Patent ID: 12251315

DETAILED DESCRIPTION

The following description discloses embodiments of a total ankle replacement device.

In the following detailed description, numerous specific details are set forth to provide a full understanding of the present disclosure. It will be apparent, however, to one ordinarily skilled in the art that embodiments of the present disclosure may be practiced without some of the specific details. In other instances, well-known structures and techniques have not been shown in detail so as not to obscure the disclosure.

The method and system disclosed herein are presented in terms of a device for use in the ankle. It will be obvious to those of ordinary skill in the art that this same configuration and method can be utilized in a variety of applications that require a prosthesis that provides motion. Nothing in this disclosure should be interpreted, unless specifically stated as such, to limit the application of any method or system disclosed herein to the ankle.

Referring now toFIGS.1A through1E, an embodiment of the invention comprises an assembly that comprises a tibial implant100, a talar implant300, and an intermediate implant200that can fit between the tibial implant100and the talar implant300. The tibial implant100may be suitable for implantation into or onto a prepared end of a tibia. The talar implant300may be suitable for implantation into or onto a prepared surface of a talus. The intermediate implant200may attach to tibial implant100and may articulate with respect to talar implant300.

Referring now toFIGS.2A through2K, there is shown a tibial implant100. Tibial implant100may comprise an anterior edge101A and a posterior edge101P, although it is understood that this nomenclature is only for sake of description. The tibial implant100may comprise a tibia-facing surface102and a lower surface104that is generally opposed to the tibia-facing surface102. The tibia-facing surface102may comprise a portion that is generally flat.

The lower surface104may comprise an outer surface106, which may be flat, and an inner surface108, which may be part of a cutout region and which may also be flat. The cutout region defines a boundary with, as shown, first, second, and third internal boundary sides,117,119, and121, respectively. It is not actually necessary that both the outer surface106and the inner surface108be flat, as other shapes are also possible in each case. The inner surface108of tibial implant100may have a centerline109generally along the anterior-posterior direction. Centerline109may be a line of symmetry of inner surface108, which would be halfway between first boundary side117and second boundary side119.

The boundary between outer surface106and inner surface108may comprise first and second dovetails122and124, which may be straight and parallel to each other. More generally, in that location there may be any geometry that allows a sliding capture of a complementary feature of intermediate implant200. Connecting between first dovetail122and second dovetail124may be yet another segment of the boundary between outer surface106and inner surface108. As illustrated, this segment may comprise a third dovetail126, which may occupy at least a portion of a remainder of the cutout perimeter other than first dovetail122and second dovetail124. Third dovetail126may be geometrically identical to first and second dovetails122,124, although it does not have to be. First dovetail122and second dovetail124may be generally straight and may be parallel to each other. Third dovetail126may also be straight and may be perpendicular to first dovetail122or second dovetail124, although this is not essential. There may be a rounded corner between the first dovetail122and third dovetail126, and similarly another rounded corner between second dovetail124and third dovetail126. These rounded corners may comprise the same dovetail shape as on the first second and third dovetails122,124,126. Third dovetail126may be complementary to a corresponding feature of intermediate implant200. At the anterior edge101A of tibial implant100, there may be provided an entrance region111to dovetails122,124such that the entrance region111is wider in the medial-lateral direction than the space between dovetails122,124. Entrance region111may be tapered or otherwise shaped so as to guide intermediate implant200into its desired position within side dovetails122,124.

Extending from the tibia-facing surface102may be a plurality of projections. The projections may comprise a somewhat planar fin130. It is possible that fin130may have one or more through-holes132therethrough. In cross-section taken perpendicular to its overall length direction, fin130may have two long sides134,136and two short sides138,139. The two long sides134,136may be part of flat surfaces that may be parallel or almost parallel to each other or may form a slight taper. Fin130may be sharp or wedge-shaped at its end away from tibia-facing surface102of tibial implant100. The projections may also comprise one or more (two shown) tibial pegs142,144that may be at least somewhat cylindrical. The joints where pegs142,144join tibia-facing surface102may be located both on a common line that is perpendicular to a direction of the dovetails122,124. Tibial pegs142,144preferably may be longer than fin130. Tibial pegs142,144preferably are located at a distance away from the centerline109, and as such are inserted into the cancellous bone in the epiphysis. It is believed, although it is not wished to be limited to this explanation, that the use of a fin130may be helpful (compared to a peg, for example) in securing anchorage of tibial implant100into the bone of the distal portion of the tibia. The distal portion of the tibia is a region where the bone can be relatively soft, and the fin130has greater surface area than a peg would have, thereby securing its position more effectively. Also, the fin130may be self-cutting into the bone, without requiring preparation such as the pre-drilling of a hole. All of this may allow placement of fin130in a position fairly far distal in the tibia, which may be helpful in anchoring to the tibia particularly in preventing the tibial implant100from separating from the tibia during various possible scenarios of motion by the patient. Additionally, the absence of need for hole preparation in the less-accessible distal region of the tibia would be a convenience for the surgeon.

At least some of the projections may have a respective defined lengthwise direction. For a projection such as tibial pegs142,144that is at least partly cylindrical or axisymmetric, the lengthwise direction may be the axis of the cylinder or the axis of symmetry of the tibial peg142,144. Tibial pegs142,144may have a portion of a sphere148A at the tip of the peg, which may be followed by a portion of a cone148B, which may be followed by surface148C formed by a circular arc in revolution around the longitudinal axis of the tibial peg, which may be followed by a cylindrical surface148D. It is believed, although it is not wished to be limited to this explanation, that such a shape of the tip of the tibial peg142,144may be helpful in guiding the pegs142,144into the corresponding hole prepared in the bone, which may involve a close fit between the peg142,144and the prepared bone. For a fin130, the lengthwise direction may be an axis that is midway between respective opposed parallel exterior surfaces of the fin. As illustrated, the tibial implant100may have a midpoint that is halfway between the anterior-most extent of the tibial implant100and the posterior-most extent of tibial implant100, and fin130may be entirely located posteriorly of the midpoint.

The defined lengthwise direction of any of the projections may be inclined at an angle gamma with respect to the generally flat portion of tibia-facing surface102of tibial implant100. The angle may be such that the angle gamma faces toward the posterior of tibial implant100and has an angular measure of between 0 and 90 degrees, more particularly between 20 and 70 degrees. As illustrated, the angle gamma is 45 degrees. Gamma is illustrated inFIG.2Bas being identical for tibial pegs142,144and for fin130, but it is possible that the angle designated as gamma for tibial pegs142,144could have a different value from the angle designated as gamma for fin130. The inequality of angle could be in either direction, in terms of which angle is greater than which other angle.

The respective lengthwise directions of at least some of the projections (tibial pegs142,144and fin130) may be parallel to each other. The directional axis of fin130may be parallel to the respective axis of one or more tibial pegs142,144. Alternatively, the axis of a tibial peg142,144may be parallel to a straight-line segment of a surface of the fin130. Pegs142,144and fin130may be spaced so as to occupy more than one position along the anterior-posterior direction of the tibial implant100, i.e. pegs142,144and fin130can be positioned so as to not all lie in a line running medial-lateral (not all in the same coronal plane). It is possible that pegs142,144may occupy the same position as each other along the anterior-posterior direction of tibial implant100, and fin130may occupy a different position (i.e. they can lie in the same coronal plane). Fin130may be more posterior than pegs142,144.

Tibial implant100may further comprise a pocket160, which may be recessed with respect to inner surface108. As described elsewhere herein, pocket160may be dimensioned so as to cooperate with a feature of intermediate implant200to latch intermediate implant200to tibial implant100. The pocket160of tibial implant100may have side edges that are parallel or at least approximately parallel to the first and second dovetails122,124of tibial implant100, or may have any other suitable geometry. Pocket160may be located either approximately or exactly midway between the first and second dovetails122,124of tibial implant100.

It is further possible that tibial implant100may comprise a tibial implant recess170, which may be located at the anterior edge101A of tibial implant100. Tibial implant recess170may have a lateral dimension that is substantially the same as the lateral dimension of pocket160or of latch260(described hereinafter) of intermediate implant200. Tibial implant recess170may substantially align with pocket160along the direction of side dovetails122,124. Tibial implant recess170may be located either approximately or exactly midway between the side dovetails122,124of tibial implant100.

Referring now toFIG.2F, there is shown a top view of tibial implant100with the tibial implant100being a transparent wireframe so that features on the underside of tibial implant100, such as dovetails122,124and126and pocket160can be seen in relation to features on the upper side of tibial implant100such as pegs142,144and fin130. Similarly,FIG.2G, which is a three-dimensional perspective view, shows tibial implant100as a transparent wireframe so as to show the relative placement of certain features on the upper side and the underside. There may be certain relations between the placement of features on the upper side and the placement of features on the underside of tibial implant100. Such relative placement can serve to connect protruding load-bearing features such as pegs142,144and fin130to portions of tibial implant100that are structurally thick and strong. In other instances, such placement may overlap thicker stronger portions of tibial implant100with regions that are thinner and structurally weaker, and may thereby help to reinforce regions that are thinner and structurally weaker. As illustrated, the connection of fin130to tibial implant100is entirely within the region of dovetails122,124and126, i.e., the connection of fin130to tibial implant100is opposite the inner surface108. However, it would also have been possible that the connection of fin130could partially overlie the inner surface108within dovetails122,124and126and could partly overlie the thicker portion of tibial implant100, outer surface106, that does not have dovetails122,124and126cut out of it. Tibial pegs142,144may, as illustrated, partially overlie the inner surface108within dovetails122,124and126and partially overlie the thicker portion of tibial implant100, outer surface106, that does not have dovetails122,124and126cut out of it. This could structurally reinforce the thinner portion (inner surface108) of tibial implant100.

Referring now toFIGS.2H and2I, there is shown a three-dimensional view of the tibial implant100, upside-down compared to its orientation inFIG.2A. It can be seen that pocket160is recessed from inner surface108. Entrance region111also is visible, as is tibial implant recess170.FIG.2Jshows the edges of first and second dovetails122,124visible in this anterior view.

Referring now toFIG.2K, the tibia-facing surface102may have an external shape that is chosen so as to match closely with the external shape of the prepared lower end of the tibia, when the tibia end is prepared as described elsewhere herein. The tibia, as with bones generally, comprises an outer region of cortical bone that is relatively strong, and an inner region of cancellous bone that is more porous and less strong. The close matching of the external shape of the tibial implant to the outside perimeter shape of the prepared end of the lower tibia is believed to give good mechanical contact and load transfer between the tibial implant and the cortical region of the bone of the tibia. It is believed, although it is not wished to be limited to this explanation, that this close matching of shapes may decrease the likelihood of problems with subsidence of the tibial implant into the tibia.

The tibial implant100may, first of all, have a perimeter that has a certain external perimeter shape, as is best illustrated inFIGS.2D and2K.FIG.2Kis a top view of the outside perimeter of tibial implant100. The perimeter may, first of all have a first straight edge190. The side dovetails122,124of tibial implant100may be close to being parallel to straight external edge190of tibial implant100, although as illustrated they are not exactly parallel.

The tibial implant100may have an outer perimeter that can be described as follows, while commencing at a location on the lateral edge of the implant100at a posterior location and proceeding counterclockwise as viewed from above. From this vantage point, the perimeter may comprise: a first straight edge190, which may be considered a vertical reference for purpose of illustration; followed by a first convex corner191that meets and is tangent to the first straight edge190; followed by a second straight edge or shallow arc192that meets and is tangent to the first convex corner191, wherein an angle alpha of the first convex corner191is greater than 90 degrees but less than 180 degrees; followed by a second convex corner193that meets and is tangent to the second straight edge or shallow arc192; followed by a first concave curve194, wherein the second convex corner193transitions to the first concave curve194at a first inflection point1934. It may be considered that there is a tangent line195that is parallel to first straight edge190and is tangent to second convex corner193at a tangency point1953, wherein the tangency point1953is farther from first straight edge190than is first inflection point1934. The second convex corner193and the first concave curve194have a common tangent line at the first inflection point1934, wherein the tangent line to the curve at the inflection point1934forms an angle beta with respect to tangent line195, with beta being greater than zero so that the perimeter shape is re-entrant with respect to the first straight edge190. First concave curve194may then continue until it again crosses tangent line195so that the perimeter crosses tangent line195to become farther from first straight edge190than is tangent line195. Continuing on from first concave curve194may be an arbitrary convex curve that returns to first straight edge190to form a complete perimeter of tibial plate100. In an anatomical sense, features such as first concave curve194may be located on the lateral side of the tibial implant100, as distinguished from the medial side of the tibial implant100. Correspondingly, first straight edge190may be located on the medial side of tibial implant100.

As illustrated, first concave curve194may be followed by a third convex corner196, wherein the first concave curve194transitions to the third convex corner196at a second inflection point1946; third convex corner196may be followed by a first convex curve197, wherein the third convex corner196transitions to the first convex curve197at a common tangency point; followed by a fourth convex corner199, wherein the first convex curve197transitions to the fourth convex corner199at a common tangency point198; wherein the fourth convex corner199continues on and meets and is tangent to the first straight edge190.

Referring now toFIGS.3A-3E, there is shown intermediate implant200. Intermediate implant200may comprise a top surface202that faces tibial implant100. First of all, the intermediate implant200may have an external perimeter, when viewed from above, that is similar to the corresponding perimeter of tibial implant100which it touches. Intermediate implant200may have a top surface202, which may be flat. There may be a projection204protruding from top surface202. Projection204may have projection surface206, which may be flat and may be parallel to top surface202. Between top surface202and projection surface206, intermediate implant200may have external dovetails suitable to engage corresponding dovetails122,124,126of tibial implant100. There may be side dovetails222and224, which may be parallel to each other. There may further be end dovetail226. End dovetail226may be continuous with side dovetails222,224through rounded corners. The rounded corners may also have dovetails, which may have the same cross-sectional shape as dovetails222,224,226.

The intermediate implant200may have a latch260, which may project beyond the surface202of intermediate implant200. Latch260may serve to lock intermediate implant200relative to tibial implant100. The latch260may be shaped generally complementary to the pocket160in the tibial implant100. The intermediate implant200may be capable of deforming or flexing slightly during insertion of the intermediate implant200into the tibial implant100, to allow the latch260to attain its final position. Alternatively, or in addition, the latch260itself may be capable of deforming or flexing slightly during insertion towards accomplishing a similar purpose. For example, latch260could comprise a living hinge.

It is further possible that intermediate implant200may comprise an intermediate implant recess270, which may be located on the anterior edge of intermediate implant200. Intermediate implant recess270may be located in a location similar to the location of recess170of tibial implant100. Intermediate implant recess270may have a lateral dimension that is substantially the same as the lateral dimension of latch260of intermediate implant200. Intermediate implant recess270may substantially align with latch260along the direction of side dovetails122,124. Tibial implant recess170may have an internal slope and latch260may have an external slope, and the tibial implant recess internal slope and the latch external slope may be equal to each other.

Opposite to tibia-facing top surface202, intermediate implant200may have an opposed surface that is an articulating surface (FIG.3E). The articulating surface may comprise, as illustrated, two condyles, although other shapes are also possible. The first condylar articulating surface272and the second condylar articulating surface274, as illustrated, may both be concave. However, in the region where the two condylar articulating surfaces approach each other, there may be a transition surface276, which may be convex. As illustrated here and elsewhere herein, first condylar surface272, second condylar surface274and transition surface276may all be formed by respective circular arcs being revolved around an axis of revolution399. Furthermore, as illustrated inFIGS.5A and5B, the circular arc for first condylar surface272and the circular arc for second condylar surface274may have identical radii of curvature, although this is not essential. As illustrated, the circular arc for first condylar surface272and the circular arc for second condylar surface274both have a radius of curvature of 0.820 inch. As illustrated, transition surface276has a radius of curvature of 0.100 inch in the opposite sense from surfaces272,274. Variations from all of these dimensions would be possible.

Referring now toFIGS.3F-3G, there may exist certain geometric relationships that relate features of tibial implant100and features of intermediate implant200. In regard to dovetail features, the respective sides of external dovetail222,224,226of intermediate implant200may have dimensions and shape that are complementary to those of the respective sides of internal dovetail122,124,126. The relationship may be such as to allow the intermediate implant200to be slid into the tibial implant100and to be retained therein. The distance between the planes of outer surface106and inner surface108of tibial implant100may approximately equal or be slightly greater than the distance between the planes of top surface202and projection surface206. Also, the end external dovetail226of intermediate implant200may be complementary to the end internal dovetail126of tibial implant100. The relationship may be such as to further help retain intermediate implant200to tibial implant100.

In regard to latching features, latch260of intermediate implant200may be complementary to pocket160in tibial implant100so as to allow latch260to reside within pocket160when intermediate implant200is assembled to tibial implant100. Furthermore, the locations of latch260and pocket160may be such that this residing occurs when the side dovetails222,224of intermediate implant200are engaged with the side dovetails122,124of tibial implant100, and when end dovetail226of intermediate implant200is engaged with the end dovetail126of tibial implant100. The engagement of latch260with pocket160may coincide with engagement of end dovetail226with end dovetail126. The distance between latch260and end dovetail226of intermediate implant200may be approximately equal to the distance between pocket160and end dovetail126of tibial implant100. It can be noted that, in general, either one of the tibial implant100and the intermediate implant200may comprise a pocket and the other of the tibial implant100and the intermediate implant200may comprise a latch.

In regard to recesses at the anterior edges of tibial implant100and intermediate implant200, tibial implant recess170may have a lateral dimension that is substantially the same as the lateral dimension of pocket160or of latch260of intermediate implant200. Intermediate implant recess270may have a lateral dimension that is substantially the same as the lateral dimension of pocket160or of latch260of intermediate implant200. Tibial implant recess170may substantially align with pocket160along the direction of side dovetails122,124. Intermediate implant recess270may substantially align with pocket160along the direction of side dovetails122,124. Intermediate implant recess270and tibial implant recess170may at least approximately align with each other to create a combined recess that may be suitable to receive and direct a surgical blade in the event that it is necessary to insert a surgical blade to cut off latch260for removal of intermediate implant200from tibial implant100. It is possible that intermediate implant recess270alone could receive and direct a surgical blade in the event that it is necessary to insert a surgical blade to cut off latch260, or tibial implant recess170alone could receive and direct a surgical blade in the event that it is necessary to insert a surgical blade to cut off latch260.

Intermediate implant200may have an outer perimeter, at or near the end that faces tibial implant100, that is generally similar in shape and dimension to the outer the outer perimeter of tibial implant100at or near the end of tibial implant100that faces intermediate implant200.

Of course, it is also possible that pocket160of tibial implant100could instead be a protrusion and latch260of intermediate implant200could instead be a complementary void, or still other designs of latching or engaging features could be used.

Referring now toFIGS.4A-4E, there is illustrated a talar implant300. Anterior edge301A and posterior edge301P are illustrated, although this is only for descriptive purposes. Talar implant300may comprise a talar-facing surface302and an articulating surface that may be generally opposed to the talar-facing surface302. Talar-facing surface may comprise three generally planar surfaces. The three planar surfaces may be anterior talar planar surface306, central talar planar surface307and posterior talar planar surface308. (It is not essential that any of these talar planar surfaces be planar.) The three generally planar surfaces306,307,308may appear, in cross-section when viewed from a lateral direction, as straight-line segments. Between adjacent planar surfaces306,307,308may be machining recesses or fillets309A,309B.

The anterior talar-facing surface306may comprise one or more talar pegs. As illustrated, two talar pegs342,344are provided. Talar pegs may be generally cylindrical with a rounded end. The shape of talar peg342,344may be similar to the shape described for tibial pegs142,144. Each talar peg342,344may comprise a piece of a sphere at the tip of the peg, followed by (tangent to) a cone, followed by a circular arc in revolution, followed by a cylinder. It is believed, although again it is not wished to be limited to this explanation, that such a shape of the tip of the talar peg342,344may be helpful for similar reasons similar to those discussed in connection with the tibial pegs142,144. Talar pegs342,344may each have a respective talar peg axis. The talar peg axis may have an angle delta, with respect to posterior talar planar surface308, which is greater than zero as illustrated inFIG.4E. Alternatively, talar pegs342,344could be parallel to posterior talar planar surface308. As illustrated and as is particularly visible inFIG.4D, when viewed from the front (anterior), talar peg342is completely within the lateral range of condylar articulating surface372of talar implant300, and talar peg344is completely within the lateral range of condylar articulating surface374.

The articulating surface may comprise, as illustrated, two condyles, although other shapes are also possible. The first condylar articulating surface372and the second condylar articulating surface374, as illustrated, may both be convex. However, in the region where the two condylar articulating surfaces approach each other, there may be a transition surface376, which may be concave. As illustrated here and elsewhere herein, first condylar surface372, second condylar surface374and transition surface376may all be formed by respective circular arcs being revolved around a common axis of revolution399. Furthermore, as illustrated, the circular arc for first condylar surface372and the circular arc for second condylar surface374may have identical radii of curvature, although this is not essential. As illustrated, the circular arc for first condylar surface372and the circular arc for second condylar surface374both have a radius of curvature of 0.600 inch. As illustrated, transition surface376has a radius of curvature of 0.125 inch in the opposite sense from surfaces372,374. Variations from all of these dimensions would be possible.

FIG.4Fillustrates the assembled total ankle replacement prosthesis with respect to nearby anatomy of a patient's body. In particular, there is illustrated axis of revolution399for forming condylar surfaces272,274and transition surface276, and for forming condylar surfaces372,374and transition surface376. The orientation of axis of revolution399relative to the anatomy is also illustrated.

Referring now toFIG.5A, intermediate implant200may have a tibial-implant-facing surface102and an opposed surface that is an articulating surface. The articulating surface may, as illustrated, be bicondylar, although other shapes are also possible. Condylar surface272of intermediate implant200may be generally concave and condylar surface274of intermediate implant200may be generally concave, and between them may be transition region276, which may be convex. As illustrated, first condylar surface272may be a surface formed by a first circular arc272A whose center272C is indicated with a cross. Similarly, second condylar surface274may be a surface formed by a second circular arc274A whose center274C is similarly indicated. Similarly, surface276may be formed by another arc276A whose center276C is indicated. The axis of revolution may be the same for all of circular arcs272A,274A, and276A. Furthermore, as illustrated, circular arcs272A,274A may have identical radii of curvature with each other, although this is not essential. The orientation of the axis of rotation may be non-horizontal, such as angled 8 degrees with respect to horizontal, as illustrated inFIGS.4F and5A.

Referring now toFIG.5B, talar implant300may have a talus-facing surface302and an opposed surface that is an articulating surface. The articulating surface may, as illustrated, be bicondylar, although other shapes are also possible. Condylar surface372of talar implant300may be generally convex and condylar surface374of talar implant300may be generally convex, and between them may be transition region376, which may be concave. As illustrated, first condylar surface372may be a surface formed by a first circular arc372A whose center372C is indicated with a cross. Similarly, second condylar surface374may be a surface formed by another arc372A whose center374C is indicated. Similarly, surface376may be formed by another arc376A whose center376C is indicated. The axis of revolution may be the same for all of circular arcs372A,374A, and376A. Furthermore, as illustrated, circular arcs372A,374A may have identical radii of curvature with each other, although this is not essential. The orientation of the axis of rotation may be non-horizontal, such as for example it may be angled 8 degrees with respect to horizontal as illustrated inFIGS.4F and5B.

There may exist certain geometric relationships between the condylar surfaces of talar implant300and the condylar surfaces of intermediate implant200. Specifically, the radii of curvature (illustrated as 0.820 inch) of the defining circular arcs272A,274A defining the concave condylar surfaces272,274of the intermediate implant200may be larger than the corresponding radii of curvature (illustrated as 0.600 inch) of the defining circular arcs372A,374A defining the convex condylar surfaces372,374of the talar implant300. Also, the arc of the condylar surfaces272,274in the intermediate implant200may extend over a larger distance or angular dimension than does the arc of the condylar surfaces372,374in the talar implant300, as can be seen by comparingFIGS.5A and5B.

It can be noted that it is not necessary for the talar-facing surface272,274,276of intermediate implant200and for the intermediate-implant-facing surface372,374,376of talar implant300to be bicondylar. Such surfaces could be unicondylar or even spherical, or other shape as appropriate. The respective shapes may be generally complementary to each other. As has been illustrated, the articulating surface of the intermediate implant200is mostly concave (272,274) and the articulating surface of the talar implant300is mostly convex (372,374). However, the opposite could be true instead. If surface272articulates with corresponding surface372and surface274illustrates with corresponding surface374, it is not necessary for surface276to actually articulate with corresponding surface376.

In regard to materials, the tibial implant100may be or may comprise a biocompatible metal. An example is titanium or a titanium alloy such as Ti-6 Al-4 V. Other biocompatible materials are also possible. In particular, the tibia-facing surface102of the tibial implant100, and also fin130and pegs142,144may comprise a material that is conducive to bone ingrowth or ongrowth, such as titanium or a titanium alloy. Such surface may be porous as desired to help promote bone ingrowth or ongrowth. If desired, some or all of the tibia-facing surface of the tibial implant100may be coated with a coating suitable to promote bone ingrowth or ongrowth. It is possible to use different materials in different places of any of these implants.

Further in regard to materials, the talar implant300may have any or all of the material characteristics just described for the tibial implant100. If desired, some or all of the talus-facing surface of the talar implant300, as well as talar pegs342,344, may be porous or may be coated with a coating suitable to promote bone ingrowth or ongrowth. It is possible to use different materials in different places of any of these implants.

Further in regard to materials, the intermediate implant200may comprise a biocompatible polymer. For example, ultra-high molecular weight polyethylene may be used. The material may be chosen to have good wear characteristics against the corresponding material of talar implant300. Other materials such as ceramic are also possible.

Further in regard to materials, it is possible that a ceramic material could be used for any of the components100,200,300.

Referring now toFIG.6A, there is illustrated an intermediate implant200N as was previously illustrated inFIG.3C. This intermediate implant200N illustrated inFIG.6Ais referred to as a neutral implant, as discussed here and elsewhere herein. In such an intermediate implant200, the articulating talar condylar surfaces272,274have an anterior edge288A and a posterior edge288P. At the anterior edge288A, the talar-facing surface may end at or may blend into an anterior planar surface. Similarly, at the posterior edge288P, the talar-facing surface may end at or may blend into a posterior planar surface. For a neutral intermediate implant200, the anterior planar surface is coplanar with the posterior planar surface. More generally, for intermediate implant200geometries that are contoured at their lower ends in any manner that is more complicated than planar, there may be defined a midplane of the intermediate implant that is a vertical plane of symmetry midway between the dovetails222,224is generally parallel to a sagittal plane in the anatomical sense, and in that midplane there may be defined a contact line292that touches but does not intersect the anterior portion of the lower surface of intermediate implant200, and also touches but does not intersect the posterior portion of the lower surface of intermediate implant200. Depending on details of geometry, either or both of those contact points could be in the form of the contact line being tangent to a curve, or could be the line overlapping with a planar surface, or could be the line touching a corner point. For a neutral intermediate implant200N, the contact line292may be generally horizontal or parallel with the top surface202of intermediate implant200.

As described, in certain embodiments of the invention, it is possible that there be an anterior edge288A of the curved articulating surface of the intermediate implant200and a posterior edge288P of the curved articulating surface of the intermediate implant200, and it is possible that the anterior edge288A and the posterior edge288P might not be at the same elevation, with elevation measured from a reference plane, such as a top surface202of the intermediate implant200. As shown inFIGS.6A,6B, and6C, offset “h” shows a distance from contact line292, which is conversely able to be measured from the top surface202. In other words, the articulating curved surface of the intermediate implant200can extend farther (FIG.6B) anteriorly than it does posteriorly, or, alternatively, the articulating curved surface of the intermediate implant200can extend farther posteriorly (FIG.6C) than it does anteriorly. It is possible that the use of unequal anterior and posterior angular extents of the articulating surfaces, or the unequal elevational positions of the corresponding endpoints of the articulating surfaces, could decrease the likelihood of subluxation in particular directions, as discussed elsewhere herein. This is illustrated inFIG.6Bfor an anterior-biased intermediate implant200A, and inFIG.6Cfor a posterior-biased intermediate implant200P. If the anterior edge288A extends farther than the posterior edge288P as inFIG.6B, this may reduce the likelihood of subluxation of the talus in the anterior direction relative to the tibia. If the posterior edge288P extends further than the anterior edge288A as inFIG.6C, this may reduce the likelihood of subluxation of the talus in the posterior direction relative to the tibia. If the extent of the curved articulating surface were to be extended equally in both directions (anterior and posterior), this might discourage subluxation in both the anterior and the posterior directions, but it would not discourage one direction of subluxation preferentially compared to the other direction of subluxation, and this could be expected to make it generally harder to bring intermediate implant200into the surgical site into its intended place, requiring greater stretching or displacement of nearby tissues and anatomical features. In particular, if the arc length of the articulating surface of intermediate implant200A is extended in the anterior direction but not the posterior, and if this intermediate implant200A is inserted surgically from the anterior-to-posterior direction after the tibial implant100and the talar implant300have already been implanted, this would not increase the difficulty of inserting the intermediate implant200A, but it would provide greater protection against subluxation in the form of the foot or the talus subluxing or moving in an anterior direction with respect to the tibia.

The anterior bias intermediate implant200A may make it especially unlikely or difficult for subluxation to occur in the sense of the foot and talus subluxing in an anterior direction relative to the tibia. The posterior bias intermediate implant200P may make it especially unlikely or difficult for subluxation to occur in the sense of the foot and talus subluxing in a posterior direction relative to the tibia.

It is possible that a kit may be provided that includes more than one type of implant, such as a neutral implant200N, an anterior bias intermediate implant200A and a posterior bias intermediate implant200P. Each of those intermediate implants200N,200A,200P may fit or be attachable to the same tibial implant100. In this way, a surgeon can choose to use any of the various intermediate implants200N,200A,200P as appropriate, while the tibial implant100and the talar implant300are unaffected by the choice of intermediate implant200. The choice may be made based at least in part on the anatomy of the patient and the likelihood of any factors that might contribute to occurrence of subluxation. It would also be possible that a kit contain more than one neutral intermediate implant200N, with varying extents of arc. A neutral intermediate implant having a larger extent of arc in both front and rear directions would provide more protection against subluxation in both directions, although it could be more difficult to insert, in the sense of requiring greater stretching of surrounding tissues.

Further, in terms of a kit, any or all of the described components may be provided in mirror image versions corresponding to the left and right sides of a patient's body. Also, any or all components may be provided in multiple sizes.

In terms of surgical procedure and use of the described apparatus, a typical procedure is described here. It is to be understood that variations in the sequence of steps are possible. First, access to the ankle may be performed from the anterior of the ankle. A fixture may be anchored to the patient's leg externally to aid in determination of position of cuts. A cutting guide may be used to direct an oscillatory saw to remove the distal portion of the tibia. Working at an angle, possibly with a right-angle drill, drilling or other bone removal may be performed to the cut surface of the tibia such as to prepare for the pegs and the fin. For the assumed surgical access from the anterior direction, it may be easier to drill trial holes for the tibial pegs142,144in the tibia, and it may be more difficult to prepare the space for the fin130because the fin location is deeper within the surgical site. The tibial implant100may be put into the surgical site, and may be hammered or urged in a posterior direction into its final position. So, the sharp end of the fin130may be advantageous in that the sharp end can force its own way into the tibial bone to some extent, as may be needed, upon application of force to the anterior end of the tibial implant100in a posterior direction. The fin130may help to prevent the posterior portion of tibial implant100from separating from the tibia upon certain motions by the patient.

The talus can be prepared by cutting a series of flats into its surface, corresponding to the underside surface of talar implant300. Holes can be drilled corresponding to talar pegs342,344. The talar implant300can be urged into place.

After the tibial implant100and the talar implant300have been implanted, the intermediate implant200may be slid into place. Intermediate implant200may be tapped or urged in a posterior direction until it engages with tibial implant100.

The preceding description is provided to enable a person of ordinary skill in the art to practice the various aspects described herein. While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Thus, the claims are not intended to be limited to the aspects shown herein, but is to be accorded the full scope consistent with the language claims, wherein reference to an element in the singular is not intended to mean “one and only one” unless specifically so stated, but rather “one or more.” Unless specifically stated otherwise, the terms “a set” and “some” refer to one or more. Pronouns in the masculine (e.g., his) include the feminine and neuter gender (e.g., her and its) and vice versa. Headings and subheadings, if any, are used for convenience only and do not limit the invention.

It is understood that the specific order or hierarchy of steps in the processes disclosed is an illustration of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged. Some of the steps may be performed simultaneously. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented.

Terms such as “top,” “bottom,” “front,” “rear” and the like as used in this disclosure should be understood as referring to an arbitrary frame of reference, rather than to the ordinary gravitational frame of reference. Thus, a top surface, a bottom surface, a front surface, and a rear surface may extend upwardly, downwardly, diagonally, or horizontally in a gravitational frame of reference.

A phrase such as an “aspect” does not imply that such aspect is essential to the subject technology or that such aspect applies to all configurations of the subject technology. A disclosure relating to an aspect may apply to all configurations, or one or more configurations. A phrase such as an aspect may refer to one or more aspects and vice versa. A phrase such as an “embodiment” does not imply that such embodiment is essential to the subject technology or that such embodiment applies to all configurations of the subject technology. A disclosure relating to an embodiment may apply to all embodiments, or one or more embodiments. A phrase such an embodiment may refer to one or more embodiments and vice versa.

The word “exemplary” is used herein to mean “serving as an example or illustration.” Any aspect or design described herein as “exemplary” is not necessarily to be construed as preferred or advantageous over other aspects or designs.

All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later come to be known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Moreover, nothing disclosed herein is intended to be dedicated to the public regardless of whether such disclosure is explicitly recited in the claims. No claim element is to be construed under the provisions of 35 U.S.C. § 112, sixth paragraph, unless the element is expressly recited using the phrase “means for” or, in the case of a method claim, the element is recited using the phrase “step for.” Furthermore, to the extent that the term “include,” “have,” or the like is used in the description or the claims, such term is intended to be inclusive in a manner similar to the term “comprise” as “comprise” is interpreted when employed as a transitional word in a claim.