the following description of the preferred embodiments concerning a unicondylar femoral prosthesis and instruments are merely exemplary in nature and are not intended to limit the invention or its application or uses . moreover , while the present invention is described in detail below with respect to a right medial unicondylar prosthesis , it will be appreciated by those skilled in the art that the present invention may be applied to various other types of knee joint prostheses such as a total knee joint prosthesis . referring to fig1 and 2 , a unicondylar knee prosthesis implanted using the instruments and method of the invention is shown . a femur 10 is shown in combination with a tibia 12 . femur 10 has a femoral component 14 implanted therein . tibia 12 has a tibial component 16 implanted therein . while a right medial surgery is shown , it is known that the method will apply to both medial and lateral components , as well as left and right knees . with reference to fig3 - 6 , tibial component 16 includes a tibial tray 18 and a tibial insert 20 . tibial component 16 is designed to resurface the proximal end of the tibia to cooperate with a unicondylar femoral component 14 . tibial tray 18 includes a generally “ d ” shaped body 22 having a pair of posts 24 extending orthogonally therefrom . tibial tray 18 also includes a tab 26 extending from body 22 in the same direction as posts 24 . body 22 includes a snap groove 28 configured to receive tibial insert 20 . it should be appreciated that the two piece tibial component described is merely exemplary and that singular or other multi - piece designs are contemplated for use with the femoral component of the present invention . tibial insert 20 may be constructed from any suitable bearing material such as ultra high molecular weight polyethylene ( uhmwpe ). tibial insert 20 includes a generally d - shaped body 30 having a wear surface 32 . a pair of snap tabs 34 extend from the opposing surface of body 30 . it should be appreciated that snap tabs 34 of tibial insert 20 engage snap groove 28 of tibial tray 18 once tibial component 16 is assembled . in this manner , a modular unicondylar tibial component may be implanted and subsequently reconstructed by removing only the wearable tibial insert 20 . accordingly , the tibial tray to tibia interconnection need not be disturbed . with reference to fig7 - 9 , femoral component 14 is depicted in detail . femoral component 14 is designed to resurface the distal and posterior portions of one of the femoral condyles of femur 10 . femoral component 14 has an articulating surface 36 and a bone mating surface 38 . articulating surface 36 in the preferred embodiment includes a pair of radial surfaces 40 and 42 that are tangent to one another forming a smooth flowing surface when viewed from the lateral direction . radial surface 42 terminates at an anterior run - out 43 of femoral component 14 . in the other plane ( fig9 ), the distal portion of femoral component 14 includes a radius 44 extending from anterior run - out 43 to a posterior portion 45 that is larger than and blends with a radius 46 that is present on posterior portion 45 . this allows for more movement between femur 10 and tibia 12 when in flexion than in extension , similar to the natural knee . bone mating surface 38 is comprised of a distal surface 48 , a posterior surface 50 , and a posterior chamfered surface 52 . extending from bone mating surface 38 is a first peg 54 and a second peg 56 . pegs 54 and 56 aid in alignment and stability . preferably , a rib 58 interconnects first peg 54 and second peg 56 to resist rotation of femoral component 14 after implantation . first peg 54 is positioned a pre - determined distance 60 from anterior run - out 43 . in addition , second peg 56 is positioned a pre - determined distance 62 from posterior portion 45 . as will be described in greater detail hereinafter , distances 60 and 62 remain constant as femoral component size changes . a surgeon has the option of choosing anterior or posterior referencing while using a common femoral component . accordingly , as the size of the femoral component increases , a distance 64 between first peg 54 and second peg 56 increases in order to maintain distances 60 and 62 constant . it should be appreciated that the femoral component previously described as having both first and second pegs is merely exemplary . for example , another embodiment of a femoral component constructed in accordance with the teachings of the present invention includes a single peg positioned predetermined distance 60 from anterior run out 43 . similarly , another femoral component embodiment exists having a single peg positioned predetermined distance 62 from posterior portion 45 . therefore , alternate femoral component embodiments may be constructed by simply removing one of first peg 54 or second peg 56 . another embodiment of the present invention positions first peg 54 a pre - determined distance 65 from chamfer 52 . in this manner , the size and location of chamfer 52 are also standardized . one skilled in the art should appreciate that first peg 54 may also be positioned a constant distance from posterior surface 50 without departing from the scope of the present invention . the method of implantation for the unicondylar knee prosthesis will now be described including a description of the instruments used for the method . with reference to fig1 - 14 , the knee is articulated in flexion and an incision is made to open the knee as is known by those skilled in the art . after exposure of the joint , tibia 12 is resected using a tibial cutting guide ( not shown ). a tibial spacer 66 is inserted at the tibial resection . at this time , the surgeon determines the proper joint tension by articulating the joint through flexion and extension with spacer 66 in place . if the joint is too lax , a spacer having a greater thickness is inserted . conversely , if the joint tension were too tight , a spacer having a lesser thickness would be inserted . once the proper joint tension is set , the corresponding spacer remains positioned between the posterior distal femur and the tibial resection . alternatively , the joint tension may be set using a tensioning device . the tensioning device ( not shown ) loads and positions femur 10 relative to tibia 12 to properly define the distance between resected tibia 12 and femur 10 without the use of spacer 66 . at this time , the surgeon must decide which referencing method is best suited for the patient . the anterior referencing method will be described first . femur 10 is sized using a sizing guide 68 . sizing guide 68 includes a body 70 having a first portion 72 and a second portion 74 . first portion 72 includes a peg aperture 76 and a pin aperture 78 . second portion 74 extends anterior of first portion 72 . second portion 74 includes a first face 80 and a second face 82 generally converging at a point 84 . sizing guide 68 also includes an indexable probe 86 . a sizing scale 88 is imprinted on an exterior surface of indexable probe 86 . indexable probe 86 has a first end 90 disposed within a probe aperture 92 located within first portion 72 . indexable probe 86 also includes a second end 94 . to determine the proper femoral component size to be implanted , sizing guide 68 is placed over a distal end of femur 10 as shown in fig1 . body 70 is aligned such that first face 80 contacts anterior reference point 96 at the edge of the anterior run - out . it should also be appreciated that sizing guide 68 is placed at a slight angle in relation to tibial spacer 66 along the line formed by the anterior and posterior portions of distal femur 10 . once aligned , sizing guide 68 is pinned in place while a first peg aperture 98 is drilled . preferably , first pin apertures 100 are machined using relatively small , headless drill bits that are left in place to align sizing guide 68 and a resection guide as will described in greater detail hereinafter . once sizing guide 68 has been aligned and pinned as previously discussed , indexable probe 86 is translated until second end 94 contacts tibial spacer 66 . the size is determined by noting where sizing scale 88 meets first portion 72 of body 70 . sizing guide 68 is removed . with reference to fig1 and 16 , an appropriately sized resection guide 102 is mounted to femur 10 . posterior resection guide 102 includes a generally rectangular body 104 having a peg 106 extending therefrom . body 104 also includes at least one pin aperture 108 used to align resection guide 102 relative to femur 10 . as mentioned earlier , in the preferred technique , the surgeon leaves the headless drill bit used to create first pin aperture 100 therewithin . accordingly , proper alignment of posterior resection guide 102 is guaranteed by disposing peg 106 within first peg aperture 98 while disposing the headless drill bit within pin aperture 108 . posterior resection guide 102 includes a slot 110 used to guide the saw blade when making the posterior chamfer cut . body 104 includes a posterior surface 114 used to guide a saw blade when making the posterior cut . the posterior chamfer cut is designed to correspond to bone mating surface 52 . the posterior cut acts in conjunction with bone mating surface 50 . posterior resection guide 102 may also include a second drill guide used to guide a drill for forming a second peg aperture ( not shown ) if desired . alternatively , a separate drill guide may be introduced to align a drill bit when forming the second peg aperture . the posterior resection guide and headless drill bit are removed to perform a final bone removal step . as shown in fig1 and 18 , a distal portion 118 is removed to correspond to distal surface 48 of femoral component 14 . if the specific femoral component chosen includes rib 58 , an additional cut is made in the distal femur to allow complete insertion of rib 58 within the cut . to complete the unicondylar implantation process , femoral component 14 is cemented to femur 10 . similarly , tibial component 16 is cemented to tibia 12 using a conventional cementing technique that is well known to those skilled in the art . the wound is then closed and post - operative care is given . as mentioned earlier , the present invention is directed to both anterior and posterior referencing methods and instruments . if the surgeon decides after initially opening the joint , that a posterior referencing method is more desirable than an anterior referencing method , a different procedure and set of instruments are used as described below . as shown in fig1 and 20 , the posterior referencing method begins by making a tibial resection as previously described in the anterior referencing method section . next , a posterior resection guide 120 is coupled to femur 10 using pins 122 . pins 122 , are preferably headless drill bits temporarily left in place to provide alignment for posterior resection guide 120 . posterior resection guide 120 includes a body 124 having a contact face 126 in contact with distal end of femur 10 . body 124 also includes a first slot 128 and a second slot 130 for guiding a saw blade . first slot 128 is used to create a posterior cut . second slot 130 is useful when making a posterior chamfer cut . a leg 132 extends from guide 120 and includes a contacting surface 134 in contact with posterior femur 10 . posterior resection guide 120 also includes a first drill guide 136 for guiding a drill to create a first peg aperture 138 . after the posterior cut , posterior chamfer cut and first peg aperture are formed , posterior resection guide 120 is removed and a sizing guide 140 is placed on the distal femur as depicted in fig2 and 22 . sizing guide 140 includes a body 142 and an extending leg 144 . body 142 includes a face 146 in contact with the distal surface of the femur . leg 144 includes a face 148 in contact with and positioned adjacent to the posterior cut . an alignment peg 150 extends from body 142 and is disposed within first peg aperture 138 . an indexable probe 152 includes a shaft 154 slidably mounted within body 142 . shaft 154 has a graduated sizing scale 156 imprinted thereon . indexable probe 152 also includes a finger 158 extending from shaft 154 . finger 158 includes a contact surface 160 . to determine the correct femoral component size , indexable probe 152 is translated until contact surface 160 contacts anterior run - out 43 of femur 10 . at this time , the surgeon reads graduated sizing scale 156 to determine the proper femoral component size . after removal of sizing guide 140 , a drill guide ( not shown ) is coupled to femur 10 to guide a bit to drill a second peg aperture if required . lastly , distal bone portion 118 ( fig1 ) is removed as previously discussed . both the femoral and tibial components are implanted and the wound is closed .
a set of femoral orthopedic devices includes a first component having a first size and a second component having a second size . the first component includes a peg positioned a predetermined distance from a first reference point the second component includes a peg positioned said predetermined distance from said first reference point . the method calls for referencing a femoral condyle at a first reference point , locating a peg aperture a predetermined distance from the first reference point , selecting a sized femoral component , and implanting the femoral component . the size of the femoral component is defined by a distance from the peg to a second reference point .