Abstract:
A medical device is provided for attachment to a patient&#39;s femur to treat a fracture in the distal region of the femur, in a patient with an artificial knee joint. The apparatus includes first and second elongate plates for attaching to the femur at the location of the fracture. The plates include coupling means to rigidly coupling the plates to the femoral component of the artificial knee joint. The apparatus further includes a transverse link for connecting the first and second plates together in a spaced apart relationship to form a rigid linkage between said plates. The invention further includes a system for treating a fracture of the femur, especially in patients with weak bones, by attaching such plates in an opposed spaced apart relationship on the lateral and medial sides of the femur, and fastening the lower ends of the plates to the femoral component of the knee. The transverse link is engaged to form a monolithic, rigid structure for bracing the femur.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to medical devices, in particular an implant for treating fractures of the femur. The invention further relates to methods of treating such fractures, and uses of such devices to treat femoral fractures. 
       BACKGROUND OF THE INVENTION 
       [0002]    Periprosthetic fractures of the distal femur are the most common fracture location around the knee with an incidence ranging from 0.3-2.5%. They account for more than 10,000 fractures per year in the US alone. Current fixation of these fractures has a high complication rate due to a paucity of bone remaining in the distal fragment for rigid fixation, particularly in osteoporotic bone. Using current techniques, fracture fixation is often inadequate and the fracture often heals in a malposition causing abnormal stresses on the preexisting knee prosthesis. This results in persistent pain, stiffness and potential for early failure of the total knee prosthesis. Furthermore, abandoning fracture fixation in favour of revision arthroplasty using more constrained hinge devices leads to high complications and early failure as well as more severe reconstructive problems in the future. Non-surgical treatment of these fractures is rarely an option because of the medical complications of prolonged immobilization and surgical fixation is generally accepted as the standard of care in most instances. 
         [0003]    It has been proposed to stabilize the fractured femur by fastening a rigid component to the femur. For example, U.S. Patent Application 2004/0122430 (Hansson) discloses an implant for fixation of femoral fractures. This device, as well as others within the prior art, requires modification of the femoral implant of the artificial knee in order to anchor the rigid component. Conventional surgical techniques also include the use of an intramedulallary nail, the “Less Invasive Stabilization System” (LISS) and lateral condylar locking plate, the dynamic condylar screw and plate system, an angled blade plate, and numerous other options. However, the use of such systems still appears to result in high complication rates, especially in osteoporotic patients. 
         [0004]    It has also been proposed to provide a bone plate for fixing a femur, which couples with the femoral component of an artificial knee joint. Examples of such systems are described in U.S. Pat. No. 5,522,902 (Yuan et al.) and published Application U.S. 2007/0225819 A1 (Eva). It is believed that these devices do not adequately address the need to rigidly fix the femur in position, with a system that is relatively straightforward to implement and can treat patients with arthritis and other conditions of weak bones. 
       SUMMARY OF THE INVENTION 
       [0005]    In light of shortcomings in the prior art, including the shortcomings noted above, it is desirable to provide an improved implant for femoral fractures, and in particular an implant that is particularly suitable for osteoporotic patients who have an existing knee prosthetic. 
         [0006]    One problem that arises in patients with osteoporosis is a lack of sufficiently dense bone at the distal end of the femur to anchor a conventional plate or other component for supporting the fractured femur. The present invention addresses this problem by utilizing an existing artificial knee in the patient to anchor a plate which supports and immobilizes the fractured femur. 
         [0007]    The invention relates generally to a method and apparatus to treat a fracture of the distal femur in a patient with weakened bones, by rigidly anchoring a pair of opposing plates to the femoral component of an artificial knee. The plates are fastened to the distal end of the patient&#39;s femur to allow bony healing and improve overall alignment of the knee prosthesis with respect to the limb. Most femoral components of total knee replacements have small metal slots on the distal-medial and distal-lateral edges of the prosthesis that are used for attachment of an insertion handle when implanting the device. These slots are not part of the articulating surface of the implant and may be as such used to anchor a fracture fixation device to improve the overall rigidity and alignment of the fracture and thus the limb. These slots typically serve no function after implantation of the artificial knee, and as such they are available to serve as anchoring points for other components. 
         [0008]    According to one aspect, the present invention comprises a pair of elongate plates, consisting of medial and lateral condylar plates, which are pre-contoured or which may be contoured on a customized basis prior to use, for engaging opposing (lateral and medial) sides of the distal end of the femur. The plates include attachment means for attaching the plates to the femur, such that at least the lateral plate overlaps the fracture for fixation thereof. At their distal ends, the opposing plates each include an engagement means for anchoring the plates to the femoral component of an artificial knee prosthesis which has been previously attached to the patient&#39;s femur. The engagement means may comprise any suitable means to rigidly attach the plates to the femoral component, as described below, so as to rigidly anchor the distal end of each plate to the artificial knee component. Preferably, the engagement means makes use of an existing feature of the femoral component and does not require modification of the femoral component. 
         [0009]    In one version, the engagement means which anchor the medial and lateral condylar plates to the femoral component of the knee prosthetic with the engagement means comprise a rectangular metal prong or tab that fits into the pre-existing anchoring slot on the femoral prosthesis. 
         [0010]    The lateral plate extends proximal to the fracture to assist reduction, alignment restoration and fixation. The shorter medial plate primarily serves as a link with the lateral plate to allow compression of the plates to increase the strength of the fixation to the femoral prosthesis. The medial plate is short in relation to the lateral plate, so as to extend only a minimal distance along the femur to minimize the possibility of disruption to the blood supply. The medial plate need not extend along the femur to the same extent as the lateral plate, since it is contemplated that the primary function of this plate is to provide structural support to the lateral plate, rather than providing substantial anchoring or support of the femur itself. 
         [0011]    According to another aspect, at least one rigid transverse link joins the first and second plates adjacent to their distal ends, so as to mechanically link the plates together to form a substantially rigid structure. In one embodiment, the structure has a generally H-shaped configuration when attached to a patient. The link holds the plates in place on the opposing lateral and medial sides of the femur in a vertical orientation. The link may consist of one or more fixed angle compression screws, or other suitable rigid member which rigidly joins the respective plates together. The plates and transverse link when fastened together form a rigid monolithic structure that resists movement relative to the femoral component, and as such this structure provides a rigid support for the fractured femur. 
         [0012]    The transverse link may comprise a compression bolt spanning the respective plates. A nut on the end of the bolt may be tightened to place the link under tension and thereby compress the plates together. The plates may be provided with openings aligned with each other when the plates are engaged to the artificial knee component, which receive the bolt. The link connects the two plates at a fixed angle. The amount of compression provided by the link is sufficient to compress the two distal tabs into the slots in the implant with sufficient force to rigidly lock the plates into position. The link passes through an opening which is formed within the patent&#39;s femur bone and is positioned partway between the anterior and posterior aspects of the femoral implant. Preferably, this position is approximately closer to the anterior one-third and posterior two-third junction. 
         [0013]    Several of the components described herein are known, or may be adapted from known medical device components. Precontoured plates that fit over the medial and lateral condyles of the distal femur are known to the art, as are non-contoured plates that may be contoured on site to fit the patient. Fixed angled devices are generally known for linking bone screws at a fixed angle to a plate. 
         [0014]    According to another aspect, the invention relates to a method of treating fractures located at or near the distal end of the femur, in patients with an existing artificial knee. According to this aspect, components as described above are utilized. The respective plates may be supplied either in a pre-contoured form or in a non-contoured form, and are contoured to fit and engage the patient&#39;s lower femur. The method involves the surgical attachment of the respective plates on opposing sides of the distal femur, anchoring the plates to the femoral component of the artificial knee, and linking the plates together with the transverse link. The plates may be held in position by a temporary clamp prior to their attachments as described above. The invention preserves the integrity of the knee prosthesis and the collateral ligaments of the knee, and the plates can be removed if necessary once the fracture has healed. 
         [0015]    The present invention will now be described by way of a detailed, non-limiting description of embodiments of the present invention. It will be understood that the detailed embodiments described herein are not intended to limit the scope of the invention, but are merely intended to illustrate the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a side elevational view of a portion of an apparatus according to the present invention; 
           [0017]      FIG. 2  is a side elevational view, opposed to  FIG. 1 , of another side portion of the apparatus; 
           [0018]      FIG. 3  is a perspective view of a temporary link for retaining the plates in position during surgical installation thereof; 
           [0019]      FIG. 4  is a front (anteroposterior) view of the present invention, fixed to a patient with a distal femur fracture; 
           [0020]      FIG. 5  is a perspective view of the first embodiment of the invention, engaged to a fractured femur; 
           [0021]      FIG. 6  is a further perspective view as in  FIG. 5 , showing an opposing side thereof; 
           [0022]      FIG. 7  is a view as in  FIG. 4 , of an alternative embodiment of the invention; 
           [0023]      FIG. 8  is an exploded view of components of the embodiment of  FIG. 7 ; 
           [0024]      FIG. 9  is a perspective view of a further alternative embodiment of the invention; 
           [0025]      FIG. 10  is a perspective view of a still further embodiment of the invention; 
           [0026]      FIG. 11  is a perspective view of the transverse link portion of the embodiment shown in  FIG. 10 . 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Turning to  FIGS. 1-6 , a first embodiment of the invention includes a pair of elongate plates  10  and  12  that are configured to be surgically attached to opposing sides of a patient&#39;s femur  14 , to immobilize the femur in the region of a distal fracture. The apparatus is intended for use for a patient who has an existing artificial knee, which includes a femoral component  16  fixed to the distal end of the femur. The apparatus is configured to engage this femoral component. Most conventional femoral components include opposed lateral slots  34 , which are provided to engage an insertion tool when implanting the device, and have no intrinsic function after implantation of the knee joint. The first embodiment described herein is configured to engage such slots  34 . 
         [0028]    The first of the plates comprises a lateral plate  10 , seen in  FIG. 1 , comprising an elongate plate body  20  contoured to contact the distal lateral region of the femur. The plate body is provided with a plurality of openings  22  to receive screws or nails  24  for attaching the plate to the femur  14  across the location of the fracture  26 . The plate  10  may be supplied in a pre-contoured form, or alternatively as a substantially flat plate which may be contoured prior to implantation to conform to the patient&#39;s femur, similar to a conventional distal lateral femoral plate. Typically, such a plate is cast from surgical-grade stainless steel, and may be sufficiently malleable to permit shaping of the plate prior to implantation. Extending distally from the base of the plate body is a generally rectangular protrusion  30  which is substantially co-planar with the plate body. The protrusion  30  is configured to extend downwardly alongside the lateral side of the femoral component  16  of the artificial knee, to a position adjacent to the distal end of the femoral component. The distal end of the protrusion comprises an engagement means to anchor the plate to the femoral component in a relatively rigid fashion. As seen in  FIGS. 1 ,  2  and  4 , the engagement means comprises an inwardly-facing rectangular tab  32 , configured to fit snugly within the pre-existing anchoring slots  34  within the femoral component  16  of the artificial knee. Tabs  32  should be configured to avoid disruption or impingement on the medial and lateral collateral ligaments which stabilize the femur to the tibia throughout motion. To do so, the shape of the tabs should curve underneath the collateral ligaments from a position just anterior to the midline such as the anterior one-third, posterior two-thirds junction for example. According to one embodiment, tabs  32  comprise a material that permits customized shaping to protect the patient from any injury to these ligaments. 
         [0029]    In order to maintain proper alignment of the plates, it is preferred to provide the plates in a precontoured form, such that only minimal adjustment to the plates, or no adjustment, is required to maintain proper alignment. Medial plate  12  may be somewhat contoured in situ, but it is preferred for lateral plate  10  to be supplied in essentially a precontoured form with only the distal tab portion  32  being somewhat contoured in situ. 
         [0030]    It will be seen that a variety of means may be used to rigidly anchor plates  10  and  12  to the femoral component. One such anchoring means that may be adapted for the present invention is described in U.S. Patent Application 2007/0225819, incorporated herein by reference. A further alternative anchoring means is shown in  FIG. 9 , which comprises a hollow semi-cylinder  40  configured to wrap around an edge portion  42  of the femoral prosthesis  16 . This latter engagement means may be shaped on site, to snugly and firmly engage the prosthesis. An engagement means of this type would be useful if the femoral component does not have conventional slots on the sides thereof. 
         [0031]    The second plate  12  comprises a medial plate, which engages the distal medial side of the femur. The medial plate is shorter in length than the lateral plate, in order to not interfere with the blood supply on the medial side of the femur. Apart from the shorter length, the medial plate is generally the mirror image of the lateral plate. 
         [0032]    The lateral and medial plates are rigidly connected together by means of a rigid transverse link  50 . Preferably, the link urges the respective plates together to compress the femoral implant between the plates so as to form a mechanically rigid monolithic structure consisting of the opposing plates  10  and  12  and the transverse link  50 . This rigid structure is believed to be more robust and to provide more support to the femur than a single plate attached to the femur, and is of particular value if the patient&#39;s bones are osteoporotic or otherwise weaker than normal. In order to direct all or most of the compressive forces through the artificial knee in order to provide the least stress on the femur, the link is located relatively close to the distal ends of the plates, as close as reasonably possible to the anchoring members. As particularly seen in  FIG. 4 , the link  50  comprises a shaft  52  extending between the respective plates  10  and  12 . The shaft  52  preferably comprises a fixed angle threaded compression screw, which is retained by a compression nut  54 . 
         [0033]    Plates  10  and  12  include holes  56  and  58  which are aligned relative to the distal ends of the plates to allow targeting of the threaded shaft  52  to cross both corresponding holes in the plates  10  and  12 . The lateral plate hole  56  is threaded so the screw will lock into the plate at a fixed angle and the medial plate  12  is unlocked with a slightly larger hole  58  to improve accuracy of screw placement. Compression is applied by attachment of threaded nut  54  to the medial side that can be tightened with a ratcheted torque wrench. The initial drill hole for screw placement is made through a threaded drill guide that fits in the lateral plate holes  22 . 
         [0034]    Link  50  is assembled onto plates  10  and  12  in medical procedure which involves forming an opening through the distal end of the patient&#39;s femur bone, aligned with holes  56  and  58 . At this location, the patient&#39;s femur bone is retained within the femoral component of the artificial knee. Shaft  52  is inserted through this opening, and one end of shaft  52  is threaded into threaded opening  56  of the lateral plate. The opposing end of shaft  52  protrudes through opening  58 , and threaded nut is fastened to this protruding portion. 
         [0035]      FIGS. 10 and 11  illustrate an alternative embodiment of the rigid link. In this version, the rigid link comprises a blade plate  130 , consisting of an elongate box-shaped structure having a flat base  132 , vertical sidewalls  134 , and an open top  136 . The profile of plate  130  is thus generally U-shaped with a flat bottom and vertical sides. Plate  130  fits within opposes openings  138  within plates  10  and  12 . Openings  138  are aligned when plate  10  and  12  are fastened to the patient&#39;s femur. One end of plate  130  includes an elevated rear wall  142  which engages plate  130  within one of the openings  138  within one of plates  10  or  12 . Plate  130  is fastened to the other of plates  10  and  12  by means of a slide-on fastener  140 . In order to install plate  130 , a hole is cut within the patient&#39;s femur in a fashion similar to the embodiments of  FIGS. 1-9 , followed by inserting plate  130  through this opening until rear wall  142  engages one of plates  10  or  12  (depending on whether plate  130  is inserted from the medial or lateral sides). Plate  130  is then fastened to the other of plates  10  or  12  by engaging fastener  140 . 
         [0036]    Plates  10  and  12  are configured so that the linking with the prosthesis will place the femoral component  16  in about a five degree valgus angle in the coronal plane and parallel to the femur in the sagittal plane. Rotation is determined by fracture reduction and by the flexion-extension axis of the knee. 
         [0037]    Transverse link  50  may be removed after the femur has healed to a sufficient degree, by using a strong wire cutting type instrument (not shown) to break through the link. The instrument may be inserted through one or more percutaneous small incisions. The link must be sufficiently robust to avoid breakage before bone healing and still weak enough that an instrument could be introduced to sever the link or otherwise separate the link from the paired plates. 
         [0038]    Plates  10  and  12  can be surgically implanted in patient by means of a removable coupler that holds the plates in position until they are attached to the patient&#39;s femur and/or until the plates are rigidly coupled together with the link. The coupler may comprise a conventional Weber™ clamp that holds the plates in position during the implantation procedure. Alternatively, the coupler may comprise a clamp  60  specifically configured to engage the plates, as seen in  FIG. 3 . The clamp comprises opposing elongate clamp jaws  62 ,  64  that are contoured to extend around the plates  10  and  12  when initially engaged to the femur. The ends of the clamp jaws comprise opposing protrusions  66  that engage aligned depressions or openings  68  within the respective plates  10  and  12 . The opposing jaws  62 ,  64  comprise angled teeth  70  which engage each other in a ratcheting fashion. The respective jaws are operated by handles (not shown) which are pivotally at their upper ends, for operation by the user. The clamp provisionally links the medial and lateral plates  10  and  12  by applying a medial and lateral force to hold the plates  10 ,  12  to the femoral prosthesis prior to the application of the rigid link. 
         [0039]      FIGS. 7 and 8  illustrate an alternative embodiment of the invention, wherein plates  10  and  12  are replaced by an intramedullary rod  100 , extending through the interior of the fractured femur. Rod  100 , which is adapted from known surgical rods of this type, comprises an elongate member configured for insertion within the medulla of the femur. The rod  100  is fixedly retained by an anchoring means engaged to the femoral prosthesis. According to this embodiment, a rigid anchor is provided which consists of opposing engagement members  102  for engaging the prosthesis. The engagement members comprise metal plates  104  having inwardly-turned tabs  106  configured to engage slots  34  within the implant, in the same fashion as in the embodiment of  FIGS. 1-6 . However, in comparison with the first embodiment described herein, these engagement members are relatively short, and are not attached directly to the femur. The respective engagement members are rigidly joined together in a compressive mode by a rigid link  50 , similar to the link of the first embodiment hereof. For example, the link may comprise a threaded shaft  52 , extending through an opening formed within the patient&#39;s femur bone at a location where the bone is within the femoral component of the artificial knee. Shaft  52  is retained by a threaded compression nut  54 . According to this version, the intramedullary rod  100  includes an internally threaded transverse bore  110  at its distal end, through which shaft  52  may be inserted. Shaft  52  is provided with external screw threads  112  which mate with the internal threads  114  of the rod  10 , so as to precisely position and fixedly retain the rod in place on the transverse shaft  110 . Following joining together of the rod and shaft, the compression nut  54  is threaded onto the shaft  52 , in order to apply compressive force between the engagement members  104 , thereby forming a rigid structure between the transverse shaft  52  and the longitudinal intramedullary rod  100 . It will be seen that the respective engagement members may comprise tabs  32  as described above in connection with the first embodiment, or alternatively the hollow cylindrical member  40  of the type shown in  FIG. 9 . 
         [0040]    The embodiments described above comprise conventional surgical grade materials, such as stainless steel. It will be seen that components with metal-to-metal contact, for example between the medial and lateral plates and the knee prosthetic, must be carefully selected to minimize any possibility of bi-metallic corrosive effects. 
         [0041]    A brief description of the surgical technique to use the device is as follows:
   (1) Use a standard medial parapatellar exposure to the knee that was already used for the previous knee replacement.   (2) Slide the lateral femoral condylar locking plate  10  submuscularly proximally alongside the femur.   (3) Place the precontoured medial low profile plate  12  on the condyle and into the medial slot  34  of the femoral prosthesis.   (4) Reduce the tabs  32  of the lateral and medial plates  10  and  12  into the slots  34  of the femoral prosthesis  16  and hold in place with the plate link clamp device  60 .   (5) Insert the distal fixed angled compression screw  50  and compression nut  52  to link the plates  10 ,  12  across the condyles in a more permanent fashion.   (6) Percutaneous K-wires can be inserted into the proximal femur through the plate holes  22  to align the limb and determine the correct length and rotation.   (7) Fill in the remaining screws  24  into the lateral plate using standard or fixed angle locking screws.   
 
         [0049]    An alternative technique for linking the two plates to the femoral prosthesis with an outrigger device  120  that can be used for targeting screw placement across the plates is also shown in  FIG. 4 . 
         [0050]    Another alternative technique for linking an intramedullary rod device to the femoral prosthesis by using a special locking screw with threaded ends that are linked to the slots in the femoral prosthesis on either side by an ‘L’ or curved metal plate. The metal piece fits over a screw which is locked and compressed into place with a threaded nut medially and laterally as shown in  FIG. 5 . 
         [0051]    Although the present invention has been described by reference to the detailed embodiments described above, persons skilled in the art will recognize that the invention is not limited to such detailed embodiments nor the particular details of the invention described herein. Rather, the invention comprises such variations, differences, departures and equivalents of the elements described and characterized herein as would be recognized by persons skilled in the art. The full scope of the invention may be derived from the specification as a whole, including the description and claims, and further including reasonable equivalents to elements described therein.