Abstract:
A handling tool for coupling to a cutting guide includes a substantially elongate first end shaped to be grasped by human hand. The tool includes at least two mating tines, disposed at a second end of the tool. The mating tines are biased to move toward each other and are forced apart from each other by a cam portioned therebetween. The mating tines each include a mating means for mating the tool with the cutting guide.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 08/972,774, filed on Nov. 18, 1997, now U.S. Pat. No. 5,910,143, which is a continuation-in-part application under 37 CFR 1.60, of U.S. application Ser. No. 08/727,281, now U.S. Pat. No. 5,688,281, filed on Oct. 9, 1996, by Phil Cripe and Michael Mauldin for INTRAMEDULLARY ALIGNMENT GUIDE, which is a continuation of 08/357,430 filed Dec. 16, 1994, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     This invention relates to medical instruments and a method for use pertaining particularly to an improved intramedullary alignment guide and tool for accurately preparing and shaping the distal femur end surface to receive a knee prosthesis to be secured thereto. 
     2. Background Information 
     Knee surgery for the replacement and repair of knee joints has become commonplace in recent years. Total knee replacement systems and prostheses are available from a variety of manufacturers. Such total knee replacement systems, when properly installed, approximate the patient&#39;s natural knee movement. However, all knee prosthetic devices need to be properly fitted and installed to achieve an optimum fit and alignment. Proper alignment of the prosthetic device is critical to the successful outcome of a total knee replacement surgery. It is well known that it is desirable to provide an effective system of instruments and methods which ensure that the distal femur end is properly prepared for receiving the prosthetic device. 
     Some prior art systems have been developed which purport to assist a surgeon in preparing distal femur and proximal tibia ends for receiving knee prosthetic devices. One such system is shown in Petersen, U.S. Pat. No. 4,524,766. Petersen teaches a surgical knee alignment and cutting guide system which references a patient&#39;s mechanical axis, and from that reference, provides a cutting guide for shaping the patient&#39;s proximal tibia to receive the tibia portion of a knee prosthesis. Cutting guides are referenced from the tibia components of the knee prostheses for shaping the distal femur end to receive the femur portion of the knee prostheses. However, referencing from the patient&#39;s tibia introduces inaccuracies into the prosthetic alignment process. It is therefore desirable to provide an alignment system which references directly from the patient&#39;s distal femur end and provides for locating the patient&#39;s mechanical axis from the anatomic axis. By referencing from the patient&#39;s mechanical axis, an improved alignment system should employ an alignment guide and cutting guide to properly prepare the distal femur end for receiving the knee prosthetic device. 
     Another system for shaping the distal femur end is taught in Dunn, et al., U.S. Pat. No. 4,759,350. Dunn teaches a system of instruments for shaping the distal femur and proximal tibia surfaces to receive components of a knee prosthesis for knee replacement surgery. The Dunn system determines a patient&#39;s mechanical axis with reference to the patient&#39;s anatomic axis by using an alignment guide that is adapted to fit into a hole drilled into the distal femur end and intersecting the femoral intramedullary canal. Cutting guides or distal femoral resectors are attached to the alignment guide and are used to prepare the distal femur end to receive the femur portion of the prosthetic device. 
     The Dunn alignment guide is used to align the distal femoral resector or cutting guide so that a cut can be made in the distal femur end so as to provide a flattened bone end surface which is perpendicular to the patient&#39;s mechanical axis. The cut in the distal femur end is based upon a determination of the relative angular displacement of the patient&#39;s mechanical axis from the patient&#39;s anatomic axis. To enable a surgeon to cut the distal femur end properly and at the appropriate angle with respect to the mechanical axis, the distal femoral cutting guide is displaced relative to the intramedullary alignment guide such that a cutting slot in the cutting guide is exactly perpendicular to the patient&#39;s mechanical axis. The distal femoral cutting guide is secured to the alignment guide using a plurality of pins. A surgeon can pivot the cutting guide such that a cutting slot in the cutting guide is exactly perpendicular to the patient&#39;s mechanical axis. A pivot pin is fitted into the distal femoral cutting guide to allow the guide to pivot slightly with respect to the intramedullary alignment guide. The surgeon uses an alignment pin which may be inserted through one of a plurality of holes in the distal femoral cutting guide to achieve the desired angular displacement between the cutting guide and the alignment guide. 
     Disadvantageously, the system taught by Dunn requires that the distal femoral cutting guide pivot about the medial condyle of the femur when a surgeon inserts an alignment pin through one of the plurality of holes in the cutting guide and into the alignment guide. By pivoting about the medial condyle of the femur, and not about the intramedullary canal, the Dunn system increases the length of the cut across the distal femur end as the angular displacement between the distal femoral cutting guide and the alignment guide is increased. Conversely, as the angular displacement between the cutting guide and the alignment guide is decreased, due to a small angular displacement between the patient&#39;s anatomic and mechanical axes, the length of the cut in the distal femur end is correspondingly decreased. Therefore, there is a need for an improved intramedullary alignment guide which provides proper angulation of the prepared distal femur end yet allows the distal femoral resector or cutting guide to be pivoted about the patient&#39;s intramedullary canal. 
     To ensure that proper limb alignment is restored to a patient, a combination of intramedullary alignment devices and extramedullary alignment check rods have been used. The combination of intramedullary alignment devices and extramedullary alignment check rods increase the probability for a successful clinical outcome. 
     The prior art systems for preparing distal femur ends for receiving knee prosthetic devices are difficult to assemble, require an inventory having a number of small, easily lost components, and require significant operating-room time for their use. For example, the system taught by Dunn includes a femoral alignment guide, an anterior femoral cutting guide with locator, a distal femoral cutting guide, an AP measuring guide, a femoral finishing guide, and a system for preparing the proximal tibia end. A surgeon, after opening the damaged knee area, sequentially uses these instruments to prepare a patient&#39;s distal femur and proximal tibia ends to receive knee components of a selected prosthetic device. The various components taught by Dunn are difficult to assemble, and have a number of components which may be lost or misplaced during use and storage. For example, the Dunn system requires use of a pivot pin, an alignment pin, and a plurality of additional pins which are used to secure the distal femoral cutting guide in place after alignment. These pins have proven difficult to use as they are small and numerous, and hence easily misplaced. 
     Therefore, there is a need for an improved intramedullary alignment guide which facilitates quick and accurate alignment guide rotation, has no loose parts, no loose pins, is easily assembled, and which therefore reduces the amount of operating-room time necessary to use. The present invention provides such an improved intramedullary alignment guide. 
     SUMMARY OF THE INVENTION 
     The present invention is an intramedullary (IM) alignment guide and method for use thereof which provides a means for aligning a distal femoral resector or cutting guide with the mechanical axis of a patient. Using the patient&#39;s intramedullary canal as a reference, the present IM guide provides a mechanism for ensuring that a surgeon positions a distal femoral resector perpendicular with the patient&#39;s mechanical axis. Using the present invention, a surgeon can quickly and easily align a distal femoral resector with the patient&#39;s mechanical axis by positioning the resector into a selected angle relative to the patients anatomic axis. The present invention includes an adjustment mechanism which includes an adjustment rod, a rocker unit, and displacement pins. The adjustment rod includes a plurality of notches having inscriptions which correspond to the desired angular displacement of the distal femoral resector and the adjustment rod. By inserting an IM rod through the adjustment rod and into the patient&#39;s IM canal, and subsequently rotating the adjustment rod into a selected notch, the surgeon causes the displacement pins to deflect the distal femoral resector into a desired angular displacement with the adjustment rod. Thus, the surgeon can quickly and easily align the distal femoral resector so that a cut can be made in the patient&#39;s distal femur end which is perpendicular with the patient&#39;s mechanical axis. 
     The present IM guide accommodates various patient anatomies. The IM guide is relatively light and compact, easily assembled, and can be used to align cutting guides for both right and left knee surgeries. The present invention also includes an external alignment checking system having a quick attach/quick release sighting tool. The sighting tool includes a plurality of openings which allows the surgeon to verify whether the distal femoral resector is properly aligned with the patient&#39;s mechanical axis. If the resector is not properly aligned, the surgeon can easily realign the resector using the adjustment rod of the present invention. The realignment process is greatly simplified using the present invention because the surgeon does not need to disassemble and reassemble the alignment guide, nor does the surgeon need to remove the distal femoral cutting guide. Hence, the present invention reduces the overall operating room time and the costs related to knee surgery. 
     The details of the preferred embodiment of the present invention are set forth in the accompanying drawings and the description below. Once the details of the invention are known, numerous additional innovations and changes will become obvious to one skilled in the art. 
    
    
     DESCRIPTION OF DRAWINGS 
     FIG. 1 shows the angular displacements between the mechanical and anatomic axes of three different human legs as determined from a developed radiograph of the three legs. 
     FIG. 2 shows a rear perspective view of an embodiment of the present intramedullary (IM) alignment guide. 
     FIG. 3 shows an exploded view of the IM alignment guide of FIG.  2 . 
     FIG. 4 shows a partial cut-away and cross-sectional view of the present invention showing details of the rocker unit, the displacement pins, and the base. 
     FIG. 5 shows the IM alignment guide of FIGS. 2-4 having an IM rod inserted through the IM guide and into the IM canal of a patient. 
     FIG. 6 shows a front perspective view of the IM guide of FIG. 5 having a quick attach/quick release sighting tool for externally verifying proper alignment of the guide with the patient&#39;s mechanical axis. 
     FIGS. 7 a  and  7   b  show details of the attach and release mechanism used to attach and release the sighting tool shown in FIG. 6 to a distal femoral resector. 
     FIG. 8 shows a view of an alternate embodiment of an IAA alignment guide. 
     FIG. 9 shows a cross-sectional view of the guide of FIG. 8, taken along line  9 — 9 . 
     FIG. 10 shows a partial cut-away and cross-sectional view of the guide of FIG. 9, taken along line  10 — 10 . 
     FIG. 11 shows a partial cut-away and cross-sectional view of an alternate embodiment of an IM alignment guide. 
     Like reference numbers and designations in the various drawings indicate like elements. 
    
    
     DETAILED DESCRIPTION 
     Throughout this description, the preferred embodiment and examples shown should be considered as exemplars, rather than as limitations on the present invention. 
     Patient Preparation and Anatomical Considerations 
     The present invention is preferably used to perform knee surgery on a patient, such as total knee replacement or arthroplasty. The success of a total knee replacement procedure is directly dependent upon re-establishing normal lower extremity alignment to the patient. To ensure that proper limb alignment is restored to the patient, the present invention provides an intramedullary guide that allows a surgeon to quickly and accurately align a distal femoral resector such that a cut can be made in the distal femur end which is perpendicular to the patient&#39;s mechanical axis. 
     As is well known, a patient&#39;s mechanical axis is preferably established by drawing a line on an appropriate x-ray of a patient from the patient&#39;s hip, through the patient&#39;s knee, and to the patient&#39;s ankle when the patient is in a stable and erect position. FIG. 1 shows the femur and tibia bones of 3 different human legs  100 ,  112 , and  120 , wherein each leg has a different angular displacement between its respective mechanical and anatomic axes. As shown in FIG. 1, the mechanical and anatomic axes of each patient can be determined from a developed radiograph of a patient&#39;s leg. More specifically, the mechanical axis of the leg  100  is determined by drawing a line from the center of the femoral head  102  to the center of the distal femur at the knee  104 . The mechanical axis of leg  100  is referred to in FIG. 1 by the line  106 . The anatomic axis  108  of leg  100  is determined by drawing a line down the middle of the distal femoral shaft. As described in more detail below, an intramedullary alignment rod is typically fitted within the femoral shaft to coincide with and represent the anatomic axis. The angle between the two axes  106  and  108  is the angle that must be reproduced by the present invention during surgery so that a cut along the distal femur end  110  is perpendicular to the mechanical axis  106 . 
     The angular difference between the mechanical and anatomic axes has been found in practice to typically be between about 5° and 6°. However, due to differences in patient anatomy, the angular displacement can range from about 3° to 9°. For example, the angular displacement between the anatomic and mechanical axes of the leg 100 is 5°. However, due to a broadened pelvis or significant coxa vara with long femoral necks, the legs  112  and  120  have angular displacements of 7° and 9°, respectively. The present invention advantageously provides a means for angulating a distal femoral resector by a range of angles relative to the anatomic axis which accommodates varied patient anatomies. 
     Once the angular difference between the patient&#39;s mechanical and anatomic axes are determined, a properly angled cut can be made in the distal femur end by referencing the patient&#39;s anatomic axis. The femoral canal, also known as the intramedullary canal, is used to reference the patient&#39;s anatomic axis. By using the intramedullary canal as a reference, and having a priori knowledge of the angular displacement between the anatomic and mechanical axes, the present invention provides an apparatus and method for aligning a distal femoral resector properly such that the distal femur end can be cut at an angle which is perpendicular to the mechanical axis of the patient. Therefore, once the anatomic axis is established, the amount of distal femur bone to be removed can be calculated, so that the resultant surface bone end forms a plane that is perpendicular to the mechanical axis. 
     Detailed Description of the Intramedullary Alignment Guide 
     FIG. 2 shows a rear perspective view of the preferred embodiment  200  of the present intramedullary (IM) alignment guide. FIG. 3 shows an exploded view of the IM alignment guide of FIG.  2 . Referring simultaneously to both FIGS. 2 and 3, the IM alignment guide  200  preferably comprises a base  202 , a distal femoral resector attachment rod  204 , a plurality of pivot pins  206 , a cylindrical rocker unit  208 , a plurality of displacement pins  210 , an adjustment rod  212  having a base  214  and a top-facing interlock unit  216 , an interlock ring  218 , a locking knob  220 , and a locking “C” ring  222 . The IM alignment guide  200  preferably comprises surgical grade, bio-compatible materials, such as stainless steel, titanium, ceramic, structural plastics, etc. Preferably, the IM guide  200  is easily sterilized by known methods, such as heat sterilization, pressurized gas, and radiation sterilization methods. In the preferred embodiment, the base  202  is cut from a solid block of surgical grade stainless steel and is manufactured so that the top and bottom faces of the base  202  are substantially parallel to each other. The bottom face  224  of the base  202  preferably contains a plurality of holes  226  which are formed or drilled through to the top face of the base  202 . The purpose of the holes  226  is described in more detail below with reference to the description of the use of the present invention during surgery. 
     The components which comprise the present invention are shaped to fit together as shown in FIGS. 2 and 3. As shown in FIG. 2, when assembled, the present IM alignment guide is a compact, easily manipulated unit. When assembled, the components are held in place by the C-ring  222  which is clamped around a threaded end  230  of the rocker unit  208 . When assembled, the pins  210  are inserted through a plurality of holes  232  which are cut into a base section  234  of the rocker unit  208 . The operation of the pins  210  and the base  234  is described in more detail below with reference to FIG.  4 . As shown in FIG. 3, the adjustment rod  212  has a substantially hollow interior canal  235  which is shaped to receive the rocker unit  208 . When assembled as shown in FIG. 2, the base  214  of the adjustment rod  212  abuts a top surface of the base section  234  of the rocker unit  208 . 
     The interlock ring  218  has an inner diameter which is slightly greater than the outer diameter of the rocker unit  208  and the threaded end  230 . During assembly of the IM guide  200 , the interlock ring  218  is slipped over the threaded end  230  of the rocker unit  208  until it rests adjacent the top unit  216  of the adjustment rod  212 . As shown in FIG. 3, the interlock ring  218  has a knob  245  which extends toward the top unit  216 . The top unit  216  includes a plurality of notches  236  which are formed into a distal surface of the top unit  216 . The notches  236  are spaced apart at precise locations on the distal surface of the top unit  216  so that when the knob  245  is placed into a selected one of the notches  236 , the adjustment rod  212  rotates by a fixed degree of rotation. A detailed description of the operation of the guide  200 , and more particularly the operation of the adjustment rod  212 , the top unit  216 , the interlock ring  218 , and the notches  236 , is given below with reference to FIGS. 4-6. 
     The locking knob  220  has a threaded interior channel which mates with the threaded end  230  of the rocker unit  208 . Once the adjustment rod  212  and the interlock ring  218  are fitted over the rocker unit  208 , the locking knob  220  is threaded onto the threaded end  230 . The threaded end  230  includes a narrow slot  240  which extends from a distal end of the threaded end  230  and is formed lengthwise along the rocker unit  208 . As shown in FIG. 3, the interlock ring  218  includes an inwardly-facing interlock knob  242  which is shaped to fit within the slot  240  of the rocker unit  208 . Therefore, when the interlock ring  218  is slipped over the threaded end  230  of the rocker unit  208 , the interlock knob  242  mates with the slot  240  and prevents the interlock ring  218  from rotating about the rocker unit  208 . Once the locking knob  220  is threaded over the threaded end  230  of the rocker unit  208 , the C-ring  222  is secured to a distal end of the threaded end  230 . The C-ring  222  prevents the inadvertent disassembly of the IM alignment guide  200  during use. The C-ring  222  is preferably positioned on the threaded end  230  of the rocker unit  208  such that the locking knob  220  can be disengaged from the interlock ring  218  thereby allowing the adjustment rod  212  to be rotated into a desired position. 
     Referring again to FIG. 3, the base section  234  of the rocker unit  208  includes an extension  244  which has an outer diameter that is less than the outer diameter of the base section  234 . The extension  244  of the base section  234  preferably includes two threaded holes  246  which are positioned at opposite sides of the extension  244 . The threaded holes  246  are shaped to receive the pivot pins  206 . The extension  244  of the base section  234  is inserted within a hole  250  formed through the base  202  of the alignment guide  200 . During assembly, the extension  244  is inserted within the hole  250  and the pivot pins  206  are threaded through pivot holes  252  formed in the side walls of the hole  250  and into the holes  246  of the extension  244 . When the rocker unit  208  is seated in the hole  250  by its extension  244 , and the pivot pins  206  are threaded into the holes  246  of the extension  244 , the rocker unit  208  pivots about the pivot pins  206 . 
     The underside of the base  214  of the adjustment rod  212  includes an inclined annular groove  256 . When the guide  200  is assembled as shown in FIG. 2, the adjustment rod  212  rotates about the rocker unit  208  and the inclined annular groove  256  rides upon distal ends of the displacement pins  210 . Depending upon the degree of rotational displacement of the adjustment rod  212 , the distal ends of the displacement pins  210  contact the inclined annular groove  256  at different locations along the groove. As described in more detail below with reference to FIG. 4, the points of contact between the distal ends of the displacement pins  210  and the inclined annular groove  256  determine the angular displacement of the base  202  with respect to the rocker unit  208 . This angular displacement is used to properly align a distal femoral resector so that the patients distal femur end can be cut at an angle which is perpendicular to the patient&#39;s mechanical axis. 
     FIG. 4 shows a cross-sectional view of the present invention showing details of the rocker unit  208 , the displacement pins  210 , and the base  202 . When the alignment guide  200  is assembled as shown in FIGS. 2 and 4, the displacement pins  210  are inserted through the holes  232  formed through the base section  234  of the rocker unit  208 . One end of each displacement pin  210  abuts against a top surface of the base  202  of the alignment guide  200  as shown in FIG.  4 . The other end of each displacement pin  210  fits within the inclined annular groove  256  formed in the underside of the base  214  of the adjustment rod  212 . As shown in phantom in FIG. 4 via the dotted line  260 , the inclined annular groove  256  varies in depth from one side of the base section  214  to the opposite side of the base section  214 . More specifically, as shown in FIG. 4, the groove  256  is most shallow at the leftmost position of the base section  214 . The groove  256  is deepest at the rightmost position of the base section  214 . The angle that the base  202  makes with respect to the rocker unit  208  varies according to the rotational position of the adjustment rod  212  as it rotates about the rocker unit  208 . Because the inclined annular groove  256  varies in depth along the diameter of the base  214 , the displacement of the base  202  caused by the pins  210  varies according to the rotational position of the rod  212 . The base  202  pivots with respect to the rocker unit  208  and rod  212  using the pivot pins  206  (FIG.  3 ). The base  202  is deflected at an angle with the rod  212  due to the degree of displacement produced by the displacement pins  210 . 
     With the adjustment rod  212  first rotated into a starting neutral position, the displacement pins  210  contact the inclined annular groove  256  at contact points which are at equal depth within the base section  214 . Therefore, at the starting neutral position, the rocker unit  208  and rod  212  are perpendicular to the base  202 . As the adjustment rod  212  is rotated about the rocker unit  208 , the displacement pins  210 , due to the varying depth of the inclined annular groove  256 , cause the base  202  to be deflected into various angles with respect to the rocker unit  208 . For example, as shown in FIG. 4, the base  202  is deflected to a maximum angular displacement from the starting neutral perpendicular position. As the adjustment rod  212  is rotated, the positions at which the displacement pins  210  contact the inclined annular groove  256  change, and the amount of angular displacement of the base  202  with respect to the rocker unit  208  and rod  212  created by the displacement pins  210  changes accordingly. When the adjustment rod  212  is rotated into a position which causes the displacement pins  210  to produce an equal amount of linear displacement (i.e., when the points of contact of the displacement pins  210  with the inclined annular groove  256  are at equal depth), the base  202  is returned to a starting neutral angular position with respect to the rocker unit  208  (i.e., the base  202  is perpendicular to the rocker unit  208 ). As the adjustment rod  212  is rotated beyond the starting neutral position, the displacement pins  210  cause the base  202  to form an angle with the rocker unit  208  which is greater than  90 °. 
     During use, the base  202  is placed into a desired angle with respect to the rocker unit  208  by manually adjusting the knob  212  and securing the knob  212  in the desired position by inserting the knob  245  of the interlock ring  218  into one of the notches  236  on the adjustment rod  212 . The device is calibrated so that particular rotational positions of the adjustment knob  212  correspond to specific angular displacements. By selecting one of the rotational positions of the adjustment knob  212  and by inserting the knob  245  into one of the notches  236 , the surgeon can quickly and easily change the angle that the base  202  makes with respect to the rocker unit  208 . This angle corresponds to the measured angular displacement between the anatomic axis and mechanical axis, as described below in more detail with respect to FIGS. 5-7. As described below in more detail, the present invention accommodates angular displacements for both right and left legs. 
     Knee Surgery Using the IM Guide 
     As described above with reference to FIG. 1, once the angular difference between the patient&#39;s mechanical and anatomic axis is determined, the patient&#39;s femur channel or canal, also known as the intramedullary (IM) canal, is used to represent the patient&#39;s anatomic axis. A very accurate method of femoral component alignment is therefore provided by using the patient&#39;s IM canal as a reference. A pre-operative x-ray film is first taken to clearly show the canal on the x-ray. The x-ray is preferably a standing radiograph showing the center of the femoral head, the knee, and as much of the tibia as possible, preferably including the ankle. Alternatively, a single A/P radiograph of the entire femur will allow for correct calculation of the mechanical and anatomic axis. Once the anatomic and mechanical axes are established, the amount of distal femur removal may be calculated in a known fashion. The present IM alignment guide is used to ensure the surgeon that the distal femur end is cut at an angle which is perpendicular to the mechanical axis. 
     In practice, the patient&#39;s knee is prepared in a known manner to receive the components of a knee prosthesis. The femur and tibia ends are prepared independently, and either one can be prepared first. In practice, the distal femur end is routinely prepared first because the resection of the posterior femoral condyles offer greater exposure of the proximal tibia, thereby facilitating its preparation. 
     With the patient&#39;s knee opened appropriately and flexed, the site for inserting the intramedullary alignment guide of the present invention is selected on the distal femur, as shown in FIG.  5 . The intramedullary canal of the femur is entered by drilling a hole  302  into the distal femur end. Care is exercised so that the drill avoids the patient&#39;s cortices. The hole drilled in the distal femur end is used for alignment in accordance with the present invention. Once the intramedullary canal is accessed, an intramedullary (IM) rod  304  is inserted therein. In practice, only the cancellous bone of the distal femur needs to be drilled, as the femur&#39;s hollow diaphysis usually provides no resistance to the insertion of the IM rod  304 . The drilled hole  302  is necessary for alignment only and is not for component positioning on the distal femur. The alignment guide  200  is positioned on the distal femur with the bottom facing surface  224  of the base  202  of the alignment guide  200  facing the distal femur, as shown in FIG.  5 . As described below in more detail, the alignment guide  200  is used in conjunction with the IM rod  304  to properly position a distal femoral resector or cutting guide  306  so that the surgeon can cut the distal femur end perpendicular to the mechanical axis. The IM guide  200  may optionally facilitate cutting the distal femur end at any desired angle with respect to the mechanical axis. 
     The T-shaped IM rod  304  includes a handle  308  and a plurality of flutes  310  cut along the length of the rod. The handle  308  of the IM rod allows a surgeon to easily manipulate the rod  304  during surgery. The flutes  310  serve two purposes: (1) they reduce air pressure which is potentially built up when the rod  304  is inserted within the IM canal, and (2) they serve as a channel for receiving the inwardly-facing interlock knob  242  described above with reference to the interlock ring  218 . When the IM rod  304  is inserted within the IM guide  200 , the interlock knob  242  is positioned within one of the plurality of flutes  310  which prevents the IM guide  200  from rotating with respect to the IM rod  304 . Therefore, a surgeon can easily manipulate both the IM guide  200  and the rod  304  when the rod  304  is inserted through the guide  200 . 
     The diameter of the rod  304  is preferably slightly smaller than the diameter of the drill bit which is used to form the hole  302  which accesses the patient&#39;s IM canal. The diameter of the rod  304  is preferably approximately 1 millimeter smaller than the diameter of the hole  302 . There are two principal motivations for making the diameter of the rod  304  slightly less than the diameter of the hole  302 . The first is to reduce the amount of pressure which is produced within the IM canal when the rod  304  is inserted therein. As is known, pressurization of the canal can lead to an increase of fat emboli in the blood stream, which can cause significant health problems. The second principal purpose for making the IM rod  304  with a smaller diameter than the hole  302  is to allow the IM rod to be principally guided by the patient&#39;s IM canal and therefore follow the patient&#39;s anatomic axis, and not be guided by the shape or orientation or position of the hole  302 . By keeping the diameter of the rod  304  smaller than the diameter of the access hole  302 , the IM rod  304  follows the patient&#39;s IM canal rather than the shape of the hole  302 . 
     After the surgeon drills the hole  302  in the patient&#39;s distal femur end, the surgeon assembles the rod  304  into the IM guide  200  and places the assembled rod and guide over the distal femur end, as shown in FIG.  5 . The rod  304  is inserted through the hole  302  and pushed into the patient&#39;s IM canal as shown. The rotation of the alignment guide  200  about the distal femur end is controlled by inserting a plurality of pins  312  through the plurality of holes  226  in the base  202  of the guide  200 . The IM guide  200  can be secured to the distal femur end by inserting the pins  312  through the base  202  and into the patient&#39;s distal femur bone. A surgeon will typically know when the alignment guide  200  is correctly placed when an equal amount of medial and lateral femoral condyles are exposed posterior to the guide  200 . When placing the guide  200  adjacent the patient&#39;s distal femur end, the surgeon should take into consideration the existence of bony anomalies. 
     Once the surgeon is satisfied with the placement of the IM guide  200  on the patient&#39;s distal femur end, a distal femoral cutting guide  306  can be attached thereto. As shown in FIG.  5 , the distal femoral cutting guide  306  includes a receptacle  314  which is shaped to receive the distal femoral resector attachment rod  204  of the alignment guide  200 . 
     The attachment rod  204  includes an insertion canal  316  (best shown in FIGS. 2 and 3) on the femur facing surface of the rod  204 . The insertion canal is shaped to receive a small knob formed along the inner diameter of the receptacle  314  of the cutting guide  306 . When the knobs in the inner diameter of the receptacle  314  is placed into the insertion canal  316  of the attachment rod  204 , the guide  306  is inhibited from rotating around the rod  204 . Therefore, once the guide  306  is placed over the rod  204 , the guide  306  is locked into position by the rod  204 . 
     The attachment rod includes a plurality of detents  318  (shown in FIGS. 2,  3 , and  5 ) on a top-facing surface. As shown in FIG. 2, the attachment rod  204  preferably includes five detents  318  along its top-facing surface opposite the insertion canal  316 . The detents  318  are preferably spaced apart at 1 millimeter increments. The detents  318  give a surgeon flexibility in positioning the distal femoral cutting guide  306  along the attachment rod  204 . By aligning a front-facing surface  320  of the guide  306  with a selected detent  318 , the surgeon can determine how far to displace the distal femoral cutting guide  306  from the base  202  of the alignment guide  200 . The more that the surgeon displaces the cutting guide  306  from the base  202  of the alignment guide  200 , the more bone the surgeon can remove from the patient&#39;s distal femur end. As shown in FIG. 5, the cutting guide  306  includes a perpendicular cutting slot  322  which is shaped to receive a cutting blade (not shown). During use, once the cutting guide  306  is properly positioned over the patient&#39;s distal femur end, the surgeon inserts the cutting blade through the perpendicular cutting slot  322  and removes bone from the patient&#39;s distal femur end. Alternatively, some surgeons dislike using a slotted cutting guide and prefer cutting along a flat surface. The present invention facilitates use of both a slotted and flat surface cutting guide, as shown in FIG.  5 . The detents  318  in the attachment rod  204  allow a surgeon to displace the cutting guide  306  further along the patient&#39;s femur to a position which aligns the flat surface  320  of the guide  306  properly. The detents  318  allow a surgeon to displace the cutting guide  306  to a position where the surface  320  of the guide  306  can be used as a guide for the cutting blade rather than the slot  322 . Thus, the present invention facilitates use of a cutting guide  306  by surgeons who prefer to use cutting slot guides similar to the cutting slot  322  and also by surgeons who prefer to use a flat surface cutting guide similar to the flat surface  320 . 
     Once the cutting block  306  is placed over the attachment rod  204 , the surgeon can properly align the cutting block  306  with the patient&#39;s mechanical axis. With the rod  304  inserted through the IM alignment guide  200  and the IM canal as shown in FIG. 5, the surgeon unlocks the interlock ring  218  from the top-facing interlock unit  216  of the adjustment rod  212  by rotating the locking knob  220  counterclockwise about the threaded end  230  of the rocker unit  208 . After rotating the locking knob  220 , the interlock ring  218 , and more specifically the interlock knob  245 , is disengaged from the top-facing unit  216  and the notch  236  into which the knob  245  was inserted. Once the interlock ring  218  is freed from the top-facing unit  216  of the adjustment rod  212 , the surgeon can rotate the adjustment rod  212  so that the interlock knob  245  aligns with a desired one of the notches  236 . As described above with reference to FIG. 4, the notches  236  are spaced apart in increments that determine the rotational displacement of the adjustment rod  212  about the rocker unit  208 . Because the rotational displacement of the adjustment rod  212  with respect to the rocker unit  208  determines the points of contact of the displacement pins  210  with the inclined annular groove  256  (FIG.  4 ), the degree of rotational displacement of the adjustment rod  212  determines the angle that the base  202  makes with respect to the adjustment rod  212  and the rocker unit  208 . In the preferred embodiment, the plurality of notches  236  in the top-facing unit  216  are spaced apart at intervals which correspond to 1° angular displacements of the base  202  with respect to the rod  212 . As shown in FIGS. 4 and 5, the top-facing unit  216  preferably includes markings which correspond to the angular displacements that the base  202  makes with the rod  212  when the knob  245  is inserted within a selected notch  236  corresponding to that marking. For example, in the preferred embodiment, the notches  236  have corresponding labels three (3) to nine (9). Each number or marking represents the angle that the base  202  makes with respect to the adjustment rod  212  and the IM canal when the knob  245  is placed into a corresponding notch  236 . There are notches  236  and corresponding markings on both sides of the neutral starting position notch  236 . As shown in FIG. 5, the top-facing unit  216  is inscribed with markings for use of the present invention in a surgery on a right leg of a patient. FIG. 6 shows a different view of the top-facing unit  216  showing markings corresponding to notches  236  for use in surgery on a patient&#39;s left leg. Thus, the present invention can be used to align the cutting guide  306  with the mechanical axis for both a left and right leg. The surgeon simply rotates the adjustment rod  212  either clockwise (when operating on a right leg) from a top center position or counterclockwise (when operating on a left leg) from a top center position so that the knob  245  of the locking ring  218  is inserted into the notch  236  which corresponds to the previously determined angular difference between the patient&#39;s mechanical and anatomic axes. 
     For example, if the difference between the patient&#39;s mechanical and anatomic axes is 6°, and the surgeon is operating on the patient&#39;s right leg, with the IM guide  200 , the IM rod  304  and the cutting block  306  assembled as shown in FIG. 5, the surgeon takes the following steps to align the cutting guide  306  with the patient&#39;s mechanical axis. The surgeon first releases the interlock ring  218  from the top-facing interlock unit  216  by rotating the locking knob  220  counterclockwise approximately one or two revolutions. The surgeon then rotates the adjustment rod  212  clockwise so that the locking knob  245  of the ring  218  is aligned with the notch  236  corresponding with the marking “R-6”. The surgeon then rotates the locking knob  220  clockwise about the threaded end  230  until the locking ring  218  and knob  245  are fully inserted within the selected notch  236 . Due to the operation of the displacement pins  210  as described above with reference to FIG. 4, the base  202  is forced into an angular displacement with the rod  212 , rocker unit  208 , and IM rod  304  exactly equal to 6°. Because the rod  304  is fully inserted within the IM canal of the patient, and because the IM canal corresponds to the patient&#39;s anatomic axis, the base  202  is therefore forced into an angle which is 6° with respect to the patient&#39;s anatomic axis. Because the attachment rod  204  is perpendicular to the base  202 , the attachment rod  204 , and thus the cutting guide  306 , also makes a 6° angle with respect to the IM canal. 
     Accordingly, by simply rotating the adjustment rod  212  to align a desired notch  236  with the knob  245  of the interlock ring  218 , the surgeon can quickly and easily align the cutting guide  306  with the patient&#39;s mechanical axis. If the surgeon determines that the alignment is inaccurate, realignment is quickly and easily accomplished using the present invention without the need to interchange parts or remove the rod. The IM guide  200 , the IM rod  304 , and the cutting guide  306  can all be left assembled as shown in FIG. 5 while the surgeon realigns the cutting guide  306 . Therefore, operating-room time is decreased, which subsequently reduces the health risks to the patient and the costs associated with knee replacement surgery. To realign the cutting guide  306 , the surgeon simply rotates the locking knob  220  counterclockwise one or two rotations to release the locking ring  218  from the rod  212 . The rod  212  can thus be rotated to realign a new notch  236  with the knob  245 . The process is repeated as described above until the surgeon is satisfied with the alignment. Once the surgeon determines that the cutting guide  306  is properly aligned, the cutting guide  306  can be secured to the patient&#39;s femur using securement pins  321 . 
     Once the distal femoral cutting guide  306  is positioned and affixed to the patient&#39;s femur, the IM rod  304  and the IM guide  200  can be removed from the femur. Once the IM guide  200  and the IM rod  304  are removed, the distal femoral cutting guide  306  can be more securely affixed to the patient&#39;s femur using additional securement pins  321 . Thereafter, the surgeon inserts a cutting blade through the cutting slot  322  formed through the distal femoral cutting guide  306 . The saw blade (not shown) is then used appropriately to cut through the distal femur end in known fashion. This cut is perpendicular to the patient&#39;s mechanical axis and is made at a depth to the resection or cut in an amount of bone as will be replaced by the thickness of the femoral component of the knee prosthesis. Alternatively, the surgeon can cut through the distal femur end using the front-facing surface  320  of the cutting guide  306  as a guide. The cut surface must be flat to ensure a proper fit of the implant. The cut surface is then checked for flatness and, if necessary, is further shaped to ensure that the surface is completely flat and adequately positioned. 
     Referring now to FIG. 6, a quick attach/quick release sighting tool  400  is shown for use with the present alignment guide  200  and cutting guide  306 . Once the surgeon properly aligns the cutting guide  306  with the patient&#39;s mechanical axis (shown in FIG. 6 as dotted line  402 ), the surgeon can externally verify proper alignment using the quick attach/quick release sighting tool  400 . The sighting tool  400  has a plurality of openings  404  shaped to receive a sighting rod  406 . Specifically, the openings  404  include: a central slot, the width of which is substantially equal to the diameter of rod  406  and a pair of upper and lower cylindrical bores  404 B and  404 C, respectively, the diameters of which are substantially equal to the diameter of the rod  406 . With the guide  306  properly aligned as described above with reference to FIG. 5, the surgeon attaches the quick attach/quick release sighting tool  400  to the guide  306  as shown in FIG.  6  and as described in more detail below with reference to FIGS. 7 a  and  7   b . When the sighting tool  400  is attached to the guide  306  as shown in FIG. 6, the openings  404  are parallel with the attachment rod  204  (FIG. 5) and therefore may be used to verify that the cutting slot  322  of the guide  306  is perpendicular to the patient&#39;s mechanical axis  402 . To verify that the cutting slot  322  is perpendicular to the patient&#39;s mechanical axis  402 , the surgeon inserts the sighting rod  406  through the openings  404 . The surgeon then verifies that the sighting rod  406  aligns with the center of the patient&#39;s femoral head  102 . If the sighting rod  406  properly aligns with the center of the femoral head  102 , the surgeon removes the IM guide  200 , the IM rod  304 , the sighting rod  406  and the sighting tool  400  from the patient&#39;s knee. The surgeon then cuts the distal femur end as described above. 
     However, if the sighting rod  406  does not properly align with the center of the femoral head  102 , the surgeon can quickly realign the cutting guide  306  by manipulating the locking knob  220  and the manual adjustment rod  212  appropriately as described above with reference to FIGS. 4 and 5. 
     FIGS. 7 a  and  7   b  show details of the attach and release mechanism used to attach and release the sighting tool  400  to the distal femoral cutting guide  306 . As shown in FIG. 7 a , the sighting tool  400  is a cylindrical and substantially elongate tool which has a pair of juxtaposed mating tines  408  formed into a distal end of the sighting tool  400 . The mating tines  408  are preferably formed from one solid piece  410  of the mating tool  400 . As shown in FIG. 7 a , when left undisturbed by an external force, mating ends  412  of the mating tines  408  are substantially proximate one another. However, the mating ends  412  can be forced apart in an elastic fashion by an elliptical cam  414  rotated between the mating ends  412  using a rotation lever  416 . Because the cam  414  is elliptical, the ends  412  can be forced away from one another by rotating the lever  416  either clockwise or counterclockwise, as shown in FIG. 7 b.    
     As shown in FIG. 7 a , the mating ends  412  of the tines  408  include insertion knobs  418  and insertion dovetails  420 . The insertion knobs  418  and dovetails  420  are used to interlock the sighting tool  400  with the cutting guide  306 . As shown in FIGS. 5 and 6, the cutting guide  306  includes a sight rod slot  422  which is shaped to receive the insertion knobs  418 . Thus, a surgeon can quickly attach the cutting guide  306  to the sighting tool  400  by inserting the insertion knobs  418  into the sight rod slot  422 . The sight rod slot  422  guides the insertion knobs  418  as the surgeon rotates the elliptical cam  414  using the lever  416 . As shown in FIG. 7 b , with the insertion knobs  418  properly aligned within the slot  422  of the guide  306 , the surgeon rotates the lever  416  so that the cam  414  pushes the tines  408  away from one another. The dovetails  420  are shaped to interlock with an interlock slot  424  formed into a top-facing surface of the cutting guide  306 . Thus, as the surgeon rotates the lever  416 , the sighting tool  400  mechanically interlocks with the cutting guide  306  due to the interlocking force (produced by the cam  414 ) of the dovetails  420  against the locking slots  424 . The interlocking force maintained by the cam  414  is easily disengaged by rotating the lever so that the cam  414  is in a neutral position, as shown in FIG. 7 a . Thus, the present invention provides a mechanism for facilitating the quick attachment and release of a sighting tool  400  from the cutting guide  306 . The length of the sighting tool allows it to be used to assure rotational alignment of both the guide and other components which can be attached to the tool. 
     FIGS. 8-10 show an alternate embodiment of an IM alignment guide  500 . Construction and operation of the guide  500  is in part similar to that of the guide  200 . The guide  500  includes a base or alignment plate  510  with a flat bottom face  512 . An attachment rod or shaft  516 , of rounded rectangular cross-section, extends downward from the base  510 . Ultimately, a cutting guide (not shown) is placed over the attachment rod  516 . 
     A handle unit  518  has a central longitudinal axis  520  which, in a neutral orientation, is perpendicular to the flat bottom face  512  of base  510 . However, as described below, the angle between the axis  520  and bottom face  512  may be varied. Centrally along the axis  520 , the handle has an outer body  522  which may have a knurled or otherwise contoured outer surface to facilitate gripping. At the bottom end of the body  522  is a flange  524  (FIG. 10) having a spiral camming surface  526  configured to engage a pair of ball bearings  528  diametrically opposite each other about the axis  520 . The ball bearings  528  also ride on an annular track  530  in the upper surface of the base  510 . The flange  524  is accommodated within a generally cylindrical compartment or bore in a cap or cap plate  532  which cap extends below and outward from the flange. The body  522  and flange  524  may rotate relative to the cap  532  about the central axis  520  but not transverse thereto. 
     An internally threaded sleeve  536  is unitarily formed with the cap  532  and depends from the underside  538  of the cap  532 . A pair of pivot pins  540  (FIG. 9) are coaxially secured at their outboard ends in sockets in the base  510 . At their inboard ends, the pins  540  ride in holes in the sleeve  536 . The pins  540  limit movement of the cap  532  relative to the base  510  to rotation about a pivot axis  542  which is orthogonal to and intersecting the handle axis  520  and extends through a central axis of the attachment rod  516 . 
     To longitudinally secure the body  522  to the cap  532  (and thus to the base  510 ), a handle shaft  550  (FIG. 10) is provided to transmit a compressive clamping force between the body  522  and cap  532 . The lower end of the shaft  550  is externally threaded to screw into the internally threaded sleeve  536 . At the upper end of the shaft  550 , a knob  552  is provided. Below the knob, an externally threaded section  554  is engaged to an internally threaded locking knob or collar  556  which may be provided with a knurled or contoured outer surface to facilitate gripping. A thrust washer  558  rides in a compartment in the upper end of the body  522 . The lower surface of the washer  558  engages the body  522  and the upper surface engages the locking collar  556 . Accordingly, if the locking collar  556  is rotated so as to drive downward along the externally threaded section  554 , the collar transmits compressive force to the thrust washer  558  which is in turn transmitted to the body  522  and therefrom through the ball bearings  528  to the base  510 . To hold the assembly together, an opposite tensile force is transmitted from the base  510  through the pivot pins  540  to the sleeve  536  and therefrom through the shaft  550 . 
     A pair of pins  560  depend from the cap member  532 . The pins preferably have sharp spiked distal or lower ends  562  which protrude through holes in the base  510 . The pins  560  have proximal or upper ends  564  which are secured to the cap  532 . By way of example, the upper ends  564  may be threaded into bores in the cap  532  to rigidly secure the pins to the cap. 
     As shown in FIG. 9, the guide further includes an alignment pin  570  extending through the cap  532  and through a hole  572  (FIG. 10) in the shaft  550 . The tip of the pin  570  protrudes slightly into the internal bore or channel of the shaft  550  and may be received by a longitudinal slot in the IM rod (not shown) to maintain angular alignment between the base and the rod relative to the axis  520 . 
     Additionally, a spring-biased ball bearing  580  rides within a radially outward facing compartment in the flange  524  and engages an inward facing surface of the cap  532 . The ball bearing  580  is engageable with a plurality of discrete detents in the wall  582  of inward to register the flange  524  in associated orientations relative to the cap  532 . Rotation of the flange  524  relative to the base  510  causes rolling of the bearings relative to the camming surface  526  which causes the base  510  to pivot about the pivot axis  542 . In the illustrated embodiment, each detent is associated with a discrete rotation of the flange  524  and its camming surface  526  which produces an associated discrete increment (e.g., 1°) in rotation of the axis  520  relative to the attachment rod  516 . 
     As shown in FIG. 10, in the illustrated embodiment, the central bore  590  of the shaft  550  is provided with a mediate portion  592  of greater diameter than at the upper or lower ends of the shaft. This enlarged mediate portion reduces binding in situations where a slightly bent IM rod is used. 
     In an alternate embodiment of FIG. 11, an IM guide  600  is provided which is generally similar to IM guide  500 . The guide  600  includes a relatively large head  652  and the central bore  690  has a counterbored area  694  at the upper end of the bore to facilitate ease of insertion of the IM rod into the bore. 
     In use, the guide  500  is inserted on the IM rod (not shown). The IM rod is then inserted into the intramedullary canal. A pair of inner and outer alignment tabs  596  (FIG. 9) are aligned with the inner and outer posterior condyles of the femur. The pins  560  may then be driven into the bone by a manual exertion on the handle body  522  or knob  552 . If necessary, the upper surface of the cap  532  may be hammered, with hammering force  598  being transmitted directly to the pins  560 . As shown in FIG. 11, hammering force  599  may also be applied to the knob which is then transferred through the shaft, to the cap and then to the pins. The locking collar  556  may then be loosened to permit angular adjustment of the guide. The body  522  may then be rotated about the axis  520  by the amount necessary to adjust the base  510  and attachment shaft  516  by the desired rotation about the axis  542 . For example, with the spring loaded ball  580  engaging detents associated with 1° changes in the angle between the attachment shaft and axis  520 , a rotation of six detents or “clicks” produces a 6° angle. When the desired angle is achieved, the locking knob  556  is retightened. The pins may be redriven so that the base contacts the condyles. The cutting guide block is then applied to the attachment rod or shaft  516  and secured to the bone whereupon the IM rod and IM guide may be removed to permit cutting of the bone. 
     An improved intramedullary alignment guide and method for use thereof have been described. The present alignment guide provides a means for positioning a distal femoral cutting guide by a range of angles relative to the anatomic axis which accommodates various patient anatomies. Using the patient&#39;s intramedullary canal as a reference, the present IM guide provides a mechanism for ensuring that a distal femoral cutting guide is perpendicular with the patient&#39;s mechanical axis. The IM guide is easily assembled, can be used in knee surgeries on both right and left legs, and can be used to easily and quickly properly align the cutting guide with the patient&#39;s mechanical axis. An external alignment checking system using a quick attach/quick release sighting tool has also been described. The sighting tool is used with the present IM alignment guide to verify proper alignment of the cutting guide with the distal femur end. 
     A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiment, but only by the scope of the appended claims.