Patent Document

BACKGROUND OF THE INVENTION 
   This invention relates to surgical implants that are designed to replace meniscal tissue and cartilage in a mammalian joint, such as a knee joint and methods to implant the same. While a knee is the primary joint of concern, the invention applies to other body joints as the hip, shoulder, elbow, temporomandibular, sternoclavicular, zygapophyseal, and wrist. 
   Compared to the hip the knee has a much greater dependence on passive soft tissues (menisci, ligaments, and the joint capsule) for stability and function. Although the mechanics of the two joints are different, known hip and knee implants are very similar in design, both consisting of a semi-rigid on rigid (polyethylene on CoCr) bearing surface. In many prosthetic knee implants, function and mobility are impaired because rigid structures are used to replace the natural soft tissues. 
   Normal anatomical knees have two pliable, mobile menisci that function to absorb shock, distribute stress, increase joint congruity, increase contact area, guide arthrokinematics, help lubrication by maintaining a fluid-film bearing surface, and provide proprioceptive input, i.e., nerve impulse via its attachment to the joint capsule. Even under physiologic loading a natural knee with natural menisci will primarily distribute stresses through a fluid film, only 10% of a load is transmitted via a solid on solid contact. Due to the fluid film bearing surface contact wear is greatly reduced. In simple terms the menisci function to reduce joint stresses, decrease wear, and help guide normal kinematics. Without menisci, peak contact stresses in the knee increase by 235% or more and degenerative changes start to progress rapidly. At 0°, 30°, and 60° of flexion, natural knees with intact menisci have approximately 6 to 8 times the contact area of typical prosthetic knee implants many of which have a similar geometry to that of a natural knee without menisci. 
   Typical existing knee replacements lack the functional features normally provided by the menisci and the common polyethylene on metal such as cobalt chrome (CoCr) bearing interface lacks the wear-reducing fluid film bearing surface. By adding a well-designed meniscal substitute, many shortcomings of existing knee replacements can be addressed. In theory, prosthetic menisci could have the same impact on a prosthetic knee as natural menisci do for natural knees. 
   The prosthetic knee meniscus of the present invention has at least one and preferably two compliant prosthetic menisci (medial and lateral in the knee) that are attached to the joint capsule and meniscal horns in a similar fashion to the way a natural meniscus is attached to a natural knee. Like a natural meniscus, the meniscal knee implant of the present invention will be able to pivot and glide on a prosthetic tibial plateau. Arthrokinematic constraint comes from the meniscal attachments and will gently guide movements, providing a highly mobile but stable joint. Also through its attachments, the Anatomical Meniscal-Bearing Knee will provide proprioceptive input, giving the central nervous system feedback for refined motor control. 
   A preferred material for the meniscal implant of the present invention is polyurethane. Polyurethane can be made flexible so it can conform to the femoral and tibial components, thus giving the knee a large contact area throughout the entire range of motion. Such a polyurethane is described in U.S. Pat. No. 5,879,387. Alternatively, a hydrogel such as a poly(vinyl) alcohol can be used as a prosthetic meniscal implant. Such a hydrogel can be cross-linked to increase its strength and wear properties. Like cartilage, it imbibes aqueous fluids and generates a fluid-film bearing surface. 
   The flexible, pliable, gel-like nature of a synthetic hydrogel (when saturated with water) arises mainly from crosslinking attachments between non-parallel fibers in the gel. Depending on the specific polymeric structure that has been chosen, these crosslinking attachments between the long “backbone” chains in a polymer can be formed by covalent bonding, by hydrogen bonding or similar ionic attraction, or by entangling chains that have relatively long and/or “grabby” side-chains. 
   Regardless of which type of bonding or entangling method is used to bind the backbone chains together to form a hydrogel, the “coupling” points between molecular chains can usually be flexed, rotated, and stretched. 
   In addition, it should be recognized that the back-bone chains in hydrogel polymers are not straight; instead, because of various aspects of interatomic bonds, they are somewhat kinked, and can be stretched, in an elastic and springy manner, without breaking the bonds. 
   In a typical hydrogel, the fibers usually take up less than about 10% of the volume; indeed, many hydrogels contain less than 2% fiber volume, while interstitial spaces (i.e., the unoccupied spaces nestled among the three-dimensional network of fibers, which become filled with water when the gel is hydrated) usually make up at least 90 to 95% of the total volume. Accordingly, since the “coupling” point between any two polymeric backbone chains can be rotated and flexed, and since any polymeric backbone molecule can be stretched without breaking it, a supple and resilient gel-like mechanical structure results when a synthetic hydrogel polymer is hydrated. 
   Various methods are known for creating conventional polymeric hydrogels. A number of such methods involve mixing together and reacting precursor materials (monomers, etc.) while they are suspended in water or other solvent. This step (i.e., reacting two or more monomers while they are suspended in a solvent) gives a desired density and three-dimensional structure to the resulting polymerized strands or fibers. The resulting material is then frozen, to preserve the desired three-dimensional structure of the fibers. The ice (or other frozen solvent) is then vaporized and removed, without going through a liquid stage, by a sublimizing process (also called lyophilizing), using high vacuum and low temperature. After the solvent has been removed, any final steps (such as a final crosslinking reaction and/or rinsing or washing steps, to remove any unreacted monomers, crosslinking agents, quenching agents, etc.) are carried out. The polymer is then gradually warmed up to room temperature, and it is subsequently saturated with water, to form a completed hydrogel. 
   In the past, effort mainly has been placed on the development of meniscal replacement. In the attempt to repair or replace torn menisci, allographs, xenographs, and autographs have been implanted for over 20 years. Current focus has been on the development of collagen-matrix meniscal implants. However, these implants do not reproduce the mechanical properties of a normal meniscus. 
   As used herein, all references to “implants” or “implantation” (and all terms such as surgery, surgical, operation, etc.) refer to surgical or arthroscopic implantation of a reinforced hydrogel device, as disclosed herein, into a mammalian body or limb, such as in a human patient. Arthroscopic methods are regarded herein as a subset of surgical methods, and any reference to surgery, surgical, etc., includes arthroscopic methods and devices. The term “minimally invasive” is also used occasionally herein, even though it is imprecise; one should assume that any surgical operation will be done in a manner that is minimally invasive, in view of the needs of the patient and the goals of the surgeon. 
   Meniscal Tissues in Knees—Each knee joint of a human contains a “medial” meniscus, and a “lateral” meniscus. The lateral meniscus is located on the outer side of the leg, directly above the location where the upper end of the fibula bone is coupled to the tibia (“shinbone”). The medial meniscus is located on the inner side of the leg. 
   Each meniscus (also referred to, especially in older texts, as a “semilunar fibrocartilage”) has a wedged shape, somewhat comparable to a segment from an orange or other citric fruit, but with a substantially larger curvature and “arc.” The thickest region is around the periphery (which can also be called the circumference, the rim, and similar terms). When implanted into a knee, this peripheral rim normally will be anchored to the surrounding wall of a fibrous “capsule” which encloses the knee joint and holds in the synovial fluid, which lubricates the cartilage surfaces in the knee. The two ends of each semi-circular wedge are coupled, via thickened collagen structures called horns to the “spine” protrusions in the center of the tibial plateau. 
   The inner edge of a meniscus is the thinnest portion of the wedge; this edge can also be called the apex, the margin, and similar terms. It is not anchored; instead, as the person walks or runs, each meniscus in a knee is somewhat free to move, as it is squeezed between the tibial plateau (beneath it) and a femoral runner or condyle (above it). The bottom surface of each meniscus is relatively flat, so it can ride in a relatively stable manner on top of the tibial plateau. The top surface is concave, so it can provide better, more closely conforming support to the rounded edge of the femoral runner. Because of its shape, location, and ability to flex and move somewhat as it is pushed, each meniscus helps support and stabilize the outer edge of a femoral runner, as the femoral runner presses, slides, and “articulates” against the portion of the tibial plateau beneath it. 
   However, because all four of the menisci inside a person&#39;s knees are in high-stress locations, and are subjected to frequently-repeated combinations of compression and tension (and sometimes abrasion as well, especially in people suffering from arthritis or other forms of cartilage damage), meniscal damage often occurs in the knees of humans, and occasionally other large animals. 
   It should be noted that, in humans, meniscal-type tissues also exist in temporomandibular, sternoclavicular, zygapophyseal, and wrist joints. 
   Various efforts have been made, using prior technology, to repair or replace damaged meniscal tissue. However, because of the complex structures and anchoring involved, and because of the need to create and sustain extremely smooth and constantly wet surfaces on the inner portions of each meniscal wedge, prior methods of replacing or repairing damaged meniscal are not entirely adequate. 
   Many meniscal implants for the knee address the need for attachment to the surrounding soft tissue but they do not address the need to resurface the femoral and/or the tibial articulating surfaces. An example of this type of implant is described by Kenny U.S. Pat. No. 4,344,193 and Stone U.S. Pat. No. 5,007,934. 
   A free-floating cobalt chrome meniscal replacement has been designed to cover the tibial bearing surface. Because this implant is rigid and because it is disconnected from the soft tissues it lacks the ability to shock absorb and/or provide proprioceptive input. In fact, because it is approximately 10–20 times more rigid than bone it may actually cause concentrated loading, increased contacts stresses, and therefore accelerate degenerative joint changes. 
   Various unicondylar knee implants for joint replacement contain a meniscus-like component. The tibial-bearing component of the known Oxford Knee (British Patent Application No. 49794/74) contains a free-floating piece of polyethylene that can glide or spin on a polished, flat, tibial CoCr surface in the transverse plane. The tibial-bearing component in turn articulates with the CoCr femoral implant. Because the polyethylene meniscus is semi-rigid it has a limited capacity to absorb shock or conform to the femoral component. Because of its materials, the Oxford knee also lacks a wear-reducing fluid film bearing surface. 
   SUMMARY OF THE INVENTION 
   The anatomical meniscal-bearing knee implant of the present invention has one or more compliant prosthetic menisci that are attached to the joint capsule and meniscal horns in a similar fashion to the way a natural meniscus is attached to a natural knee. Like a natural meniscus, the meniscal implant will be able to pivot and glide on the prosthetic tibial plateau. Arthrokinematic constraint will come from the meniscal implant&#39;s attachments, which will gently guide movements, providing a highly mobile but stable joint. Also through its attachments, the Anatomical Meniscal-Bearing Knee will provide proprioceptive input, giving the central nervous system feedback for refined motor control. Like a natural knee with intact menisci, the outer border of the menisci implants will be mechanically linked to the tibial plateau via the coronary ligament, such as for example by the implant being attached such as by its being sutured directly to the joint capsule/coronary ligament or indirectly by attaching it to the remaining meniscal rim which is in turn attached to the coronary ligament. Tendon slips from the quadriceps, attached to both medial and lateral meniscus, will pull the meniscal replacements forward during active extension and likewise, the semimembranosus (medial meniscus) and/or popliteus tendons (lateral meniscus) will pull the meniscal replacements posteriorly during active flexion. 
   The proposed anatomical meniscal-bearing arthroplasty has one or multiple prosthetic menisci that are attached to either the diarthrodial joint capsule and/or the remnant of the natural menisci. The knee will be used to describe the preferred embodiment of this concept. However, the proposed meniscal bearing can be used to repair cartilage in other body joints. 
   The prosthetic is preferably implanted in the knee via a minimally invasive procedure, leaving the quadriceps muscle group intact. A small arthrotomy will be performed, allowing the access to the knee joint. Then the central portion of the meniscus will be resected, leaving the horns, a peripheral meniscal rim, and the coronary ligament intact. One or more well-defined cavities will then be formed in the articular surfaces of the tibia and/or femur. One or more resurfacing implants would then either be press-fit, cemented or sutured into the prepared pocket. The meniscal prosthetic is then sewed into the meniscal rim. 
   The non-meniscal articular resurfacing portion of the implants which contact the meniscus consists of cobalt chrome alloys, stainless steel, ceramics, polyethylene, and/or polyurethane and will closely approximate the normal articular geometry. 
   The bulk of the meniscal prosthetic implant will preferably consist of a compliant polyvinyl alcohol polymer and/or polyurethane. A meshed fabric may be molded into the peripheral rim of the prosthetic body, allowing biological glues and/or sutures to connect the implant to the surrounding soft tissue. If the entire original meniscus needs to be removed, a flexible tube can be placed in the space bordered by the tibial plateau, coronary ligament, and anatomical meniscus in order to measure the natural soft tissue laxity. Different diameters of tubing represent different amounts of laxity/mobility in the natural meniscus/coronary ligament construct. This tubing can then be reused as a spacer to balance the soft tissue connections, simulating the restraint of the natural meniscus. 
   One preferred material for the meniscal implant is polyurethane. Polyurethane can be made flexible so it can conform to the femoral and tibial components, thus giving the knee a large contact area throughout the entire range of motion. Likewise, a polyvinyl alcohol polymer which imbibes aqueous fluids can be used. Like cartilage, it imbibes aqueous fluids and generates a fluid-film-bearing surface. 
   The shape of the meniscal implants will closely conform to the tibial plateaus and femoral condyles, generating large areas of contact. They can either be congruent or, to distribute stresses more evenly they can be slightly incongruent as described by Goodfellow et al., The Design of Synovial Joints, Scientific Foundations of Orthopaedics and Traumatology, pp. 78–88. The meniscal portions of the implant will be flexible so they can conform to the tibial and femoral bearing surfaces throughout the entire range of motion. 
   The anatomical meniscal-bearing concept could also be used in a unicondylar knee replacement. Because the meniscal portion of the implant is able to spin and glide on the tibial plateau, and because the meniscal replacement is flexible, the implant will be less sensitive to malalignement. With existing unicondylar knee replacements if the implant is malaligned the entire joint will likely experience abnormal stresses. 
   Another possible use for this implant would be in the meniscal replacement surgery. The meniscal portion of the implant can be used by itself, being sewed to the joint capsule and meniscal horns of the knee. Also, variation in the meniscal implant can be made for replacement of menisci from other joints, i.e., sternoclavicular, temperomandibular, and zygapophyseal. 
   The invention also relates to a surgical procedure which is minimally invasive when compared to standard techniques currently used for resurfacing the knee joint or other body joints. In this method, the incision length is limited between 2 and 2½ times the patellar width. During forming the incision, the surgeon should avoid turning the patella (everting) over from its natural position. Steps should also be taken to leave the quadriceps muscle in its natural position by making sure it is not severed or twisted. Attachments to the peripheral tibial plateau, horns and surrounding ligaments and musculature is maintained through the meniscal rim. For example, the anterior cruciate ligament, if attached to the meniscal rim, should be maintained. Likewise, the transverse ligament should be left attached to the meniscal horns. The inner portion of the meniscus is then removed. Preferably, the incision/resection is made within or at the border of the zone of the meniscus known as the red or vascularized region. Tibial sizing guides are used to measure the size of the meniscal resection (length of resection arc and thickness at the red-zone border). 
   If femoral resurfacing is needed, the femoral resection may be done using a femoral alignment guide which has a rod extending externally of the incision, which rod points to the femoral head. The rod indicates implant flexion and implant rotation within the frontal plane. Once properly aligned, a femoral sizing template is used to measure and guide a posterior femoral cut. Obviously, there will be several different size templates corresponding to the several femoral implant sizes. The template may include a saw blade slot for preparing the posterior surface of the femur. 
   A tibial-sizing tray is utilized to prepare the tibial bone cuts within the inner portion of the meniscus. Preferably, the meniscus will be removed in an oval or “D”-shape with the oval aligned with the two anatomic meniscal horns. Obviously, again, there are various size templates corresponding to different size tibias. Once aligned, the tray template is pinned in position and a burr or end mill is used to mill a pocket into the tibial plateau. A second template or deeper layer of the first template-shaped like an “I” beam (if a second template is used, it is placed over the pins after the initial template is removed) and a deeper recess is formed within the initial recess or cavity. In other words, the “I”-shaped pocket is deeper than the original “D”-shaped or oval pocket to accommodate an “I”-shaped keel on the implant. Preferably as the “D”-shaped pockets grow in size, the “I”-shaped keel receiving recess also increases, however, it may remain the same size if desired. The “D”-shaped pocket formed should encompass the entire tibial plateau within the rim with the “I”-shaped recess in the center. 
   On the femoral side, a femoral burr template is pinned in position and a recess of general uniform depth is formed, as by milling with a burr, along the condyle of the distal femur. A femoral implant, preferably made of a cobalt chrome alloy such as Vitallium® alloy or a ceramic material is implanted in the recess formed on the femoral condyle. Preferably, this implant has a thickness corresponding to the depth of the recess formed so that the outer surface of the implant is located at the correct anatomical position. 
   A tibial resurfacing implant is provided and has a “D”-shaped corresponding the various size templates provided. For each implant profile, several implant thicknesses are provided. The thickness is chosen such that the implant will be aligned in the varus/valgus direction. Once the implant thickness is determined, the actual implant will either be press fit or cemented into place. The tibial plateau implant has a contact surface preferably made of polyethylene and will have a porous titanium surface against the bone. The bone contacting porous surface attached to the polyethylene preferably is made of titanium or cobalt chrome or any other biocompatible porous material. Alternatively, the tibial implant can be made of polyurethane, cobalt chrome, ceramics, or a polyvinyl alcohol hydrogel. Alternatively, the implant may be in the shape of a circular disc with a periphery located immediately inside the remaining rim of the tibia. 
   Once the tibial plateau is resurfaced, a meniscal implant is attached to the remaining meniscal rim such by suturing. A sizing template is used to determine the required implant size in all three anatomical planes. The meniscus, which is attached to the remaining rim of the tibial plateau is preferably made of a polyvinyl alcohol hydrogel or a polyurethane but can be made of any biocompatible soft, compliant material that is able to withstand the functional loading and tribiological conditions. The implant is sutured into the remaining meniscal rim. The sutures can be made part of the implant such as by molding. See, for example, the implant of Kenny U.S. Pat. No. 4,344,193. The sutures may be made integral with a mesh that is also molded into the implant. The mesh can abut the meniscal rim and allow for the potential of soft tissue ingrowth. Bioactive factors such as tissue cultures, resorbables, bone morphogenic proteins can be added to the mesh to encourage the tissue ingrowth. See Stone U.S. Pat. No. 5,007,934. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is an isometric view of a knee joint capsule showing the exposed tibial meniscal portions; 
       FIG. 2  shows the capsule of  FIG. 1  after removal of the central portion of the lateral meniscus but leaving a meniscal rim; 
       FIG. 3  shows the location of a femoral sizing template and alignment guide mounted within the joint capsule; 
       FIG. 4  shows a tibial tray sizing template located within the remaining meniscal rim on the tibial plateau; 
       FIG. 5  shows the template of  FIG. 4  pinned in a position aligned with the meniscal horns; 
       FIG. 6  shows a burr used to mill a pocket in the tibial plateau conforming to the tibial sizing template; 
       FIG. 7  shows an “I” beam template placed within the pocket milled in  FIG. 6  on the resected tibial plateau; 
       FIG. 8  shows the “I” beam template of  FIG. 7  pinned in position; 
       FIG. 9  shows a burr shaping the “I”-shaped pocket; 
       FIG. 10  shows the “I”-shaped pocket of  FIG. 9  within the oval or “D”-shaped pocket formed in  FIG. 6  along with a femoral burr template for forming a recess in the lateral femoral condyle; 
       FIG. 11  shows the recess formed in  FIG. 10 ; 
       FIG. 12  shows both the femoral resurfacing implant on the femur and the tibial resurfacing implant attached to the tibial plateau; 
       FIG. 13  shows the tibial resurfacing implant of  FIG. 12  covered by a compliant meniscal implant which is attached to the remaining natural meniscal rim; and 
       FIG. 14  is a bottom view of a medial and lateral tibial resurfacing implant including lateral implants of  FIGS. 12 and 13 . 
   

   DETAILED DESCRIPTION 
   Referring to  FIG. 1  there is shown, for purposes of reference, an open knee joint capsule including a lateral femoral condylar surface  10  and a medial femoral condylar surface  12 . The anterior cruciate ligament  14  is shown running through the joint. The quadriceps  16  is shown coupled to the tibia  17  and the lateral collateral ligament  18  is shown connecting the tibia and the femur. The lateral meniscus  20  which includes a rim area  22  is located above the tibial plateau  24 . 
   Referring to  FIG. 2 , there is shown the joint capsule of  FIG. 1  with the inner portion of the meniscus  20  removed leaving meniscal rim  22 . In the preferred method, which will be discussed below, the incision/resection of the meniscus  20  is made within or at the border of what is known as the red zone of the meniscus, i.e., the vascularized region of the meniscus. The resection of the inner part of meniscus  20  leaves meniscal horns  26 ,  28  in place. Since the meniscal rim  22  remains, all the attachment points to the peripheral tibial plateau  24  are left and the surrounding ligaments and musculature is maintained through the meniscal rim. 
   Referring to  FIG. 3 , a femoral alignment guide  30  includes an alignment rod  32  which extends outwardly of the knee capsule and can be aligned with the femoral head and laid parallel to the femoral shaft in the frontal plane for referencing the location of the femoral sizing template. Specifically, implant flexion and implant rotation with regard to the frontal and sagittal planes can be set. A femoral sizing template  34  is thus aligned with alignment guide  30  on the lateral condyle  10  of the femur. In the preferred embodiment, femoral sizing template  34  includes a handle  36  and a posterior saw guide  38 . The posterior saw guide  38  is used to make the posterior femoral cut via a slotted saw guide  40 . 
   With regard to  FIG. 4 , there is shown a tibial sizing template  42 . In the preferred embodiment, template  42  has a “D”-shaped outer surface  44  and a generally oval inner surface  46 . In the preferred embodiment, template  42  includes a handle  48  so that a straight side  50  of the “D”-shaped template  42  may be aligned with the meniscal horns  26 ,  28 . Preferably, a series of templates  42  of varying sizes are provided in a kit, each corresponding to a population of different size tibial plateaus. It is contemplated that a series of 5 to 7 templates  42  would be provided in a kit to be used during the surgical procedure. This is also true for template  34  in which a variety of sizes may be provided to accommodate different size femurs. In the preferred embodiment, template  42  includes a series of through bores  52 . 
   Referring to  FIG. 5 , there is shown the template  42  of  FIG. 4  pinned in position utilizing three pins  54  which are sunk into the bone of the tibial plateau through holes  52  of “D”-shaped template  42 . Pins  54  locate template  42  on the tibial plateau in a location which, in the preferred embodiment, places a surface  44  of template  42  in close proximity of the remaining rim portion  22  of the natural meniscus. As can be seen in  FIG. 6 , there is shown a burr or end mill  60  which is used to form a recess surface in tibial plateau  24  having the shape of inner surface  46  of template  42 . Burr  60  is driven by any convenient means via a drive shaft  62 . In the preferred embodiment, burr  60  includes a stop plate  64  which contacts an upper surface  48  of template  42 . Stop plate  64  is set at a predetermined distance from the lower most cutting face of mill or burr  64  so that a depth of resection into the surface of tibial plateau  24  is set. In the preferred embodiment, this is at least 0.2 and preferably 0.24 inches. 
   Referring to  FIGS. 7 and 8 , there is shown a second template  72  having an outer surface  74  matching outer surface  44  of template  42 . As shown in  FIG. 8 , template  72  includes a series of preferably three through holes  76  for receiving the same series of pins  54  as used for template  42 . In the preferred embodiment, template  72  includes an “I”-shaped inner recess  80 . While recess  80  is preferably “I”-shaped, it is conceivable that other shapes may be used which would the keel of receive an implant to be discussed below and prevent the translation and rotation thereof. Resection template  72  is located in a manner similar to that of resection template  42  and recess  80  is centrally located within the generally oval recess previously cut with template  42 . 
   In the preferred embodiment, template  72  includes a handle  82  to facilitate its alignment on the tibial plateau. Pins  78  are placed through throughbores  76  and the original pin holes used with template  42  to maintain the resection template  72  in its aligned orientation. Alternately the pins used to hold down template  42  can be left in place and template  72  can be slid over the remaining pins. 
   Referring to  FIG. 9 , a burr or end mill  84 , which is similar or identical to end mill  60 , is utilized to form an “I”-shaped recess within the oval recess already formed. Obviously, this recess has to be deeper into the tibial bone than the original oval shaped recess formed. Thus, burr  84  includes a stop plate  86  spaced at a greater distance from upper surface  88  of template  72  than stop  64  of burr or end mill  60 . Generally, the thickness of template  42  and  72  will be identical, however, the dimensions between the bottom surface end mill or burr  84  and the guide surface  88  is dimensioned to produce an “I”-shaped recess of the desired depth. In the preferred embodiment, this depth is 0.240 inches and at least 0.2 inches below the recess surface initially formed in tibial plateau  24  with template  42 . 
   Referring to  FIG. 10  there is shown the two level recess formed in plateau  24 . As discussed above, the recess has a first recessed area  66  and a more recessed area, in the shape of an “I”,  82 . As indicated above, the size of the resection templates  42  and  72  may change to match varying anatomy. In general, for each template  42  there will be a corresponding identically sized template  82 . Consequently, if there are five templates  42  in a kit, there will be preferably five templates  82  in a kit. Thus, the size of the pockets or recesses  66 ,  82  will get larger as the template size increases. The use of the two depth recesses or pockets  66 ,  82  will be discussed below. 
   Referring again to  FIG. 10 , there is shown a femoral burr template  90  attached to lateral condyle  10  via pins  92 . In the preferred embodiment, template  90  includes a pair of through bores  94  for receiving pins for attaching template  90  to the femoral condyle  10 . Obviously, more pins  92  than two may be used. An end mill or burr similar to that discussed above with regard to elements  60 ,  84  is used to mill a recess within the inner surface  96  of template  90 . If a thin wall of bone is left due to the center island, that remaining portion of bone is resected free-handed with the burr. 
   As best seen in  FIG. 11 , a recess  100  is formed in the lateral condyle  10  of the femur. 
   Referring to  FIGS. 12–14 , there is shown the tibial and femoral resurfacing implants  102 ,  106  respectively. Tibial implant  102  includes an “I”-shaped keel  104  (shown in phantom in  FIG. 12 ) which extends to the base of the “I”-shaped recess  82 . Implant  102  has a periphery  105  which has a portion extending into the upper level, i.e., extending at a lesser distance from the base of the tibial resurfacing implant  104  and engaging with outer recess  66 . Referring to  FIG. 14 , there is shown a bottom view of a preferred medial and lateral implant  102 ′ and  102 ″ each having a keel  104 . The arcuate portion of the implants is placed adjacent remaining rim  22  of a tibial plateau  107 . The tibial implant  102  is either press fit or cemented into recesses  66 ,  82 . Femoral resurfacing implant  106  has an outer bearing surface  108  shaped to be congruent with the natural surface of the femoral condyle  10 . Preferably, this component will be a cobalt chrome alloy implant having a thickness such that outer surface  108  is placed at or about the level of the natural femoral condyle  10  prior to resurfacing. Again, implant  108  may be either press fit or cemented into position. Alternately, the femoral resurfacing implant  106  may be made of a ceramic and cemented in position. In the preferred embodiment, tibial implant  104  is preferably made of polyethylene having a porous surface contacting the bone. Alternately, the tibial contact can be made of polyurethane, cobalt chrome, ceramic or a polyvinyl alcohol hydrogel. 
   Referring to  FIG. 13 , there is shown a meniscal implant  110  which is positioned proximally of the resurfacing implant  104 . In the preferred embodiment, meniscal implant  110  is made of a polyvinyl alcohol hydrogel or a polyurethane but can be made of any biocompatible soft, compliant material that is able to withstand the loading in the knee joint and capable of the wear properties requires. Such a hydrogel meniscus is described in U.S. Publication No. 2002/0022884 published Feb. 21, 2002, the teachings of which are incorporated herein by reference. In the most preferred embodiment, the meniscus is made of a polyurethane which is molded to include an inner mesh or sutures. In the preferred embodiment, meniscal implant  110  is attached to the meniscal rim  22  via the sutures or mesh integrally molded into the hydrogel implant. Preferably, this is done around the entire circumference  112  of implant  110  so that it is maintained in position by the remaining natural meniscal rim  22 . The mesh of the implant, for example that shown in U.S. Pat. No. 5,007,934, the teachings of which are incorporated herein by reference, may be coated or impregnated with bioactive factors, tissue cultures, BMPs or other resorbable polymers to encourage potential soft tissue ingrowth. This ingrowth would supplement or, in some cases, replace the suture attachment to meniscal rim  22 . 
   While only the resurfacing of the lateral side of the tibial plateau and femur have been described, the process could as easily be used on the medial condyle  12  and medial tibial plateau. 
   The preferred surgical procedure utilizes a minimally invasive method which, when compared to standard techniques current used for resurfacing the knee joint of other body joints, uses a smaller incision. In this preferred method, the incision length is between 2 and 2 ½ times the patellar width. During forming the incision, everting or turning the patella over from its nature position should be avoided. Steps should also be taken to leave the quadriceps muscle  16  in its natural position by making sure it is not severed or twisted. Attachments to the peripheral tibial plateau such as horns  26 ,  28  and surrounding ligaments and musculature should be maintained through the meniscal rim  22 . For example, the anterior cruciate ligament  14 , if attached to the meniscal rim, should be maintained. Likewise the transverse ligament should be left attached to the meniscal horns. Initially, the posterior surface of the femur is prepared. This is done using femoral alignment guide  30  which has rod  32  extending externally of the incision, which rod points to the femoral head. The rod indicates implant flexion and implant rotation within the frontal and sagittal planes. Once properly aligned, a femoral sizing template  34  is used to measure and guide a posterior femoral cut. Obviously, there will be several different size templates corresponding to the several femoral implant sizes. The template may include guide  38  having saw blade slot  40  for preparing the posterior surface of the femur in a known manner. 
   Tibial sizing template  42  is then utilized to prepare the inner portion of the meniscus. Preferably, the meniscus will removed in an oval shape with the oval aligned via surface  50  with the two anatomic meniscal horns  26 ,  28 . Obviously, again, there are various size templates  42  corresponding to different size tibias. Once aligned, the template  42  is pinned in position via pins  54  and burr  60  is used to mill pocket  66  into tibial plateau  24 . A second “I” beam template  72  is placed over pins  54  after the initial template  42  is removed and a deeper recess is formed within the initial cavity. In other words, the “I”-shaped pocket  88  is deeper than the original “D”-shaped or oval pocket  66  to accommodate an “I”-shaped keel on the implant. Preferably, as the “D”-shaped pockets grow in size, the “I”-shaped keel receiving recess also grows. The “D”-shaped pocket  66  formed should encompass the maximum possible tibial plateau area within rim  22  with the “I”-shaped recess  82  in the center. 
   On the femoral side, a femoral burr template  90  is pinned in position via pins  92  and a recess of general uniform depth is formed, as by milling with a burr similar to burr  60  along with the condyle  10  of the distal femur. A femoral implant  106 , preferably made of a cobalt chrome alloy such as Vitallium® alloy or a ceramic is implanted in the recess formed on the femoral condyle. Preferably, this implant has a thickness corresponding to the depth of the recess formed so that outer surface  108  of implant  106  is located at the correct anatomical position. 
   A tibial resurfacing implant  104  which may be circular or preferably have a general “D”-shape corresponding the various size template provided is implanted in recesses  66 ,  82 . For each implant profile, several implant thicknesses are provided. The thickness is chosen such that the implant will be aligned in the varus/valgus direction. Once the implant thickness is determined, implant  104  will either be press fit or cemented into place. The tibial plateau implant bearing surface is preferably made of polyethylene and will have a porous metal surface against the bone. Alternatively, the tibial implant can be made of polyurethane, cobalt chrome, ceramics or a poly vinyl alcohol hydrogel. If the implant is made in the shape of a “D”, the arcuate periphery of the “D” is located immediately inside the remaining rim  22  of the tibia. 
   Once the tibial plateau is resurfaced with implant  104 , meniscal implant  10  is attached to the remaining meniscal rim  22  such by suturing. A sizing template is used to determine the required meniscal implant size in all three anatomical planes. The sizing template is similar to the D-shaped resection template with the arcuate portion sizing the meniscal implant. The meniscus, which is attached to remaining rim  22  of tibial plateau  24  preferably made of poly vinyl alcohol hydrogel or polyurethane but can be made of any biocompatible soft, compliant material that is able to withstand the functional loading and tribiological conditions. The implant is sutured into the remaining meniscal rim. The sutures can be made part of the implant such as by molding. See, for example, the implant of Kenny U.S. Pat. No. 4,344,193. The sutures may be made integral with a mesh that is also molded into the implant. The mesh can abut the meniscal rim and allow for the potential of soft tissue ingrowth. Bioactive factors such as tissue cultures, resorbables, bone morphogenic proteins can be added to the mesh to encourage the tissue ingrowth. 
   Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

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