Patent Description:
Conventional hip implants are inserted into the femur about <NUM> to <NUM> (<NUM> to <NUM> inches). The use of such conventional hip implants requires removal of a significant quantity of a patient's bone, which can be undesirable. There is a need for hip implant systems that eliminate the need for removal of such significant quantities of bone.

Described herein, in various aspects, is a femoral head arthroplasty system.

A femoral head arthroplasty system according to the invention is defined in claim <NUM>.

The femoral head arthroplasty system comprises a femoral prosthesis. The femoral prosthesis comprises a mounting plate having a first side and an opposed second side. An implant body extends from the first side of the mounting plate by a distance no greater than <NUM>. The mounting plate and the implant body can cooperate to define a recess. A femoral head replacement can have a generally spherical portion and an adapter extending distally from the generally spherical portion. The adapter can be configured for complementary receipt within the recess of the femoral prosthesis.

The implant body can comprise at least one radially extending spline.

The implant body can comprise a plurality of radially extending splines.

The implant body can comprise mounting hardware. The mounting plate can define at least one opening configured to receive the mounting hardware.

The mounting hardware can comprise at least one screw.

The femoral prosthesis can comprise a porous or textured metal.

The femoral prosthesis can comprise a coating.

The femoral head replacement can be angularly offset from the femoral prosthesis.

A kit can comprise a femoral head arthroplasty system and a plurality of femoral head replacements, each femoral head replacement having a generally spherical surface and comprising a recess that is shaped to complementarily receive the adapter of the femoral prosthesis, wherein each femoral head replacement of the plurality of femoral head replacements differs from every other femoral head replacement of the plurality of femoral head replacements in size or material.

Additional advantages of the invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.

These and other features of the preferred embodiments of the invention will become more apparent in the detailed description in which reference is made to the appended drawings wherein:.

It should be understood that any dimensions or other measurements indicated within the figures are merely exemplary and that other dimensions and measurements are contemplated.

The present invention now will be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all embodiments of the invention, are shown. Indeed, this invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. It is to be understood that this invention is not limited to the particular methodology and protocols described, as such may vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to limit the scope of the present invention.

Many modifications and other embodiments of the invention set forth herein will come to mind to one skilled in the art to which the invention pertains having the benefit of the teachings presented in the foregoing description and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

As used herein the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. For example, use of the term "a screw" can refer to one or more of such screws, and so forth.

All technical and scientific terms used herein have the same meaning as commonly understood to one of ordinary skill in the art to which this invention belongs unless clearly indicated otherwise.

As used herein, the term "at least one of" is intended to be synonymous with "one or more of. " For example, "at least one of A, B and C" explicitly includes only A, only B, only C, and combinations of each.

The word "or" as used herein means any one member of a particular list and also includes any combination of members of that list.

Optionally, in some aspects, when values are approximated by use of the antecedent "about," it is contemplated that values within up to <NUM>%, up to <NUM>%, up to <NUM>%, or up to <NUM>% (above or below) of the particularly stated value can be included within the scope of those aspects. Similarly, in some aspects, when values or characteristics are approximated by the use of the antecedent "approximately," "generally," or "substantially," it is contemplated that values within up to <NUM>%, up to <NUM>%, up to <NUM>%, or up to <NUM>% (above or below) of the particularly stated value or characteristic can be included within the scope of those aspects.

As used herein, the term "patient" can refer to a human or an animal that receives an implant as further disclosed herein. In exemplary aspects, a patient can be a human who has been determined to be in need of receiving an implant as disclosed herein.

It is to be understood that unless otherwise expressly stated, it is in no way intended that any method set forth herein be construed as requiring that its steps be performed in a specific order. Accordingly, where a method claim does not actually recite an order to be followed by its steps or it is not otherwise specifically stated in the claims or descriptions that the steps are to be limited to a specific order, it is in no way intended that an order be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps or operational flow; plain meaning derived from grammatical organization or punctuation; and the number or type of aspects described in the specification.

The following description supplies specific details in order to provide a thorough understanding. Nevertheless, the skilled artisan would understand that the apparatus, system, and associated methods of using the apparatus can be implemented and used without employing these specific details. Indeed, the apparatus, system, and associated methods can be placed into practice by modifying the illustrated apparatus, system, and associated methods and can be used in conjunction with any other apparatus and techniques conventionally used in the industry.

Disclosed herein, in various aspects and with reference to <FIG>, is a femoral prosthesis <NUM> of a femoral head arthroplasty system. The femoral prosthesis <NUM> can comprise a mounting plate <NUM> having a first side <NUM> and an opposing second side <NUM>. The mounting plate <NUM> can have a planar or substantially planar profile and a thickness <NUM> between about three and about seven millimeters (e.g., about five millimeters) in a first dimension (measured along a first axis <NUM>) that is perpendicular to the first side's surface. The mounting plate <NUM> can extend about twenty-five to about forty millimeters (e.g., about thirty-four millimeters) in a second dimension (measured along a second axis <NUM>) and a length <NUM> of about sixteen to about twenty five millimeters (e.g., about twenty-two millimeters) in a third dimension (measured along a third axis <NUM>). The femoral prosthesis's mounting plate <NUM> can have a major dimension that is greater than the major radial dimension of the patient's femur so that, when implanted within the femur, the mounting plate abuts the femur's outer radial wall. A pair of top corners can define a radius r1 (optionally, of about two millimeters), and a bottom of the mounting plate <NUM> can define a continuous arcuate profile (optionally, having a radius of eleven millimeters, or about half of the width of the mounting plate measured along the third axis <NUM>).

The mounting plate <NUM> can define one or more through-holes <NUM> (e.g., a pair, as shown) that can receive mounting hardware for attaching the femoral prosthesis to a patient. The holes <NUM> can have respective diameters d5 (optionally, a diameter ranging from about <NUM> millimeters to about <NUM> millimeters, or more preferably, being about seven millimeters). In some aspects, the holes <NUM> can be spaced from respective side edges of the mounting plate by distances <NUM> (e.g., at least one millimeter, between one and <NUM> millimeters, or, more preferably, about two millimeters). The pair of through holes <NUM> can optionally define female threads <NUM> therein for receiving male threads of mounting screws (see also <FIG>). In some optional aspects, the pair of through holes <NUM> can be centered along the third axis <NUM> so that the femoral prosthesis is symmetrical about a plane that extends in the first and third dimensions (containing axes <NUM>, <NUM>) and bisects the femoral prosthesis <NUM>. Although embodiments described herein comprise features for attachment via screws, in further embodiments, other attachment means, such as wires, sutures, or cables, may be used.

An implant body <NUM> can extend from the first side <NUM> of the mounting plate <NUM>. The implant body <NUM> can be disposed below (i.e., offset in the second dimension (along second axis <NUM>) from) the pair of through-holes <NUM>. The implant body <NUM> can comprise a first cylindrical or generally cylindrical protrusion <NUM> that extends perpendicularly to the face of the mounting plate's first side <NUM>. The first generally cylindrical protrusion <NUM> can extend less than ninety and greater than twenty millimeters, and optionally less than seventy-five and greater than thirty millimeters or between thirty-five and sixty millimeters, (e.g., about forty millimeters or about forty-five millimeters) from the first side <NUM> of the mounting plate along a first axis <NUM>. The first generally cylindrical protrusion <NUM> can optionally have a diameter d1 between about ten and about eighteen millimeters (e.g., about fourteen millimeters). A distal end of the first generally cylindrical protrusion <NUM> (i.e., the end farthest away from the mounting plate <NUM>) can have an arcuate edge <NUM> that extends a length <NUM> in the first dimension <NUM> ranging from about three millimeters to about eight millimeters, or more preferably, being about five millimeters. The distal end of the first generally cylindrical protrusion <NUM> can optionally have a planar face <NUM> that is generally parallel to the mounting plate. The first generally cylindrical protrusion <NUM> can be spaced from the bottom of the mounting plate <NUM>, for example by about two millimeters. The first axis <NUM> of the first generally cylindrical protrusion <NUM> can optionally be spaced from the bottom of the mounting plate by a distance <NUM> (e.g., optionally, from about seven millimeters to about <NUM> millimeters, or about nine millimeters). In some optional aspects, the first generally cylindrical protrusion <NUM> can be spaced from the lower end of the mounting plate by a distance <NUM> (e.g., optionally, from about one millimeter to about four millimeters, or about two millimeters).

The implant body <NUM> can further comprise a second cylindrical or generally cylindrical protrusion <NUM> that extends along a second axis <NUM> that is parallel to the first axis <NUM>. The second axis <NUM> can optionally be directly vertically above the first axis <NUM>. The second generally cylindrical portion <NUM> can extend a length <NUM> about ten to about forty millimeters (e.g., from about ten millimeters to about twenty millimeters, or about fifteen millimeters) from the first side <NUM> of the mounting plate <NUM>. The second generally cylindrical portion <NUM> can therefore have an end opposite the mounting plate <NUM> that is a length <NUM> (e.g., from about <NUM> millimeters to about <NUM> millimeters, or about thirty millimeters) from the end of the first generally cylindrical portion <NUM> opposite the mounting plate. The first and second axes <NUM>, <NUM> can be spaced by less than the sum of the respective radiuses of the first and second generally cylindrical portions so that the second generally cylindrical protrusion <NUM> overlaps the first generally cylindrical protrusion <NUM>. Accordingly, in a cross sectional plane perpendicular to the first axis <NUM>, the overlapping first and second generally cylindrical protrusions <NUM>, <NUM> can have a figure-eight shape. Optionally, the second axis <NUM> can extend along a top edge of the first generally cylindrical protrusion <NUM>. The second axis <NUM> can be spaced from the top of the mounting plate by a distance <NUM> (e.g., optionally, from about <NUM> millimeters to about <NUM> millimeters, or about eighteen millimeters) and can be spaced from the bottom of the mounting plate by a distance <NUM> (e.g., optionally, from about <NUM> millimeters to about <NUM> millimeters, or about sixteen millimeters). That is, the second axis <NUM> can be spaced from the first axis by the radius of the first generally cylindrical protrusion <NUM>. The second generally cylindrical protrusion <NUM> can have a radius r3 of about five to about nine millimeters (e.g., about seven millimeters). The first and second generally cylindrical protrusions <NUM>, <NUM> can cooperate to provide an oblong cross section so that the implant body <NUM> is inhibited from rotation. Moreover, the combined cross sectional shape of the first and second generally cylindrical protrusions (e.g., a figure-eight shape) can cooperate with a bone preparation site that is easily prepared by a surgeon. In further embodiments, the implant body <NUM> can have various other cross sectional profiles in planes perpendicular to the implant body's longitudinal dimension, including a generally cylindrical profile, an oval profile, a polygonal profile (e.g., a square or rectangular profile), or an oblong profile.

Optionally, the implant body <NUM> can extend from the mounting plate by a distance of no greater than ninety millimeters, or no greater than seventy-five millimeters, or no greater than sixty millimeters, or no greater than fifty millimeters, or no greater than forty-five millimeters. As further disclosed herein, it is contemplated that the minimal length of the implant body <NUM> can reduce the amount of native bone of a subject that must be removed to accommodate the implant body.

An adapter <NUM> can extend from, and be oriented perpendicularly or substantially perpendicularly to, the second side <NUM> of the mounting plate <NUM>. The adapter <NUM> can optionally have a central axis <NUM> that is collinear with the second axis <NUM>. Accordingly, the adapter <NUM> can be superiorly axially offset from (i.e. above) the axis <NUM> of the first generally cylindrical protrusion <NUM>. In this way, for some patients, a femoral head attached to the adapter <NUM> can most accurately recreate the patient's normal anatomy. In further embodiments, the adapter can have an axis offset from the axis <NUM>. Optionally, in some such embodiments, the adapter <NUM> can be axially aligned with the axis <NUM>. The adapter <NUM> can comprise a frustoconical portion <NUM> that attaches, via a neck portion <NUM>, to the mounting plate <NUM>. The neck portion can have a length <NUM> of from about three millimeters to about seven millimeters, or of about five millimeters. The frustoconical portion <NUM> can taper from a proximal end <NUM> to a distal end <NUM> (moving away from the mounting plate <NUM>). The frustoconical portion <NUM> can optionally have a Morse taper. The proximal end <NUM> can optionally have a diameter d2 of about twelve to about sixteen millimeters (e.g., about fourteen millimeters), and the distal end <NUM> can optionally have a diameter d3 of about ten millimeters to about fourteen millimeters (e.g., about twelve millimeters). The frustoconical portion <NUM> can extend axially a length <NUM> of about ten to about eighteen millimeters (e.g., about fourteen millimeters) from the proximal end <NUM> to the distal end <NUM>. In some aspects, the adapter's central axis can be spaced from the top of the mounting plate by a length <NUM> (optionally, from about <NUM> millimeters to about <NUM> millimeters, or about eighteen millimeters) and spaced from the bottom of the mounting plate by a length <NUM> (optionally, from about <NUM> millimeters to about <NUM> millimeters, or of sixteen millimeters). The adapter's radial-most surface can be spaced from the respective opposing side edges of the mounting plate in the third dimension <NUM> by a distance <NUM> (optionally, from about three millimeters to about six millimeters, or of about four millimeters). Optionally, at least a portion of the frustoconical portion's circumferential surface can comprise a texture. Said texture can improve frictional engagement between the adapter <NUM> and the femoral head replacement. In some optional aspects, a helical groove having a pitch of <NUM> millimeters can define said texture.

The neck portion <NUM> of the adapter <NUM> can have a cross section that varies along its axis in an arcuate profile. At a halfway point along its axis, the neck portion <NUM> can have a minimum diameter d4, which, in some embodiments, can be about twelve millimeters. Opposing ends of the neck portion <NUM> can each have a diameter d2 of about fourteen millimeters. Accordingly, the minimum diameter can be about two millimeters less than the maximum diameter of the neck portion <NUM>. The neck portion's narrowing diameter can provide a location to grip the femoral prosthesis during implantation and removal of the femoral prosthesis.

Although shown extending parallel to the implant body <NUM>, in further embodiments, the adapter <NUM> can extend at various angles with respect to the implant body <NUM> in order to vary the varus/valgus angle of the femoral head with respect to the longitudinal dimension of the femur.

Referring to <FIG>, the adapter <NUM> can receive a femoral head replacement <NUM>. The femoral head replacement <NUM> can have a shape that cooperates with a hip socket of the patient's pelvis or an artificial hip socket. In some embodiments, the femoral head replacement <NUM> can have the shape of a natural femoral head. The femoral head replacement <NUM> can have a generally spherical profile. The femoral head replacement <NUM> can define a recess <NUM>. The recess <NUM> can have a complementary shape to the adapter <NUM> (<FIG>) of the femoral prosthesis <NUM> (<FIG>). For example, the recess <NUM> can have a frustoconical profile. The prosthesis <NUM> can optionally be a conventional component known to those skilled in the art.

The femoral prosthesis <NUM> can couple to the femoral head replacement <NUM> to create a femoral head arthroplasty system <NUM>. In some embodiments, the femoral prosthesis <NUM> and the femoral head replacement <NUM> can couple permanently, while in further embodiments, the pair can couple via a non-permanent means. The adapter <NUM> and femoral head replacement <NUM> can have an interference fit (e.g., via a Morse taper) so that the respective components frictionally engage each other. As stated above, at least one of the adapter <NUM> and the femoral head replacement <NUM> can optionally have a texture (i.e., surface texture) to improve the engagement between the respective components.

Referring to <FIG>, in further examples, a femoral head replacement <NUM>' can comprise a generally spherical portion <NUM>' and an adapter <NUM>' that extends distally from the generally spherical portion <NUM>'. A femoral prosthesis <NUM>' can comprise a recess <NUM>' and can otherwise have the same shape and dimensions as that of the femoral prosthesis <NUM> (<FIG>). Although shown as a frustoconical protrusion, the adapter <NUM>' and recess <NUM>' can have profiles similar to that of the adapter <NUM> (<FIG>) and the recess <NUM> (<FIG>), respectively, or any other adapter profile known to those skilled in the art.

In some examples, the femoral prosthesis can comprise at least one radially extending spline <NUM> or, as shown, a plurality of radially extending splines <NUM>. The radially extending spline(s) <NUM> can provide surfaces against which bone can grow as well as inhibit rotation of the femoral prosthesis about its axis of elongation.

The femoral prosthesis <NUM> and/or the femoral head replacement <NUM> can comprise various materials known to those skilled in the art, such as, for example, porous, coated titanium, ceramics, tantalum, cobalt chromium alloy, or various other porous metals. The material(s) can be porous or textured in order to allow bone in-growth or on-growth. The material(s) can be strong enough to bear the weight of the patient without fracturing.

The femoral prosthesis <NUM> and/or the femoral head replacement <NUM> can comprise a coating. Said coating can comprise one or more of the following: hydroxyapatite, titanium oxide, titanium nitride, zirconium oxide, and pyrolytic carbon. In further examples, the coating can comprise gold, ceramics, polymers (e.g., ultra-high molecular weight polyethylene), diamond-like carbon (DLC) coatings, oxidized zirconium, titanium nitride or various other coatings known to those skilled in the art. The coating(s) can optionally be low friction and can optionally be hydrophobic.

Referring to <FIG>, which illustrate an embodiment of the invention, the implant body <NUM> of the prosthesis <NUM> can have an elongate profile in the second dimension (along the second axis <NUM>). That is, in cross sections perpendicular to the second axis <NUM>, the implant body <NUM> has a major dimension measured along the second axis <NUM> and a minor dimension measured along the third axis <NUM>. The implant body <NUM> defines two hemi-cylindrical surfaces <NUM> that are spaced along the second axis <NUM> and connected via planar faces <NUM>. This non-axially symmetric profile can inhibit rotation of the implant body relative to the femur. In some aspects, the implant body can have a major dimension of between <NUM> and <NUM> millimeters (e.g., about <NUM> millimeters) measured along the second axis <NUM> and a minor dimension of between <NUM> and <NUM> (e.g., about <NUM> millimeters) measured along the third axis <NUM>.

In some optional aspects, the centerline <NUM> of the implant body (i.e., the line extending through the centroid of the cross sections in planes perpendicular to the first dimension (first axis <NUM>)) can be collinear with the central axis <NUM> of the adapter <NUM>. In further optional aspects, as shown in <FIG>, the centerline <NUM> can be offset from the central axis <NUM> of the adapter <NUM> (optionally, offset from the central axis <NUM> in the second dimension (relative to the second axis <NUM>)).

In some optional aspects, the distal end of the implant body <NUM> can optionally have a planar face <NUM> that is parallel or generally parallel to the mounting plate. In further aspects, it is contemplated that the distal end of the implant body can define a rounded, oblong surface <NUM> or other non-planar surface that extends parallel to the mounting plate. For example, the implant body <NUM> can define first and second radii <NUM> (optionally, spherical surfaces) that are spaced relative to each other along the second dimension <NUM> (and that are measured in a plane containing the first and second axes).

The centerline <NUM> of the implant body extends perpendicularly to the mounting plate <NUM> along an entire length of the implant body. For example, within any plane that intersects the implant body and is perpendicular to the first axis <NUM>, a center point (which can optionally correspond to a center of mass) of the portion of the implant body within the plane will be intersected by the centerline <NUM>. In further aspects, it is contemplated that the apparatus can be symmetric about a plane that is perpendicular to the second dimension <NUM> and bisects the implant body (and, therefore, includes the centerline <NUM>). Optionally, in still further aspects, it is contemplated that the implant body can be symmetric about both (a) a first plane that is perpendicular to the second dimension <NUM> and bisects the implant body; and (b) a second plane that is perpendicular to the third dimension <NUM> and bisects the implant body. It is contemplated that the above-described configurations, by avoiding the need for providing an angled or asymmetric implant body (for example, as might be necessary to permit deeper advancement of an implant body within a native bone), can provide advantageous balance and force transmission properties while minimizing the amount of bone that is removed from the patient to accommodate the implant body.

Referring to <FIG>, it is further contemplated that in some aspects, the neck portion <NUM> can have a constant diameter (instead of the narrowing diameter as depicted in <FIG>) to increase the strength of the prosthesis.

Referring to <FIG>, a fixation screw <NUM> can have a head <NUM> defining a first thread (or plurality of threads) <NUM> and a body <NUM> defining a second thread (or plurality of threads) <NUM>. Optionally, the head of the screw can define a taper. Accordingly, the hole <NUM> (<FIG>) can define a corresponding taper. The fixation screw can comprise one or more (e.g., optionally, three equally circumferentially spaced) self-tapping features <NUM> for tapping the bone during insertion of the screw. The fixation screw can further comprise one or more (e.g., optionally, three equally circumferentially spaced) self-tapping features <NUM> for tapping the bone during removal of the screw. It should be understood that the dimensions (in millimeters) provided in the figures should be understood to be optional aspects.

It is further contemplated that the prosthesis can be fixated to the femur, additionally or alternatively, with bone ingrowth and/or ongrowth and/or cemented fixation.

A kit can comprise a femoral prosthesis <NUM> and a plurality of femoral head replacements <NUM>. Each of femoral head replacements <NUM> can differ from the others in at least one of size or material.

Referring to <FIG>, a medical professional (e.g., an orthopedic surgeon) can form a prepared site within a femur <NUM>. For example, the medical professional can cut off a portion of the patient's natural femoral head. Optionally, the surgeon can use a patient-specific cutting guide that locates the optimal location and angle for removing the femoral head. According to one embodiment, the cutting guide can comprise a frame that defines a slot for guiding a cutting saw. The cutting guide can temporarily be fastened to the femur using pins or screws and subsequently be removed from the femur after cutting. The surgeon can drill/ream a pair of overlapping holes to receive the first and second cylindrical portions <NUM>, <NUM>. In further aspects, the overlapping holes can further be bored to provide an opening to receive the implant body <NUM> (e.g., for the embodiments shown in <FIG>). The prepared site can be positioned further proximally along the neck of the femur (toward the original femoral head) than prepared sites of conventional femoral prostheses for hip replacement. The prepared site can optionally extend no more than thirty millimeters distal to the lesser trochanter <NUM> of the femur <NUM> (i.e., past the lesser trochanter along femoral shaft's longitudinal axis in the direction toward the patient's foot). The medical professional can then implant the femoral prosthesis so that the implant body is received within the prepared site. The femoral prosthesis can be inserted so that the mounting plate abuts a superior end of the femur. The medical professional can drill holes in the patient's bone for receiving the screws or other fasteners. Screws <NUM> or other fasteners can be used to secure the femoral prosthesis in place. Optionally, the surgeon can drill holes into the femur to receive screws <NUM>. The femoral head replacement can then be attached to the femoral prosthesis.

Compared to conventional implants, embodiments disclosed herein can enable hip implants that require less bone removal. That is, a shorter segment of bone can be removed, leaving a portion of the femoral neck through which the femoral prosthesis can extend. The disclosed embodiments can reduce blood loss during surgery and enable easier insertion for the surgeon, particularly in cases of anterior approach surgery. The disclosed embodiments can be associated with smaller incisions than conventional implants and can provide for easier re-do surgery if need arises.

Claim 1:
A femoral head arthroplasty system comprising:
a femoral prosthesis (<NUM>) comprising:
a mounting plate (<NUM>) having a first side (<NUM>) and an opposed second side (<NUM>), wherein the first side (<NUM>) of the mounting plate (<NUM>) is configured to abut a cut proximal end of a femur, and
an implant body (<NUM>) extending from the first side (<NUM>) of the mounting plate (<NUM>), wherein the implant body (<NUM>) extends from the mounting plate (<NUM>) by a distance no greater than <NUM>, wherein, in cross section in a plane that is perpendicular to a first axis (<NUM>), the implant body (<NUM>) has a major cross sectional dimension along a second axis (<NUM>) and a minor cross sectional dimension along a third axis (<NUM>) that is different than the second axis (<NUM>), wherein the minor cross sectional dimension is less than the major cross sectional dimension, and wherein the implant body (<NUM>) has a centerline (<NUM>) that is perpendicular to the mounting plate (<NUM>): and
a femoral head replacement (<NUM>) having a generally spherical surface,
wherein one of the femoral prosthesis (<NUM>) and the femoral head comprises an adapter (<NUM>), and wherein the other of the femoral prosthesis (<NUM>) and the femoral head defines a recess (<NUM>) that is complimentarily shaped to receive the adapter (<NUM>), characterised in that the implant body (<NUM>) has an outer circumferential surface comprising two hemi-cylindrical surfaces (<NUM>) being spaced along the second axis (<NUM>), and two parallel planar faces (<NUM>) that are spaced along the third axis (<NUM>) and extend between and to the two hemi-cylindrical surfaces (<NUM>) along a respective entirety of each of the lengths of the two hemi-cylindrical surfaces, wherein the implant body (<NUM>) has a distal end defining a distal surface through which the centreline (<NUM>) extends.