Abstract:
A method for performing an open wedge, high tibial osteotomy, the method comprising:
       identifying a cutting plane through the tibia and a boundary line for terminating a cut made along the cutting plane, wherein the boundary line is located within the tibia, parallel to the anterior-posterior slope of the tibia and parallel to the sagittal plane of the patient;   positioning a hollow cylinder adjacent to an exterior surface of the tibia and co-axial with the boundary line;   positioning a fluoroscope so that its field of view is parallel to the anterior-posterior slope of the tibia, parallel to the sagittal plane of the patient, and co-axial with the hollow cylinder;   imaging with the fluoroscope and observing the profile of the hollow cylinder so as to confirm that the hollow cylinder is aligned co-axial with the boundary line;   advancing an apex pin through the hollow cylinder and into the tibia along the boundary line so as to provide a positive stop at the boundary line for limiting cutting along the cutting plane;   cutting the tibia along the cutting plane, with the cut terminating at the boundary line;   moving the tibia on either side of the cut apart so as to form a wedge-like opening in the tibia; and   stabilizing the tibia.       
 
     A method for performing an open wedge, high tibial osteotomy, the method comprising:
       identifying a cutting plane through the tibia and a boundary line for terminating a cut made along the cutting plane, wherein the boundary line is located within the tibia, parallel to the anterior-posterior slope of the tibia and parallel to the sagittal plane of the patient;   positioning a hollow apex pin adjacent to an exterior surface of the tibia and co-axial with the boundary line;   positioning a fluoroscope so that its field of view is parallel to the anterior-posterior slope of the tibia, parallel to the sagittal plane of the patient, and co-axial with the hollow apex pin;   imaging with the fluoroscope and observing the profile of the hollow apex pin so as to confirm that the hollow apex pin is aligned co-axial with the boundary line;   advancing the hollow apex pin into the tibia along the boundary line so as to provide a positive stop at the boundary line for limiting cutting along the cutting plane;   cutting the tibia along the cutting plane, with the cut terminating at the boundary line;   moving the tibia on either side of the cut apart so as to form a wedge-like opening in the tibia; and   stabilizing the tibia.

Description:
REFERENCE TO PENDING PRIOR PATENT APPLICATIONS 
       [0001]    This patent application claims benefit of pending prior U.S. Provisional Patent Application Ser. No. 60/861,869, filed Nov. 30, 2006 by Kelly Ammann et al. for METHOD AND APPARATUS FOR PERFORMING AN OPEN WEDGE, HIGH TIBIAL OSTEOTOMY (Attorney&#39;s Docket No. NOVAK-20 PROV). 
         [0002]    The above-identified patent application is hereby incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0003]    This invention relates to surgical methods and apparatus in general, and more particularly to surgical methods and apparatus for performing open wedge, high tibial osteotomies of the knee. 
       BACKGROUND OF THE INVENTION 
       [0004]    Osteotomies of the knee are an important technique for treating knee osteoarthritis. In essence, knee osteotomies adjust the geometry of the knee joint so as to transfer weight bearing load from arthritic portions of the joint to relatively unaffected portions of the joint. 
         [0005]    Knee osteotomies are also an important technique for addressing abnormal knee geometries, e.g., due to birth defect, injury, etc. 
         [0006]    Most knee osteotomies are designed to modify the geometry of the tibia, so as to adjust the manner in which the load is transferred across the knee joint. 
         [0007]    There are essentially two ways in which to adjust the orientation of the tibia: (i) the closed wedge technique; and (ii) the open wedge technique. 
         [0008]    With the closed wedge technique, a wedge of bone is removed from the upper portion of the tibia, and then the tibia is manipulated so as to close the resulting gap, whereby to reorient the lower portion of the tibia relative to the tibial plateau and hence adjust the manner in which load is transferred from the femur to the tibia. 
         [0009]    With the open wedge technique, a cut is made into the upper portion of the tibia, the tibia is manipulated so as to open a wedge-like opening in the bone, and then the bone is secured in this position (e.g., by screwing metal plates to the bone or by inserting a wedge-shaped implant into the opening in the bone), whereby to reorient the lower portion of the tibia relative to the tibial plateau and hence adjust the manner in which load is transferred from the femur to the tibia. 
         [0010]    While both closed wedge osteotomies and open wedge osteotomies provide substantial benefits to the patient, they are procedurally challenging for the surgeon. Among other things, with respect to open wedge osteotomies, it can be difficult to create the wedge-like opening in the bone with the necessary precision and with a minimum of trauma to the surrounding tissue (e.g., the neurological and vascular structures at the back of the knee). Furthermore, with open wedge osteotomies, it can be difficult to stabilize the upper and lower portions of the tibia relative to one another and to maintain them in this position while healing occurs. 
         [0011]    The present invention is directed to open wedge, high tibial osteotomies of the knee, and is intended to provide increased precision and reduced trauma when creating the wedge-shaped opening in the bone, and to provide increased stability to the upper and lower portions of the tibia while healing occurs. 
       SUMMARY OF THE INVENTION 
       [0012]    The present invention comprises a novel method and apparatus for performing an open wedge, high tibial osteotomy. More particularly, the present invention comprises the provision and use of a novel method and apparatus for forming an appropriate osteotomy cut into the upper portion of the tibia, manipulating the tibia so as to open an appropriate wedge-like opening in the tibia, and then inserting an appropriate wedge-shaped implant into the wedge-like opening in the tibia, so as to stabilize the tibia with the desired orientation, whereby to reorient the lower portion of the tibia relative to the tibial plateau and hence adjust the manner in which load is transferred from the femur to the tibia. 
         [0013]    In one form of the present invention, there is provided apparatus for performing an open wedge, high tibial osteotomy, the apparatus comprising: 
         [0014]    a wedge-shaped implant for disposition in a wedge-shaped opening created in the tibia, wherein the wedge-shaped implant comprises at least one key for disposition in at least one corresponding keyhole formed in the tibia adjacent to the wedge-shaped opening created in the tibia, wherein each of the at least one keys comprises an interior bore for receiving a fixation screw; 
         [0015]    at least one fixation screw for disposition in the interior bore of the at least one key; 
         [0016]    and further wherein the apparatus is configured so that when the at least one fixation screw is received in the interior bore, the at least one fixation screw terminates within the bore. 
         [0017]    In another form of the present invention, there is provided a method for performing an open wedge, high tibial osteotomy, the method comprising: 
         [0018]    cutting the bone along a cutting plane, with the cut terminating at a boundary line, and forming at least one keyhole in the tibia adjacent to the cut; 
         [0019]    moving the bone on either side of the cut apart so as to form a wedge-like opening in the bone; 
         [0020]    positioning a wedge-shaped implant in the wedge-shaped opening created in the tibia, wherein the wedge-shaped implant comprises at least one key for disposition in at least one corresponding keyhole formed in the tibia adjacent to the wedge-shaped opening created in the tibia, wherein each of the at least one keys comprises an interior bore for receiving a fixation screw; and 
         [0021]    positioning at least one fixation screw in the interior bore of the at least one key; 
         [0022]    wherein the apparatus is configured so that when the at least one fixation screw is received in the interior bore, the at least one fixation screw terminates within the bore; 
         [0023]    and further wherein the at least one key is disposed in the at least one keyhole formed in the tibia. 
         [0024]    In still another form of the present invention, there is provided apparatus for performing an open wedge, high tibial osteotomy, the apparatus comprising: 
         [0025]    a wedge-shaped implant for disposition in a wedge-shaped opening created in the tibia, wherein the wedge-shaped implant comprises at least one key for disposition in at least one corresponding keyhole formed in the tibia adjacent to the wedge-shaped opening created in the tibia, wherein each of the at least one keys comprises an interior bore for receiving a fixation screw, and a counterbore communicating with the interior bore; 
         [0026]    at least one draw nut disposed in the counterbore, wherein the draw nut comprises an interior bore for receiving the fixation screw; and 
         [0027]    at least one fixation screw for disposition in the interior bore of the at least one key and the interior bore of the draw nut. 
         [0028]    In still yet another form of the present invention, there is provided a method for performing an open wedge, high tibial osteotomy, the method comprising: 
         [0029]    cutting the bone along a cutting plane, with the cut terminating at a boundary line, and forming at least one keyhole in the tibia adjacent to the cut; 
         [0030]    moving the bone on either side of the cut apart so as to form a wedge-like opening in the bone; and 
         [0031]    positioning a wedge-shaped implant in the wedge-shaped opening created in the tibia, wherein the wedge-shaped implant comprises:
       at least one key for disposition in at least one corresponding keyhole formed in the tibia adjacent to the wedge-shaped opening created in the tibia,       
 
         [0033]    wherein each of the at least one keys comprises an interior bore for receiving an interior fixation screw, and a counterbore communicating with the interior bore;
       at least one distal draw nut disposed in the counterbore, wherein the draw nut comprises an interior bore for receiving the distal end of a fixation screw; and positioning a fixation screw in the interior bore of the at least one key and the interior bore of the draw nut.       
 
         [0035]    In still yet another form of the present invention, there is provided apparatus for performing an open wedge, high tibial osteotomy, the apparatus comprising: 
         [0036]    a wedge-shaped implant for disposition in a wedge-shaped opening created in the tibia, wherein the wedge-shaped implant comprises at least one open key for disposition in the at least one corresponding keyhole formed in the tibia adjacent to the wedge-shaped opening created in the tibia, wherein each of the at least one open keys comprises opposed longitudinal edges, and further wherein each of the at least one keys comprises a threaded recess for receiving a fixation screw; and 
         [0037]    at least one fixation screw for disposition in the interior bore of the at least one key. 
         [0038]    In still yet another form of the present invention, there is provided a method for performing an open wedge, high tibial osteotomy, the method comprising: 
         [0039]    cutting the bone along a cutting plane, with the cut terminating at a boundary line, and forming at least one keyhole in the tibia adjacent to the; 
         [0040]    moving the bone on either side of the cut apart so as to form a wedge-like opening in the bone; and 
         [0041]    positioning a wedge-shaped implant in the wedge-shaped opening created in the tibia, wherein the wedge-shaped implant comprises: 
         [0042]    at least one open key for disposition in the at least one corresponding keyhole formed in the tibia adjacent to the wedge-shaped opening created in the tibia, wherein each of the at least one open keys comprises opposed longitudinal edges, and further wherein each of the at least one keys comprises a threaded recess for receiving a fixation screw, and 
         [0043]    at least one fixation screw for disposition in the interior bore of the at least one key; 
         [0044]    positioning at least one fixation screw in the interior bore of the at least one key; 
         [0045]    and further wherein the at least one key is disposed in the at least one keyhole formed in the tibia. 
         [0046]    In a further form of the present invention, there is provided a method for performing an open wedge, high tibial osteotomy, the method comprising: 
         [0047]    identifying a cutting plane through the tibia and a boundary line for terminating a cut made along the cutting plane, wherein the boundary line is located within the tibia, parallel to the anterior-posterior slope of the tibia and parallel to the sagittal plane of the patient; 
         [0048]    positioning a hollow cylinder adjacent to an exterior surface of the tibia and co-axial with the boundary line; 
         [0049]    positioning a fluoroscope so that its field of view is parallel to the anterior-posterior slope of the tibia, parallel to the sagittal plane of the patient, and co-axial with the hollow cylinder; 
         [0050]    imaging with the fluoroscope and observing the profile of the hollow cylinder so as to confirm that the hollow cylinder is aligned co-axial with the boundary line; 
         [0051]    advancing an apex pin through the hollow cylinder and into the tibia along the boundary line so as to provide a positive stop at the boundary line for limiting cutting along the cutting plane; 
         [0052]    cutting the tibia along the cutting plane, with the cut terminating at the boundary line; 
         [0053]    moving the tibia on either side of the cut apart so as to form a wedge-like opening in the tibia; and 
         [0054]    stabilizing the tibia. 
         [0055]    In a further form of the present invention, there is provided a method for performing an open wedge, high tibial osteotomy, the method comprising: 
         [0056]    identifying a cutting plane through the tibia and a boundary line for terminating a cut made along the cutting plane, wherein the boundary line is located within the tibia, parallel to the anterior-posterior slope of the tibia and parallel to the sagittal plane of the patient; 
         [0057]    positioning a hollow apex pin adjacent to an exterior surface of the tibia and co-axial with the boundary line; 
         [0058]    positioning a fluoroscope so that its field of view is parallel to the anterior-posterior slope of the tibia, parallel to the sagittal plane of the patient, and co-axial with the hollow apex pin; 
         [0059]    imaging with the fluoroscope and observing the profile of the hollow apex pin so as to confirm that the hollow apex pin is aligned co-axial with the boundary line; 
         [0060]    advancing the hollow apex pin into the tibia along the boundary line so as to provide a positive stop at the boundary line for limiting cutting along the cutting plane; 
         [0061]    cutting the tibia along the cutting plane, with the cut terminating at the boundary line; 
         [0062]    moving the tibia on either side of the cut apart so as to form a wedge-like opening in the tibia; and 
         [0063]    stabilizing the tibia. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0064]    These and other objects and features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the preferred embodiments of the invention, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts, and further wherein: 
           [0065]      FIGS. 1-3  are schematic views showing the formation of a wedge-like opening in the tibia for an open wedge, high tibial osteotomy, and positioning of a wedge-shaped implant into the wedge-like opening in the tibia; 
           [0066]      FIG. 3A  is a schematic view showing selected anatomical planes; 
           [0067]      FIGS. 4-9  show the relevant planar surfaces in an open wedge, high tibial osteotomy conducted in accordance with the present invention; and 
           [0068]      FIGS. 10-30  are schematic views showing a preferred method and apparatus for forming an appropriate osteotomy cut into the upper portion of the tibia, manipulating the tibia so as to open an appropriate wedge-like opening in the tibia, and then inserting an appropriate wedge-shaped implant into the wedge-like opening in the tibia. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Overview of an Open Wedge, High Tibial Osteotomy 
       [0069]    Looking first at  FIGS. 1-3 , there is shown a knee joint  5  upon which an open wedge osteotomy is to be performed. Knee joint  5  generally comprises a tibia  10  and a femur  15 . In accordance with the present invention, the open wedge osteotomy is effected by first making a cut  20  ( FIG. 1 ) into the upper tibia, and then manipulating the lower portion of the tibia so as to open a wedge-like opening  25  ( FIG. 2 ) in the bone, with the wedge-like opening  25  being configured so as to adjust the manner in which load is transferred from the femur to the tibia. In this respect, it should be appreciated that a variety of methods are well known in the art for determining the degree of correction necessary to correctly re-align the weight-bearing axis of the knee. Furthermore, cut  20  and wedge-like opening  25  may be formed in a variety of ways well known in the art. 
         [0070]    Among other things, the present invention provides a new and improved method and apparatus for forming cut  20  and wedge-like opening  25 , as will be discussed in detail below. 
         [0071]    Once the desired wedge-like opening  25  has been formed in tibia  10  so as to reconfigure tibia  10  to the desired geometry, the bone may be secured in position in a variety of ways well known in the art (e.g., by screwing metal plates to the bone or by inserting a wedge-shaped implant into the opening in the bone), whereby to adjust the manner in which the load is transferred from the femur to the tibia. By way of example,  FIG. 3  shows a wedge-shaped implant  27  inserted into the wedge-like opening  25  formed in the tibia, whereby to stabilize the tibia in its reconfigured geometry. 
         [0072]    Among other things, the present invention also provides a new and improved wedge-shaped implant, and an associated method and apparatus for deploying the same into the wedge-shaped opening in the tibia, as will be discussed in detail below. 
       Discussion of the Relevant Planar Surfaces in the Open Wedge, High Tibial Osteotomy of the Present Invention 
       [0073]    In order to appreciate certain aspects of the present invention, it is helpful to have a thorough understanding of the planar surfaces of the tibia that are relevant in performing the open wedge, high tibial osteotomy of the present invention. Thus, the following discussion presents a geometric description of the planar surfaces that are relevant to the open wedge, high tibial osteotomy of the present invention. For the purposes of the present discussion, it can sometimes be helpful to make reference to selected anatomical planes, e.g., the coronal plane, the sagittal plane and the transverse plane ( FIG. 3A ). 
         [0074]    Looking now at  FIGS. 1-4 , for the purposes of the present invention, the tibial plateau  30  may be described as a horizontal (or transverse) plane that extends along the top surface of tibia  10 . For reference, the sagittal plane  32  is also shown in  FIG. 4 . As seen in  FIG. 5 , tibial plateau  30  is also perpendicular to the frontal (or coronal) plane  40 . The anterior-posterior (A-P) slope is defined by an anterior-posterior (A-P) slope plane  45  that extends along the sloping top surface of the tibia, from anterior-to-posterior. Published research has demonstrated that the anterior-posterior (A-P) slope typically extends at an angle of approximately 7° to 11° to the tibial plateau  30 ; however, the specific angle may vary from individual to individual. 
         [0075]    Looking next at  FIG. 6 , for the open wedge, high tibial osteotomy of the present invention, it is generally desirable to stay about 2 cm inferior to the A-P slope plane  45 . This offset can be referred to as the A-P offset plane  50 . 
         [0076]    As seen in  FIG. 7 , the lateral aspect and cut depth of the cut  20  may be defined by a lateral aspect plane  55  and a cut depth plane  60 , with the cut depth being about 1 cm medial to the lateral aspect of the tibia. 
         [0077]    Looking next at  FIG. 8 , the osteotomy cut plane  65  (when seen from the direct frontal view of  FIG. 8 ) is formed by a plane that is rotated away from the A-P offset plane  50  through an axis which is formed by the intersection of the cut depth plane  60  and the A-P offset plane  50 . The degree of rotation is selected so as to be sufficient to place the entry of the osteotomy cut plane  65  at the medial neck  66  ( FIG. 8 ) of the tibia. It should be noted that the A-P offset plane  50  and the osteotomy cut plane  65  are “tilted” slightly from anterior to posterior (but not seen in the direct frontal view of  FIG. 8 ), since the A-P offset plane  50  and the osteotomy cut plane  65  follow the tilt of the A-P slope plane  45  ( FIG. 6 ). The intersection of the A-P offset plane  50  and the cut depth plane  60  forms an axis  70  which, in accordance with the present invention, defines the lateral limit of the osteotomy cut  20 . In other words, axis  70  defines a line through the tibia which is (i) parallel to A-P slope plane  45 , and (ii) contained within osteotomy cut plane  65 . Furthermore, in accordance with the present invention, axis  70  is used to define the lateral limit of the osteotomy cut  20  which is to be made into the tibia. 
         [0078]    As seen in  FIG. 9 , the direct view of the osteotomy cut plane is a direct view in line with the osteotomy. This view is tilted downward (e.g., at an angle of approximately 7°) from the direct frontal view. Again, the angle of tilt downward is equal to the A-P slope. In other words, with the present invention, the osteotomy cut plane  65  extends parallel to the A-P slope plane  45  (in the anterior-to-posterior direction, although not in the medial-to-lateral direction), and typically slopes downward (e.g., at an angle of approximately 7-11°) when viewed in the anterior-to-posterior direction. Furthermore, with the present invention, the axis  70  (which defines the lateral limit to the osteotomy cut  20 ) is contained within the osteotomy cut plane  65 . 
       Novel Method and Apparatus for Performing the Open Wedge, High Tibial Osteotomy of the Present Invention 
       [0079]    In one preferred embodiment of the present invention, there is provided a novel osteotomy system which comprises instrumentation for use in making precise and repeatable osteotomy cuts for use in open wedge, high tibial osteotomies, preferably using an antero-medial approach. The novel osteotomy system generally comprises a positioning guide  100  ( FIG. 16 ), a slope guide  200  ( FIG. 11 ), an apex pin  300  ( FIG. 16 ), a keyhole drill guide  400  ( FIG. 18 ), a posterior protector  500  ( FIG. 20 ), and a cutting guide  600  ( FIG. 20 ), as will hereinafter be discussed in further detail. 
         [0080]    The novel osteotomy system preferably also comprises a novel opening jack  700  ( FIG. 22 ) for opening the cut  20  in the tibia so as to form the wedge-like opening  25  in the tibia, as will also hereinafter be discussed in further detail. 
         [0081]    And the novel osteotomy system preferably also includes a novel implant  800  ( FIG. 24 ) for positioning in the wedge-like opening in the tibia so as to stabilize the tibia in its corrected configuration, as will also hereinafter be discussed in further detail. Furthermore, in some instances, it may be advantageous to use an implant trial base  830  ( FIGS. 27 and 28 ) in the course of preparing the tibia to receive implant  800 , and in order to confirm proper fit of implant  800  in its seat, as will also hereinafter be discussed in further detail. 
         [0082]    Thus, with the present invention, the surgeon first determines (using methods well known in the art) the degree of correction necessary to correctly re-align the weight-bearing axis of the knee; then the surgeon uses the system to make the appropriate cut  20  into the tibia; then the surgeon opens the bone cut to the extent required so as to form the desired wedge-like opening  25  in the tibia; and then the surgeon stabilizes the tibia in its corrected configuration (e.g., with the novel implant  800 ) while healing occurs. 
         [0083]    In a preferred form of the invention, the novel osteotomy system is configured so that: 
         [0084]    (i) the axis  70  formed at the lateral limit of the osteotomy cut  20  (which forms the lateral limit of the remaining bony hinge when the osteotomy cut  20  is thereafter opened) is parallel to the A-P tibial slope; 
         [0085]    (ii) the axis of the lateral limit of the bony hinge created by the osteotomy cut lies in a plane that is perpendicular to the frontal (i.e., coronal) plane; and 
         [0086]    (iii) when the osteotomy cut  20  is completed and the wedge is opened, the distal (i.e., lower) tibia is rotated about the bony hinge so as to substantially maintain, in anatomical alignment, the A-P slope and the frontal plane. 
         [0087]    In a preferred form of the invention, the novel osteotomy system is also configured so that: 
         [0088]    (iv) the osteotomy can be performed less invasively; and 
         [0089]    (v) the osteotomy can be performed with minimum incising of soft tissue such as the medial collateral ligament, the lateral collateral ligament, and the hamstrings. 
         [0090]    In a preferred form of the invention, the novel osteotomy system is also configured so that the delicate neurological and vascular tissues at the back of the knee are fully protected during the osteotomy procedure. 
         [0091]    In one preferred form of the present invention, the novel osteotomy system is constructed and used as follows. 
         [0092]    1. A vertical incision is first made on the antero-medial portion of the knee, approximately 1 cm from the medial edge of the patellar tendon, with the incision beginning approximately 2.5-3 cm superior to the anterior tibial tubercle, and extending approximately 6-10 cm in length. 
         [0093]    2. The soft tissue between the patellar tendon and the proximal surface of the tibia is then dissected in order to make a small tunnel-like opening beneath the patellar tendon, just above the patellar tendon&#39;s insertion to the proximal tibia. 
         [0094]    3. Looking now at  FIG. 10 , an assembly comprising positioning guide  100  ( FIGS. 10 and 16 ), slope guide  200  ( FIGS. 10 and 11 ) and an introducer  105  ( FIGS. 10 and 11 ) is advanced to the surgical site. Preferably the assembly of positioning guide  100 , slope guide  200  and introducer  105  is pre-assembled prior to opening the skin. This assembly is assembled by first mounting slope guide  200  to positioning guide  100 , and then mounting introducer  105  to both slope guide  200  and positioning guide  100  by using a screw  115  ( FIG. 10 ) which passes through slope guide  200  and is received in a threaded bore  120  ( FIG. 16 ) formed in positioning guide  100 . 
         [0095]    In one preferred form of the invention, slope guide  200  may comprise two separate elements which are secured together, e.g., a base  210  and a guide element  215  which are connected together by pins  205 , with base  210  being formed out of a radio-translucent material (e.g., plastic) and guide element  215  being formed out of a radio-opaque material (e.g., stainless steel), whereby guide element  215  will be visible under fluoroscopy and base  210  will be effectively invisible under fluoroscopy, as will hereinafter be discussed. In one preferred form of the invention, introducer  105  may comprise an arm  125  and a handle  130 . Arm  125  and handle  130  may be formed as two separate elements secured together, or arm  125  and handle  130  may be formed as a singular construction. 
         [0096]    4. Next, the foregoing assembly is maneuvered so that a tibial tubercle locating tab  135  ( FIGS. 10 and 16 ) of positioning guide  100  is inserted between the patellar tendon (not shown) and the tibia, and so that tibial tubercle locating tab  135  is set against the superior margin of the tibial tubercle. In this way, the tibial tubercle provides a rough alignment guide for aligning positioning guide  100  with the tibia. If desired, the underside of tibial tubercle locating tab  135  may include serrations, ridges, ribs, etc. ( FIG. 11E ) so as to facilitate stabilization of tibial tubercle locating tab  135  (and hence the instrumentation) against the tibia. 
         [0097]    5. Using a lateral fluoroscope view, taken from the medial side at the level of the tibial plateau, the assembly is then aligned so that the underside surface  220  ( FIG. 11 ) of guide element  215  of slope guide  200  is aligned with the top of the medial condyle  75  of the tibia. Alternatively, if the surgeon prefers to shift the osteotomy slightly distally on the tibia, the top edge  225  of guide element  215  of slope guide  200  can be aligned with medial condyle  75 , thereby offsetting the osteotomy by a fixed distance distally (e.g., 3 mm). 
         [0098]    By forming the guide element  215  of slope guide  200  out of a radio-opaque material and by forming the base  210  of slope guide  200  out of a radio-translucent material, base  210  will be effectively invisible under fluoroscopy and guide element  215  will stand out in clear relief against the bone. 
         [0099]    It should be noted that guide element  215  of slope guide  200  is preferably formed with a “Z shape” ( FIGS. 10 and 11A ) so as to provide additional functionality. More particularly, by forming guide element  215  with a “Z shape”, several significant advantages are obtained. First, this construction permits guide element  215  to wrap around the perimeter of the tibia. Second, the “Z shape” of guide element  215  also operates to indicate if the slope guide is not vertically aligned with the level of the fluoroscope. More particularly, if slope guide  200  is not vertically aligned with the level of the fluoroscope, the “Z shape” of guide element  215  will appear as a jagged or zig-zag shape on the fluoroscope ( FIG. 11B ). However, if guide element  215  is vertically aligned with the level of the fluoroscope, then the guide element will appear as a straight line on the fluoroscope ( FIGS. 11 and 11C ). This vertical alignment is important, since it enables alignment of slope guide  200  (and hence positioning guide  100 ) with the medial condyle, i.e., with the A-P slope plane. 
         [0100]    If desired, and looking now at  FIGS. 11D ,  11 E and  11 F, it is also possible to provide guide element  215  of slope guide  200  with an “L shape” configuration, rather than the “Z shape” configuration discussed above. Again, this construction provides several benefits. First, the “L shape” configuration permits guide element  215  to wrap around the perimeter of the tibia. Second, the “L shape” of guide element  215  also operates to indicate if the slope guide is not vertically aligned with the level of the fluoroscope. More particularly, if slope guide  200  is not vertically aligned with the level of the fluoroscope, the “L shape” of guide element  215  will appear as an “L shape” on the fluoroscope. However, if guide element  215  is vertically aligned with the level of the fluoroscope, then the guide element will appear as a straight line on the fluoroscope. Again, this vertical alignment is important, since it enables alignment of slope guide  200  (and hence positioning guide  100 ) with the medial condyle, i.e., with the A-P slope plane. 
         [0101]    7. The assembly is then maneuvered so that the medial locating pin  140  ( FIGS. 10 ,  11  and  16 ), preferably formed as a pin although it could also be formed as a tab, fin, etc., is located against the medial aspect  80  ( FIG. 16 ) of the tibia. As further adjustments in position are made, medial locating pin  140  is held in contact with the medial aspect of the tibia, thereby ensuring proper alignment of the instrumentation. Medial locating pin  140  references the medial aspect of the tibia, thus setting the distance from the medial aspect of the tibia to the apex pin  300  ( FIG. 10 ), as will hereinafter be discussed. This reference distance is used in conjunction with the sizing of the osteotomy implant  27  ( FIG. 3 ) so as to ensure a proper tibial reconstruction, e.g., the distance from the medial aspect of the tibia to the center of apex pin  300  may correspond to the distance from the medial aspect of the implant to the vertex of the wedge angle of the implant. 
         [0102]    In another form of the invention, the reference distance may be the distance from the medial aspect of the tibia to a neutral axis of rotation in the bony hinge, which could be estimated by calculation. In this case, the distance from the medial aspect of the tibia to the neutral axis of the bony hinge may correspond to the distance from the medial aspect of the implant to the vertex of the wedge angle of the implant. 
         [0103]    8. The assembly is then rotated around the primary tibial anatomical axis, by sliding introducer handle  130  in a side-to-side motion, such that the instrumentation is aligned perpendicular to the frontal (coronal) plane, i.e., so that introducer  105  and apex pin  300  (see below) will extend parallel to the sagittal plane of the patient. To this end, slope guide  200  is provided with a ball  230  and a groove  235  ( FIG. 10 ). With the fluoroscope arranged so that it is set in the lateral mode, with the image being taken from the medial side at the level of the tibial plateau (see  FIG. 11 ), the assembly is maneuvered until ball  230  is centered in groove  235  ( FIG. 11 ). When this occurs, the system is aligned with the sagittal plane (i.e., positioning guide  100  is disposed so that apex pin  300  will extend perpendicular to the frontal plane, as will hereinafter be discussed). 
         [0104]    9. Thus, when slope guide  200  is aligned with the medial condyle  75 , and when ball  230  is aligned with groove  235 , the system is aligned with (i) the A-P slope, and (ii) the sagittal plane. In other words, when slope guide  200  is aligned with medial condyle  75 , and when ball  230  is aligned with groove  235 , the instrumentation is positioned so that apex pin  300  (see below) is aligned with both the A-P slope and the sagittal plane, as will hereinafter be discussed. 
         [0105]    10. With all of the previous adjustments established, the positions of (i) tibial tubercle locating tab  135 , (ii) slope guide  200 , (iii) medial locating pin  140 , and (iv) the ball and groove sights  230 ,  235  are verified. With all positions confirmed, the frontal pin  145  ( FIG. 16 ) and the antero-medial (A-M) pin  150  ( FIG. 16 ) are inserted through positioning guide  100  and into the tibia. This secures positioning guide  100  to the tibia with the desired alignment. 
         [0106]    11. Next, apex pin  300  is inserted through positioning guide  100  and into the tibia. An apex aimer  155  ( FIGS. 14 and 16 ) serves to guide apex pin  300  into the tibia with the proper orientation, i.e., so that apex pin  300  is positioned along the axis  70  which is located at the lateral limit of the intended osteotomy cut, with apex pin  300  extending parallel to the A-P slope and perpendicular to the coronal plane, and being coplanar with cutting plane  65 . As a result, apex pin  300  can serve as the lateral stop for the osteotomy saw, whereby to clearly define the perimeter of the bony hinge, as will hereinafter be discussed. Apex pin  300  may be tapped or drilled into virgin bone, or it may be received in a pre-drilled hole (e.g., formed using apex aimer  155  and a standard surgical drill). A thumbscrew  160  ( FIG. 16 ) may be used to secure apex pin  300  to positioning guide  100 . 
         [0107]    Apex pin  300  may be generally cylindrical in shape and, if desired, apex pin  300  may be provided with a rounded, or “bullet-shaped”, nose  303 , or other tapered end configuration, so as to facilitate deployment into the tibia ( FIG. 11G ). 
         [0108]    Furthermore, if desired, apex pin  300  may have a flat  305  ( FIGS. 12 and 13 ) formed thereon to promote a complete cut-through of the osteotomy. Where apex pin  300  is provided with a distinct flat  305 , it is preferably provided with a counterpart flat  310  ( FIGS. 12 and 13 ), such that when apex pin  300  is positioned within the tibia and thumbscrew  160  is tightened against flat  310 , the aforementioned flat  305  will be aligned with the osteotomy cut, whereby to ensure that the osteotomy blade cuts completely through the bone to reach the apex pin. See  FIG. 13 . 
         [0109]    In another version of this construction (not shown), the flats  305 ,  310  may be diametrically opposed to one another, with thumbscrew  160  also being aligned with the osteotomy cut, whereby to make insertion of apex pin  300  less prone to error. 
         [0110]    And in another embodiment of the present invention, apex pin  300  may be necked down to a smaller diameter in the area of the osteotomy. As a result of this construction, a slight relief area exists to accommodate the saw blade so as to help promote a complete cut-through, but does not require any specific orientation of the apex pin with respect to the osteotomy plane, as is the case where the apex pin is formed with distinct flats. 
         [0111]    In one preferred form of the present invention, apex pin  300  is formed with a hollow configuration. By forming apex pin  300  with a hollow configuration, a fluoroscope may be used to confirm proper positioning of the apex pin with respect to the tibia. More particularly, by positioning the fluoroscope so that its field of view is parallel to the A-P slope of the tibia and parallel to the sagittal plane of the patient, and so that the fluoroscope is centered on the desired axis for the apex pin, the appearance of the hollow apex pin  300  as a perfect circle will ensure that the apex pin extends parallel to the A-P slope of the tibia and parallel to the sagittal plane of the patient (i.e., that the apex pin is properly positioned relative to the tibia). On the other hand, if the hollow apex pin  300  appears as an ovoid or other shape on the fluoroscope, the apex pin is not properly positioned relative to the tibia. 
         [0112]    Alternatively, the hollow apex aimer  155  may be used in an analogous fashion. 
         [0113]    Significantly, as the fluoroscope is used to “look down the throat” of hollow apex pin  300 , or hollow apex aimer  155 , the anticipated position of apex pin  300  can be seen relative to the top and sides of the tibia. Specifically, the anticipated position of axis  70  ( FIG. 8 ), which will sit at the lateral limit of the osteotomy cut, can be seen relative to the top and sides of the tibia. This can be extremely useful, since it is generally desired to position axis  70  at least as far from the tibial plateau as it is from the lateral cortex, in order to protect the articular surface when the osteotomy wedge is opened. By using the fluoroscope to look down axis  70 , such positioning of the apex pin can be ensured. 
         [0114]    And in another version of the present invention, apex aimer  155  may be used with a guide sleeve  161  ( FIG. 14 ) and a small-diameter guide pin  165  in order to first check the position of the small-diameter guide pin  165  relative to the desired axis for the apex pin, before thereafter deploying the larger-diameter apex pin  300 . In this respect, it will be appreciated that repositioning a misdirected small-diameter guide pin  165  is easier and less traumatic to the host bone than repositioning a misdirected larger-diameter apex pin  300 . 
         [0115]    As seen in  FIG. 15 , tibial tubercle locating tab  135  is preferably sized so that it also functions as an anterior protector, by providing a protective shield between the oscillating saw blade (to be used later in the procedure to form the osteotomy cut  20 ) and the anterior soft tissue structures, e.g., the patellar tendon. Thus, tibial tubercle locating tab  135  also functions as a patellar tendon protector. 
         [0116]    12. By virtue of the foregoing, it will be seen that apex pin  300  is positioned in the patient&#39;s tibia so that the apex pin extends (i) parallel to the A-P slope of the tibia, and (ii) parallel to the sagittal plane of the patient. As a result, when the osteotomy cut  20  is subsequently formed in the bone (see below) by cutting along the osteotomy cut plane until the apex pin is engaged by the bone saw, so that the perimeter of the bony hinge is defined by the location of the apex pin, the bony hinge will extend (i) parallel to the A-P slope of the tibia, and (ii) parallel to the sagittal plane of the patient. By ensuring that apex pin  300  is set in the aforementioned fashion, and hence ensuring that the bony hinge is so created, the final configuration of the tibia can be properly regulated when the bone cut is thereafter opened so as to form the open wedge osteotomy. 
         [0117]    13. Once apex pin  300  has been properly positioned in the bone, slope guide  200  and introducer  105  are removed, leaving positioning guide  100  properly aligned on, and secured to, the tibia, with apex pin  300  extending parallel to the A-P slope and parallel to the sagittal plane of the patient. See  FIG. 16 . 
         [0118]    The size of positioning guide  100  and the associated instrumentation are used to prepare the osteotomy to fit a particular implant sizing of small, medium or large. More particularly, the medial locating pin  140 , the size of positioning guide  100 , and apex pin  300  all combine to implement an implant sizing scheme of small, medium or large. As seen in  FIG. 17 , medial locating pin  140 , positioning guide  100  and apex pin  300  combine to provide a known, fixed distance from the medial aspect of the tibia to the apex pin. The size of the planned osteotomy is then set, allowing a specifically-sized implant (e.g., small, medium or large) to nominally fit between the medial aspect of the tibia and the apex pin. 
         [0119]    In the embodiment shown in  FIG. 17 , there is a known lateral offset between medial locating pin  140  and the entry point of the osteotomy. The implant size is reduced slightly to factor in this offset distance so as to yield a proper fit. 
         [0120]    In a more preferred construction, and looking now at  FIG. 17A , medial locating pin  140  is substantially aligned with the entry point of the planned osteotomy. 
         [0121]    14. Looking next at  FIG. 18 , keyhole drill guide  400  is then attached to positioning guide  100  by passing keyhole drill guide  400  over frontal pin  145  and apex aimer  155 . Keyhole drill guide  400  is then secured in this position with thumbscrew  405 . At this point, a distal pin  410  is inserted through keyhole drill guide  400  and into the tibia. Distal pin  410  further secures the instrumentation to the tibia. Next, a surface locator pin  415  is inserted through keyhole drill guide  400 . Surface locator pin  415  slides through keyhole drill guide  400  until the distal tip of surface locator pin  415  contacts the surface of the tibia. For the purposes of the present invention, this surface may be referred to as the “antero-medial surface” or the “A-M surface”, which is the anatomical surface of the tibia corresponding to the antero-medial approach of the osteotomy. When surface locator pin  415  contacts the A-M surface, the surface locator pin can act as an indicator as to the location of the A-M surface. This information can then be used to set the depth of the keyholes which are to be formed in the tibia (see below) for an improved implant fit. 
         [0122]    Next, an end mill  420  is inserted into the distal hole  425  (i.e., the bottom hole  425 ) of keyhole drill guide  400  and drilled until a stop flange  430  on end mill  420  contacts the proximal end of surface locator pin  415 , whereby to form the distal keyhole  85  ( FIG. 21 ) in the tibia. As end mill  420  forms distal keyhole  85 , the bone matter is preferably retained for later repacking at the osteotomy site. The drilling procedure is then repeated for the proximal hole  435  (i.e., the top hole  435 ), whereby to form the proximal keyhole  90  ( FIG. 21 ) in the tibia. Again, as end mill  420  forms proximal keyhole  90 , the bone matter is preferably retained for later repacking at the osteotomy site. Thus, keyholes  85  and  90  are formed so that one keyhole (i.e., proximal keyhole  90 ) sits above the other keyhole (i.e., distal keyhole  85 ). While it is possible to drill the proximal keyhole before the distal keyhole, it is generally preferable to drill the distal keyhole first. This is because drilling the distal keyhole before the proximal keyhole reduces the possibility that the sloping nature of the bone will cause a later-drilled keyhole to slip into an earlier-drilled keyhole. It should be appreciated that keyhole drill guide  400  is configured so that distal hole  425  and proximal hole  435  will overlap the osteotomy cutting plane  65  to some extent ( FIG. 21 ), so that when osteotomy cut  20  is thereafter formed and the tibia subsequently opened so as to create the wedge-like opening  25 , distal keyhole  85  and proximal keyhole  90  will overlap, and communicate with, the wedge-like opening  25  ( FIG. 29 ). 
         [0123]    15. Once the two implant keyholes have been drilled into the tibia, end mill  420  is removed, thumbscrew  405  is loosened, and then keyhole drill guide  400  is removed. 
         [0124]    16. Next, and looking now at  FIG. 19 , posterior protector  500  is attached to an introducer  505  with a thumbscrew  510 . Posterior protector  500  preferably comprises a far tip  515  and a curved portion  520 . Far tip  515  is preferably formed out of a flexible material so as to facilitate passage of the posterior protector along the surface of the posterior cortex and beneath overlying soft tissue. Curved portion  520  comprises a relatively stiff material which provides support for far tip  515 . Far tip  515  of posterior protector  500  is inserted into the incision and worked along the posterior cortex of the tibia until far tip  515  of posterior protector  500  substantially crosses the axis of, and in some cases actually engages, apex pin  300  ( FIG. 21 ). Once posterior protector  500  has been properly deployed, the thumbscrew  510  is unscrewed, and introducer handle  505  is removed, leaving posterior protector  500  extending along the posterior cortex of the tibia, interposed between the tibia and the delicate neurological and vascular structures located at the back of the knee. 
         [0125]    17. Looking next at  FIG. 20 , cutting guide  600  is then attached to positioning guide  100  and secured in place using cutting guide thumbscrew  605 . Cutting guide  600  comprises alignment rods  610  ( FIG. 21 ) that extend from the cutting guide into the pre-drilled keyholes  85 ,  90  ( FIG. 21 ) to assist with cutting alignment. More particularly, alignment rods  610  ensure proper alignment between cutting guide  600 , its cutting slot  615  ( FIGS. 20 and 21 ) and the pre-drilled keyholes  85 ,  90  previously formed in the tibia with end mill  420  and, ultimately, ensure the desired fit between the implant and the tibia. 
         [0126]    Then, posterior protector  500  is attached to cutting guide  600  using thumbscrew  620  ( FIG. 20 ). 
         [0127]    At this point, the instrumentation is ready to form the osteotomy cut, with cutting slot  615  of cutting guide  600  properly aligned with the osteotomy cut plane, apex pin  300  properly positioned at the far (lateral) limit of the osteotomy cut, tibial tubercle locating tab  135  forming a protective shield for the patellar tendon, and with posterior protector  500  forming a protective shield for the vascular and neurological structures at the back of the knee. In this respect it should be appreciated that cutting guide  600  is sized and shaped, and cutting slot  615  is positioned, so that, in addition to being aligned with the apex pin  300 , the entry point of the cutting plane into the tibia is located at an appropriate location on the tibia&#39;s medial neck  66 . 
         [0128]    18. Next, a saw blade  625  (attached to an oscillating saw, not shown) is inserted into cutting slot  615  of cutting guide  600 . The osteotomy cut is then made by plunging the oscillating saw blade through cutting slot  615  and into the bone ( FIG. 20 ). The saw blade is used to cut completely through the medial and posterior cortices. The saw is operated until saw blade  625  contacts posterior protector  500  and apex pin  300 . As the saw blade cuts through the tibia, it is constrained by cutting slot  615 , apex pin  300  and posterior protector  500 , so that the saw blade may only cut bone along the osteotomy plane, up to (but not beyond) the desired location of the bony hinge, and does not cut soft tissue. During cutting, tibial tubercle locating tab  135  also ensures that the saw blade will not inadvertently cut the patellar tendon. 
         [0129]    After saw blade  625  forms the desired osteotomy cut  20  along the cutting plane, the saw blade is removed, and a hand osteotome (not shown) of the sort well know in the art is inserted through cutting slot  615  and into the osteotomy cut  20 , and then the cut is completed through the posterior cortical bone near apex pin  300  and posterior protector  500 . Then the hand osteotome is removed. 
         [0130]    At this point the osteotomy cut  20  has been completed, with the osteotomy cut terminating on the lateral side at apex pin  300 , so that the bony hinge is properly positioned at the desired location, i.e., parallel to the A-P slope and perpendicular to the coronal plane. 
         [0131]    Next, thumbscrew  620  is loosened and posterior protector  500  removed. Then thumbscrew  605  is loosened and cutting guide  600  is removed. 
         [0132]    At this point, the desired osteotomy cut  20  has been formed in the tibia, with keyholes  85  and  90  formed below and above, respectively, the osteotomy cut. 
         [0133]    In order to complete the procedure, the bone must now be opened so as to reconfigure the tibia to the desired geometry, and then the tibia stabilized with the desired configuration, e.g., by inserting a wedge-shaped implant  27  into wedge-like opening  25 . 
         [0134]    19. Looking next at  FIG. 22 , opening jack  700  is assembled onto the instrumentation by receiving frontal pin  145  in a hole  705  formed in jack arm  710 , by receiving apex aimer  155  in another hole  715  formed in jack arm  710  and jack arm  725 , and by receiving distal pin  410  in a slot  720  formed in jack arm  725 . Opening jack  700  is secured to positioning guide  100  with a thumbscrew  730 . 
         [0135]    Once opening jack  700  is in place, the jack is opened by rotating jack screw  735 . This causes jack arm  725  to pivot about apex aimer  155  so as to open the jack and thereby open the desired wedge-like opening  25  in the tibia. See  FIG. 23 . Preferably the patient&#39;s lower leg is manipulated as jack screw  735  is turned so as to assist in opening of the bone. As the wedge-like opening  25  is created in the bone, the tibia will be reoriented in a highly controlled manner, due to the fact that the bony hinge will be precisely positioned at axis  70  through the use of apex pin  300 , i.e., the bony hinge will extend parallel to the A-P slope and parallel to the sagittal plane. Furthermore, as the wedge-like opening  25  is created in the bone, the risk of bone cracking will be minimized, due to the fact that apex pin  300  forms an oversized hole  95  ( FIGS. 23A and 27 ) at the lateral end of the bone cut, i.e., “oversized” relative to the thickness of the osteotomy cut, whereby to reduce the occurrence of stress risers and the like as the bone is opened. 
         [0136]    The surgeon uses opening jack  700  to open the bone to the extent necessary to correctly re-align the weight-bearing axis of the knee. 
         [0137]    20. Then, with opening jack  700  still in place, an implant is positioned in the wedge-like opening  25 . 
         [0138]    If desired, the implant may be a “generic” implant such as the implant  27  shown in  FIG. 3 . 
         [0139]    More preferably, however, and looking now at  FIG. 24 , there is shown a wedge-shaped implant  800  formed in accordance with the present invention. Wedge-shaped implant  800  is characterized by a wedge-like side profile configured to match the geometry of the wedge-like opening  25  (i.e., to match the prescribed correction angle of the open wedge, high tibial osteotomy). Preferably, wedge-shaped implant  800  is also formed so as to have a U-shaped top profile, such that it can form a barrier about the perimeter of the wedge-like opening  25 , whereby to contain graft material (e.g., bone paste, bone cement, etc.) which may be positioned within the interior of the wedge-like opening  25 . By way of example but not limitation, the bone matter retained during the drilling of keyholes  85 ,  90  may be positioned within the interior of the wedge-like opening  25 . In one preferred form of the present invention, wedge-shaped implant  800  is formed so as to have an asymmetric configuration when viewed in a top view, so as to mate with the geometry of the tibia when the implant is positioned using an antero-medial approach. Wedge-shaped implant  800  is sized so as to match the known distance from the medial aspect of the tibia to the axis of the bony hinge, which is set by the position of apex pin  300 . Wedge-shaped implant  800  may be formed out of absorbable material or non-absorbable material, as desired. 
         [0140]    In one preferred form of the invention, and looking now at  FIGS. 25 and 26 , implant  800  preferably comprises a three-part assembly, comprising posterior graft containment arm (GCA)  805 , a base  810  and an anterior graft containment arm (GCA)  815 . The individual components of implant  800  may each be formed out of absorbable material and/or non-absorbable material, as desired. Furthermore, where one or more of the implant components is formed out of an absorbable material, the absorption characteristics of the material may vary as desired. By way of example but not limitation, base  810  may be formed out of a relatively slowly-absorbing material, while posterior graft containment arm (GCA)  805  and anterior graft containment arm (GCA)  815  may be formed out of a relatively faster-absorbing material. Base  810  preferably comprises a pair of keys  820 ,  825 . 
         [0141]    In one preferred form of the invention, implant  800  is formed so that posterior graft containment arm (GCA)  805  has a generally wedge-shaped profile including an engagement seat  826  comprising an alignment post  827 , and an introducer hole  828  opening on the antero-medial side of the component for engagement with introducer  845  (see below). A strengthening rib  829  is preferably provided as shown. Additionally, raised points or dimples  831  may be provided to help fix posterior graft containment arm (GCA)  805  to the bone. An alignment tab  832  is provided for extension into upper keyhole  90  ( FIG. 29 ) when posterior graft containment arm (GCA)  805  is positioned in the wedge-shaped opening  25 . 
         [0142]    And in one preferred form of the invention, base  805  is formed so that its keys  820 ,  825  each includes a bore  833 ,  834 , respectively, with the keys being slotted longitudinally so as to permit expansion of the keys when screws  865  are thereafter deployed in the bores, whereby to help lock the implant against the hard cortical bone of the tibia. External ribs  836  may be provided on the outer surfaces of keys  820 ,  825  so as to help fix keys  820 ,  825  in keyholes  85 ,  90 , respectively, when keys  820 ,  825  are expanded, as will hereafter be discussed in further detail. External ribs  836  may extend longitudinally or circumferentially. Keys  820 ,  825  protrude from the upper and lower surfaces of base implant  810 , and accommodate shear loads which may be imposed across the implant. Furthermore, expansion of keys  820 ,  825  creates an interference fit with the cortical bone of the tibia, and can help support tensile loads which may be imposed across the implant. An alignment mechanism (not shown) is provided for mating with alignment post  827  of posterior graft containment arm (GCA)  805 . 
         [0143]    The bores  833 ,  834  may be axially aligned with the longitudinal axes of keys  820 ,  825 , respectively. Alternatively, the bores  833 ,  834  may be arranged so that they diverge from one another, downwardly and upwardly, respectively, so as to direct screws  865  deeper into the adjacent portions of the tibia. 
         [0144]    Anterior graft containment arm (GCA)  815  also comprises a generally wedge-shaped profile, and an alignment tab  837  is provided for extension into lower keyhole  85  when GCA  815  is positioned in the wedge-shaped opening  25 . 
         [0145]    Implant  800  is preferably assembled in situ. 
         [0146]    In some instances, it may be advantageous to use an implant trial base  830  ( FIGS. 27 and 28 ) in the course of preparing the tibia to receive implant  800 , and in order to confirm proper fit of implant  800  in its seat. 
         [0147]    More particularly, a pre-assembled assembly comprising posterior graft containment arm (GCA)  805 , an implant trial base  830  and two guide sleeves  835 ,  840  are first inserted into wedge-like opening  25  in the bone using an introducer  845 . See  FIGS. 27 and 28 . 
         [0148]    Next, a drill sleeve  850  and a drill  855  are inserted into guide sleeve  840  ( FIG. 27 ). An upper hole is drilled into the tibia with the drill. The drilling procedure is then repeated for guide sleeve  835  so as to create a lower hole. Then drill sleeve  850  and drill  855  are removed from the surgical site. Next, a tap  860  is inserted into guide sleeve  840  and the upper hole is tapped. See  FIG. 28 . Then the tap is inserted into guide sleeve  835  and the lower hole is tapped. Then tap  860  is removed from the surgical site. 
         [0149]    21. Next, posterior graft containment arm (GCA)  805  is released from introducer  845 , and then introducer  845  and implant trial base  830  are removed. Posterior graft containment arm (GCA)  805  remains in wedge-like opening  25 . 
         [0150]    22. Then, if desired, graft material is packed into the osteotomy opening. 
         [0151]    23. Next, anterior graft containment arm (GCA)  815  is placed into the osteotomy opening and aligned with the prepared implant holes. See  FIG. 29 . If necessary, jack screw  735  is rotated as needed so as to facilitate insertion of anterior GCA  815 . At this point in the procedure, posterior graft containment arm (GCA)  805  and anterior graft containment arm (GCA)  815  are positioned in wedge-like opening  25 . 
         [0152]    24. Then implant base  810  is inserted into the prepared osteotomy, with keys  820  and  825  seated in tibial holes  85  and  90 , respectively, and with base  810  capturing posterior graft containment arm (GCA)  805  and anterior graft containment arm (GCA)  815  against the bony hinge. Keys  820  and  825 , seating in keyholes  85  and  90 , help ensure a precise fit of the implant to the bone. As this is done, jack screw  735  is adjusted as necessary so as to facilitate insertion of the base into the osteotomy. Then jack screw  735  is tightened slightly so as to ensure that the implant components are fully seated into the osteotomy wedge, with at least implant base  810 , and preferably also posterior graft containment arm (GCA)  805  and anterior graft containment arm (GCA)  815 , providing load bearing support to the tibia. Next, fixation screws  865  are inserted through keys  820  and  825  in base  810  and into the tapped holes in the tibia, and then tightened into place. As this occurs, fixation screws  865  expand keys  820 ,  825  so as to lock keys  820 ,  825  to the adjacent cortical bone, and fixation screws  865  extend into the tibia, so as to further lock the implant in position. See  FIG. 30 . Finally, opening jack  700 , positioning guide  100 , apex pin  300 , distal pin  410 , frontal pin  145  and A-M pin  150  are removed from the surgical site, and the incision closed. 
         [0153]    Providing implant  800  with two graft containment arms, e.g., posterior graft containment arm (GCA)  805  and anterior graft containment arm (GCA)  815 , is frequently preferred. However, in some circumstances, it may be desirable to omit one or both of posterior graft containment arm (GCA)  805  and anterior graft containment arm (GCA)  815 . Thus, in one preferred form of the invention, implant  800  comprises only base  810  and omits both posterior graft containment arm (GCA)  805  and anterior graft containment arm (GCA)  815 . 
         [0154]    Providing implant  800  with a pair of keys  820 ,  825  is generally preferred. However, in some circumstances, it may be desirable to omit one or the other of keys  820 ,  825 . Furthermore, in other circumstances, it may be desirable to provide more than two keys, e.g., to provide three keys. 
         [0155]    Furthermore, each of the keys  820 ,  825  may include more than one bore  833 ,  834 . Thus, for example, a key may include two bores, one angled leftwardly so as to direct a fixation screw leftwardly into the tibia to the left of the key, and/or one angled rightwardly so as to direct a fixation screw rightwardly into the tibia to the right of the key. 
         [0156]    The use of apex pin  300  is significant for a number of reasons: 
         [0157]    (1) the oversized, circular diameter hole  95  formed in the tibia by apex pin  300 , which forms the limit of bone cut  20 , effectively displaces the stress forces created at the edge of the bony hinge when the cut is opened to form the wedge-like opening  25 , thereby adding significantly to the effective strength of the bony hinge; 
         [0158]    (2) by using apex pin  300  to control the length of bone cut  20  (as measured from the medial aspect of the tibia to the apex pin), the seat for the implant is always of known size, thereby simplifying proper fitting of the implant to its seat in the bone, and also reducing the inventory of different-sized implants which must be on hand during the surgery; 
         [0159]    (3) with apex pin  300  in place, bone resecting tools can be used with increased confidence, without fear of inadvertently cutting into, or even through, the bony hinge; and 
         [0160]    (4) since apex pin  300  controls the depth of bone cut  20 , the implant can be reliably manufactured to appropriately address the required degree of correction needed to effect knee realignment (e.g., a 4 degree implant slope will always provide a 4 degree angle of correction). 
         [0161]    Furthermore, the provision of (i) apex pin  300 , posterior protector  500  and tibial tubercle locating tab  135  creates a “protection zone”, and (ii) cutting guide  600  creates a closely constrained cutting path for saw blade  625 , thereby together ensuring that only the desired portion of the bone is cut. Among other things, the provision of posterior protector  500  ensures that the delicate neurological and vascular tissues at the back of the knee are protected during cutting of the tibia. 
         [0162]    The provision of keyholes  85 ,  90  in the tibia, and the provision of keys  820 ,  825  in the implant, is significant inasmuch as they provide improved stabilization of the implant, particularly against rotational and shearing forces. This is particularly true inasmuch as keyholes  85 ,  90  extend through the hard cortical bone at the periphery of the tibia. 
       Anterio-Lateral Osteotomies 
       [0163]    In the foregoing description, the present invention is discussed in the context of performing an open wedge osteotomy using an antero-medial approach so as to effect a medial opening wedge osteotomy. Of course, it should be appreciated that the present invention may also be used in antero-lateral approaches so as to effect a lateral opening wedge osteotomy, or in other approaches which will be well known to those skilled in the art. 
       Modifications 
       [0164]    It will be understood that many changes in the details, materials, steps and arrangements of parts, which have been herein described and illustrated in order to explain the nature of the invention, may be made by those skilled in the art without departing from the principles and scope of the present invention.