Osteosynthesis device with quick fixing deviceTechnical Field
The present invention relates to an osteosynthesis device comprising a plate and a fixation means allowing a pin to be held through said plate.
Background
One contemplated field of application is notably the field of fracture reduction, a plate for fracture extending along two bones delimited by the fracture, and at least two pins mounted through the plate and screwed into said two bones, respectively. Thus, because the two pins are held in fixed positions relative to each other by the plate, the two bones are correspondingly held together. Devices such as these are typically installed for a predetermined time, on the order of about one month, during which the two bones are engaged.
A plurality of devices of this type are already known, the plate having at least two recesses (recesses) formed in its thickness direction and passing completely through the plate. The recesses are spaced apart in a manner to fit against the two bones, respectively. These recesses are designed to receive fastening means of the type described above. These pockets typically include a ring or ring (collar) that is rotatably mounted within the pocket. The pins are then mounted by means of the ring, which guides the pins in a set direction with respect to the plate, for example a direction pin inclined at an appreciable angle with respect to the vertical direction of the plate. Document EP1583478, for example, discloses a device in which the pin is held in a fixed position with respect to the plate by means of a locking sleeve, in which the pin engages, and in which the sleeve is screwed into the ring along an axis in the vicinity of the pin, said axis being angularly offset with respect to the axis of the pin. Thus, due to this angular offset, this rotation of the locking sleeve gradually causes an irreversible locking of the pin with respect to the plate.
Such a device works well if the pins are in a direction substantially perpendicular to the plate or in a direction having a relatively small angular offset with respect to said perpendicular direction. In comparison, it is relatively difficult to maintain the pins inclined through the plate in a fixed position. Furthermore, the pin must be precisely mounted in the locking sleeve, which itself must be mounted in the ring with very precise tolerances. Therefore, machining the above-mentioned parts requires special machining tools and, in particular, relatively long machining times with respect to other machine parts of the same type. Therefore, these components are correspondingly more expensive.
Disclosure of Invention
Thus, one problem that has been raised and that the present invention is intended to solve is that of providing an osteosynthesis device which not only enables the pins to be held in a fixed position through the plate, in a direction inclined with respect to the plate, with considerable robustness, but which can also be produced at relatively low cost.
To solve this problem, the invention proposes an osteosynthesis device comprising a plate able to extend along a bone and a fixing means for retaining a pin passing through said plate, said pin being screwed into said bone, said plate having a recess formed along its thickness to receive said fixing means, said recess defining a closed inner edge, said fixing means comprising a ring for receiving said pin, said ring being designed to engage with said inner edge, and said fixing means further comprising a locking means which can be screwed in order to lock said pin in a fixed position with respect to said plate; according to the invention, the plate has at least one threaded opening formed at the margin (margins) of the recess to present an axial hole open into the inner edge, while the ring is radially split so as to be diametrically compressible; and, said screwable locking means comprises a screw for screwing into said threaded opening to press against said ring through said axial hole, causing said ring to be forced against a portion of said inner edge diametrically opposite said threaded opening, and said ring to be tightened on said pin, whereby said pin is held in a fixed position relative to said plate.
One feature of the invention is therefore the way: the ring, which can be housed in the recess, cooperates with a pin which is then engaged by the ring and by the combined action of a screwable fixing means, in the form of a screw, which is pressed against the ring as the screw is progressively tightened, said threaded opening being partially open into said recess. In this way, the ring is not only driven against the inner edge of the recess in a direction substantially parallel to the plate and diametrically away from the screw, but, in particular due to its radial split, can tighten around the pin, wedging it. Thus, the ring engages between the screw entering the pocket and the opposite inner edge of the pocket, while the pin itself engages within the ring. Thus, the pin is held in a fixed position relative to the plate. This omits the nut connection between the ring and the plate, as explained in more detail in the following description. In particular, the ring can then be held in a position: the average plane defined by the rings is inclined with respect to the plate. The pins can thus be held in a fixed position by the plate at a relatively pronounced inclination.
Advantageously, the screwable locking means comprise a conical screw widening from the top towards the head. Thus, when screwed into the threaded opening, the screw pushes transversely in relation to its screwing axis through the axial hole towards the inside of the recess formed in the plate and presses against the ring, the pressure exerted on the ring increasing progressively. Furthermore, because the threaded opening has substantially cylindrical symmetry, the tapered screw progressively applies increased pressure to the wall of the opening as it is threaded. When this pressure becomes too great with respect to the screwing effect, the conical screw locks.
Furthermore, the plate has another threaded opening formed at the margin of the recess at a position diametrically opposite the at least one threaded opening, so as to allow the pin to be locked in both cases. In particular, as explained above, the ring can be held in a position inclined with respect to the plate, and this is an advantageous feature of the invention. Thus, a larger or smaller portion of the ring would extend opposite the axial bore of the threaded opening, taking into account such tilting. Thus, the threaded opening selected for insertion of the screw will be the one in which the greater part of the ring faces its axial bore. In this way, the screw will press the ring better, as it presses on a larger surface area of the ring. It is quite obvious that the plate according to the invention is not in any way limited to two threaded openings, but has more openings.
According to an advantageous embodiment of the invention, the threaded opening, preferably with cylindrical symmetry, extends substantially perpendicular to the plate, so that the screw can exert a significant pressure on the ring without the risk of loosening.
According to a particular embodiment, the threaded opening has an axis of symmetry that is appreciably inclined with respect to a direction perpendicular to the plate, so that the conical screw has a wide portion inside the recess, the generatrix of which is perpendicular to the plate. In this way, the pressure exerted by the expanse on the ring is more symmetrically distributed and the risk of loosening of the screw is reduced.
Furthermore, according to a particular advantageous embodiment variant, said threaded opening has an axis of symmetry substantially tangential to said inner edge, so that the threaded opening looks like a half cylinder on a circular base with axial slits. In this way, when the conical screw is screwed into the threaded opening with it resting on the ring in the recess in the plate, the conical screw has a tendency to emerge laterally from the opening by applying pressure to the axial hole of the ring and cannot lock by jamming in the opening. In comparison, the pressure applied to the ring is more easily adjusted by varying the degree to which the screw is screwed in.
In addition, irrespective of the inclination of the ring, the inner edge of the recess is concave so as to form a spherical ring surface, in view of increasing the surface area against which the ring bears, whereas the ring defines a spherical portion that acts like a ball inside the recess. This increase in bearing surface area not only facilitates adjustment, but also makes the connection between the ring and the plate stronger.
In addition, the ring is advantageously made of metal, which is soft in comparison to the plate and the screws, so that the screws self-tap into the ring when being forced into the threaded openings. Thus, not only does the screw press against the ring, but its threads bite into the material of the ring, holding the ring more stably in a fixed position with respect to the plate.
Preferably, the plate has at least one additional recess spaced from the recess for receiving a further fixing means to retain a further pin in exactly the same manner as described previously.
Drawings
Further details and advantages of the invention appear on reading the following description of a particular embodiment of the invention, given purely by way of non-limiting indication and with reference to the accompanying drawings, in which:
fig. 1 is a partially schematic top view of an osteosynthesis device according to the invention;
FIG. 2 is a schematic view of the osteosynthesis device shown in FIG. 1 taken along line II-II;
fig. 3 is a schematic view of the osteosynthesis device shown in fig. 1 taken along the line III-III.
Detailed Description
Figure 1 partially shows an osteosynthesis plate 10 in which a circular recess 12 is formed completely through the plate. A plate such as this very obviously comprises a plurality of circular recesses arranged along its length. Mounted in the recess 12 is a circular ring 14, which circular ring 14 is radially split so as to form two free ends 16, 18 facing each other. In addition, a pin 20 of circular cross-section is slidably fitted within the ring 14. Fig. 2 again shows the osteosynthesis plate 10 with a circular recess 12 formed in its thickness direction. The ring 14 is mounted in the circular recess 12, and a pin 20 having a longitudinal axis a is slidably fitted in the ring 14 and oriented in a direction substantially perpendicular to the plane P defined by the plate 10. The ring 14 mounted in the plate 10 also serves to guide the pin 20 in a translational movement within a bone when the device is mounted on a patient. As can be seen in the figures, the plane P' defined by the ring 14 coincides with the plane P of the plate. Now, when the device is mounted on a patient, the two planes are generally tilted with respect to each other, since the ring 14 is pivoted significantly to tilt the pin 20 with respect to the plate 10.
The circular recess 12 defines a closed inner edge 22, the concave surface of the inner edge 22 extending into the thickness of the plate 10 and extending around the entire periphery of the recess 12. Furthermore, correspondingly, the ring 14 has a convex outer edge 24, so that the ring can act as a ball inside the recess 12, as will be explained below when mounting the device.
Returning now to fig. 1, the plate 10 has two diametrically opposed threaded openings 26, 28. These openings are formed substantially perpendicular to the plate 10 and their threaded axes T, T' are tangential to the pockets 12, which means that they form a U-shaped receptacle on the inner edge 22. These threaded openings 26, 28 define axial bores 30, 31, respectively, that open into the pocket 12.
According to a particular embodiment of the invention, the pins 20 have a diameter of between 0.8mm and 5mm, for example a diameter of 4mm, while the plate 10 has a thickness of between 3mm and 7 mm. The circular recess 12 accordingly has a diameter of between 2.5mm and 15 mm. These elements are made, for example, of 316L-shaped stainless steel, which is the most widely used steel in orthopaedic surgery. In contrast, the ring 14 itself is made of stainless steel which is not so hard.
Reference is now made to fig. 3 in order to describe in more detail the working of the osteosynthesis device according to the invention. This figure again shows the osteosynthesis device 10 in section, with the pin 20 engaged in the ring 14, which itself is engaged in the recess 12. In contrast, unlike fig. 2, an additional element, a frustoconical tapered screw 32, made of a surgical steel harder than the steel forming the ring 14, has been screwed at least partially into the threaded opening 26. The tapered screw 32 has a widened head 34, the hexagonal socket of which 34 has been axially formed to receive a fastening tool, and a head 36, which head 36 engages in the threaded opening 36 and bears transversely against a first portion 38 of the outer edge 24 of the ring 14.
Thus, the second outer edge portion 24 is diametrically opposed to the first edge portion 38, pressing against the inner edge portion 22 diametrically opposed to the tapered screw 32. In this position, the ring 14 is captured within the annular recess 12. In contrast, because the tapered screw 32 is not fully engaged within the threaded opening 26, the ring 14 is then able to pivot within the circular recess and in a direction perpendicular to the plane P of the plate 10, so that the inclination of the pin 20 relative to the plate 10 can be adjusted over a relatively large range of movement. This is an advantage of the present invention. When adjustment has been effected, the taper screw 32 is then forced to turn and fully enter the thickness of the plate, through the threaded opening 26 and against the ring 14. Thus, as the widened head 34 is progressively screwed in, the ring is driven laterally to press forcibly against the lateral edge portion 22 opposite the tapered screw 32. At the same time, the loop tightens and its two free ends 16, 18 facing each other move closer together, thus tightening and then locking the pin 20 in a fixed position with respect to the loop 14. Thus, the pin 20 is in turn held in a fixed position relative to the plate 10, as the ring 14 itself engages between the inner edge 22 and the conical screw 32 threaded into the threaded opening 26.
Furthermore, because the ring 14 is made of a softer material than the material from which the tapered screws 32 and the cut-out plate 10 are machined, the threads of the tapered screws bite into and embed into the outer edge 24 of the ring 14 as the screws are progressively screwed in. Because the screws are anchored in the ring 14, the ring becomes very firmly fixed to the plate 10.
[0027] The plate of the osteosynthesis device according to the invention is intended to be mounted along a fractured bone piece, receiving a plurality of pins of the aforementioned type in order to constantly hold in position the various pieces of the fractured bone piece with respect to said plate and thus to maintain them in a fixed position with respect to each other.