Patent Publication Number: US-2006015110-A1

Title: Cutting device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to bone canal reaming devices and methods. More particularly, the present invention relates to a cutting or reaming device usable with a guide rod.  
      2. Description of Related Art  
      The treatment of long bone fractures typically involves internal stabilization. An intramedullary nail or rod, which is typically a cylindrical hollow rod, is inserted in the center of the intramedullary canal or marrow cavity. The rod, which is typically titanium alloy or stainless steel, is strong enough to support the bone loads during the bones healing process. The bones that are fixed in this manner are the femur, tibia, humerus, radius and ulna. Nails are typically generally circular in cross section or have a shape nearly circular.  
      One step in the surgical technique is the preparation of the canal. The bone canal varies in shape depending upon the position along the bone axis. The center of the bone is called the isthmus, which is a narrowing of the canal. This is especially true in the femur where in order to carry the body weight, the bone gets quite thick in its center.  
      A nail must be sized to carry the body weight. In order to get present day nails large enough to carry these loads, typically one and a half to three times body weight, the rod must be larger than the canal. What is presently done is enlarging of the canal. To do so, a guide rod is inserted in the canal along its entire length. It is usually about two to about four millimeters in diameter and is about 250 to about 1000 millimeters long. It serves several purposes including aligning the fragments of bone where the surgeon uses the guide rod to thread the segments through their canals, as well as being used to guide cutters through the canal to enlarge it to accept the nail.  
      The reaming process includes several components. A drill with a hole through its driving axis is used to supply power. Bone is difficult to cut, especially in young males, who are frequently the fracture patient. The drill is either pneumatic or battery powered. It can impart a high torque on all driving components in order to ream the bone. As the canal of the bone is curved, a flexible shaft is used to connect the drill and the reamer. The flexible shaft is usually about 450 millimeters long and about eight to about twelve millimeters in diameter. The flexible shaft is cannulated, and has a hole along its length slightly larger than the guide rod. The flexible shaft has a connector or connection means on one end for the drill and on the other end for connection with the reamer head (cutters).  
      The reaming set is a number of cutters that increase in diameter in increments of one half to one millimeter. A set of reamer heads for the femur may have reamer heads from nine to fourteen millimeters. The reamers are typical less than three centimeters in length, as longer cutter could not follow the curve of the bone. The reaming is done to one-half to one millimeter over the selected nail size so it is easy to insert.  
      The reaming is done by attaching a reamer head to the flexible shaft and then threading these two parts over the end of the guide rod. They are advanced to bone, cut the bone and are withdrawn. The cutter is pulled back off the guide rod and then disconnected from the flexible shaft by moving the cutter radially. The next size reamer head is connected to the flexible shaft radially, and then the assembly is axially threaded onto the guide rod. The process is repeated until the desired cavity size is prepared.  
      It is common for six to ten reaming steps to be needed to make the bone canal of sufficient size to accept a nail. This is a slow and tedious part of the surgery. The difficulty arises in that the guide rod is very long and is only slightly more rigid than a coat hanger. The flexible shaft is also pretty flimsy and almost as long. The guide rod&#39;s long length outside the body makes it a hard target for connection with the cutter and the flexible shaft. The guide rod, which is typically three millimeters in diameter, must be axially aligned with a hole in the flexible shaft having a three millimeter nominal size, with only about a quarter millimeter of tolerance. This connection step requires the surgeon to perfectly axially align two long, flexible parts in order to be threaded.  
      The connection requires the surgeon to hold the dovetail style cutter to the flexible shaft while trying to do the threading process. At the same time, the drill must be supported. This requires at least three hands: one to hold the drill, one to hold the flexible shaft reamer connection and one to hold the guide rod steady so they can be axially aligned. This connection is further complicated because the surgeon&#39;s gloves are wet with blood and fat from the canal, rendering them very slick.  
      The contemporary guide rods are constructed of non-resilient or non-flexible material. This provides additional difficulty in manipulating the cutter or reamer heads onto the guide rod by requiring the drill and drill head to be lifted high into the air to perform the connection or exchange.  
      Some surgeons that are very skilled can hold the drill with one hand, and use the other to hold the reamer to the shaft, and capture the bouncing guide rod, then align it all together with one hand. Few indeed are those who have this type of dexterity. This is further complicated by the fact that if the reamer head is dropped from the hand onto the floor during this process, it must be sterilized delaying the surgical procedure even further. Clearly, reaming is a frustrating part of the long bone fracture fixation procedure, and it is no wonder it is left to residents and those in their medical training to do this tedious task.  
      Accordingly, there is a need for a reaming device and related apparatus that addresses these drawbacks.  
     SUMMARY OF THE INVENTION  
      It is an object of the present invention to facilitate the exchanging of cutters during a bone reaming process.  
      It is another object of the present invention to facilitate the more rapid exchanging of cutters during the bone reaming process.  
      It is a further object of the present invention to provide a cutter that facilitates the connection of the cutter to a guide rod.  
      It is a yet another object of the present invention to provide a cutter that facilitates the more rapid connection of the cutter to the guide rod.  
      It is still another object of the present invention to provide a cutter that allows for a non-axial insertion of the guide rod into the cutter.  
      These and other objects and advantages of the present invention are provided by a cutter for use with a guide rod for reaming of a bone canal. The cutter has a body with a cutting surface, a distal end, a proximal end and a channel between the distal and proximal ends. The channel has a longitudinal axis. The distal end has an opening in communication with the channel. At least a portion of the opening is disposed in a first plane that is non-orthogonal to the longitudinal axis.  
      In another embodiment, a cutter for use with a guide rod for reaming of a bone canal is provided that has a body having a cutting surface, a distal end, a proximal end and a channel between the distal and proximal ends. The channel has a cross-sectional area. The distal end has an opening in communication with the channel. The opening has an area that is larger than the cross-sectional area.  
      In still another embodiment, a reaming device for reaming of a bone canal is provided. The reaming device has a driving device, a guide rod and a cutter. The cutter has a body with a cutting surface, a distal end, a proximal end and a channel between the distal and proximal ends. The channel has a cross-sectional area. The distal end has an opening in communication with the channel, and the opening has an area that is larger than the cross-sectional area.  
      In a further embodiment, a method of connecting a cutter to a guide rod for reaming of a bone canal is provided which includes, but is not limited to:  
      (I) providing a guide rod;  
      (II) providing a cutter that is removably connectable to the guide rod, wherein the cutter has a longitudinal axis, a channel disposed therethrough and an opening in communication with the channel;  
      (III) loading the cutter on the guide rod by inserting an end of the guide rod into the opening at an angle to the longitudinal axis; and  
      (IV) advancing said cutter along said guide rod.  
      In still another embodiment, a method of connecting a cutter to a guide rod for reaming of a bone canal is provided which includes, but is not limited to:  
      (I) providing a guide rod;  
      (II) providing a cutter that is removably connectable to the guide rod, wherein the cutter has a longitudinal axis, a channel disposed therethrough and an opening in communication with the channel, and wherein the opening has a radial slot extending along only a portion of the cutter or part way along its length;  
      (III) loading the cutter on the guide rod by inserting an end of the guide rod through the radial slot; and  
      (IV) advancing the cutter along the guide rod.  
      The opening can have first and second portions. The first portion may be in a second plane that is orthogonal to the longitudinal axis and the second portion can be in the first plane. The first plane may be parallel to the longitudinal axis. The opening can be defined at least in part by walls that are splayed. The channel has a longitudinal axis, and the opening may have at least a portion that is in a first plane that is non-orthogonal to the longitudinal axis.  
      The opening can be defined at least in part by walls that converge in a direction of the longitudinal axis. The opening may also be defined at least in part by walls that diverge in a direction of the distal end. The opening can be defined at least in part by walls that have a chamfered edge.  
      The connection method may provide for rotating the guide rod toward the longitudinal axis prior to advancing the cutter along the guide rod. The connection method can also provide for inserting the guide rod through the radial slot until it abuts a channel wall that is opposite to the radial slot. The connection method may also provide for locking the cutter to a driving device.  
      Other and further objects, advantages and features of the present invention will be understood by reference to the following:  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view of a prior art cutter;  
       FIG. 2  is plan view of a prior art cutter connected with a flexible shaft;  
       FIG. 3  is a plan view of the insertion of a guide rod into the prior art cutter of  FIG. 1  for connection;  
       FIG. 4  is a plan view of the prior art cutter being advanced along the guide rod with the flexible shaft not shown;  
       FIG. 5  is a perspective view of a cutter of the present invention;  
       FIG. 6  is a plan view of the cutter of  FIG. 5 ;  
       FIG. 7  is a perspective cross sectional view of the cutter of  FIG. 6  taken along line  7 - 7  of  FIG. 6 ;  
       FIG. 8  is a top view of the cutter of  FIG. 5 ;  
       FIG. 9  is a perspective view of the cutter of  FIG. 5  connected to a flexible shaft;  
       FIG. 10  is a perspective view of a guide rod partially inserted into the cutter of  FIG. 5 ;  
       FIG. 11  is a cross-sectional view of a first method of inserting a guide rod into the cutter of  FIG. 5 ;  
       FIG. 12  is a cross-sectional view of a second method of inserting the guide rod into the cutter of  FIG. 5 ;  
       FIG. 13  is a cross-sectional view of an alternative embodiment of a cutter of the present invention;  
       FIG. 14  is an enlarged view of the upper portion of the cutter of  FIG. 13  including the opening;  
       FIG. 15  is a perspective view of another alternative embodiment of a cutter of the present invention;  
       FIG. 16  is a perspective view of another alternative embodiment of a cutter of the present invention; and  
       FIG. 17  is a perspective view of another alternative embodiment of a cutter of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to the drawings, and in particular  FIGS. 1 through 4 , a prior art cutter is shown, as well as the prior art method of connecting or loading the cutter with a guide rod. A guide rod bore or channel of the prior art cutter is along the longitudinal axis of the cutter and defines an opening that is perpendicular to the longitudinal axis.  
      In order to connect the prior art cutter with the guide rod, the surgeon must align the guide rod along the longitudinal axis of the cutter and insert it through the opening. The cutter then travels along the guide rod, which is disposed through the guide rod channel of the cutter. During the surgical procedure, this is a difficult task at best, especially due to the tight tolerance between the central bore in the reamer and the outer surface of the guide rod.  
      Referring to  FIGS. 5 through 10 , a cutter of the present invention is shown and generally represented by reference numeral  5 . Cutter  5  has a body  10  with a distal end  15 , a proximal end  20  and a guide rod bore or channel  25  disposed therebetween. The channel  25  is centrally located along the longitudinal axis of the cutter  5  to define the center bore of the cutter. Preferably, the channel  25  is cylindrical or substantially cylindrical in shape, with a uniform diameter.  
      Proximal end  20  of the cutter  5  has a shaft connector  30 . The shaft connector  30  provides for connection of a flexible shaft  11  (shown in  FIG. 9 ) with the cutter  5 . The shaft connector  30  can have various connection structures, methods or means, which provide for releasable connection of the flexible shaft  11  and the cutter  5 . Additionally, the present invention contemplates the use of cutter  5  with a shaft  11  that is integrally fixed thereto.  
      The cutter  5  has an opening  50  disposed therethrough at the distal end  15  of the cutter. In the preferred embodiment of cutter  5 , opening  50  is defined by a first portion  60  that is substantially perpendicular or orthogonal to the longitudinal axis of the cutter  5  and a second portion or radial slot  70  that is substantially non-perpendicular or non-orthogonal to the longitudinal axis of the cutter, as shown in  FIG. 8 . Preferably, the first portion  60  of opening  50  lies in a plane that is perpendicular to the longitudinal axis of the cutter  5  and the second portion  70  of the opening lies in a plane that is parallel to the longitudinal axis. However, the present invention contemplates the opening having portions that are at different angles with respect to each other and to the longitudinal axis of the cutter channel  25 , as shown in  FIG. 7 .  
      The second portion  70  of the opening  50  is preferably defined by a rim  75  having a substantially U-like shape, as shown in  FIG. 5 . The size and shape of first portion  60  of the opening  50  is adaptable for receiving the guide rod  12  (shown in  FIG. 10 ) and allowing it to slide therethrough into position. The size and shape of the second portion  70  is adaptable for facilitating the insertion of the guide rod  12  into the opening  50  and allowing it to be moved into axial alignment with the first portion  60  of the opening and the longitudinal axis of the cutter  5 . Second portion  70  also has a size and shape that maintains the strength and integrity of the cutter  5  and, in particular, the distal end  15  of the cutter.  
      The second portion  70  of the opening  50  preferably has a width that is equal to or nearly equal to the cutter channel  25 . The height of the second portion  70  of the opening  50  allows for insertion of the guide rod  12  therethrough, while preventing a large stress riser on the cutter  5  or creating an opening for bone fragments to become lodged in.  
      The rim  75  of the second portion  70  of opening  50  is preferably defined or partially defined by non-parallel walls  80 , such as, for example, splayed walls, as shown in  FIG. 6 . The walls  80  in this preferred embodiment converge toward the longitudinal axis and diverge in the direction of the distal end  15  of cutter  5  (as shown in  FIGS. 6 and 8 ). The non-parallel alignment or configuration of the walls  80  with respect to each other further facilitates the insertion of the guide rod  12  into the second portion  70  of the opening  50  by increasing the target that is presented by the second portion. However, the present invention contemplates the use of other configurations of the walls  80 , such as, for example, parallel, partially parallel, and/or partially splayed, where these configurations facilitate insertion of the guide rod  12  into the guide rod channel  25  of the cutter  5 .  
      The body  10  of cutter  5  has a number of cutting flutes  90 , as shown in  FIG. 5 . The opening  50  is preferably positioned between a pair of the cutting flutes  90 . This allows for easier access to the opening  50 , while also maintaining the cutting efficiency of the cutter  5  by not removing any of the cutting surfaces of the cutting flutes  90 . While the preferred embodiment uses a number of cutting flutes  90 , the present invention contemplates the use of other structures, methods or means for cutting or reaming of the bone canal, such as alternative cutting surfaces. Additionally, the present invention contemplates opening  50  being positioned over a portion of one or more of the cutting flutes  90 , which would remove a portion of the cutting surface. Further, the cutting surfaces preferably are a number of cutting surfaces (for one or more cutting flutes  90 ), and more preferably are between three and eight cutting edges.  
      As shown in  FIG. 10 , the opening  50  having first and second portions  60  and  70  (shown in  FIG. 5 ) allows the guide rod  12  to be initially inserted into the opening at an insertion angle a with respect to the longitudinal axis of the cutter  5  and channel  25 . During surgery, where the guide rod  12  can be extended a great length above the patient, this non-axial insertion greatly facilitates the ability to connect the cutter  5  with the guide rod. In the preferred embodiment of cutter  5 , insertion angle a is up to at least 90°.  
      Referring to  FIG. 11 , a method of connecting the cutter  5  with the guide rod  12  is shown in the steps I through V. The direction of movement of the guide rod  12  with respect to the cutter  5  is shown by arrow  13 . The guide rod  12  is initially non-axially aligned with the cutter  5  at an insertion angle α, as shown in step I. The end of the guide rod  12  is then inserted into opening  50  through first and second portions  60  and  70 , as shown in step II.  
      The opening  50  is comprised of a portion (second portion  60 ) that lies in a plane that is non-orthogonal to the longitudinal axis of the cutter  5 , which results in the overall size of the opening being larger than the size or diameter of guide rod channel  25 . The size of the portion (first portion  60 ) of the opening  50  along the distal end  15  of the cutter  5  is equal to or nearly equal to the size or diameter of the channel  25 . The overall increased size of opening  50  facilitates connection of the cutter  5  with the guide rod  12  by providing a much larger target for insertion.  
      A channel wall  26 , which is disposed opposite to the second portion  70  of opening  50 , acts as a guide for the placement of the end of the guide rod  12  into the guide rod channel  25 . Once partially inserted therein, the guide rod  12  can be rotated into axial alignment with the cutter  5  and channel  25  using channel wall  26  as an abutment or guide, as shown in steps III and IV. The channel wall  26  and rim  75  of opening  50  acts as a hinge for the rotation of the guide  12  rod into axial alignment with the cutter  5 . The guide rod  12  then travels along the channel  25 , as shown in step V.  
      Referring to  FIG. 12 , an alternative method of connecting the cutter  5  with the guide rod  12  is shown in the steps I through III. The direction of movement of the guide rod  12  with respect to the cutter  5  is shown by arrow  14 . The guide rod  12  is initially aligned parallel or substantially parallel with the longitudinal axis of the cutter  5  and channel  25 , as shown in step  1 . The end of the guide rod  12  is below the distal end  15  of the cutter  5  but above the lower most portion of the rim  75  of opening  50 .  
      The end of the guide rod  12  is then moved towards the cutter  5  and passes through the second portion  70  of opening  50 , as shown in step II. This movement is facilitated by the splayed walls  80 , which create a larger opening than the diameter of the guide rod  12 . The channel wall  26  acts as a stopper for the placement of the end of the guide rod  12  in the channel  25 . Once partially inserted therein, the guide rod  12  travels along the channel  25 , as shown in step III.  
      Additionally, a combination of the insertion methods described above with respect to  FIGS. 11 and 12  can be utilized with the present invention. The guide rod  12  can be aligned at the angle α and also below the distal end  15  but above the lower most portion of the rim  75  of opening  50 . The end of the guide rod  12  is moved through the second portion  70  of opening  50 . The guide rod  12  is then also rotated into axial alignment with the longitudinal axis of the cutter  5  and the channel  25 , and travels along the cutter channel into position. The channel wall  26  acts as both a stopper and a hinge to facilitate the insertion of the guide rod  12  through the guide rod channel  25  of cutter  5 .  
      Referring to  FIG. 13 , an alternative embodiment of the cutter of the present invention is shown and generally represented by reference numeral  100 . The cutter  100  has features similar to the features of cutter  5  such as a body  110 , a distal end  115 , a proximal end  120 , a guide rod bore or channel  125  disposed therebetween, a shaft connector  130 , an opening  150  disposed through the distal end that has first and second portions  160  and  170 , and cutting flutes  190 .  
      The opening  150  is defined by a rim  175  that is formed in part by splayed wall  180 . A lower portion of the wall  180  has a chamfered, angled or non-symmetrical edge  185 . The chamfered edge  185  further facilitates the insertion of the guide rod  12  into the guide rod channel  125  by eliminating and/or smoothing a portion of the edge. The guide rod  12  is rotated into axial alignment with the cutter  100  and the channel  25  using both a channel wall  126  and the chamfered edge  185  as a hinge or guide. Additionally, the chamfered edge  185  facilitates sliding of the guide rod  12  along the channel  125  since the edge has been eliminated and/or smoothed over reducing friction.  
      The present invention has first and second portions  60  or  160  and  70  or  170 , which increase the area or size of opening  50  or  150 , respectively. These portions are orthogonal or substantially orthogonal to each other. However, the present invention contemplates the use of other angles, sizes or shapes for the openings  50  or  150  in order to facilitate the insertion of the guide rod  12  into the cutter  5  or  100 . The present invention also contemplates the use of other features on the cutters  5  or  100 , such as, for example, alternative types of cutting flutes  90  or  190 , as well as a variety of materials or combinations of materials from which the cutters  5  or  100  can be made.  
      The present invention contemplates the use of more than two portions for openings  50  or  150  that are positioned at different angles with respect to each other and/or the longitudinal axis of the guide rod channel  25  or  125  of the cutters  5  and  100 , respectively.  
      Referring to  FIG. 15 , another alternative embodiment of the cutter of the present invention is shown and generally represented by reference numeral  200 . The cutter  200  has features similar to the features of cutter  5  such as a body  210 , a distal end  215 , a proximal end  220 , a guide rod bore or channel  225  disposed therebetween, a shaft connector  230 , an opening  250  disposed through the distal end that has first and second portions  260  and  270 , and cutting flutes  290 .  
      The opening  150  is defined in part by an angled wall  280 . First and second portions  260  and  270  increase the size of opening  250 . First and second portions  260  and  270  are non-orthogonal to each other. The angle with respect to the longitudinal axis of the guide rod channel  225  at which the second portion  270  lies, as well as the slope or angle of wall  280  facilitates insertion of the guide rod  12  into the opening  250 . This can be especially useful where the guide rod  12  is being inserted into the cutter  200  at a large angle a (shown in  FIG. 11 ), as well as where the end of the guide rod is near or abutting the body  210  so that the end of the guide rod can be slid more easily over and into the opening  250 .  
      Referring to  FIG. 16 , yet another alternative embodiment of the cutter of the present invention is shown and generally represented by reference numeral  300 . The cutter  300  has features similar to the features of cutter  5  such as a body  310 , a distal end  315 , a proximal end  320 , a guide rod bore or channel  325  disposed therebetween, a shaft connector  330 , an opening  350  disposed through the distal end that has first and second portions  360  and  370 , and cutting flutes  390 .  
      The opening  350  has first and second portions  360  and  370  that are disposed substantially parallel to each other but are offset from each other along the length of cutter  300 . First portion  360  has a substantially U-like shape and is offset from second portion  370  by a first wall  326 . The first wall  326  is defined partially by the body  310  and the cutting flutes  390 . The first wall  326  acts as both a stopper and a hinge to facilitate the insertion of the guide rod  12  through second portion  370  and then the guide rod channel  325  of cutter  300 . Second portion  370  is defined in part by a second wall  380 . Preferably second wall  380  is chamfered or angled inwardly to facilitate insertion of the guide rod  12  into the opening  350 . This can be especially useful where the guide rod  12  is being inserted into the cutter  300  at a large angle a (shown in  FIG. 11 ), as well as where the end of the guide rod is near or abutting the body  310  so that the end of the guide rod can be slid more easily over and into the opening  350 .  
      Referring to  FIG. 17 , still another alternative embodiment of the cutter of the present invention is shown and generally represented by reference numeral  400 . The cutter  400  has features similar to the features of cutter  5  such as a body  410 , a distal end  415 , a proximal end  420 , a guide rod bore or channel  425  disposed therebetween, a shaft connector  430 , an opening  450  disposed through the distal end, and cutting flutes  390 .  
      Cutter  400  provides for the use of a single opening, e.g., an opening in a single plane or a substantially single plane, where the plane is non-orthogonal to the longitudinal axis of the cutter. This type of angled opening allows for an enlarged area for insertion, as compared to the diameter of the center bore channel, and allows for insertion at an angle to the longitudinal axis of the cutter.  
      The present invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined in the appended claims.