FR2929829A1 - Vertebral body replacing apparatus for use in orthopedic spinal field, has rod inserted in one orifice so as to exert pressure on implant in order to lock frame forming structure and implant with one another - Google Patents

Abstract

The apparatus (20) has a spinal implant (22) with an external surface (30). A frame forming structure (24) has an inner surface (28) defining a channel (29) sized and configured in a manner to be adapted to a part of the outer surface. The structure has orifices (32) crossing the outer surface and the inner surface in such a manner that the orifices communicate with the channel. A rod (26) is inserted in one of the orifices in a manner to exert pressure on the implant so as to lock the structure and the implant with one another.

Description

The present invention relates to an apparatus for replacing a part or all of a vertebral body and its relationship with orthopedic instrumentation. The present invention specifically relates to devices for connecting this type of device to this type of instrumentation. In the field of orthopedic spinal medicine, there are cases where it is necessary to remove the entirety of one or more vertebrae or a significant portion of one or more vertebrae. For example in cases of trauma where the vertebrae are too damaged to retain a significant portion of the vertebrae, or cases of tumors requiring the removal of a significant amount of the vertebrae. In such cases, a vertebral body replacement implant, or ICV, can be implanted between two healthy vertebrae to replace the excised bone tissue. For example, if a substantial portion or the entirety of the L3 vertebra is to be removed, then it is possible to insert an ICV between the L2 vertebra and the L4 vertebra so as to replace the lost L3 bone tissue. Other types of spinal instrumentation are used to support parts of the spine that are damaged, need to be corrected, or lack the entirety or part of a vertebra or a spine. other fabric. Elongated elements, such as plates, rods, or bars, may be connected to one or more spinal mobility elements to correct curvature, support weakened or damaged tissue, or allow the fusion of one or more vertebral segments, among others. The vertebra assembly of these elongate members can be accomplished by a variety of fasteners, including bone screws, hooks, clips, cables, and the like. The subject of the invention is an apparatus comprising a spinal implant having an outer surface, a frame structure having an inner surface defining a channel dimensioned and configured to fit at least a portion of said outer surface of said implant and a outer surface, said frame structure further comprising a plurality of orifices passing through said outer surface and said inner surface, such that said ports communicate with said channel; and a rod inserted into one of said ports for exerting pressure on said implant, thereby locking said frame structure and said implant together. Said rod may be an elongate member deviating from said frame structure a sufficient distance to allow attachment of an orthopedic device to said rod, said orthopedic device being remote from said frame structure. The apparatus may further include a second rod inserted into a second port, said second shaft exerting pressure on said implant. Said second rod may be a clamping screw.

Said second rod may be an elongate member spaced from said frame structure a sufficient distance to allow attachment of an orthopedic device to said rod, said orthopedic device being remote from said frame structure. Said orifices in which said rods are inserted may have respective longitudinal axes, and said axes are substantially between the spinous process and an articular facet of a vertebra adjacent to said implant. Said rod may be an elongated element having a first end and a second end, said first end comprising a frustoconical tip. Said rod may comprise a threaded portion adjacent to said tip, and said orifice in which said rod is inserted is threaded, and said rod and said frame structure are threadedly engaged. Said rod may comprise a flange adjacent to said threaded portion, and said flange abuts against said frame structure. Said frame structure may comprise a thickened portion adjacent said orifice in which said rod is inserted, and said flange abuts against said thickened portion. The shape of said frame structure may be substantially cylindrical. The frame structure may be substantially C-shaped. The spinal implant may be an implant for replacing a vertebral body.

Said implant intended to replace a vertebral body may be intended to touch two vertebrae. The invention also provides a method comprising the steps of providing a spinal implant, assembling a frame structure with said spinal implant so that said frame structure is slidable along the length of said implant, inserting a shaft through said frame structure so that the rod exerts pressure on said implant and limits or prevents slippage of said frame structure relative to said spinal implant; and connecting said rod to a spinal fixation apparatus. The method may further include inserting a second rod through said frame structure such that said second rod exerts pressure on said implant. The method may further include inserting a clamping screw through said frame structure such that said clamping screw exerts pressure on said implant and limits or prevents slippage of said frame structure relative to said spinal implant. Said method may further comprise the steps of releasing said clamping screw; and adjusting said frame structure with respect to said implant. The method may further include removing the clamping screw, and wherein said step of inserting the stem comprises inserting said rod into the previously occupied location of said clamping screw. The method may further include the steps of inserting a second rod through said frame structure such that said second rod exerts pressure on said implant and limits or prevents slippage of said frame structure relative to said implant. spinal; and connecting said second rod to a spinal fixation apparatus. Said frame structure may comprise a channel, and said step of connecting the frame structure comprises placing said frame structure such that at least a portion of said implant is located at least in a portion of said channel.

Said channel may be closed, and said step of connecting the frame structure comprises sliding said frame structure over said implant. Said channel may be open, and said step of connecting the frame structure comprises moving said frame structure toward said implant and rotating said frame structure with respect to said implant. The invention also relates to an apparatus comprising a frame structure defining a channel adapted to fit at least a portion of an implant replacing a vertebral body, said frame structure further comprising a plurality of orifices communicating with said channel; and a rod inserted into one of said orifices and rigidly connected to and departing from said frame structure. The frame structure may include a thickened portion adjacent to said hole. The apparatus may further include a second rod inserted into a second port and rigidly connected to and departing from said frame structure. Said rod may comprise a threaded portion and said orifice in which is inserted said rod is at least partially threaded, said rod being threaded in said orifice. The apparatus may further include a threaded set screw and inserted into a second port. Said rod may comprise a frustoconical tip.

Said rod may comprise a flange that abuts against said frame structure when the rod is rigidly connected to said frame structure. The invention will be better understood on reading the description which follows, given with reference to the following appended figures.

Figure 1 is a perspective view of an embodiment of a connecting apparatus connected to an implant replacing a vertebral body. FIG. 2 is a perspective view of another embodiment of the apparatus illustrated in FIG.

Fig. 3 is a cross-section of the embodiment illustrated in Fig. 1, taken along the axis 3-3 of Fig. 1 and viewed in the direction of the arrows. FIG. 4 is a view from above of an embodiment of a frame structure of an embodiment of the apparatus illustrated in FIG. 1. FIG. 5 is a top view of another embodiment of FIG. embodiment of a frame structure usable with the embodiment of the apparatus illustrated in FIG. 1. FIG. 6 is a perspective view of the embodiment illustrated in FIG. 1 implanted in the spinal column. For a better understanding of the principles of the invention, the following description refers to the embodiments illustrated in the drawings, and uses a specific language to describe them. It is clear, however, that adjustments and other modifications of the illustrated devices, and additional applications of the principles of the description as they will be illustrated, are conceivable by those skilled in the art while remaining within the framework of the principles on which they are based. the invention. The drawings generally depict an embodiment of an apparatus adapted to be attached to a spinal implant 22. The particular type of spinal implant 22 shown is an implant replacing a vertebral body of which the shape is almost cylindrical. The illustrated embodiment is cylindrical over most of its circumference, a posterior portion being generally concave, and is tubular, having a passage extending from top to bottom. Openings or orifices may exist in the side wall, extending from the outside to the inner passage. Irregularities such as ridges or grooves may be located in the upper and / or lower surfaces to enhance the fulcrums with trays or other bone tissue of adjacent vertebrae. By the term implant replacing a vertebral body, one hears not only the type of device already mentioned, but also any of the devices conceivable to replace one or more vertebrae, including lattices, cages or other structures , as well as possible devices for replacing parts of vertebrae or intervertebral discs. By the term spinal implant is meant not only implants replacing the vertebral bodies, but also other devices that can be inserted into or attached to one or more vertebrae, such as screws, hooks, rods, plates, pliers and other kinds of implants.

The illustrated embodiment of the apparatus 20 includes a frame structure 24 and one or more rods 26 connected thereto. The frame structure 24 has a generally circular shape in one embodiment, it has an inner surface 28 defining a central channel 29, and an outer surface 30. This embodiment of the frame structure 24 can be considered closed, because it has a continuous body which surrounds the central channel 29. The inner surface 28 (and the channel 29) can be particularly shaped so as to conform substantially to at least a portion of the outside of a spinal implant. For example, in the illustrated embodiment where the implant 22 is an ICV whose outside is substantially cylindrical and has a generally concave or chamfered rear portion, the inner surface 28 is also substantially cylindrical and has a curved rear portion. and projected or convex. In some embodiments, the channel 29 is slightly larger than the cross section of the implant 22 so that the frame structure 24 can slide along the implant 22.

The outer surface 30 may be substantially concentric with the inner surface 28, and follow for example substantially the same curvature or the same shape of the inner surface 28. In another embodiment, a frame structure 24 '(FIG. 5) may comprise an empty space G and forming an open or substantially C-shaped frame structure. As with the frame structure 24, the frame structure 24 'has an interior surface 28 which defines a channel 29 and substantially conforms to at least one part of the outer surface of the spinal implant 22, and an outer surface 30 which is concentric with or substantially follows the shape of the inner surface 28. The frame structure 24 'surrounds more than half of the circumference of the spinal implant. implant 22, and in some embodiments about two-thirds or more of this circumference. The width of the empty space G may be about the same or slightly greater than the smallest width of a spinal implant, for example in the case of the implant 22, the distance of a tangent to the two curved surfaces adjacent to its concave surface at an opposite edge through the center of the implant 22. The frame structure 24 may further comprise one or more orifices 32 passing through the outer surface 30 and the inner surface 28. In the illustrated embodiment, two such orifices 32 are provided adjacent to the rear convex portion of the inner surface 28. The orifices 32 are threaded and pass through a thickened portion 34 of the frame structure 24, in a particular embodiment. The orifices 32 respectively have longitudinal axes L1, L2, and in the illustrated embodiment the axes L1 and L2 are not parallel. In some embodiments, the angle between the axes L1 and L2 is less than about 90 degrees, in some embodiments this angle is less than about 45 degrees, and in one particular embodiment, this angle is about 40 degrees. The orientation of the orifices 32 (and their axes) relative to the frame structure 24 can also be determined according to physiological parameters, in particular such that the axes L1 and L2 generally extend between the spinous processes and the facet joints of adjacent vertebrae. In this orientation, the rods 26 leaving the orifices 32 are relatively close to the instrumentation, for example a plate or a longitudinal spinal rod, which can be connected to a pedicle (or between the spinous process and the articular facet) an adjacent vertebra. It can be seen that the axes L1 and L2 could be parallel or could form any angle. On the other hand, in other embodiments, more than one or two orifices 32 may be provided in the frame structure 24, and may be spaced around the frame structure 24, with or without thickened portions 34. For example, in a four-port embodiment 32, these orifices may be regularly or irregularly spaced around the frame structure 24 at 90, 180 or 360 degree angles.

The illustrated embodiment of the apparatus 20 comprises one or more rods 26. Each rod 26 is generally cylindrical in this embodiment, with one end 36 distal to the frame structure 24 and one end 38 which is adjacent or connected to the frame structure 24. The end 36 includes an internal recess 40 in the illustrated embodiment which may be hexagonal or otherwise configured to accommodate a holding or rotating tool (not shown) . The end 38 comprises a frustoconical tip 42, a boss or flange 44, and in embodiments in which the orifices 32 are threaded, a threaded zone 46 between the tip 42 and the rim 44. In particular embodiments , the rod 26 may be tubular, a passage 48 traversing the entire length of the rod 26 (as in the illustrated embodiment) or a part of this length. The rods 26 can be inserted into the orifices 32, and in one embodiment the tips 42 abut the implant 22 and / or lock it. As seen in an example in Figure 3, the frustoconical tips 42 are uniform or conical, this conical surface can then engage the outer rounding of the implant 22 along substantially a line. In this example, as the tips 42 engage the implant 22, the rim 44 can engage the frame structure 24 at the thickened portion 34. Thus, in the illustrated embodiment of the apparatus 20, the rim 44 and the tip 42 of the rod 26 frictionally engage, respectively, the thickened portion 34 of the frame structure 24 and the implant 22. The rod 26 can thus be considered as a component of which locks the frame structure 24 to the implant, and in this embodiment, this lock may comprise two engagement zones for each rod 26. In other embodiments, the tips 42 (regardless of their configuration) do not touch the implant 22. The tips 42 being spaced at least a minimum distance from the implant 22, the frame structure 24 is kept free, able to slide along the implant 22. The rods 26 are firmly attached to the frame structure 2 4 as indicated above, but instead of having two friction anchoring zones (between the tips 42 and the implant 22 and between the flanges 44 and a portion 34 of the frame structure 24), only occurs the engagement between the flange 44 and the portion 34 of the frame structure 24. The ability of the frame structure 24 to continue to slide along the implant 22 even when the rod (s) 26 are fixed to the frame structure 24 allows freedom of adaptation of the construction to various devices or corrective procedures. This also allows adjustment, either automatic or by additional surgery, which may be necessary when the patient is growing. Maintaining a gap between the stems 26 and the implant 22 also eliminates any pressure on the implant 22, which may be desirable for implants 22 whose exterior is malleable or less rigid.

With the stems 26 attached to other implants (described hereinafter), the frame structure 24 can also provide the implant 22 with support or stability, and hold it in place or help it stay in place. One or more other locking elements, such as clamping screws 50, may also be provided and used with the frame structure 24 in addition to, or instead of, one or more rods 26. The clamping screws 50 may be used when the orifices 32 are threaded, or another locking element or other locking elements may be used with other configurations of orifices 32. In the illustrated embodiment, the clamping screws 50 are threaded and introduced. in one or more orifices 32 against the implant 22. These clamping screws 50 may have a frustoconical tip resembling the tip 42 of the rod 26 to block the implant 22 as mentioned above, and may be of a size such that they do not come out of the thickened parts 34 when they engage in the implant 22. The clamping screws 50 also include an internal cavity 52 which may be hexagonal, or which may have the same configuration. That is, one or more clamping screws 50 can be used to temporarily hold the frame structure 24 on the implant 22 during implantation, or as a permanent fixation or filling for the implant. any orifice in which a rod 26 is neither necessary nor desirable.

The rod 26 is generally configured to be connected to other orthopedic implant elements. For example, a rod 26 may be attached to a connector 60 which, in turn, is connected to a screw (e.g., a pedicle screw 62), hook, clamp, cable, or other fastener. As a result, the shank 26 is of a suitable diameter to be connected to a connector 60 and, in particular embodiments, this diameter may be from about 5.5 mm to about 6.5 mm. Similarly, the rod 26 is of sufficient length to extend from the spinal implant to a connector. In the illustrated embodiment where the apparatus 20 connects the implant 22 to a connector 60, and wherein a frame structure 24 is relatively thin with respect to the shank 26, a suitable shank length may be from about three to about five centimeters. With such lengths, the connector 60 can be connected to the rod 26 so that the connector 60 is spaced from the frame structure 24. Longer rods 26 can be provided and then cut by the surgeon to the size desired. Connector 60 and screw 62 may be of a wide variety of types, including those described in U.S. Patent No. 6,485,491 to Farris, et al. The use of the connector 60 and the screw 62, or other connectors and fasteners, allows the rod 26 to be connected to a fixation device or system which may include one or more elongate spinal rods or other structures. As illustrated in FIG. 6, these devices or systems constitute a posterior fixation system in the illustrated embodiment, for example a system placed adjacent to the spinous processes or along a posterior portion of one of the vertebrae or several vertebrae. vertebrae (for example vertebra V, and vertebra V2) of the vertebral column. In practice, the apparatus 20 is attached to the implant 22. In the embodiment where the frame structure 24 is a closed circle, the frame structure 24 slides on a portion of the implant 22 before the latter not set up in relation to the spine. In one embodiment where the frame structure is a substantially C-shaped open member, the frame structure 24 is slidable on the implant 22 as previously described. Alternatively, if this substantially C-shaped open member is properly sized and configured relative to the implant 22, it can be attached to the implant 22 by placing the open side of the frame structure 24 adjacent to the implant 22. 22, advancing the frame structure 24 'so that the implant 22 is at least partially inside the open side, and rotating the frame structure 24' so that the open side is opposite the concave surface of the implant 22. This insertion by lateral insertion and rotation can be performed before or after the introduction of the implant 22 relative to the vertebral elements or the vertebral tissue that it is supposed to concern.

The frame structure 24 can slide along the length of the implant 22. The frame structure 24 can be temporarily held against the implant 22 by one or more clamping screws 50 and / or one or more rods 26 by inserting them ( for example by threading) in orifices 32 and relatively slightly against the implant 32, to produce sufficient friction between the frame structure 24, the implant 22 and the clamping screws 50 and / or the rods 26 to limit or prevent the sliding of the frame structure 24 along the implant 22. At the appropriate time during the surgical procedure, for example just before or just after the placement of the implants such as pedicle screws in the vertebra (s) ) adjacent, the surgeon can remove the clamping screw (50) (if present) and replace it with a stem (s) 26. When the frame structure 24 is located along the the implant 22 as desired by the surgeon, e t one or more rods 26 are connected to the frame structure 24, the rod (s) 26 (and the clamping screw (s) 50 as appropriate) are tightened or pressed against the implant 22 so that it (s) engage (s) firmly on the implant 22. In the embodiment where the orifices 32, the rod (s) 26 and the clamping screw (s) 50 are threaded, the surgeon turns the rods 26 and the clamping screws 50 (if any) to tighten them. The rod (s) 26 and the clamping screw (s) 50 exert a force which makes it possible to lock the frame structure 24, the implant 22, the rod (s) 26 and the clamping screw (s) 50 (where applicable) in relation to each other. In embodiments where the rod (s) 26 do not touch the implant (2), and the frame structure (24) remains slidable along the implant (22), one or more clamping screws (50) may be used to stabilize or temporarily maintain the frame structure 24 at the implant 22. For example, a clamping screw 50 can be placed in an orifice 32 of the frame structure 24 and be engaged on the implant 22, to maintain the frame structure 24 and the implant 22 on top of each other. With an open port 32, a rod 26 can be inserted therein and attached to other devices or implants as indicated below. The choice to insert the rod 26 into the orifice 32 before or after its assembly with another device depends on the anatomy of the patient, the type of the other device with which the rod 26 must be assembled, and similar factors. With a rod 26 connected to another apparatus and another frame structure 24, the stability of the frame structure 24 is maintained when the clamping screw 50 is released and removed. Another rod 26 can then be placed in the orifice 32 from which this clamping screw 50 has been removed.

In one embodiment of the frame structure 24 having two orifices 32, two rods 26 may be assembled to the frame structure 24, or a rod 26 in one orifice 32 and a clamping screw 50 in the other orifice 32. Of course, it is possible to use two setscrews 50, one in each port 32, thereby locking the frame structure 24 to the implant 22, but this apparatus configuration 20 may be more difficult to connect. to other orthopedic devices. The rods 26 may be connected to a connector (s) 60 of a fastening system, as mentioned above. The fixation system can be set up according to the needs of the surgeon and the requirements of the specific devices integrated into the fixation system. The rods 26 may be loosely connected to the connectors 60 before or after the rods 26 are joined to the frame structure 24, and in many embodiments a connector 60 is spaced from the frame structure 24 when the connector 60 is engaged. is connected to the rod 26. When the apparatus and the fixation system 20 are placed as desired by the surgeon, the rods 26 and the clamping screws 50 (if any) are locked with respect to the frame structure 24, and the rods 26 are locked or fixed relative to the connectors 60 and / or to other parts of the fastening system. As mentioned above, the clamping screw (s) 50 may be used as temporary supports for the frame structure 24 at the implant 22 as the stem (s) 26 are placed with respect to the frame structure 24 and / or to another device. Moreover, if necessary, the rod (s) 26 may be shortened if it (s) has (s) an unnecessary length. Other types of orthopedic procedures may be performed in conjunction with placement of implant 22 or other implants and frame structure 24, particularly removal of a portion or all of a or multiple vertebrae, intervertebral discs, or other tissues; compressing, deflecting, rotating, or otherwise manipulating the vertebrae into a desired relationship; placing additional implants such as a screw (62) and connector (s) 60; etc. The rods 26 may have different shapes as indicated by the required stress and bending characteristics for a given patient, implant system or procedure. Thus, in addition to the substantially cylindrical forms, the rods 26 may also be generally square, rectangular, hexagonal, octagonal or any other shape along part of their length or over their entire length. Other forms of spikes 42 are also contemplated, such as those comprising annular disks, projections, roughened surfaces or other configurations. Other connections and locking configurations between the rods 26 and the frame structure 24, such as snaps, springs or dowels, are also contemplated. The rods 26 and the frame structure 24 may be made of different biocompatible materials, including stainless steel, titanium or titanium alloys, ceramic or some plastics. The materials are also selected to be compatible with the fixation system and the implant 22. As mentioned above, the frame structure 24 has an interior configuration that is compatible with the external surface of the implant 22. The structure forming frame 24 can be made to have a relatively close fit with some spinal implants 22. For other spinal implants, or for any spinal implant with which the frame structure 24 does not exhibit this type of close fit , an insert of a suitable shape and / or of a suitable material can be introduced into the frame structure 24 (or between the frame structure 24 and the spinal implant 22) to produce a fit or seal more tight or more complete between the frame structure 24 and the spinal implant 22. This type of insert part (s) can be particularly useful to allow a config uration of the frame structure 24 to be used with several types of implants 22.

Although the invention has been illustrated and described in detail with the drawings and in the foregoing description, it should be considered illustrative and not restrictive. It is clear that only the preferred embodiment has been illustrated and described, and that all variations and modifications that fall within the scope of this disclosure are intended to be protected. Of course, the invention is not limited to the embodiments described above and shown, from which the skilled person can provide other modes and other embodiments, without departing from the scope of the invention.

Claims (21)

REVENDICATIONS1. An apparatus comprising: a spinal implant (22) having an outer surface (30); a frame structure (24) having an inner surface (28) defining a channel (29) dimensioned and configured to fit at least a portion of said outer surface (30) of said implant (22) and an outer surface (30), said frame structure (24) further comprising a plurality of orifices (32) extending through said outer surface (30) and said interior surface (28), such that said orifices (32) communicate with said channel (29). ); and a rod (26) inserted into one of said ports (32) to exert pressure on said implant (22), thereby locking said frame structure (24) and said implant (22) with each other other. An apparatus according to claim 1, wherein said shank (26) is an elongated member spaced from said frame structure (24) a sufficient distance to allow attachment of an orthopedic device to said shank (26) said orthopedic device being remote from said frame structure (24). The apparatus of claim 2, further comprising a second rod (26) inserted into a second port (32), said second shaft (26) exerting pressure on said implant (22). Apparatus according to claim 3, wherein said second rod (26) is a clamping screw (50). An apparatus according to claim 3, wherein said second shank (26) is an elongate member spaced from said frame structure (24) a sufficient distance to allow attachment of an orthopedic device to said shank (26). ), said orthopedic device being remote from said frame structure (24). An apparatus according to claim 3, wherein said orifices (32) in which said rods (26) are inserted have respective longitudinal axes, and said axes may extend substantially between the spinous process and a joint facet of a vertebra adjacent to said implant (22) after placement of the implant (22). 7. Apparatus according to one of claims 1 to 6, wherein said rod (26) is an elongated member having a first end and a second end, said first end comprising a frustoconical tip (42). An apparatus according to claim 7, wherein said rod (26) comprises a threaded portion adjacent said tip (42), and said orifice (32) into which said rod (26) is inserted is threaded, and said rod (26) ) and said frame structure (24) are threadedly engaged. The apparatus of claim 8, wherein said rod (26) comprises a flange (44) adjacent said threaded portion, and said flange (44) abuts said frame structure (24). An apparatus according to claim 9, wherein said frame structure (24) comprises a thickened portion adjacent said orifice (32) into which said rod (26) is inserted, and said flange (44) abuts against said thickened portion. Apparatus according to one of claims 1 to 10, wherein the shape of said frame structure (24) is substantially cylindrical. Apparatus according to one of claims 1 to 10, wherein said frame structure (24) is substantially C-shaped. The apparatus of one of claims 1 to 12, wherein said spinal implant (22) is an implant (22) for replacing a vertebral body. The apparatus of claim 13, wherein said implant (22) for replacing a vertebral body is for touching two vertebrae. An apparatus comprising: a frame structure (24) defining a channel (29) adapted to fit at least a portion of an implant (22) replacing a vertebral body, said frame structure (24) further comprising a plurality of orifices (32) communicating with said channel (29); and a rod (26) inserted into one of said orifices (32) and rigidly connected to and departing from said frame structure (24). The apparatus of claim 15, wherein said frame structure (24) comprises a thickened portion adjacent said orifice (32). Apparatus according to claim 15 or 16, further comprising a second rod (26) inserted into a second port (32) and rigidly connected to and departing from said frame structure (24). 18. Apparatus according to one of claims 15 to 17, wherein said rod (26) has a threaded portion and said orifice (32) in which said rod (26) is inserted is at least partially threaded, said rod (26). being threaded in said orifice (32). 19. Apparatus according to one of claims 15 to 18, further comprising a clamping screw (50) threaded and introduced into a second orifice (32). 20. Apparatus according to one of claims 15 to 19, wherein said rod (26) comprises a frustoconical tip (42). Apparatus according to one of claims 15 to 20, wherein said rod (26) comprises a flange (44) abutting against said frame structure (24) when the rod (26) is rigidly connected to said structure forming frame (24).