VERTEBRAL OSTEOSYNTHESIS EQUIPMENT The present invention concerns vertebral osteosynthesis equipment. A vertebral osteosynthesis equipment comprises generally one or two rachis propping rods, bony anchoring members, such as pedicular screws or hooks, and connection parts of this or these rods to these anchoring members. In the case of two rods, such a material comprises moreover one or several crosslinks of these rods, which enable to prevent the rods from moving apart. Certain types of crosslinks are relatively difficult to connect to the propping rods, and it is an object of this invention to remedy this shortcoming. Moreover, certain existing crossbeams enable connection of the rods solely perpendicular to these rods. Still, it may happen that the rods are not perfectly parallel to one another and/or it may be necessary to place the crossbeam along a direction non perpendicular to the rods. This absence of latitude for positioning the crossbeam with respect to the rods generates problems when installing the equipment, and the invention also aims at remedying this shortcoming. Besides, generally speaking, it is an object of the invention to provide a vertebral osteosynthesis equipment which is simultaneously simple to be implanted and able to sustain perfectly repeated stresses to which it may be exposed. It is also known, by the documents US 2003/114853 and WO 02/30307 to provide a crosslink of said rachis propping rods and connection parts of these crossbeams to these rods ; at least one connection part comprises a bent part shaped into a hook, which defines a housing for receiving a rod and a recess through which a rod may be engaged in this housing, and a bore ; at least one crosslink comprises a stud fitted with a head exhibiting a lateral flat surface, whereas this stud may be engaged in said bore and pivot in this bore between a retracted position, wherein the flat surface is turned to the housing so that said head does not oppose the engagement of the rod in the housing, and a locking position, wherein the stud is pivoted in the bore so that its head protrudes in said recess and locks in the housing the rod previously engaged
in this housing ; the equipment comprises moreover means for immobilising the stud in locking position. The existing equipment is, however, not totally satisfactory, either because it is relatively complex of use, or because it enables assemblies whereof the durable lifetime is not ensured, or still because it is complex and expensive to realise. The equipment concerned by the present invention is of the type specified above. According to the invention, said head is conical in shape and is off- centered with respect to the pivoting axis of the stud, this head being shaped in order to, in locking position, clamp the rod therebetween and the connection part. Thus, the connection part may be engaged on a rod, then the stud that it includes may be pivoted to the locking position, for retaining the connection part on the rod. The immobilising means are then actuated to immobilise the stud in this locking position. Thanks to the equipment according to the invention, the connection part may be engaged at any point of a rod, and its locking is realised particularly simply and quickly, while being perfectly resistant. The means immobilising the stud in locking position may be realised in the form of a thread provided on the stud, of a nut resting, when clamping, against the connection part, and of bearing surfaces of the stud against the connection part. Clamping the nut thus enables to clamp the stud with respect to the connection part and to realise the immobilisation in rotation of this stud by friction. Said bearing surfaces may notably be the head of the stud, on the one hand, and a surface corresponding to the connection part, on the other hand. Advantageously, said immobilising means are shaped to also enable to link the connection part to the crossbeam. Notably, the stud may be threaded and receiving a nut linking the connection part to the crossbeam. Preferably, the equipment comprises means forming a stop to determine said retracted position and/or said locking position.
These positions are thus easy to find. According to a preferred embodiment of the invention in this case, - the stud comprises a radial hole ; - the connection part comprises a circle sector slot centred on the axis of the bore receiving the stud, this slot running through the wall of the connection part which delineates this bore and emerging on the outside ; - the equipment comprises a pin which may be engaged through this slot then in said hole and may be attached to the stud. This pin and the portions of the connection part delineating the longitudinal ends of the slot form two stops limiting the pivoting motion of the stud between said retracted and locking positions. This pin enables moreover the assembly of the stud to the connection part. According to a preferred embodiment of the equipment according to the invention, the crossbeam comprises two oblong holes at its ends, whereas said stud may be engaged in a pivoting motion through one of these oblong holes and receive a nut. These oblong holes enable adjustment of the longitudinal position of the connection part with respect to the crossbeam, and the pivoting motion of the stud in these openings enables adjustment of the orientation of the connection part with respect to the crossbeam, if it is necessary taking into account the orientation of the rods. There is thus realised a latitude in the positioning of the connection part with respect to the crossbeam, which facilitates greatly the link of this crossbeam to the rods. Said nut may notably contain a cylindrical tapped wall, receiving the stud inwardly and having a diameter adapted to close-fit engagement through an oblong hole of the crossbeam. The invention will be better understood, and other characteristics and advantages thereof will appear, with reference to the appended schematic drawing, this drawing representing, for non limiting exemplification purposes, a preferred embodiment of the vertebral osteosynthesis equipment according to the invention.
Figure 1 is a perspective view of different parts contained in this equipment ; Figure 2 is an exploded perspective view of a crossbeam and of a connection part of this crossbeam to a propping rod ; Figure 3 is a side view of a stud contained in this crossbeam ; Figure 4 is a top view of this stud ; Figure 5 is a side view of this crossbeam, after engagement on two propping rods contained in the equipment ; Figure 6a is a top view of this crossbeam, and Figure 6b is a view of this crossbeam from beneath. Figure 1 represents a vertebral osteosynthesis equipment 1 , which comprises two rods 2 propping the rachis, bony anchoring pedicular screws 3, connection parts 4 of a rod 2 to a screw 3, and at least one crossbeam 5 for transversal link of the rods 2, to prevent these rods from moving apart. The rods 2 are cylindrical and made of a rigid, but deformable, material, notably of titanium. Each screw 3 may be of the "polyaxial" type, i.e. contain a pedicular anchoring threaded portion 6 and a proximal threaded stud 7 connected to the portion 6 by a ball joint. This type of screw is well known, and one may notably refer to the international application n° WO 98/55038 for more detailed information on such a screw. In the example represented, the proximal stud 7 is threaded for receiving a nut and comprises two flat surfaces 8 enabling to maintain it in rotation when screwing the nut. This stud 7 also comprises a threaded proximal rod 9 enabling assembly of an extension (not represented) for easier installation of the rod 2 and of the connection part 4 on the stud 7. This connection part 4 is in the form of a yoke, i.e. comprises two parallel branches and a rounded portion defining a housing for receiving the rod 2 by a sliding motion. The nut aforementioned enables to clamp both these parallel branches in order to clamp said rounded portion around the rod 2. This type of connection part 4 is also well-known, and it may be referred to the previous document aforementioned for more information pertaining thereto.
The crossbeam 5 comprises a flattened lug 10, two parts 11 for connecting this lug 10 to the rods 2, and studs 12 and nuts 13 for assembling these connection parts 11 to this lug 10, more particularly visible on Figures 2 to 4. As shown on Figure 2, the lug 10 comprises two oblong holes 15 at its ends. Each connection part 11 comprises a bent part 16 shaped into a hook, a bore 17 and a slot 18. The bent part 16 defines a housing 20 for receiving a rod 2 and a recess 21 through which a rod 2 may be engaged in this housing 20. The bore 17 may receive the stud 12 for a pivoting motion. Its engagement orifice of the stud 12 is bordered by a conical span. The slot 18 is in the form of a circle sector centred on the axis of the bore 17. It runs through the wall of the connection part 11 which delineates this bore 17 and emerges on the outside of this part 11. The stud 12 is fitted with a head 22, comprises a radial hole 23, and exhibits, on the side opposite the head 22, a thread 24 and a transversal groove 25. The head 22 exhibits a conical shape and a lateral flat surface 26 ; as visible on Figure 4, it is off-centered with respect to the axis of the stud 12. The radial hole 23 is designed for receiving a pin 30. This pin 30 is engaged through the slot 18 then in this hole 23 and is attached to the stud 12. The thread 24 is designed for receiving the nut 13, and the transversal groove 25 may receive an appropriate tool for operating the stud 12 in rotation. The nut 13 comprises a hexagonal portion 31 for its control in rotation, a collar 32 bearing against the lug 10 and a tapped cylindrical portion 33, receiving the stud 12 inwardly and having a diameter adjusted to the width of a hole 15. For assembling a crossbeam 5, a stud 12 is engaged in the bore 17 of a connection part 11 , then the pin 30 is engaged in the slot 18, then in the hole 23, and the stud 12 is engaged through a hole 15 then receives the nut 13.
In practice, as may be understood with reference to Figures 5 and 6b, the stud 12 may pivot in the bore 17 between both positions defined by the pin 30 stopping against the portions of the connection part 11 delineating said longitudinal ends of the slot 18. One of these positions, illustrated for the part 11 situated on the left of Figures 5 and 6b, is a retracted position of the head 22. In this position, the flat surface 26 is turned to the housing 20 so that the head 22 does not protrude in this housing 20 and does not oppose therefore the engagement of the rod 2 in this housing 20. The other position, illustrated for the part 11 situated on the right of Figures 5 and 6b, is a locking position, wherein the head 22 of the stud 12 protrudes in the recess 21 and locks in the housing 20 the rod 2 previously engaged in this housing. The eccentric portion of the head 22 enables to clamp the rod 2 between this head 22 and the bent part 16 of the part 11. Once the head 22 brought in locking position by operating the stud 12 by means of an appropriate tool engaged in the groove 25, the nut 13 is clamped in order to immobilise the part 11 with respect to the lug 10. As shown on Figures 6a and 6b, the possibility of pivoting the stud 12 in the hole 15 enables orientation of the part 11 in a direction non parallel to the longitudinal direction of the lug 10 and enables thus to assemble this lug 10 to a rod 2 in a position of the rod 2 non perpendicular to the lug 10. Besides, the oblong shape of the holes 15 enables to adjust the longitudinal position of each part 11 with respect to the lug 10. As appears from the foregoing, the invention provides a vertebral osteosynthesis equipment exhibiting the following decisive advantages : - connection parts 11 which may be engaged at any point of a rod 2 and non by a sliding motion from one end of this rod, hence relatively easy to manipulate, - connection parts 11 which may be adjusted in position and in orientation with respect to the lug 10, hence enabling to facilitate the connection of these parts to the rods 2, and
- generally speaking, to be relatively simple to implant and to be able perfectly to resist the repeated stresses to which it may be exposed. It goes without saying that the invention is not limited to the embodiment described above for exemplification purposes but it extends to all the embodiments covered by the claims appended thereto.