Abstract:
An apparatus and method for reaming a bone, facilitating pre-implantation alignment of a prosthesis using trial components, and preparing a bone site for anti-rotational implantation of the prosthesis is provided. The apparatus includes a boring end, a mating end disposed opposite the boring end, and a keying aid disposed between the boring end and mating end. The keying aid facilitates preparation of the bone canal for anti-rotational placement of a prosthesis having an anti-rotational component, or key. The method includes using the apparatus to ream a bone canal, conduct alignment trials, mark the bone canal with the desired orientation of the trial component, and insert the prosthesis into the marked bone canal for anti-rotational engagement with the reamed bone.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a surgical tool and method for preparing a bone site for implantation of an orthopedic endoprosthesis having anti-rotational components as well as facilitating pre-implantation alignment of the prosthesis. More particularly, the invention relates to aligning and implanting a femoral component of a total hip joint or a humeral component of a shoulder joint. However, it may also be used to align and implant femoral and tibial components of a prosthetic knee joint. 
   The method and surgical tool that is used to open and form the bone canal also facilitates pre-implantation alignment of the prosthesis using trial components, as well as preparation of the bone site for anti-rotational implantation of the prosthesis. Most commonly, this invention would be employed in connection with the implantation of prostheses into long bones, but it would not be limited thereto. The quantity of medical instruments, as well as the time and number of movements required in forming a bone canal and conducting pre-implantation alignment of the prosthesis using trial components is reduced with the use of this surgical tool. Also, the risk of rotational failure of the prosthesis is reduced when it is implanted into a bone canal that is shaped to accept it&#39;s anti-rotational features. 
   As used herein, when referring to bones or other body parts, the term “proximal” means closest to the heart, and the term “distal” means more distant from the heart. When referring to tools and instruments, the term “proximal” means closest to the practitioner, and the term “distal” means distant from the practitioner. 
   2. Description of Related Art 
   Proper alignment of orthopedic implants, such as joint replacement prostheses, is essential to the success of surgical procedures involving replacing damaged joints. Such prostheses commonly include stems for insertion into the canals of long bones. A stem is used to anchor the prosthesis in a bone cavity. 
   A bone cavity is commonly prepared by forming a hole in the bone, such as by drilling or reaming, and creating an opening sized and contoured to receive the stem of the prosthesis. The stem is inserted into the bone cavity, and optionally, a joint bearing member may be attached or coupled to the stem, with the joint bearing member extending out of the bone cavity. 
   Typically, once a stem that is coupled to a femoral component, for example, is inserted into a prepared bone cavity, it is necessary to rotate the stem to properly orient it. Sometimes, the stem must be removed and reinserted, which may damage the bone cavity and surrounding bone, as well as increase intra-operative time. 
   To achieve pre-implantation alignment of the prosthesis, the prosthesis stem is typically manipulated, and the desired position identified, by marking the bone and the stem. Subsequent alignment during implantation is then achieved by using the marks to align the stem with respect to the bone. The drawback to this method is the potential imprecision in the alignment. Because the marks on the stem and bone are not in close proximity to each other, parallax and other problems associated with alignment by eye may result. Also, the stem may move from its aligned position as it is inserted. 
   Misalignment of an implanted prosthesis in the human body is an undesirable result in joint replacement surgery. To alleviate implant misalignment, past efforts have been directed toward providing some pre-implantation trialing and marking methods that strive to achieve an implanted prosthesis having the optimal orientation. 
   One such effort is presented in U.S. Pat. No. 4,678,471 to Noble et al., entitled “Method and Apparatus for Preventing Rotational Failure of Orthopedic Endoprostheses”. Noble et al. relates to an apparatus for making at least one groove in a medullary canal in a bone. The apparatus is an elongate member having a flattened head portion and a stem, and having one channel that receives a cutting tool for cutting a groove in the canal, remote from the resected bone surface. 
   Another effort is presented in U.S. Pat. No. 5,053,037 to Lackey, entitled “Femoral Instrumentation for Long Stem Surgery”. Lackey relates to a bone cutting block in conjunction with a reamer, for forming the end of a long bone. 
   Yet another effort is presented in U.S. Pat. No. 6,206,884 to Masini, entitled “Reduction-Based Joint Replacement Apparatus and Methods”. Masini relates to a reduction-based orthopedic system facilitating the installation of a properly oriented prosthetic component. Separate elements of the system for trialing and marking the bone include an anchoring unit, a trialing component, and a cutting guide. 
   Despite these efforts, there is still a continuing need for improving tools and methods for preparing a bone site for implantation of a prosthesis having anti-rotational components as well as facilitating pre-implantation alignment of the prosthesis. 
   It is therefore an object of the present invention to provide a surgical tool which facilitates reaming a bone canal, attaching and manipulating a trial component, and marking the rotational alignment of the trial component on the bone. 
   It is a further object of the present invention to provide a surgical tool which facilitates engagement to various tools and components for the purposes of both reaming a bone canal as well as facilitating trialing. 
   It is yet another object of the present invention to provide a surgical tool for cutting keyways in the bone once the rotational alignment of the trial component is determined. 
   SUMMARY OF THE INVENTION 
   These and other objects are achieved by the present invention, which is a surgical tool for reaming a bone, determining the rotational alignment of a prosthesis, and marking this alignment on the bone. 
   The surgical tool has a first end adapted to extend into a bone canal in a bone, a second end opposite the first end preferably adapted to engage various instruments and other tools, and at least one keying aid that is adapted to facilitate identifying the tool&#39;s orientation on a bone. The surgical tool also has a central longitudinal axis. 
   The first end of the tool is cylindrical and has a cross-section that is perpendicular to the longitudinal axis. In the preferred embodiment, the first end has flutes and cutting surfaces, or teeth, to shape a bone canal. The cutting teeth are intended to cut away undesired bone, while the flutes convey the cut bone out of the bone canal. It is understood, however, that other bone-removing features may be incorporated on the first end of the reamer to help prepare the bone canal for insertion of an implant. It is further noted that a set of surgical tools may be provided, each surgical tool having a differently sized cross-section. For example, a set of surgical tools having cross-sectional diameters ranging from 11 to 19 millimeters may be provided. 
   In the preferred embodiment, the second end of the surgical tool has a mating geometry that enables it to be engaged by various mating instruments and trial implants. For example, the second end may be engaged by a power tool, or a manual tool such as a T-handle, that would rotate the surgical tool, causing the first end to ream and remove undesired bone from the bone canal. The second end may also be engaged by a trial component used for determining the rotational alignment of a prosthesis in the bone. 
   In the preferred embodiment, once placed on the second end of the surgical tool, the trial component, such as a femoral component of a knee implant, may be rotated with the surgical tool in the bone canal, thereby allowing a surgeon to determine the desired orientation in which he wishes to permanently set the prosthesis. When these motions are performed in conjunction with articulation of the joint being operated upon, as is commonly known to those skilled in the art, this is referred to as “trial reduction”. 
   Once the desired orientation is determined, the surgical tool advantageously has a combination of features or guides on the second end, that facilitate marking the bone to identify this orientation thereon so that a prosthesis may be inserted in accordance with this orientation. The combination of features includes a flange with two alignment grooves on its outer periphery, and at least one, but preferably four guide channels that penetrate the flange. 
   With regard to the flange, preferably one or both of the two grooves may be used as guides for a surgical marker to mark the bone after rotational alignment of the trial component has been performed. Once the bone is marked, the surgical tool may be removed from the bone canal. Thereafter, additional procedures known to those skilled in the art may be employed to further prepare the bone canal for anti-rotational implantation of a prosthesis in accordance with the marks on the bone. For example, a surgeon may manually cut out a keyway in the bone adjacent to the bone canal and, using a prosthesis having a feature, or key, corresponding to the keyway, insert the prosthesis so that it engages both the bone canal and keyway. This results in implanting the prosthesis in accordance with the mark relating to the desired position previously set by the trial component. 
   Alternatively, once the desired orientation for the prosthesis is determined, the trial component may be disengaged from the surgical tool while maintaining the tool&#39;s position in the bone canal. The four guide channels may then be used to shape the bone canal by forming keyways, thereby preparing the bone canal for implantation of a prosthesis having anti-rotational components, or keys. 
   Preferably, the four guide channels each have a longitudinal guide channel axis, as well as a cross-section, or profile, that is perpendicular to the guide channel axis. The four guide channels are advantageously located on the surgical tool such that their profiles overlap, or intersect the cross section of the first end of the surgical tool. In the preferred embodiment, the four guide channels are spaced equidistantly, equiangularly and parallel to the longitudinal axis of the surgical tool, but other variations are possible. For example, the guide channels may be oriented such that their guide channel axes are not parallel to the longitudinal axis of the surgical tool. 
   The guide channels are each adapted to accept a drill bit and direct the drill bit to cut anti-rotation channels, or keyways, on the periphery of the bone canal, thereby forming a non-circular bone canal cross-section. It is also recognized, however, that other tools, such as a rasp or punch, may be used in conjunction with the guide channels to form the keyways. 
   In the preferred embodiment, the grooves on the flange and the guide channels are preferably used in combination. The grooves are used to mark the surgical tool&#39;s orientation on the bone, and then the guide channels are used to form the keyways in the bone canal. Thereafter, the markings made by using the grooves help validate the correct positions of the keyways. 
   In the preferred embodiment, the distal portion of the flange that faces the first end of the surgical tool, transitions smoothly into the second end of the surgical tool via a chamfer or fillet, such that, when applied, it registers a countersink on the top surface of the bone canal. However, it is envisioned that a substantially perpendicular transition may be made as well. Therefore, according to the preferred embodiment, keyways are formed on the countersink or radius in the bone canal. Alternatively, with a flange having a substantially perpendicular transition, the keyways would be formed on the top surface of the bone canal without the countersink or radius. 
   Once the anti-rotation channels are formed, the surgical tool is removed from the bone canal. The prepared bone canal then receives a prosthesis having a stem with anti-rotational components, such as keys, that align with the cut keyways, and help secure the prosthesis from rotating in the bone canal. 
   The preferred method of using the present invention includes attaching a power tool to the second end of the surgical instrument, advancing the surgical instrument into the bone canal, disengaging the power tool from the surgical instrument, attaching a trial component to the second end of the surgical instrument, determining the desired orientation of a prosthesis by moving the trial component relative to the bone canal, marking the desired orientation on the bone with the aid of the surgical instrument, disengaging the trial component from the surgical instrument while holding the surgical instrument stationary in the bone canal, drilling keyways adjacent to the bone canal with drill bits guided by guide channels in the second end of the surgical tool, removing the surgical tool from the shaped bone canal and implanting a prosthesis having anti-rotational elements, such as keys thereon, for engaging the keyways in accordance with the desired orientation previously determined with the trial component. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the drawings, wherein similar reference characters denote similar elements throughout the several view: 
       FIG. 1  is a perspective view of the surgical tool. 
       FIG. 2  is a top view of the surgical tool depicted in FIG. Â  1 . 
       FIG. 2A  is a cross-section of the surgical tool along line  2 A in  FIG. 1 . 
       FIG. 3  is an exploded view of a driving tool, the surgical tool and a resected end of a proximal femur. 
       FIG. 4  is a partially exploded view of a trial component positioned over the surgical tool which is situated in the bone canal of the proximal femur. 
       FIG. 5  is a partially exploded view of a marker positioned over the surgical tool which is situated in the bone canal of the proximal femur. 
       FIG. 6  is a partially exploded view of a drill bit positioned over the surgical tool which is situated in the bone canal of the proximal femur. 
       FIG. 7  is an exploded view of a prosthesis positioned over a bone canal in the proximal femur that was formed with the surgical tool. 
   

   DETAILED DESCRIPTION 
   Referring to  FIGS. 1 and 2 , there is illustrated the surgical tool or instrument of the present invention, generally denoted as  10 . In the preferred embodiment, instrument  10  has a first distal end  100  and a second proximal end  200  extending along longitudinal axis  110 . First end  100  is in the form of a reamer  102  used to ream a bone canal in a long bone, while second end  200  has multiple applications including providing an attachment interface to various instruments, and providing elements facilitating marking and forming keyways in the bone. Both ends  100  and  200  of instrument  10  will be discussed in more detail, below. 
   With reference to  FIGS. 1–3 , in the preferred embodiment, reamer  102  has multiple spiraled cutting teeth  120  for reaming bone canal  710  to a desired diameter. Cutting teeth  120  form a circular cutting profile  130  that is perpendicular to longitudinal tool axis  110 . Profile  130  is essentially the cutting perimeter of first end  100  of instrument  10 . It is also envisioned that other forming elements may be incorporated at first end  100  of surgical instrument  10  to facilitate other common methods of preparing bone canal  710 , such as features for cutting, rasping, impacting or otherwise forming bone canal  710 . 
   Referring to  FIGS. 1 and 2 , reamer  102  is a standard bone reamer wherein each spiral cutting tooth  120  has a cutting edge  122  that engages the inner circumferential surface  712  of bone canal  710 . When reamer  102  is rotated clockwise R, undesired bone in bone canal  710  is cut away by cutting edges  122  and conveyed out of bone canal  710 , toward second end  200 , via flutes, or channels  124  on reamer  102 . In this manner, loose bone particles do not remain in bone canal  710  during drilling. 
   In the preferred embodiment, as best seen in  FIG. 1 , between reamer  102  and flange  280 , is a circumferential series of cutting teeth  220  and guide channels  230 . Straight cutting teeth  220  run substantially from the end of spiraled teeth  120  up to the bottom of flange  280 . These straight cutting teeth  220  further facilitate shaping bone canal  710 . Four guide channels  230  are formed intermediate the straight cutting teeth  220 , although it is recognized that at least one guide channel would suffice. Since guide channels  230  are straight, cutting teeth  220  must also be straight, as opposed to spiraled, so that guide channels  230  do not have interruptions in their lengths. 
   A recessed transition portion  150  is provided as a separation between spiraled teeth  120  and straight teeth  220 . This is primarily for machining purposes. It is understood, however, that various other transition configurations may exist for this purpose. 
   Proximal of cutting teeth  220 , second end  200  includes flange  280  which, in the preferred embodiment, has a generally cylindrical shape centered about longitudinal axis  110 . The distal portion of flange  280  that faces first end  100  of surgical tool  10 , transitions smoothly into second end  200  via a chamfer or fillet, such that, as shown in  FIG. 7 , it registers a countersink or radius  716  on top surface  740  of bone canal  710 . 
   Flange  280  further has two oppositely oriented substantially flat surfaces  282  extending parallel to axis  110  and two radially extending mating surfaces  284  positioned perpendicularly to axially extending surfaces  282 . As best seen in  FIG. 1 , second end  200  also has a cylindrical surface  290  terminating in an annular mounting recess  272 , and an annular mounting lip  270  just above recess  272 . Lip  270 , recess  272 , and surfaces  282  and  284  provide features and surfaces for engaging, or facilitating the mounting of, various instruments such as driving tools and trial components, which will be discussed in more detail, below. Numerous alternative configurations and features, however, are also envisioned. Additionally, a counter-rotation hole  250 , and a retraction hole  260 , both located on the second end  200  of instrument  10 , are provided, and will be discussed in more detail, below. Moreover, it is recognized that while having any of the features of second end  200  described herein, second end  200  may also be shaped, at least in part, as a trial component. 
   Flange  280  further has oppositely oriented alignment marking grooves  240  on its periphery. These grooves  240  may be used to mark the rotational orientation, or position of instrument  10 , on resected bone surface  740  of bone  700 . 
   In the preferred embodiment, second end  200  of instrument  10  also has four peripherally located guide channels  230  that run distally along surface  290  of second end  200 , penetrate flange  280 , and terminate at transition portion  150 . With particular reference to  FIG. 2A , preferably each guide channel  230  has a circular profile  232  which is perpendicular to a guide channel axis  210 , and at least in the area of teeth  220  distal of flange  280 , is partially open. As seen in  FIG. 2 , each guide channel  230  is oriented on instrument  10  such that guide channel axis  210  is substantially parallel to longitudinal tool axis  110 , and profile  232  intersects cutting profile  130 , i.e., the full circular profile  232  of each channel  230  extends beyond the diameter of profile  130 . However, other configurations of guide channel axes relative to the longitudinal tool axis are also envisioned. As will be explained in more detail below, the intersecting profiles on instrument  10  facilitate forming a cylindrical bone canal having anti-rotation keyways. 
   Guide channels  230  are shown in  FIGS. 1 and 2  as being equidistantly and equiangularly spaced apart from each other, however it is envisioned that other geometric configurations are conceivable as well. In addition, as few as one channel can be used. As will be discussed below in more detail, grooves  240 , as well as guide channels  230 , are used to the mark the rotational position of instrument  10  on resected bone surface  740 , and guide channels  230  may be further used to form keyways in bone canal  710  in order to prepare it to receive an implant having complimentary anti-rotational elements, or keys, formed thereon. 
   Referring to  FIG. 3 , instrument  10  is shown positioned over an unreamed bone canal  710  in a bone section such as the resected proximal femur  700 . It is recognized, however, that the bone section may also be a distal femur, or an end of the tibia or humerus. Above instrument  10  is the driver interface portion  310  of a driving tool, or driver  300  such as a manual or power drill. In operation, driver interface  310  of driver  300  engages instrument  10  at end  200  via mounting lip  270 , mounting recess  272 , vertical mating surfaces  282  and horizontal mating surfaces  284 . Such an engagement of parts facilitates controlled manipulation of instrument  10 . Specifically, if driver  300  is a drill, then clockwise R rotation of driver  300  translates through second end  200  into rotation of reamer  102 , thereby causing first end  100  of instrument  10  to shape bone canal  710 . 
   With reference to  FIG. 4 , once bone canal  710  has been reamed, and the underside of flange  280  of instrument  10  is in flush contact with resected bone surface  740 , driver  300  is disengaged from proximal second end  200 . At this point, without removing instrument  10  from bone canal  710 , a trial component, such as the one depicted by hip joint element  400 , may be placed on second end  200 . In the preferred embodiment, trial component  400  has a similar interface configuration  410  as the interface  310  of driver  300 , and mates similarly with second end  200 . 
   While engaged to second end  200 , trial component  400  and instrument  10  may be freely rotated to any position, and trial reduction may be performed. This allows a surgeon to determine the optimal orientation of trial component  400  for implantation into proximal femur  700  in view of the actual expected function of a prosthesis in the hip joint. 
   Referring to  FIGS. 5–7 , once the optimal orientation of trial component  400  is set, this position may be marked on proximal femur  700  in at least one of two ways. In one approach, without disengaging trial component  400  from second end  200 , a marking instrument  500 , such as a marker  510 , may be set against groove  240  on flange  280  of instrument  10 , and used to mark resected bone surface  740 . Optionally, both grooves  240  may be used to make such marks on bone surface  740 . These marks identify the desired rotational orientation in which implant  600  should be implanted into proximal femur  700 . Alternately, marking may be done by using the drill bit  520  of  FIG. 6 , which may be guided along grooves  240  to make indentations (not shown) in resected bone surface  740 . Once the marks are made on bone surface  740 , instrument  10  may be removed from bone canal  710 , and further preparatory measures may be implemented in accordance with procedures known to those skilled in the art, for preparing the marked implant site for anti-rotational implantation of implant  600 . 
   Alternatively, once the optimal orientation of trial component  400  is set, while keeping instrument  10  in its determined rotational position in bone canal  710 , trial component  400  is disengaged from second end  200  of instrument  10 . Drill bit  520  is then attached to a drill (not shown), inserted into at least one guide channel  230 , and used to drill at least one keyway  730  on the periphery of bone canal  710 . It is also recognized, however, that other tools, such as a rasp or punch, may be used in conjunction with the guide channels to form the keyways. Straight and uninterrupted guide channels  230  advantageously facilitate insertion and controlled manipulation of drill bit  520  during this process. 
   In the preferred embodiment, the grooves on the flange and the guide channels are used in combination. The grooves are used to mark the surgical tool&#39;s orientation on the bone, and then the guide channels are used to form the keyways in the bone canal. Thereafter, the markings made by using the grooves help validate the correct positions of the keyways. 
   In order to prevent instrument  10  from rotating in bone canal  710  while anti-rotational channels  730  are being drilled, there is provided a counter-rotation hole  250  on instrument  10 . Counter-rotation hole  250  penetrates instrument  10  through flange  280 , substantially perpendicularly to longitudinal tool axis  110 , and in between vertical mating surfaces  282 . During the drilling of channels  730 , a bar or tool (not shown) may be inserted into hole  250 , and held in position to prevent instrument  10  from rotating. 
   Once anti-rotation channels  730  are prepared, drill bit  520  may be removed from instrument  10 . To assist in removing instrument  10  from bone canal  710 , there is optionally provided a threaded retraction hole  260  on second end  200  of instrument  10 . A tool (not shown) may be threadably inserted into hole  260 , and then used to facilitate the retraction of instrument  10  from bone canal  710 . The result of the reaming and drilling process described by the second approach herein, is a bone canal  710  having a countersink  718 , smooth circumferential canal surface  714 , and at least one keyway  730 . It is understood, however, that if the transition between flange  280  and second end  200  is substantially perpendicular, the keyway  730  would be formed on top surface  740  of bone canal  710  without countersink  716 . 
   Now that the forming of bone canal  710  has been completed, an implant such as the one depicted in  FIG. 7  by element  600 , having anti-rotational components, or keys  610 , may be implanted into bone canal  710  according to the previously measured, marked and machined orientations of keyways  730 . The mating of keys  610  with keyways  730 , on the periphery of bone canal  710 , helps prevent the rotation of implant  600  about its axis  110  within bone canal  710  after implantation. 
   Instrument  10 , as taught herein, is used to prepare an intramedullary bone canal  710  in the proximal femur  700  for anti-rotational implantation of implant  600 . However, it is noted that in a variety of sizes, instrument  10  and the methods for its use, may be implemented on other joints for similar procedures. For example, the distal femur, tibia and the proximal humerus may be prepared in a similar manner to accept a prosthesis for interaction with the knee or shoulder joint, respectively. 
   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.