Patent Description:
The present application relates to the technical field of joint prostheses, and more particularly to orthopedic implants facilitating at least some restoration in anatomical mobility to an ankle joint.

Joint prostheses can be used to restore a certain amount of freedom of movement to a joint, after the joint has been damaged due to injury or disease. For example, ankle joints can be damaged by arthritis, and an ankle replacement joint prosthesis can bring such patients a reduction in pain and improvement in mobility.

Ankle prosthesis are designed to replace the ankle joint and replicate the anatomic motion of the ankle joint which includes loadbearing and flexion of the foot through the gait cycle. Flexion of the foot includes dorsi-flexion, or upward motion of the forefoot relative to the hindfoot, and plantar-flexion, downward motion of the forefoot relative to the hindfoot. As the foot flexes, minor rotation, internal for dorsi-flexion and external for plantar-flexion must occur between the foot and the tibia. To account for this complex dynamic motion, optimally, the prosthetic joint would be located such that the load-bearing central axis of the tibia is aligned with the apex of the talar dome. In addition, such a joint would not be cylindrical, but would form the partial surface of a cone. This frustoconical surface is defined by locating the smaller radius of the cone on the interior side of the ankle (the lateral side closer to the median axis of the body) and the larger radius on the outer side of the ankle (the lateral side further from the median axis of the body).

Insertion of an ankle prosthesis includes providing surgical access to the joint being replaced, preparing the surfaces of the distal tibia and the talar dome for acceptance of the prosthesis, and providing just enough space for the prosthesis for fit and function. Generally, a diseased ankle, even when surgically prepared to accept a prosthesis, would be mal-aligned to accept the prosthesis "out of the box". Therefore, certain surgical intervention would be necessary to balance the ankle joint including, but not limited to, osteotomies (in order to shorten, lengthen, or reorient bones), soft tissue excision (in order to alleviate unwanted tension to the skeletal structure), or the support or tightening of soft tissue (in order to add tension and support to the skeletal structure). Even in the best of surgical hands, the ankle prosthesis would still have to support loading which may not be matched to the perfect anatomy of the complex healthy ankle joint. Thus, an ankle prosthesis which is adaptable to the variations of the anatomy and of the surgical placement of the fixed components of the prosthesis would be beneficial to restoring motion of the replaced ankle joint.

Ankle prostheses are composed of components moveable relative to each other, such as a talar implant, a tibial implant, and an intermediate implant interposed between said tibial implant and said talar implant. The intermediate implant and the talar implant can move relative to each other. In certain ankle prostheses, the tibial implant and the intermediate implant are fixed relative to each other.

Once surgical access is achieved and the ankle joint is balanced and prepared to accept the prosthesis, the tibial implant and the talar implant are fixed to the bones of the tibia and the talus, respectively. In most surgical instances, the center of the tibia implant may or may not be aligned with the central axis of the tibia bone and the talar implant may be rotated, internally or externally, relative to the central axis of the tibia bone. In addition, the center of the tibial implant may not be aligned with the apex of the talar implant to provide and maximize full flexion of the foot.

Current ankle prostheses available are either (i) "mobile bearing" in that the intermediate implant to tibia implant interface is a planar friction joint allowing for anterior-posterior and lateral translation, coupled with relatively free internal and external rotation of the intermediate implant relative to the tibial implant; or (ii) "semi-constrained" in that the intermediate implant is fixed to the tibial implant in a predetermined fashion (referred to herein as "fixed bearing" as well), regardless of the anatomic placement of the tibial implant relative to the talar implant.

The mobile-bearing design, due to its relatively low level of constraint, accommodates variability in anatomy and surgical placement of the tibial and talar implants. However, the lack of constraint introduces circumstances requiring significant surgical skill in placing the implant while balancing the skeletal and soft tissue anatomy about the ankle prosthesis. Anatomic balancing is required in order to prevent subluxation or, sometimes, fracture of the mobile-bearing intermediate implant when the tibial and talar components of the prosthesis are loaded in a condition of mal-alignment In addition, highly diseased or deformed ankles may not be candidates for the mobile-bearing design.

The semi-constrained design, due to its relatively high level of constraint, does not accommodate variability in anatomy and surgical placement of the tibial and talar implants. The intermediate implant is rigidly affixed to the tibial implant either in vitro, that is while the tibial implant and intermediate implant are outside the patient or in vivo, where the fixation of the intermediate implant takes place in the patient after implantation of the tibial implant. However, the presence of constraint introduces circumstances requiring significant surgical skill in placing the implant in that the talar and tibial implants must be expertly aligned by the surgeon utilizing techniques for balancing the skeletal and soft tissue anatomy about the ankle prosthesis. Anatomic balancing is required in order to prevent abnormal loading and subsequent wear of the fixed intermediate implant when the tibial and talar components of the prosthesis are loaded in a condition of mal-alignment. Advantages of this design, due to the constraint, include use in patients with poor soft tissue support of the ankle joint or in patients where large deformity has been corrected by the surgeon. Each of these instances require a more stable, semi-constrained prosthesis.

<CIT> discloses an ankle prosthesis with simplified adjustment.

Embodiments of the invention described herein combine the advantages of both a mobile-bearing design and a semi-constrained design to treat a broader spectrum of patients and to better adapt the implant to the patient anatomy and placement of the talar and tibial components. Further embodiments of the invention can allow for adjusting the relative position of the ankle prosthesis components, particularly, the position of an intermediate implant relative to a tibial implant, and then securely fixing these components to each other. Moreover, embodiments of this invention can allow for components, particularly the intermediate implant, to be replaced and adjusted when clinically indicated due to, for example, wear of the component.

The invention is defined in claim <NUM> and comprises an ankle prosthesis having a tibial implant, an intermediate implant, and an implant lock. The intermediate implant comprises a first surface and a second, curved surface opposite the first surface and a projecting member extending outwardly from the first surface. The projecting member is configured to extend into a recess of the tibial implant and rotate relative to the tibial implant. The implant lock is configured to resist rotation of the projecting member relative to the tibial implant by applying a force that is substantially perpendicular to the axis of rotation of the projecting member. The projecting member comprises a first end and a second end opposite the first end and a lateral surface extends between the first and second end, wherein the first end is closer to the first surface of the intermediate implant than the second end. The implant lock is configured to engage with the lateral surface of the projecting member such that rotation of the projecting member is resisted.

Other embodiments of the present disclosure can also comprise an ankle prosthesis having a tibial implant, an intermediate implant, and an implant lock. The tibial implant can define a recess and a slot, wherein the slot is in communication with the recess. The intermediate implant can comprise a first surface and a second, curved surface opposite the first surface and a projecting member extending outwardly from the first surface. The projecting member can be configured to extend into the recess of the tibial implant and rotate relative to the tibial implant. The implant lock can be configured to be at least partially disposed within the slot and to resist rotation of the projecting member relative to the tibial implant, wherein the slot is configured such that the implant lock is inserted into the slot along a direction that is substantially perpendicular to the axis of rotation of the projecting member.

Still other embodiments of the present disclosure can also comprise an ankle prosthesis having a tibial implant, an intermediate implant, and an implant lock. The intermediate implant can comprise a first surface and a second, curved surface opposite the first surface and a projecting member extending outwardly from the first surface, wherein the projecting member is configured to be disposed in a recess of the tibial implant and rotate relative to the tibial implant. The implant lock can be configured to resist rotation of the projecting member relative to the tibial implant. The projecting member can comprise a lateral surface, and the implant lock can be configured to engage with the lateral surface of the projecting member such that rotation of the projecting member is resisted.

Still other embodiments of the present disclosure can comprise an ankle prosthesis having a talar implant, a tibial implant, and an intermediate implant. The intermediate implant can comprise a first surface and a second, curved surface opposite the first surface and a projecting member extending outwardly from the first surface The talar implant can be configured to move relative to the to the intermediate implant along the second surface, and the projecting member can be configured to extend into a recess of the tibial implant and rotate at least <NUM> degrees relative to the tibial implant.

Other embodiments of the present disclosure can comprise an ankle prosthesis component having an intermediate implant. The intermediate implant can comprise a base having a first surface and a second, curved surface opposite the first surface and a projecting member extending outwardly from the first surface of the base. The projecting member can have a width and the base has a width and wherein the projecting member width is <NUM>% to <NUM>% of the base width.

Any method disclosed herein is excluded from patentability according to Article <NUM>(c) EPC and merely serves informative purposes. An example can comprise a method of fixing the relative position of an intermediate implant of an ankle prosthesis, wherein the intermediate implant is configured to be disposed between a tibial implant and a talar implant, and the method can comprise rotating the intermediate implant relative to the tibial implant while the tibial implant, the talar implant, and the intermediate implant are implanted in the ankle and fixing the position of the intermediate implant relative to the tibial implant by applying a force that is substantially perpendicular to the axis of rotation of the intermediate implant.

Yet another exmaple can comprise a method of replacing an intermediate implant of an ankle prosthesis, wherein the intermediate implant is configured to be disposed between a tibial implant and a talar implant, and the method can comprise releasing an implant lock of a first intermediate implant of the ankle prosthesis such that the first intermediate implant can rotate relative to the tibial implant, wherein the implant lock is released by removing a force that is substantially perpendicular to the axis of rotation of the intermediate implant; hereafter, removing the first intermediate implant from the ankle prosthesis; and inserting a second intermediate implant into the ankle prosthesis.

These and other aspects, objects, features, and embodiments will be apparent from the following description and the appended claims. Those skilled in the art may use the components of the ankle prosthesis together or separate and may apply techniques provided herein for other applications.

The drawings illustrate only example embodiments of ankle prostheses and are therefore not to be considered limiting of its scope.

An embodiment of an ankle prosthesis according to the invention is illustrated in <FIG>. Ankle prosthesis <NUM> includes a tibial implant <NUM>, a talar implant <NUM>, an intermediate implant <NUM>, and an implant lock <NUM>. The tibial implant <NUM> is configured to be implanted in or on the base of the tibia <NUM> of a patient. The talar implant <NUM> is configured to be implanted in or on the talus <NUM> of a patient. The intermediate implant <NUM> is configured to be disposed between the talar implant <NUM> and the tibial implant <NUM>. The implant lock <NUM> is configured to fix the position (e.g., angular position) of the intermediate implant <NUM> relative to the tibial implant <NUM>. <FIG> depicts an anterior, upper perspective view of the tibial implant <NUM> coupled to the intermediate implant <NUM> and the implant lock <NUM>. <FIG> depicts an exploded view of the tibial implant <NUM>, the intermediate implant <NUM>, and the implant lock <NUM>. <FIG> depicts an upper perspective view of the talar implant <NUM> and <FIG> depicts a bottom perspective view of the talar implant <NUM>.

To facilitate the function of the prosthetic joint, the intermediate implant <NUM> and the talar implant <NUM> are configured to be moveable relative to each other along a contact interface <NUM> (<FIG>) between a lower bearing surface <NUM> (<FIG>) of the intermediate implant <NUM> and an upper bearing surface <NUM> (<FIG>) of the talar implant <NUM>. To this end, the lower bearing surface <NUM> of the intermediate implant is designed to bear against the upper bearing surface <NUM> of the talar implant <NUM> that is of complementary shape, so that the intermediate implant <NUM> can move by sliding relative to the talar implant <NUM> and vice versa. The talar implant upper surface <NUM> and intermediate implant lower surface <NUM> are rounded in shape, e.g., substantially spherical, cylindrical or frustoconical, so as to form a contact interface <NUM> (<FIG>) that allows the foot to move in plantar flexion and in dorsal flexion relative to tibia <NUM> (<FIG>).

In the embodiment shown, the contact interface <NUM> between the intermediate implant <NUM> and the talar implant <NUM> can be considered as defining a surface that is a fraction of the surface of a substantially frustoconical shape (see <FIG> as an example of a fraction of the surface <NUM> of a substantially frustoconical shape <NUM>). The contact interface <NUM> can be oriented such that its portion with larger radius R (<FIG>) is directed substantially towards the outer side <NUM> of the ankle <NUM>, i.e., away from the median axis of the body, when the prosthesis <NUM> is in place.

In the embodiment shown, the intermediate implant <NUM> comprises a concave lower surface <NUM>, and the talar implant's upper surface <NUM>, being complementary in shape and dimension to the lower surface <NUM>, is convex. However, an inverse mechanical disposition is envisioned where the lower surface of the intermediate implant <NUM> is convex while the upper surface <NUM> of the talar implant <NUM> is concave.

In the embodiment shown, in order to restrain the lateral movement of the intermediate implant <NUM>, the talar implant <NUM> can comprise rails <NUM>, the pair of rails maintaining equal distance from each other along their length and each extending upwardly on a corresponding side of the upper surface <NUM>. The rails <NUM> are spaced apart a distance that permits the lateral surface <NUM> of the intermediate implant base <NUM> to be disposed between the two rails. Because of the presence of rails <NUM>, the intermediate implant <NUM> is guided by bearing on surface <NUM> against the rails during the movement of the talar implant <NUM> relative to the intermediate implant <NUM>.

The talar implant <NUM> can be configured to be affixed to the talar bone. For example, the talar implant <NUM> can comprise an anterior plate <NUM> (<FIG>). The anterior plate <NUM> projects outwardly (in a general posterior-to-anterior direction) from the anterior edge <NUM> of the talar implant <NUM>. As shown in <FIG>, the anterior plate <NUM> extends from the anterior edge <NUM> of the upper surface <NUM>. The anterior plate <NUM> can contain one or more holes <NUM> (<FIG>) to facilitate fixation with orthopaedic screws.

In the embodiment shown, with particular reference to <FIG>, <FIG>, <FIG>, the tibial implant <NUM> comprises a base <NUM> defining an upper surface <NUM> and an anterior shield <NUM>. The upper surface <NUM> is configured to abut the end of the tibia <NUM>. Anti-slip elements <NUM> can project outwardly from the upper surface <NUM> and are configured to maintain the alignment of the tibial implant <NUM> relative to the tibia <NUM>. In an embodiment, the anti-slip elements <NUM> can be pointed and configured to penetrate bone. In the embodiment shown, the upper surface <NUM> is planar. Other anti-slip elements maybe also be considered suitable for use with the invention including elements extending upward past the sides of the tibia implant that can be secured to the sides thereof either through pressure or mechanical means including pins or screws.

The lower surface <NUM> of the tibial implant <NUM>, which is viewable in <FIG>, is configured to couple with the intermediate implant <NUM>. At an interior region of the lower surface <NUM> is a recess <NUM>. The recess <NUM> is configured to receive a portion of the intermediate implant, particularly, a projecting member <NUM>. The recess <NUM> is configured to receive the projecting member <NUM>. A sidewall <NUM> defines the perimeter of the recess. The recess <NUM> is shaped to permit the projecting member <NUM> to bear against the sidewall <NUM>, and the sidewall <NUM> is configured to impede lateral movement of the projecting member <NUM>. For example, the sidewall <NUM> extends vertically (e.g., extends in a plane that is parallel to the Z-Z axis) or may be angled or curved.

The recess <NUM> is sized and shaped to allow for rotation of the projecting member <NUM> within the recess <NUM>. For example, the recess <NUM> can have a minimum transverse dimension (e.g., the width or the dimension along the Y-Y axis, shown in <FIG>) that is slightly more than the maximum transverse dimension of the projecting member <NUM>, as discussed below. Also to facilitate rotation of the projecting member <NUM> within the recess <NUM>, the sidewall <NUM> of the recess <NUM> can define a fraction of a circular shape.

The tibial implant <NUM> is also configured to couple with the implant lock <NUM> (<FIG>, <FIG>, <FIG>, and <FIG>). In the embodiment shown, tibial implant <NUM> comprises a slot <NUM> configured to receive at least a portion of the implant lock <NUM>. Slot <NUM> is in communication with the recess <NUM> such that the implant lock <NUM> is able to couple directly with the projecting member <NUM> when the projecting member <NUM> is disposed within the recess <NUM>. In the embodiment shown, slot <NUM> has a first end <NUM> and a second end <NUM>. The first end <NUM> is closer to the recess <NUM> than the second end <NUM>. An exposed surface of the tibial implant <NUM>, such as anterior face <NUM>, defines the second end <NUM>.

The tibial implant <NUM> can be configured such that the implant lock <NUM> is inserted into the slot <NUM> at a direction that is substantially perpendicular to the Z-Z axis (e.g., the axis of rotation of the projecting member <NUM>). For example, the slot <NUM> extends within a plane through which the recess <NUM> also extends, and such plane can be substantially perpendicular to the Z-Z axis (e.g., the axis of rotation of the projecting member <NUM>). In embodiments, substantially perpendicular can be within <NUM>°, <NUM>°, <NUM>°, <NUM>°, or <NUM>° of the perpendicular. Implant lock <NUM> is configured to be inserted into slot <NUM>. In order to facilitate insertion, the height (e.g. dimension along the Z-Z axis shown in <FIG>) of the implant lock <NUM> can be of a dimension which is smaller than the height of slot <NUM>.

The implant lock <NUM> and the tibial implant <NUM> can be configured to interlock with each other. When interlocked, movement of the implant lock <NUM> relative to the tibial implant <NUM> is constrained. For example, in the embodiment shown, the sidewall <NUM> defining the slot comprises two notches 136a, 136b. The notches 136a, 136b can be located on opposing sidewall surfaces such that they face each other. Each notch 136a, 136b is configured to receive and interlock with a projection 410a, 410b of the implant lock <NUM> (<FIG>). The implant lock <NUM> can be configured such that the projections 410a, 410b are pushed or snapped into interlocking engagement with the notches 136a and 136b.

The slot <NUM> and the implant lock <NUM> can be configured such that the implant lock <NUM> is retrievable from the slot <NUM>. A tool, for example a surgical grasper commonly used during surgery, can be used to retrieve the implant lock. <FIG> shows an example of such a grasper that can be used as grasper <NUM>. To facilitate retrieval, slot <NUM> has an overall width (e.g., dimension along the Y-Y axis shown in <FIG>) which is greater than the width of the implant lock <NUM>. This width at the second end <NUM> is sufficient to provide some space 138a, 138b on both sides of the implant lock <NUM>. This space 138a and 138b (<FIG>) permits the nose portions 738a and 738b of grasper <NUM> to be inserted into the slot <NUM> on both lateral sides 405a, 405b of the implant lock <NUM> in order to pull and retrieve the implant lock <NUM>. The lateral sides 405a, 405b of the implant lock <NUM> can each comprise surface contours <NUM> configured to interlock with the retrieval tool. Similarly, a roughened surface on lateral sides 405a, 405b and nose portions 738a, 738b can provide sufficient coupling force to facilitate removal of implant lock <NUM>.

The tibial implant <NUM> is likewise provided with an anterior shield <NUM> configured to resist the tibial implant <NUM> from migrating posteriorly. The anterior shield <NUM> projects upwardly from the anterior edge <NUM> of the implant <NUM>. When said implant is in place in the patient, the anterior shield <NUM> would extend upwards along the tibia bone <NUM>. Thus, as shown in <FIG>, the anterior shield <NUM> extends from the anterior edge <NUM> of the implant <NUM> upward and obliquely relative to upper surface <NUM>. The anterior shield <NUM> can define one or more holes <NUM> for inserting one or more screws to facilitate fixing the implant to the tibia bone.

The tibial implant <NUM> and the talar implant <NUM> can be made of a biocompatible metal alloy, such as cobalt chromium alloy, titanium alloy, stainless steel or any other material that is comparably able to withstand the forces in and around the ankle joint as well as being physiologically tolerated.

In some embodiments, the tibial implant <NUM> and/or the talar implant <NUM> can comprise a coating of one or more layers on the surface intended to be in contact and adhere to bone. Such coatings can facilitate bone apposition, osteointegration and/or osteoinduction. In some embodiments, a coating of plasma-sprayed titanium is applied to the talar implant <NUM> and/or the tibial implant <NUM> on the surfaces in contact with bone to promote bone apposition and osteointegration. The plasma-sprayed titanium coating can comprise an average thickness between <NUM> to <NUM>, such as <NUM> to <NUM>. In some embodiments, a coating of calcium phosphate, such as hydroxyapatite, is applied to the talar implant <NUM> and/or the tibial implant <NUM> on the surfaces in contact with bone to promote bone apposition, osteointegration and/or osteoinduction. The calcium phosphate coating can comprise an average thickness between <NUM> to <NUM>, such as <NUM> to <NUM>. In some embodiments, a dual coating of plasma-sprayed titanium, followed by a coating of calcium phosphate is applied to the talar and/or the tibial implant. The dual coating can comprise an average thickness between <NUM> and <NUM>, such as <NUM> to <NUM>. A tibial implant <NUM> and/or the talar implant <NUM> can comprise a titanium coating, a calcium phosphate coating, or both.

With particular reference to <FIG>, <FIG>, and <FIG>, the intermediate implant <NUM> comprises a base <NUM> and the projecting member <NUM>. The base <NUM> defines an upper surface <NUM> and the curved lower surface <NUM> opposite the upper surface <NUM>, and the projecting member <NUM> extends outwardly from the upper surface <NUM>. The intermediate implant <NUM> can be in frictional contact with the tibial implant <NUM> and talar implant <NUM> at the upper surface <NUM> and the lower, curved surface <NUM>, respectively.

The projecting member <NUM> is configured to extend into the recess <NUM> of the tibial implant <NUM> and to rotate relative to the tibial implant <NUM>. In particular, the projecting member <NUM> is sized to rotate within the recess <NUM>. As mentioned above, the projecting member <NUM> is sized to have a maximum transverse dimension that is slightly less than the minimum transverse dimension of the recess <NUM>. In embodiments, the maximum transverse dimension of the projecting member <NUM> can be at least <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, <NUM>%, or <NUM>% less than the minimum transverse dimension of the recess <NUM>. In some embodiments, the projecting member <NUM> can rotate at least <NUM> degrees, at least <NUM> degrees, or <NUM> degrees relative to the tibial implant <NUM> when disposed in the recess <NUM>. In some embodiments, the projecting member <NUM> can freely rotate relative to the tibial implant <NUM> when disposed in the recess <NUM>.

The projecting member <NUM> can have a transverse cross-sectional shape that facilitates load distribution along the lateral surface <NUM> of the projecting member <NUM> as it bears against the sidewall of the recess <NUM>. For example, the transverse cross-section of the projecting member <NUM> can define a rounded shape, such as a substantially circular shape. However, the transverse cross-sectional shape of the projecting member <NUM> can be any shape such as a square, pentagon, star, or other regular or irregular, convex or non-convex polygonal shape.

The projecting member <NUM> is configured to interlock with a portion of the implant lock <NUM>, such as the first end <NUM> of the implant lock <NUM>. For example, in the embodiment shown, the projecting member <NUM> comprises a lateral surface <NUM> having one or more interlocking surface features, such as cogs <NUM>, which are configured to interlock with corresponding cog(s) <NUM> on the first end <NUM> of the lock <NUM>.

The projecting member <NUM> can be configured to have a lateral surface <NUM> that is more wear resistant than the lower surface <NUM>. For example, the projecting member <NUM> or a portion thereof defining the lateral surface <NUM> can comprise a material that is tougher, harder, and/or of a higher modulus than the material of the intermediate implant <NUM> that defines the lower surface <NUM>. In the embodiment shown, the projecting member <NUM> comprises an inner core <NUM> of a first material and a circumscribing member <NUM> of a second material, wherein the second material is tougher, harder, and/or of a higher modulus than the first material. In some embodiments, the circumscribing member <NUM> can be made of a biocompatible metal alloy, such as titanium alloy, cobalt chromium alloy or stainless steel, or any other material that is tougher, harder, and/or of a higher modulus than the material used for the intermediate implant <NUM>. The portion of the intermediate implant <NUM> defining the lower surface <NUM> can be made of polyethylene, polytetrafluoroethylene, polyether-ether-ketone, nylon, copolymers or composites thereof, or other suitable material which can withstand the forces of and about the ankle joint and provide relatively low friction contact with the talar implant <NUM>.

Moreover, the circumscribing member <NUM> can be configured so that it is coupled in fixed relation to the remainder of the intermediate implant <NUM>. For example, the inner core <NUM> and the circumscribing member <NUM> are coupled so that the circumscribing member <NUM> resists rotation relative to the inner core <NUM> (see <FIG>. ) In some embodiments, the inner core <NUM> has a non-circular, transverse cross-sectional shape and the circumscribing member <NUM> defines an interior opening that has a transverse cross-sectional shape that is the same as the transverse cross-sectional shape of the inner core <NUM>. In the embodiment shown, the transverse cross-sectional shape is a polygonal shape. Alternatively, or in addition thereto, the circumscribing member <NUM> can be configured to couple in fixed relation to the base <NUM> of the intermediate implant <NUM>. For example, the circumscribing member <NUM> can interlock with the base <NUM>, such as through one or more mortise-tenon structures <NUM>.

The transverse dimension of the projecting member <NUM> can be any suitable size. In some embodiments, the transverse dimension of the projecting member <NUM> is the same as or less than that of the base <NUM>. In some embodiments, the maximum transverse dimension of the projecting member <NUM> can be between <NUM>% and <NUM>% of the maximum transverse dimension of the base <NUM> of the intermediate implant, such as between <NUM>% to <NUM>% or <NUM>% to <NUM>% or <NUM>% to <NUM>%.

To facilitate obtaining an ankle prosthesis that has an alignment which is closer to the specific anatomy of the patient, an ankle prosthesis kit or an intermediate implant replacement kit can comprise a plurality of intermediate implants <NUM> that provide different configurations to allow varied alignment of the lower, curved surface <NUM> relative to the tibial implant <NUM>. In particular, variance of alignment can be effected by the position of the projecting member <NUM> relative to the apex <NUM> of the lower curved surface <NUM>. <FIG> show three variations in alignment of the projecting member <NUM> relative to the apex <NUM> of the lower curved surface <NUM>. The three variations shown in the figures comprise a shift in the position of the projecting member <NUM> only along an anterior-posterior axis. A first intermediate implant 300a of the kit can be configured such that a center <NUM> of the projecting member <NUM> be posterior to the apex <NUM>. (<FIG> illustrates an embodiment of the first intermediate implant 300a. ) A second intermediate implant 300b of the kit can be configured such that a center <NUM> of the projecting member <NUM> be disposed directly above (e.g., vertically aligned or substantially aligned along an axis that is parallel with the Z-Z axis) the apex <NUM>. (<FIG> illustrates an embodiment of the second intermediate implant 300b. ) A third intermediate implant 300c of the kit <NUM> can be configured such that a center <NUM> of the projecting member <NUM> be anterior to the apex <NUM>. (<FIG> illustrates an embodiment of the first intermediate implant 300c. The amount of anterior or posterior offset, Δ, from the apex <NUM> would be dependent upon the size of the tibial implant <NUM>. In particular the offset would be a fraction of the anterior-posterior length dimension of the tibial implant and can be between <NUM> to <NUM>% of the anterior-posterior length, such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>%.

To facilitate obtaining an ankle prosthesis that has an alignment which is closer to the specific anatomy of the patient, the intermediate implant <NUM> can be configured such that the position of the projecting member <NUM> on the upper surface of the intermediate implant is adjustable. (Embodiment not illustrated. ) For example, a plurality of fastening points (e.g., mortise structures) can be provided on the upper surface of the intermediate implant to which the projecting member <NUM> can be coupled A clinician can select which fastening points to which the projecting member <NUM> should be coupled based on the patient's anatomy.

Another factor influencing fit of the ankle prosthesis is the thickness (or height) of the intermediate implant <NUM>, particularly the base <NUM>. To account for this variation amongst patients, an ankle prosthesis kit or an intermediate implant replacement kit can comprise a plurality of intermediate implants <NUM> that have different thicknesses. The thickness can be between <NUM> and <NUM> at the thinnest cross sectional point of the base <NUM>, such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM>.

With particular reference to <FIG>, <FIG>, and <FIG>, the implant lock <NUM> is configured to resist rotation of the projecting member <NUM> relative to the tibial implant <NUM> by applying a force to the projecting member that is only substantially perpendicular to the axis of rotation of the projecting member <NUM> (e.g., substantially perpendicular to the Z-Z axis). (In embodiments, substantially perpendicular can be within <NUM>°, <NUM>°, <NUM>°,<NUM>°, or <NUM>° of the perpendicular. ) The implant lock <NUM> can also be configured to interlock with the tibial implant <NUM>. The interlocking can be releasable.

In the embodiment shown, the implant lock <NUM> comprises an insert or main body portion <NUM>, which is formed from two sub-portions, namely a head portion <NUM> and a tail portion <NUM>. When inserted into the slot <NUM>, the tail portion <NUM> would be closer to the projecting member <NUM> than the head portion <NUM>.

These two portions <NUM> and <NUM> are configured to move relative to each other along an axis that is generally perpendicular to the axis of rotation of the projecting member <NUM> or that passes through the first end <NUM> and the second end <NUM> of the implant lock <NUM>. In the embodiment shown, the implant lock <NUM> further comprises a screw <NUM> and is configured such that the head portion <NUM> and the tail portion <NUM> move away from each other as the screw <NUM> is rotated in a first direction and move toward each other as the screw <NUM> is rotated in a second direction. In particular, each of the head portion <NUM> and the tail portion <NUM> comprise a through-bore <NUM> and <NUM>, respectively, through which the screw <NUM> can extend. Through-bore <NUM> of the tail portion <NUM> is threaded. The through-bore <NUM> of the head portion <NUM> is not threaded, and the screw <NUM> is able to freely rotate within the through-bore <NUM>.

In addition, head portion <NUM> and screw <NUM> are configured such that the axial position of the screw <NUM> relative to the head portion <NUM> does not change as the screw <NUM> is rotated. For example, in the embodiment shown, screw <NUM> comprises a head <NUM> coupled to a shaft <NUM> and a collar <NUM> spaced apart from the head <NUM> and circumscribing the shaft <NUM>. The through-bore <NUM> of the head portion <NUM> has a transverse dimension that is narrower at an intermediate section <NUM> than at the end sections <NUM> and <NUM>. The section of the shaft <NUM> that is disposed within the narrower, intermediate section <NUM> of through-bore <NUM> is the section between the collar <NUM> and the head <NUM>. In the embodiment shown, this narrower intermediate section <NUM> can be formed by two retaining pins 466a, 466b pressed into holes 468a, 468b intersecting through-bore <NUM> and capturing the shaft <NUM> above the collar <NUM>. As the screw <NUM> is rotated, the collar <NUM> or the head <NUM> of the screw <NUM> bears against the retaining pins 466a, 466b. This facilitates the movement of the tail portion <NUM> away from the head portion <NUM>.

Head portion <NUM> can also be configured to interlock with the tibial implant <NUM>. For example, in the embodiment shown, head portion <NUM> comprises a body <NUM> coupled to two legs 439a, 439b projecting from the body <NUM> such that the legs 439a, 439b flank the tail portion <NUM>. Each leg 439a, 439b comprises two projections, a first projection 410a, 410b facing outward and a second projection 411a, 411b facing inward. The tail portion <NUM> tapers such that it has a wider transverse dimension nearer the head portion <NUM>. The tapering of the tail portion <NUM> facilitates the sidewall <NUM> of the tail portion <NUM> to bear against the inward facing, second projection 411a, 411b and press projections 410a, 410b into the respective notch 136a, 136b in the sidewall <NUM> defining the slot <NUM>.

By rotating the screw <NUM> in a first direction, such as to partially withdraw it from the through-bore <NUM> of the tail portion <NUM>, the tail portion <NUM> moves away from the head portion <NUM> and toward the recess <NUM> or toward the projecting member <NUM> disposed within the recess <NUM>. This motion facilitates the tail portion <NUM> interlocking with the projecting member <NUM>, such as by the cog(s) <NUM> of the tail portion <NUM> interlocking with cogs <NUM> of the projecting member <NUM> (see <FIG>). This motion can also facilitate the head portion <NUM> interlocking with the tibial implant <NUM> through the wedge surface interface of sidewall <NUM> with second projections 411a and 411b.

Implant lock <NUM> can further be configured to bind the screw <NUM> such that rotation of the screw <NUM> is impeded when locking the implant lock <NUM>. For example, to facilitate impeding rotation of the screw <NUM> when locking, in the embodiment shown, implant lock <NUM> can further comprise an abutment pin 470a and a hole 470b intersecting through-bore <NUM> of the tail portion <NUM>. As screw <NUM> is rotated, such as to partially advance it into the through-bore <NUM> of the tail portion <NUM>, the threads of the screw <NUM> will abut the pin 470a, thereby binding the screw by galling and impeding its rotation.

By rotating the screw <NUM> in a second direction, such as to advance it into the through-bore <NUM> of the tail portion <NUM>, the tail portion <NUM> moves toward the head portion <NUM> and away from the recess <NUM> or away from the projecting member <NUM> disposed within the recess <NUM>. This motion facilitates the tail portion <NUM> unlocking with the projecting member <NUM>, such as by the cog(s) <NUM> of the tail portion <NUM> releasing or decoupling from the cogs <NUM> of the projecting member <NUM> (see <FIG>). This motion can also facilitate the head portion <NUM> unlocking with the tibial implant <NUM> through the freeing of the wedge surface interface of sidewall <NUM> with second projections 411a and 411b retracting from the respective notches 136a, 136b in the sidewall <NUM>.

As mentioned above, there can be different configurations of the intermediate implant <NUM> that provide different degrees of alignment of the lower, curved surface <NUM> relative to the tibial implant <NUM>. When a particular configuration of the intermediate implant <NUM> is inserted in vivo, its curvature on the lower surface <NUM> will align with that of the upper surface <NUM> of the talar implant <NUM>. Whether or not this particular configuration is optimal as compared to the other options, with reference to <FIG>, a measurement tool assembly <NUM> can be used to indicate where the projecting member <NUM> is within the recess <NUM> or the slot <NUM>, whether it is anterior, posterior, or generally in alignment with the apex <NUM> of upper surface <NUM> of the talar implant <NUM>. The measurement tool assembly <NUM> comprises a bar <NUM> that is sized to extend through the slot <NUM> and the recess <NUM> and a trial intermediate member <NUM>. In the embodiment shown, the bar <NUM> defines a hole <NUM> configured to receive a trial projecting member <NUM> coupled to and extending from base <NUM>. The bar <NUM> also comprises marking <NUM> which indicated the distance from the hole <NUM>, thereby indicating the relative anterior position of the apex <NUM> of upper surface <NUM> talar implant <NUM> to that of the anterior face <NUM> of tibia implant <NUM>. The markings <NUM> can comprise numerical values and/or can comprise symbols or colors which represent the numerical vales.

To use the measurement tool assembly <NUM>, a trial intermediate implant <NUM> is assembled to bar <NUM>, such as by disposing the trial projecting member <NUM> of the trial intermediate implant <NUM> in the hole <NUM>. The trial projecting member <NUM> with the bar <NUM> coupled thereto is inserted into position between the tibial implant <NUM> and talar implant <NUM> such that the trial projecting member <NUM> and the bar <NUM> are disposed within the recess <NUM> and slot <NUM>. The marking <NUM> that is visible at the anterior face <NUM> of the tibial implant <NUM> is indicative of whether the trial intermediate implant <NUM> is generally in neutral alignment (<FIG>), posterior (<FIG>), or anterior (<FIG>).

An embodiment of the trial intermediate implant <NUM> can be the same as embodiments of the intermediate implant <NUM> described above except that the trial projecting member <NUM> has smaller transverse dimensions than that of the intermediate implant <NUM> and the trial projecting member <NUM> is configured to assemble to the bar <NUM>.

With reference to <FIG>, another embodiment of a tibial implant and an intermediate implant of an ankle prosthesis is shown. A tibial implant <NUM> and an intermediate implant <NUM> shown in <FIG> are similar to those of described above for ankle prosthesis <NUM>, except that the projecting member <NUM> and the implant lock <NUM> are different than those of the ankle prosthesis <NUM>. In particular, the projecting member <NUM> comprises an circumscribing member <NUM> disposed around an inner core <NUM>, where the circumscribing member <NUM> is composed of a material (e.g., stainless steel, titanium and its alloys, cobalt chrome alloys or any other biocompatible metal) that is capable of being permanently deformed by the implant lock <NUM>. The circumscribing member <NUM> and the inner core <NUM> are configured such that they resist rotation relative to each other when coupled. Like in ankle prosthesis <NUM>, the implant lock <NUM> can be inserted into a slot <NUM> in a direction that is perpendicular to the axis of rotation of the intermediate implant <NUM>.

The implant lock <NUM> is configured to press into the circumscribing member <NUM> thereby permanently deforming the circumscribing member <NUM>. For example, the implant lock <NUM> can define a threaded bore <NUM> configured to receive a screw <NUM>. Rotating the screw <NUM> into the threaded bore <NUM> can force a moveable component <NUM> to extend and press into the circumscribing member <NUM>. The pressure applied by the moveable component <NUM> can deform the circumscribing member <NUM>, thereby causing the circumscribing member <NUM> to impede rotation of the intermediate implant <NUM> relative to the tibial implant <NUM>.

Following methods are excluded from patentability according to Article <NUM>(c) EPC. A method of determining the relative position of a talar implant to a tibial implant while the implants are in the body can comprise determining whether an apex of the upper surface of the talar implant is posterior to, anterior to, or aligned with a center of a recess of the tibial implant. The center of the recess is the center of curvature of the curve along which the sidewall defining the recess extends. The method of determining the relative position of the two implants can comprise inserting a measurement tool into the recess of the tibial implant. An intermediate implant can be selected from amongst implants with varied projection member positions depending on whether the apex of the upper surface of the talar implant is posterior to, anterior to, or aligned with a center of a recess of the tibial implant.

Once an appropriate intermediate implant is selected, the implant can be inserted between the tibial implant and the talar implant such that the projecting member is disposed within the recess of the tibial implant. In some embodiments, the projecting member while disposed within the recess of the tibia implant is able to freely rotate within the recess.

A method of establishing the position of the intermediate implant relative to a tibial implant can comprise rotating the intermediate implant relative to the tibial implant and fixing the position of the intermediate implant relative to the tibial implant. Fixing the position of the intermediate implant comprises engaging an implant lock with the intermediate implant such that the implant lock resists rotation of the intermediate implant by applying a force that is only substantially perpendicular to the axis of rotation of the intermediate implant. The implant lock can be inserted into the ankle prosthesis along a direction that is substantially perpendicular to the axis of rotation of the intermediate implant. In some embodiments, only a portion of the implant lock is advanced toward the projecting member of the intermediate implant to engage the projecting member. This can occur while the tibial implant, the talar implant, and the intermediate implant are implanted in the ankle. In some embodiments, rotating the screw of the implant lock fixes the position of the intermediate implant relative to the tibial implant.

A method of inserting the ankle prosthesis can comprise inserting an implant lock into the ankle prosthesis along a direction that is substantially perpendicular to the axis of rotation of the intermediate implant (e.g., the axis of rotation that extends along the Z-Z axis shown in <FIG>). In some embodiments, only a portion of the implant lock is advanced toward the projecting member of the intermediate implant in the substantially perpendicular direction to engage the projecting member. In some embodiments, rotating the screw of the implant lock fixes the position of the intermediate implant relative to the tibial implant.

A method of replacing an intermediate implant of an ankle prosthesis (such as that described above) can comprise accessing an ankle prosthesis within the patient, releasing a first intermediate implant from a locked position, removing the first intermediate implant from the ankle prosthesis, and inserting a second intermediate implant into the ankle prosthesis. In some embodiments, releasing the intermediate implant from a locked position can comprise removing a force that is only substantially perpendicular to the axis of rotation of the intermediate implant, such as by releasing/unlocking the implant lock. Unlocking the implant lock to release the intermediate implant can comprise rotating the screw of the implant lock. Once the first intermediate implant is removed and the second intermediate implant is inserted, the same or a second implant lock can be inserted into the ankle prosthesis. In some embodiments, the second intermediate implant is allowed to rotate relative to the tibial implant and then the position of the intermediate implant can be fixed relative to the tibial implant.

Another aspect of the present disclosure pertains to an ankle prosthesis kit comprising a single talar implant configured for use in either a mobile bearing device or a fixed bearing device. Such kits can allow a surgeon to choose intraoperatively between implanting a mobile bearing device or a fixed bearing device. In an embodiment, as shown in <FIG>, the kit can comprise one talar implant <NUM>, an implant lock <NUM>, and two different types of intermediate implants and tibial implants, namely, a first intermediate implant <NUM> and a first tibial implant <NUM> as well as a second intermediate implant <NUM> and a second tibial implant <NUM>. The talar implant <NUM>, the implant lock <NUM>, the first intermediate implant <NUM>, and the first tibial implant <NUM> are the same as those described above and shown in <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG> and 10A to 10D. Both the first and second intermediate implants <NUM>, <NUM> have identical lower bearing surfaces <NUM>, <NUM>, which are shaped to correspond to the upper bearing surface <NUM> of the talar implant <NUM>. However, the upper surface contours <NUM>, <NUM> of each intermediate implant <NUM>, <NUM> are different. The first intermediate implant <NUM> is configured to couple in fixed relation to the first tibial implant <NUM> as described with respect to the embodiment shown in <FIG>. The second intermediate implant <NUM> is configured to slide or rotate relative to the second tibial implant <NUM> and not couple in fixed relation thereto. As such, the upper bearing surface <NUM> of the second intermediate implant <NUM> is planar, and the lower bearing surface <NUM> of the second tibial implant <NUM> is also planar.

A system in which the talar implant <NUM> can be utilized in either a mobile-bearing or a fixed-bearing device, such as that described above and shown in <FIG>, can also be useful in scenarios where one style of ankle prosthesis (mobile-bearing or fixed-bearing) is implanted into a patient but after some time, a determination is made to use the other style. In such circumstances, a revision arthroplasty procedure can be conducted that would leave the talar implant <NUM> in place but would swap the intermediate implant <NUM> or <NUM> and tibial implant <NUM> or <NUM> for those of the alternative style.

A method of implanting an ankle prosthesis can comprise implanting a talar implant <NUM> into a patient; selecting a tibial implant for implantation by choosing between a first tibial implant <NUM> configured to couple in fixed relation to a first intermediate implant <NUM> and a second tibial implant <NUM> being configured to be mobile bearing in relation to a second intermediate implant <NUM>; implanting the selected tibial implant <NUM> or <NUM>; selecting an intermediate implant for implantation by choosing between the first intermediate implant <NUM> and the second intermediate implant <NUM> based upon the selection of the tibial implant <NUM> or <NUM>; implanting the selected intermediate implant <NUM> or <NUM>, wherein both the first and second intermediate implants <NUM>, <NUM> have a lower bearing surface <NUM>, <NUM> that is shaped to correspond to an upper bearing surface <NUM> of the talar implant <NUM>.

Embodiments described herein are useful in primary ankle replacements but can also be used in a revision arthroplasty procedure, including disarthrodesis.

Four ankle prostheses for a right ankle were constructed in accordance with the present disclosure. The intermediate implant was composed of a UHMWPE and had a circumscribing member composed of Titanium alloy ASTM F136. The talar implant was composed of CoCr (ISO <NUM> / ASTM F75), and had a titanium and hydroxyapatite coating. The bearing surface of the talar implant is an <NUM> degree frustoconical-shaped surface. The tibial implant was composed of a titanium alloy ASTM F136. The implant lock insert was composed of titanium alloy ASTM F136 and the implant locking screw is composed of titanium alloy ASTM F136.

A servo hydraulic six station joint stimulator (Endolab, Rosenheim) was used for the wear testing. Three stations and one load-soak station were used.

All tests were performed in accordance with Endolab's TP-<NUM>-<NUM> (April <NUM> as amended May <NUM>) using the parameters specified in Table <NUM> below.

The test fluid was a calf serum diluted with deionized water to <NUM> grams of protein per liter with <NUM>/l of EDTA, of <NUM>/l of amphotericin solution (<NUM>µg/ml), and <NUM>/l of gentamicin solution (<NUM>/ml).

All intermediate implants were presoaked in a test fluid for a period of <NUM> days. The test fluid was held at a temperature between <NUM>° and <NUM>° C.

For the load-soak control and the test articles, the test fluid was replaced every <NUM>,<NUM> cycles. The load-soak control underwent the same joint reaction force as the other samples but did not undergo any translational / angular motion.

When installing a sample into the simulator, the intermediate implant was locked to the tibial implant by tightening the implant lock screw to a torque of <NUM>.

Samples are dismounted, inspected for wear, and cleaned every <NUM> million cycles, <NUM> million cycles, and at <NUM> million cycle intervals thereafter. The wear of the intermediate implant was determined according to gravimetric change of the component according to ISO <NUM>-<NUM>: <NUM>.

The data collected from the three wear samples was corrected by the weight loss of the load-soak control. After such correction, a mean wear rate of <NUM> per million cycles was observed between <NUM> and <NUM> million cycles for the three samples (SDev = <NUM> per million cycles).

Visual inspection revealed that the teeth on the circumscribing member and the corresponding implant lock did not change in appearance throughout testing indicating that the tibial implant and the intermediate implant remained secure throughout the testing.

All three ankle prosthesis samples were still mechanically sound after <NUM> million cycles.

Similar wear testing was conducted on the mobile-bearing design shown in <FIG>. The data collected from the three mobile-bearing wear samples was corrected by the weight loss of the load-soak control. After such correction, a mean wear rate of <NUM> per million cycles was observed between <NUM> and <NUM> million cycles for the three samples (SDev = <NUM> per million cycles).

All three mobile-bearing ankle prosthesis samples were still mechanically sound after <NUM> million cycles.

An ankle prosthesis as described in Example <NUM> was constructed. The intermediate implant was coupled to the tibial implant with the implant lock. Static torque was applied to the intermediate implant. The amount of torque was well above the amount that would be encountered during use by the full range of potential patients. Visual inspection revealed that the teeth on the circumscribing member and the corresponding implant lock did not change in appearance throughout testing indicating that the tibial implant and the intermediate implant remained secure throughout the testing.

An ankle prosthesis as described in Example <NUM> was constructed. The ankle prosthesis as shown in <FIG> was assembled and secured to a stand. A dynamic force in a posterior to anterior direction was applied to the intermediate implant for <NUM>,<NUM> cycles. The maximum of the dynamic force was well above the amount that would be encountered during use by the full range of potential patients. Visual inspection revealed that the teeth on the circumscribing member and the corresponding implant lock did not change in appearance throughout testing indicating that the tibial implant and the intermediate implant remained secure throughout the testing.

Claim 1:
An ankle prosthesis (<NUM>) comprising:
a) a tibial implant (<NUM>, <NUM>);
b) an intermediate implant (<NUM>, <NUM>) comprising a first surface (<NUM>) and a second, curved surface (<NUM>) opposite the first surface and a projecting member (<NUM>, <NUM>) extending outwardly from the first surface, wherein the projecting member is configured to extend into a recess (<NUM>, <NUM>) of the tibial implant and rotate relative to the tibial implant, and
c) an implant lock (<NUM>, <NUM>) configured to resist rotation of the projecting member relative to the tibial implant by applying a force that is substantially perpendicular to the axis of rotation of the projecting member
wherein
the projecting member (<NUM>, <NUM>) comprises a first end and a second end opposite the first end and a lateral surface (<NUM>) extends between the first and second end, wherein the first end is closer to the first surface (<NUM>) of the intermediate implant (<NUM>, <NUM>) than the second end,
characterized in that
the implant lock (<NUM>) is configured to engage with the lateral surface (<NUM>) of the projecting member (<NUM>, <NUM>) such that rotation of the projecting member is resisted.