Abstract:
An orthopedic cutting block for use in shaping a bone. The cutting block having at least two components, one of which is made of a polymeric material. The cutting block allowing for precise and accurate cuts to be made, while being inexpensive to manufacture and disposable after a single use.

Description:
FIELD OF THE INVENTION 
   The present invention relates to orthopedic cutting blocks for use in shaping a bone and, more particularly, to an orthopedic cutting block that has been designed to permit low-cost manufacturing methods while still maintaining the required accuracy of the cuts. 
   BACKGROUND OF THE INVENTION 
   Many surgical operations call for the precise and accurate cuts of bone material. Generally, these cuts, or resections, are made using surgical saws or milling devices. These instruments, while excellent at cutting the bone material, typically require cutting guides in surgical procedures calling for accurate cuts. For example, a surgeon performing a total knee arthroplasty must make several cuts on the distal end of the femur to properly fit a prosthetic femoral component. If these resections are incorrectly made, the surgery can result in failure and require further corrective procedures. 
   For this and other reasons, surgeons often employ the use of surgical cutting blocks, known also as cutting guides. These blocks aid in guiding the cutting device during the cutting of the bone material. A specific type of cutting block is one used to create four cuts on an already resected distal portion of the femur as part of a total knee replacement. These four cuts are the anterior and posterior cuts and the anterior and posterior chamfer cuts. Examples of these femoral cutting blocks are shown in U.S. Pat. No. 5,454,816 to Ashby, U.S. Pat. No. 6,258,095 to Lombardo et al., and U.S. Pat. No. 6,558,391 to Axelson, Jr. et al. 
   While cutting blocks such as those described above are useful in performing the various cuts on a bone, they have their drawbacks. Most importantly, the manufacturing costs associated with such blocks are often quite high. A standard block is typically constructed of metallic material machined from a solid block or from several solid metal pieces and assembled to allow for the various cuts to be performed. The high costs require these expensive cutting blocks to be utilized in multiple surgeries. This re-use requires the cleaning and sterilization of such a block before each use, which adds additional cost. Furthermore, multiple uses of a cutting block allows for greater chance of misaligning a cutting tool, such as a flat oscillating saw blade, due to wear of the cutting guide surfaces. Hence, a disposable single use cutting block would be advantageous. Therefore, there is a need for a cutting block that can be inexpensively manufactured, while maintaining the required precise and accurate dimensions needed for making cuts. 
   SUMMARY OF THE INVENTION 
   A first aspect of the present invention is a bone cutting block comprising a polymeric first body portion having at least one aperture extending therethrough for receiving a bone cutting tool and a non-polymeric second body portion having a cutting tool guide surface thereon, the second body portion coupled to the first body portion with the cutting tool guide surface thereon in communication with the aperture. 
   In some embodiments, the first body portion has a first external surface for facing a bone and second external surface for facing away from the bone with the second body portion coupled to one of the first or second surfaces. In other embodiments, the bone cutting block further comprises a non-polymeric third body portion coupled to the other of the external surfaces. In other embodiments, one of the first, second, or third body portions further comprises means for attaching to a bone surface. In other embodiments, the means for attaching to bone surface are pins. In certain embodiments, the third body portion has a cutting tool guide surface thereon in communication with the aperture of the first body portion and the cutting tool guide surface of the second body portion. In any of these embodiments, the second and third portion may be made of metal. In some embodiments, the first body portion further comprises four apertures and the second and third body portion further comprise four cutting tool guide surfaces respectively, groups of the apertures and the cutting tool guide surfaces in communication with one another to form four passages. The cutting tool guide surfaces of this embodiment may be slots. 
   Another embodiment of the present invention is an orthopedic cutting block for performing four cuts on the resected distal end of the femur. This block comprises a base portion having a first side, a second side, and three slots extending from the first side to the second side, a first guide portion having four slots extending through the first guide portion, and a second guide portion having four passages extending through the second guide portion. In this embodiment, the first guide portion is attached to the first side of the base portion, the second guide portion is attached to the second side of the base portion, and the three passages of the base portion, the slot on the first guide portion and the second guide portion align to form four passages extending through the cutting block. In this embodiment, the base portion may be made of polymer material and the first and second guide portions may be made of metal. Finally, the embodiment may further include means for attaching the cutting block to a bone surface, such as pins. 
   Another aspect of the present invention is a method for forming an orthopedic cutting block for guiding bone saws. This method comprising injection molding a polymeric body having passageways therein, placing first and second metal plates on respective first and second sides of the polymeric body, the plates having saw guides thereon, the placement including aligning the guides with the passageways, and coupling the first and second plates with the body therebetween. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be better understood on reading the following detailed description of non-limiting embodiments thereof, and on examining the accompanying drawings, in which: 
       FIG. 1  is a perspective view of the apparatus according to an embodiment of the present invention for use in resecting a distal femur in its fully constructed form with a saw blade extending through a passage; 
       FIG. 2  is an exploded perspective view of the apparatus according to an embodiment of the present invention showing outer metal plates and a molded plastic body; 
       FIG. 3  is a cross-sectional view of the apparatus according to an embodiment of the present invention as shown in  FIG. 1 ; 
       FIG. 4  is a perspective view of a base portion according to an embodiment of the present invention; 
       FIG. 5  is a perspective view of a first guide portion according to an embodiment of the present invention, where the guide portion is flipped 180° from that shown in  FIGS. 1 and 2 ; and 
       FIG. 6  is a perspective view of a second guide portion according to an embodiment of the present invention. 
   

   DETAILED DESCRIPTION 
   In describing the preferred embodiments of the subject matter illustrated and to be described with respect to the drawings, specific terminology will be resorted to for the sake of clarity. However, the invention is not intended to be limited to the specific term so selected, and is to be understood that each specific term includes all technical equivalence which operate in a similar manner to accomplish a similar purpose. 
   As used herein, the term “distal” means more distant from the heart and the term “proximal” means closest to the heart. The term “inferior” means toward the feet and the term “superior” means towards the head. The term “anterior” means towards the front part of the body or the face and the term “posterior” means towards the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. 
   Referring to the drawings, wherein like reference numerals represent like elements, there is shown in  FIGS. 1-6 , in accordance with embodiments of the present invention, a cutting guide, or cutting block, designated generally by reference numeral  10 . In the preferred embodiment, cutting block  10  is designed to be used in resecting a distal femur and includes a base or first body portion  12 , a first guide or second body portion  14 , and a second guide or third body portion  16 . The preferred embodiment of the present invention is a cutting block  10  used to make four cuts on the distal end of the femur, during a total knee arthroplasty, the anterior and posterior cuts and the anterior and posterior chamfer cuts subsequent to the distal cut being made. However, it should be noted that cutting block  10  could also have broad utility during any orthopedic procedure where a guide for a cutting instrument is required. For example, a cutting block using the technology used in cutting block  10  can be used during tibial preparation of a total knee arthroplasty. Cutting block  10  is shown in the figures along with oscillating saw blade  18 . Saw blade  18  is used to perform the cutting, or resecting, of the bone surface. It should be noted that other devices for cutting, as known in the art, can also be utilized, such as reciprocating saws or milling cutters. 
   The base portion  12 , as best shown in  FIG. 4 , is made of a polymeric material. In the preferred embodiment, the base portion is manufactured by an injection molding process from commercially available Ultem® polymer. However, it should be noted that other materials can be utilized. For example, it is contemplated that polypropylene or polycarbonate can also be used to manufacture base portion  12 . Preferably, the material should be one that is easy to utilize in manufacturing the base portion  12 , while also being relatively inexpensive. 
   In the preferred embodiment, base portion  12  is rectangularly shaped having rectangular faces  13  and an opposite face (not shown) and passages  20   a ,  23 , and  26   a  extending therethrough. However, in other embodiments, base portion  12  can be other shapes and can include any number of passages therethrough. For example, a base portion  12  including only one passage can be utilized in preparing the proximal end of the tibia during a total knee arthroplasty. In the preferred embodiment, passages  20   a ,  23 , and  26   a  extend in the direction of axis or plane  38  (as best shown in  FIG. 3 ). However, passage  23  includes walls  25  and  29   a  which extend in a direction along axis or plane  40  and walls  25   b  and  29   b  which extend in a direction along axis of plane  42  (also best shown in  FIG. 3 ). In use, axes  38 ,  40 , and  42  determine the angle of the planar cuts to be made on the bone surface. As such, the angles of axes  38 ,  40 , and  42  can vary depending upon the particular implant to be placed on the bone or the type of surgery being performed. Furthermore, the location of passages  20   a ,  23 , and  26   a , in the anterior-posterior direction, on base portion  12  will determine the location of the cuts actually made on the bone surface. In the preferred embodiment, passages  20   a ,  23 , and  26   a  allow a surgeon to make the typical four cuts on the distal end of the femur, during a total knee arthroplasty. 
   In a preferred embodiment, saw blade  18  does not contact the various surfaces of base portion  12 . Rather, base portion  12  provides the aforementioned passages to allow saw blade  18  to traverse through base portion  12 , while working in conjunction with guide portions  14  and  16 . As shall be discussed herein, guide portions  14  and  16  provide the support needed to operate saw blade  18 . In essence, in the preferred embodiment, base portion  12  is a skeleton that provides spacing and further support to rigid guide portions  14  and  16 . However, it is contemplated that base portion  12  can be designed so as to support a cutting tool during resection of the bone surface. 
   The construction of base or spacer portion  12  does not require a solid piece of polymeric material to be utilized, although such could be utilized. In the preferred embodiment, as best shown in  FIG. 4 , the molded polymeric base portion  12  has walls  100 ,  102 ,  104 ,  106  around the four sides thereof with bosses  108  molded at the corners thereof. Preferably bosses  108  are threaded after molding. A stiffening rib  110  may be molded on each wall extending from a central portion of each wall generally perpendicular thereto. Flat plate portions  112 ,  114  are molded adjacent surfaces  100  and  104  and spaced therefrom to provide space for a saw blade  18  to traverse the spacer portion  12 . Plate portion  112 ,  114  may include integrally molded stiffening ribs  116  for rigidity. Two centrally located walls  118 ,  120  extend inwardly towards the center of base portion  12 . Walls  118 ,  120  are stiffened by a series of ribs  122  which are preferably spaced at regular intervals along each wall forming compartments  124  therebetween. Walls  118  and  120  are spaced at the center of base portion  12  to allow the saw blade to make the chamfer cuts. Preferably the ends of ribs  122  adjacent this central area are tapered inwardly to provide clearance for the saw blade. The taper may be equal to the 45° angle of the champfer cuts. In the preferred embodiment, walls  102  and  106  include integrally molded extensions  52  for receiving optional handles as will be discussed below. Also bone pin holes  126  are preferably molded in each side  102  and  106  to allow for a pair of pins to penetrate base portion  12 . Besides making the cutting block lighter, this type of design allows for the further reduction of expenses associated with the construction of base portion  14  and the overall expense of cutting block  10 . Such a molding results in less polymeric material being required in the manufacture of base portion  12 . However, the design allows base portion  12  to remain rigid enough to provide the proper support required in use of cutting block  10 . It is contemplated that the dimensions of base portion  12  can vary. Depending upon the type of cutting tool used, the type or size of implant to be installed, the type or size of bone to be resected, or the dimensions of the other elements of cutting block  10 , the dimensions of base portion  12  may vary accordingly. For example, base portion  12  can decrease in size with the increase in size of the other elements of cutting block  10  or can increase in size along with an overall increase in size of cutting block  10  for resecting a larger bone. 
   First guide portion  14  is best shown in  FIG. 5 . Typically guide portion  14  is constructed of a metal, but can be constructed of any material suitable for properly supporting and guiding saw blade  18 . For example, in the preferred embodiment, first guide portion  14  is a plate 0.080 inches thick and constructed of 316 stainless steel (commonly used in medical instruments), but in another embodiment, first guide portion  14  can be constructed of other suitable material. Preferably, the material should be one that produces low friction and wear and can support a saw blade, as well as being relatively inexpensive. Such a stainless steel plate can easily be stamped in large quantities which reduces the cost of manufacturing. However, it is noted that stamping is only one method of manufacturing guide portion  14 . Depending upon the thickness of guide portion  14 , other methods of manufacturing might be required. 
   In the preferred embodiment, first guide portion  14  includes passages  20   b ,  22   b ,  24   b , and  26   b  extending therethrough (best shown in  FIG. 5 ). While passages  20   b  and  26   b  extend in a generally perpendicular direction with respect to the face of first guide portion  14  (i.e. in the direction of axis  38 ), passages  22   b  and  24   b  extend at an angle typically of 45 degrees. However, this angle can vary depending upon the angle of chamfer cuts required. First guide portion  14  also includes section  27   b  extending between passages  22   b  and  24   b . This section is essentially a triangular section extending from first guide portion  14 . Section  27   b  provides a support surface for saw blade  18  and guides one side of saw blade  18  along either the axis  40  or the axis  42 . 
   Second guide portion  16  is shown in  FIG. 6  and is similar to first guide portion  14 . In the preferred embodiment, the shape and dimensions of second guide portion  16  vary from that of first guide portion  14 , while the material utilized is the same. The variation in size and dimension is dictated by the location and angle of cuts to be made. However it is contemplated that other designs for second guide portion  16  can be utilized including a mirror image of first guide portion  14  in both shape and material. In the preferred embodiment, second guide portion  16  includes passages  20   c ,  22   c ,  24   c , and  26   c  extending therethrough (best shown in  FIG. 6 ). While passages  20   c  and  26   c  extend in a generally perpendicular direction with respect to the face of second guide portion  16  (i.e. in the direction of axis  38 ), passages  22   c  and  24   c  extend at an angle typically of 45 degrees. However, this angle can vary depending upon the angle of chamfer cuts required. Second guide portion  16  also includes section  27   c  extending between passages  22   c  and  24   c . This section is essentially a triangular section extending from second guide portion  16 . Section  27   c  provides a support for saw blade  18  and guides one side of saw blade  18  along either the axis  40  or the axis  42 . 
   Passages  20   c  and  26   c  of second guide portion  16  correspond to passages  20   a  and  26   a  of base portion  12  and passages  20   b  and  26   b  of first guide portion  14 . In operation, the aforementioned passages cooperate with one another so that corresponding passages (e.g.  20   a ,  20   b , and  20   c ) form one continuous passage (e.g.  20 ) through cutting block  10 . Furthermore, sections  27   b  and  27   c  allow for passages  22   b  and  24   b  and  22   c  and  24   c , respectively, to correspond with passage  23 , thereby forming continuous passage  22  along axis  40  and continuous passage  24  along axis  42 . It should be noted that other embodiments are envisioned. For example, passage  23  in base portion  12  could be replaced with two separate passages extending along axes  40  and  42  respectively. In this alternate embodiment, first guide portion  14  would not include section  27   b  and second guide portion  16  would not include section  27   c.    
   In the preferred embodiment, a fully constructed cutting block  10  (as best shown in  FIG. 1 ) includes first guide portion  14  and second guide portion  16  attached to the opposing faces  13  and  15  of base portion  12 . The mode of attachment of first guide portion  14  and second guide portion  16  to base portion  12  can be accomplished in any manner. For example, rivets, pins, screws, or adhesive, as well as many other means for attachment can be utilized. In the preferred embodiment, as shown in  FIG. 1 , screws  34  extend from first guide portion  14  through base portion  12 , and into threaded holes of second guide portion  16 . In this mode, base portion  12 , first guide portion  14  and second guide portion  16  include extended portions  35  for facilitating connection. However, it is contemplated that other configurations can also be utilized. For example, base portion  12  may include bosses or extensions that insert into guide portions  14  and  16  and retain them in contact with base portion  12 . In another embodiment, first and second guide portions  14  and  16  can be molded into the polymer of base portion  12 . Finally, base portion  12  may be designed so that guide portions  14  and  16  snap into place. It is also noted that cutting block  10  may include any variation of the elements discussed above. 
   In the preferred embodiment, the fully constructed cutting block includes four passages  20 ,  22 ,  24 , and  26  extending therethrough. Each of these passages corresponds to a different cut on the distal end of the femur, matching an implant surface. It is contemplated that cutting block  10  can include any number of passages that correspond to any required cut on any bone surface. For example, cutting block  10  can include only two passages for making only two of the aforementioned four cuts on the distal end of the femur. In the preferred embodiment, the four passages  20 ,  22 ,  24 , and  26  extending through cutting block  10  include passages  20   a ,  23 , and  26   a  of base portion  12 ,  20   b ,  22   b ,  24   b , and  26   b  of first guide portion  14 , and  20   c ,  22   c ,  24   c , and  26   c  of second guide portion  16 . Perpendicular passages (i.e. passages  20  and  26 ) include like passages (e.g.  20   a ,  20   b , and  20   c ) which correspond with one another to form one continuous passage extending through cutting block  10  (e.g. passage  20 ), while angled passages (i.e.  22  and  24 ) include sections  27   b  and  27   c  which correspond with like passages (e.g. passages  22   b  and  22   c ) and passage  23  to form one continuous passage extending at an angle through cutting block  10  (e.g. passage  22 ). Each passage accommodates saw blade  18  and guides the same during the cutting of the bone surface. The first guide portion  14  and second guide portion  16  provide the support needed to guide saw blade  18 . It is recognized that the metallic composition of these portions allows for better support of the saw blade  18 . For this reason, as stated above, first guide portion  14  and second guide portion  16  are constructed from material that is as hard or harder than saw blade  18  and only allows movement within the aforementioned passages. 
   Cutting block  10  may also include elements for attaching to a bone surface. In the preferred embodiment, locating pins  28  (shown in  FIG. 1-3 ) allow for the fixation of cutting block  10  to the previously resected surface of the distal end of the femur. Locating pins  28  are attached to second guide portion  14  and during use extend therefrom into the bone surface. It is noted that locating pins  28  can either be fixably attached or removably attached to second guide portion  14 . In the preferred embodiment, second guide portion  16  includes flat sections  44  and  46  for mounting pins  28 . Flat sections  44  and  46  include apertures for receiving pins  28 . These apertures can be threaded for removable attachment of pins  28 . However, other modes of attachment are contemplated. It is also contemplated that locating pins  28  can be located on any part of cutting block  10 , with or without flat sections  44  and  46 . Furthermore, locating pins  28  are only one example of a way of attaching cutting block  10  to a bone surface. Another way for attaching the cutting block  10  to a bone surface is by using bone pins  32  extending through holes in cutting block  10  (shown in  FIGS. 1 and 2 ). Bone pins  32  can be aligned so as to contact the bone surface at an angle from cutting block  10 . When bone pins  32  are used, metal bushings  50  (shown in  FIG. 2 ) can be inserted into polymeric portion  12  to provide better support. Additionally, an external support system can be employed to fix cutting block  10  with respect to the bone surface to be resected. 
   The width of cutting block  10  in the medial-lateral direction of the femur and the height of the cutting block  10  in the anterior-posterior direction of the femur are chosen based on the size of the distal femur being resurfaced and the femoral implant being used. Thus, various sized cutting blocks  10  may be utilized. Cutting block  10  may be aligned on the distal femur in any well known manner, such as by using an intramedulary or extramedulary alignment systems or by computer assisted navigation. 
   As depicted in  FIGS. 1 and 2 , the preferred cutting block  10  of one embodiment of present invention includes handles  30 . Handles  30  are preferably detachable from cutting block  10 , such as by being threaded. It is also contemplated that base portion  12  can include extensions  52  for more easily attaching handles  30 . As is known, handles  30  aid in the aligning and fixing of cutting block  10  with respect to the bone surface to be resected. In use, a surgeon grasps handles  30  and guides cutting block  10  into place. Thereafter, cutting block  10  is fixed using any of the means for attaching to a bone surface described above. 
   Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.