Apparatus for bracing a plurality of vertebras of the human spine

Abstract: An apparatus (12) for bracing a plurality of vertebras of the human spine, comprising at least two pedicel screws (16) having an annular head (34) including a slot (36) which extends into the opening and including internal thread portions, a securing screw (38) to be screwed in said slot, a relatively stiff threaded rod (14) to be inserted into the opening in the head of the pedicel screw and secured by said securing screws, and adjusting nuts (18) screwed on said rod and cooperating which said head.

Description: The present invention relates to an apparatus for bracing a plurality of vertebras of the human spine according to the preamble of claim 1. Known supporting means operate with so-called lamina hooks which are disposed on a threaded rod. A compressing means is disclosed in British patent 2 131 300. A distracting means is disclosed in US 4 383 438. The threaded rod bridges a plurality of vertebras and is not suited to act on vertebras which are disposed between the lamina hooks. The thread of the rod is used to fix the lamina hooks. Before using the supporting means a distraction or, respectively, compression has to be provided by means of an additional device. German 90 06 646 U1 discloses an apparatus in which a lamina hook is replaced by a clamp-shaped holding member having a pair of legs of which one can be bent with respect to the other. Thereby the giapophysis of the vertebras may be used as anchoring points for the compressing and distracting apparatus. German 88 02 112 U1 teaches a supporting device for the human spine, according to which the so-called pedicel screws are screwed in the pedicel body of the vertebras. The pedicel screws cooperate with tensioning means which bridge across one or more vertebras to introduce forces between the vertebras. The known device affords a primary stabilization of the vertebras with respect to all degrees of freedom. However, when a number of vertebras of a non-traumatic spine for example, shall be repositioned, separate means necessary to perform the reposition before the known supporting device may be effectively used. EP-A-0 452 792 discloses an apparatus which both allows a fixation of a stiff threaded rod to pedicle screws and a repositioning of the verterbras as well. To this purpose the slotted head of the pedicle screws has conical extensions on both front sides thereof, and nuts to be screwed onto the rod have inner conical portions cooperating with the conical extensions to retain the nut within the throughgoing opening of the head of the pedicle screws. WO 91/01691 discloses an apparatus for bracing vertebras of the human spine, comprising pedicel screws having slotted heads to receive a rod. The legs of the slotted screw heads include an outer thread on which a nut is screwed which contacts the rod to fix a predetermined position. EP 0 443 892 discloses a similar device comprising a pedicel screw, the slotted head thereof including internal threaded portions for receiving a fixing screw which is brought into engagement with a serrated or similarly roughened rod to fix the relative position of the rod and the individual pedicel screw. A ring disposed around the head of a pedicel screw is provided so that the legs of the screw head do not spread apart while fixing the rod, as otherwise the engagement between the fixing screw and the screw head may be lost. A similar apparatus is disclosed in WO 90/09156. Again, the devices last mentioned require separate means for repositioning, thus being suited to maintain a repositioned condition, but not suited to perform repositioning. It is the object of the present invention to provide an apparatus which is suited to reposition the vertebras of the human spine as well as to support the vertebras in the repositioned position thereafter. The object is solved by the features of claim 1. According to the invention, the apparatus uses a threaded rod as it has become known as a distracting rod (in combination with lamina hooks). The thread of the rod, however, is not only used to fix the pedicel screws, but further is used to reposition the vertebras in that an adjusting nut sitting on the threaded rod is turned with respect to the head of the pedicel screw and thus the vertebra has obtained the desired position. By means of the apparatus according to the invention a spine portion is not only distracted or compressed, but individual vertebras can be effectively positioned with respect to each other. To this end the threaded rod is designed to be relatively stiff and has a diameter between 7 to 8 mm, for example. On the other hand the rod must be bent to be implanted close to the spine along a bent spine portion. This is facilitated by the design of the pedicel screw heads having slots for receiving the threaded rod. To hold the rod in the slot, a securing screw is provided. Whereas the screw in the pedicel screw head according to EP 0 443 892, for example, axially fixes the rod, the securing screw of the present invention is merely used to prevent a deflection of the rod out of the receiving slot. After resetting, the adjusting nut must be fixed on the threaded rod. This can be obtained by means of a suitable counter-nut. Still further, it is possible, to provide the adjusting nut and the front faces of the pedicel screw head with a rotary safety means in form of a toothing or another irregularity cooperating in a clamping fashion. In both cases the nuts are merely fixed by a frictional force. According to a further embodiment of the invention, however, the head of the pedicel screw has a width smaller than the diameter of the securing screw, whereas at least one front face of the adjusting nut has a recess cooperating with the securing screw. Preferably, the adjusting nut includes a plurality of peripherally spaced indentations, wherein the final rotary position of the nut is such that the securing screw cooperates with the indentation. This affords a positive locking of the adjusting nut resulting in a precise rotary locking which cannot be loosened. The pedicel screws must take up relatively large forces. There is the danger that a pedicel screw breaks out of the bone, primarily when the available bony substance does not provide a sufficiently rigid seat in the vertebra. According to an embodiment of the invention, a mounting strap is attached to the shaft of the pedicel screw laterally extending therefrom, which strap includes an opening for receiving a spongiose screw. The strap has, for example, a pair of openings, wherein one opening receives the shaft of the pedicel screw, while the other opening disposed at the other end of the strap, for example, receives a spongiose screw which is screwed into the vertebra. In this manner, the pedicel screw is laterally stabilized and can receive sub-stantial forces. According to an alternate embodiment of the invention, a mounting strap may be provided to the shaft of the pedicel screw extending therefrom, which strap has a blade or the like to be mounted in the vertebra. The blade is preferably integral with the strap. The blade is beaten into the vertebra wherein the strap may additionally include a hole for receiving a spongiose screw which is screwed into the vertebra. In some cases, a vertebra is displaced with respect to the adjacent vertebra. When the pedicel screw is completely screwed in, it cannot be connected any more with the threaded rod. To accomplish a connection, the pedicel screw is partly screwed into the vertebra bone. According to an embodiment of the invention, the head of the pedicel screw is then rotatably mounted on the screw shaft so that by rotating the shaft the vertebra can be pulled up to the threaded rod for resetting. Preferably the shaft includes tool engaging faces adjacent the head to rotate the shaft of the screw in the desired manner. In case of very specially displaced individual vertebras, not even the features referred to above are suffient. According to a further embodiment of the invention, the upper end of the pedicel screw shaft is ball-shaped, while the pedicel screw head is defined by a ball-engaging cage including a slot for the rod. The cage can be arbitrarily positioned with respect to the shaft of the screw, but can exert a tensioning force to the screw shaft when being screwed in the vertebra. According to both embodiments just referred to, the threaded rod is inserted through a slot of the pedicel screw head, wherein a securing screw referred to several times prevents the rod from sliding out of the slot. Alternatively a closed passage may be provided in the head of the pedicel screw as it is known per se. In addition to the pedicel screw the apparatus of the present invention provides a hook cooperating with a lamina of a vertebra. Those lamina hooks are generally known. According to the invention, however, the lamina hook is provided with a slotted receiving portion to insert the threaded rod. The slot has threaded portions again to secure the rod in the receiving slot. Preferred embodiments of the invention will now be described by way of example with reference to the accompanying drawing. Fig. 1 schematically shows an apparatus according to the invention to be used as a distracting system, Fig. 2 schematically shows an apparatus according to the invention used as a compressing system, Fig.3 shows a pedicel screw for the apparatuses according to Figs. 1 and 2, Fig. 4 shows the pedicel screw of Fig. 3 cooperating with a threaded rod, Fig. 5 schematically shows a side view of a further embodiment of a pedicel screw for the apparatuses of Fig. 1 and 2, Fig. 6 shows a side view of the pedicel screw of Fig. 5 rotated about 90°, Fig. 7 shows a plain view of the pedicel screw of Fig. 5, Fig. 8 shows a side view of an adjusting nut of the apparatus of Figs. 1 and 2, Fig. 9 shows a stabilizing strap for the apparatus of Figs. 1 and 2, Fig. 10 shows a further embodiment of a stabilizing strap of the apparatus of Fig. 1 and 2, Fig. 11 shows a section of a lamina hook for the apparatus of Figs. 1 and 2, Fig. 12 shows a plain view of the hook of Fig. 11, Fig. 13 shows a side view of a further embodiment of a pedicel screw for an apparatus according to the invention, Fig. 14 shows a side view of the pedicel screw of Fig. 13 turned about 90°, Fig. 15 shows a side view partly in section of a further embodiment of a pedicel screw for an apparatus according to the invention and Fig. 16 shows a side view of the pedicel screw of Fig. 15 turned around 90°. Fig. 1 shows a bent spine portion 10 wherein the individual vertebras shall be distracted by means of a distracting system 12. The system comprises a relatively stiff threaded rod 14 having a diameter of 6 to 9 mm, preferably 7 to 8 mm. It cooperates with an individual pedicel screw 16 screwed in the vertebras. Details of the screws are shown in the following figures. The threaded rod 14 is received in slots of the pedicel screw heads and a plurality of adjusting nuts 18 is disposed on the rod 14, at least one nut each for a pedicel screw 16. Stabilizing latches 20 cooperate with the pedicel screws, which latches include a hole 22 in a distance from the pedicel screw to receive a spongise screw screwed in the vertebra. By means of the adjusting nut 18 a pedicel screw screwed in the vertebra may be displaced relative to the rod 14 and thus with respect to the vertebra receiving the screw. By means of the adjusting nuts 18 the vertebras of the portion 10 may be thus adjusted to accomplish a distraction. The spine portion 30 shown in Fig. 2 comprises a compressing means including components identical with those shown in the system 12 so that identical components carry identical reference numerals. To reduce the bending of the spine portion 30 a tension force must be exerted on the vertebras to straighten the bent threaded rod 14. This is accomplished by adjusting the individual pedicel screws 16 as described in Fig. 1. In the following the com-ponents of the system referred to are described in more detail. Fig. 3 shows a pedicel screw 16a having a shaft 32 and an annular head 34. The head 34 includes a slot 36 in which the rod 14 is inserted. A securing screw 38a cooperating with threaded portions in the slot 36 holds the threaded rod 14 in the slot 36. Fig. 4 shows adjusting nuts 18a located on either side of the head 34 to displace the screw 16a along the rod 14. In the embodiment of Figs. 5 and 6 the pedicel screw 16b has a relatively narrow head 34b so that the securing screw 38b laterally projects. This is shown by the dashed line in Fig. 7. when an adjusting nut 40 according to Fig. 8 is used, which nut is provided with indentations 42 on the opposite front faces thereof, the nut 40 can be secured to the rod 14 when an indentation 42 of the screw 38b cooperates with the adjusting nut 38b. Fig. 9 shows a mounting strap. The plate-shaped strap 20 includes a first hole 44 receiving the shaft of a pedidel screw. A second hole 22 receives a spongiose screw as mentioned before. Fig. 10 shows an alternate embodiment 20a of a stabilizing latch, again comprising a hole 44a for a pedicel screw and a hole 22a located substantially in the center for receiving a spongiose screw. Fig. 10 further shows a blade 46 integrally shaped on the end opposite the hole 44a which blade is driven home in the vertebra. Figs. 11 and 12 show a lamina hook 50 comprising a hook portion 52 and a receiving portion 54 including a slot 56. The slot 56 receives a threaded rod such as the rod 14 shown in Figs. 1 and 2. Threaded portions as indicated at 58 in Fig. 11 are provided inside the slot 56 to receive a securing screw not shown to hold the rod in the slot 56. The position of the rod in the slot 56 is determined by the position of the securing screw not shown, wherein a relative position between the hook 50 and the rod is possible to a limited extent. Figs. 13 and 14 show a pedicel screw 16c comprising a shaft 32c and an annularly closed head 34b through which a rod 14 extends. A fixing screw 60 in the head 34b is used to fix the threaded rod 14. However, adjusting nuts may be used as mentioned before. According to the embodiment of Figs. 13, 14 the shaft 32c is rotatably mounted in the head 34b. Accordingly, a circular blind bore 62 holds a ring 64 cooperating with an annular groove 66 in the shaft 32. Tool faces 68 facilitate a rotation of the shaft 32c relative to the head 34c when it fixedly sits on the rod 14 for example. It should be understood that the head 34c may provide a slot as shown in Figs. 3 to 7 for example. In the embodiment of Figs. 15 and 16 a pedicel screw 16d is provided comprising a shaft 32d which upper end is formed as a ball 50. A cage 72 cooperates with the ball, the cage further having a passage 74 to receive a threaded rod 14. Furthermore, the cage 72 has threaded portions to receive a securing screw 38c. This allows to rotate the shaft 32, wherein tool faces 68d are provided. Furthermore, the shaft 32d may be pivoted relative to the cage 72 in a limited angle.

Claims: An apparatus for bracing a plurality of vertebras of the human spine, comprising at least two pedicle screws (16, 16a, 16b, 16d) having a head (34a, 34b, 34c, 34d), the head (34a, 34b, 34c, 34d) having an opening therethrough and an outer circumference around the opening, a slot (36, 36b) extending from the circumference of the head (34a, 34b, 34c, 34d) into the opening, a relatively stiff threaded rod (14) to be inserted into the opening in the head of the pedicle screws (16, 16a, 16b, 16c, 16d) through the slot, and adjusting nuts (18, 18a, 40) screwed on the rod (14) and cooperating with the head (34, 34b, 34c, 72), characterized in that the slot (36, 36b) includes an internal thread portion, and a securing screw (38, 38a, 38b, 38d) is screwed in the slot (36, 36b). The apparatus of claim 1, wherein the threaded rod (14) has a diameter of between 6 to 9, preferably 7 to 8 mm. The apparatus of claim 1 or 2, wherein the head (34b) of the pedicel screw (16b) has a width smaller than the diameter of the securing screw (38b) and wherein the adjusting nut (40) has a recess (42) provided on at least one front face cooperating with said securing screw (38b). The apparatus of one of claims 1 to 3, wherein a laterally extending mounting latch (20) may be attached to the shaft of the pedicel screw (16) which latch has an opening (22) to receive a spongiose screw. The apparatus of one of claims 1 to 3, wherein a laterally extending mounting strap (20a) is attached to the shaft of the pedicel screw (16) which strap has a blade (46b) or the like to be mounted in the vertebra. The apparatus of claim 5, wherein the blade (46) is integrally formed on the strap (20a) preferably at the free end thereof. The apparatus of one of claims 1 to 6, wherein the head (34c, 72) of the pedicel screw (16c, 16d) is rotatably mounted on the shaft (32c, 32d). The apparatus of one of claims 1 to 6, wherein the upper end of the shaft (32d) of the pedicel screw (16d) is shaped as a ball (70) and wherein the head of the pedicel screw is formed by a cage (72) receiving said ball (70) including a passage for the threaded rod (14). The apparatus of one of claims 1 to 8, wherein a lamina hook (50) is provided comprising a slotted receiving portion (54) for the threaded rod (14) and comprising threaded portions (58) in the receiving slot to receive a securing screw fixing the threaded rod in the slot (56).

Inventors: METZ-STAVENHAGEN PETER DR MED, METZ-STAVENHAGEN, PETER, DR. MED.
Applicants: HOWMEDICA GMBH
Application year: 1993
Main classification: A61B17
IPC codes: A61B17, A61F2