AU2015202216B2 - Low Profile Patient Specific Cutting Blocks for a Knee Joint - Google Patents

Abstract

H:\jII\Interwoven\NRPortbI\DCC\JLL\7733374I.docx-29/04/2015 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 5 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 10 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. WO 200)9/111512 PCT/US2009/035935 [1/3] .. . . . .. I1. ...

Description

2015202216 20 Apr 2017

Low Profile Patient Specific Cutting Blocks for a Knee Joint Cross-Reference to Related Application [0001] This application is a divisional of Australian Patent Application

No. 2009221920, the entire content of which is incorporated herein by reference. 5 Field of the Invention [ΘΘ02] This invention relates generally to cutting blocks for bone resections at a knee joint and, more particularly, for cutting blocks designed for a patient’s specific bone and cartilage and further configured to a surgeon’s preferences. 10 Summary of the Invention [0003] It is in view of problems related to the field above that the present invention was developed.

[0004] In accordance with the present invention there is provided a low profile patient specific cutting block for a knee, comprising: a plurality of bone interfacing portions configured to 15 overlie portions of an end of a bone, the bone interfacing portions each having a surface generally a negative of the portion of the bone that the bone interfacing portion is configured to overlie, the bone interfacing portions being angularly offset from each other such that a first of the bone interfacing portions is configured to overlie an anterior portion of the bone extending in a first direction and a second of the bone interfacing portions is configured to overlie another portion of 20 the bone extending in a second direction generally perpendicular to the first direction; a cutting slot 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; and an anteriorly-facing exterior surface defining an index marking that provides an indication of an orientation of the cutting block relative to the bone, wherein the index marking comprises a 25 mechanical axis index positioned along a mid-portion of the cutting block and extending in a superior-inferior direction transverse to a longitudinal axis of the cutting slot to provide an - 1 - 2015202216 20 Apr 2017 indication of the orientation of the cutting block relative to the bone.

[0005] The low profile patient specific cutting block may further comprise bosses having a thickness and an aperture extending through the bosses, the aperture having a diameter, the bosses configured to direct a pin through the boss, the thickness of the boss being greater than 5 the diameter of the aperture.

[0006] The bone interfacing portions may further include medial and lateral paddles oriented medially and laterally at a posterior portion of the low profile patient specific cutting block. The paddles may each have a raised portion anteriorly oriented on the low profile patient specific cutting block such that the paddles do not touch the tibia on an anterior proximal surface 10 and do touch the tibia on a posterior proximal surface.

[0007] The low profile patient specific cutting block may be a tibial cutting block and the cutting slot may be medially offset relative to the anterior portion of the bone and oriented entirely along a medial half of the tibial cutting block and not extend along a lateral half of the tibial cutting block. 15 [0008] The index marking may comprises an M-L index axis positioned between a medial portion and a lateral portion of the cutting block. The low profile patient specific cutting block may be a femoral cutting block, wherein the mechanical axis index comprises a groove or score extending into the anteriorly-facing exterior surface of the femoral cutting block.

[0008A] The low profile patient specific cutting block may further comprise an 20 epicondylar index marking extending in a medial-lateral direction to provide an indication of a rotational position of the cutting block relative to the bone. The low profile patient specific cutting block may be a femoral cutting block wherein the epicondylar index marking comprises a groove or score extending into the anteriorly-facing exterior surface of the femoral cutting block.

[0008B] The index marking may comprise a groove or score extending into the 25 anteriorly-facing exterior surface of the cutting block.

[0OO8C] In accordance with the present invention there is also provided a low profile -2- 2015202216 20 Apr 2017 patient specific cutting block for a knee, comprising: a plurality of bone interfacing portions configured to overlie portions of an end of a bone, the bone interfacing portions each having a surface generally a negative of the portion of the bone that the bone interfacing portion is configured to overlie, the bone interfacing portions being angularly offset from each other such that 5 a first of the bone interfacing portions is configured to overlie an anterior portion of the bone extending in a first direction and a second of the bone interfacing portions is configured to overlie another portion of the bone extending in a second direction generally perpendicular to the first direction; a cutting slot oriented in a fixed position relative to the bone interfacing portions, such that the cutting slot directs a cutting tool, wherein the bone interfacing portions include an anterior 10 portion generally oriented in the middle of the low profile patient specific cutting block, and wherein the bone interfacing portions further include medial and lateral paddles oriented medially and laterally at a posterior portion of the low profile patient specific cutting block; and wherein the low profile patient specific cutting block is a tibial cutting block, and wherein the cutting slot is medially offset relative to the anterior portion of the bone and is oriented entirely along a medial 15 half of the tibial cutting block and does not extend along a lateral half of the tibial cutting block.

[0008D] The cutting block may include an anteriorly-facing exterior surface defining an M-L index axis marking positioned between the medial half and the lateral half of the tibial cutting block.

[00Θ8Ε] The cutting slot may open at a lateral opening defined by the tibial cutting 20 block, the lateral opening facing the lateral half of the tibial cutting block.

[0008F] The low profile patient specific cutting block may further comprise a paddle extending posteriolaterally from a middle portion of the patient specific cutting block, the paddle having 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 25 posterior proximal surface. -3- 2015202216 20 Apr 2017 [0008G] In accordance with the present invention there is also provided a low profile patient specific cutting block for a knee, comprising: a plurality of bone interfacing portions configured to overlie portions of an end of a bone, the bone interfacing portions each having a surface generally a negative of the portion of the bone that the bone interfacing portion is 5 configured to overlie, the bone interfacing portions being angularly offset from each other such that a first of the bone interfacing portions is configured to overlie an anterior portion of the bone extending in a first direction and a second of the bone interfacing portions is configured to overlie another portion of the bone extending in a second direction generally perpendicular to the first direction; a cutting slot oriented in a fixed position relative to the bone interfacing portions, such 10 that the cutting slot directs a cutting tool; and wherein the low profile patient specific cutting block is a tibial cutting block, and wherein the cutting slot is medially offset relative to the anterior portion of the bone and is oriented entirely along a medial half of the tibial cutting block and does not extend along a lateral half of the tibial cutting block.

[0008H] The cutting block may include an anteriorly-facing exterior surface defining an 15 M-L index axis marking positioned between the medial half and the lateral half of the tibial cutting block.

[00081] The bone interfacing portions may include an anterior portion generally oriented in the middle of the low profile patient specific cutting block, wherein the bone interfacing portions further include medial and lateral paddles oriented medially and laterally at a posterior portion of 20 the low profile patient specific cutting block.

[0008J] The cutting slot may open at a lateral opening defined by the tibial cutting block, the lateral opening facing the lateral half of the tibial cutting block.

[0008K] The low profile patient specific cutting block may further comprise a paddle extending posteriolaterally from a middle portion of the patient specific cutting block, the paddle 25 having 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 -3A- 2015202216 20 Apr 2017 posterior proximal surface.

[0008L] In accordance with the present invention there is also provided a low profile patient specific cutting block for a knee, comprising: a plurality of bone interfacing portions configured to overlie portions of an end of a bone, the bone interfacing portions each having a 5 surface generally a negative of the portion of the bone that the bone interfacing portion is configured to overlie, the bone interfacing portions being angularly offset from each other such that a first of the bone interfacing portions is configured to overlie an anterior portion of the bone extending in a first direction and a second of the bone interfacing portions is configured to overlie another portion of the bone extending in a second direction generally perpendicular to the first 10 direction; a cutting slot 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; and an anteriorly-facing exterior surface defining an index marking that provides an indication of an orientation of the cutting block relative to the bone, wherein the index marking comprises an M-L index axis positioned between a medial portion and a lateral portion of 15 the cutting block and extending in a superior-inferior direction transverse to a longitudinal axis of the cutting slot to provide an indication of the orientation of the cutting block relative to the bone.

[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. 20 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] Figure 1 is a view of a knee joint with a femoral patient specific cutting block 25 and a tibial patient specific block; [0012] Figure 2 is an anterior view of a femoral patient specific cutting block according -3B- 2015202216 20 Apr 2017 to an embodiment of the invention; [0Θ13] Figure 3 is a proximal posterior view of a femoral patient cutting specific block according to an embodiment of the invention; [0014] Figure 4 is an anterior view of a tibial patient specific cutting block according to 5 an embodiment of the invention; and [0015] Figure 5 is a distal posterior view of a tibial patient specific cutting block according to an embodiment of the invention.

Detailed Description of the Embodiments 10 [0016] Referring to the accompanying drawings in which like reference numbers indicate like elements, Figure 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 15 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 20 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. -3C- PCT/US2009/035935 WO 2009/111512 2015202216 29 Apr 2015 [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 5 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 10 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. 15 [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. 2 0 [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 -4- PCT/US2009/035935 WO 2009/111512 2015202216 29 Apr 2015 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 5 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 10 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, 15 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 2 0 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 25 tibial eminence extending posterior-laterally toward the lateral plateau. These features may -5- PCT/US2009/035935 WO 2009/111512 2015202216 29 Apr 2015 allow the guide to be used in a MTS 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. 5 [0026] Turing now to Figures 2 and 3, Figure 2 is an anterior view of a femoral patient specific cutting block according to an aspect of the invention. Figure 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 10 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 Figure 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 15 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 2 0 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 2 5 slot helps to direct the orientation of the cutting tool as the cutting tool advances through the -6- PCT/US2009/035935 WO 2009/111512 2015202216 29 Apr 2015 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. 5 [0029] Turing now to Figures 4 and 5, Figure 4 is an anterior view of a tibial patient specific cutting block according to an aspect of the invention. Figure 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 10 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 15 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 Figure 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 2 0 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 die AP direction. By using relatively small portions of die surfaces, die 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 2 5 of the patient specific cutting block to the bone. The paddles 32 and 34 may also be relatively -7- PCT/US2009/035935 WO 2009/111512 2015202216 29 Apr 2015 thin posteriorly and may be elevated from the tibial plateau surface anteriorly to avoid poor placement. This further minimizes the profde 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 5 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 10 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 15 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 2 0 second protocol has lower TE than the third protocol, which in turn offers more T1 and less PD properties. The increased T1 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 25 used to determine the mechanical axis alignment. Femoral and tibial cutting blocks may -8- 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’s 5 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. 2015202216 20 Apr 2017 [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 10 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 15 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.

[0038] Throughout this specification and the claims which follow, unless the context 20 requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. -9-

Claims (11)

1. THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

   1. A low profile patient specific cutting block for a knee, comprising: a. a plurality of bone interfacing portions configured to overlie portions of an end of a bone, the bone interfacing portions each having a surface generally a negative of the portion of the bone that the bone interfacing portion is configured to overlie, the bone interfacing portions being angularly offset from each other such that a first of the bone interfacing portions is configured to overlie an anterior portion of the bone extending in a first direction and a second of the bone interfacing portions is configured to overlie another portion of the bone extending in a second direction generally perpendicular to the first direction; and b. a cutting slot oriented in a fixed position relative to the bone interfacing portions, such that the cutting slot directs a cutting tool; and wherein the low profile patient specific cutting block is a tibial cutting block, and wherein the cutting slot is medially offset relative to the anterior portion of the bone and is oriented entirely along a medial half of the tibial cutting block and does not extend along a lateral half of the tibial cutting block.
2. 2. The low profile patient specific cutting block of claim 1, wherein the cutting block includes an anteriorly-facing exterior surface defining an M-L index axis marking positioned between the medial half and the lateral half of the tibial cutting block.
3. 3. The low profile patient specific cutting block of claim 1, wherein the bone interfacing portions include an anterior portion generally oriented in the middle of the low profile patient specific cutting block, and wherein the bone interfacing portions further include medial and lateral paddles oriented medially and laterally at a posterior portion of the low profile patient specific cutting block.
4. 4. The low profile patient specific cutting block of claim 1, wherein the cutting slot opens at a lateral opening defined by the tibial cutting block, the lateral opening facing the lateral half of the tibial cutting block.
5. 5. The low profile patient specific cutting block of claim 1, further comprising a paddle extending posteriolaterally from a middle portion of the patient specific cutting block, the paddle having 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.
6. 6. A low profile patient specific cutting block for a knee, comprising: a. a plurality of bone interfacing portions configured to overlie portions of an end of a bone, the bone interfacing portions each having a surface generally a negative of the portion of the bone that the bone interfacing portion is configured to overlie, the bone interfacing portions being angularly offset from each other such that a first of the bone interfacing portions is configured to overlie an anterior portion of the bone extending in a first direction and a second of the bone interfacing portions is configured to overlie another portion of the bone extending in a second direction generally perpendicular to the first direction; and b. a cutting slot oriented in a fixed position relative to the bone interfacing portions, such that the cutting slot directs a cutting tool, wherein the bone interfacing portions include an anterior portion generally oriented in the middle of the low profile patient specific cutting block, and wherein the bone interfacing portions further include medial and lateral paddles oriented medially and laterally at a posterior portion of the low profile patient specific cutting block; and wherein the low profile patient specific cutting block is a tibial cutting block, and wherein the cutting slot is medially offset relative to the anterior portion of the bone and is oriented entirely along a medial half of the tibial cutting block and does not extend along a lateral half of the tibial cutting block.
7. 7. The low profile patient specific cutting block of claim 6, wherein the cutting block includes an anteriorly-facing exterior surface defining an M-L index axis marking positioned between the medial half and the lateral half of the tibial cutting block.
8. 8. The low profile patient specific cutting block of claim 6, wherein the cutting slot opens at a lateral opening defined by the tibial cutting block, the lateral opening facing the lateral half of the tibial cutting block.
9. 9. The low profile patient specific cutting block of claim 6, further comprising a paddle extending posteriolaterally from a middle portion of the patient specific cutting block, the paddle having 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.
10. 10. The low profile patient specific cutting block of claim 9, wherein the low profile patient specific cutting block is a femoral cutting block, and wherein the mechanical axis index comprises a groove or score extending into the anteriorly-facing exterior surface of the femoral cutting block.
11. 11. A low profile patient specific cutting block for a knee, comprising: a. a plurality of bone interfacing portions configured to overlie portions of an end of a bone, the bone interfacing portions each having a surface generally a negative of the portion of the bone that the bone interfacing portion is configured to overlie, the bone interfacing portions being angularly offset from each other such that a first of the bone interfacing portions is configured to overlie an anterior portion of the bone extending in a first direction and a second of the bone interfacing portions is configured to overlie another portion of the bone extending in a second direction generally perpendicular to the first direction; and b. a cutting slot 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; and c. an anteriorly-facing exterior surface defining an index marking that provides an indication of an orientation of the cutting block relative to the bone, wherein the index marking comprises an M-L index axis positioned between a medial portion and a lateral portion of the cutting block and extending in a superior-inferior direction transverse to a longitudinal axis of the cutting slot to provide an indication of the orientation of the cutting block relative to the bone.