Abstract:
A technique for preparing a bone to receive an implantable orthopedic component. The technique utilizes a modular bone impaction preform. The preform holds the shape of the implantable component during impaction of bone replacement material to fill defects formed in the bone via disease, congenital defect, or trauma. Typically, the bone impaction preform is used with an instrument that may comprise a trial stem, a trial stem adapter, and a handle. The bone impaction preform and trial stem, as well as the other components, can be made in modular form to facilitate interchangeability.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to the implanting of orthopedic prostheses for replacing portions of skeletal joints, and more particularly, to surgical instruments and their use in preparing bones to receive implantable orthopedic prostheses. 
     BACKGROUND OF THE INVENTION 
     Implant able orthopedic prostheses, in one form, comprise man-made replacements for the ends and articulating surfaces of the bones of the skeleton. Such prostheses are implanted to repair or reconstruct all or part of an articulating skeletal joint that is functioning abnormally due to disease, trauma, or congenital defects. Among the various articulating skeletal joints of the human body, for example, that are eligible to be fitted with implantable orthopedic prostheses, the knee, hip, and shoulder joints are often beneficial recipients. 
     The hip and knee joints play an important role in ambulation, and the shoulder joint plays an important role in manual dexterity. This results in great demand for surgical correction of abnormalities in these joints, and the ability to correct such abnormalities can have an important affect on the quality of life. 
     As used herein, the words proximal and distal are terms of reference that indicate a particular portion of a bone or prosthesis component according to the relative disposition of the natural bone or implanted prosthesis. Proximal indicates that portion of a component nearest the torso, whereas distal indicates that portion of a component farthest from the torso. 
     In a variety of implantation procedures, the bone receiving a prosthetic component is initially prepared for receipt of that component. For example, certain prosthetic components include a stem and an expanded boss that are placed into the medullary canal of the subject bone, e.g., the proximal end of a tibia prepared for receipt of a prosthetic knee joint component having a stem and a tibial boss. Preparation of the bone includes reaming the medullary canal to a size and shape able to receive the stem and expanded boss of the prosthetic component. This surrounding bone tissue supports the prosthetic component. 
     Prior to insertion of the stem, a trial stem is inserted into the reamed region to ensure a proper fit of the prosthetic component. In some procedures, the trial stem remains in the reamed cavity during additional cuts that are made to properly shape the bone. In fact, the trial stem can be used to support cutting instruments utilized in shaping the end of the bone for receipt of the prosthetic component. 
     In some cases, disease, congenital defect, or trauma can create voids in the bone tissue at a location where bone tissue is required to support the implant component. For example, certain degenerative diseases can lead to the formation of a cavity at the proximal end of the tibia or at other joint locations that could benefit from the implantation of a prosthetic device. Such voids, whether cavity or non-cavity voids, must be repaired in such a manner that will allow tissue to attach to the component and provide support for the prosthetic component. 
     A variety of bone replacement materials, such as allograft bone, autograft bone, bone graft substitutes, bone matrix, and suitable biological products may be used to repair voids or other defects in the bone tissue. The bone replacement material is impacted into the contained or uncontained defect to bond with and support the implanted prosthetic component. During this impaction procedure, it would be desirable to prevent the impacted bone from falling into the medullary canal or other areas that will be occupied by the prosthetic component upon implantation. It also would be desirable to provide for proper formation of the bone replacement material so as to accommodate receipt of the prosthetic component. 
     SUMMARY OF THE INVENTION 
     The present invention provides a technique for preparing a bone to receive an implantable orthopedic prosthesis. In one embodiment, the technique comprises the use of a bone impaction preform to hold the shape of an implantable component during impaction of the bone replacement material. In this embodiment, the bone impaction preform is a modular component that may be selectively coupled and uncoupled with a trial stem and/or a trial stem adapter. 
     In modular form, a variety of bone impaction preforms and trial stems can be combined according to the type and size of the joint being prepared for receipt of an implantable orthopedic prosthesis. With this modularity, a relatively small number of trial stems and modular preforms can be combined in a relatively large number of configurations. In one exemplary application of the present technique, a practitioner selects a desired combination of a modular trial stem in a modular preform. The inner region or medullary canal of a bone is then reamed to sufficient size to accommodate the stem of an implantable prosthetic component. The modular trial stem is moved into the reamed canal until the modular preform is at least partially positioned within the void to be prepared. Once positioned, bone replacement material is readily packed around the modular preform. The modular preform prevents bone replacement material from falling into the medullary canal while holding the shape of the component to be implanted. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements, and: 
     FIG. 1 is a front view of a bone impaction instrument, according to one embodiment of the present invention; 
     FIG. 2 is an exploded view of the instrument illustrated in FIG. 1; 
     FIG. 3 is an alternate embodiment of the instrument illustrated in FIG. 1; 
     FIG. 4 is an exploded view of the instrument illustrated in FIG. 3; 
     FIG. 5 illustrates a bone, e.g., the proximal end of a tibia, having a void to be filled with bone replacement material prior to implantation of an orthopedic prosthetic component; 
     FIG. 6 illustrates the use of a reamer for reaming a portion of the medullary canal of the bone illustrated in FIG. 5; 
     FIG. 7 illustrates the use of a cone reamer for removing bone material that would interfere with the preform and the prosthetic component to be implanted; 
     FIG. 8 illustrates the instrument of FIG. 1 disposed within the proximal end of a tibia; 
     FIG. 9 is similar to FIG. 8 except for removal of the instrument handle; and 
     FIG. 10 illustrates one example of additional preparation of the bone replacement material to accommodate a particular orthopedic prosthetic component. 
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     Referring generally to FIG. 1, a bone impaction instrument  20  is illustrated according to one embodiment of the present invention. Although the embodiment illustrated is designed for use in the proximal tibial region during implantation of an orthopedic prosthesis at the knee joint, the selection of this design is to facilitate explanation and should not be construed as limiting. For example, similar bone impaction instruments  20  can be designed for use at the proximal or distal ends of the femur, proximal or distal ends of the humerus, one or more ends of the ulna, and potentially at other joint locations by appropriately modifying the shape and size of the instrument. 
     In the embodiment illustrated, bone impaction instrument  20  comprises a trial stem  22 , a bone impaction instrument or preform  24 , a trial stem adapter  26 , and a handle  28 . Each of these components can be constructed from a suitable, biocompatible material, such as surgical stainless steel. In this embodiment, trial stem  22 , bone impaction preform  24 , trial stem adapter  26 , and handle  28  are modular in form to allow the interchange of components. 
     As illustrated best in FIG. 2, each of the components may be selectively separated to permit the removal and/or substitution of desired components. As illustrated, trial stem  22  comprises a distal end  30  designed for insertion into the bone. (It should be noted that end  30  is described as a distal end because the illustrated instrument is for use on the proximal tibia. However, the lead end  30  could actually be the proximal end when the instrument is designed for other joint locations.) Trial stem  22  also comprises a proximal coupling end  32  designed for connection to bone impaction preform  24  or other components, such as trial stem adapter  26 . 
     Bone impaction preform  24  includes a distal coupling end  34  designed to engage proximal coupling end  32  of trial stem  22 . A variety of mechanisms can be utilized to permit selective coupling of preform  24  with trial stem  22 . However, one exemplary design utilizes a threaded protrusion  36  extending axially at proximal coupling end  32  for receipt in a corresponding threaded opening  38  of distal coupling end  34 . 
     Regardless of the specific coupling mechanism, the modular design facilitates the assembly of a desired bone impaction instrument by permitting selection of interchangeable trial stems, e.g., trial stem  22 A, and interchangeable bone impaction to preforms, e.g., preform  24 A. 
     Bone impaction preform  24  also may be designed for selective coupling with trial stem adapter  26 . In the embodiment illustrated, preform  24  includes a proximal coupling end  40  having, for example, a threaded protrusion  42 . Trial stem adapter  26  has a corresponding distal coupling end  44  with a threaded, axial opening  46  for threadably receiving protrusion  42 . Thus, trial stem  22 , bone impaction preform  24 , and trial stem adapter  26  may be readily connected and disconnected to permit the substitution and removal of components to adjust parameters for a given procedure or patient. 
     In the illustrated embodiment, handle  28  also may be selectively attached and detached from trial stem adapter  26 . An exemplary handle for use with the instrument is a quick-release handle as known to those of ordinary skill in the art. 
     Bone impaction preform  24  is designed for preforming an appropriate opening in bone replacement material impacted in a void at the proximal end of a tibia. In other words, the preform is generally of the size and shape of a tibial boss portion of an implantable prosthetic component, as will be explained more fully below. Bone impaction preform  24  has an outer surface that tapers generally radially outwardly intermediate distal coupling end  34  and proximal coupling end  40 . Specifically, the maximum diameter of bone impaction preform  24  is greater than the maximum diameter of trial stem  22  and, in this embodiment, the diameter of bone impaction preform  24  increases moving from distal coupling end  34  towards proximal coupling end  40 . 
     It should be noted that the actual configuration of bone impaction preform  24  can be adjusted according to the shape of the component to be implanted. Additionally, the shape of bone impaction preform  24  typically varies when used at other skeletal locations. For example, a modular system for use at a proximal femur location for repair of a hip joint is illustrated in FIGS. 3 and 4. In this embodiment, a trial stem  50  may be selectively coupled to a bone impaction preform  52  via a proximal coupling end  54  of trial stem  50  and a distal coupling end  56  of preform  52 . In this design, preform  52  expands outwardly from trial stem  50  such that the cross sectional area of preform  52  increases moving in the direction away from trial stem  50 . However, the overall shape of preform  52  is substantially different than that of bone impaction preform  24  to accommodate specific implantable prosthetic components used in a hip or partial hip replacement. A wide variety of trial stems and preforms can be adapted to the desired shape of prosthetic components implanted at a given joint. 
     An exemplary implementation of bone impaction instrument  20  will now be described with reference to an exemplary proximal tibia being prepared for implantation of a prosthetic component. As illustrated in FIG. 5, a proximal tibial region  60  has a void  62  created by a deterioration of the bone tissue. Void  62  may comprise a cavitary or non-cavitary void that must be filled with appropriate bone replacement material to support the prosthetic component. Void  62  leads to a medullary canal  64  generally at the longitudinal center of the bone. 
     Initially, a reamer  66  having a cutter portion  68  and a handle  70  is used to remove bone for receipt of an implant stem, as illustrated in FIG.  6 . Specifically, the cutter portion is inserted into canal  64  and rotated to remove bone tissue and form a reamed region  72 . Preferably, the tissue is sufficiently removed to expose hard, cortical bone. 
     If bone tissue interferes with the positioning of preform  24  and the subsequent prosthetic component, an additional reamer, such as a cone reamer  67 , may be used in the area of void  62 , as illustrated in FIG.  7 . Cone reamer  67  also may be moved, e.g., rotated, by handle  70  until the area is cleared for bone impaction preform  24 . Once cleared, cone reamer  67  is pulled from void  62  and bone impaction instrument  20  is moved into position. Handle  28  and trial stem adapter  26  are used by the practitioner to insert trial stem  22  into the reamed region  72  of canal  64 . Trial stem  22  is positioned such that preform  24  is disposed at least partially within void  62 , as illustrated best in FIG.  8 . 
     Subsequently, handle  28  is removed from trial stem adapter  26  (see FIG. 9) and a bone replacement material  74  is disposed in void  62  and impacted around bone impaction preform  24 . An exemplary bone replacement material may be a granulated bone structure, such as allograft bone, autograft bone, bone graft substitutes, bone matrix, or other suitable bone replacement materials. At this point, handle  28  may be reattached to trial stem adapter  26  for removal of preform  24  and trial stem  22 . The preform  24  and trial stem  22  are then pulled from void  62  and reamed region  72  for insertion of a suitable orthopedic prosthetic component. 
     However, certain procedures may require additional preparation of proximal tibia  60  and bone replacement material  74 . For example, in this exemplary implantation procedure, a trial tibia base plate  76 , and the trial stem  22  are inserted into the cavity formed in bone replacement material  74 . Once trial tibia base plate  76  is properly positioned at the pre-prepared end of proximal tibia  60 , additional bone replacement material formation procedures can be performed, if necessary, to accommodate the particular shape of a prosthetic device. For example, in the embodiment illustrated in FIG. 10, a keel broach  78  is inserted through trial tibia base plate  76  to create a keel geometry within bone replacement material  74 . This is just one example of a variety of finishing steps that may be conducted with respect to either the tissue itself or the bone replacement material. 
     Once the proper geometry is created in bone replacement material  74 , a trial reduction may be performed. Typically, a trial reduction is used to check the movement of other prosthetic joint components with the various trial components in place. Subsequently, the trial tibia base plate  76 , keel broach  78  and trial stem  22  are removed to leave reamed region  72  along with a preformed cavity region  80  within impacted bone replacement material  74 . 
     The prosthetic component to be implanted is then cemented and moved into the appropriately shaped cavity region  80  and reamed region  72 . In the particular example discussed, the implanted component would have a stem corresponding to trial stem  22  and a tibial boss corresponding to the shape of preform  24  and keel broach  78 . It should be noted that this same procedure for forming an appropriate receptacle to receive an implantable component also can be utilized with cementless applications. 
     It will be understood that the foregoing description is of exemplary embodiments of this invention, and that the invention is not limited to the specific form shown. For example, the modular bone impaction instrument can be designed for use at a variety of joints other than those illustrated and discussed herein. The shape and configuration of the trial stem and bone impaction preform can be adjusted to correspond with the specific design of the component to be implanted. The procedural steps discussed above for use of the bone impaction instrument may be altered depending on the particular procedure. For example, a variety of other preparation steps, including bone cutting and other bone formation techniques may be utilized in preparing the tissue for attachment of the orthopedic prosthetic device. These and other modifications may be made in the design and arrangement of the elements without departing from the scope of the invention as expressed in the dependent claims.