Abstract:
A device for expedited reaming of a medullary canal and method of using the same are disclosed. The device includes a reamer head connected at the distal end of a rotatable drive shaft. The reamer head has a cutting head with a plurality of blades and flutes therebetween. Each blade has a front cutting portion. The blades can also include a side cutting portion. The disclosed method for removing material from the medullary canal of a bone includes the steps of reaming an area of the medullary canal to remove material; irrigating the material to be removed while reaming to reduce generation of heat and move removed material from the reaming area; and aspirating the removed material while reaming to create a negative intramedullary canal pressure to assist in the removal of the material.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     Priority of Provisional Application No. 60/118,485 filed Feb. 3, 1999 is claimed under 35 U.S.C. §119(e). 
    
    
     FIELD OF THE INVENTION 
     The present invention is directed to a device and method for bone tissue removal, and in particular to a device and method for expedited reaming of a medullary canal. 
     BACKGROUND OF THE INVENTION 
     A wide variety of devices for cutting and removing bone tissue are known in the air. Examples of such include those described in U.S. Pat. No. 5,269,785 issued to Bonutti, U.S. Pat. No. 4,830,000 to Shutt, and U.S. Pat. No. 5,190,548 to Davis. In general, these and similar devices utilize a rotating cutting tip similar to a drill displaced at the distal end of drive shaft. Bone cutting devices for use in reaming the medullary canal typically use a flexible drive shaft because the medullary canals of bones are seldom straight and usually will have some degree of curvature. Most reamers also have a central bore through both the reamer and the drive shaft. The central bore is intended to receive a long, small diameter guide pin or wire which is initially inserted into the medullary canal to act as a track for the advancing reamer. 
     Reamers are used in orthopedic surgery to prepare the medullary canals of bone for a wide variety of surgical procedures. Such procedures include total hip and knee replacement, nail insertion to stabilize a long bone fracture, an intramedullary osteotomy, and bone harvesting for grafting purposes. 
     From both a mechanical and a biological point of view, medullary reaming is particularly beneficial in improving the performance of implants. Specifically, reaming expands the medullary canal so that larger diameter implants can be inserted. These larger diameter implants are less likely to fail. In fact, certain fractures require over-reaming so that larger implants can be used. Without reaming, the surgeon must use a “best guess” estimate when selecting the diameter of the implant. The medical literature contains numerous case studies reporting the adverse consequences of an inaccurate estimate. Reaming provides a direct measurement of the diameter of the medullary canal, and thereby allows for the selection of an implant that precisely fills the canal. As a result, the stability of the fracture site is enhanced by achieving endosteal contact. When implants do not fill the medullary canal, load sharing between the implant and the bone is decreased. This increases the load that is transferred to the implant and promotes both implant failure and stress shielding of the bone. 
     Despite such benefits, negative consequences have also been associated with medullary reaming. In particular, current procedures for reaming the medullary cavity can result in an increase in both temperature and pressure. Like any process in which material is being removed, reaming causes generation of heat. Furthermore, a hydraulic pressure, which far exceeds that of blood pressure, builds up in the cavity during reaming. The reamer acts as a hydraulic piston within the bone cavity, and if the contents of the canal, which include a mixture of medullary fat, blood, blood clots, and bone debris, enter the blood stream, an embolism can result. Excessive heat has been associated with an increased incidence of aseptic necrosis of the cortex and elevated pressure has been associated with an increased risk of fat emboli. These complications are more likely to occur in patients when extenuating factors such as shock, existing lung contusion, multiple traumas, or pre-existing pulmonary impairment are present. In these situations, the preferred method of reaming would usually not be performed due to the increased risks involved. 
     Various devices and methods exist for reducing the intramedullary pressure build-up during reaming. For example, in prosthetic joint replacement, a distal venting hole, a large insertion hole, and a modified technique for cement insertion have all been shown to have some success ill reducing pressure, and presumably, the chance of fat embolism. Venting holes in the bone only have little effect because their diameter is typically too small and local peak values must be assumed during the passage of the reamer. Similarly, reaming the medullary cavity less does not prevent pressure increase. In fact, pressure can be high even for reamers of small diameter. 
     Another technique which has been used in an attempt to reduce temperature and pressure is to perform the reaming in multiple steps with increasing size of reamers with each step. As a result, reaming procedures are done slowly with the application of gentle pressure and requiring multiple passes. Usually reaming is performed in 1 mm diameter increments until the bone cortex is reached and then in 0.5 mm increments thereafter. In this regard, the reaming is carried out with less compression force and the intramedullary pressure can be easily reduced with most reaming devices utilizing this slow process. A faster reaming process utilizing fewer passes would be desirable in order to reduce operating time and medical costs. 
     Another disadvantage associated with current devices and methods is the reuse of reamers. Because current methods involve the use of multiple reamers of variable sizes to create one large opening in the medullary canal, reamers are usually reused in subsequent bone reaming procedures. As a result, reamers may become blunt over time and their continued use can produce greater intramedullary pressures and a greater increase in cortical temperature. Consequently, the careful attention of surgeons and operating staff to treat the reamers gently and replace them whenever necessary is trying and costly. A single use device is desirable to avoid the problems associated with the dulling of reamers which occurs with time. 
     Another disadvantage of current devices is due to the use of reamer designs with shallow flutes and large shafts. It has been shown that reamers with small shafts and deep flutes are more beneficial in reducing intramedullary pressure and temperature. 
     Thus, there exists a need for a device and method for reaming a medullary canal at an enhanced rate without increasing the risk of fat emboli and heat necrosis upon cutting and removal of bone tissue. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a device for reaming a medullary canal of a bone. The device includes a rotatable drive shaft connected at the proximal end to a rotational drive element and a reamer head rotatably coupled to the distal end of the drive shaft. The reamer head has a tubular shank engaging the distal end of the drive shaft and a cutting head integral with the shank and having a plurality of blades. Flutes are located between adjacent blades. At least some and preferable all of the blades have a front cutting portion that includes at least two planar surfaces. A helical side cutting portion may be added to any or all of the blades. Preferably, there are at least five blades and each blade has at least three planar surfaces. 
     In one embodiment, each blade has a front cutting edge defined by the intersection between the inner blade wall and one of the planar surfaces. This front cutting edge may be oriented at an angle of approximately 30° to 45° with respect to the longitudinal axis of the tubular shank. In another embodiment, the helical side cutting portion further includes a side cutting edge defined by the intersection between the inner blade wall and the outer blade wall. 
     The drive shaft and reamer head each may have a cannulation. These two cannulations are aligned when the tubular shank is engaged with the drive shaft to form a center channel. One use for this channel is for receiving a guide wire that can be used to direct the device in the medullary canal. 
     The device may also include an aspiration tube for removing cut material generated by the reamer head. The aspiration tube has a manifold assembly at a proximal end, a reamer head retainer at a distal end, and a lumen configured and dimensioned to receive the drive shaft. Preferably, the center channel is in fluid communication with an irrigation source to provide irrigation to the cutting head. The manifold assembly may include an irrigation port connected to the irrigation source and an irrigation chamber in fluid communication with the irrigation port. The irrigation fluid travels from the irrigation chamber through an opening on the drive shaft and into the center channel. In one embodiment in which the reamer head is larger than the aspiration tube, the reamer head retainer has a substantially spherical outer profile. 
     The distal end of the lumen of the aspiration tube is in fluid communication with the flutes of the reamer head and the proximal end of the lumen is in fluid communication with a suction source. Preferably, the manifold assembly includes an aspiration port connected to the suction source to assist in the removal of the cut material. 
     The invention also relates to a method for removing tissue from a medullary canal of a bone. This method includes the steps of reaming an area of the medullary canal to remove the material; irrigating the material to be removed while reaming to reduce generation of heat and move removed material from the reaming area; and aspirating the removed material while reaming to create a negative intramedullary canal pressure to assist in the removal of the material. 
     The method may also include the step of inserting an implant in the medullary canal after the removal of material. Preferably, the reaming is done with a single reaming device, and the device may be guided to the appropriate location in the medullary canal using a guide wire which passes through a cannulation in the device. In another embodiment, the method includes the step of harvesting the removed tissue for use as a graft. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Preferred features of the present invention are disclosed in the accompanying drawings, wherein similar reference characters denote similar elements throughout the several views, and wherein: 
     FIG. 1A is a perspective view from the distal left side of one embodiment of a reamer device according to the present invention. 
     FIG. 1B is a perspective view from the proximal right side of the device of FIG.  1 A. 
     FIG. 2 is a top view of the reamer device of FIGS. 1A and 1B. 
     FIG. 3 is a cross-sectional view of the device taken along line A—A of FIG.  2 . 
     FIG. 4 is a perspective view of one embodiment of a drive shaft assembly according to the present invention. 
     FIG. 5 is a side view of one embodiment of a reamer head according to the present invention. 
     FIG. 6 is a front view of the reamer head of FIG.  5 . 
     FIG. 7 is a rear view of the reamer head of FIG.  5 . 
     FIG. 8 is a front perspective view of the reamer head of FIG.  5 . 
     FIG. 9 is a rear perspective view of the reamer head of FIG.  5 . 
     FIG. 10 is an enlarged view of the side view of FIG.  5 . 
     FIG. 11 is an enlarged and partially fragmented perspective and cross-sectional view of the reamer shown in FIGS. 1A and 1B. 
     FIG. 12 shows an exemplary sample of a graph expressing a pressure-time curve of a system using the reamer of FIG. 1, the reamer head of FIG. 5, and the drive shaft assembly of FIG. 4 . 
     FIG. 13 is a perspective view of a portion of the drive shaft assembly of FIG. 4 with a guide wire inserted in the cannulation of the drive shaft. 
     FIG. 14 is a cross-sectional view of the drive shaft assembly taken along line A—A of FIG.  13 . 
     FIG. 15 is a top view of another embodiment of a reamer device according to the present invention. 
     FIG. 16 is a front perspective view of another embodiment of a reamer head according to the present invention. 
     FIG. 17 is an enlarged view of the side view of the reamer head of FIG.  16 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     For convenience, the same or equivalent elements in the various embodiments of the invention illustrated in the drawings have been identified with the same reference numerals. Further, in the description that follows, any reference to either orientation or direction is intended primarily for the convenience of description and is not intended in any way to limit the scope of the present invention thereto. 
     Referring to FIGS. 1-3, a first embodiment of a reamer  10  according to the present invention comprises a reamer head  20  located at a distal end of reamer  10  for reaming a medullary canal, a flexible aspiration tube  13  for suction and removal of the emulsified bone and other material generated by reamer head  20 , a reamer head retainer  14  for retaining reamer head  20  on aspiration tube  13  while still allowing rotation of reamer head  20  with respect to aspiration tube  13 , and a manifold assembly  12  at a proximal end of reamer  10 . Thus, as used in this application, the term distal designates the end or direction near reamer head  20  and toward the front of reamer  10 , and the term proximal designates the end or direction near manifold assembly  12  and toward the rear of reamer  10 . The term longitudinal designates an axis central to aspiration tube  13 . 
     Aspiration tube  13  is flexible so that it can bend to accommodate curvature of the bone and is preferably made of a translucent material so that the aspirated material can be observed. Manifold assembly  12  has an irrigation port  15  and an aspiration port  16  for connecting to an irrigation source and aspiration means respectively. A drive shaft coupling  17  is located at the proximal end of manifold assembly  12 . Drive shaft coupling  17  can be readily attached and detached to a drive shaft or some other means for rotating reamer head  20 . 
     FIG. 4 shows a drive shaft assembly  100  that can be used with reamer  10  to rotate reamer head  20  at sufficient speeds to ream the medullary canal. The use of a drive shaft assembly  100  with reamer  10  (or any modular system in which the driving means is contained in a unit that is independent from the reamer) allows drive shaft assembly  100  to be reused with many different reamers. Such modularity is advantageous because different patients and clinical conditions will require different sized reamer heads. Furthermore, the reamer head, and not the drive means, experiences the wear and abrasion of cutting bone. Thus, reamer  10  can be a single-use, disposable item and drive shaft assembly  100  can be used for an extended period. 
     Drive shaft assembly  100  includes a flexible drive shaft  102  having a reamer head connector  104  on the distal end for releasably engaging reamer head  20  so that reamer head  20  rotates when flexible drive shaft  102  rotates, a power source connector  106  for connection to a source of power to initiate the rotation of drive shaft  102 , and a manifold coupling  108  located between reamer head and power source connectors  104 ,  106  for engaging drive shaft coupling  17 . Drive shaft  102  is sized to fit within the lumen of aspiration tube  13 . However, as will be described in more detail later, there is sufficient space between the outer wall of drive shaft  102  and the inner wall of aspiration tube  13  to allow transport of aspirated material from reamer head  20  through aspiration tube  13  to aspiration port  16 . As was the case for aspiration tube  13 , drive shaft  102  is flexible to conform to any curvature of the bone being reamed. Drive shaft  102  has a cannulation  110  for accommodating a guide wire  120 . 
     As seen best in FIGS. 11,  13 , and  14 , there is sufficient space between the outer wall of guide wire  120  and the inner wall of cannulation  110  to allow transport of an irrigation fluid from irrigation port  15  through cannulation  110  to reamer head  20 . Drive shaft  102  has an opening  126  that extends from the outer surface of drive shaft  102  to cannulation  110 . Opening  126  is positioned on drive shaft  102  so that when drive shaft assembly  100  is coupled to reamer device  10 , opening  126  is in fluid communication with irrigation port  15  to allow irrigation to flow through cannulation  110 . Opening  126  has curved walls  128 ,  130 . Curved wall  128  bows out to have a convex profile and curved wall  130  curves inward to have a concave profile. The curvature of curved walls  128 ,  130  helps to draw water into cannulation  110  as drive shaft  102  rotates (which with respect to FIG. 14 is in the counter-clockwise direction). 
     Any suitable means for releasably joining manifold coupling  108  and drive shaft coupling  17  can be used. Preferably, a quick connect mechanism is used for rapid coupling and uncoupling. For example, manifold coupling  108  can have a spring loaded latch mechanism, such as ball bearings, which engage a groove in drive shaft coupling  17 . Similarly, any suitable power source and means for securing drive shaft assembly  100  to the power source can be used. As pneumatic tools are widely used in orthopaedic surgery, the power source is preferably an air drive such as the Compact Air Drive available from Synthes (U.S.A.) of Paoli, Pa. 
     Referring back to FIG. 3, housed within manifold assembly  12  is a sealing element  34  and a sleeve bearing  31 . Scaling means  34  and sleeve bearing  31  define an irrigation chamber  35  and provide a hermetic seal to prevent irrigation fluid from escaping irrigation chamber  35  into aspiration port  16  or out the proximal end of reamer device  10  during operation. In addition, sleeve bearing  31  prevents the aspirated emulsified material from entering irrigation chamber  35 . 
     Reamer head  20  is positioned coaxially within reamer head retainer  14  at the distal end of aspiration tube  13 . FIG. 15 shows a reamer  210  that has a head retainer  14 ′ with a generally spherical outer profile shape. As head retainer  14 ′ follows reamer head  20 , the shape of head retainer  14 ′ allows head retainer  14 ′ to glance off of the medullary canal walls should flexing occur with aspiration tube  13  with respect to drive shaft  102 . Thus, head retainer  14 ′ can move smoothly while advancing through the medullary canal, retracting after reaming, and negotiating the fracture site. 
     Reamer head  20  is preferably made of a stainless steel, although any metallic, polymeric, ceramic, or composite material suitable for cutting bone can be used. A reamer cannulation  22  extends from the distal tip to the proximal end of reamer head  20  (FIGS.  7  and  8 ). Reamer cannulation  22  is aligned with cannulation  110  of drive shaft  102  so that a guide wire can extend from the proximal end of drive shaft  102  through the distal end of reamer head  20 . 
     Although many different reamer heads can be used with reamer  10 ,  210 , one embodiment is shown in FIGS. 5-10. As shown in these figures, reamer head  20  consists of a cutting head  40  integral with a tubular shank  25 . The periphery of tubular shank  25  is cylindrical and has a retaining groove  26  indented around the periphery which accommodates an extension from the inside of reamer head retainer  14  and permits reamer head  20  to rotate while maintaining a fixed location longitudinally at the distal end of the aspiration tube  13 . Tubular shank  25  has a drive shaft receptor  23  at the proximal end which is configured to accommodate reamer head connector  104  of drive shaft  102  so that reamer head  20  must rotate when drive shaft  102  rotates. Although drive shaft receptor  22  can be of any shape conforming to the exterior profile of reamer head connector  104 , it is preferably a female hex feature. 
     Cutting head  40  of reamer head  20  has a plurality of blades  41 , preferably at least five in number, extending radially outwardly from reamer cannulation  22  to form a substantially helical pattern. Correlating the number of blades to the particular blade geometry and rotation speed is advantageous in order to allow for appropriate amount of bone material to be removed while providing efficient cutting. When too many blades are used with a given blade shape, the flutes become very shallow and less bone material can be removed as a result. When an insufficient number of blades is used, the reamer head is not efficient in cutting bone tissue. In fact, the reamer head may bind or jam while cutting bone matter. 
     Each blade  41  has a multiple surfaced angular distal end with a straight front cutting edge  42  joined to a helical side cutting edge  44 . Front cutting edge  42  is defined by the intersection between an inner blade wall  45  and a planar first lip surface  51 . The angle between inner blade wall  45  and first lip surface  51  is acute. A planar second lip surface  52  intersects first lip surface  51  at an obtuse angle to form a first lip edge  56 . A planar third lip surface  53  intersects second lip surface  52  at an obtuse angle to form a trailing lip edge  58 . Side cutting edge  44  is defined by the intersection between inner blade wall  45  and an outer blade surface  46  and is at a constant radial distance from the longitudinal axis and extends longitudinally in a helical fashion. Outer blade surface  46  whorls radially inward from side cutting edge  44  along an arc toward an inner blade wall of an adjacent blade. The space between such adjacent blades defines a flute  43  which, during operation, functions to funnel the cut medullary canal material towards the proximal end of reamer head  20  for removal from the bone cavity through aspiration tube  13  under vacuum. Inner blade wall  45  and outer blade surface  46  extend longitudinally on cutting head  40  terminating at the proximal end in a shoulder surface  48 . Shoulder surface  48  abuts tubular shank  25 . 
     FIGS. 16 and 17 show another embodiment of a reamer head  20 ′ according to the present invention. Reamer head  20 ′ does not have any side cutting edges, thereby substantially minimizing the risk of laterally reaming through the cortex of the bone. Each blade  41  has a multiple surfaced angular distal end with a straight front cutting edge  42 . Front cutting edge  42  is defined by the intersection between an inner blade wall  45  and a planar first lip surface  51 . The angle between inner blade wall  45  and first lip surface  51  is acute. A planar second lip surface  52  intersects first lip surface  51  at an obtuse angle to form a first lip edge  56 . Outer blade surface  46  whorls radially inward along an arc toward an inner blade wall of an adjacent blade. The space between such adjacent blades defines a flute  43  which, during operation, functions to funnel the cut medullary canal material towards the proximal end of reamer head  20 ′ for removal from the bone cavity through aspiration tube  13  under vacuum. 
     The use of reamer  10 , which can be during open surgical, percutaneous, or any other minimally invasive procedure, will now be described referring primarily to FIG.  11 . It should be noted that the use of reamer  210  is analogous to the use of reamer  10 , the primary difference between reamer  10  and reamer  210  being the different geometries of head retainer  14  shown in FIG.  2  and head retainer  14 ′ shown in FIG.  15 . After the bone to be reamed has been accessed, guide wire  120  is inserted into medullary canal  122  of bone  124 . The insertion of guide wire  120  is typically done using fluoroscopy to ensure proper placement of guide wire  120 . Reamer  10 , with an appropriate cutter (such as reamer head  20  or  20 ′) attached and coupled with drive shaft  100 , is then placed over guide wire  120  so that guide wire  120  passes completely through aspiration tube  13  and provides a track which reamer  10  follows as it reams canal  122 . Preferably, reamer  10  coupled with drive shaft  100 , has been connected to a driving means prior to insertion into medullary canal  122 . Thus, guide wire  120  actually passes through cannulation  110  of drive shaft  102  and cannulation  22  of reamer head  20 . 
     While reaming medullary canal  122 , irrigation and aspiration are applied simultaneously. The irrigation substantially cools reamer head  20 , medullary canal  122 , and bone  124 . A preferable irrigation source, which delivers the irrigation fluid at a sufficient rate and pressure, is a normal saline bag suspended one meter above irrigation port  15 . It should also be noted that, in addition to a saline bag, any biological compatible solution and delivery system can be used as the irrigation source. The irrigation fluid passes from the irrigation source into irrigation port  15  and enters irrigation chamber  35 . The irrigation fluid, traveling along the path indicated by arrows I, flows through cannulation  110  in the space between the inner wall of cannulation and guide wire  120  and out of reamer head  20 . 
     The aspiration alleviates intramedullary pressure and helps to remove emulsified material from reamer head  20 . The removal of material not only improves reaming, but also provides for the possibility of harvesting the emulsified material for grafting purposes. Suction created by an aspiration source travels along the path indicated by arrows A. Specifically, the irrigation fluid helps to channel the emulsified material generated by reamer head  20  through flutes  43  and into the space between the outer wall of drive shaft  102  and the inner wall of aspiration tube  13  to transport the emulsified material from reamer head  20  through head retainer  14 , aspiration tube  13 , and aspiration port  16  and into a suitable container. 
     A significant advantage of the system that includes reamer  10 ,  210 , reamer head  20 , and drive shaft assembly  100  is the ability to ream the medullary canal to the desired diameter in one pass, i.e. without the need to use multiple reaming heads of gradually increasing diameter until the desired reamed size is achieved. In this regard, supplying irrigation to reamer head  20  while simultaneously providing aspiration, and using a reamer head with an efficient front cutting geometry (an optionally a side cutting geometry) produces less pressure and heat than prior art reaming devices. 
     FIG. 12 shows an exemplary sample of a graph expressing a pressure-time curve of the system according to the present invention in an animal model. Region I shows that no increase in pressure is induced when an access opening to the medullary canal is made. The increase in pressure in Region II results from standard techniques to gain access to the medullary canal. Region III shows that no increase in pressure is induced when the guide wire is inserted. As opposed to standard reaming process, the present invention reduces or eliminates intramedullary pressure. Specifically, the combined reaming, irrigating and aspirating functions to decrease intramedullary pressure below 100 mm Hg. In fact, as shown in Region IV, a negative intramedullary pressure is achieved with the system according to the present invention. Because the biologic threshold in the medullary canal for fat emboli and pulmonary emboli is known to be greater than or equal to 200 mm Hg, the incidence of fat and pulmonary emboli is reduced. Additionally, heat necrosis of the cortex is also eliminated due to the cooling caused by the flow of fluid during the process. 
     FIG. 12 shows another important advantage of the system according to the present invention. Specifically, the medullary canal reaming (Region IV) requires approximately 50 seconds. In contrast, conventional reaming in the same animal model requires approximately 500 seconds. This decrease in reaming time by a factor of ten means that reaming in clinical situations can be reduced from 30 minutes to 3 minutes. Thus, operating times (and costs) can be significantly reduced without any increased risks. 
     While various descriptions of the present invention are described above, it should be understood that the various features can be used singly or in any combination thereof. Therefore, this invention is not to be limited to only the specifically preferred embodiments depicted herein. 
     Further, it should be understood that variations and modifications within the spirit and scope of the invention may occur to those skilled in the art to which the invention pertains. Accordingly, all expedient modifications readily attainable by one versed in the art from the disclosure set forth herein that are within the scope and spirit of the present invention are to be included as further embodiments of the present invention. The scope of the present invention is accordingly defined as set forth in the appended claims.