Abstract:
An orthopaedic implant includes a flexible bag; a structural support at least partially within the bag; and a hardened polymer within the bag. The orthopaedic implant is implanted within the bone by forming a cavity in the bone; inserting a flexible bag into the cavity; filling the bag with a polymer; and hardening the polymer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to orthopaedic implants, and, more particularly, to fracture fixation devices for femoral neck fractures. 
     2. Description of the Related Art 
     Treatment of bone fractures, voids and other defects may include the use of metal orthopaedic hardware such as implants, plates, screws, etc. In the case of a fracture in the neck region of a femur adjacent to the femoral head, a common surgical technique utilizes a compression tube and plate system (FIG.  1 ). The plate is attached to the lateral side of the femur and then screwed in place to the femur. A compression tube extends into an opening formed in the femur and is generally aligned with the femoral head. A screw is placed within the compression tube that is screwed into the femoral head. 
     SUMMARY OF THE INVENTION 
     The present invention provides an orthopaedic implant and corresponding implanting method utilizing a porous flexible bag, one or more structural supports within the bag and a high strength polymer within the bag. 
     The invention comprises, in one form thereof, an orthopaedic implant including a flexible bag; a structural support at least partially within the bag; and a hardened polymer within the bag. 
     The invention comprises, in another form thereof, a method of implanting an orthopaedic implant in a bone, including the steps of forming a cavity in the bone; inserting a flexible bag into the cavity; filling the bag with a polymer; and hardening the polymer. 
     An advantage of the present invention is that the shape of the orthopaedic implant conforms to the shape of the cavity formed in the bone. 
     Another advantage is that only a small incision is required to insert the various components of the orthopaedic implant into the cavity within the bone. 
     Yet another advantage is that compression loading of the bone may be effected. 
     A further advantage is that the bag may be porous to allow the polymer to pass therethrough to some extent; may be contoured to fit within a predefined cavity shape; or may be contourable to fit within a varying cavity shape. 
     Still another advantage is that a flexible reamer may be utilized to ream extension portions of the cavity within the bone. 
     Another advantage is that the polymer within the bag may be curable using thermal energy, light energy, X-ray energy, or a chemical catalyst. 
    
    
     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 will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a side view of conventional orthopaedic hardware used to fixate a femoral head on a femur; 
     FIG. 2 illustrates the formation of a cavity within the proximal end of a femur using a drill; 
     FIG. 3 illustrates a guide tube placed within the cavity; 
     FIG. 4 illustrates a flexible reamer inserted through the guide tube of FIG. 3 to form an extension portion of the cavity extending into the femoral head; 
     FIG. 5 illustrates another guide tube placed within the cavity in the femur; 
     FIG. 6 illustrates the flexible reamer inserted through the curved guide tube of FIG. 6 to form an extension portion which extends into the shaft of the femur; 
     FIG. 7 illustrates a flexible bag being inserted within the cavity in the femur; 
     FIG. 8 illustrates the curved tube portion within the flexible bag, as well as the injection tubes which may be inserted within the flexible bag; 
     FIG. 9 illustrates injection of the high strength polymer within the femoral head using an injection tube shown in FIG. 8; 
     FIG. 10 illustrates injection of a high strength polymer within a distal portion of the bag using another injection tube shown in FIG. 8; 
     FIG. 11 illustrates the flexible fill hoses being snipped from the implant within the femur; 
     FIG. 12 illustrates one technique for curing the polymer within the flexible bag; 
     FIG. 13 is an exploded view of the porous, flexible bag and injection tubes; 
     FIG. 14 is a side, partially fragmentary view of the flexible reamer shown in FIGS. 4 and 6; and 
     FIG. 15 is a perspective view of a number of the drive gears located within the hollow tube of the flexible reamer shown in FIG.  14 . 
    
    
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrates one preferred embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and more particularly to FIGS. 2-12, an embodiment of the method of implanting an orthopaedic implant  10  (FIG. 10) in a bone  12  will be described in further detail. In general, orthopaedic implant  10  is in the form of a flexible bag  13  having a high strength polymer  14  which is injected under pressure therein and hardened. A plurality of structural supports, such as indicated by reference numbers  16 ,  18  and  20  are used to provide structural reinforcement of orthopaedic implant  10 , as well as for delivery of the high strength polymer within bag  13  as will be described in greater detail hereinafter. In the method of implanting orthopaedic implant  10  described hereinafter, bone  12  is in the form of a femur. However, it is to be understood that orthopaedic implant  10  has a variety of applications and may thus be adapted accordingly. 
     Femur  12  is shown as including a head  22 , neck  24 , greater trochanter  26  and shaft  28 . Head  22  is assumed to have fractured relative to neck  24 , as indicated by fracture line  30 . Conventionally, head  22  is fixated relative to neck  24  using a compression tube and plate system, as described above under the section entitled “Background of the Invention” and shown in FIG.  1 . On the other hand, orthopaedic implant  10  of the present invention and the corresponding implantation method uses a novel bag and polymer as described hereinafter. 
     Preliminarily, a small incision (e.g., 18-25 mm) is cut adjacent greater trochanter  26  of femur  12 . The incision location may be approximately the same as used for the placement of a gamma nail within femur  12 . After forming an access hole in greater trochanter  26  using a bit  32  (FIG.  2 ), a flexible reamer  52  is used to form a cavity  34  in femur  12 . Reamer  52  may be moved in an axial direction in and out of cavity  34  as well as being swept in the distal direction as shown to assist in the formation of fan-shaped cavity  34 . Cavity  34  is generally formed to provide access to femoral head  22 , as well as intramedullary (IM) canal  38  of shaft  28  defining an anatomical axis  40  of femur  12 . 
     Cavity  34  is then formed with a first extension portion  42  extending into femoral head  22  (FIGS.  3  and  4 ). More particularly, a guide tube  44  with an attached handle  46  is inserted within cavity  34 . Guide tube  44  has a curvature allowing the formation of first extension portion  42  of cavity  34  into femoral head  22 . Guide tube  44  preferably has a curvature which terminates generally parallel to a load axis  48  on femoral head  22  when engaged with an acetabular cup in the pelvic bone of the patient. Guide tube  44  may have a knurled outer surface  50  which at least under certain conditions assists gripping and placement within cavity  34 . Handle  46  also assists in proper placement of guide tube  44  within cavity  34 . 
     After guide tube  44  is positioned within cavity  34  as shown in FIGS. 3 and 4, a flexible reamer  52  is used to form first extension portion  42  within femoral head  22 . Flexible reamer  52  generally includes a flexible, hollow tube  54 , cutting head  56  and driven shank  58 . Driven shank  58  is rotatably driven by a drive source  60 , such as a hand-held rotatable drive source. Flexible tube  54  allows flexible reamer  52  to flex during extension through curved guide tube  44 . Cutting head  56  at least includes axially facing cutting teeth and preferably also includes radially facing cutting teeth. Cutting head  56  forms an extension portion  42  of cavity  34  which extends into femoral head  22  approximately to the center of femoral head  22 . First extension portion  42  has a diameter of between 0.25 and 0.35 inch. Upon insertion of flexible reamer  52  through curved guide tube  44 , as indicated by arrow  62 , cutting head  56  impinges against femur  12  adjacent the end of curved guide tube  44 , at which point some resistence is felt by the surgeon. The position of flexible, hollow tube  54  relative to handle  46  may be observed by the surgeon, after which flexible reamer  52  is moved in an axial direction into curved guide tube  44  a predetermined amount which causes first extension portion  42  to extend generally to the center of femoral head  22 . Flexible, hollow tube  54  may optionally be provided with visual indicia at incremented placement locations along its length to assist in the formation of first extension portion  42  in femoral head  22 . After first extension portion  42  is formed in femoral head  22 , flexible reamer  52  and curved guide tube  44  are each removed from within cavity  34 . 
     A second extension portion  64  of cavity  34  may also optionally be formed within femur  12  (FIGS.  5  and  6 ). Second extension portion  64  preferably extends into IM canal  38  within femur  12 . To this end, a second hollow guide tube  66  is inserted within cavity  34 . Guide tube  66  preferably also includes a handle  68  for locating and placement within cavity  34 . Guide tube  66  has a curvature which is different from the curvature of guide tube  44 , thus allowing second extension portion  64  to extend into IM canal  38  of femur  12 . The exact curvature of guide tube  66  and guide tube  44  of course may vary from one application to another, or in fact may be the same under certain circumstances. In general, the curvature of a guide tube used to form first extension portion  42  is selected such that first extension portion  42  extends generally parallel to load axis  48  of femoral head  22 , while another guide tube is selected such that second extension portion  64  extends into and preferably parallel with IM canal  38 . Guide tube  66  may also include a knurled outer surface  70  which at least in some circumstances provides gripping engagement with interior walls of cavity  34 . For example, if the diameter of knurled outer surface  70  is slightly larger than the diameter of drill bit  32 , guide tube  66  may at least grip the interior walls of cavity  34  extending generally parallel to the drawings of FIGS. 5 and 6 at opposite sides of guide tube  66 . 
     After placement of guide tube  66  within cavity  34  as shown in FIG. 6, flexible reamer  52  is used to form second extension portion  64  within femur  12 . The depth of second extension portion  64  generally corresponds to the length of a bag  13  which is implanted within cavity  34 , as will be described in more detail hereinafter. 
     In the embodiment shown in the drawings, a same flexible reamer  52  is used to form each of first extension portion  42  and second extension portion  64  of cavity  34 . However, it is to be appreciated that a flexible reamer having a different diameter cutting head may be utilized if it is desirable to form first extension portion  42  and second extension portion  64  with different diameters. 
     After formation of cavity  34  within femur  12 , including first extension portion  42  and second extension portion  64 , flexible bag  13  is inserted within cavity  34  (FIG.  7 ). Bag  13  may be folded in a suitable manner and inserted within a pre-load tube  72 . Pre-load tube  72  has an outside diameter which is sized to fit within the entrance opening to cavity  34  within femur  12 . A plunger  74  having an outside diameter which is slightly less than a inside diameter of pre-load tube  72  may be moved in an axial direction, indicated by arrow  76 , to push bag  13  into cavity  34 , as indicated by arrow  78 . Bag  13  has a shape which generally corresponds to the shape of cavity  34 , including first extension portion  42  and second extension portion  64 . Alternatively, bag  13  may be formed from an elastomeric material allowing expansion under pressure into first extension portion  42  and second extension portion  64 . Bag  13  is preferably formed from a porous material such that polymer  14  is allowed to seep therethrough at least to some extent into cancellous bone surrounding cavity  34 . 
     Bag  13  (FIG. 8) includes structural support  16  with a curved tube portion  80  extending from an entrance of cavity  34  to an entrance of extension portion  42 . Bag  13  may be suitably attached to curved tube portion  80 , such as by using an adhesive, ultrasonic welding, etc. Curved tube portion  80  has an inside diameter allowing structural support  18  in the form of a hollow injection tube to be inserted therethrough. Injection tube  18  includes a plurality of apertures  82  at an end thereof through which the polymer may be injected. Hollow injection tube  18  and curved tube portion  80  are each formed from metal with complimentary curvatures, in the embodiment shown. A flexible hose  84  is connected to an end of injection tube  18  opposite from apertures  82 , and receives pressurized high strength polymer from a pressure source such as a pump or the like (not shown). Structural support  16  also includes a distal opening  86  adjacent greater trochanter  26  of femur  12  allowing structural support  20  in the form of a second hollow injection tube to be inserted therethrough and into bag  13 . 
     Hollow injection tube  18  is inserted into curved tube portion  80 , and an end of injection tube  18  is positioned within femoral head  22  such that apertures  82  are near the end of first extension portion  42 . The high strength polymer is then injected through hose  84  and injection tube  18  to apertures  82 . The polymer may be polymethylmethacrylate (PMMA). The polymer is preferably a curable polymer, such as with thermal energy, light energy, X-ray energy or a chemical catalyst. 
     To allow loading between femoral head  22  and neck  24 , injection tube  18  is structured and arranged to be slidably disposed within curved tube portion  16  after implanting within femur  12 . More particularly, injection tube  18  may include a sealant  92  such as a resorbable sealant surrounding a portion thereof adjacent the inside diameter of curved tube portion  16  (FIG.  9 ). For example, the sealant may be in the form of glycerin which surrounds injection tube  18 . The glycerin is resorbed over time after implanting of orthopaedic implant  10  within femur  12 . A small clearance distance thus exists between injection tube  18  and curved tube portion  16  after resorption of the glycerin. In this manner, injection tube  18  is slidably movable within curved tube portion  16 . 
     Injection tube  20  is slid through distal opening  86  of structural support  16  within bag  13 . Injection tube  20  is selected with a curvature which preferably extends into second extension portion  64 . A polymer is injected under pressure within bag  13  such that bag  13  extends into and substantially fills second extension portion  64  of cavity  34 . Bag  13  can either be contoured to fit within second extension portion  64 , or may be contourable (e.g., expandable) to fit within second extension portion  64 . The polymer may be a same type of polymer as is injected into first extension portion  42  within femoral head  22 , or may be different. In the embodiment shown in FIGS. 9 and 10, the polymer includes a chemical catalyst prior to injection which causes the polymer to cure. Flexible hoses  84  and  94  may thus be cut from injection tubes  18  and  20 , which remain within orthopaedic implant  10 . Alternatively, the polymer within bag  13  may be cured with another source of energy, such as X-ray energy emitted from an X-ray source  96  (FIG.  12 ). 
     Referring now to FIGS. 14 and 15, flexible reamer  52  is shown in greater detail. Cutting head  56  is carried by and extends from an end  98  of hollow tube  54 . Driven shank  58  is carried by and extends from an opposite end  100  of flexible tube  54 . A plurality of drive gears  102  are rotatably disposed within flexible tube  54 . Drive gears  102  engage each other in an end-to-end manner and interconnect driven shank  58  with cutting head  56 . Thus, rotation of driven shank  58  using drive source  60  in turn causes rotation of cutting head  56 . Each drive gear  102  includes four axially facing gear teeth  104  at each end thereof. Gear teeth  104  are angled to allow flexible hollow tube  54  to bend, while still ensuring positive driving engagement between adjacent drive gears  102  within tube  54 . 
     While this invention has been described as having a preferred design, the present invention can be further modified within the spirit and scope of this 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 and which fall within the limits of the appended claims.