UNICONDYLAR KNEE IMPLANT AND INSTRUMENT SYSTEM

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims priority to Provisional Application No. 60/672,211 filed April 18, 2005, U.S. Patent Application No. 11/304958 filed December 14, 2005, and U.S. Patent Application entitled "Unicondylar Knee Instrument System" attorney docket no. 20427/ 1203406-US2, filed January 23, 2006, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention The present invention is related to an orthopedic medical device. In particular, the present invention is related to a unicondylar knee implant, surgical instrumentation system, and method of preparing a distal femur for the implantation of a unicondylar femoral implant.

2. Description of the Related Art Orthopedic knee implant systems have been used for many years to treat patients with knee joints that have been damaged by trauma or disease, such as osteoarthritis, rhumetoid arthritis, and avascular neurosis. A knee arthroplasty resects, cuts, or resurfaces the damaged sections of the knee and replaces them with an prosthetic or implant. Most knee implant systems are tricompartmental implants and the surgical procedure used with tricompartmental implants is commonly known as total knee arthroplasty. These implants are known as tricompartmental implants because they are used when the femur is prepared to receive an implant by resurfacing or resecting the

three compartments of the distal femur, i.e., the medial and lateral condyles and the trochlear groove. Regardless of the type of implant used, all arthroplasties require the bone to be specifically prepared to receive a corresponding implant by resecting, resurfacing, or deforming the bone to accept the implant. Most knee implant systems are modular systems with multiple sizes and thicknesses and degrees of interchangeability between the sizes. For example, a typical total knee implant system may consist of 6 femoral implant sizes, 6 tibial tray implant sizes, and 6 tibial bearing implant sizes with each tibial bearing size having 7 different thicknesses. The various implant sizes are required to meet the various size bones of patients. Typical implant systems often allow interchangeability between sizes for example; a medium size femoral implant may be used with a single larger size tibial implant and tibial bearing implant to match the specific needs of a patient. However, most knee implant systems are limited with regards to the range of interchangeability between sizes; for example, the largest size femoral implant component typically cannot be used and is not compatible with the smallest size tibial tray and tibial bearing component. This is because such a high degree of mismatch between sizes often affects the range of constraint designed into the implants. Moreover, conventional implant systems require a prepared bone surface to be further resected or resurfaced whenever a different size implant is required, adding to the overall surgical time, complexity of the surgery, and bone loss.

Tibial tray implants typically have some sort of keel associated with the tibial tray to provide a level of initial fixation. Other methods if initial fixation have also been used with tibial trays, such as spikes protruding from the bone engaging surface of the implant

or screws inserted through the tibial tray into the bone. However, the use of screws has been associated with osteolysis and provides a pathway for debris to enter the tibial bearing tibial tray interface. Typical keel designs have simply been of a straight cylindrical or vertical plane geometry extending from the bone engaging surface of the tibial tray implant. Accordingly, these tibial tray keel designs provide minimal initial fixation and require a significant amount of exposure of the knee joint to implant as these designs are implanted with a top down approach. A top down approach is defined for example, as implanting the tibial tray into a prepared horizontal tibial surface when the tibia is set in a vertical orientation. Minimally invasive surgery ("MIS") has become of great interest within the field of orthopedics. Thus, unicondylar or unicompartmental knee implants have become of great interest in the orthopedic industry due to their small size and applicability to MIS surgical approaches. Unicondylar knee implants are designed to replace only a single condyle (e.g., the medial or lateral condyle) of the distal femur. Minimally invasive knee surgery has not yet been fully defined. However, minimally invasive knee surgery has generally been considered to include a smaller incision. A typical incision length for a total knee replacement can be up to 10 to 12 inches long. The general theory behind MIS is that with a smaller incision length, the patient will be able to recover from surgery faster. Generally, the clinical outcomes for unicondylar knee implants have varied.

Studies have reported long term survival rates for unicondylar implants to be less than that of comparable total knee implants. One particular cause for such discrepancies is due to the surgical technique associated with implanting the implant.

The unicompartmental implant most widely reported on is the Oxford implant. The Oxford implant is a mobile bearing unicompartmental implant that is implanted with a free-hand technique, i.e., where the bone resections are not guided by instrumentation. Thus, the clinical outcomes for these implants have in part been associated with a particular surgeon's ability in implanting the device. Accordingly, a surgeon proficient in this technique is more likely to have a better surgical outcome compared to a less experienced surgeon who is less technically proficient with the surgical technique for implanting the implant.

Recent advancements in unicondylar knee implants and instruments have resulted in instrumented techniques for implantation. U.S. Patent No. 6,554,838 to McGovern et al. discloses a unicondylar knee implant that uses a guided burring technique to implant the femoral component. However, conventional instrumentation systems are bulky and are required to be operated from various angles as opposed to a single orientation. Such instrument designs are also not completely conducive to minimally invasive surgical approaches or a reproducible surgical result.

U.S. Patent No. 5,326,361 to Hollister discusses an alternative approach to knee biomechanics that views the knee to move through a range of motion from flexion to extension about a single axis of rotation. This view is a departure from the traditional view that the knee profile is defined by multiple centers of curvature and thus multiple axis of rotation. In particular U.S. Patent No. 5,326,361 discloses a total knee implant system having a single cross-sectional sweep from zero to over 120 degrees.

The development of orthopedic implant designs has been moving towards meeting the requirements of high demand patients. Patients nowadays are requiring more

from their implants and since patients are living longer these days, are requiring implants to last longer. Accordingly, developments have been made in materials used to make orthopedic implants to improve implant survival rates, such as the use of cobalt chromium alloys, titanium alloys, diamond-like coatings, ceramics, hydroxyapatite coatings, and ultra-high molecular weight polyethylene materials. Moreover, implant designs have changed to meet the ever increasing demands of patients, for example the general population of Asian countries prefers implants that allow for a higher degree of flexion than traditional implants.

The relationship between flexion angle and femoral-tibial conformity is determined by gait analysis studies. For example, gait data for Caucasian population is presented in Harrington I. J., et al. "Static and Dynamic Loading Patterns in Knee Joints with Deformities", J.B.J.S., Vol. 65-A, No. 2, February 1983, pp. 247-259. Based upon such studies the relationship between flexion angle and femoral-tibial conformity varies for different genders and races. Thus, there is a need for a unicompartmental knee implant system that addresses the above mentioned deficiencies in current implant designs while simultaneously being suitable for minimally invasive surgical techniques. In addition, there is a need for a unicompartmental knee instrument system that addresses the above mentioned deficiencies in current instrument designs while simultaneously being suitable for minimally invasive surgical techniques.

BRIEF SUMMARY OF THE INVENTION

The present invention provides for a unicondylar knee prosthesis having a tibial bearing component, a tibial tray component, and a femoral knee component. The present

invention also provides for a locking mechanism for locking the tibial bearing component onto the tibial tray component.

The tibial bearing component includes a top portion having an articulating surface and a bottom portion. The bottom portion further includes at least one flexible catch for engaging a corresponding latch on the tibial tray component. The tibial bearing component's flexible catch and the tibial tray component's latch form part of the locking mechanism for securing the tibial tray bearing component onto the tibial tray component. Preferably, the locking mechanism has at least four flexible catches while the tibial tray component has two latches. The flexible catches are configured to have an opening on the bottom portion of the bearing component facing the peripheral vertical rim of the tibial tray component when attached. The opening is further configured to be in fluid communication with a second opening on the distal surface of the bottom portion of the tibial bearing component. The locking mechanism also includes a peripheral vertical rim on the tibial tray component and at least one latch or lip extending from the peripheral vertical rim.

The tibial tray component includes a tray member and a keel connected to a distal surface of the tray member. The keel further includes a vertical keel section extending from the distal surface of the tray member and a keel foot having a posterior slope and a posterior taper. The keel is a self-locking keel that generates a securing force to secure the tibial tray onto a prepared tibia.

The femoral knee component of the unicondylar knee prosthesis includes a bone engaging surface and an articulating surface having a single sagittal radius of curvature from about 10 degrees of hyperextension to about 140 degrees of flexion. The femoral

knee component can farther include a posterior flange and at least one peg, angled relative to the posterior flange, for engaging a distal femur. Preferably the peg is angled at about 25 degrees relative to the posterior flange. More preferably, the femoral knee component has two substantially parallel pegs angled about 25 degrees from the posterior flange. The femoral knee component can also be configured to have a single medial- lateral radius of curvature. The single medial-lateral radius of curvature can be at about 38mm.

The present invention also provides for a keel for a device. The keel includes a vertical keel section for extension from a surface of the device. The keel foot is connected to the end of the vertical keel section and has a sloped and tapered configuration. This keel can be used for devices such as an orthopedic tibial prosthesis of a unicondylar or total knee implant.

Another aspect of the present invention provides for a unicondylar femoral knee implant system having at least two unicondylar femoral knee implants. The unicondylar femoral knee implant system has a distal bone engaging surface having an anterior end, a distal-to-posterior chamfer bone engaging surface disposed between the distal and the posterior bone engaging surface. The unicondylar femoral knee implant system also has at least one peg extending from the distal bone engaging surface at a constant distance from the anterior end for the at least two unicondylar femoral knee implants. The present invention also provides for the aforementioned prosthesis and devices to further include biological coatings. Such coatings may include hydroxyapatite and Osteogenic Protein-1 (OPl).

The present invention provides for an apparatus for cutting a tibia in support of a unicondylar knee surgery that includes a unicondylar tibial alignment guide having a tibia anchor and a unicondylar tibial resection guide adjustably connectable to the unicondylar tibial alignment guide and configured to operate concurrently with the unicondylar tibial alignment guide that includes, an extended arm having at least one cutting guide surface, and a tibial resection guide base connected to the extended arm. The apparatus can further include an extended arm such that the extended arm is the only element of the unicondylar tibial resection guide within a wound area and wherein the unicondylar tibial resection guide is adjustable in three degrees of freedom. The three degrees of freedom are heaving, pitching, and rolling. In addition, the apparatus can be configured with an overall thickness of the extended arm to be about 1 to about 100 mm thick and preferably about 2 to about 5 mm thick. Moreover, the unicondylar tibial alignment guides includes at least two telescoping sections and a screw clamp connected to the tibial resection guide base attaching the unicondylar tibial resection guide to the unicondylar tibial alignment guide.

The present invention also provides for a tibial stylus for use in support of a unicondylar knee surgery that includes a tibial stylus pointer, a member having an open top surface, and a tibial stylus base. The tibial stylus base has a posterior end configured to slidingly engage along the open top surface and an elongated anterior end connectable to the tibial stylus configured such that the tibial stylus pointer moves along the anterior end of the tibial stylus base. The member can be a unicondylar tibial resection guide having an extended arm having at least one cutting surface and a tibial resection guide

base connected to the extended arm. The posterior end of the tibial stylus base can be U- shaped.

The present invention also provides for an apparatus for cutting a femur in support of a unicondylar knee surgery including an instrument handle assembly having an elongated handle having a base and a spacer block removably connectable to the base, and a unicondylar resection guide removeably connectable to the base and configured to operate concurrently with the space block. The unicondylar resection guide has at least one channel for guiding a cutting tool and at least one opening for receiving a fixing element. The unicondylar resection guide can also be configured to be slidingly and removeable connectable to the base. Moreover, the spacer block and unicondylar resection guide can be configured to operate independently of each other. The present invention further provides for an apparatus for aligning a unicondylar femoral cutting guide for use in support of a unicondylar knee surgery that includes an instrument handle assembly having a base and an alignment rod holder connected to the instrument handle assembly that slides substantially in the medial and lateral direction. This apparatus can further include a unicondylar resection guide removably connectable to the base or a unicondylar resection guide slidingly and removeably connectable to the base or a spacer block removably connectable to the base. The alignment rod holder includes a first alignment rod holder base having at least one substantially vertical passage, a second alignment rod holder base having at least one substantially vertical passage, and at least one dowel connecting the first and second alignment rod holder bases such that the first and second alignment rod holder bases slide within the instrument handle assembly in a substantially medial and lateral direction.

The present invention also provides for an ankle clamp for supporting an apparatus for cutting a tibia in support of a unicondylar knee surgery that includes an ankle clamp base that includes a pair of base arms, each having a slot, a pair of clamping arms, each having a slot and pivotably connected to the pair of base arms, and a pair of springs, each respectively connecting the base arm and the clamping arm such that an opening force is provided to open the clamping arms. The pair of springs can also be configured to provide a clamping force to close the clamping arms. The pair of springs is connected to a pair of dowels respectively, offset a predetermined distance from the pivotable connection of the clamping arms and base arms. The ankle clamp can further include a unicondylar tibial alignment guide connected to the ankle clamp base.

The present invention further provides for a method of preparing a femoral condyle of a femur for the implantation of a unicondylar femoral knee implant which includes the steps of, resecting a tibia, determining a least affected site, wherein the site is a distal femoral condyle or a posterior femoral condyle, positioning the knee such that the least affected site faces the tibia, positioning a spacer block between the resected tibia and the least affected site, determining an overall thickness for balancing the knee and resecting the femur to a thickness of a corresponding unicondylar femoral implant, determining a spacer block and unicondylar femoral cutting block combination that equals the overall thickness when the knee is in extension, and resecting the distal femoral condyle.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein:

Figure 1 is a perspective view of an embodiment of a unicondylar femoral knee implant of the present invention;

Figures 2a and 2b are illustrations of the knee joint at flexion and hyperextension;

Figure 3 is a perspective anterior/medial view of the embodiment of the unicondylar femoral knee implant of Figure 1;

Figure 4 is perspective view of another embodiment of a unicondylar femoral knee implant of the present invention;

Figure 5 is a perspective inferior view of an embodiment of a tibial bearing implant of the present invention; Figure 6 is a perspective superior view of the embodiment of the tibial bearing implant of Figure 5;

Figure 7 is a posterior view of the unicondylar femoral knee implant of Figure 1 assembled to the tibial bearing implant of Figure 5 at full extension;

Figure 8 is a perspective inferior view of the embodiment of the tibial bearing implant of Figure 5 ;

Figure 9a is perspective superior view of an embodiment of a tibial tray implant of the present invention;

Figure 9b is a detailed perspective superior view of a latch protruding from a peripheral vertical rim of the tibial tray implant of Figure 9a; Figure 10 is a perspective inferior view of the embodiment of the tibial tray implant of Figure 9a;

Figure 11 is a perspective inferior view of another embodiment of a tibial tray implant of the present invention;

Figure 12 is a perspective view of an embodiment of a unicondylar tibial alignment guide assembled to a unicondylar tibial resection guide of the present invention;

Figure 13 is a perspective view of an ankle clamp of the unicondylar tibial alignment guide of Figure 1;

Figure 14 is a perspective view of the ankle clamp of Figure 13 in the open position;

Figure 15 is a perspective view of section 4 of Figure 12 of the unicondylar tibial alignment guide assembled to the unicondylar tibial resection guide of Figure 12; Figure 16 is a perspective view of an embodiment of a tibial stylus assembled to the unicondylar tibial resection guide of Figure 12;

Figure 17 is a perspective view of the unicondylar tibial resection guide of Figure 12;

Figure 18 is a perspective view of an embodiment of a knee joint instrument handle assembly of the present invention with an exploded view of a spacer block and base assembly;

Figure 19 is a perspective view of an embodiment of a unicondylar femoral distal resection guide of the present invention;

Figure 20 is a perspective view of an embodiment of a series of spacer blocks of the present invention;

Figure 21 is perspective view of an embodiment of a series of unicondylar femoral distal resection guides of the present invention;

Figure 22a is an anterior view of a knee joint at full extension with a damaged distal condyle surface and resected tibia;

Figure 22b is a side view of a knee joint at 90 degrees of flexion with a resected tibia; Figure 23a is an anterior view of a knee joint at full extension with a resected tibia;

Figure 23b is a side view of knee joint at 90 degrees of flexion with a damaged posterior condyle surface and resected tibia;

Figure 24 is a perspective view of an embodiment of a unicondylar femoral posterior resection guide of the present invention;

Figure 25 is a perspective view of a series of unicondylar femoral posterior resection guides of the present invention;

Figure 26 is a perspective view of an embodiment of a unicondylar femoral chamfer and peg-hole guide of the present invention; Figure 27 is a perspective view of a series of femoral chamfer and peg hole guides of the present invention; and

Figure 28 is a flowchart of a method for preparing a femoral condyle for the implantation of a unicondylar knee implant.

DETAILED DESCRIPTION OF THE INVENTION As used herein, the following definitional terms apply. The term "unicondylar" is synonymous with "unicompartmental." "Anterior" and "posterior" mean nearer to the front or the back of the body respectively. "Proximal" and "distal" mean nearer and farther from the center of the body respectively. "Medial" and "lateral" mean nearer or

farther from the median plane respectively. The median plane is an imaginary, vertical plane that divides the body into a right and left half. The coronal plane is an imaginary, vertical plane that divides the body into a front half and a back half. "Superior" and "inferior" mean above or below respectively. For example, the distal femur has medial and lateral condyles that are superior to the proximal tibia. "Sagittal" means a side profile. Varus means turned inward and valgus means turned outward or away from the body. The terms "resection guide", "cutting guide", "resection block", and "cutting block" are used synonymously.

The present invention allows for complete interchangeability between all sizes of the femoral and tibial components. In an embodiment, the unicondylar knee prosthesis is of a modular design with multiple sizes for its femoral, tibial tray, and tibial bearing components, along with multiple thicknesses for its tibial bearing components. The tibial tray components can have about 6 sizes growing in size in both the anterior/posterior and medial/lateral directions. The tibial bearing components can have about 6 sizes growing in both the anterior/posterior and medial/lateral directions. The femoral components have a left and right component with each component having about 6 sizes growing in both the anterior/posterior and medial/lateral directions. Moreover, the smallest femoral component can be used with the largest tibial component and vice versa, thus allowing for unlimited interchangeability between sizes. As a result, the present inventive system can be used for any patient with extreme variations between tibial and femoral sizes.

Referring now to the drawings in detail wherein like numerals refer to like elements throughout the several views, FIGS. 1-11 represent embodiments of the present invention for a unicondylar knee implant.

FIG. 1 is a perspective view of an embodiment of a unicondylar femoral knee component 100. Orientation references, such as medial or lateral, are given assuming the femoral component is implanted in the medial compartment of a patient's left knee.

However, it will be understood that the same femoral component can be implanted into the lateral compartment of the opposite knee.

Surfaces 102, 104, and 106 of the present embodiment's femoral knee component define the bone engaging or interface surfaces. A bone engaging or interface surface as used herein is used to describe the non-articulating, attachment side of the implant. The bone engaging or interface surface does not necessarily need to contact the bone and may instead only come in contact with an adhesive such as bone cement. The bone interface surfaces consist of a distal surface 102, a posterior surface 106, and a distal-to-posterior chamfer surface 104 disposed between the distal surface 102 and the posterior surface 106. The posterior bone interface surface 106 is at an angle of about 83 degrees with respect to the distal bone interface surface 102. The distal-to-posterior chamfer surface 104 is equiangular from the distal bone interface surface 102 and the posterior bone interface surface 106. Equiangular is defined as being at the same angle. By defining a chamfer surface 104 equiangular to both the distal 102 and posterior 106 bone interfaces, the articulating surface of the femoral component is allowed to maintain a constant radius of curvature that extends from the distal portion of the femur through the distal-to- posterior chamfer and onto the posterior portion of the femoral knee component 100. The femoral knee component's constant radius of curvature when viewed from a sagittal profile can be defined by a single sagittal radius of curvature. The single sagittal radius of curvature starts at about 10 degrees of hyperextension, and preferably at about 1

degree of hyperextension, and extends to about 145 degrees of flexion. As shown in FIG 2a, flexion is when the angle θ is positive or the knee is "bent." FIG. 2b, illustrates the knee in hyperextension Le, when the angle θ defined by the femur and the tibia goes beyond zero and into the negative range. Typically when an average person stands and "locks" out his knees, his knees are in hyperextension. Advantages of an equiangular distal and posterior bone interface as defined above includes a more bone conserving implant geometry and control of implant thickness across the major regions of the implant, i.e., flexion, mid-flexion, and extension regions.

Having a unicondylar femoral knee component 100 with a single sagittal radius of curvature allows for better adaptation of femoral/tibial articulation to meet the load and performance requirements of regional patients, i.e., patients from various regions such as Europe, USA, Asia, Latin America, etc. A single sagittal radius of curvature allow for easier adaptation of femoral/tibial articulation by varying the medial/lateral radius of the femoral knee component or by varying the medial/lateral radius of the corresponding tibial bearing component or by some combination of both.

The unicondylar femoral knee component 100 of the present embodiment, as shown in FIG. 3 in a perspective anterior/medial view, has a single medial/lateral ("M/L") radius 116 of about 38mm that sweeps through the entire single sagittal radius to define the articulating surface. The femoral knee component 100 also has relatively large transitional radii 118 at the edges. The anterior/medial curvature 110 of the femoral component can have an anteriorly tapered curvature to allow good coverage of the bone without anterior overhang. The anterior/lateral curvature 112 has a non-tapered configuration to provide good coverage of the bone without anterior overhang or patellar

interference. The medial/lateral width 114 is designed to provide good bone coverage without patella interference. The resulting configuration results in a distal geometry that better matches the anatomy of patients from various regions. Patients from various regions are known to have variations in knee anatomy, more specifically patients from various regions have different anterior to posterior : medial to lateral (A/P : M/L) ratios of length. The present inventive system is designed to provide bone coverage taking into account these variations in A/P : M/L ratios.

The unicompartmental femoral knee component 100 can also include fixation members. The fixation members can be of any shape such as a cylindrical peg. FIG. 4 shows another embodiment that includes first and second fixation pegs 120, 122, respectively. The first fixation peg 120 protrudes from the distal bone interface surface 102 and the second fixation peg 122 protrudes from the distal-to-posterior chamfer bone interface surface 104. The axes of the fixation pegs 120, 122 are parallel and coplanar to a plane normal to all three bone interface surfaces 102, 104, 106. The axes of the fixation pegs 120, 122 are angled at about 25 degrees with respect to the posterior bone interface surface 106. The angle of the fixation pegs can range from about 20 degrees to about 30 degrees.

Each fixation peg can also contain a plurality of axial "flutes" 124 to further increase the surface area e.g., for either cemented or press-fit applications. The femoral knee component can also be configured to include only one fixation member extending from any region of the bone interface surface. In the present embodiment the bone interface surfaces 102, 104, 106 are optionally shown to include a waffle pattern 108 to

enhance the surface area of the interface surface. However, other types of surfacing are equally possible as described below.

The about 25 degree angle of the fixation pegs 120, 122 of the present embodiment advantageously allows the femoral component to be implanted using an anterior approach. Moreover, the about 25 degree angle is especially advantageous when implanting the femoral component using a minimally invasive surgical approach where the incision is small and consequently exposure of the knee joint is small.

Another aspect of the present invention includes positioning the fixation member (e.g., peg 120) at a fixed position relative to the anterior aspect of the unicondylar femoral knee implant 100 for all femoral implant sizes. Referring back to FIG. 4, the first fixation peg 120 is at a fixed position at a predetermined constant distance D from the anterior aspect of the unicondylar femoral knee implant 100. Maintaining the fixation member 120 at a fixed or constant position relative to the anterior aspect of the unicondylar femoral knee implant 100 for all femoral implant sizes allows for an easier transition when changing sizes. Typically, knee implants are good in extension and tight in flexion when assessing a knee during trialing or the trial phase. Accordingly, a larger or smaller size implant may be required, thus necessitating the need for additional bone cuts. However, with the present inventive unicondylar femoral knee implant 100, the need for additional distal resections is substantially eliminated for a knee tight in flexion, resulting in a simplification of the overall technique required to intraoperatively change implant sizes.

A unicondylar femoral knee implant component made in accordance with the present invention can be made from any suitable biocompatible material, such as

titanium, commercially pure titanium or titanium alloy, cobalt chromium alloy, nickel- cobalt, ceramics, or stainless steel. The unicondylar femoral knee component 100 can also be configured to have a bone engaging surface texture such as prismatic pattern, waffle pattern, porous structures, insets, recesses, or the like to increase the surface area for either cemented or press-fit applications. The present inventive femoral components can also be coated with biologic substances such as osteoinductive {e.g., Osteogenic Protein-1 (OPl)) and/or osteoconductive materials (e.g., hyrdoxyapatite) that facilitates fixation of the implant to bone. However, any surface texture that allows on-growth or in-growth of the bone may also be used. FIGS. 5 and 6 illustrate an embodiment of a tibial bearing component 200 according to the present invention. FIG. 5 illustrates a perspective inferior view of the tibial bearing component. The tibial bearing component 200 has a top portion 202 and a bottom portion 204. The tibial bearing component 200 is symmetric about a midline plane M and can be used for either a right or left knee. The top portion 202 has a superior articulating surface 206 that articulates with a corresponding unicondylar femoral knee component 100, as shown in a perspective superior view in FIG. 6. The top portion 202 is anatomic in shape and approximately matches the outside shape of a corresponding tibial tray component 300 (FIG. 9a). The tibia bearing articulating surface 206 has a single medial/lateral radius 208 as shown in FIG. 7 and an elliptical anterior/posterior radius i.e., the single sagittal radius (not shown). In an embodiment, the medial/lateral radius of the tibial bearing articulating surface 208 is about 127 mm. When the tibial bearing component is mated with a corresponding unicondylar femoral knee component 100 having a single medial/lateral radius 116 of about 38mm, the

resulting system advantageously allows for plus or minus about 10 degrees of varus/valgus misalignment and a decreasing amount of constraint at higher degrees of flexion.

Referring again to FIG. 5, the bottom portion 204 of the tibial bearing component 200 is geometric and matches the inside shape of the mating tibial tray component 300 (FIG. 9a). The bottom portion 204 has an undercut 210a, 210b on the posterior and anterior aspects. During engagement with the tibial tray component 300, the undercut 210a or 210b will engage a corresponding posterior lip 316 (FIG. 9a), on the posterior aspect of the peripheral vertical rim 310 of the tibial tray component 300, depending upon whether the implant is implanted into the left or right knee. The bottom portion 204 also has four flexible catches 212, 214, 216, 218 to receive corresponding latches 317, 318 on the tibial tray component 300 (FIG. 9a). The catches 212, 214, 216, 218 are used to secure the tibial bearing component 200 onto the tibial tray component 300. In the present embodiment the catches 212, 214, 216, 218 are positioned as shown in FIG. 5 and only engage two latches 317, 318 on the tibial tray component 300 (FIG. 9a). The additional two catches are available to allow the implant to be used in either a right or left configuration.

The catches 212, 214, 216, 218 are formed within the bottom portion of the tibial bearing implant component. As shown in FIG. 8, each catch has an opening 220 in the bottom portion of the tibial bearing component 300 such that the opening 220 faces the peripheral vertical rim 310 of the tibial tray component 300 when seated. The opening 220 is in fluid communication with a second opening 222 on the distal surface 224 of the

tibial bearing component 300. The resulting configuration of the two openings 220, 222 results in a flexible catch.

The flexible catches 212, 214, 216, 218 are positioned to catch or latch onto corresponding protrusions or latches 316, 318, on the tibial tray component 300. The flexible catches 212, 214, 216, 218 allows for the tibial bearing to be press-fitted onto the tibial tray component 300 for secure fixation of the tibial bearing to the tibial tray component. The tibial bearing component 200 allows for insertion onto the tibial tray component 300 by applying a predominately posteriorly directed force, thus enabling the assembly of the tibial bearing 200 and the tibial tray 300 to be more compatible with a MIS surgical approach.

The tibial bearing component 200 can be made from any suitable material, such as ultra-high molecular weight polyethylene ("UHMWPE"), ceramics, or other suitable polymers.

The tibial bearing 200 is assembled or attached onto the tibial tray 300 to form a tibial knee prosthesis. The assembly can take place either before or after implantation of the tibial tray 300 into the prepared tibia. A preferred technique for fixing or seating the tibial bearing 200 onto the tibial tray 300 is to slide the tibial bearing 200 onto the tibial tray 300 from the anterior direction so as to engage the tibial tray's posterior lip 316. After engagement of the posterior lip 316, a slight anterior-downward force is applied to the anterior portion of the tibial bearing 200 to snap the tibial bearing 200 onto the tibial tray 300. The flexible catches and undercuts of the tibial bearing 200 forms part of the tibial prosthesis' s locking mechanism.

An advantage of the present invention is that the mutually engaging bearing surfaces of the femoral component 100 and the tibial bearing component 200 provides better contact stress where the loads are greater and less constraint where more motion is necessary. Another advantage is that the articulation between the femur and tibia allows for a high degree of anterior clearance during flexion and good femoral-tibial contact throughout the entire range of motion. An advantage of the tibial bearing 200 is that the flexible catches allows for a tight assembly onto the tibial tray by allowing the flexible catches to deflect during insertion and take up laxity after catching the latches. Yet another advantage is that the tibial bearings are symmetric, thus reducing the amount of inventory required for a unicondylar implant system. An advantage of the tibial prosthesis' s locking mechanism is that the design eliminates the need for any third body locking feature, such as a metal wire or ring, which makes the tibial prosthesis more compatible with gas sterilization techniques and reduces micromotion as a result of third- body wear. FIG. 9a illustrates a tibial tray component 300 according to one embodiment of the present invention. FIG. 9a is a perspective superior view of the tibial tray component 300. The tibial tray 300 includes a tray member 302 and a keel 322 (shown in FIG. 10). The tray member 302 has a peripheral vertical rim 310 with an exterior profile defined by a posterior curvature 304, medial curvature 306, an anterior curvature 308, and a medial section 312. This overall profile provides good cortical bone coverage without overhang in the posterior, medial, or anterior aspects. The tibial tray geometry 300 is designed to match regional anatomy (e.g., patients from Europe, USA, Asia, Latin America, etc.) and can be adapted region-by-region.

The interior profile 314 of the peripheral vertical rim 310 is configured as shown in FIG. 9a and matches the bottom portion 204 geometry of the tibial bearing component 200. A protrusion or lip 316 is positioned on the posterior aspect of the tibial tray 300 that extends inwards from the upper most portion of the peripheral vertical rim 310. The tray member 302 also has two latches 317, 318, that protrude inward from the peripheral vertical rim 310. The latches 317, 318, are positioned to correspond in position with the catches 212, 214, or 216, 218 on the tibial bearing component 200 depending on whether a right or left knee is being operated on. The latches may also be chamfered 320, for example at about 30 degrees, to allow for easier insertion of the tibial bearing component, as shown in FIG. 9b.

FIG. 10 is a perspective view of the inferior side or underside of the tibial tray component 300. Orientation references such, as medial or lateral, are given assuming the device is implanted in the medial femoral compartment of the left knee. The same tibial tray 300 can be implanted in the lateral compartment of the opposite knee. According to one embodiment, the tibial tray component 300 has a tibial keel 322.

The tibial keel 322 has a vertical keel section 324 extending from the inferior surface 326 of the tibial tray 300 to a keel foot region 328. The keel foot region 328 has a bottom planar surface 330 angled at about 30 degrees relative to the inferior surface 326 of the tibial tray 300 so as to form a down-plane or posterior slope. The term down-plane is used herein to describe the keel foot region being at an angle relative to the inferior surface of the tibial tray. The keel foot 328 is shaped to have a posterior taper, so as to have a tapered angle leading from the anterior aspect to the posterior aspect of the keel foot 328, i.e., the anterior aspect being wider than the posterior aspect. The angle of the

keel foot 328 can be any angle less than 90 degrees relative to the inferior surface of the tibial bearing tray 326 so as to maintain a horizontal aspect of the keel foot region 328. A horizontal aspect is maintained so long as when describing the angle of the foot region relative to the inferior surface 326 of the tibial tray 300 in X-Y coordinates, the X coordinate value is greater than zero. In one embodiment, the keel foot region 328 can be in the shape of a planar isosceles triangle. The shape of the keel foot region 328 is described for illustrative purposes and not for purposes of limitation. The shape of the keel foot region 328 can be of any configuration that results in a narrowing of the posterior aspect of the foot region, such as that of a "Danforth^" style boat anchor. The tibial keel 322 can be used with any device, such as a tibial prosthesis for a total knee implant; its use is not limited to unicondylar knee implant systems.

The tibial keel 322 is a self-locking keel that provides resistance to anterior and posterior translation, liftoff, and subsidence as a result of its keel foot design. The horizontal aspect of the keel foot 328 resists liftoff and subsidence. The vertical aspect of the keel foot 328 resists anterior and posterior motion.

The downward angled keel foot 328 allows the tibial tray component 300 to be implanted from the anterior aspect of the knee joint so as to be compatible with a MIS surgical approach. The downward angled keel foot 328 also provides a securing or clamping force to further secure the tibial tray component 300 to the prepared proximal tibia bone. The tibial tray component 300 also allows for implantation of the tibial tray component 300 onto the prepared tibia by applying a force predominantly in the posterior direction. Thus, the tibial tray 300 advantageously eliminates or minimizing the need for a force normal to the prepared tibia to implant a tibial bearing component. Consequently,

the amount of expose required for a unicompartmental knee implant surgery is further minimized.

The illustrated and described tibial tray can also include keel pegs 332, 334 as shown in another embodiment in FIG. 11. The pegs 332, 334 can further include normalizations 336 for additional fixation when implanted. Normalizations 336 are step- like contours along the surface of the pegs.

A tibia tray component made in accordance with one of the present embodiments can be made from any suitable biocompatible material such as titanium, titanium alloy, commercially pure titanium, cobalt chromium alloy, nickel-cobalt, ceramics, or stainless steel. The tibial tray component can also be configured to have a bone engaging surface texture, such as a prismatic pattern, waffle pattern, porous structures, insets, recesses, or the like to increase the surface area for either cemented or press-fit fixation. Biologies, such as osteoinductive {e.g., OPl) and/or osteoinductive materials {e.g., hyrdoxy apatite) that facilitates fixation of the implant to bone, can also be added to the bone engaging surfaces of the tibial tray component. However, any surface texture that allows on- growth or in-growth of the bone may also be used.

The tibial implant prosthesis can also be made as an all-poly one piece construction. That is the tibial bearing component and the tibial bearing component is unitized and fully constructed from a polymeric material. The present invention also provides for a unicondylar knee instrument system that can be used for implanting a unicondylar knee prosthesis in either the medial or lateral condyle of the left or right knee.

FIG. 12 illustrates an embodiment of a unicondylar tibial alignment guide 1100 assembled to a unicondylar tibial resection guide 1200. The unicondylar tibial alignment guide 1100 can be provided with an ankle clamp 1102, a connecting rod 1104, a bottom sliding section 1112, a middle sliding section 1110, a top sliding section 1114, a pivoting tibia anchor 1118, a varus/valgus clamp 1122, a flexion/extension clamp 1124, a middle slide clamp 1126, and a top slide clamp 1128. The bottom sliding section 1112 can be configured with a metatarsal pointer 1106. The unicondylar tibial resection guide 1200 attaches to the top sliding section 1114 as shown. The unicondylar tibial resection guide 1200 is adjustably connectable to the unicondylar tibial alignment guide 1100 and configured to operate concurrently with the unicondylar tibial alignment guide 1100.

The ankle clamp 1102 may be attached to an ankle by spring loaded arms, elastic straps, extension springs, or other like devices known in the art. The ankle clamp 1102 has a varus/valgus clamp 1122 about which a connecting rod 1104 slides in a substantially medial/lateral direction. As further detailed in FIG. 13, the ankle clamp 1102 includes an ankle clamp base

110, a pair of base arms 112a, 112b, a pair of clamping arms 120a, 120b and a pair of springs 118a, 118b connected to the base arms 112a, 112b and the pair of clamping arms 120a, 120b. The base arms 112a, 112b each has a slot or opening 114a, 114b (not shown) for a spring to pass through. At one end of the slot, for example 114a, is connected a dowel 116a upon which one end of the spring 118a is attached. The other end of the slot 114a is connected to the clamping arm 120a by a pair of pins 122a, 122b such that the clamping arm 120a pivots about the pins 122a, 122b. The opposing end of the spring 118a is connected to a dowel 124a that is offset a certain distance from the pins

122a, 122b along the clamping arm 120a having a slot or opening 126a for the spring 118a to pass through. The opposing base arm 112b, clamping arm 120b, and spring 118b are configured in the same manner as base arm 112a, clamping arm 120a, and spring 118a. The slots 114a, 114b & 126a, 126b of the base arms and clamping arms along with the offset dowels 124a, 124b allow the clamping arms 120a, 120b to toggle about pins 122a, 122b & 122c, 122d as a result of springs 118a, 118b.

The springs 118a, 118b connect the clamping arms 120a, 120b to the ankle clamp base 110 such that the springs constantly provides a force to open the clamping arms 120a, 120b. In addition, the springs 118a, 118b can also be configured to provide a clamping force to close the clamping arms 120a, 120b around the ankle of a patient. It is understood that the ankle clamp 1102 can clamp over the patient's ankle that is completely covered by soft tissue as well as surgical wrap. The present ankle clamp embodiment advantageously allows the instrument to be easily cleaned and steam sterilized as a result of its design. FIG. 14 illustrates the position of the clamping arms 120a, 120b in the open position. The connection between the ankle clamp base arms 112a, 112b and the springs 118a, 118b can be configured to allow the clamping arms 120a, 120b to remain open when the ankle clamp 1102 is in the open position. The ankle clamp design advantageously allows the user to toggle the ankle clamp from the open to close position and easily assemble the ankle clamp to the patient without the use of manual force to keep the clamp open during assembly to the patient. However, the present unicondylar tibial alignment guide embodiment can also be used with any conventional ankle clamp.

Additional suitable ankle clamp designs are discussed in U.S. Patent No. 5,197,944 to Steele, which is hereby incorporated by reference in its entirety.

Referring back to FIG. 12, the main shaft of the unicondylar tibial alignment guide 1100 includes three sections, a top sliding section 1114, a middle sliding section 1110, and a bottom sliding section 1112. The top and middle sliding sections 1114, 1110 slide into the bottom sliding section 1112 in a telescoping-like manner. The bottom sliding section 1112 has a middle slide clamp 1126 that fixes or locks-in the position of the middle sliding section 1110 relative to the bottom sliding section 1112. The middle sliding section 1110 has a top slide clamp 1128 that fixes the position of the top sliding section 1114 in a fixed position relative to the middle sliding section 1110. The shape of the sliding sections can be of any suitable shape that allows one section to slide against or into another section. In the present embodiment, the middle slide clamp 1126 can be positioned at the superior end of the bottom sliding section 1112. The middle slide clamp 1126 has a knob 1130 for engaging a screw (not shown) and a casing 1132 rigidly fixed to the bottom sliding section 1112. The bottom sliding section 112 can be configured to have an I-shaped shaft. The middle sliding section 1110 can be configured to have an elongated U-shape that slides against the inset region formed by the I-shaped shaft of the bottom sliding section 1112. The top of the middle sliding section 1110 can have a corresponding top slide clamp 1128, similar to the middle slide clamp 1126, about which the top sliding section 1114 slides against. The top sliding section 1114 can be configured to have an elongated rectangular shape and a curved top section 1116. The top sliding section 1114 can also be configured with a scale 1134 for measuring the depth of a tibia resection as further described below and illustrated in FIG. 15. The unicondylar

tibial alignment guide 1100 can alternatively be configured with more than two telescoping sections.

Attached to the end of the curved top section 1116 can be a pivoting tibia anchor 1118 as shown in FIG. 15. The pivoting tibia anchor 1118 has openings 1120a, 1120b, and 1120c (not shown) that allows for a fixing element such as a fixation pin (not shown) to secure the tibia anchor 1118 to a tibia bone. The orientation of the openings 1120a-c varies depending upon the pivot of the tibia anchor 1118. The pivoting tibia anchor can alternatively be configured to have any reasonable number of passages to allow for additional fixation pins to be used. Referring back to FIG. 12 the bottom sliding section 1112 can be configured with a metatarsal pointer 1106 at its most distal end. The bottom portion of the bottom sliding section 1112 also has a substantially horizontal passage 1108 that allows for the connecting rod 1104 to slide in a substantially anterior/posterior direction. The position of the connecting rod 1104 sliding about the horizontal passage 1108 can be fixed in position by the flexion/extension clamp 1124, similar to that of the middle slide clamp 1126.

The connecting rod 1104 connects the ankle clamp 1102 and the bottom sliding section 1112. The connecting rod 1104 can be shaped to have two substantially orthogonal sliding ends 1104a, 1104b. FIG. 16 illustrates an embodiment of a tibial stylus 1300 slidingly engaged with the unicondylar tibial resection guide 1200. The tibial stylus 1300 has a tibial stylus base 1302 and a tibial stylus pointer 1308. The tibial stylus base 1302 can have an elongated base end 1304 and a U-shaped connector end 1306 for slidingly engaging the extended

arm 1202 of the unicondylar tibial resection guide 1200. The tibial stylus pointer 1308 can be shaped as shown in FIG 16. The tibial stylus pointer 1308 has a base member 1310 and a tibial stylus point 1314. The base member 1310 has an opening 1312 to allow the tibial stylus pointer 1308 to slide along the length of the elongated base end 1304 of the tibial stylus base 1302. The position of the tibial stylus point 1314 can be configured to be at about 0 mm above the surface of the unicondylar tibial resection guide cutting guide surface 1204.

The tibial stylus base 1302 engages the unicondylar tibial resection guide 1200 by sliding engagement of the U-shaped connector end 1306 along the open top surface of the extended arm 1202 of the unicondylar tibial resection guide 1200. The tibial stylus 1300 is free to move anteriorly/posteriorly, medially/laterally, or to rotate internally and externally when assembled. The tibial stylus point 1314 slides freely along the tibial stylus base 1302. The overall assembly allows for the tip of tibial stylus point 1314 to freely move along the entire surface of a proximal tibia. In an alternative embodiment the tibial stylus can be configured as a single piece construct having a tibial stylus point and a magnetized base member. The base member therefore can be magnetically fixed to the cutting surface of the tibial resection guide. Thus, the tibial stylus, while semi-rigidly fixed to the surface of the tibial resection guide, can move freely along the plane of the unicondylar tibial resection guide, advantageously allowing the tibial stylus point to move freely along the entire surface of a proximal tibia. In yet another embodiment, a tibial stylus can be configured for sliding engagement of the tibial stylus base along a top surface of a member. The member can be a cutting guide, flange, or any other structure configured to support the tibial stylus.

In operation, the unicondylar tibia resection guide 1200 can be assembled to the top sliding section 1114 as shown in FIG. 12. The unicondylar tibial resection guide 1200 can be configured to slide proximally and distally along the top sliding section 1114 of the unicondylar tibia alignment guide 1100. Proximal and distal positioning can be fixed by use of the tibial resection guide locking screw clamp 1210. The tibial stylus 1300 can then be assembled to the unicondylar tibia resection guide 1200 as shown in FIG. 16.

With the unicondylar tibia resection guide 1200 and unicondylar tibia alignment guide 1100 positioned against the anterior aspect of the knee, the tibial stylus point 1314 is positioned on the proximal surface of the tibia, such as the sulcus, to indicate a zero reference point. The top sliding section 1114 is then repositioned such that the unicondylar tibia resection guide 1200 is set to the zero mark position 1136 located on the scale 1134 of the top sliding section 1114. The unicondylar tibial resection guide 1200 can be then secured to the unicondylar tibial alignment guide 1100 and the pivoting tibia anchor 1118 pinned (via opening 1120a) to the proximal tibia by fixation pins (not shown) to provide a tibia reference point. After the unicondylar tibial resection guide 1200 is fixed in position, the tibial stylus 1300 can be removed. The unicondylar tibia alignment guide 1100 however can advantageously remain in place for the distal and posterior resections, allowing the flexion space to be easily adjusted relative to the extension space by increasing or decreasing the tibia slope, if necessary, and allowing for the tibial resection to be made with the unicondylar tibial alignment guide 1100 in position. Thus, overall alignment can be improved since the tibial resection can be simultaneously made with the unicondylar tibial alignment guide 1100 in place.

An advantage of the present embodiment is that it allows for the user to easily adjust resection levels compared to commercial tibial resection systems which typically only allow for limited adjust means. The present embodiment also allows for ease in repositioning fixation pins or for adding additional fixation pins. In addition, the present embodiment allows for the tibial resection guide to be adjustable in three degrees of freedom, moving up and down (heaving), tilting up and down (pitching), and tilting side to side (rolling).

The length of the tibia alignment guide can be adjusted by extending or retracting the middle sliding section 1110 and by extending or retracting the top sliding section 1114. Having at least two telescoping sections allows for a greater range of length adjustment to accommodate for larger or smaller patients. Once the correct length is achieved the length adjustments can be locked in position by securing the middle slide clamp 1126 and the top slide clamp 1128.

The unicondylar tibia alignment guide 1100 is free to rotate in a varus/valgus orientation about the pivoting tibial anchor (via a fixation pin through opening 1120a) when the varus/valgus clamp 1122 is not secured. Varus/valgus alignment can be accomplished by aligning the metatarsal pointer 1106 with the second metatarsal bone and also by aligning the vertical axes of the metatarsal pointer 1106, middle sliding section 1110, and top sliding section 1114 with the vertical axis of the tibia. Once varus/valgus alignment is achieved varus/valgus rotation can be fixed in position by securing the varus/valgus clamp 1122. Varus/valgus constraint can be further enhanced by a second or third fixation pin (not shown) through additional passages or openings in the pivoting tibia anchor 1118.

The unicondylar tibia alignment guide 1100 is free to rotate in a flexion/extension orientation about the pivoting tibia anchor 1118 when the flexion/extension clamp 1124 is not tightened. Flexion/extension alignment can be achieved by referencing tibial slope. Accordingly, the unicondylar tibia alignment guide 1100 can be rotated in the flexion/extension orientation until the cutting guide surface 1204 of the unicondylar tibial resection guide 1200 is parallel with the tibial slope. Once flexion/extension alignment is achieved flexion/extension rotation can be fixed by securing the flexion/extension clamp 1124.

FIG. 17 illustrates an embodiment of a unicondylar tibial resection guide 1200. The unicondylar tibial resection guide 1200 includes an extended arm 1202 having a cutting guide surface 1204, a tibial resection guide base 1206, and a tibial resection guide locking screw 1210.

The extended arm 1202 of the unicondylar tibial resection guide 1200 has a planar cutting guide surface 1204 that guides a cutting instrument such as a surgical saw blade. The posterior aspect of the extended arm 1202 can be contoured to match the profile of an anterior tibial bone surface. The extended arm 1202 can be connected to the tibial resection guide base 1206. The extended arm 1202 and the tibial resection guide base 1206 can be a modular design or of a single piece design. The tibial resection guide base 1206 has a substantially vertical passage 1208 that allows for the guide base 1206 to be assembled with the unicondylar tibial alignment guide 1100. The locking screw 1210 can be positioned orthogonally to the passage 1208 to secure the unicondylar tibial resection guide 1200 to the unicondylar tibial alignment guide 1100 as shown in FIG. 15. An advantage of the present unicondylar tibial resection guide 1200 embodiment is that the

extended arm 1202 having the cutting guide surface 1204 can be made to any needed thickness. The overall thickness of the extended arm can be about 1 to about 100 mm or preferably about 2 to about 5 mm. Alternatively, the unicondylar tibial resection guide 1200 can be configured with multiple cutting guide surfaces. FIG. 18 illustrates an embodiment of a knee joint instrument handle assembly

1400. As shown in FIG. 18, the instrument handle assembly 1400 includes an elongated handle 1402, a base 1406, and a spacer block 1408. The elongated handle 1402 can be curved downward to allow greater clearance for cutting instruments during use. The base 1406 has a pair of slide tracks 1404a and 1404b (not shown). The spacer block 1408 attaches to the base 1406. In the present embodiment, the spacer block 1408 attaches to the base 1406 via magnetic attraction i.e., magnets. However, other similar mechanisms known in the art, such as ball plungers, detents, spring connectors, screws, snaps, and temporary epoxy, can also be used. The elongated handle 1402 can also be configured to have two openings 1410a, 1410b for attaching an alignment rod holder 1500. The alignment rod holder 1500 has two dowels 1502a, 1502b that pass through the two openings 1410a, 1410b in the alignment rod handle 1402. The dowels 1502a, 1502b are connected to a first and second alignment rod holder base 1504a, 1504b having two dowel openings 1506a, 1506b. The alignment rod holder 1500 can alternatively be configured with a single dowel and a single dowel opening. In the present embodiment, the alignment rod holder 1500 can be configured to have four substantially vertical passages or openings 1508a, 1508b, 1508c, 1508d for supporting an alignment rod (not shown). In operation, the sliding alignment rod holder 1500 slides substantially in the medial/lateral direction to allow the alignment rods to be positioned adjacent the anterior

tibia when used in a unicondylar surgery of the medial or lateral compartment of the left or right knee. An advantage of the present embodiment of the knee joint instrument handle assembly and alignment rod holder is that the alignment rod can be placed directly anterior of the tibia, thus eliminating possible error such as parallax error, especially during unicondylar knee surgery.

FIG. 19 illustrates an embodiment of a unicondylar femoral distal resection guide 1600. The unicondylar femoral distal resection guide 1600 has a channel 1602 to guide the path of a cutting instrument, such as a surgical saw. The unicondylar femoral distal resection guide 1600 can be configured to be reversible, such that it can be used for either the right or left knee while the open side of the channel 1602 always faces the outside of the knee. The unicondylar femoral distal resection guide 1600 can also be provided with openings 1604a, 1604b for the passage of a fixing element such as a fixation pin (not shown) to secure the cutting block to the distal femur. A pair of shoulders 1606a, 1606b are positioned on the ends of the unicondylar femoral distal resection guide 1600 for sliding engagement with the slide tracks 1404a, 1404b of the instrument handle assembly

1400. The unicondylar femoral distal resection guide 1600 is symmetric about a horizontal plane H. In an alternative embodiment the unicondylar femoral distal resection guide can be provided with multiple channels for guiding a cutting instrument.

In operation, after a tibia has been prepared or resected, the instrument handle assembly 1400, alignment rod holder 1500, and unicondylar femoral distal resection guide 1600 are assembled and positioned within the knee joint. A series of incrementally sized spacer blocks 1408' as shown in FIG. 20, are then used to evaluate flexion and extension space after the tibia resection is made. Spacer block thicknesses are designed

to represent the corresponding tibial implant thicknesses, which are typically incremented in whole millimeters, such as 6, 7, 8, 9, and 10 mm. Fixation pins (not shown) are then used to secure the unicondylar femoral resection guide 1600 to the femur.

The knee joint instrument handle assembly 1400 provides for easy removal from the knee joint even when the unicondylar femoral resection guide 1600 is fixed to the femur manually or with pins. The positioning of the openings 1604a, 1604b in the unicondylar femoral resection guide 1600 allows for easy access for the saw while the fixation pins are in place. Moreover, the distal femoral resection can be advantageously made with or without the knee joint spacer block in place. The unicondylar femoral distal resection guide 1600 can be removably connetable or slidingly and removably connectable to the base 1406. The unicondylar femoral distal resection guide 600 can be configured to operate concurrently and independently with the space block 1408.

A series of unicondylar femoral distal resection blocks 1600' is shown in FIG. 21. Each unicondylar femoral distal resection block 1600 can be configured to have a different femoral resection depth D _R relative to the superior surface of the base 1406. Accordingly, the resection level T, as shown in FIGS. Ilia and 111b can be made with varying combinations of spacer blocks 1408'and unicondylar femoral distal resection guides 1600'.

FIG. 24 illustrates a unicondylar femoral posterior resection guide 1700. Similar to the unicondylar femoral distal resection guide 1600, the unicondylar femoral posterior resection guide 1700 has a channel 1702 to guide the path of a cutting instrument. The unicondylar femoral posterior resection guide 1700 can be configured to be reversible, such that it can be used for either a right or left knee while the open side of the channel

always faces the outside of the knee. The unicondylar femoral posterior resection guide 1700 can also be provided with openings 1704a, 1704b, 1704c for the passage of fixation pins (not shown) to secure the cutting block to the femur. A pair of shoulders 1706a, 1706b is positioned on the ends of the posterior resection guide for sliding engagement with the slide tracks 1404a, 1404b of the instrument handle assembly 1400.

The unicondylar femoral posterior resection guide 1700 can be provided as a series of unicondylar femoral posterior resection guides 1700' (FIG. 25), similar to the series of unicondylar femoral distal resection guides 1600'. Likewise, each unicondylar femoral posterior resection guide 1700 can be configured to have a different posterior resection depth DR relative to the superior surface of the base 1406 (e.g., 4, 5, 6, 7, 8, 9, and 10mm). The resection level T for making a distal resection can be made with varying combinations of spacer blocks 1408' and unicondylar femoral posterior resection guides 1700'.

The present unicondylar knee instrument system allows for femoral resection depths to be determined based upon the knee joint pathology, i.e., the least affected or least damaged surface of the femoral knee. That is, if the distal surface of the femur is damaged (FIG. 22a), it would be desirable to reference off the posterior condyle to determine the appropriate spacer block/resection guide combination to use. Alternatively if the posterior surface of the femur is damaged (FIG. 23b), it would be desirable to reference off the distal condyle to determine the appropriate spacer block/resection guide combination to use.

For example, if the least affected site is the posterior condyle (FIG. 22b), the appropriate knee joint spacer block thickness needed to fill the flexion space F would be

determined with knee in flexion. Once the appropriate spacer block thickness is determined, for example a 10mm spacer block, then the overall thickness T can be determined taking into account the implant thickness, for example a 5mm thick implant {i.e., a 5mm resection guide is necessary). The appropriate spacer block thickness is one that properly balances the knee {i.e., collateral ligaments are not too tight or too loose). Thus, the proper spacer block/resection guide combination can be one that provides for an overall thickness T of 15mm. Thereafter, the extension space E can be filled with an appropriate spacer block 1400, (most likely a larger thickness than that necessary to fill the flexion space) and the appropriate distal resection guide can be selected to provide for an overall thickness of 15mm. That is, if the necessary spacer block to fill the extension space E is 12mm, then the appropriate distal resection guide would be 3mm. Thus, the present unicondylar knee instrument system allows the user to compensate for diseased or damaged surfaces of the bone by choosing different size spacer blocks 1408' and unicondylar femoral resection guides 1700 ^* and initially referencing off the least affected region of the femur (either distal or posterior) to provide for the most accurate restoration of the anatomic joint line.

Regardless of whether the distal femur is damaged or not, the distal resection is made first. Making the distal resection first allows for a much better angular reference surface to make the posterior resection later in the surgery. An advantage of the present system is that the instrumented technique reduces the need for up-sizing or down-sizing the implant size as the bone resection and knee balancing steps are concurrently conducted. That is, the resection guides are used concurrently with the balancing and alignment instruments. This allows for greater

accuracy in femoral resections and in balancing the knee joint, compared to conventional systems that make separate tibial and femoral resections that are not referenced off of each other. The present system also advantageously allows for determining the proper resection depth based upon the least affected condyle and then assembling the necessary combination of spacer block and resection block to provide the appropriate resection depth.

FIG. 26 illustrates an embodiment of a unicondylar femoral chamfer and peg-hole guide 1800. The guide 1800 can align a femoral chamfer cut on the distal femur and guides the drilling of peg holes for implanting a unicondylar femoral implant having pegs. The guide 1800 can be L-shaped having a distal end 1802 and a posterior end 1804. The distal end 1802 has two openings 1806, 1808 and a flange opening 1810, for guiding a cutting instrument, such as a surgical drill, for making peg holes. The position of the openings 1806, 1808, 1810 correspond to the position of peg holes on a corresponding unicondylar femoral knee implant having pegs. The distal end has an additional opening 1812 for accepting a fixation pin (not shown) to secure the guide 1800 to the distal femur. The opening 1812 can be oriented to allow for easy saw and drill access when the fixation pin is in place. The unicondylar femoral chamfer and peg-hole guide 1800 can also be configured to have multiple openings for accepting multiple fixation pins. A chamfer resection guide slot 1814 extends from the distal end 1802 to the posterior end 1804 to guide a cutting instrument in making a chamfer cut on the distal femur to closely match that of a unicondylar femoral knee implant having a chamfer bone engaging surface.

In operation, a chamfer resection can be made using the chamfer resection guide slot 1810 and a cutting instrument, such as a sagittal saw. The peg holes are made by using the peg-hole guides 1806, 1808, 1810 and a cutting instrument, such as a step drill.

The unicondylar femoral chamfer and peg-hole guide 1800 can be fixed to the femur with at least one fixation pin.

The chamfer and peg-hole guide 1800 can also be used to size the femur and to determine the medial lateral position of the definitive implant. The distal and posterior resections are not size dependent thus, the user does not need to determine implant sizing until the last femoral resections are made i.e., femoral chamfer resection. The femoral chamfer cut is the only implant size dependent resection. The distal profile 1816 closely matches the distal profile of the definitive implant to allow for proper sizing and medial/lateral positioning based upon fit and bone coverage. The posterior profile 1818 also closely matches that of the definitive implant so that a check for overhang and coverage can be made. The unicondylar chamfer and peg hole guide can also be provided as a series of chamfer and peg hole guides 1800', as shown in FIG. 27, similar to the series of unicondylar femoral distal resection guides 1600'. Likewise, each chamfer and peg hole guide can be configured to match the resection levels of the corresponding unicondylar femoral distal 1600' and posterior 1700' resection guides.

The present unicondylar knee instrument system also provides for a method of preparing a femoral condyle of a knee for the implantation of a unicondylar femoral knee implant (as shown in FIG. 28) that includes the steps of resecting a tibia (Step 900), determining a least affected site (Step 902), wherein the site is a distal femoral condyle or a posterior femoral condyle, positioning the knee such that the least affected site faces the

tibia (Step 904), positioning a spacer block between the resected tibia and the least affected site (Step 906). Then the step of determining an overall thickness for balancing the knee and resecting the femur to a thickness of a corresponding unicondylar femoral implant (Step 908), determining a spacer block and femoral cutting block combination that equals the overall thickness when the knee is in extension (Step 910), and resecting the distal femoral condyle (Step 912).

The embodiments of the present unicondylar knee implant and instrument system are shown and described for purposes of illustration only and not for purposes of limitation. While there have been shown, described, and pointed out fundamental novel features of the invention as applied to several embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the devices illustrated, and in their operation, may be made by those skilled in the art without departing from the spirit and scope of the invention. Substitutions of elements from one embodiment to another are also fully intended and contemplated. It is also to be understood that the drawings are not necessarily drawn to scale, but that they are merely conceptual in nature. The invention is defined solely with regard to the claims appended hereto, and equivalents of the recitations therein.

The above mentioned patents, applications, test methods, and publications are hereby incorporated by reference in their entirety.