Abstract:
Apparatus for removing bone from a femoral notch, or the like, which includes a guidewire and a router assembly. The router assembly comprises a cutting head fixed to a shaft rotatably disposed in a hole through a body portion of a shield assembly. A hood portion of the shield assembly extends from the body portion of the shield assembly and covers a first portion of the cutting head while leaving exposed a second portion of the cutting head. The guidewire extends through a hole in the shaft, a hole in the cutting head, and a hole in the shield assembly hood portion, such that the router assembly is movable along the guidewire. The shaft is rotatable in the shield assembly body portion such that the second portion of the cutting head is engageable with the bone and operative to remove portions of the bone. The guidewire is installed in the knee so that it extends along the length to be occupied by a graft ligament. The guidewire and router assembly are flexible so that the bone-trimming operation may be conducted dynamically as the knee is moved through a range of natural motions.

Description:
This is a continuation of U.S. patent application Ser. No. 09/379,997, filed Aug. 24, 1999, now U.S. Pat. No. 6,364,886, which is in turn a continuation of prior application Ser. No. 09/083,889, filed May 22, 1998, now U.S. Pat. No. 5,941,883, which is in turn a contiuation of prior applicaiton Ser. No. 08/658,003, filed Jun. 4, 1996, now U.S. Pat. No. 5,755,713. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to medical apparatus and methods in general, and more particularly to apparatus and methods for reconstructing ligaments. 
     BACKGROUND OF THE INVENTION 
     Ligaments are tough bands of tissue which serve to connect the articular extremities of bones, or to support or retain organs in place within the body. Ligaments are typically composed of coarse bundles of dense white fibrous tissue which are disposed in a parallel or closely interlaced manner, with the fibrous tissue being pliant and flexible, but not extensible. 
     In many cases, ligaments are torn or ruptured as a result of accidents. As a result, various procedures have been developed to repair or replace such damaged ligaments. 
     For example, in the human knee, the anterior and posterior cruciate ligaments (i.e., the ACL and PCL) extend between the top end of the tibia and the bottom end of the femur. The ACL and PCL cooperate, together with other ligaments and soft tissue, to provide both static and dynamic stability to the knee. Often, the anterior cruciate ligament (i.e., the ACL) is ruptured or torn as a result of, for example, a sports-related injury. Consequently, various surgical procedures have been developed for reconstructing the ACL so as to restore normal function to the knee. 
     In many instances, the ACL may be reconstructed by replacing the ruptured ACL with a synthetic or harvested graft ligament. More particularly, with such procedures, bone tunnels are typically formed in the top end of the tibia and the bottom end of the femur, with one end of the graft ligament being positioned in the femoral tunnel and the other end of the graft ligament being positioned in the tibial tunnel. The two ends of the graft ligament are anchored in place in various ways well known in the art so that the graft ligament extends between the femur and the tibia in substantially the same way, and with substantially the same function, as the original ACL. This graft ligament then cooperates with the surrounding anatomical structures so as to restore normal function to the knee. 
     It will, of course, be appreciated that a complex interdependency exists between the ACL and the other elements of the knee, e.g., the bones, the other knee ligaments, and other soft tissue. Consequently, it is critical that the craft ACL be disposed in exactly the right position relative to the other anatomical structures of the knee if normal knee function is to be restored. Correspondingly, it has been found that the aforementioned bone tunnels must be precisely positioned in the tibia and femur if successful reconstruction of the ACL is to be achieved. Unfortunately, proper positioning of these bone tunnels to satisfy isometric considerations can sometimes lead to anatomical conflicts within the knee when the graft ACL is installed within the knee. 
     More particularly, the ACL normally extends between the bottom end of the femur and the top end of the tibia, with the body of the ACL passing through the femur&#39;s intercondylar notch and across the interior of the knee joint. See, for example, FIGS. 1 and 2, which show a natural ACL  5  extending between the bottom end of a femur  10  and the top end of a tibia  15 , with the body of ACL  5  passing through the femur&#39;s intercondylar notch  20 . Also shown is a natural PCL  25  extending between the bottom end of femur  10  and the top end of tibia  15 . 
     It is to be appreciated that the position of the various knee elements move relative to one another as the knee is flexed through a range of natural motions. See, for example, FIG. 3, which shows ACL  5  moving across a 40° arc as the knee joint is flexed through a 140° motion. 
     Due to the complex geometries of the knee, where a damaged ACL is to be replaced by a graft ACL, it is critical that the graft ACL be connected at precisely the right locations on the bottom end of the femur and top end of the tibia. Thus, and looking now at FIGS. 4 and 5, where a damaged ACL is to be replaced by a graft ACL, the damaged ACL is first cleared away and then bone tunnels  30  and  35  are formed in the tibia and femur, respectively. The precise locations of these bone tunnels  30  and  35  are dictated by the isometric relationships of the knee. In practice, bone tunnels  30  and  35  are formed using a surgical drill guide which is keyed to certain parts of the patient&#39;s anatomy, e.g., to the patient&#39;s tibial plateau. Once bone tunnels  30  and  35  have been formed, the graft ACL may be installed in ways well known in the art. See, for example, FIGS. 6 and 7, which show a graft ACL  5 A having one end mounted to femur  10  and the other end mounted to tibia  15 . 
     Unfortunately, in some situations, proper isometric placement of bone tunnels  30  and  35  may cause anatomical conflicts within the knee when the graft ACL is installed in the patient. By way of example, and of particular interest in connection with the present invention, proper isometric placement of bone tunnels  30  and  35  may result in portions of the femur impinging upon the graft ACL as the knee is moved through its full range of natural motions. See, for example, FIG. 8, which shows one of the femur&#39;s condyles  40  impinging upon a graft ACL  5 A extending through the femur&#39;s intercondylar notch  20 ; and FIG. 9, which shows the roof the femur&#39;s intercondylar notch impinging on the graft ACL  5 A in the vicinity of arrow  42 . 
     Impingement can occur for a variety of reasons. For one thing, the intercondylar notch of many patients (particularly those who are susceptible to rupture of the ACL) is frequently small to begin with. For another thing, the graft ACL (i.e., the synthetic or harvested graft ligament which is being installed in place of the damaged natural ACL) is generally fairly large. 
     Additionally, slight mispositioning of bone tunnels  30  and  35  can also lead to impingement problems. 
     Unfortunately, impingement of the femur on the graft ligament can reduce the effectiveness of the ACL reconstruction procedure or even cause it to fail altogether. 
     Thus, when performing an ACL reconstruction procedure, the surgeon generally tries to ensure that there is sufficient room within the patient&#39;s intercondylar notch to receive the graft ligament. This is generally done by performing notchplasty, i.e., by surgically removing any impinging bone from the sides and/or roof of the intercondylar notch. At the same time, of course, it is also important that the surgeon remove no more bone than is absolutely necessary, so as to minimize trauma to the patient. 
     Unfortunately, it is difficult for the surgeon to accurately gauge the precise amount of bone that must be removed from the notch in order to avoid impingement. For one thing, the ACL reconstruction procedure is typically performed arthroscopically, so that the surgeon&#39;s view of the surgical site is frequently fairly restricted. For another thing, the surgeon typically will not know the precise space that the graft ACL will occupy until the graft is actually in place; but at that point in the procedure, it is frequently difficult to insert additional bone-cutting instruments into the joint so as to remove more bone, particularly without cutting the graft ACL. Furthermore, experience has shown that the most serious problems with impingement occur superiorly; but even with the graft ligament in place, the surgeon is generally unable to see impingement at this location due to limitations in arthroscopic visualization. Also, the surgeon typically performs the ACL reconstruction procedure in a relatively static context, i.e., with the knee being relatively stationary at any given moment during the reconstruction procedure. However, the knee must perform (and impingement must be avoided) in a relatively dynamic context, i.e., as the knee is moved throughout a full range of natural motions. This complicates the surgeon&#39;s task of eliminating impingement. 
     OBJECTS OF THE INVENTION 
     Accordingly, one object of the present invention is to provide improved apparatus for reconstructing a ligament. 
     Another object of the present invention is to provide improved apparatus for reconstructing an anterior cruciate ligament (ACL). 
     And another object of the present invention is to provide improved apparatus for quickly, easily and reliably eliminating impingement problems when reconstructing an anterior cruciate ligament. 
     Still another object of the present invention is to provide improved apparatus for quickly, easily and reliably removing any anatomical structures (e.g., bone) which will conflict with the location of a graft ACL at the completion of an ACL reconstruction procedure. 
     Yet another object of the present invention is to provide improved apparatus for quickly, easily and reliably removing any anatomical structures (e.g., bone) which will conflict with the location of a graft ACL as the knee is moved through a full range of natural motions. 
     And an object of the present invention is to provide an improved method for reconstructing a ligament. 
     Another object of the present invention is to provide an improved method for reconstructing an anterior cruciate ligament (ACL). 
     And another object of the present invention is to provide an improved method for quickly, easily and reliably eliminating impingement problems when reconstructing an anterior cruciate ligament. 
     Still another object of the present invention is to provide an improved method for quickly, easily and reliably removing any anatomical structures (e.g., bone) which will conflict with the location of a graft ACL at the completion of an ACL reconstruction procedure. 
     Yet another object of the present invention is to provide an improved method for quickly, easily and reliably removing any anatomical structures (e.g., bone) which will conflict with the location of a graft ACL as the knee is moved through a full range of natural motions. 
     SUMMARY OF THE INVENTION 
     These and other objects are addressed by the present invention, which comprises the provision and use of novel apparatus for removing impinging bone during a ligament reconstruction procedure. 
     In one preferred form of the invention, the novel apparatus comprises a guidewire and a router assembly. 
     The guidewire is similar to other guidewires of the sort well known in the art, except that it is preferably formed out of a pseudoelastic material, i.e., a “shape memory alloy (SMA)/stress induced martensite (SIM)” material such as Nitinol. 
     The router assembly comprises a cannulated router device and a shield assembly. The cannulated router device comprises a cannulated cutting head which is attached to a cannulated shaft. The shield assembly comprises a body and a hood. The body includes a hole therein. The hood extends about one end of the body. The router assembly is assembled so that the router device has its cutting head disposed at one end of the shield assembly&#39;s body and the router device has its shaft extending through the hole in the shield assembly&#39;s body. The shield assembly&#39;s hood covers a first portion of the router device&#39;s cutting head while leaving a second portion of the cutting head exposed. 
     The guidewire is deployed in the body so that it extends along the length where the graft ACL will reside. The router assembly is mounted on the guidewire by passing the guidewire through the router device&#39;s shaft and cutting head, such that the router assembly is movable along the guidewire. The router device&#39;s shaft is rotatable in the shield assembly such that the cutting head can be turned so as to remove bone while the router assembly is riding on the guidewire. Portions of the router assembly engaging the guidewire are formed so as to be flexible. On account of the fact that both the guidewire and portions of the router assembly are formed so as to be flexible, the router assembly can be used to remove impinging bone as the knee is flexed through a full range of natural motions. 
     In accordance with another form of the invention, there is provided alternative apparatus for removing impinging bone, the alternative apparatus comprising a guidewire and a cannulated router device. Again, the guidewire is preferably formed out of a pseudoelastic material. The cannulated router device comprises a cannulated cutting head which is attached to a cannulated shaft. In this embodiment of the invention, the cutting head is devoid of cutting means on a first portion of the periphery thereof and is provided with cutting means on a second portion of the periphery thereof. The second portion of the cutting head is engageable with the impinging bone portions which are to be removed. 
     Again, the guidewire is deployed in the body so that it extends along the length where the graft ACL will reside. The router device is mounted on the guidewire by passing the guidewire through the router device&#39;s shaft and cutting head, such that the router device is movable on the guidewire. The router device is rotatably movable in an oscillating fashion such that the cutting head&#39;s second portion moves in alternating opposite directions across the impinging bone to remove portions thereof. The first portion of the cutting head is smooth and non-destructive with respect to any anatomical structures which the first portion may come into contact with. Portions of the router device engaging the guidewire are formed so as to be flexible. On account of the fact that both the guidewire and portions of the router device are formed so as to be flexible, the router device can be used to remove impinging bone as the knee is flexed through a full range of natural motions. 
     In accordance with another form of the invention, there is provided alternative apparatus for removing impinging bone, the alternative apparatus comprising a guidewire and a cannulated router device. Again, the guidewire is preferably formed out of a pseudoelastic material. The cannulated router device comprises a cannulated cutting head which is attached to a cannulated shaft. In this embodiment of the invention, the cutting head is adapted to cut bone which comes into contact with the cutting head, but to leave unharmed soft tissue which comes into contact with the cutting head. 
     Again, the guidewire is deployed in the body so that it extends along the length where the ACL graft will reside. The router device is mounted on the guidewire by passing the guidewire through the router device&#39;s shaft and cutting head, such that the router device is movable on the guidewire. The router device is rotatably movable on the guidewire so as to cut away impinging bone. Again, portions of the router device engaging the guidewire are formed so as to be flexible. On account of the fact that both the guidewire and portions of the router device are formed so as to be flexible, the router device can be used to remove impinging bone as the knee is flexed through a full range of natural motions. 
     In accordance with another form of the invention, there is provided apparatus for marking portions of impinging bone which are to be thereafter removed, the apparatus comprising a guidewire and a cannulated marking device. Again, the guidewire is preferably formed out of a pseudoelastic material. The cannulated marking device comprises a cannulated marker head attached to a cannulated shaft. 
     Again, the guidewire is deployed in the body so that it extends along the length where the graft ACL will reside. The marking device is mounted on the guidewire by passing the guidewire through the marking device&#39;s shaft and marking head, such that the marking head is movable on the guidewire. The marking head is adapted to hold a dye and to release that dye upon contact with bone, whereby to mark the impinging portions of the bone proximate to the guidewire as the marking head moves on the guidewire. Portions of the marking device engaging the guidewire are formed so as to be flexible. On account of the fact that both the guidewire and portions of the marking device are formed so as to be flexible, the marking device can be used to mark impinging bone as the knee is flexed through a full range of natural motions. 
     In accordance with a further feature of the invention, there is provided a method for removing impinging portions of bone, the method comprising the steps of providing a flexible guidewire and a flexible cannulated router device. The guidewire is anchored in the bone so that it extends along the length where the graft ACL will reside, and the cannulated router device is rotatably mounted on the guidewire so that it is movable on the guidewire. Then the cannulated router device is rotated on the guidewire as the knee is flexed through a range of natural motions so as to dynamically remove impinging bone. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which are to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein: 
     FIG. 1 is a schematic front view of a normal knee, where the leg is substantially straight; 
     FIG. 2 is a schematic side view, partially in section, of the knee shown in FIG. 1; 
     FIG. 3 is a schematic side view, showing how the ACL moves about within the knee joint as the knee is flexed through a range of natural motions; 
     FIG. 4 is a schematic front view of a knee, where the knee is bent at approximately a 90° angle, and where a damaged ACL has been removed and bone tunnels have been formed in the tibia and the femur; 
     FIG. 5 is a schematic side view of the knee shown in FIG. 4; 
     FIG. 6 is a schematic front view of a knee, where the knee is bent at approximately a 90° angle, showing a graft ACL installed in the knee; 
     FIG. 7 is a schematic side view of the knee shown is FIG. 6; 
     FIG. 8 is a schematic front view showing how portions of the femur can impinge upon a craft ACL; 
     FIG. 9 is a schematic side view showing how portions of the femur can impinge upon a graft ACL; 
     FIG. 10 is a schematic side view of the guidewire used in connection with the present invention; 
     FIG. 11 is a schematic perspective view showing one form of router assembly formed in accordance with the present invention; 
     FIG. 12 is a schematic perspective view of the router assembly&#39;s cannulated router device; 
     FIG. 13 is a schematic side view, in section, of the cannulated router device shown in FIG. 12; 
     FIG. 14 is a schematic side view, in section, of a portion of the router assembly&#39;s shield assembly; 
     FIG. 15 is a schematic perspective view of the shield assembly&#39;s collar; 
     FIG. 16 is a schematic side view, in section, of the router assembly shown in FIG. 11; 
     FIG. 17 is a schematic side view of a knee, where the knee is bent at approximately a 90° angle, and where a damaged ACL has been removed and a bone tunnel has been formed in the tibia, and showing a guidewire extending through the tibial bone tunnel and into the femur; 
     FIG. 18 is a schematic side view of the knee shown in FIG. 17; 
     FIG. 19 is a schematic front view like that of FIG. 17, except showing a router assembly removing lateral bone structures from the femoral notch so as to prevent those lateral bone structures from impinging on a graft ACL; 
     FIG. 20 is a schematic side view showing a router assembly removing lateral bone structures from the femoral notch so as to prevent those lateral bone structures from impinging on a graft ACL; 
     FIG. 21 is a schematic front view, showing the leg substantially straight and the router assembly removing roof bone structures from the femoral notch so as to prevent those roof bone structures from impinging on a graft ACL; 
     FIG. 22 is a schematic side view of the knee and router assembly shown in FIG. 21; 
     FIG. 23 is a schematic side view, showing the knee flexed at approximately a 140° angle and the router assembly removing bone structures from the femoral notch so as to prevent those bone structures from impinging on a graft ACL; 
     FIG. 24 is a schematic perspective view showing an alternative form of router assembly formed in accordance with the present invention; 
     FIG. 25 is a schematic perspective view showing the collar used in connection with the router assembly shown in FIG. 24; 
     FIG. 26 is a schematic side view, in section, of the router assembly shown in FIG. 24; 
     FIG. 27 is a schematic perspective view of another form of router device which can be used in connection with the present invention; 
     FIG. 28 is a schematic perspective view of yet another form of router device which can used in connection with the present invention; 
     FIG. 29 is a schematic side view of a cannulated marking device formed in accordance with the present invention; and 
     FIG. 30 is a schematic side view of a novel type of guidewire assembly formed in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Looking first at FIGS. 10-16, the present invention provides apparatus and a method for removing bone structures from the femoral notch so as to prevent those bone structures from impinging upon a graft ACL installed as part of an ACL reconstruction procedure. The apparatus and method of the present invention are intended to be utilized in an ACL reconstruction procedure aster the damaged ACL has been removed from the knee and after bone tunnel  30  has been formed in tibia  15 , but before bone tunnel  35  has been formed in femur  10  and the graft ACL has been positioned in the joint. 
     Still looking now at FIGS. 10-16, in one preferred embodiment of the present invention, the apparatus of the present invention comprises a guidewire  50  (FIGS. 10 and 11) and a router assembly  55  (FIGS.  11 - 16 ). 
     Guidewire  50  is generally of the sort well known in the art for guiding cannulated elements to a target structure. As such, guidewire  50  includes a sharp point  60  (FIG. 10) on its distal end, whereby the guidewire can be drilled or tapped into a target structure (e.g., femur  10 , as will hereinafter be described in further detail). However, unlike other guidewires of the sort known in the art, and in accordance with one preferred embodiment of the present invention, guidewire  50  is preferably formed out of a highly elastic yet firm material. Preferably, guidewire  50  is formed out of a so-called pseudoelastic material, i.e., a “shape memory alloy (SMA)/stress induced martensite (SIM)” material such as Nitinol. By forming guidewire  50  out of such a highly elastic yet firm material, the guidewire has the rigidity needed to penetrate into bone, yet has the high elasticity needed to undergo substantial elastic deformation during joint flexure, as will hereinafter be described in further detail. 
     Still looking now at FIGS. 11-16, router assembly  55  comprises a cannulated router device  65  (FIGS. 11-13 and  16 ) which comprises a cannulated cutting head  67  attached to a cannulated shaft  70 . At least the distal portion  70 ′ (FIGS. 12,  13  and  16 ) of cannulated shaft  70  is flexible; the proximal portion  70 ″ of cannulated shaft  70  may or may not be flexible, as desired. On account of this construction, cannulated router device  65  can ride on guidewire  50  as rotary cutting notion is imparted to cutting head  67  by means of shaft  70 . In particular, by forming at least the distal portion  70 ′ of cannulated shaft  70  so as to be flexible, router device  65  can ride on guidewire  50  and rotate even as guidewire  50  is subjected to substantial bending during knee joint flexure, as will hereinafter be discussed in further detail. 
     Router assembly  55  also comprises a shield assembly  75  (FIGS.  11  and  14 - 16 ). Shield assembly  75  comprises a body assembly  80  and a hood  85 . 
     Body assembly  80  comprises a hollow outer tube  82  (FIGS. 14 and 16) and an inner collar  83  (FIGS.  15  and  16 ). At least the distal portion  82 ′ (FIGS. 14 and 16) of hollow outer tube  82  is flexible; the proximal portion  82 ″ of hollow outer tube  82  may or may not be flexible, as desired. Collar  83  is sized and positioned so as to terminate at the juncture of the hollow tube&#39;s distal portion  82 ′ and its proximal portion  82 ″ (FIG.  16 ). Collar  83  includes a hole  90  (FIGS. 15 and 16) for receiving shaft  70  of router device  65 . Hole  90  is preferably centered within body  80 , whereby the router device&#39;s cutting head  67  will be centered within shield assembly  75 . 
     Hood  85  is attached to body  80  and includes a hole  95  (FIGS. 14 and 16) for receiving guidewire  50 . Hood  85  surrounds a portion of the router device&#39;s cutting head  67  but leaves another portion of the cutting head (i.e., the portion extending outboard or hood  85 ) exposed for routing operations. By way of example but not limitation, hood  85  might cover approximately ⅔ of the circumferential region surrounding cutting head  67  and leave approximately ⅓ of the circumferential region surrounding cutting head  67  exposed for cutting purposes. Hood  85  may be formed flexible or rigid, as desired. 
     As a result of this construction, router assembly  55  can ride on guidewire  50  as a unit, with shaft  70  rotating cutting head  67  so as to cut away any material (e.g., impinging bone) exposed to the cutting head, even as hood  85  shields a substantial portion of the cutting head from inadvertently cutting other material (e.g., the patient&#39;s PCL). Significantly, due to the flexible nature of shaft portion  70 ′ and tube portion  82 ′, router assembly  55  is able to ride on guidewire  50  even as guidewire  50  is subjected to substantial deformation during knee joint flexure. 
     Looking next at FIGS. 17-23, guidewire  50  and router assembly  55  are intended to be used as follows. 
     First, femur  10  and tibia  15  are set at approximately a 90° angle and tibial bone tunnel  30  is formed in tibia  15 . Then guidewire  50  is passed through tibial bone tunnel  30  and into femur  10  until the sharp distal end  60  of the guidewire is embedded in the femur, e.g., by drilling or tapping in ways well known in the art (see FIGS.  17  and  18 ). If desired, a cannulated guide of the sort well known in the art (not shown) may be disposed about guidewire  50  to help stabilize it as it is embedded into femur  10 . Guidewire  50  is positioned in the patient so that it will extend along the length where the graft ACL will reside. 
     Next, router assembly  55  is loaded onto the proximal end of guidewire  50  and moved down into the interior of the knee joint so that the router assembly&#39;s cutting head  67  is in the vicinity of femoral notch  20  (see FIGS.  19  and  20 ). Then body  80  of router assembly  55  is turned so that the router assembly&#39;s cutting head  67  is directed toward the impinging portions of the femur which are to be removed, and so that the router assembly&#39;s protective hood  85  is placed between the cutting head and the PCL so as to protect the PCL from the cutting head. Then shaft  70  is rotated, e.g., with a power driver (not shown) of the sort well known in the art, so as to rotate cutting head  67  and thereby cut away any anatomical structures it comes into contact with. 
     By turning body  80  circumferentially as required, cutting head  67  can be used to enlarge femoral notch  20  while keeping the cutting head from engaging (and thereby cutting) the PCL and/or other sensitive anatomical structures. In particular, by turning router assembly  55  so that it faces in the manner shown in FIGS. 19 and 20, lateral notch structures can be removed. Similarly, by turning router assembly  55  so that it faces in the manner shown in FIGS. 21 and 22, roof notch structures can be removed. 
     Significantly, the impinging bone can be removed quickly, easily and safely, without direct visualization of the anatomical structures being trimmed away, due to the use of guidewire  50  and the guidewire-following router assembly  55 . 
     In particular, it is to be appreciated that, by positioning guidewire  50  so that it will extend along the length where the graft ACL will reside, and by properly sizing the radial dimensions of router assembly  55  relative to the graft ACL which will thereafter be installed, the router assembly will clear away only as much bone as is required to properly size the femoral notch and eliminate impingement problems. Furthermore, by properly sizing the longitudinal dimensions of router assembly  55  relative to the notch region where impingement occurs, impingement can be eliminated by just circumferential movement of router assembly  55  on guidewire  50 , i.e., without requiring longitudinal movement of router assembly  55  on guidewire  50  during bone-trimming operations. 
     Significantly, since guidewire  50  is preferably formed out of a highly elastic material, and since the router assembly&#39;s shaft portion  70 ′ and body portion  82 ′ are formed so as to be flexible, it is possible to use router assembly  55  to remove impinging bone in a dynamic sense, i.e., to use the router assembly to cut away impinging bone even as the knee is flexed through a full range of natural motions. See, for example, FIGS. 19 and 20, where router assembly  55  is shown enlarging the femoral notch while the patient&#39;s leg is bent at approximately a 90° angle; FIGS. 21 and 22, where router assembly  55  is shown enlarging the femoral notch while the patient&#39;s knee is substantially straight; and FIG. 23, where router assembly  55  is shown enlarging the femoral notch while the patient&#39;s knee is bent at approximately a 140° angle. It should be noted in FIGS. 21 and 22, and again in FIG. 23, how guidewire  50  and router assembly  55  are capable of undergoing substantial elastic Wok deformation during such knee flexing even as bone-trimming operations are under way. 
     Looking next at FIGS. 24-26, in another preferred embodiment of the present invention, the apparatus of the present invention comprises guidewire  50  and a router assembly  55 A. 
     Router assembly  55 A is substantially the same as router assembly  55  described above, except as is shown in the drawings and/or hereinafter described. In particular, router assembly  55 A utilizes a collar  83 A (FIGS. 25 and 26) rather than the collar  83  described above. Collar  83 A has its hole  90  disposed off-center within the collar, whereby the router device&#39;s cutting head  67  will be clocked to one side relative to the body&#39;s hollow outer tube  82  (see FIG.  26 ). In particular, with router assembly  55 A, collar  83 A is arranged so that the router device&#39;s cutting head  67  is clocked outboard relative to the central axis of hollow outer tube  82 . This permits the router device to engage impinging bone more readily. In order to accommodate such lateral displacement of router device  65 , the router assembly&#39;s hood  85 A has its hole  95 A shifted laterally as well, in the manner shown in FIG.  26 . 
     In operation, router assembly  55 A is intended to be used in substantially the same way as router assembly  55 . 
     Looking next at FIG. 27, in another preferred embodiment of the present invention, the apparatus of the present invention comprises guidewire  50  and a cannulated router device  65 A. Router device  65 A is generally similar to the router device  65  discussed above, except that with router device  65 A, its cutting teeth  89  are disposed about only a portion of the periphery of its cutting head  67 A, with the remainder of the cutting head being smooth and non-abrasive. Accordingly, by moving cannulated router device  65 A on guidewire  50  so as to oscillate the router device through only a fraction of a complete revolution, bone can be removed adjacent to the cutting teeth  89  while the remainder (i.e., the non-cutting portion) of the cutting head  67 A safely opposes any delicate structures Which are to be safeguarded (e.g., the PCL). Thus, with the apparatus of FIG. 27, impinging bone may be safely removed without providing a shield assembly (e.g., such as the shield assembly  75  described above) for the router device. 
     In another form of the invention, the cannulated router device  65 A of FIG. 27 could be replaced with a cannulated router device of the sort adapted to remove hard bone while leaving soft tissue unharmed. By way of example, the cannulated router device  65 A of FIG. 27 might be replaced by the cannulated router device  65 B shown in FIG.  28 . More particularly, router device  65 B includes a cutting head  673  having an outer configuration similar to that disclosed in U.S. Pat. No. 4,445,509 issued May 1, 1984 to David C. Auth for METHOD AND APPARATUS FOR REMOVAL OF ENCLOSED ABNORMAL DEPOSITS, which patent is hereby specifically incorporated herein by reference. Alternatively, cutting head  67 B could have some other configuration of the sort well known in the art which permits cutting of hard bone without harming soft tissue. As a result of such a construction, a cannulated router device  65 B having such a configuration could then be safely rotated completely about guidewire  50  so as to remove impinging bone without risking damage to delicate soft tissue. Thus, with the apparatus of FIG. 28 or with equivalent cutting apparatus, impinging bone can be safely removed without providing a shield assembly (such as the shield assembly  75  described above) for the router device. 
     The foregoing apparatus may be used in an ACL reconstruction procedure as follows. First, the patient&#39;s knee is extended at an angle of approximately 90°. Then, a bone tunnel  30  is formed in the tibia in ways well known in the art. Next, guidewire  50  is passed through bone tunnel  30  and up into the femur. Then a cannulated router device (in the form of either router assembly  55 , or router assembly  55 A, or router device  65 A, or router device  65 B) is loaded onto guidewire  50  and used to perform the desired notchplasty in the manner previously described. Next, the cannulated router device is dismounted from guidewire  50 . Then bone tunnel  35  is formed in femur  10  in ways well known in the art. Then guidewire  50  is removed from femur  10 . Finally, a graft ACL  5 A is installed in femoral bone tunnel  35  and tibial bone tunnel  30  in ways well known in the art. 
     Looking next at FIG. 29, in another preferred embodiment of the present invention, the apparatus of the present invention comprises guidewire  50  and a marking device  100 . Marking device  100  preferably comprises a resilient cannulated head  105  and a flexible cannulated shaft  110  connected to head  105 . Cannulated head  105  is formed so that it can hold and release a dye without cutting bone. Marking device  100  is used by moving the device up and down guidewire  50 , with or without rotation, whereby the marking head  105  will contact any bone in its way. By sizing marking device  100  properly relative to the size of the graft ACL which is to be installed, movement of marking device  100  along guidewire  50  while the knee is moved through a range of natural motions will cause the marking element to leave its dye on any portions of the femur which might impinge upon the graft ACL which will thereafter be installed in the knee. Thereafter, marking device  100  and guidewire  50  are removed from the surgical site and the surgeon may utilize a conventional cutting element to remove the marked bone. Then the graft ACL may be installed in the knee without fear of impingement. 
     In the foregoing description of the preferred embodiments of the invention, it was noted that guidewire  50  is preferably formed out of a pseudoelastic material so as to provide the desired characteristics of firmness and flexibility. However, it should also be appreciated that a guidewire made out of a non-pseudoelastic material can also be utilized in connection with the present invention. Of course, inasmuch as the preferred use of the present invention involves flexing the knee over a wide range of motions with the guidewire in place, limitations in wire flexibility can inhibit the range of knee movements performed with the guidewire in place. Thus, in the situation where a non-pseudoelastic guidewire is to be used, it can be helpful to mount the distal end of the guidewire in a fixture by means of a universal joint. This fixture can then be attached to the bottom surface of the femur or, more advantageously, it can be disposed in a bore formed in the bottom of the femur. Preferably this bore is the femoral bone tunnel  35  used for the ACL reconstruction procedure. 
     More particularly, and looking now at FIG. 30, the distal end of a non-pseudoelastic guidewire  50 A can be mounted in a fixture  115  by a universal joint  120  whereby the proximal end of the guidewire can move about relative to fixture  115 . As a result of this construction, when fixture  115  is positioned in the femoral bone tunnel, universal joint  120  will help guidewire  50 A to accommodate the degree of deformation required as the knee is moved through a full range of natural motions. Of course, with this embodiment of the invention, the femoral bone tunnel  35  must be formed before the notchplasty procedure is performed, since fixture  115  is intended to be received in bone tunnel  35 . 
     Modifications of the Preferred Embodiments 
     It is to be appreciated that modifications may be made to the preferred embodiments described and illustrated above without departing from the scope of the present invention 
     Thus, for example, while in the foregoing description the present invention has been described in the context of reconstructing an ACL, it should also be appreciated that the present invention has application to the reconstruction of other ligaments as well, where similar impingement problems can occur. Thus, for example, the present invention might be used in connection with reconstructing the posterior cruciate ligament (PCL). 
     The present invention can also be used to clear away impinging structures in other anatomical and non-anatomical settings. 
     Advantages of the Invention 
     Numerous advantages are achieved through the use of the present invention. 
     For one thing, the present invention provides improved apparatus for reconstructing a ligament. 
     And the present invention provides improved apparatus for reconstructing an anterior cruciate ligament (ACL). 
     Also, the present invention provides improved apparatus for quickly, easily and reliably eliminating impingement problems when reconstructing an anterior cruciate ligament. 
     And the present invention provides improved apparatus for quickly, easily and reliably removing any anatomical structures (e.g., bone) which will conflict with the location of a graft ACL at the completion of an ACL reconstruction procedure. 
     The present invention also provides improved apparatus for quickly, easily and reliably removing any anatomical structures (e.g., bone) which will conflict with the location of a graft ACL as the knee is moved through a full range of natural motions. 
     The present invention also provides an improved method for reconstructing a ligament. 
     And the present invention provides an improved method for reconstructing an anterior cruciate ligament (ACL). 
     And the present invention provides an improved method for quickly, easily and reliably eliminating impingement problems when reconstructing an anterior cruciate ligament. 
     Also, the present invention provides an improved method for quickly, easily and reliably removing any anatomical structures (e.g., bone) which will conflict with the location of a graft ACL at the completion of an ACL reconstruction procedure. 
     And the present invention provides an improved method for quickly, easily and reliably removing any anatomical structures (e.g. bone) which will conflict with the location of a graft ACL as the knee is moved through a full range of natural motions.