LOCKING DEVICE AND METHOD FOR USING THIS DEVICE
TECHNICAL FIELD
The present invention relates to a device for the locking of wires, cables, preferably made of metal, monofilament wires and braided wires, cables, against a bar-shaped element, preferably made of metal, the device to be used for spinal surgical measures, in which mutual stabilization and positional adjustment of vertebrae is indispensable, as well as a method of locking said wires, cables against a bar-shaped element.
BACKGROUND ART
Within the above-mentioned technical field metal wires, cables, are conventionally used in order to tie up vertebrae and fix them against bar-shaped elements and in this way try to obtain stabilization between the vertebrae and to try to retain them in an appropriate position during the time, when deposited bone material is incorporated between the vertebrae for the purpose of attaining bone healing. Thus, it is known, that metal wires, cables, which are fastened to a vertebra and in most cases in the rear part of the vertebra, are fastened against a metal bar, the ends of the wires, cables, being twisted around each other and around the bar and enveloping it. However, with this method it has not been possible to obtain a satisfactory stabilization, which in its turn has resulted in, that it has not been possible to bring about an optimal bone healing.
As far as we know up till now, no satisfactory technical solution has been developed to solve this problem and obtaining a completely stable and reliable connection between the wires, cables and the bar.
BRIEF DISCLOSURE OF THE INVENTION
The object of the present invention is to eliminate the above-mentioned drawbacks and to develop a device, which brings about a substantially improved locking between the wires, cables and the bar, preferably during spinal surgery measures.
According to the inventive idea the above mentioned problems are solved by positioning the bar-shaped element in a ring-shaped fastener as well as by mounting an expandable body in a space between the bar-shaped element and the ring-shaped fastener, which expandable body jointly with a conical screw, which is active in the center of the body, also allows space for holes in its circumferential part, preferably two, arranged in this circumferential part, and through which holes the wire, e.g. subsequent to an anchoring in the rear part of a vertebra, are guided, said expandable body, when the conical screw is driven into it, at the same time stably fixing the ring-shaped fastener as well as the wire, cable against the bar-shaped element.
According to the invention a device is obtained, which prevents the sliding of the wire, cable along the bar as well as the twisting of it around the bar, brings about a reliable anchoring of the rear part of the vertebra and consequently also the vertebra per se against the bar-shaped element, fixes several
vertebrae against the same bar and gives the vertebrae a mutual stability, which is indispensable as far as the growing together of the vertebrae is concerned, and is simple to handle, is eonomic to manufacture and is flexible
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 show the parts of the device according to the invention, i.e. the bar-shaped element and a double ring-shaped fastener, seen at an angle in a lateral perspective view, the bar being positioned in the double ring-shaped fastener with the expandable body and the conical screw being positioned above the fastener.
Fig. 2 shows the expandable body, which is a part of the device, in a perspective view from below.
Fig. 3 shows the expandable body in Fig. 2 : a)showing the expandable body from above; b)showing a central longitudinal cross-section of the expandable body with its lower threaded part; c)showing the expandable body from below ; d)showing a central cross-section of the expandable body ; and e)showing the expandable body in cross-section with a conical screw partially screwed into the locking device.
Fig. 4 shows : a)a cross-sectional view of the locking device according to the invention ; and
b)the same cross-sectional view as in a), but the locking device according to the invention is now shown with its conical screw fully screwed into the expandable body.
It is shown in the drawings, that the device according to the invention comprises a bar-shaped element 23, a wire, cable 18, a double ring-shaped fastener 17 and an expandable body 1, which comprises a partially cylindrical part having a plane head. Bar-shaped element 23 preferably is a metal bar 23, which is positioned in double ring-shaped fastener 17 and against its bottom. Bar-shaped element 23 and ring-shaped fastener 17, which is connected to this element, form an opening 24 between ring-shaped fastener 17 and bar-shaped element 23. The expandable body is provided with slits in an axial direction, gaps from its top down to about 2/3 of its length, which gaps run at right angles to each other through center 4 and outwards to outer sides la, lb of expandable body 1, which slits have variable widths, one wider 2 and one more narrow 3. This central hole has an opening facing upper part 4-0 of the expandable body. In this part there is a space having a cylindrical shape 5 for a screw head 22. In the center of the lower part of expandable body 1 a hole 6 is made, provided with a thread for screw 22, which is to be driven into center 4 of expandable body 1. Between upper cylindrical hole 5 and hole 6 of the threaded part in the central hole the space has a conical shape 7. Below the area, where the wide slit, gap 2, is terminated on both sides, there is a hole 9 inside the body wall, which leads to lower end 10 of exandable body 1. Lower part of hole 9 faces an additional slit, gap 11.
Upper part of expandable body 1 is provided with a collar 12, which is partially bevelled at 14 towards the projecting part of plane side la of expandable body 1 and towards the diametrically opposite side of collar 12 above cylinder-shaped part lb. Below this part of collar 12 a shoulder 15 is arranged on outer side lb of the cylinder. Similar shoulders 16 are arranged adjacent wide slit 2, a gap, at the same distance from the collar 12 as the above-mentioned shoulder 15.
A screw 22 having a key socket is a part of the device according to the invention. Screw 22, the head of which is cone-shaped, is provided with a machine thread 13.
Fig. 4a and b shows expandable body 1, arranged in double ring-shaped fastener 17, which is fastened to an imaginary bar-shaped element 23, against which wire, cable 18 will be indirectly fixed. Wire, cable 18 runs downwards into the slit, gap 2, within the upper part of the locking body at opposite sides of cone-shaped screw 22, and then passes holes 9 in the sides of the expandable body. When conical screw 22 is threaded into cylinder hole 6, the cone will press sides 20 of expandable body 1 apart. At the same time the cone of • screw 22 exerts a pressure on wire, cable 18, which is positioned in the slit, gap 2, within the upper part of exandable body 1. The continued driving of screw 22 downwards compresses wire, cable 18. It will then be deformed against edge 21, which the upper part of the double ring-shaped fastener forms against screw 22. Wire, cable 18 is efficiently locked in this way. The final phase of the driving of conical screw 22 causes also an expansion of the upper part of the expandable body. Expandable body 1 is then pressed between bar-shaped element 23 and
double ring-shaped fastener 17. Plane part la of expandable body 1 is pressed against bar-shaped element 23 and round part lb of the expandable body against the inner round shape of double ring-shaped fastener 17. Expandable body 1 will in this way be efficiently locked against bar-shaped element 23. When body 1 expands, shoulders 15,16 will be pressed inwards below the lower edge of upper ring fastener 17. They will prevent expandable body 1 from being pressed out from the ring of ring-shaped fastener 17, when the conical screw is driven into expandable body 1. Shoulders 15,16 on the outer side of the cylinder prevent the locking body from being pressed out of ring fastener 17 during the final phase of the driving of screw 22 into expandable body 1.
The wire, cable which preferably is made of a metal (a monofilament or braided) is guided around the rear part of a vertebra. Ring-shaped fastener 17 (double ring) is pressed against bar-shaped element 23. The two wire, cable ends are guided through space 24, which is obtained, when ring-shaped fastener 17 abuts bar-shaped element 23. The two free ends of wire, cable 18 are then guided through holes 9 in the lower part of expandable body 1 and past the loosely inserted conical screw. While holding the two wire, cable ends body 1 is inserted into the ring-shaped fastener. A screw driver is inserted into the key hole of the screw. The wires, cable are stably fastened against a contraction device having a gear. Wires, cables 18 are drawn and stretched by means of the gear, until a stable connection between the rear part of the vertebra and bar-shaped element 23 is obtained. When wires, cables 18 have obtained a sufficiently drawn position, the screw driver is rotated several turns, until conical screw 22 will be stably fastened in expandable body 1. When this has been done, wires, cables 18 are also fixed in
expandable body 1. Wires, cables 18 are cut off at the same level as conical screw 22.
According to the inventive idea a stable locking can be obtained in the following manner. When wires, cables 18 have formed a loop, the wire, cable ends are guided through partially cylindrical expandable body 1, which in its center 4 is provided with a conical screw 22. Upper part 4-0 of the cylindrical expandable body is divided into sectors 20 having slits, gaps 2,3 , between them, in the shape of a cross. The two wires, cables 18 are positioned opposite each other in the slits, gaps 2,3, which dimensionally fit the diameter of wires, cables 18. A condition of the functioning of the invention is, that expandable body 1 is surrounded by a ring-shaped surrounding element, in this case designed as a ring 17, jointly with a bar-shaped element 23, but a simpler embodiment, which only includes expandable body 1 and ring-shaped fastener 17 is of course possible. Expandable body 1 with the two wires, cables 18 is inserted into space 24, which is obtained between bar-shaped element 23 and double ring-shaped fastener 17, which abuts element 23 (see Fig. 1). When screw 22 of the device is driven into the expandable body, an expansion of upper part 4-0 of expansion body 1 takes place, expansion body 1 being locked against bar-shaped element 23. At the same time a locking of metal wires, cables 18, which are placed in expandable body 1, takes place.
By means of the present invention a complete stability between wire, cables 18 and supporting bar- shaped element 23 is obtained. Thus, this new device cannot slide along the bar of rotate around it. The rear part of the vertebra and consequently also the vertebra per se will in this way be firmly conncected
to the bar-shaped element. Several vertebrae can be fixed against the same bar-shaped element and in this way a stability between the vertebrae is obtained, which stability is a condition of the ability of the vertebrae to grow together.
It must be pointed out, that the present invention can be modified in a plurality of ways within the scope of protection set forth in the attached claims.