Patent Description:
Prosthetic cup assemblies are well known and commonly used to provide a functional joint where the corresponding bone has become damaged, diseased or degraded. In particular, the acetabulum of a hip is partially replaced with an acetabular cup assembly. During surgery, an acetabular cup is implanted in the patient's hip using a type of impactor tool. Once implanted in the bone, the spherical head of a femoral implant or of the anatomical femur is receivable within the implanted cup, such that the cup and the femoral implant or femur may act like a ball-and-socket joint.

A first example of such an impactor tool is disclosed in <CIT>. The impactor tool comprises a cylindrical head, removably added to the distal end of the handle for actioning the acetabulum to be implanted. The head has four quadrants, of which two are rigid, fixed quadrants diametrically opposed to one another, and the other two are mobile quadrants. Each of the mobile quadrants connects to one of the rigid quadrants by an elastically deformable hinge. The two mobile quadrants can be pivoted by screwing the handle. However, the use of these two mobile quadrants means that the impactor head only engages a small area of the inner face of the acetabular cup, thus with only a limited gripping force and concentrating the force applied to a small surface.

A second example is disclosed in U. patent <CIT>. This acetabular cup impactor assembly described has a handle attached to a head, and the head has a gripping surface to engage the inner surface of a two-part acetabular cup. The head has two gripping elements or jaws which are spaced apart from each other by a compression spring. To insert the head into the prosthetic cup assembly, the surgeon compresses the spring to bring the two jaws towards each other. Upon release of the spring, the jaws grip the inside of the cup. However, the impactor tool is complex to manufacture and operate with the effort of grip depending directly on the force of the compression spring. Furthermore, in gripping the cup by applying forces to the inside surface, there is a risk of damaging the inside surface of the acetabular cup.

<CIT> relates to an instrument for manipulating an acetabular cup having attachment elements which are bendable between a first position in which the attachment element does not engage the acetabular cup, and a second position in which the acetabular cup is held by the attachment element.

<CIT> pertains to a surgical tool for insertion of a prosthetic acetabular cup. The surgical tool has movable claws for engaging with the acetabular cup.

<CIT> relates to an instrument for positioning a cup component. The instrument includes an actuator and jaw members which can grip an acetabular cup.

As gripping the inside of the acetabular cup risks damaging the articulating surface of the cup, an impactor tool gripping the outside of the acetabular cup is preferable. However, additional bone would generally need to be removed to accommodate gripping elements external to the cup, such as claws or hooks; such is not accepted in hip surgery. Releasing the cup from the gripping claws could further result in bone being damaged or space being required, particularly if the rim of the cup, or part thereof, is recessed into the bone. In such an operation, it is preferable to remove as little extra bone as possible.

The present invention seeks to provide a solution to these problems by providing an impactor head which is adapted to externally hold different kinds or styles of acetabular cups of different dimensions. The impactor head of the invention ensures both an efficient grip of the cup and a good application of the force of impaction, without damaging the inner surface of the cup whilst reducing an amount of bone interference, disturbance or that needs to be removed.

According to a first aspect of the invention, there is provided an impactor head for releasably holding an outer surface of a cup implant, the impactor head comprising a head body; at least one rotatable implant-engagement arm being at least in part translatable; an actuation mechanism which moves the implant-engagement arm to an implant-engagement condition or an implant-release condition; and an implant outer-surface engagement element which is at or adjacent to a lateral arm end of said implant-engagement arm, the said implant-engagement arm includes a lateral pivot axis about which the implant-engagement arm is rotatable to adopt said implant-engagement condition or said implant-release condition, characterised in that the lateral pivot axis is radially translatable to linearly move the implant-engagement arm radially as it rotates. Beneficially, the said implant-engagement arm may have a lateral hook portion, the implant outer-surface engagement element being on an inner face of the lateral hook portion. In this case, the impactor head is able to grasp an acetabular cup on the outer surface of the cup via the implant outer-surface engagement element on the lateral hook portion, thereby not damaging the internal surface of the cup. The implant-engagement arm being simultaneously rotatable and translated inwards during motion allows the outer-surface engagement to follow the cup outer surface more closely, thus minimising bone disturbance or bone to be removed.

The terms 'proximal', 'distal', 'medial' and 'lateral' are used to clarify the relative position of features in relation to a central axis of the impactor head and/or device in general. Features which are closer to the surgeon or user when gripping the device are considered to be 'proximal'. Features that are remote from the surgeon or user are considered to be 'distal'.

Furthermore, features which are at or adjacent to a central axis of the impactor head or device may be termed 'medial' or 'proximal'. Those features which are remote relative to the central axis or spaced at or towards a radially outer surface or edge may be termed 'lateral' or 'distal'.

In this case, the implant-engagement arm is able to engage with the outer surface of the cup by rotating about its pivot and the translation of the implant-engagement arm is inwards into the head or outwards of the head in the radial direction. Additionally, the pivot is also movable with the implant-engagement arm, being mobile relative to the head body.

Furthermore, the head body may include a radial guiding channel in which the lateral pivot axis may be slidable, so that the implant-engagement arm may be translatable to linearly move radially as it rotates. In this case, the pivot axis is mobile relative to the channel and the implant-engagement arm is moveable into and out of along a radius of the head body.

Advantageously, the said implant-engagement arm may be translatably rotatable about a virtual pivot point, so that the implant outer-surface engagement element may be able to follow an arcuate path about a rim of the cup implant. Preferably, the head body has a distal head end and the virtual pivot point is spaced from the lateral pivot axis in a direction of the said distal head end during at least part of the translatable rotation of the implant-engagement arm. Furthermore, the virtual pivot point may be dynamically-movable. This arrangement allows the implant outer-surface engagement element to be in close proximity to the cup outer surface and the implant-engagement arm to be retracted into the head body, thereby reducing the amount of unnecessary bone to be disturbed, compressed and/or removed. Furthermore, the said implant-engagement arm may include a medial pivot axis about which the implant-engagement arm may be rotatable to adopt said implant-engagement condition or said implant-release condition. Additionally, the said actuation mechanism may engage said medial pivot axis to operate the said implant-engagement arm. This arrangement provides a mechanism to act upon the implant-engagement arm via the medial pivot.

Advantageously, the medial pivot axis may be translatable to enable linear movement of the implant-engagement arm radially as it rotates. Optionally, the implant-engagement arm may include a further channel in which the medial pivot axis and/or the lateral pivot axis may be slidable, so that the implant-engagement arm may be translatable to linearly move radially as it rotates. Preferably, the actuation mechanism includes an actuator body receivable at least in part in the cup implant, and an axially-translatable actuator for operating the said rotatably translatable implant-engagement arm. The medial pivot being translatable in both an axial and a radial direction provides further degrees of freedom in the motion of the implant-engagement arm. The actuator mechanism allows transmission of a force applied by the surgeon to alter the condition of the implant-engagement arm.

According to an embodiment, not in accordance with the present invention, there is provided an impactor head for releasably holding an outer surface of a cup implant, the impactor head comprising a head body; at least one non-rotatable implant-engagement arm which is radially and axially translatable; an actuation mechanism which moves the implant-engagement arm to an implant-engagement condition or an implant-release condition; and an implant outer-surface engagement element which is at or adjacent to a lateral arm end of said implant-engagement arm. Additionally, the said implant-engagement arm may have a lateral hook portion, the implant outer-surface engagement element being on an inner face of the lateral hook portion. In this case, the impactor head is able to hold an acetabular cup on the outer surface of the cup, thereby not damaging the internal surface of the cup. The implant-engagement arm being solely translatable allows the amount of the bone to be removed or damaged to be minimised.

Beneficially, the head body may include a diagonal guiding channel in which an arm body of said implant-engagement arm may be longitudinally linearly slidable by which the implant-engagement arm may be radially movable to adopt said implant-engagement condition and said implant-release condition. In this case, the impactor head is able to grasp a cup via the implant-engagement arm being able to translate into and out of the implant-engagement condition.

Additionally, the actuation mechanism may include an actuator body receivable at least in part in the cup implant, and an axially-translatable actuator for moving the said non-rotatable translatable implant-engagement arm linearly axially and radially. In this case, the actuator mechanism allows transmission of a force applied by the surgeon to alter the condition of the implant-engagement arm.

Additionally, the head body may have a distal head end and the implant outer-surface engagement element may be moveable on a linear implant-engagement path angled towards the said distal head end of the head body when moving towards the implant-engagement condition. In this arrangement, the amount of bone to be removed or damaged is reduced as much as possible. Additionally, it may be easier to remove bone along a straight line than a curve.

According to a further aspect of the invention, there is a provided a surgical introducing kit comprising a surgical introducer in combination with the impactor head, the introducer having an elongate impactor shaft having an attachment element to releasably engage the head body of the impactor head, the attachment element having a user-operable actuator to engage and release the impactor head. Optionally, the attachment element of the introducer may include a remotely operable clamp at the end of the impactor shaft for clamping a receiving head portion on the head body. In this arrangement, the surgical introducing kit allows the surgeon to engage with the head body at a distance, and action the implant-engagement arm. Additionally, when engaged, the surgical introducing kit provides a clear indication of the alignment of the head.

According to a further aspect of the invention, there is provided a method of engaging a cup implant (<NUM>) with an impactor head (<NUM>), the method comprising the steps of: a] providing a dynamically-movable virtual pivot point of the rotatably translatable implant-engagement arm of the impactor head; and b] providing a release path on which the implant outer-surface engagement element travels, the release path originating at the implant-engagement condition of the implant outer-surface engagement element, so that the implant outer-surface engagement element has at least a reduced movement outwardly when moving to the implant-release condition, thereby reducing a bone space required to accommodate a lateral arm end of the implant-engagement arm. This method allows an acetabular cup to be implanted using an impactor head having an implant-engagement arm that is both rotatable and translatable. The result is that no or little extra bone is disturbed, damaged and/or removed.

Alternatively, a method may comprise the steps of providing the implant outer-surface engagement element of the impactor head with a linear implant-engagement path angled towards a distal head end of the head body when moving towards the implant-engagement condition, so that the implant outer-surface engagement element moves axially and radially outwardly to the implant-release condition, thereby reducing a bone space required to accommodate a lateral arm end of the implant-engagement arm. This method allows an acetabular cup to be implanted using an impactor head having an implant-engagement arm that is solely translatable. The result is that no or little extra bone is disturbed, damaged or removed.

Optionally, either method may be performed using the surgical introducing kit. This method allows an acetabular cup to be implanted using an impactor head having an actionable implant-engagement arm and a surgical introducing kit which transmits a force applied by the surgeon to the actionable implant-engagement arm.

The invention will now be more particularly described, with reference to the accompanying drawings, in which:.

Referring firstly to <FIG>, there is shown a first embodiment of an impactor head <NUM> for releasably holding an outer surface <NUM> of a cup implant <NUM>. The impactor head <NUM> comprises a head body <NUM>, an actuation mechanism <NUM>, and at least one rotatable implant-engagement arm <NUM>.

The head body <NUM>, being in this case at least partly hemispherical, is a supporting structure which is shaped to be at least partly insertable into an acetabular cup implant <NUM>. The head body <NUM> may beneficially be formed of plastics or metals, or a combination thereof.

In this embodiment, one or more dimples <NUM> are formed on an outer head surface <NUM> of the head body <NUM>. However, these may be omitted dependent on necessity.

As shown in <FIG>, the head body <NUM> has a top body portion <NUM> and a bottom body portion <NUM>, which are held together by fastening means, such as at least one internal screw and/or snap-fit engagement, by way of examples.

The top body portion <NUM> has a receiving head portion <NUM>, at least one radial guiding channel <NUM>, and at least one, but preferably three, arm-recesses <NUM> through which the implant-engagement arms <NUM> protrude out from the head body <NUM>. Although the radial guiding channel <NUM> is preferably in the top body portion <NUM>, it may be in, overlap and/or shared with the bottom body portion. Additionally or alternatively, a plurality of implant-engagement arms may be accommodated in a single arm-recess.

The bottom body portion <NUM> is at least in part hemispherical, and thus has a distal pole and a central axis <NUM>, an overhanging lip <NUM> and at least one axial guiding channel <NUM>. The distal pole may also be referred to as the distal head end <NUM>; and the opposite end of the head body <NUM> may be referred to as the proximal head end <NUM>. The bottom body portion <NUM> is dimensioned to be receivable in a cup implant <NUM>, and thus the overhanging lip <NUM> preferably provides a seat for abutment of a rim <NUM> of the cup implant <NUM>. In this case, the entire rim <NUM> seats flushly on the shoulder defined by the overhanging lip <NUM>. This is beneficial in providing stability for impaction of the cup implant <NUM> during surgery. However, it is feasible that there may gaps or spaces between the rim and the overhanging lip and/or the overhanging lip may be discontinuous along the circumference of the head body.

Alternatively, the bottom body portion need not necessarily be hemispherical. Instead, it may be cylindrical or any shape that is able to fit within the cup implant whilst providing sufficient space for the internal components, such as the actuation mechanism. Additionally or alternatively, it may be feasible to accommodate the actuation mechanism entirely within the top body portion, whereby the bottom body portion does not or has limited protrusion into the cavity defined by the part-spherical inner surface of the cup implant.

The receiving head portion <NUM> comprises a head element <NUM> and a neck portion <NUM> which extends from the head element <NUM> to meet the main body <NUM> of the top body portion <NUM>. In this case, the receiving head portion <NUM> is unitarily formed as a one-piece with the main body <NUM>. However, the head element, neck portion and main body may be separate parts which are connected together. Although the receiving head portion <NUM> is, in this embodiment, circular or substantially circular in a plane perpendicular to the central axis <NUM>, it may be non-circular, such as being multi-faceted and/or polygonal.

As shown in <FIG> or <FIG>, the radial guiding channel <NUM> is an internal cavity or chamber primarily located in the top body portion <NUM>. The cavity or aperture is longitudinally elongate along at least a radial axis <NUM> or radial direction of the head body <NUM> and has a medial wall <NUM>, a lateral wall <NUM>, and a radial-floor wall <NUM> in this case provided by the bottom body portion <NUM>.

The lateral wall <NUM> is, in this case partially rounded, but it could be envisaged that the lateral wall may be fully planar. There is preferably a said radial guiding channel <NUM> adjacent to one or both opposing longitudinal sides of each implant-engagement arm <NUM>.

In this arrangement, each arm-recess <NUM> is open, whereby a slot is provided in the outer head surface <NUM> of the top body portion <NUM>. However, in an alternative embodiment, each implant-engagement arm may extend from the head body within a projecting sleeve or cover. The arm-recesses <NUM> in this case are equiangularly spaced apart. However, in some situations, it is envisaged that a Y-shaped configuration may be beneficial. In this arrangement, two or more said arm-recesses and their associated implant-engagement arms would be positioned closer together relative to one or more further arm-recesses and associated implant-engagement arms on a generally opposing side of the head body.

The axial guiding channel <NUM> is a cavity or aperture within the bottom body portion <NUM>, adjacent to an implant-engagement arm <NUM>. The axial guiding channel <NUM> is longitudinally elongate to provide a depth along an axis parallel to the central axis <NUM>. Although in this embodiment, a plurality of discrete or separate axial guiding channels <NUM> are associated with the implant-engagement arms <NUM>, it may be feasible to provide a single axial guiding channel formed as a continuous or semi-continuous ring or trough. Similarly, a single radial guiding channel formed as a continuous or semi-continuous ring or trough could be envisaged.

Preferably, the radial and axial guiding channels <NUM>, <NUM> are each longitudinally elongate along a respective axis, whereby the respective axes are perpendicular or substantially perpendicular to each other.

In an alternative arrangement, the axis of the axial guiding channel may be at a non-perpendicular angle relative to the axis of the radial guiding channel.

In a further alteration to the present embodiment, the axis of one of or both the axial and the radial guiding channels may be at least partly curved. Furthermore, the radial guiding channel may be partly curved and continuously transitions into the axial guiding channel without forming an edge.

The impactor head <NUM> has an actuation mechanism <NUM> which is, in this case, at least partly housed within the head body <NUM>. The actuation mechanism <NUM> includes an actuator body <NUM> and an axially-translatable actuator <NUM>.

The actuator body <NUM> is, in this arrangement, an elongate cylindrical core shaft <NUM> extending from the receiving head portion <NUM> towards the distal pole or distal head end <NUM> of the bottom body portion <NUM>, such that the elongate core shaft <NUM> is coaxial with the central axis <NUM>. Although preferably coaxial, it can be envisaged that the core shaft may be offset from the central axis.

The core shaft <NUM> is made of metal, plastics, or any combination thereof. The core shaft <NUM> may be a solid or tubular, and cylindrical or substantially cylindrical. The core shaft <NUM> has a top actuator surface <NUM>, and an outer radial core surface <NUM>. The core shaft <NUM> is threaded and preferably the thread is on the outer radial core surface <NUM>.

Alternatively, the core shaft may have at least one elongate groove, slit or through-hole, within which a portion of the axially-translatable actuator may be receivable. Alternatively, there may be an elongate protrusion receivable within the axially-translatable actuator. The slit or elongate protrusion may be elongate at least in part in an axial direction. The slit may be linearly elongate in the axial direction only, such that the axially-translatable actuator may move linearly axially away from or in the direction of the proximal head end without the core shaft being rotatable. Alternatively, the slit or groove may be helical around the core shaft, such that rotation of the core shaft causes the axially-translatable actuator to be made to move linearly axially.

In an alternative embodiment, the core shaft may have another mechanism for moving the axially-translatable actuator, such as magnets, cranks or a cable or hydraulic transmission system, and/or electrically actuated via a servo motor or solenoid.

In this case, the top actuator surface <NUM> has a tool-receivable recess <NUM>, shaped to receive a head of a rotation tool <NUM>.

The axially-translatable actuator <NUM>, which in this embodiment is fully located within the head body <NUM>, comprises a shaft-facing surface having a portion of a thread complementarily engageable with the thread of the core shaft <NUM>. In this way, the rotational motion of the core shaft <NUM> causes the axially-translatable actuator <NUM> to move linearly along the core shaft <NUM>, with the direction depending on the direction of rotation of the top actuator surface <NUM>.

The axially-translatable actuator <NUM> also includes an actuator recess <NUM>, as shown in <FIG> and <FIG>. There may be one single axially-translatable actuator <NUM> entirely or substantially entirely surrounding the core shaft <NUM>, having one actuator recess <NUM> for each implant-engagement arm <NUM> or a pair of adjacent implant-engagement arms <NUM>. Alternatively, there may be multiple axially-translatable actuators per head body, each axially-translatable actuator having one or multiple actuator recesses, for operating implant-engagement arms separately.

The actuator recess <NUM> is slightly elongate radially relative to the central axis <NUM> to receive a part of an implant-engagement arm <NUM>. In this way, during axial movement of the axially-translatable actuator <NUM>, the implant-engagement arm <NUM> is able to move linearly radially within the actuator recess <NUM>. In this case, the impactor head <NUM> has at least one, and preferably three, rotatable implant-engagement arms <NUM>. The or each implant-engagement arm <NUM> has an arm body <NUM> which is longitudinally elongate along a substantially radial axis <NUM> of the head body <NUM>. The or each implant-engagement arm <NUM> may be moveable within a plane comprising the central axis <NUM> or alternatively, the plane may be offset from the central axis.

The arm body <NUM> has a medial arm end <NUM>, a guiding protrusion <NUM> and a lateral arm end <NUM>. The arm body <NUM> is rigid and may be made of plastics, metal or a combination thereof.

The medial arm end <NUM> is, in this case, rounded and has a medial pivot axis <NUM> formed by a medial pivot element <NUM>, at or around which the medial arm end <NUM> is rotatable.

The medial pivot element <NUM> is translatable along an axis parallel to the central axis <NUM>. Additionally, the medial pivot element <NUM> is translatable within the actuator recess <NUM>, along an at least in part radial direction with respect to the central axis <NUM>. In this case, the medial pivot element <NUM> is unable to translate relative to the arm body <NUM>. Furthermore, the medial pivot element <NUM> is separate from the arm body <NUM>, but in an alternative embodiment, the medial pivot element could be integrally formed with the arm body, for example, as one or more stub axles extending laterally from the arm body.

In an alternative embodiment, the medial pivot element may not be able to move linearly radially within the actuator recess, regardless of whether the medial pivot is separate or integrally formed with the arm body or whether the medial pivot is able or unable to translate relative to the arm body.

The guiding protrusion <NUM> is located between the medial arm end <NUM> and the lateral arm end <NUM> of the arm body <NUM> as shown in <FIG> or <FIG>. The guiding protrusion <NUM> is preferably an integrally-formed rounded supporting portion, which extends at an angle to the longitudinal extent of the arm body <NUM>. The guiding protrusion <NUM> may also have a lateral extent to be received in the axial guiding channel <NUM>. The guiding protrusion <NUM> abuts a radially lateral axial wall <NUM> of the axial guiding channel <NUM> against which the guiding protrusion <NUM> or portion is able to slide or translate axially. As shown in <FIG> and <FIG>, the lateral arm end <NUM> has a lateral pivot axis <NUM> defined by a lateral pivot element <NUM>, around which the lateral arm end <NUM> is rotatable, along with a lateral hook portion <NUM>. The medial and lateral pivot elements <NUM>, <NUM> are preferably axles, but may be captive ball-bearings or rollers.

In this case, the lateral pivot element <NUM> does not translate relative to the arm body <NUM>. Furthermore, the lateral pivot element <NUM> is, in this case, separate from the arm body <NUM>, but the lateral pivot element could be integrally formed with the arm body. The lateral pivot element <NUM> does not move axially parallel to the central axis but is translatable in an at least in part radial direction. This radial translation is due to the lateral pivot element <NUM> being contained within the radial guiding channel <NUM>. The most lateral extent of the lateral pivot element <NUM> translating along the radial axis <NUM> is bounded by the lateral wall <NUM> of the radial guiding channel <NUM>. Additionally, the lateral pivot element <NUM> is preferably biased into a position abutting against the lateral wall <NUM> of the radial guiding channel <NUM> by a spring.

In an alternative arrangement, the lateral pivot element may translate at least partially in an axial direction, parallel to the central axis. This may be possible if, for example, the radial guiding channel were to be partly curved and/or were to continuously transition into the axial guiding channel, without forming an edge. In a further alternative arrangement, the lateral pivot element may coincide with the guiding protrusion.

The spring has a first spring end and a second spring end. The first spring end is attached to the head body <NUM> whilst the second spring end is connected at or adjacent to the lateral pivot element <NUM>. Preferably, in this case, the first spring end is attached to the medial wall <NUM>, in which case the spring is a compression spring, for biasing the lateral pivot element <NUM> away from the central axis <NUM> in a radial direction.

In an alternative embodiment, the spring could be an extension spring having the first spring end attached to the lateral wall. In a further alternative to the current embodiment, a magnet may be contained within or placed upon the lateral pivot element and the complementary magnet of opposite polarity may be on or adjacent to the lateral wall. Alternatively or additionally, a magnet of polarity identical to that of the lateral pivot element may be placed in or on the medial wall of the radial guiding channel. Furthermore, in addition to the above arrangements, the medial pivot element may be biased into a certain position by a spring and/or a magnet.

In this case, the lateral hook portion <NUM> is integrally-formed with the arm body <NUM> and is preferably made of a biocompatible material, such as plastics or metal although other materials may be possible. The lateral hook portion <NUM> is finger-like to protrude in depending fashion from the top body portion <NUM>. The lateral hook portion <NUM> has an outwards-facing surface <NUM> and an implant outer-surface engagement element <NUM> or cup-facing surface which contacts the outer surface <NUM> of a cup implant <NUM>. The outwards-facing surface <NUM> in this case is curved, although it could alternatively be linear in cross-section.

Whilst in this case the lateral hook portion <NUM> is integrally formed with the arm body <NUM>, in an alternative arrangement, the lateral hook portion may be hingeably connected to the arm and/or may be fully separable. The lateral hook portion may alternatively be at least partially retractable within the arm body, whether the lateral hook portion is linear or curved in cross-section.

The implant outer-surface engagement element <NUM> is preferably complementarily shaped to a prosthetic cup outer surface <NUM> and may be partly curved. To aid with gripping, the implant outer-surface engagement element may be coated with a gripping layer such as rubber or another suitable material. This may also reduce a risk of damage to the outer surface of a cup implant.

During translation and rotation into or out of the implant-engagement condition, the implant outer-surface engagement element <NUM> moves through a series of positions which describe a movement path <NUM>, also referred to as an implant-engagement path, a release path or a virtual locus.

The movement of the lateral hook portion <NUM>, starting with being out of the implant-engagement condition or in the implant-release condition and finishing upon being in the implant-engagement condition is referred to as the `gripping phase' or `cup-gripping phase'. The opposite movement, starting with being in the implant-engagement condition and finishing with being in the implant-release condition is the `release phase.

In this case, the axial cross-sectional geometry of the movement path <NUM> is an approximate arc of an ellipse or a circle around the rim <NUM> of a cup implant <NUM>, the circle being centred around a, preferably dynamically-movable, virtual pivot point <NUM> as shown in <FIG> and <FIG>. The ellipse or circle may be changing in dimensions or be of fixed dimensions. In this case, both of these features may occur at different parts or sub-phases of the gripping and release phases.

The virtual pivot point <NUM> is, in this case, separate and spaced below the lateral pivot element <NUM> in an axially proximal-to-distal direction of the impactor head <NUM> throughout at least part of the cup-release phase and at least a first part of the cup-gripping phase. In a second part of the cup-gripping phase, the virtual pivot point <NUM> may travel to coincide with the lateral pivot element <NUM>. In use and with reference to <FIG>, to grasp an acetabular cup implant <NUM> with the impactor head <NUM>, the user first inserts the bottom body portion <NUM> of the head body <NUM> into the cup implant <NUM>, as shown in <FIG>, such that the overhanging lip <NUM> abuts the rim <NUM> of the cup implant <NUM>. The rotation tool <NUM>, shown in <FIG>, is engaged with the actuator recess <NUM> and operated to actuate the actuation mechanism <NUM>. Rotary motion in one direction of the rotation tool <NUM>, indicated as Arrow A, is imparted to the top actuator surface <NUM> integrally formed with the actuator body <NUM>. The rotation may be clockwise or anti-clockwise depending on the orientation of the thread on the core shaft <NUM>. Rotation of the actuator body <NUM> causes the axially-translatable actuator <NUM> to translate linearly along the central axis <NUM> in a direction of the proximal head end <NUM> of the impactor head <NUM>.

The translation of the axially-translatable actuator <NUM> towards the proximal head end <NUM> causes the medial pivot element <NUM> to translate axially along the central axis <NUM>, also in the direction of the proximal head end <NUM>. The medial arm end <NUM> of the implant-engagement arm <NUM> pivots around the medial pivot element <NUM> and the lateral arm end <NUM> pivots around the lateral pivot element <NUM>.

During a first part of the gripping phase, the radially translatable lateral pivot element <NUM> is biased away from the central axis <NUM> by the or multiple springs. The lateral translation in a radial direction may be, in this case, at least partly counteracted by the guiding protrusion <NUM> abutting the axial guiding channel <NUM>, as shown in <FIG>. In this case, the guiding protrusion <NUM> is axially-translatable whilst abutting the axial guiding channel <NUM>. However, in an alternative arrangement, the guiding protrusion may be fixed and unable to translate axially.

In a further modification to the present embodiment, the guiding protrusion may be able to translate along a radial direction in addition to or instead of an axial direction.

In this case, during a second part of the gripping phase, the lateral pivot element <NUM> abuts the lateral wall <NUM> of the radial guiding channel <NUM>, biased into position by the or multiple springs. Thus, during the second part of the gripping phase, the lateral pivot element <NUM> does not translate radially outwards.

When the pivoting implant-engagement arm <NUM> is moved from an implant-release condition into the implant-engagement condition by being rotated about both the medial and the lateral pivot elements <NUM>, <NUM> and, during the first part of the gripping phase, translated laterally along a radial axis <NUM>, the lateral hook portion <NUM> is moved out of the head body <NUM>, along the movement path <NUM> around the cup rim <NUM>. The movement path <NUM> is arcuate about the virtual pivot point <NUM>. In this case, during the first part of the gripping phase, the virtual pivot point <NUM> is inwards of the outer surface <NUM>, and below the rim <NUM> of the cup implant <NUM>. During the second part of the gripping phase, the virtual pivot point <NUM> coincides with the lateral pivot element <NUM>. As such, the virtual pivot point <NUM> is above the rim <NUM> of the cup implant <NUM>. In an alternative embodiment, at any time of the gripping phase or during the release phase the virtual pivot point may be above the rim and/or outwards of the cup and/or may be partly translatable or fixed. The virtual pivot point may coincide with the guiding protrusion or may be spaced-apart from the guiding protrusion.

The virtual pivot point <NUM> being dynamically-movable or dynamically-varying is due to having a plurality of pivot axes on a single body, the arm body <NUM>. Due to the interactions of the translating medial and lateral pivot elements <NUM>, <NUM>, and the guiding protrusion <NUM> during the first part of the gripping phase, the movement path <NUM> can be described as approximately elliptical and/or an arc around a circle decreasing in diameter. The virtual pivot point <NUM> in this case may be considered to be translating radially outwards.

During the second part of the gripping phase, the movement path <NUM> is rotated about the virtual pivot point <NUM> which now coincides with the lateral pivot element <NUM>. As such, the movement path <NUM> is an arc of a circle of unchanging diameter. The movement path <NUM> may transition smoothly between the two parts of the gripping phase, without forming an edge. This is the case if the longitudinal extent of arm body <NUM> is parallel or substantially parallel to a radius of the head body <NUM> at the transition between the first and second parts of the gripping phase.

In an alternative embodiment, the movement path at the transition between the first and second parts of the gripping phase may form an edge. This might be the case if the lateral hook portion is hinged or if the arm body is not aligned solely along a radial direction at the transition between the first and second parts of the gripping phase.

The implant outer-surface engagement element <NUM> engages with the outer surface <NUM> of the cup implant <NUM>, thus enabling the impactor head <NUM> to grasp the cup implant <NUM> as shown in <FIG>. The gripping force of the impactor head <NUM> can be increased by rotating the rotation tool <NUM> further. The head of the rotation tool <NUM> is then disengaged from the impactor head <NUM>.

A surgical introducing kit or surgical introducing tool kit <NUM> comprising the impactor head <NUM> and a surgical introducer <NUM> is used to insert the prosthetic cup implant <NUM> into the hip <NUM>. The surgical introducer <NUM> has an elongate impactor shaft <NUM> having a first end <NUM> shaped to be a graspable portion and a second end <NUM> having an attachment element <NUM>. The attachment element <NUM> is preferably a releasably engageable clamp which is remotely operably by an operable lever <NUM>. The releasably engageable clamp needs to be in the open position and arranged to receive the receiving head portion <NUM>.

The user than manipulates an operable lever <NUM>, causing the clamping attachment element <NUM> to close around the receiving head portion <NUM> of the impactor head <NUM>. The impactor head <NUM> holding the cup implant <NUM> is then inserted into a pre-drilled hole in the hip <NUM> as shown in <FIG> using the surgical introducer <NUM>. The impactor shaft <NUM> may be used to verify the alignment of the impactor head <NUM>, and thereby the cup implant <NUM> within the hip <NUM>. Once the orientation of the cup implant <NUM> is correct, the operable lever <NUM> is operated to release the impactor head <NUM>.

With the surgical introducer <NUM> removed, to disengage the impactor head <NUM> from the cup implant <NUM>, the head of the rotation tool <NUM> is reengaged with the tool-receivable recess <NUM> of the top actuator surface <NUM>. Rotary motion in the opposite direction to that of the gripping phase, indicated as Arrow B, is imparted to the top actuator surface <NUM>, whilst the impactor head <NUM> is gripped by an anti-rotation tool. This motion causes the actuator body <NUM> to rotate in the opposite direction. Therefore, the axially-translatable actuator <NUM> and thus the medial pivot element <NUM> are made to translate linearly along the central axis <NUM> by the rotating actuator body <NUM> and towards the distal head end <NUM> of the impactor head <NUM>.

When the rotatably translatable implant-engagement arm <NUM> is moved out of the implant-engagement condition by being rotated about at least the lateral pivot element <NUM> and preferably both the medial and lateral pivot elements <NUM>, <NUM> and translated inwards along a radial direction, the lateral hook portion <NUM> is moved along the arcuate release path <NUM> and retracted into the head body <NUM> about the virtual pivot point <NUM>. Upon travelling the arcuate release path <NUM>, the lateral hook portion <NUM> does not move laterally beyond the movement path <NUM> followed during the gripping phase, resulting in a reduction of the bone removed or damaged.

Preferably, as the release phase is a mirror image of the gripping phase, the same movement path <NUM> is followed during the gripping and the release phases, in reverse order. As such, during the first part of the release phase when the virtual pivot point <NUM> and the lateral pivot element <NUM> coincide, the lateral hook portion <NUM> may move marginally laterally but in any event disengages by rotating around the lateral pivot element <NUM>. During the second part of the release phase, the implant-engagement arm <NUM> additionally translates radially medially towards the central axis <NUM>, resulting in the virtual pivot point <NUM> being spaced-apart from the lateral pivot element <NUM>. Due to this inward translation, the lateral hook portion <NUM> does not travel laterally beyond its maximal lateral extent from the central axis <NUM> which occurs at the transition between the two parts of the release phase or the gripping phase.

The head of the rotation tool <NUM> is then disengaged from the impactor head <NUM> and the impactor head <NUM> is removed from the cup implant <NUM>, indicated as Arrow C in <FIG>. The impactor head <NUM> may be removed using an anti-rotation tool, a lifting tool or the surgical introducer <NUM>.

In a modification to the above-described impactor head, the implant-engagement arm has at least one internal slot or channel in the arm body. The or each internal channel may be elongate along the same extent as the arm body. The or each internal channel is suitable for one of or a plurality of pivot elements to translate within the internal channel such that the or both pivot elements are translatable relative to the arm body. The pivot element or elements may be fixed relative to the head body or alternatively, may be translatable relative to both the head body and the arm body.

Now referring to <FIG>, there is shown a second embodiment of an impactor head <NUM>, not in accordance with the invention, for releasably holding an outer surface <NUM> of a cup implant <NUM>. Features which are similar or identical to those of the first embodiment may use similar or identical references to those of the first embodiment, typically starting above '<NUM>'.

The head body <NUM> of the second embodiment is similar to the head body <NUM> of the first embodiment, having a top body portion <NUM>, a bottom body portion <NUM>, a radial guiding channel <NUM> and an actuation mechanism. Detailed description of the common features has been omitted for brevity. In this case, the head body <NUM> has a diagonal guiding channel <NUM> in addition to or instead of the axial guiding channel <NUM> of the first embodiment. The longitudinal extent of the diagonal guiding channel <NUM> is angled towards the distal pole or distal head end and is at an angle relative to the central axis.

The implant-engagement arm <NUM> of the second embodiment is similar to the implant-engagement arm <NUM> of the first embodiment, having a medial arm end <NUM>, a lateral arm end <NUM>, a lateral hook portion <NUM> and a guiding protrusion <NUM>. Detailed description of common features is therefore again omitted for brevity.

In this case, the implant-engagement arm <NUM> is not rotatable. The arm in this embodiment is solely translatable simultaneously along a radial axis <NUM> and along an axial direction, such that the resulting direction of motion is a diagonal axis <NUM>, along the axis defined by the diagonal guiding channel <NUM>.

The implant-engagement arm <NUM> may still be biased away from the central axis, by a spring and/or another means such as a magnet. In this way, the guiding protrusion <NUM> is biased to run on the radially outer surface <NUM> of the diagonal guiding channel <NUM>, similarly to the first embodiment. The lateral hook portion <NUM>, in this case, has an outwards-facing surface <NUM> and cup-facing surface or an implant outer-surface engagement element <NUM> which opposes the outwards-facing surface <NUM>. The outwards-facing surface <NUM> and the implant-outer surface engagement element <NUM> are arranged to taper towards each other in a direction of the distal head end.

An axial cross-sectional geometry of the movement path or virtual locus of the implant outer-surface engagement element <NUM> is linear. There is no virtual pivot point in this embodiment.

The uses of the second embodiment are similar to those of the first embodiment, using the surgical introducing kit and detailed description of the common features is here omitted for brevity.

Using the impactor head <NUM> of the second embodiment, during the gripping phase, the axially-translatable actuator causes the implant-engagement arm <NUM> to translate axially in the direction of the distal head end, instead of towards the proximal head end, along the core shaft. The diagonal guiding channel <NUM> forces the implant-engagement arm <NUM> to translate inwards along a radial direction, whilst the spring biases the implant-engagement arm <NUM> to move outwards, laterally along the radial direction relative to the central axis such that the guiding protrusion <NUM> abuts the radially outer surface <NUM>. The path or virtual locus is a straight line, angled towards the distal pole, parallel with the longitudinal axis of the diagonal guiding channel <NUM>. Thus, the head body <NUM> has a distal head end and the implant outer-surface engagement element <NUM> is moveable on a linear implant-engagement path angled towards the said distal head end of the head body <NUM> when moving towards the implant-engagement condition.

The implantation procedure of the cup implant <NUM> is similar to the procedure described in the first embodiment. During the release phase, the axially-translatable actuator is operated to translate along the core shaft in direction of the proximal head end, with the spring biasing the implant-engagement arm <NUM> laterally.

It is therefore possible to provide an impactor head for releasably holding an outer surface of a cup implant which, by having a gripping arm that both rotates along with translating inwardly and outwardly, minimises an amount of bone resection required to release the cup following insertion into a patient's acetabulum. Furthermore, it is also possible to provide an impactor head, not in accordance with the present invention, for releasably holding an outer surface of a cup implant, by having at least one non-rotatable implant-engagement arm which is translatable in both radial and axial directions. Such an impactor head also reduces the amount of bone resection required to release the cup implant. Additionally it is also possible to provide a surgical introducing kit and a method using either one of the said impactor heads for introducing the cup implant into an acetabulum during surgery whilst minimising the amount of bone resection needed during the cup implant release.

Claim 1:
An impactor head (<NUM>) for releasably holding an outer surface (<NUM>) of a cup implant (<NUM>), the impactor head (<NUM>) comprising a head body (<NUM>); at least one rotatable implant-engagement arm (<NUM>) being at least in part translatable; an actuation mechanism (<NUM>) which moves the implant-engagement arm (<NUM>) to an implant-engagement condition or an implant-release condition; and an implant outer-surface engagement element (<NUM>) which is at or adjacent to a lateral arm end (<NUM>) of said implant-engagement arm (<NUM>), said implant-engagement arm (<NUM>) includes a lateral pivot axis (<NUM>) about which the implant-engagement arm (<NUM>) is rotatable to adopt said implant-engagement condition or said implant-release condition, characterised in that the lateral pivot axis (<NUM>) is radially translatable to linearly move the implant-engagement arm (<NUM>) radially as it rotates.