Patent Description:
The present invention also concerns a milling tool equipped with the milling head as above.

In general, milling tools are known that can be used during prosthetic surgery operations and are conformed to make coordinated and mating bone seatings suitable for the disposition and implantation of corresponding components of surgical prostheses.

In particular, milling tools are known that can be used to make the hemispherical seatings, or in any case seatings with a spherical cap, suitable for the installation of coordinated acetabular cups of the hip prostheses.

These known milling tools generally provide an internally hollow milling head, with sizes correlated to the bone seating to be made and on which a plurality of through apertures are made, provided with cutting and protruding edges, to perform a mechanical excavation action on the bone.

In this way, rotating about an axis of rotation, or of milling, and performing a mechanical removal action of the bone material, this type of milling tools creates an impression on the bone of desired size and conformation, substantially corresponding to the shape of the milling head.

It is known that the milling tools as above are operatively associated with manipulator devices, which can be both of the manual and also of the automatic type.

In particular, the manipulator devices can be associated with an attachment part stably fixed to the base of the milling head as above, with an anchoring function for the manipulator device and for the transmission of the torque.

Documents <CIT> and <CIT> describe examples of surgical milling instruments provided with a milling cap and an attachment part distinct and separate from the milling cap and with which the handpiece is coupled. The milling cap is provided with seatings for coupling the attachment part. However, the solutions proposed have obvious disadvantages connected to the complexity of the attachment, which can be complicated and not very intuitive. In fact, in <CIT> each seating has an entry portion, parallel to the axis of rotation of the milling cap, and an end-of-travel portion able to receive, during use, a respective element for holding the attachment part. The entry portion has a size substantially equal to the corresponding size of the holding element so that it is very difficult and not convenient to insert. In document <CIT> the holding elements are inserted into the seatings from the inside of the milling cap toward the outside, where they are locked in position by additional holding means. This solution is very complicated and bulky, reducing the useful milling surface due to the presence of the holding means.

Additional documents, for example <CIT> and <CIT>, disclose other solutions for surgical milling instruments.

It is also known that these milling tools must be subjected to washing and sterilization operations after each intervention, including by using washing and sterilization machines designed for this purpose.

Said washing and sterilization operations naturally entail an increase in overall costs resulting from the use of such known instruments or tools.

Documents <CIT>, <CIT> and <CIT> describe milling instruments for orthopedic surgery, in particular for prosthetic surgery, of a known type.

Other limitations and disadvantages of conventional solutions and technologies will be clear to a person of skill after reading the remaining part of the present description with reference to the drawings and the description of the embodiments that follow, although it is clear that the description of the state of the art connected to the present description must not be considered an admission that what is described here is already known from the state of the prior art.

There is therefore a need to perfect a milling tool for prosthetic surgery operations which can overcome at least one of the disadvantages of the state of the art.

One purpose of the present invention is therefore to provide a milling tool for prosthetic surgery operations which allows to drastically reduce the risk of contamination by external agents, such as viruses, bacteria or suchlike, thus allowing to reduce the risks of contamination for a patient.

It is also a purpose of the present invention to provide a milling tool which allows to limit further washing and sterilization operations, to be carried out possibly only on determinate zones or parts of the milling tool, thereby optimizing the washing and sterilization operations, and possibly even eliminating them at least for the operative cutting parts of the milling tool.

Another purpose of the present invention is to provide a milling tool for prosthetic surgery operations which is simple and compact in shape, thus allowing production and supply at lower costs compared to what occurs with known milling tools.

Another purpose of the invention is to provide a milling tool which is simple, effective and which allows to perform the milling operations for which it is intended in an optimal and precise manner.

The dependent claims describe other characteristics of the invention or variants to the main inventive idea.

In accordance with some embodiments, a milling head for a milling tool for prosthetic surgery operations is made of metal and has a base perimeter edge.

The milling head is provided with an external cutting part which has a milling surface from which a plurality of protruding cutting elements project, and a coupling part defined along the base perimeter edge as above and provided with a plurality of recessed coupling seatings, circumferentially present along the base perimeter edge.

Each recessed coupling seating comprises one lead-in portion that is inclined, at least in a first part thereof, with respect to an operative axis of symmetry for the milling head, and one end-of-travel portion.

In accordance with some embodiments, a milling tool is provided comprising the milling head as above and an attachment part connected in a selectively releasable manner to the milling head in correspondence with the coupling part of the milling head.

The coupling part has a discoidal shape and comprises a peripheral band with a continuous annular shape provided with a plurality of holding elements projecting from the peripheral band in a radial direction toward the outside.

The recessed coupling seating is configured to determine a releasable bayonet-type connection between the milling head and the attachment part.

Each recessed coupling seating is provided with one lead-in portion that is inclined, at least in a first part thereof, with respect to the operative axis as above and which allows access to any one of the holding elements whatsoever, and with an end-of-travel portion configured to receive a respective holding element constraining, to each other and in a releasable manner, the milling head and the attachment part at least in the axial direction.

We will now refer in detail to the possible embodiments of the invention, of which one or more examples are shown in the attached drawings. Each example is supplied by way of illustration of the invention and shall not be understood as a limitation thereof. For example, one or more characteristics shown or described insomuch as they are part of one embodiment can be varied or adopted on, or in association with, other embodiments to produce other embodiments. It is understood that the present invention shall include all such modifications and variants.

Embodiments described using the attached drawings concern a milling head <NUM> for a milling tool <NUM> for prosthetic surgery operations, in particular to make concave seatings for the implantation of prostheses, for example of the shoulder or hip, and also concern the milling tool <NUM> provided with the milling head <NUM>.

In accordance with the invention, the milling head <NUM> is made of metal and has a base perimeter edge <NUM>.

The milling head can have the shape of a cap, in particular hemispherical, or other suitable shapes, advantageously axisymmetric, such as for example a cylindrical shape, or other shapes suitable to make concave seatings for the implantation of a prosthesis.

The milling head <NUM> is provided with an external cutting part <NUM> which has a milling surface 12a from which a plurality of protruding cutting elements <NUM> project.

The milling head <NUM> is also provided with a coupling part <NUM> defined along the base perimeter edge <NUM> and provided with a plurality of recessed coupling seatings <NUM> circumferentially present along the base perimeter edge <NUM>.

In accordance with the invention, the recessed coupling seatings <NUM> are disposed angularly distanced with a regular pitch on the coupling part <NUM>.

In accordance with possible embodiments, the milling head <NUM> can comprise three recessed coupling seatings <NUM> disposed at <NUM>° from each other.

In accordance with some embodiments, the milling head <NUM> can comprise four recessed coupling seatings <NUM> disposed at <NUM>° from each other.

In accordance with some embodiments, the recessed coupling seatings <NUM> are open in a direction orthogonal to an operative axis A of symmetry for the milling head <NUM>, that is, they are through, orthogonally, toward the inside of the milling head <NUM>.

In accordance with the invention, each of the recessed coupling seatings <NUM> comprises a lead-in portion <NUM> and an end-of-travel portion <NUM>, disposed circumferentially downstream with respect to the respective lead-in portion <NUM>.

The lead-in portion <NUM> is open in a direction parallel to the operative axis A, and the end-of-travel portion <NUM> is open in a circumferential direction only toward the respective lead-in portion <NUM>.

The recessed coupling seating <NUM> is configured to determine a releasable bayonet-type connection, in which the lead-in portion <NUM> allows access for a holding element and the end-of-travel portion <NUM> is configured to receive the holding element determining a constraint thereof at least in the direction of the operative axis A, as will be better described below with reference to the milling tool <NUM>.

In accordance with some embodiments, the base perimeter edge <NUM> defines an end aperture <NUM> having a circular shape and having a circumferential extension greater than the circumferential extension of each of the recessed coupling seatings <NUM>.

In accordance with some embodiments, the milling head can be disposable, or it can be reused after appropriate sterilization.

In accordance with some embodiments, the cutting elements <NUM> of the external cutting part <NUM>, preferably, can be distributed uniformly on the milling surface 12a, and through apertures are made in correspondence therewith for the discharge of the material removed.

The cutting elements <NUM> can have various shapes and have the function of cutting or milling the bone component, while the through apertures allow the bone residues to be removed from the cutting or milling zone.

According to a possible solution, the cutting elements <NUM> defined above are made in the thickness of the milling head <NUM> and are each provided with at least one cutting edge to allow the removal of the material.

In accordance with possible embodiments, at least the cutting part <NUM> is made of titanium.

Advantageously, the milling head <NUM> can be entirely made of titanium since it is hypoallergenic and biocompatible.

In accordance with some embodiments, the milling tool <NUM> comprises a milling head <NUM>.

The milling tool <NUM> also comprises an attachment part <NUM> connected in a selectively releasable manner to the milling head <NUM> in correspondence with the coupling part <NUM>.

The milling tool <NUM> comprises an attachment head <NUM> provided with clamping means <NUM> which can be selectively activated for a stable and releasable connection to the attachment part <NUM>, said attachment head <NUM> being able to be connected to a manipulator device <NUM>.

The attachment part <NUM> is provided with a central connection seating <NUM> having a polygonal shape to allow a selectively releasable connection with the attachment head <NUM>.

In accordance with some embodiments, the attachment part <NUM> has a discoidal shape and comprises a peripheral band <NUM> with a continuous annular shape provided with a plurality of holding elements <NUM> configured to engage, each one, a respective one of said recessed coupling seatings <NUM> of the coupling part <NUM> of the milling head <NUM>.

In accordance with some embodiments, the base perimeter edge <NUM> defines the end aperture <NUM> having a circular shape in which the attachment part <NUM> is connected in a removable manner.

In accordance with some embodiments, the milling head <NUM> and the attachment part <NUM> are made in a separate body and are selectively connected to each other in a removable manner immediately before the surgical operation, for example during the preparation of the milling tool <NUM>.

The attachment part <NUM> can be disposable or it can be reused after appropriate sterilization.

If it is reusable, the attachment part <NUM> is therefore, to all effects, a component of the surgical instruments.

The possibility of separating the milling head <NUM> from the attachment part <NUM> allows to significantly simplify the sterilization operations of the milling tool <NUM>.

In particular, the internal zone defined by the milling head <NUM> and by the attachment part <NUM> is the zone where the organic waste generated by the milling operation mostly collects. The possibility of having complete access to the internal zone as above by removing the attachment part <NUM> simplifies the sterilization operations and reduces the time required for them.

Furthermore, the absence of fixing means such as screws, pins, bolts or other, limits the number of components considerably simplifying and speeding up the assembly and disassembly operations of the attachment part <NUM> onto/from the milling head <NUM>.

The attachment part <NUM>, at least in an operative condition, is aligned with the milling head <NUM> along the operative axis A, which in this case is through both through the center of the connection seating <NUM> and also through the center of the milling head <NUM>, orthogonally to the aperture <NUM>.

The operative axis A is therefore an axis of symmetry for the milling head <NUM> and for the attachment part <NUM>.

The attachment part <NUM> has a transverse size, that is, orthogonal to the operative axis A, slightly smaller than the size of the aperture <NUM>. In this way, the attachment part <NUM> can be inserted into the aperture <NUM>.

In particular, the peripheral band <NUM> of the attachment part <NUM> has an external diameter substantially equal to, or slightly smaller than, the internal diameter of the aperture <NUM>. In this way, the peripheral band <NUM> can substantially come into sliding contact with the internal surface of the coupling part <NUM>.

The peripheral band <NUM> of the attachment part <NUM> can be positioned in part of the cavity defined by the milling head <NUM>, that is, it can be at least partly recessed in it. This positioning of the attachment part <NUM> allows to obtain an increase in the containing rigidity of the milling head <NUM>, preventing its collapse in correspondence with the coupling part <NUM>, made particularly lighter by the presence of the recessed coupling seatings <NUM>.

In accordance with some embodiments, the holding elements <NUM> can be projecting from the peripheral band <NUM> in a radial direction toward the outside, that is, in the opposite direction with respect to the connection seating <NUM> disposed in a central position.

The holding elements <NUM> can be disposed angularly distanced with a regular pitch on the peripheral band <NUM>, so as to correspond, at least in the operative condition, to the recessed coupling seatings <NUM>.

The number of holding elements <NUM> is correlated to the number of recessed coupling seatings <NUM>.

In accordance with some embodiments, the shape of the recessed coupling seating <NUM> is mating with the shape of the holding element <NUM>. For example, the holding elements <NUM> can have the shape of a parallelepiped, a cylinder or portions thereof, and the corresponding recessed coupling seatings <NUM> can have a rectangular, semicircular, or other suitable mating shape.

Evidently, it is advantageous for the coupling between the holding element <NUM> and the respective recessed coupling seating <NUM> to be rather precise, so as to avoid unwanted vibrations and guarantee an optimal transfer of the torque.

In accordance with some embodiments, the attachment part <NUM> also comprises spokes, or arms, <NUM> substantially equally distanced angularly and converging in a central hub <NUM> where the central connection seating <NUM> is present.

According to some embodiments, shown in <FIG> and <FIG>, the attachment part <NUM> can comprise three spokes <NUM> equally distanced angularly by about <NUM>°.

In possible further embodiments, the attachment part <NUM> can be formed by a bar, or crosspiece, provided with the central connection seating <NUM> and defining only two diametrically opposite spokes, or arms, <NUM>.

In accordance with the invention, each recessed coupling seating <NUM> comprises the lead-in portion <NUM> configured to allow the sliding of a respective holding element <NUM>, and the end-of-travel portion <NUM> configured to clamp the holding element <NUM> into position.

The end-of-travel portion <NUM> is disposed circumferentially downstream with respect to the lead-in portion <NUM>. The terms "downstream" and "upstream" define a spatial circumferential reference with respect to a rotation of the milling head in a clockwise direction.

The lead-in portion <NUM> is positioned before the end-of-travel portion <NUM> of a respective recessed coupling seating <NUM>, which constitutes a natural extension thereof.

With particular reference to <FIG> and according to the invention, the lead-in portion <NUM> is inclined with respect to the operative axis A, at least in a first part thereof.

The lead-in portion <NUM> has a first part 27a inclined with respect to a plane perpendicular with respect to the operative axis A and defined by the base perimeter edge <NUM> by an angle of inclination α between about <NUM>° and about <NUM>°, preferably between <NUM>° and <NUM>°. In a possible example, the angle of inclination α is approximately <NUM>°.

The lead-in portion <NUM> has a second part 27b which constitutes the continuation of the first part 27a. The second part 27b is substantially orthogonal to the operative axis A and ends in the end-of-travel portion <NUM>.

The first part 27a of the lead-in portion <NUM> configures a kind of slide that leads toward the end-of-travel portion <NUM>.

Such a configuration of the lead-in portion 27a allows the holding element <NUM> to enter into the end-of-travel portion <NUM> along a curved trajectory that facilitates its insertion.

The lead-in portion <NUM> is open in a direction parallel to the operative axis A so that when the attachment part <NUM> is associated with the milling head <NUM>, the attachment part <NUM> can rest on the lead-in portion <NUM>.

In particular, when the attachment part <NUM> enters the aperture <NUM>, the holding elements <NUM> rest on the lead-in portion <NUM>. In the event there is no suitable initial alignment, it is sufficient to slightly rotate the attachment part <NUM> in a clockwise direction with respect to the milling head <NUM> so that the holding elements <NUM> engage respective recessed coupling seatings <NUM> in correspondence with respective lead-in portions <NUM>.

The lead-in portion <NUM> has a linear extension in the circumferential direction much greater than a circumferential length L of the holding element <NUM>, <FIG>.

The circumferential length of the lead-in portion <NUM> is between about <NUM> times and about <NUM> times the circumferential length L of the holding element <NUM>, preferably between about <NUM> and about <NUM> times.

This ratio allows, during the step of inserting the attachment part <NUM>, to facilitate the engagement of the holding elements <NUM> in the end-of-travel portions <NUM>. In fact, it is not necessary to carry out an extremely precise first entry as occurs for traditional solutions, but it is sufficient to slide the attachment part <NUM> in a clockwise direction with respect to the coupling part <NUM>.

The end-of-travel portion <NUM> is defined by a recess made directly in the coupling part <NUM>.

The end-of-travel portion <NUM> is open in the direction of the lead-in portion <NUM> so as to allow the entry of a respective holding element <NUM> of the attachment part <NUM>.

In accordance with some embodiments, the recessed coupling seating <NUM> is configured to determine a releasable bayonet-type connection between the milling head <NUM> and the attachment part <NUM>, in which each lead-in portion <NUM> allows access to any one of said holding elements <NUM> and the end-of-travel portions <NUM> are configured to receive respective ones of said holding elements <NUM> constraining, to each other and in a releasable manner, the milling head <NUM> and the attachment part <NUM> at least in the axial direction, that is, the direction of the operative axis A.

The end-of-travel portion <NUM> is closed in the direction opposite the lead-in portion <NUM> allowing to clamp in position the attachment part <NUM>, at least in the direction of the operative axis A and with respect to a rotation in a clockwise direction with respect to the operative axis A.

In this way, the attachment part <NUM> is, at least temporarily, integral with the milling head <NUM>.

Another clockwise rotation of the attachment part <NUM> causes the complete rotation of the milling head <NUM>.

In particular, during use, the milling head <NUM> is made to rotate by means of the attachment head <NUM> in a clockwise direction and the end-of-travel portion <NUM>, as well as allowing the transmission of the torque, also acts as a safety system preventing the milling head <NUM> from being decoupled from the attachment part <NUM>.

At the end of the milling operation, it is possible to decouple the milling head <NUM> from the attachment part <NUM> by simply rotating the attachment part <NUM> in an anti-clockwise direction, since no other constraints are present.

This uncoupling mode is particularly simple. In fact, thanks to the inclination of the lead-in portion <NUM>, it is sufficient to rotate the attachment part <NUM> in an anti-clockwise direction. The rotation imparted determines a single combined movement with which the attachment part <NUM> is both disengaged from the coupling seatings <NUM> and also extracted from the milling head <NUM> in a direction parallel to the operative axis A.

In accordance with some embodiments, the end-of-travel portion <NUM> has a shape mating with the shape of the holding element <NUM>.

In particular, the sizes of the end-of-travel portion <NUM> are slightly larger, but not much larger, than the holding element <NUM>, so as to define a clearance sufficiently narrow to allow the circumferential coupling with the holding element <NUM>, preventing vibrations during use.

The holding elements <NUM> have a radial thickness S1 correlated to a radial thickness S2 of the milling head <NUM>.

In particular, the radial thickness S1 of the holding elements <NUM> is equal to the radial thickness S2 of the milling head <NUM>.

In this way, the connection between the attachment part <NUM> and the milling head <NUM> is stable and secure. Furthermore, the holding elements <NUM> are not radially protruding from the recessed coupling seatings <NUM>, but remain advantageously confined therein.

In possible implementations, the milling head <NUM> has a radial thickness S2 comprised between <NUM> and <NUM>.

In other possible implementations, the holding elements <NUM> have a radial thickness S <NUM> comprised between <NUM> and <NUM>.

In accordance with some embodiments, by aligning the attachment part <NUM> with the milling head <NUM> with respect to the operative axis A and resting it on the latter in correspondence with the coupling part <NUM>, it is sufficient to rotate the attachment part <NUM> about the operative axis A in a clockwise direction until the holding elements <NUM> engage respective recessed coupling seatings <NUM>. Each holding element <NUM> rests on the lead-in portion <NUM> of the respective recessed coupling seating <NUM> sliding along it, until it ends its travel in the end-of-travel portion <NUM>. The inclination of the lead-in portion <NUM> is therefore particularly effective for guaranteeing a correct insertion of the holding elements <NUM> in the respective recessed coupling seatings <NUM>, with a combined movement that simultaneously has an axial component, along the operative axis A, and a circumferential component. Obviously, the entity of the axial component depends on the angle α, as defined above.

Since the lead-in portion <NUM> is inclined with respect to the operative axis A at least in a first part thereof, the rotation of the attachment part <NUM>, while it slides on the lead-in portion <NUM>, determines a translation thereof in the direction of the operative axis A and an insertion thereof in the aperture <NUM> in a gradual manner.

According to some embodiments, the attachment part <NUM> can be at least partly made of titanium.

Advantageously, the milling tool <NUM> can be entirely made of titanium.

Titanium is particularly advantageous since it is hypoallergenic and biocompatible.

Alternatively, one, several or all of the components as above can be made of steel. For example, the central hub <NUM> of the attachment part <NUM> where the central connection seating <NUM> is present can be made of steel, so as to allow a possible fixing, of the magnetic type, to respective clamping means <NUM>.

According to possible embodiments, shown in <FIG>, the attachment part <NUM> can be made in a single piece. That is, the central hub <NUM>, the arms <NUM>, the peripheral band <NUM> and the holding elements <NUM> constitute, already in the production step, a single component, without needing to join together the elements as above in successive steps. This configuration is particularly advantageous because it makes the attachment part <NUM> more rigid and stable during the rotation of the milling head <NUM>. Furthermore, the production and storage process of the components is simplified. For example, the attachment part <NUM> can be made by means of laser cutting starting from a continuous flat metal sheet <NUM>, <FIG>. As shown, the metal sheet <NUM> can be used to make attachment parts <NUM> for milling heads <NUM> of even different sizes. This production method allows to reduce working waste to a minimum, optimizing the overall surface of the metal sheet <NUM> to the fullest.

As an alternative to laser cutting, it is possible to provide the monolithic production of the attachment part <NUM> also by means of punching, always starting from a flat metal sheet <NUM>.

In possible embodiments, the attachment head <NUM> has a polygonal section shape, for example quadrangular or hexagonal (<FIG> and <FIG>) mating with the shape of the connection seating <NUM>.

The polygonal, in particular the hexagonal, shape of the central connection seating <NUM> is advantageous for an effective transmission of the torque required for the rotation of the milling tool <NUM> in question.

In particular, the attachment head <NUM> is provided with a connection portion 16a projecting from the protruding annular ring <NUM> and having the hexagonal section shape as above.

The hexagonal shape of the central connection seating <NUM> and of the attachment head <NUM> allows to distribute the connection force between the attachment head <NUM> and the attachment part <NUM> in a more homogeneous manner. With the same transmitted force, the hexagonal shape allows to reduce the size of the connection seating <NUM>. This attachment head <NUM> can be provided for the connection to a manipulator device <NUM>.

In possible embodiments described using <FIG> and <FIG>, the attachment head <NUM> is provided with a protruding annular ring <NUM> for abutment against the attachment part <NUM> (see for example <FIG>). The provision of the protruding annular ring <NUM> is advantageous, since it defines an end-of-travel or a safety abutment for the connection between the attachment head <NUM> and the attachment part <NUM>, also preventing the rise of situations in which, by applying a thrust and pressure on the manipulator device <NUM>, the attachment head <NUM> is thrust excessively and in an undesired manner beyond the attachment part <NUM>, toward the inside of the milling head <NUM>, with the evident risks this situation entails.

In accordance with some embodiments, the clamping means <NUM> of the attachment head <NUM> comprise a magnetic element <NUM> configured to selectively abut with the attachment part <NUM> in correspondence with the connection seating <NUM>.

In accordance with some embodiments, shown in <FIG>, the attachment head <NUM> is provided with a groove <NUM>, made on the protruding annular ring <NUM> and circumscribed to the connection portion 16a, in which the magnetic element <NUM> is positioned.

The magnetic element <NUM> has an annular shape, substantially mating with the shape of the groove <NUM>.

Advantageously, the presence of the magnetic element <NUM> allows to transmit a uniform connection force onto the attachment part <NUM>. In fact, the annular shape of the magnetic element <NUM> allows to act on the whole perimeter zone around the connection seating <NUM>.

In accordance with possible embodiments, the clamping means <NUM> are provided with an elastic retractable element configured to selectively engage the attachment part <NUM> in correspondence with the connection seating <NUM>.

The elastic retractable element, therefore, acts as an advantageous selective clamping element with the attachment part <NUM>. This is favorably useful, for example, to prevent undesired slippage or uncoupling between the attachment part <NUM> and the attachment head <NUM> associated with the manipulator device <NUM>.

It is clear that modifications and/or additions of parts may be made to the milling tool for prosthetic surgery operations as described heretofore, without departing from the field of the present invention as defined in the claims.

It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art shall certainly be able to achieve many other equivalent forms of a milling tool for prosthetic surgery operations, having the characteristics as set forth in the claims and hence all coming within the field of protection defined thereby.

Claim 1:
Milling head for a milling tool for prosthetic surgery operations, said milling head (<NUM>) being made of metal and having a base perimeter edge (<NUM>), said milling head (<NUM>) being provided with an external cutting part (<NUM>) which has a milling surface (12a) from which a plurality of protruding cutting elements (<NUM>) project, and a coupling part (<NUM>) defined along said base perimeter edge (<NUM>) and provided with a plurality of recessed coupling seatings (<NUM>) circumferentially present along said base perimeter edge (<NUM>), wherein said coupling part (<NUM>) comprises three or four recessed coupling seatings (<NUM>) respectively disposed at <NUM>° or <NUM>° from each other, each of said recessed coupling seatings (<NUM>) comprising one lead-in portion (<NUM>) that is inclined, at least in a first part thereof, with respect to an operative axis (A) of symmetry for said milling head (<NUM>), and one end-of-travel portion (<NUM>), wherein said lead-in portion (<NUM>) has a first part (27a) extending from said base perimeter edge (<NUM>) and inclined, with respect to a plane perpendicular with respect to the operative axis (A) and defined by the base perimeter edge (<NUM>), by an angle of inclination α of between <NUM>° and <NUM>°, the first part (27a) defining a slide leading toward said end-of-travel portion (<NUM>), further wherein the lead-in portion (<NUM>) has a second part (27b) which constitutes the continuation of the first part (27a), the second part (27b) being substantially orthogonal to the operating axis (A) and ending in said end-of-travel portion (<NUM>).