Patent Publication Number: US-11653933-B2

Title: Method of designing and manufacturing low-profile customized patient-specific orthopaedic surgical instruments

Description:
This application is a continuation of and claims priority to U.S. patent application Ser. No. 15/878,717, filed Jan. 24, 2018, now U.S. Pat. No. 10,716,581, the entirety of which is expressly incorporated herein by reference. 
    
    
     CROSS-REFERENCE 
     Cross-reference is made to U.S. patent application Ser. No. 15/878,715, entitled “LOW-PROFILE CUSTOMIZED PATIENT-SPECIFIC ORTHOPAEDIC SURGICAL INSTRUMENTS,” filed Jan. 24, 2018, now U.S. Pat. No. 10,537,343, and to U.S. patent application Ser. No. 15/878,710, entitled “CUSTOMIZED PATIENT-SPECIFIC ANTERIOR-POSTERIOR CHAMFER BLOCK AND METHOD,” filed Jan. 24, 2018, now U.S. Pat. No. 10,631,878, which are expressly incorporated herein by reference. 
     TECHNICAL FIELD 
     The present disclosure relates generally to orthopaedic surgical instruments and, more particularly, to customized patient-specific orthopaedic surgical instruments. 
     BACKGROUND 
     Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged natural joint is replaced by a prosthetic joint. For example, in a total knee arthroplasty surgical procedure, a patient&#39;s natural knee joint is partially or totally replaced by a prosthetic knee joint or knee prosthesis. A typical knee prosthesis includes a tibial tray, a femoral component, and a polymer insert or bearing positioned between the tibial tray and the femoral component. In a hip replacement surgical procedure, a patient&#39;s natural acetabulum is replaced by a prosthetic cup and a patient&#39;s natural femoral head is partially or totally replaced by a prosthetic stem and femoral ball. 
     To facilitate the replacement of the natural joint with a prosthesis, orthopaedic surgeons use a variety of orthopaedic surgical instruments such as, for example, cutting blocks, drill guides, milling guides, and other surgical instruments. Typically, the orthopaedic surgical instruments are reusable and generic with respect to the patient such that the same orthopaedic surgical instrument may be used on a number of different patients during similar orthopaedic surgical procedures. 
     The orthopaedic surgical instruments may also be customized to a specific patient. Such “customized patient-specific orthopaedic surgical instruments” are single-use surgical tools for use by a surgeon in performing an orthopaedic surgical procedure that is intended, and configured, for use on a particular patient. It should be appreciated that these instruments are distinct from standard, non-patient specific orthopaedic surgical instruments that are intended for use on a variety of different patients. These customized patient-specific orthopaedic surgical instruments are distinct from orthopaedic prostheses, whether patient-specific or generic, which are surgically implanted in the body of the patient. Rather, customized patient-specific orthopaedic surgical instruments are used by an orthopaedic surgeon to assist in the implantation of orthopaedic prostheses. 
     SUMMARY 
     According to one aspect of the disclosure, a method of manufacturing a customized patient-specific orthopaedic surgical instrument is disclosed. The method comprises generating a three-dimensional model of a patient&#39;s bone based on patient-specific data, identifying a first region of the three-dimensional model of the patient&#39;s bone, defining an outer boundary of a customized patient-specific surgical instrument on the three-dimensional model of the patient&#39;s bone, generating a customized patient-specific surgical instrument model within the outer boundary, the customized patient-specific surgical instrument model comprising a bone-facing surface including a customized patient-specific negative contour that receives a corresponding positive contour of the patient&#39;s bone, and fabricating the customized patient-specific orthopaedic surgical instrument from metallic material based on the customized patient-specific surgical instrument model. The step of generating the customized patient-specific surgical instrument model comprises defining a cavity in the bone-facing surface over the first region of the three-dimensional model of the patient&#39;s bone. The cavity has an outer edge that is aligned with or larger than the outer edge of the first region. The step of generating the customized patient-specific surgical instrument model also comprises generating an outer surface of the customized patient-specific surgical instrument opposite the bone-facing surface, extending a guide body outward from the outer surface of the customized patient-specific surgical instrument model to a free end, and defining a guide slot in the guide body, the guide slot being sized and shaped to guide a surgical tool into engagement with the patient&#39;s bone. 
     In some embodiments, method may also comprise identifying a planned resection plane on the three-dimensional model of the patient&#39;s bone based on the patient-specific data. The step of defining the guide slot through the guide body may include aligning the guide slot with the planned resection plane, and sizing and shaping the guide slot to guide the cutting saw blade along the planned resection plane into engagement with the patient&#39;s bone. 
     Additionally, in some embodiments, the step of sizing and shaping the guide slot includes defining the guide slot between a medial sidewall and a lateral sidewall of the guide body, and at least one of the medial sidewall and the lateral sidewall are angled relative to the other of the medial sidewall and the lateral sidewall. 
     In some embodiments, the guide slot may be a first guide slot, and generating the customized patient-specific surgical instrument model may further comprise extending a boss outward from the outer surface of the customized patient-specific surgical instrument model to a free end that is spaced apart from the free end of the guide body and defining a drill guide slot in the boss. In some embodiments, the step of extending the boss outward from the outer surface may include defining a tapered surface on a first side of the boss, and fabricating the customized patient-specific orthopaedic surgical instrument from metallic material includes layering metallic material in a fabrication machine such that the tapered surface faces downward in the fabrication machine. 
     In some embodiments, the step of generating the customized patient-specific surgical instrument model may further comprise defining a plurality of apertures that extend through the outer surface and the bone-facing surface. 
     In some embodiments, the step of generating the customized patient-specific surgical instrument model may further comprise defining a second plurality of apertures through the guide body of the customized patient-specific surgical instrument model. Additionally, in some embodiments, n each of the apertures may include a diamond-shaped opening. 
     In some embodiments, the step of extending the guide body outward from the outer surface of the customized patient-specific surgical instrument model to the free end may include defining a tapered surface on a first side of the guide body, and fabricating the customized patient-specific orthopaedic surgical instrument from metallic material may include layering metallic material in a fabrication machine such that the tapered surface faces downward in the fabrication machine. 
     In some embodiments, the step of fabricating the customized patient-specific orthopaedic surgical instrument from metallic material based on the customized patient-specific surgical instrument model may include forming the customized patient-specific orthopaedic surgical instrument as a single monolithic component. 
     In some embodiments, the single monolithic component may include a plurality of laminations of metallic material. 
     According to another aspect, a method of manufacturing a customized patient-specific orthopaedic surgical instrument comprises generating a three-dimensional model of a patient&#39;s bone based on patient-specific data, defining an outer boundary of a customized patient-specific surgical instrument on the three-dimensional model of the patient&#39;s bone, generating a customized patient-specific surgical instrument model within the outer boundary, the customized patient-specific surgical instrument model including a customized patient-specific bone facing surface, and fabricating the customized patient-specific orthopaedic surgical instrument from metallic material based on the customized patient-specific surgical instrument model. The step of generating the customized patient-specific surgical instrument model comprises generating an outer surface of the customized patient-specific surgical instrument opposite the bone-facing surface, extending a guide body outward from the outer surface of the customized patient-specific surgical instrument model to a free end, and defining a guide slot in the guide body. The guide slot may be sized and shaped to guide a surgical tool into engagement with the patient&#39;s bone. 
     In some embodiments, the method may include planning a resected surface of the patient&#39;s bone, and generating the customized patient-specific surgical instrument model may include shaping an outer edge of the bone-facing surface to match an outer edge of the planned resected surface of the patient&#39;s bone. 
     In some embodiments, the guide body may be a first guide body, and generating the customized patient-specific surgical instrument model further may comprise extending a second guide body outward from the outer surface of the customized patient-specific surgical instrument model to an end spaced apart from the free end of the first guide body, defining a second guide slot in the second guide body, the second guide slot being sized and shaped to guide a surgical tool into engagement with the patient&#39;s bone and extending transverse to the first guide slot. 
     In some embodiments, the step of generating the customized patient-specific surgical instrument model may further comprise extending a third guide body outward from the outer surface of the customized patient-specific surgical instrument model to a free end spaced apart from the first guide body, and defining a third guide slot the second guide slot being sized and shaped to guide a surgical tool into engagement with the patient&#39;s bone and intersecting the second cutting guide slot. 
     Additionally, in some embodiments, the second guide body may include a boss having a tapered outer surface, and the second guide slot may be a drill guide slot sized and shaped to guide a surgical drill into engagement with the patient&#39;s bone. 
     In some embodiments, the step of fabricating the customized patient-specific orthopaedic surgical instrument from metallic material based on the customized patient-specific surgical instrument model may include forming the customized patient-specific orthopaedic surgical instrument as a single monolithic component. 
     In some embodiments, the step of fabricating the customized patient-specific orthopaedic surgical instrument may include operating a three-dimensional metal printer to fabricate the customized patient-specific surgical instrument by forming laminations of metallic material. 
     According to another aspect, a method of designing a customized patient-specific orthopaedic surgical instrument comprises generating a three-dimensional model of a patient&#39;s bone based on patient-specific data, defining an outer boundary of a customized patient-specific surgical instrument on the three-dimensional model of the patient&#39;s bone, and generating a customized patient-specific surgical instrument model within the outer boundary. The customized patient-specific surgical instrument model includes a customized patient-specific bone facing surface. In some embodiments, generating the customized patient-specific surgical instrument model comprises generating an outer surface of the customized patient-specific surgical instrument opposite the bone-facing surface, extending a guide body outward from the outer surface of the customized patient-specific surgical instrument model to a free end, and defining a guide slot in the guide body, the guide slot being sized and shaped to guide a surgical tool into engagement with the patient&#39;s bone. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The detailed description particularly refers to the following figures, in which: 
         FIG.  1    is a perspective view of a customized patient-specific orthopaedic femoral cutting block; 
         FIG.  2    is a posterior side elevation view of the cutting block of  FIG.  1   ; 
         FIG.  3    is an anterior side elevation view of the cutting block of  FIG.  1   ; 
         FIG.  4    is a proximal plan view of the cutting block of  FIG.  1   ; 
         FIG.  5    is a distal plan view of the cutting block of  FIG.  1   ; 
         FIG.  6    is a side elevation view of the cutting block of  FIG.  1    shown positioned relative to a distal end of a patient&#39;s femur; 
         FIG.  7    is another side elevation view of the cutting block of  FIG.  1    shown positioned relative to the distal end of the patient&#39;s femur; 
         FIG.  8    is a cross-sectional elevation view taken along the line  8 - 8  in  FIG.  3   ; 
         FIG.  9    is a side elevation view of a guide pin body of the cutting block of  FIG.  1   ; 
         FIG.  10    is a distal plan view of the guide pin body of  FIG.  9   ; 
         FIGS.  11 A-B  illustrate a simplified flow diagram of a process of designing and fabricating the cutting block of  FIG.  1   ; 
         FIGS.  12 - 15    illustrate some of the steps of the process outlined in  FIGS.  11 A-B ; 
         FIG.  16    is a perspective view of a customized patient-specific orthopaedic tibial cutting block; 
         FIG.  17    is a posterior side elevation view of the cutting block of  FIG.  16   ; 
         FIG.  18    is an anterior side elevation view of the cutting block of  FIG.  16   ; 
         FIG.  19    is a distal plan view of the cutting block of  FIG.  16   ; 
         FIG.  20    is a proximal plan view of the cutting block of  FIG.  16   ; 
         FIG.  21    is a side elevation view of the cutting block of  FIG.  16   ; 
         FIG.  22    is another side elevation view of the cutting block of  FIG.  16   ; 
         FIG.  23    is a perspective view of a customized patient-specific orthopaedic femoral cutting guide; 
         FIG.  24    is a distal plan view of the femoral cutting guide of  FIG.  23   ; 
         FIG.  25    is a proximal plan view of the femoral cutting guide of  FIG.  23   ; 
         FIG.  26    is a side elevation view of the femoral cutting guide of  FIG.  23   ; 
         FIG.  27    is a cross-sectional elevation view taken along the line  27 - 27  and  FIG.  24   ; 
         FIG.  28    is a perspective view of the femoral cutting guide of  FIG.  23    aligned with a resected distal end of the patient&#39;s femur; 
         FIG.  29    is an elevation view showing that the femoral cutting guide of  FIG.  23    is sized and shaped to match the resected distal end of the patient&#39;s femur; 
         FIG.  30    is a perspective view of the femoral cutting guide of  FIG.  23    positioned on the resected distal end of the patient&#39;s femur; 
         FIGS.  31 - 37    are views of another embodiment of a customized patient-specific femoral cutting block; 
         FIG.  38    is a perspective view of another embodiment of a customized patient-specific femoral cutting block; 
         FIG.  39    of another embodiment of a customized patient-specific femoral cutting block; and 
         FIGS.  40 - 41    are perspective views of another embodiment of a customized patient-specific femoral cutting block. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     While the concepts of the present disclosure are susceptible to various modifications and alternative forms, specific exemplary embodiments thereof have been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the concepts of the present disclosure to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     References in the specification to “one embodiment”, “an embodiment”, “an example embodiment”, etc., indicate that the embodiment described may include a particular feature, structure, or characteristic, but every embodiment may not necessarily include the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to effect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. 
     Referring to  FIGS.  1 - 10   , a customized patient-specific orthopaedic surgical instrument  10  is shown. What is meant herein by the term “customized patient-specific orthopaedic surgical instrument” is a surgical tool for use by a surgeon in performing an orthopaedic surgical procedure that is intended, and configured, for use on a particular patient. As such, it should be appreciated that, as used herein, the term “customized patient-specific orthopaedic surgical instrument” is distinct from standard, non-patient specific orthopaedic surgical instruments (i.e., “patient-universal instruments” such as patient-universal cutting blocks) that are intended for use on a variety of different patients and were not fabricated or customized to any particular patient. Additionally, it should be appreciated that, as used herein, the term “customized patient-specific orthopaedic surgical instrument” is distinct from orthopaedic prostheses or implants, whether patient-specific or generic, which are surgically implanted in the body of the patient. Rather, an orthopaedic surgeon uses customized patient-specific orthopaedic surgical instruments to assist in the implantation of orthopaedic prostheses. Examples of “customized patient-specific orthopaedic surgical instruments” include customized patient-specific drill/pin guides, customized patient-specific tibial cutting blocks, customized patient-specific femoral cutting blocks, and customized patient-specific alignment guides. The surgical instrument  10  shown in  FIGS.  1 - 10    is one embodiment of a customized patient-specific femoral cutting block including a cutting guide slot  12  positioned to guide a customized, patient-specific resection of a distal end  14  of a patient&#39;s femur  16  (see  FIGS.  6 - 7   ) along a predetermined resection plane. As described in greater detail below, the femoral cutting block  10  is configured to be coupled to the patient&#39;s femur  16  in a unique pre-determined location and orientation. In the illustrative embodiment, the structure of the cutting block  10  has been contoured to reduce its size relative to conventional cutting blocks and avoid contact with undesirable regions of the patient&#39;s bone. 
     As shown in  FIG.  1   , the femoral cutting block  10  includes a base plate  20  and a number of surgical tool guide bodies  22  that are attached to, and extend outwardly from, the base plate  20 . In the illustrative embodiment, the femoral cutting block  10  is a single monolithic component formed from a metallic material such as, for example, stainless steel. In that way, the base plate  20  and the guide bodies  22  form a single monolithic metallic block. As described in greater detail below, the femoral cutting block  10  is formed by Direct Metal Laser Sintering (DMLS), also known as Selective Laser Sintering (SLS), which is a form of 3-D printing technology. In DMLS, the femoral cutting block  10  is formed in a layer-by-layer fashion using laser sintering in which light fuses metallic powder, forming the metallic structures that define the femoral cutting block  10 . It should be appreciated that other forms of 3-D printing technology such as, for example, optical fabrication, photo-solidification, or resin printing may be used to fabricate the femoral cutting block  10 . 
     The base plate  20  includes a pair of arms  24 ,  26  that are configured to engage the distal end  14  of the patient&#39;s femur  16 . The arms  24 ,  26  are spaced apart from each other such that a notch  28  is defined between the inner edges of the arms  24 ,  26 . The notch  28  is sized and shaped to correspond to the natural intercondylar notch  30  (see  FIG.  12   ) of the patient&#39;s femur  16 , which is defined between the natural condyles  32 ,  34  of the patient&#39;s femur. In that way, contact within bone surfaces with the natural intercondylar notch  30 , which may be difficult to model, is avoided. 
     As shown in  FIGS.  1 - 4   , each of the arms  24 ,  26  has a bone-contacting or bone-facing surface  36  that engages one of the natural condyles  32 ,  34 . In the illustrative embodiment, each bone-facing surface  36  includes a number of negative contours  38  that are configured to receive a portion of the natural condyles  32 ,  34 . As shown in, for example,  FIGS.  2 ,  4 , and  6 - 8   , each contour  38  has a unique set of ridges  40  and depressions  42  that are shaped to engage a corresponding unique set of depressions  44  and ridges  46  of the natural condyles  32 ,  34 . Each of the arms  24 ,  26  also includes an outer surface  48  that is positioned opposite its corresponding bone-facing surface  36 . In the illustrative embodiment, each outer surface  48  is substantially smooth. As used herein, the term “substantially” should be understood to refer to permit the normal tolerances created by manufacturing variation and other design criteria. As such, a “substantially smooth surface” is one that is smooth within the normal tolerances created or permitted by manufacturing variation and other design criteria. 
     As shown in  FIG.  1   , the base plate  20  also includes an anterior flange  50  that is configured to engage the distal end  14  of the patient&#39;s femur  16 . The anterior flange  50  includes a bone-facing surface  52  that includes a number of negative contours  54  that are configured to receive a portion of the patient&#39;s femur  16 . As shown in, for example,  FIGS.  2 ,  4 , and  8   , the contour  54  of the anterior flange  50  has a unique set of ridges  56  and depressions  58  that are shaped to engage a corresponding unique set of depressions  60  and ridges  62  of the patient&#39;s femur  16 . The anterior flange  50  also includes an outer surface  64  that is positioned opposite the bone-facing surface  52 . In the illustrative embodiment, the outer surface  64  is substantially smooth. 
     The negative contours  38 ,  54  of the base plate  20  permit the cutting block  10  (and hence the tool guide bodies) to be positioned on the patient&#39;s femur  16  in a unique pre-determined location and orientation. As shown in  FIGS.  4  and  6 - 8   , the bone-facing surface  52  includes a pair of curved posterior edges  66 ,  68  that define a portion of the contour  54  and are shaped to match a portion of the patient&#39;s femur. As a result, each of the edges  66 ,  68  includes convex and concave portions to receive corresponding concave and convex portions of the patient&#39;s femur. The edge  66  includes a posterior tip  69  that is sized and shaped to be positioned in the patient&#39;s natural trochlear groove  166 . 
     The base plate  20  also includes a number of customized cavities  70 , which are sized to be positioned over regions in the pre-determined location of the bone that may include a defect or are damaged or difficult to model. In that way, the cavities  70  are sized such that contact with those regions may be avoided so as to not interfere with positioning the cutting block  10  in the pre-determined location and orientation. In the illustrative embodiment, the notch  28  defined between the arms  24 ,  26  is one of the customized cavities. As shown in  FIGS.  1 - 3   , the customized cavities  70  also include an aperture  72  that extends through the bone-facing surface  52  of the anterior flange  50 . As shown in  FIG.  2   , the customized cavities  70  also include a pair of channels  74 ,  76  that are defined in the bone-facing surface  52  of the anterior flange  50 . In the illustrative embodiment, each channel  74 ,  76  extends from an end  78  that opens into the aperture  72  to an open end  80  that is defined in the outer edge of the anterior flange  50 . 
     In the illustrative embodiment, the base plate  20  of the cutting block  10  has a low-profile to reduce the size of the incision and reduce the amount of bone displacement needed to position the cutting block  10 . The low-profile has been customized for block  10  by minimizing the thicknesses of the arms  24 ,  26  and the anterior flange  50 . As shown in  FIG.  3   , a thickness  82  is defined between the outer surface  48  and the bone-facing surface  36  of each arm. To minimize the thickness  82 , the outer surface  48  of each arm is convexly curved to follow the concave curvature of the bone-facing surface  36 . Similarly, as shown in  FIG.  4   , a thickness  84  is defined between the outer surface  64  and the bone-facing surface  52  of the anterior flange  50 , and the outer surface  64  of the flange  50  is shaped to follow the geometry of the bone-facing surface  52  to minimize the thickness  84 . 
     As shown in  FIGS.  1 - 8   , each of the surgical tool guide bodies  22  of the cutting block  10  is attached to and extends outwardly from the outer surfaces  48 ,  64  of the arms  24 ,  26  and the anterior flange  50  to a free end  90  that is spaced apart from the base plate  20 . In the illustrative embodiment, the guide bodies  22  include an anterior guide body  100  that extends anteriorly from the anterior ends of the arms  24 ,  26  and the anterior flange  50  to its free end  102 . The anterior guide body  100  includes a distal flange  104  and a pair of bosses  106 ,  108  that extend proximally from the flange  104 . As shown in  FIG.  1   , the aperture  72  defined in the base plate  20  is positioned proximal of the distal flange  104  and between the bosses  106 ,  108 . 
     The distal flange  104  of the anterior guide body  100  includes an elongated opening  110  that is defined in the free end  102  and a number of inner walls  112  that extend inwardly from the opening  110 . As shown in  FIG.  2   , the inner walls  112  extend to another opening  114  that is defined in the bone-facing surface  52 . As shown in  FIGS.  4  and  6 - 8   , the opening  114  extends through the contour  54  of the base plate  20  such that the opening  114  is defined by edges  66 ,  68  of the bone-facing surface  52 , which follow a curved, irregular path that matches the shape of the patient&#39;s femur  16  in that region. The opening  114  cooperates with the inner walls  112  and the elongated opening  110  to define the guide slot  12 , which is sized and shaped to guide a surgical tool such as, for example, a cutting blade, into engagement with the patient&#39;s bone. As described above, the cutting guide slot  12  is positioned to guide a customized, patient-specific resection of a distal end  14  of a patient&#39;s femur  16 . Because the edge  66  follows the shape of the patient&#39;s femur and the posterior tip of the edge  66  extends into the patient&#39;s trochlear groove, the cutting guide slot  12  provides support for the cutting blade in close proximity to the region under resection. 
     As shown in  FIG.  1   , each of the bosses  106 ,  108  extend from a proximal surface  116  of the distal flange  104  to a curved proximal end  118 . It should be appreciated that in other embodiments one or both of the bosses  106 ,  108  may be spaced apart from the distal flange  104 , thereby forming separate guide bodies. An opening  120  is defined in the free end  102  of each of the bosses  106 ,  108  adjacent to the proximal end  118 . An inner wall  122  extends inwardly from the opening  120 . As shown in  FIG.  2   , each inner wall  122  extends to another opening  124  that opens into one of the channels  74 ,  76  to define a guide slot  126  extending through the cutting block  10 . In the illustrative embodiment, each guide slot  126  is a drill guide and fixation pin guide hole, which is sized and shaped to guide a surgical drill to prepare the patient&#39;s bone to receive a fixation pin to couple to the block  10  to the bone. 
     Referring now to  FIGS.  9 - 10   , the guide bodies  22  include a pair of posterior guide bosses  140 , which are attached to, and extend distally from, the outer surfaces  48  of the arms  24 ,  26 , respectively. Each posterior guide boss  140  includes a guide slot  142  that is sized and shaped to guide surgical drill and a fixation pin into engagement with the patient&#39;s bone to couple to the block  10  to the bone. Each guide boss  140  includes a post  144  that extends from a base  146  attached to the outer surface  48  of one of the arms  24 ,  26  to a free end  148  that is spaced apart from the outer surface  48 . 
     As shown in  FIGS.  9  and  10   , the base  146  is wider in the anterior-posterior direction than the free end  148 . Each post  144  also includes a convex curved posterior surface  150  that extends substantially orthogonal to the arm outer surface  48 . In the illustrative embodiment, each post  144  also includes a curved tapered anterior surface  152  that extends obliquely relative to the arm outer surface  48 . The curved tapered anterior surface  152  improves the manufacturability of the cutting block  10  by eliminating a flat, horizontal surface, which, during fabrication, would face downward and require a support structure. 
     Returning to  FIG.  8   , an opening  154  is defined in the free end  148  of each boss  140 . An inner wall  156  extends inwardly from the opening  154  to another opening  158  that is defined in a bone-facing surface  36  of one of the arms  24 ,  26 . The openings  154 ,  158  and inner wall  156  cooperate to define the guide slot  142 . As described above, each guide slot  142  is a drill guide and fixation pin guide hole, which is sized and shaped to guide a surgical drill or self-drilling fixation pin to prepare the patient&#39;s bone to receive a fixation pin to couple to the block  10  to the bone. 
     As shown in  FIG.  8   , the inner walls  112 ,  122 ,  156  define a number of relief sections  160 ,  162 ,  164  in the guide slots  12 ,  126 ,  142 , respectively, of the cutting block  10 . Each of the relief sections  160 ,  162 ,  164  is larger (e.g., wider) than the rest of the guide slots  12 ,  126 ,  142  to improve manufacturability. 
     Referring now to  FIGS.  11 A-B , a routine  200  for fabricating the customized patient-specific orthopaedic surgical instrument  10  is illustrated. The method  200  includes process steps  212  and  214 , in which an orthopaedic surgeon performs pre-operative planning of the orthopaedic surgical procedure to be performed on a patient. The process steps  212  and  214  may be performed in any order or contemporaneously with each other. In process step  212 , a number of medical images of the relevant portions of a patient&#39;s bone are generated. For example, for a knee replacement surgery, the medical images may include images of the distal end of a patient&#39;s femur and the proximal end of a patient&#39;s tibia. For a hip replacement surgery, the medical images may include images of the patient&#39;s acetabulum and surrounding bony anatomy, as well as images of the proximal end of the patient&#39;s femur. To do so, the orthopaedic surgeon or other healthcare provider may operate an imaging system to generate the medical images. The medical images may be embodied as any number and type of medical images capable of being used to generate a three-dimensional rendered model of the patient&#39;s acetabulum and surrounding bony anatomy. For example, the medical images may be embodied as any number of computed tomography (CT) images, magnetic resonance imaging (MRI) images, or other three-dimensional medical images. Additionally, or alternatively, as discussed in more detail below in regard to process step  216 , the medical images may be embodied as a number of X-ray images or other two-dimensional images from which a three-dimensional rendered model of the relevant area of the patient&#39;s bone. 
     In process step  214 , the orthopaedic surgeon may determine any additional pre-operative constraint data. The constraint data may be based on the orthopaedic surgeon&#39;s preferences, preferences of the patient, anatomical aspects of the patient, guidelines established by the healthcare facility, or the like. For example, in a knee replacement surgery, the constraint data may include the type and size of the knee prosthesis, the amount of distal and posterior resections to be performed on the patient&#39;s femur and so forth. In a hip replacement surgery, the constraint data may include the orthopaedic surgeon&#39;s preference for the amount of inclination and version for an acetabular prosthesis, the amount of the bone to ream, the size range of the orthopaedic implant, and/or the like. In some embodiments, the orthopaedic surgeon&#39;s preferences are saved as a surgeon&#39;s profile, which may be used as a default constraint values for further surgical plans. 
     The medical images and the constraint data, if any, may be transmitted or otherwise provided to an orthopaedic surgical instrument vendor or manufacturer for processing the images. The orthopaedic surgical instrument vendor or manufacturer processes the medical images in step  216  to facilitate the determination of the proper resection planes, instrument location, implant sizing, and fabrication of the customized patient-specific orthopaedic surgical instrument as discussed in more detail below. The images may also be processed on-site at the hospital, for example, or the surgeon&#39;s offices. 
     In process step  218 , three-dimensional images may be converted or otherwise generated from the medical images. For example, in embodiments wherein the medical images are embodied as a number of two-dimensional images, the vendor may use a suitable computer algorithm to generate one or more three-dimensional images form the number of two-dimensional images. Additionally, in some embodiments, the medical images may be generated based on an established standard such as the Digital Imaging and Communications in Medicine (DICOM) standard. In such embodiments, an edge-detection, thresholding, watershed, or shape-matching algorithm may be used to convert or reconstruct images to a format acceptable in a computer aided design application or other image processing application. 
     In process step  220 , the medical images, and/or the converted/reconstructed images from process step  218  may be processed, to determine a number of aspects related to the bony anatomy of the patient such as the anatomical axis of the patient&#39;s bones, the mechanical axis of the patient&#39;s bone, other axes and various landmarks, and/or other aspects of the patient&#39;s bony anatomy. Any suitable algorithm may be used to process the images. In some embodiments, a three-dimensional model of the patient&#39;s bone including a three-dimensional rendering of the bone may be generated from the processed images. One such three-dimensional bone model is the femoral bone model  170  is shown in  FIGS.  12 - 15   , which are referenced below. 
     In process step  222 , a surgeon, vendor, or other user may identify one or more problematic regions of the bone to avoid using the three-dimensional model. Such regions may include osteophytes, damaged regions of the bone, undercuts that would cause the instrument to get stuck on the bone, or other regions that are known to be difficult to model based on the medical images. One such region may include a portion of the patient&#39;s trochlear groove. As shown in  FIG.  12   , the user may outline an outer edge  172  of one such region  174  on the distal end  14  of a patient&#39;s femur  16  using the femoral bone model  170 . The user may also create a raised or offset surface  176  within the outer edge  172  to define a desired location of a cavity  70  of the orthopaedic surgical instrument. 
     The routine  200  may advance to process step  224  in which an outer boundary  178  of the patient-specific orthopaedic surgical instrument is defined on the femoral bone model  170 . As shown in  FIG.  13   , the outer boundary  178  defines the outer edge of the planned surgical instrument, which may be, for example, the femoral cutting block  10  described above. The boundary  178  identifies the locations and shapes of the arms  24 ,  26  as well as the location and shape of the anterior flange  50  of the base plate  20  of the cutting block  10 . 
     In process step  226 , a model of the customized patient-specific orthopaedic surgical instrument is generated. In some embodiments, the model is embodied as a three-dimensional rendering of the customized patient-specific orthopaedic surgical instrument. In other embodiments, the model may be embodied as a mock-up or fast prototype of the customized patient-specific orthopaedic surgical instrument. The patient-specific orthopaedic surgical instrument to be modeled and fabricated may be determined based on the orthopaedic surgical procedure to be performed, the constraint data, and/or the type of orthopaedic prosthesis to be implanted in the patient. 
     The particular shape of the customized patient-specific orthopaedic surgical instrument is determined based on the planned location and implantation angles of the orthopaedic prosthesis relative to the patient&#39;s bone. Additionally, the planned location of the orthopaedic surgical instrument may be based on the identified landmarks of the patient&#39;s bone identified in process step  220 . 
     In some embodiments, the particular shape or configuration of the customized patient-specific orthopaedic surgical instrument may be determined based on the planned location of the instrument relative to the patient&#39;s bony anatomy. That is, the customized patient-specific orthopaedic surgical instrument may include a bone-facing surface having a negative contour that matches the corresponding contour of a portion of the bony anatomy of the patient such that the orthopaedic surgical instrument may be coupled to the bony anatomy of the patient in a unique location, which corresponds to the pre-planned location for the instrument. Such negative contours may include a unique set of ridges and depressions shaped to match a corresponding set of ridges and depressions on the patient&#39; bone. When the orthopaedic surgical instrument is coupled to the patient&#39;s bony anatomy in the unique location, one or more guides (e.g., cutting or drilling guide) of the orthopaedic surgical instrument may be aligned to the inclination and version planes, as discussed above. 
     The process sub-steps  228 - 234  shown in  FIG.  11 B  outline an exemplary sub-routine that may be followed to generate the model of the patient-specific orthopaedic surgical instrument. In process sub-step  228 , the femoral bone model  170  may be used to generate the customized patient-specific negative contour or contours of the patient-specific surgical instrument. To do so, the user may create an infinitely thin sheet  180  within the boundary  178  shown in  FIG.  13   . The thin sheet  180  may include the depressions and ridges to be included in the negative contour of the patient-specific surgical instrument. 
     In process sub-step  230 , the user may add thickness to the sheet  180  within the boundary  178  to generate the outer surface of the customized patient-specific surgical instrument and thereby define the base plate of the instrument. As discussed above, the user may minimize the thickness of the instrument to reduce the size of the incision necessary to place the instrument on the patient&#39;s bone. In process sub-step  232 , the user may define a cavity  70  over each of the problematic regions  174  identified in process step  222 . As part of defining the cavity or cavities, the user may adjust the shape and size of the planned base plate to adjust the planned size and/or weight of the instrument. Each cavity may have an outer edge that is aligned with the edge  172  of the region  174 . 
     In process sub-step  234 , the user may position the surgical instrument guide bodies in position on the femoral bone model  170  to create the model  182  of the patient-specific orthopaedic surgical instrument shown in FIG.  15 . To do so, the desired cutting planes for implantation of the orthopaedic prosthesis may be determined. The planned cutting planes may be determined based on the type, size, and position of the orthopaedic prosthesis to be used during the orthopaedic surgical procedure; the process images, such as specific landmarks identified in the images; and the constraint data supplied by the orthopaedic surgeon in process steps  212  and  214 . The type and/or size of the orthopaedic prosthesis may be determined based on the patient&#39;s anatomy and the constraint data. For example, the constraint data may dictate the type, make, model, size, or other characteristic of the orthopaedic prosthesis. The selection of the orthopaedic prosthesis may also be modified based on the medical images such that an orthopaedic prosthesis that is usable with the bone of the patient and that matches the constraint data or preferences of the orthopaedic surgeon is selected. 
     When positioning the guide bodies on the femoral bone model  170 , the user may adjust the size, shape, and location of each guide body as needed. As shown in  FIGS.  14 - 15   , the user may include a cutting guide slot and one or more drill guide slots for preparing the patient&#39;s bone to receive a fixation pin. The orientation of the drill guide slots may be based on the planned resection planes and may be adjusted to facilitate the resection of the patient&#39;s bone. As shown in  FIGS.  14 - 15   , the guide bodies for the guide slots may be formed by extending the bodies outwardly from the outer surface of the model  182  to their free ends. 
     It should be appreciated that the sub-steps  228 ,  230 ,  232 ,  234  may be performed in an order different from that described above. For example, a user may choose to identify the planned resection plane first and insert the cutting guide body into the femoral bone model prior to generating the customized patient-specific negative contour. Additionally, in some embodiments, one or more of the sub-steps may be omitted. 
     After the model of the customized patient-specific orthopaedic surgical instrument has been generated in process step  226 , the model is validated in process step  236 . The model may be validated by, for example, analyzing the rendered model while coupled to the three-dimensional model of the patient&#39;s anatomy to verify the correlation of cutting guides, reaming guides, inclination and version planes, and/or the like. Additionally, the model may be validated by transmitting or otherwise providing the model generated in step  226  to the orthopaedic surgeon for review. 
     After the model has been validated in process step  236 , the customized patient-specific orthopaedic surgical instrument is fabricated in process step  238 . As described above, the customized patient-specific orthopaedic surgical instrument may be formed by DMLS, which, as described above, is a form of 3-D printing technology. In DMLS, the orthopaedic surgical instrument is formed in a layer-by-layer fashion using laser sintering in which light fuses metallic powder, forming the metallic structures that define the orthopaedic surgical instrument. As part of the process of fabricating the orthopaedic surgical instrument, the metallic powder may be fused in layers, resulting in an orthopaedic surgical instrument that is a single monolithic component that includes a plurality of fused laminations  184 . For example, as shown in  FIG.  8   , the cutting block  10  includes a plurality of fused laminations  184  of metallic material of uniform thickness. It should be appreciated that other forms of 3-D printing technology such as, for example, optical fabrication, photo-solidification, or resin printing may be used to fabricate the orthopaedic surgical instrument. 
     As described above, the cutting block  10  includes a pair of guide bosses  140  that have tapered anterior surfaces  152 . In one exemplary process, the cutting block  10  may be fabricated with the anterior elongated opening  110  cutting slot  12  pointing downward. By tapering the anterior surfaces  152 , no support structure is needed to keep the bosses  140  from collapsing during fabrication. It should be appreciated that other surfaces that face downward during the build may be tapered/angled to minimize the amount of support structure needed. In the illustrative embodiment, the tapered surfaces  152  are angled by about 35 degrees. As used herein, the term “about” should be understood to refer to permit the normal tolerances created by manufacturing variation and other design criteria. 
     After the customized patient-specific orthopaedic surgical instrument is fabricated, the surgeon may perform the orthopaedic surgical procedure using the customized patient-specific orthopaedic surgical instrument. As discussed above, because the orthopaedic surgeon does not need to determine the proper location of the orthopaedic surgical instrument intra-operatively, which typically requires some amount of estimation on part of the surgeon, the guesswork and/or intra-operative decision-making on part of the orthopaedic surgeon is reduced. 
     It should also be appreciated that variations in the bony of anatomy of the patient may require more than one customized patient-specific orthopaedic surgical instrument to be fabricated according to the method described herein. For example, the patient may require the implantation of two orthopaedic prostheses. As such, the surgeon may follow the method  200  of  FIGS.  11 A-B  to fabricate a different customized patient-specific orthopaedic surgical instrument for use in replacing each portion of the patient&#39;s bony anatomy. Each customized patient-specific orthopaedic surgical instrument defines a cutting plane or other relevant parameter relative to each bone that is different due to the variation in the bony anatomy. 
     One such instrument—a customized patient-specific tibial cutting block  310 —is shown in  FIGS.  16 - 22   . The tibial cutting block  310  includes a cutting guide slot  312  position to guide a customized, patient-specific resection of a proximal end of a patient&#39;s tibia along a predetermined resection plane. As described in greater detail below, the tibial cutting block  310  is configured to be coupled to a patient&#39;s tibia in a unique pre-determined location and orientation. It illustrative embodiment, the structure of the cutting block  310 , like the structure of the femoral cutting block  10  described above, has been contoured to reduce its size relative to conventional cutting blocks and avoid contact with undesirable regions of the patient&#39;s bone. 
     As shown in  FIG.  16   , the tibial cutting block  310  includes a base plate  320  and a number of surgical tool guide bodies  322  that are attached to, and extend outwardly from, the base plate  320 . Like the femoral cutting block  10 , the tibial cutting block  310  is a single monolithic component formed via a 3-D printing process from a metallic material such as, for example, stainless steel. In the illustrative embodiment, the base plate  320  includes a pair of arms  324 ,  326  that are configured to engage a proximal end of the patient&#39;s tibia. The arms  324 ,  326  are spaced apart from each other such that a notch  328  is defined between their respective inner edges. The notch  328  is sized and shaped to receive the natural spine of the patient&#39;s tibia. In that way, base plate  320  is shaped to engage the medial and lateral tibial compartments of the patient&#39;s natural tibia in avoid contact with the spine. 
     Each of the arms  324 ,  326  includes a bone-facing surface  336  that engages the medial or lateral tibial compartment. As shown in  FIG.  19   , each bone-facing surface  336  includes a negative contour  338  that is configured to receive a portion of the patient&#39;s tibia. Each contour  338  includes a unique set of ridges  340  and depressions  342  that are shaped to engage a corresponding set of depressions and ridges of the patient&#39;s tibia. Each of the arms  324 ,  326  also includes an outer surface  344  that is positioned opposite the corresponding bone-facing surface  336 . In the illustrative embodiment, a plurality of apertures  346  extend through the surfaces  336 ,  344 . Each aperture  346  is illustratively diamond-shaped and includes edges that are configured to grip the bone. 
     The base plate  320  also includes an anterior flange  350  that is configured to engage the proximal end of the patient&#39;s tibia. As shown in  FIG.  17   , the anterior flange  350  includes a bone-facing surface  352 , and a negative contour  354  is defined in the bone-facing surface  352 . The negative contour  354  is configured to receive a portion of the patient&#39;s tibia in includes a unique set of ridges  356  and depressions  358  that are shaped to engage a corresponding set of depressions and ridges of the patient&#39;s tibia. The anterior flange  350  also includes an outer surface  364  that is positioned opposite the bone-facing surface  352 . In the illustrative embodiment, a plurality of apertures  346  also extend through the surfaces  352 ,  364 . Each aperture  346  is illustratively diamond-shaped and includes edges that are configured to grip the bone. It should be appreciated that in other embodiments the apertures may have different geometric shapes or may be omitted. Similarly, it should be appreciated that the femoral cutting block  10  described above may, in other embodiments, include such apertures. 
     In the illustrative embodiment, the notch  328  defined between the arms  324 ,  326  is a customized cavity similar to the customized cavity  70  described above in regard to the femoral cutting block  10 . It should also be appreciated that in other embodiments the base plate  320  may include additional customized cavities similar to the customized cavities  70 . Such cavities may be sized and shaped to be positioned over problematic regions of the patient&#39;s tibia in the pre-determined location of the bone such that those regions may be avoided so as to not interfere with the positioning of the cutting block  310 . 
     In the illustrative embodiment, the base plate  320  of the cutting block  310  also has a low-profile to reduce the size of the incision and reduce the amount of bone displacement needed to position the cutting block  310 . The low-profile has been customized for block  310  by minimizing the thicknesses of the arms  324 ,  326  and the anterior flange  350 . As shown in  FIG.  17   , a thickness  382  is defined between the outer surface  348  and the bone-facing surface  336  of each arm. The outer surfaces  348  are shaped to follow the geometries of the bone-facing surfaces  336  of the arms  324 ,  326 . Similarly, as shown in  FIG.  19   , a thickness  384  is defined between the outer surface  364  and the bone-facing surface  352  of the anterior flange  350 , and the outer surface  364  of the flange  350  is shaped to follow the geometry of the bone-facing surface  352  to minimize the thickness  384 . 
     As shown in  FIGS.  16 - 22   , each of the surgical tool guide bodies  322  of the cutting block  310  is attached to and extends outwardly from the outer surfaces  348 ,  364  of the arms  324 ,  326  and the anterior flange  350  to a free end  390  that is spaced apart from the base plate  320 . In the illustrative embodiment, the guide bodies  322  include an elongated body  400  and a pair of bosses  402 ,  404  that extend outwardly from the anterior flange  350 . The elongated body  400  includes an elongated opening  410  that is defined in its free end  390 , and a number of inner walls  412  extend inwardly from the opening  410 . As shown in  FIG.  17   , the inner walls  412  extend to another opening  414  that is defined by an edge  416  of the bone-facing surface  352 . The edge  416  illustratively follows a curved path to match the shape of the patient&#39;s tibia in that region. The opening  414  cooperates with the inner walls  412  and the elongated opening  410  to define the guide slot  312 , which is sized and shaped to guide a surgical tool such as, for example, a cutting blade, into engagement with the patient&#39;s bone. As described above, the cutting guide slot  312  is positioned to guide a customized, patient-specific resection of the proximal end of a patient&#39;s tibia. Because the edge  416  follows the shape of the patient&#39;s tibia, the cutting guide slot  312  provides support for the cutting blade in close proximity to the region under resection. 
     As shown in  FIG.  16   , each of the bosses  402 ,  404  are positioned distal of the elongated body  400 . An opening  420  is defined in the free end  390  of each of the bosses  402 ,  404 , and an inner wall  422  extends inwardly from the opening  420 . As shown in  FIG.  17   , each inner wall  422  extends to another opening  424  in the bone-facing surface  352  to define a guide slot  426  extending through the cutting block  310 . In the illustrative embodiment, each guide slot  426  is a drill guide and fixation pin guide hole, which is sized and shaped to guide a surgical drill to prepare the patient&#39;s bone to receive a fixation pin to couple to the block  310  to the bone. 
     Another customized patient-specific orthopaedic surgical instrument that may be modeled and fabricated using the routine  200  is the customized patient-specific anterior-posterior chamfer cutting block  510  shown in  FIGS.  23 - 30   . The cutting block  510  includes a base plate  512  that has been customized to fit a distal end  514  of a patient&#39;s femur  16  that has been resected using, for example, the femoral cutting block  10  described above. The cutting block  510  also includes a plurality of surgical tool guide bodies  516 , which are attached to an extend outwardly from the base plate  512  and which are configured to guide surgical tools into contact with the patient&#39;s femur, as described in greater detail below. In the illustrative embodiment, the cutting block  510  is a single monolithic component form from a metallic material such as, for example, stainless steel. In that way, the base plate  512  and the guide bodies  516  form a single monolithic metallic block. Like the cutting blocks  10 ,  310 , the cutting block  510  is formed by DMLS. As shown in  FIG.  27   , the cutting block  510  includes a plurality of fused laminations  184  of metallic material of uniform thickness. 
     The base plate  512  includes a bone-facing surface  520  and an outer surface  522  that is positioned opposite the bone-facing surface  520 . An outer wall  524  extends between the surfaces  520 ,  522  to define the outer perimeter of the base plate  512 . As shown in  FIG.  25   , the bone-facing surface  520  includes an outer edge  526  that is connected to the outer wall  524  and has been customized to match an outer edge  528  (see  FIG.  28   ) of the resected distal end  514  of a patient&#39;s femur  16 . In that way, the cutting block  510  is configured to be coupled to the patient&#39;s femur  16  in a unique pre-determined location and orientation. 
     The outer edge  526  includes a superior section  530  that defines a notch  532  in the base plate  512 . In the illustrative embodiment, the superior section  530  is curved to match the curvature of the anterior edge section  534  (see  FIG.  28   ) of the resected distal end  514  of a patient&#39;s femur  16 . The outer edge  526  of the bone-facing surface  520  also includes an inferior section  540  that defines a notch  542  in the base plate  512 . In the illustrative embodiment, the inferior section  540  is curved to match the curvature of the posterior edge section  544  (see  FIG.  28   ) of the resected distal end  514  of a patient&#39;s femur  16 , and the shape of the notch  532  substantially matches the shape of the edge of the intercondylar notch  30 . 
     In the illustrative embodiment, the base plate  512  of the cutting block  510  has a low-profile to reduce the size of the incision and reduce the amount of bone displacement needed to position the cutting block  510 . Similar to the blocks  10 ,  310 , the low-profile has been customized for block  510  by minimizing the thickness of the base plate  512  defined between the outer surface  522  and the bone-facing surface  520 . 
     As shown in  FIGS.  22 - 27   , each of the surgical tool guide bodies  516  of the cutting block  510  is attached to and extends outwardly from the outer surface  522  to an outer end  550  that is spaced apart from the base plate  512 . In the illustrative embodiment, the guide bodies  516  include an anterior resection guide body  560  that is positioned over the notch  532  of the base plate  512 . The resection guide body  560  includes an elongated opening  562  that is defined in its outer end  550 , which is a free end spaced apart from the outer ends of the other guide bodies  516 . The resection guide body  560  also includes a number of inner walls  564  that extend inwardly from the opening  562 . As shown in  FIG.  25   , the inner walls  564  extend to an opening  566  that opens into the superior notch  532  of the base plate  512 . The opening  566  cooperates with the inner walls  564  and the elongated opening  562  to define the guide slot  568 , which is sized and shaped to guide a surgical tool such as, for example, a cutting blade, into engagement with the patient&#39;s femur and guide the anterior resection of the femur along a predetermined resection plane. The cutting guide slot  568  is positioned in a unique, predetermined position and orientation that has been customized for that patient. 
     The guide bodies  516  include a posterior resection guide body  570  that is positioned over the inferior notch  542  of the base plate  512 . The resection guide body  570  includes an elongated opening  572  that is defined in its outer end  550 , which is a free end spaced apart from the outer ends of the other guide bodies  516 . The resection guide body  570  also includes a number of inner walls  574  that extend inwardly from the opening  572 . As shown in  FIG.  25   , the inner walls  574  extend to an opening  576  that opens into the inferior notch  542  of the base plate  512 . The opening  576  cooperates with the inner walls  574  and the elongated opening  572  to define the guide slot  578 , which is sized and shaped to guide a surgical tool such as, for example, a cutting blade, into engagement with the patient&#39;s femur and guide the posterior resection of the femur along a predetermined resection plane. The cutting guide slot  568  is positioned in a unique, predetermined position and orientation that has been customized for that patient. 
     The guide bodies  516  also include a pair of chamfer resection guide bodies  580 ,  590  that are positioned between the anterior and posterior resection guide bodies  560 ,  570 . The resection guide body  580  includes an elongated opening  582  that is defined in its outer end  550 , and a number of inner walls  584  that extend inwardly from the opening  582 . As shown in  FIG.  25   , the inner walls  584  extend to an opening  586  defined in the bone-facing surface  520  of the base plate  512 . The opening  586  cooperates with the inner walls  584  and the elongated opening  582  to define a chamfer resection guide slot  588 , which is sized and shaped to guide a surgical tool such as, for example, a cutting blade, into engagement with the patient&#39;s femur and guide a chamfer resection of the femur along a predetermined resection plane, which extends at an angle relative to the resection planes defined by the other cutting guide slots. The cutting guide slot  588  is positioned in a unique, predetermined position and orientation that has been customized for that patient. 
     The resection guide body  590  includes an elongated opening  592  that is defined in its outer end  550 , and a number of inner walls  594  that extend inwardly from the opening  592 . As shown in  FIG.  25   , the inner walls  594  extend to an opening  596  defined in the bone-facing surface  520  of the base plate  512 . The opening  596  cooperates with the inner walls  594  and the elongated opening  592  to define another chamfer guide slot  598 , which is sized and shaped to guide a surgical tool such as, for example, a cutting blade, into engagement with the patient&#39;s femur and guide another chamfer resection of the femur along a predetermined resection plane, which also extends at an angle relative to the resection planes defined by the other cutting guide slots. The cutting guide slot  598  is positioned in a unique, predetermined position and orientation that has been customized for that patient. 
     As shown in  FIGS.  22 - 27   , the outer ends  550  of the chamfer resection guide bodies  580 ,  590  are coupled together, and a passageway  600  is defined between the surfaces of the guide bodies  580 ,  590  and the base plate  512 . In the illustrative embodiment, the passageway  600  has a triangular cross-section. As shown in  FIG.  27   , the guide slots  588 ,  598  of the guide bodies  580 ,  590  intersect, and the inner walls  584 ,  594  of the guide bodies  580 ,  590  include a number of openings  602  at the intersection such that the guide slots  588 ,  598  are in communication with each other. 
     The guide bodies  516  also include a pair of bosses  604 ,  606  that extend outwardly from the base plate  512  between the chamfer resection guide bodies  580 ,  590  and the posterior resection guide body  570 . An opening  610  is defined in the outer end  550  of each of the bosses  604 ,  606 , and an inner wall  612  extends inwardly from the opening  610 . As shown in  FIG.  17   , each inner wall  612  extends to another opening  614  in the bone-facing surface  520  to define a guide slot  616  extending through the cutting block  510 . In the illustrative embodiment, each guide slot  616  is a drill guide and fixation pin guide hole, which is sized and shaped to guide a surgical drill to prepare the patient&#39;s bone to receive a fixation pin to couple to the block  510  to the patient&#39;s femur. 
     As described above, the cutting block A-P chamfer cutting block  510  is customized to fit a resected distal end  514  of a patient&#39;s femur  16 , which is shown in  FIG.  28   . The resected distal end  514  includes a resected distal surface  620  that is bounded by the outer edge  528 . As shown in  FIG.  28   , the outer edge  528  includes an anterior edge section  534  that defines the distal opening of the patient&#39;s trochlear groove  166  and a posterior edge section  544  that defines the distal opening of the patient&#39;s intercondylar notch  30 . In the illustrative embodiment, the size and shape of the resected distal surface  620  is pre-operatively planned during, for example, the execution of the routine  200 . In other words, when the surgeon or other user defines the distal resection plane to be created using the cutting block  10 , the size and shape of the resected distal surface  620  is also modeled. With the model of the resected distal surface  620 , the user may generate a 3-D computer model of the A-P chamfer cutting guide block  510  during the process step  226  of the routine  200 . 
     As shown in  FIG.  29    and described above, the outer edge  526  of the base plate  512  of the cutting block  510  is shaped to match the outer edge  528  of the resected distal surface  620 . In particular, the superior section  530  of the plate outer edge  526  is curved to match the curvature of the anterior edge section  534  of the outer edge  528  of the resected distal surface  620 , and the inferior section  540  of the plate outer edge  526  is curved to match the curvature of the posterior edge section  544  of the outer edge  528  of the resected distal surface  620 . The superior notch  532  of the base plate  512  is shaped to match the distal opening of the patient&#39;s trochlear groove  166 . The base plate  512  also includes the inferior notch  542  that is shaped to match the distal opening of the patient&#39;s intercondylar notch  30 . As shown in  FIG.  30   , the outer edges  526 ,  528  of the block and bone are coincident when the cutting block  510  is properly positioned on the patient&#39;s bone, with the notches  532 ,  542  aligned with the distal openings of the groove  166  and the notch  30 . In that way, the surgeon or other user are informed when the block is properly positioned and any misalignment with the patient&#39;s bone can be corrected prior to beginning any resection with the block  510 . 
     Referring now to  FIGS.  31 - 37   , another embodiment of a customized patient-specific femoral cutting block (hereinafter the cutting block  710 ) is shown. The embodiment of  FIGS.  31 - 37    includes many features that are the same or similar to features shown in the embodiment of  FIGS.  1 - 10   . Similar features will be identified in  FIGS.  31 - 37    with the same reference numbers as were used in  FIGS.  1 - 10   . The cutting block  710  includes a cutting guide slot  712  positioned to guide a customized, patient-specific resection of a distal end of a patient&#39;s femur. As described in greater detail below, the femoral cutting block  710  is configured to be coupled to the patient&#39;s femur in a unique pre-determined location and orientation. In the illustrative embodiment, the structure of the cutting block  710  has been contoured to reduce its size relative to conventional cutting blocks and avoid contact with undesirable regions of the patient&#39;s bone. 
     As shown in  FIG.  31   , the femoral cutting block  710  includes a base plate  720  and a number of surgical tool guide bodies  722  that are attached to, and extend outwardly from, the base plate  720 . In the illustrative embodiment, the femoral cutting block  710  is a single monolithic component formed from a metallic material such as, for example, stainless steel, via a DMLS technique. In that way, the base plate  720  and the guide bodies  722  form a single monolithic metallic block. 
     The base plate  720  includes a posterior section including a pair of arms  24 ,  26  that are configured to engage the distal end of the patient&#39;s femur. The arms  24 ,  26  are spaced apart from each other such that a notch  28  is defined between the inner edges of the arms  24 ,  26 . The notch  28  is sized and shaped to correspond to the natural intercondylar notch of the patient&#39;s femur. In that way, contact within bone surfaces with the natural intercondylar notch  30 , which may be difficult to model, is avoided. 
     Each of the arms  24 ,  26  has a bone-contacting or bone-facing surface  36  that engages one of the natural condyles  32 ,  34 . In the illustrative embodiment, each bone-facing surface  36  includes a number of negative contours  38  that are configured to receive a portion of the natural condyles  32 ,  34 . Each of the arms  24 ,  26  also includes an outer surface  48  that is positioned opposite its corresponding bone-facing surface  36 . In the illustrative embodiment, each outer surface  48  is substantially smooth. 
     As shown in  FIG.  31   , the base plate  720  also includes an anterior section including an anterior flange  750  that is configured to engage the distal end of the patient&#39;s femur. In the illustrative embodiment, the flange  750  is spaced apart from the arms  24 ,  26 . The anterior flange  750  includes a bone-facing surface  752  that includes a number of negative contours  754  that are configured to receive a portion of the patient&#39;s femur. As shown in, for example,  FIGS.  32  and  34   , the contour  754  of the anterior flange  750  has a unique set of ridges  756  and depressions  758  that are shaped to engage a corresponding unique set of depressions and ridges of the patient&#39;s femur. The anterior flange  750  also includes an outer surface  764  that is positioned opposite the bone-facing surface  752 . In the illustrative embodiment, the outer surface  764  is substantially smooth. 
     The base plate  720  also includes a number of customized cavities  70 , which are sized to be positioned over regions in the pre-determined location of the bone that may include a defect or are damaged or difficult to model. In that way, the cavities  70  are sized such that contact with those regions may be avoided so as to not interfere with positioning the cutting block  10  in the pre-determined location and orientation. In the illustrative embodiment, the notch  28  defined between the arms  24 ,  26  is one of the customized cavities. As shown in  FIGS.  31 - 33   , the customized cavities  70  also include an aperture  772  that extends through the bone-facing surface  752  of the anterior flange  750 . As shown in  FIGS.  31 - 32   , the customized cavities  70  also include a pair of channels  74 ,  76  that are defined in the bone-facing surface  752  of the anterior flange  750 . 
     As described above, the cutting block  710  includes a number of surgical tool guide bodies  722  configured to guide a surgical tool into contact with the patient&#39;s bone. In the illustrative embodiment, the guide bodies  722  include a distal resection guide body  780  that extends anteriorly from the anterior ends of the arms  24 ,  26 . The distal resection guide body  780  includes an elongated opening  782  that is defined in its outer end  784  and a number of inner walls  786  that extend inwardly from the opening  782 . As shown in  FIG.  32   , the inner walls  786  extend to another opening  788  that is defined in the bone-facing surface  762 . The opening  788  cooperates with the inner walls  786  and the elongated opening  782  to define the cutting guide slot  712 , which is sized and shaped to guide a surgical tool such as, for example, a cutting blade, into engagement with the patient&#39;s bone. As described above, the cutting guide slot  712  is positioned to guide a customized, patient-specific resection of a distal end of a patient&#39;s femur. 
     As shown in  FIG.  35   , the inner walls  786  include a medial inner wall  790  that defines the medial side of the guide slot  712  and a lateral inner wall  792  that defines the lateral side of the guide slot  712 . In the illustrative embodiment, the lateral inner wall  792  extends at an oblique angle relative to the medial inner wall  790  to guide the resection of the patient&#39;s bone. The oblique angle, like the rest of the cutting guide block  710 , is customized to the bony anatomy of the patient. It should be appreciated that the medial inner wall may be angled in other embodiments. 
     The tool guide bodies  722  of the block  710  also includes a pair of guide bosses  796 ,  798  that are integrated into the anterior flange  750 , which extends proximally from the guide body  780 . An opening  800  is defined in the outer surface  802  of each of the bosses  796 ,  798 , and an inner wall  804  extends inwardly from the opening  800 . As shown in  FIG.  32   , each inner wall  804  extends to another opening  806  that opens into one of the channels  74 ,  76  to define a guide slot  808  extending through the cutting block  710 . In the illustrative embodiment, each guide slot  808  is a drill guide and fixation pin guide hole, which is sized and shaped to guide a surgical drill to prepare the patient&#39;s bone to receive a fixation pin to couple to the block  710  to the bone. 
     The cutting block  710  has a low-profile to reduce the size of the incision and reduce the amount of bone displacement needed to position the cutting block  710 . The low-profile has been customized for block  710  by adjusting the shape and sizes of the base plate and the guide bodies. For example, as shown in  FIG.  36   , the guide boss  796  has a length  810  that is shorter than the length  812  of the guide boss  798 , which is shown in  FIG.  36   . Similarly, the outer surface  48  of each arm is convexly curved to follow the concave curvature of the bone-facing surface  36  of the arm. 
     The guide bodies  722  of the cutting block  710  also include a pair of posterior guide bosses  140 , which are attached to, and extend distally from, the outer surfaces  48  of the arms  24 ,  26 , respectively. Each posterior guide boss  140  includes a guide slot  142  that is sized and shaped to guide surgical drill and a fixation pin into engagement with the patient&#39;s bone to couple to the block  710  to the bone. 
     Referring now to  FIGS.  38 - 41   , other embodiments of customized patient-specific cutting blocks (hereinafter the cutting block  910 ,  1010 ,  1110 ) are shown. The embodiments of  FIGS.  38 - 41    include many features that are the same or similar to features shown in the embodiments described above. Similar features will be identified in  FIGS.  38 - 41    with the same reference numbers as were used in reference to the embodiments above. Referring now to  FIG.  38   , the cutting block  910  includes a cutting guide slot  912  positioned to guide a customized, patient-specific resection of a distal end of a patient&#39;s femur. In the illustrative embodiment, the cutting block  910  includes a number of bone-facing surfaces  916  that have negative contours  38  that are configured to receive portions of the patient&#39;s bone. 
     Similar to the tibial cutting block  310 , the cutting block  910  includes a plurality of apertures  914  that extend through the bone-facing surfaces  916  and the outer surfaces  918  of the cutting block  910 . Each aperture  914  is illustratively cylindrical in shape and includes a circular edge that is configured to grip the bone. The apertures  914  also extend through the surfaces of the anterior resection guide body  920  and open into the guide slot  912 . In that way, the apertures  914  provide viewing windows for the surgeon or other user to monitor the movement of the cutting saw blade and review the fit of the block  910  on the bone. It should be appreciated that similar apertures may be incorporated into any of the embodiments described herein. Additionally, it should be appreciated that the apertures may take other sizes and shapes depending on the nature of the patient&#39;s bony anatomy. 
     The cutting block  910  includes a number of other surgical tool guide bodies  920 . In the illustrative embodiment, each of the tool guide bodies  920  is a drill guide and fixation guide configured to guide a fixation pin into engagement with a patient&#39;s bone to couple the cutting block  910  to the bone. 
     Referring now to  FIG.  39   , the cutting block  1010  includes a cutting guide slot  1012  positioned to guide a customized, patient-specific resection of a distal end of a patient&#39;s femur. In the illustrative embodiment, the cutting block  1010  includes a number of bone-facing surfaces  1016  that have negative contours  38  that are configured to receive portions of the patient&#39;s bone. 
     Similar to the cutting block  710 , the cutting block  1010  includes a distal resection guide body  1020  includes an elongated opening  1022  that is defined in its free end  1024  and a number of inner walls  1026  that extend inwardly from the opening  1022  to define the cutting guide slot  1012 , which is sized and shaped to guide a surgical tool such as, for example, a cutting blade, into engagement with the patient&#39;s bone. 
     As shown in  FIG.  39   , the inner walls  1026  include a medial inner wall  1030  that defines the medial side of the guide slot  1012  and a lateral inner wall  1032  that defines the lateral side of the guide slot  1012 . In the illustrative embodiment, the lateral inner wall  1032  extends at an oblique angle relative to the medial inner wall  1030  to guide the resection of the patient&#39;s bone. The oblique angle, like the rest of the cutting guide block  1010 , is customized to the bony anatomy of the patient. 
     The cutting block  1010  includes a number of other surgical tool guide bodies  1028 . In the illustrative embodiment, each of the tool guide bodies  1028  is a drill guide and fixation guide configured to guide a fixation pin into engagement with a patient&#39;s bone to couple the cutting block  1010  to the bone. 
     Referring now to  FIGS.  40 - 41   , the cutting block  1110  includes a pair of cutting guide slots  1112 ,  1114  positioned to guide a customized, patient-specific resection of a distal end of a patient&#39;s femur. In the illustrative embodiment, the cutting block  1110  includes a number of bone-facing surfaces  1116  that have negative contours  38  that are configured to receive portions of the patient&#39;s bone. 
     The cutting block  1110  includes a distal resection guide body  1120  includes a pair of elongated openings  1122  that are defined in its free end  1124  and a number of inner walls  1126  that extend inwardly from the openings  1122 . Each opening  1122  and the inner walls  1126  cooperate to define the cutting guide slots  1112 ,  1114 , which are sized and shaped to guide a surgical tool such as, for example, a cutting blade, into engagement with the patient&#39;s bone. The cutting guide slot  1114  is arranged distally of the cutting guide slot  1112  to offer the surgeon the option of making a second, pre-planned resection during surgery, thereby providing the surgeon with additional flexibility during surgery while at the same time maintaining the benefits of the pre-operative planning. 
     As shown in  FIGS.  40 - 41   , the cutting block  1110  includes a number of other surgical tool guide bodies  1130 . In the illustrative embodiment, each of the tool guide bodies  1130  is a drill guide and fixation guide configured to guide a fixation pin into engagement with a patient&#39;s bone to couple the cutting block  1110  to the bone. 
     It should be appreciated that in some embodiments the metallic customized patient-specific surgical instrument comprises a base plate sized to be positioned on a resected surface of a distal end of a patient&#39;s femur. The base plate has a bone-facing surface, a distal surface positioned opposite the bone-facing surface, and an outer wall extending between the bone-facing surface and the distal surface. The metallic customized patient-specific surgical instrument comprises a body attached to, and extending from, the distal surface to a free distal end, and the body includes an elongated opening that is defined in its free distal end. A cutting guide slot extends from the opening in the body through a first opening defined in the bone-facing surface, and the cutting guide slot is sized to receive a cutting saw blade. A boss is attached to, and extends from, the distal surface to a free distal end spaced apart from the free distal end of the body. The boss includes an opening that is defined in its free distal end. The metallic customized patient-specific surgical instrument also comprises a drill guide slot extending from the opening in the boss through a second opening defined in the bone-facing surface. The drill guide slot is sized to receive a surgical drill. 
     In some embodiments, the bone-facing surface may include a customized patient-specific outer edge that is shaped to match an outer edge of the resected surface of the distal end of the patient&#39;s femur. 
     Additionally, in some embodiments, the metallic customized patient-specific surgical instrument may include a notch that is defined by a section of the outer edge, and the cutting guide slot may open into the notch. In some embodiments, the section of the outer edge may be a superior section such that the notch is defined at a superior end of the metallic customized patient-specific surgical instrument. 
     In some embodiments, the section of the outer edge may be an inferior section such that the notch is defined at an inferior end of the metallic customized patient-specific surgical instrument. 
     In some embodiments, the body may be a first body, the cutting guide may be a first cutting guide, and the metallic customized patient-specific surgical instrument may further comprise a second body attached to, and extending from, the distal surface to a distal end spaced apart from the distal ends of the first body and the boss. The second body may include an elongated opening that is defined in its distal end. A second cutting guide slot may extend from the opening in the second body through a third opening defined in the bone-facing surface. The second cutting guide slot may be sized to receive a cutting saw blade. 
     In some embodiments, the first cutting guide may define a first cutting plane, and the second cutting guide may define a second cutting plane that is angled relative to the first cutting plane. Additionally, in some embodiments, the metallic customized patient-specific surgical instrument may further comprise a third body attached to, and extending from, the distal surface to a distal end attached to the distal end of the second body. The third body may include an elongated opening that is defined in its distal end. A third cutting guide slot may extend from the opening in the third body through a fourth opening defined in the bone-facing surface. The third cutting guide slot may be sized to receive a cutting saw blade and may intersect the second cutting guide slot. 
     In some embodiments, the third cutting guide may define a third cutting plane that is angled relative to the first cutting plane and the second cutting plane. Additionally, in some embodiments, a passageway may be defined between a surface of the second body, a surface of the third body, and the distal surface of the base plate. 
     In some embodiments, the metallic customized patient-specific surgical instrument may further comprise a fourth body attached to, and extending from, the distal surface to a free distal end spaced apart from the distal ends of the first, second, and third bodies. The fourth body may include an elongated opening that is defined in its distal end, and a fourth cutting guide slot may extending from the opening in the fourth body through a fifth opening defined in the bone-facing surface. The fourth cutting guide slot may be sized to receive a cutting saw blade and crossing the second cutting guide slot. 
     In some embodiments, the metallic customized patient-specific surgical instrument may include a plurality of laminations of metallic material. 
     It should also be appreciated that in some embodiments a metallic customized patient-specific surgical instrument comprises a base plate sized to be positioned on a resected surface of a distal end of a patient&#39;s femur. The base plate has a bone-facing surface, a distal surface positioned opposite the bone-facing surface, and an outer wall extending between the bone-facing surface and the distal surface. The metallic customized patient-specific surgical instrument also comprises an anterior resection guide body attached to, and extending from, the distal surface to a free distal end. The anterior resection guide body includes an anterior cutting guide slot sized to receive a cutting saw blade. A posterior resection guide body is attached to, and extending from, the distal surface to a free distal end, and the posterior resection guide body includes a posterior cutting guide slot sized to receive a cutting saw blade. The metallic customized patient-specific surgical instrument also comprises a pair of chamfer resection guide bodies attached to, and extending from, the distal surface. Each chamfer resection guide body includes a chamfer cutting guide slot sized to receive a cutting saw blade, and each chamfer cutting guide slot extends obliquely relative to the other cutting guide slots. 
     In some embodiments, the metallic customized patient-specific surgical instrument may further comprise a boss attached to, and extending from, the distal surface to a free distal end spaced apart from the free distal end of the body. The boss may include an opening that is defined in its free distal end, and a drill guide slot may extend from the opening in the boss through a second opening defined in the bone-facing surface. The drill guide slot may be sized to receive a surgical drill. 
     In some embodiments, the bone-facing surface may include a customized patient-specific outer edge that is shaped to match an outer edge of the resected surface of the distal end of the patient&#39;s femur. 
     Additionally, in some embodiments, the metallic customized patient-specific surgical instrument may include a superior notch that is defined by a section of the outer edge, and the anterior cutting guide slot may open into the superior notch. 
     In some embodiments, the metallic customized patient-specific surgical instrument may include an inferior notch that is defined by a section of the outer edge, and the posterior cutting guide slot may open into the inferior notch. 
     In some embodiments, the metallic customized patient-specific surgical instrument may include a plurality of laminations of metallic material. 
     It should also be appreciated that in some embodiments a method of performing an orthopaedic surgery comprises aligning a customized patient-specific surgical instrument with a resected distal surface of a patient&#39;s bone, positioning the customized patient-specific surgical instrument in contact with the resected distal surface, and rotating the customized patient-specific surgical instrument on the resected distal surface to align an outer perimeter edge of the resection distal surface with a customized, patient-specific outer edge of a bone-facing surface of the customized patient-specific surgical instrument, and inserting a cutting saw through a cutting guide slot defined in the customized patient-specific surgical instrument to resect the patient&#39;s bone. 
     In some embodiments, the customized patient-specific surgical instrument used in the method includes an anterior cutting guide slot, a posterior cutting guide slot, and a pair of chamfer cutting guide slots. 
     It should be appreciated that in some embodiments an orthopaedic surgical instrument comprising a customized patient-specific surgical instrument is disclosed. The customized patient-specific surgical instrument comprises a metallic base plate sized to be positioned on a patient&#39;s bone. The base plate has a bone-facing surface including a customized patient-specific negative contour configured to receive a corresponding positive contour of the patient&#39;s bone and an outer surface positioned opposite the bone-facing surface. The customized patient-specific surgical instrument also comprises a metallic guide body attached to, and extending from, the outer surface to a free end. The guide body includes an elongated opening that is defined in its free end. A guide slot extends from the opening in the guide body through a first opening defined in the bone-facing surface. The guide slot is sized and shaped to guide a surgical tool into engagement with the patient&#39;s bone. 
     In some embodiments, the guide slot may be sized and shaped to guide a fixation pin into engagement with the patient&#39;s bone. In some embodiments, the guide slot may be sized and shaped to guide a cutting saw blade into engagement with the patient&#39;s bone. 
     In some embodiments, the customized patient-specific surgical instrument may also comprise a boss attached to, and extending from, the outer surface to a free end spaced apart from the free end of the guide body. The boss may include an opening that is defined in its free end, and a drill guide slot may extend from the opening in the boss through a second opening defined in the bone-facing surface. The drill guide slot may be sized and shaped to guide a surgical drill or fixation pin into engagement with the patient&#39;s bone. 
     In some embodiments, the boss may extend from a base attached to the outer surface of the base plate to the free end. The base may be wider than the free end, and the boss may include a tapered surface that extends from the base to the free end. 
     In some embodiments, the cutting guide slot may extend in an anterior-posterior direction, the drill guide slot may be a first drill guide slot extending in a superior-inferior direction, and the customized patient-specific surgical instrument may further comprise a second drill guide slot extending in an anterior-posterior direction from a second opening in the body through a third opening defined in the bone-facing surface. The second drill guide slot may be sized and shaped to guide a surgical drill into engagement with the patient&#39;s bone. 
     In some embodiments, the base plate may include a pair of posteriorly-extending arms. Each arm may include a portion of the customized patient-specific negative contour configured to receive a portion of the corresponding positive contour of the patient&#39;s bone. 
     In some embodiments, the customized patient-specific surgical instrument may include a customized patient-specific cavity that is defined in the base plate. The cavity may be sized and shaped to be positioned over a portion of the patient&#39;s bone to prevent contact between the portion of patient&#39;s bone and the customized patient-specific surgical instrument. Additionally, in some embodiments, the cavity is positioned proximal of the guide body. 
     In some embodiments, the base plate may include a first section attached to one of a distal end and a proximal end of the guide body, and a second section that is spaced apart from the first section of the base plate and is attached to the other of the distal end and the proximal end of the guide body. 
     In some embodiments, the first section may include a pair of posteriorly-extending arms. Each arm may include a portion of the customized patient-specific negative contour configured to receive a portion of the corresponding positive contour of the patient&#39;s bone. Additionally, in some embodiments, the customized patient-specific surgical instrument may include a plurality of openings extending through the bone-facing and outer surfaces of the posterior-extending arms of the first section and the bone-facing and outer surfaces of the second section of the base plate. 
     In some embodiments, the customized patient-specific surgical instrument may be a single monolithic metallic component including a plurality of laminations. 
     It should be appreciated that in some embodiments a customized patient-specific surgical instrument comprises a metallic guide body extending from a posterior end to a free anterior end. The guide body includes an elongated opening that is defined in its free anterior end. A cutting guide slot extends from the opening in the guide body. The guide slot is sized and shaped to guide a cutting saw blade into engagement with a patient&#39;s bone. The customized patient-specific surgical instrument also includes a first plate section extending from the posterior end of the metallic guide body, and the first plate section includes a pair of posterior-extending arms. Each arm includes a first portion of a customized patient-specific negative contour configured to receive a first portion of a corresponding positive contour of the patient&#39;s bone. The customized patient-specific surgical instrument also includes a second plate section spaced apart from the first plate section and extending from the posterior end of the metallic guide body. The second plate section includes a bone-facing surface including a second portion of the customized patient-specific negative contour configured to receive a second portion of the corresponding positive contour of the patient&#39;s bone. 
     In some embodiments, the customized patient-specific surgical instrument may also comprise a first boss attached to, and extending from, the second plate section to an end spaced apart from the free anterior end of the guide body. The first boss may include an opening that is defined in its end, and a first drill guide slot may extend from the opening in the first boss. The first drill guide slot may be sized and shaped to guide a surgical drill into engagement with the patient&#39;s bone. 
     In some embodiments, the customized patient-specific surgical instrument may further comprise a second boss attached to, and extending from a first arm of the pair of posterior-extending arms to a free end. the second boss may include an opening that is defined in its free end, and a second drill guide slot extending from the opening in the second boss. The second drill guide slot may be sized and shaped to guide a surgical drill into engagement with the patient&#39;s bone. 
     In some embodiments, the customized patient-specific surgical instrument may further comprise a third boss attached to, and extending from, a second arm of the pair of posterior-extending arms to a free end. The third boss may include an opening that is defined in its free end, and a third drill guide slot extending from the opening in the third boss. The third drill guide slot may be sized and shaped to guide a surgical drill into engagement with the patient&#39;s bone. 
     Additionally, in some embodiments, the customized patient-specific surgical instrument may be a single monolithic metallic component including a plurality of laminations. 
     While the disclosure has been illustrated and described in detail in the drawings and foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only illustrative embodiments have been shown and described and that all changes and modifications that come within the spirit of the disclosure are desired to be protected. 
     There are a plurality of advantages of the present disclosure arising from the various features of the method, apparatus, and system described herein. It should be noted that alternative embodiments of the method, apparatus, and system of the present disclosure may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of the method, apparatus, and system that incorporate one or more of the features of the present invention and fall within the spirit and scope of the present disclosure as defined by the appended claims.