Abstract:
A low profile patient specific cutting block for a knee comprises a plurality of bone interfacing portions and a cutting slot. The plurality of bone interfacing portions are configured to overlie portions of an end of a bone. The bone interfacing portions each have a surface generally a negative of the portion of the bone the bone interfacing portion overlies. The bone interfacing portions are angularly offset from each other such that a first of the bone interfacing portions overlies an anterior portion of the bone and a second of the bone interfacing portions overlies a portion of bone generally perpendicular to the anterior portion of bone. The cutting slot is oriented in a fixed position relative to the bone interfacing portions such that the cutting slot directs a cutting tool at a fixed angle and at a fixed depth from the bone interfacing portions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/033,419, filed Mar. 3, 2008 and further claims the benefit of U.S. Provisional Application No. 61/089,373, filed Aug. 15, 2008. The disclosure of each application is incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to cutting blocks for bone resections at a knee joint and, more particularly, for cutting blocks designed for a patient&#39;s specific bone and cartilage and further configured to a surgeon&#39;s preferences. 
       SUMMARY OF THE INVENTION 
       [0003]    It is in view of problems related to the field above that the present invention was developed. 
         [0004]    In one aspect of the invention, a low profile patient specific cutting block for a knee comprises a plurality of bone interfacing portions and a cutting slot. The plurality of bone interfacing portions are configured to overlie portions of an end of a bone. The bone interfacing portions each have a surface generally a negative of the portion of the bone the bone interfacing portion overlies. The bone interfacing portions are angularly offset from each other such that a first of the bone interfacing portions overlies an anterior portion of the bone and a second of the bone interfacing portions overlies a portion of bone generally perpendicular to the anterior portion of bone. The cutting slot is oriented in a fixed position relative to the bone interfacing portions such that the cutting slot directs a cutting tool at a fixed angle and at a fixed depth from the bone interfacing portions. 
         [0005]    In another embodiment of the invention the low profile patient specific cutting block is a femoral cutting block. The block further comprises bosses having a thickness and an aperture extending through the bosses. The aperture has a diameter. The bosses are configured to direct a pin through the boss. The thickness of the boss is greater than the diameter of the aperture. 
         [0006]    In yet another embodiment, the bone interfacing portions are generally oriented in the middle of the low profile patient specific cutting block in an anterior portion of the low profile patient specific cutting block and are oriented medially and laterally at a posterior portion of the low profile patient specific cutting block. 
         [0007]    Alternatively, the low profile patient specific cutting block is a tibial block and the cutting slot is offset and medialized relative to the tibial bone. 
         [0008]    Another embodiment includes a paddle extending posteriolaterally from a middle portion of the patient specific cutting block. The paddle has a raised portion anteriorly oriented on the low profile patient specific cutting block such that the paddle does not touch the tibia on an anterior proximal surface and does touch the tibia on a posterior proximal surface. 
         [0009]    Further features, aspects, and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
           [0011]      FIG. 1  is a view of a knee joint with a femoral patient specific cutting block and a tibial patient specific block; 
           [0012]      FIG. 2  is an anterior view of a femoral patient specific cutting block according to an aspect of the invention; 
           [0013]      FIG. 3  is a proximal posterior view of a femoral patient cutting specific block according to an aspect of the invention; 
           [0014]      FIG. 4  is an anterior view of a tibial patient specific cutting block according to an aspect of the invention; and 
           [0015]      FIG. 5  is a distal posterior view of a tibial patient specific cutting block according to an aspect of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0016]    Referring to the accompanying drawings in which like reference numbers indicate like elements,  FIG. 1  illustrates a view of a knee joint with a femoral patient specific cutting block  10  and a tibial patient specific block  14 . The femoral patient specific cutting block  10  is attached to a femur  12 . The tibial patient specific cutting block  14  is attached to a tibia  16 . The patient specific cutting blocks  10  and  14  are configured to engage portions of bone and cartilage on the femur  12  and tibia  16  to align cutting surfaces within the patient specific cutting blocks so that a distal cut (on the femur) and a proximal cut (on the tibia) may be made without using either intramedullary or extramedullary guides. 
         [0017]    The femoral patient specific cutting block  10  includes an anterior femoral portion  20 , a medial femoral paddle  22  and a lateral femoral paddle  24 . These portions overlie portions of the anterior face, medial condyle and lateral condyle of the femur  12 , respectively. Because the portions  20 ,  22 , and  24  only overlie portions of the femur  12  instead of an entire conforming overlay of the end of the femur  12 , the patient specific cutting block  10  may have a lower profile, both in the medio-lateral and anterior-posterior direction. 
         [0018]    Pin holes  40  and  48 , guide bosses  42 , a mechanical axis index  44 , and a femoral cutting slot  46  are oriented on the exterior surface of the femoral patient specific cutting block  10 . The pin holes  40  and  48  are oriented to pin the cutting block  10  to the femur  12 . Guide bosses  42  are oriented in order to set pins for the other box cuts necessary to prepare the femur  12  for an implant. 
         [0019]    The pin holes  40  and  48  are oriented on the anterior face of the patient specific cutting block  10 . The pin holes  40  and  48  may have bosses (as shown with reference to pin holes  40 ) or may be flush with the surface (as shown with pin hole  48 ). The bosses may be used to direct the pins, for example, away from the edges of the bone. The low profile of the patient specific cutting block  10  would allow a pin hole without a boss to allow a pin to extend in a wide variety of angular directions. By extending bosses a thickness greater than the diameter of the aperture through the boss, the bosses may orient the pins by adding a guide through the patient specific cutting block  10  so that the pins are directed as they are impacted or drilled into the bone. 
         [0020]    The mechanical axis index  44  is oriented along the mechanical axis of the femur  12 . A cutting slot  46 , oriented relative to anatomical structures and defined by the surgeon, directs the distal cut for an implant. As will be described below, MR and X-rays of the patient are used to align the mechanical axis index  44  to the patient specific cutting block  10 . 
         [0021]    In addition to the MR and X-ray information, surgeon preferences are used to place the cutting slot  46  on the patient specific cutting block  10 . The cutting slot  46  may be oriented relative to the mechanical axis in a varus or valgus orientation (according to surgeon preference based upon the X-ray data). The flexion gap may be adjusted by adjusting the angle of the cutting slot  46  relative to the patient specific cutting block  10 . The depth of the resection cut is also determined by the placement of the cutting slot  46  and is determined from the distal point on the condyles. 
         [0022]    The guide bosses  42  are also placed on the patient specific cutting block  10  according to MR data, X-ray data and surgeon preference. The guide bosses  42  may set the rotation of the implant by adjusting the posterior bosses  42  relative to one another. The relative placement of the bosses  42  allows for pins to be placed so that the pins guide a further cutting guide over the distal cut of the femur in order to make the anterior and posterior cuts and any chamfer cuts required by the bone interfacing surfaces of the implant. Internal/external rotation is directed by moving the depth of one of the posterior bosses relative to the other posterior boss. A-P placement of the implant is adjusted by moving both of the posterior bosses  42  together in the A-P direction. 
         [0023]    The tibial patient specific cutting block  14  includes an anterior femoral portion  300 , a medial femoral paddle  32  and a lateral femoral paddle  34 . These portions overlie portions of the anterior face, medial plateau and lateral plateau of the tibia  16 , respectively. Because the portions  20 ,  22 , and  24  only overlie portions of the tibia  16  instead of an entire conforming overlay of the end of the tibia  16 , the patient specific cutting block  14  may have a lower profile, both in the medio-lateral and anterior-posterior direction. 
         [0024]    Pin holes  50  and  52 , an M-L index  54  and a cutting slot  56  are oriented on the outer surface of the tibial patient specific cutting block  14 . The pin holes  50  and  52  may fix the patient specific cutting block  14  to the bone and may additionally align the pins relative to one another for further orientation, if necessary, in tibial preparation. 
         [0025]    The tibial cutting slot  56  is medialized relative to the anterior surface of the tibia  16  (i.e., the tibial cutting slot  56  is oriented on the medial half of the anterior side of the patient specific cutting block  14 ). The lateral paddle  34  may extend around the front of the tibial eminence extending posterior-laterally toward the lateral plateau. These features may allow the guide to be used in a MIS procedure, where lateral clearance is minimized by cutting the tibia from the medial half of the anterior face of the tibia while minimizing the medial approach to the tibia, which would involve additional soft tissue issues. Thus, the medialized and rotated cutting slot  56  is oriented for clearance and accessibility even for an MIS approach. 
         [0026]    Turing now to  FIGS. 2 and 3 .  FIG. 2  is an anterior view of a femoral patient specific cutting block according to an aspect of the invention.  FIG. 3  is a proximal posterior view of a femoral patient cutting specific block according to an aspect of the invention. In addition to the features described above, the patient specific cutting block  10  may also include an epicondylar index  68 . The epicondylar index  68  may be used as a visual “feel good” for the rotation of the holes and the A-P placement of the holes, similar to the purpose of the mechanical axis index described above. 
         [0027]    In  FIG. 3 , the bone interfacing surfaces  80 ,  82 ,  84  and  86  are shown. The anterior bone interfacing portion overlies a portion of the anterior surface of cartilage and bone. The medial bone interfacing portion  82 , the lateral bone interfacing portion  84  and the intracondylar bone interfacing portion  86  overlie the medial, lateral and intracondylar notch portions of the condyles, respectively. The bone interfacing portions  80 ,  82  and  84  align to the anterior and distal faces of the femur while the intracondylar bone interfacing portion  86  orients the block medio-laterally. By using relatively small portions of the surfaces, the profile of the patient specific cutting block  10  may be lowered. Additionally, the fit may be better as smaller portions may result in fewer osteotomes on the bone surface (which may cause poor fit of the patient specific cutting block to the bone. The paddles  22  and  24  may also be relatively thin posteriorly. This further minimizes the profile of the patient specific cutting block. 
         [0028]    The cutting slot  46  may be formed through the bone interfacing portions of the patient specific cutting block or may be recessed from the surface. The thickness of the cutting slot helps to direct the orientation of the cutting tool as the cutting tool advances through the cutting slot  46 . As previously discussed, the relative angle of the cutting slot  46  to the patient specific cutting block  10  (and particularly to the bone interfacing portions) orients the flexion gap while the translation of the cutting slot  46  relative to the patient specific cutting block  10  sets the resection depth. 
         [0029]    Turing now to  FIGS. 4 and 5 ,  FIG. 4  is an anterior view of a tibial patient specific cutting block according to an aspect of the invention.  FIG. 5  is a distal posterior view of a tibial patient specific cutting block according to an aspect of the invention. In addition to the features described above, the tibial patient specific cutting block also may include a posterior chamfer  96  and a planar proximal surface  100 . The posterior chamfer  96  allows for the tibial patient specific cutting block to be positioned posteriorly without distracting the soft tissue around the knee more than necessary. Similar to other features, this feature helps the overall profile of the implant. 
         [0030]    The planar proximal surface  100  may match the distal femur resection plane from the femoral patient specific cutting block. This feature may allow intraoperative flexion/extension testing when the tibial patient specific cutting block is secured to the tibia. 
         [0031]    Bone interfacing surfaces  90 ,  92 , and  94  are shown in  FIG. 5 . The anterior bone interfacing portion  90  overlies a portion of the anterior surface of cartilage and bone. The medial bone interfacing portion  92  and the lateral bone interfacing portion  84  overlie the medial and lateral portions of the tibia, respectively. The bone interfacing portions  92  and  94  align to the proximal faces of the tibial plateaus (thus orienting the patient specific cutting block proximally) while the anterior bone interfacing portion  90  orients the block medio-laterally and in the AP direction. By using relatively small portions of the surfaces, the profile of the patient specific cutting block may be lowered. Additionally, the fit may be better as smaller portions may result in fewer osteotomes on the bone surface (which may cause poor fit of the patient specific cutting block to the bone. The paddles  32  and  34  may also be relatively thin posteriorly and may be elevated from the tibial plateau surface anteriorly to avoid poor placement. This further minimizes the profile of the patient specific cutting block. 
         [0032]    The cutting slot  56  may be formed through the bone interfacing portions of the patient specific cutting block or may be recessed from the surface. If the cutting slot  56  is recessed from the surface, then impingement of the block on bone may be minimized, again increasing the fit of the patient specific cutting block to the bone. The thickness of the cutting slot helps to direct the orientation of the cutting tool as the cutting tool advances through the cutting slot  56 . As previously discussed, the relative angle of the cutting slot  56  to the patient specific cutting block  10  (and particularly to the bone interfacing portions) orients the flexion gap while the translation of the cutting slot  46  relative to the patient specific cutting block  10  sets the resection depth. 
         [0033]    The MR data and X-ray data may be taken by known means. As an example, the following protocols may be used. Different MR protocols may be executed on different patients. To minimize scan time, a fast spin echo imaging technique may be used for any protocol, essentially producing a proton density (PD) weighted image. One protocol may use the spoiled gradient echo technique with a low repetition time (TR) and low echo time (TE) and a flip angle of 30 degrees combined with a fat saturation technique. A second protocol and third protocol may use a high TR and a low TE combined with a fat saturation technique. The only difference between the second protocol and third protocol is that the second protocol has lower TE than the third protocol, which in turn offers more T 1  and less PD properties. The increased T 1  relaxation time may help to increase the image contrast within the different tissues in the MR image. 
         [0034]    Bone models of the femur and tibia may be extracted from the MR images and appropriate anatomic reference landmarks may be identified. Full leg x-rays may be used to determine the mechanical axis alignment. Femoral and tibial cutting blocks may then be designed through computer aided design (CAD) modeling such that they conform to the bone models on one side for proper seating and have cutting slots at the appropriate resection depth and angle specific to the patient. The cutting blocks may be made from medical grade Nylon 12 using the EOSint P system. Since the surface geometries of these blocks are based on the patient&#39;s MR data set, clean data (properly differentiating between bone and cartilage and soft tissue) should be used to ensure the fit and functionality of the blocks. 
         [0035]    In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. 
         [0036]    The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. 
         [0037]    As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.