the prosthetic  2  and attempt flexion and extension movement on the finger  30  in order to determine if the movement falls within an acceptable range of motion, such that flexion and extension occurs relatively uninhibited over a predetermined range of motion. Those with ordinary skill in the art may determine the acceptable threshold amount of uninhibited range of motion for a given patient. In order to insert the component, the surgeon may insert first stem  8  into bore  42  of the middle phalanges  34 . Second stem  10  may then be inserted into bore  44  of the proximal phalanges  36 , as depicted in  FIG. 7 . 
     Once the prosthetic  2  has been implanted, the surgeon may close the site using techniques known in the art. Generally, the capsule may be sutured, if necessary. In addition, the exterior mechanism may also be sutured. 
     After implantation, the hydrogel composition of the stems  8 ,  10  allows the stems  8 ,  10  to swell within the finger  30  as the prosthetic absorbs water. Accordingly, less reaming of the phalanges  34 ,  36  is necessary since the stems  8 ,  10  will initially be relatively short but grow in size and extend into the bores  42 ,  44  of the phalanges  34 ,  36  as water is absorbed by the prosthetic to provide initial fixation. In addition, the outer layer of metal comprising the weave portion  6  represents a substantially open cell or porous structure promoting osseointegration into which the bone of the phalanges  34 ,  36  may grow into after the implant has been implanted for long-term fixation. It should be noted that the expansion of stems  8 ,  10  due to the absorption of water will force the outer metal layer of weave portion  6  into contact with the bone of the phalanges  34 ,  36 , thereby aiding in the interconnection of the growing bone and the weave  6 . Furthermore, the general properties of the hydrogel comprising body portion  4  functions to cushion the joint in which the prosthetic  2  is inserted. 
     While this invention has been described as having exemplary designs, the present invention may be further modified within the spirit and scope of the disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains.