An apparatus for correcting a spinal column having a damaged vertebrae

Abstract: An apparatus for correcting a spinal column having damaged vertebrae comprising a fastener (10) to be secured to adjacent vertebrae, said fastener including a shaft portion (12), preferably a pedicle screw, which fastener (10) has a receiving slot (16) to receive a distracting or compressing bar (18) at its free end, and a first locking element (26) including a threaded portion which may be secured onto the bar (18) disposed in that receiving slot (16), wherein a second locking element (28) is provided which can be fixed to the free end of said fastener (10) and which threadably receives said first locking element (26).

Description: The present invention relates to an apparatus for correcting a spinal column having damaged vertebrae according to the preamble of claim 1. Supporting means for the human spinal column including co-acting lamina hooks and pedicle screws are conventional. British patent 2 131 300 discloses a compressing apparatus, while U.S. patent 4,382,483 relates to a distracting apparatus. The bar bridges a number of vertebrae and does not allow to properly affect the vertebrae lying between the lamina hooks. WO 91/01691 discloses an apparatus for lacing vertebrae of a spinal column in which pedicle screws having slotted heads are used into which a bar is inserted. The legs of the slotted screw heads comprise an outer threaded portion, onto which a nut is screwed which abuts against the bar to fix it in position. EP 0 443 892 discloses a similar apparatus in which the slotted head of the pedicle screw includes an internal threaded portion receiving a solid screw which is brought into engagement with a fluted or, respectively, roughened bar to again fix the relative position of the bar and the individual pedicle screws. A ring surrounding the head of the pedicle screw prevents the legs of the screw head from spacing apart when the bar is fixed, otherwise the threaded engagement between the fixing screw and the pedicle screw head would be lost. A similar apparatus is shown in WO 90/09156. Still further, G 92 02 745 discloses an apparatus of the type referred to in which the pedicle screw is formed as a bipartite member, wherein the screw shaft includes a spherical end which is received in a ball-shaped recess which forms a receiving slot for the distracting or compressing bar. A fixing screw is screwed into an internal thread portion of the ball-shaped recess to urge the distracting bar onto the all. G 93 02 700 further teaches to provide a similar ball-shaped recess with an internal threaded portion onto which a head nut is screwed which includes a central pin which can be brought into engagement with the distracting or compressing bar for fixing. The support between the ball-shaped recess and the hook or the pedicle screw which is pivotal before the final fixing is completed results in the advantage that the fastener at one hand and the ball-shaped recess at the other hand may be angularly oriented with respect to each other. Accordingly, the bar has to be bent to a less extent which is true for a sagittal and lateral orientation. US-A-4 887 596 discloses a pedicle screw for use an internal fixation of the spine comprising a threaded shaft and a yoke for receiving a rod. The receiving slot has grooves triangular in cross section, and a plate-like locking element has two dove-tail portions to co-operate with the grooves so that the locking element is guided by the grooves if slided laterally into the receiving slot. The locking plate accommodates two threaded fasteners which are in engagement with a rod within the receiving slot. By the two fasteners the rod can be tilted. As far as the devices just referred to provide for screwing the primary locking element shaped as a cap nut or as a screw is screwed on the locking element, the distracting or compressing bar is initially fixed and a distraction or compression may be performed in a manner known per se. Subsequently, the primary locking element is completely locked to produce a rigid connection between the locking element and the bar. The known devices require primary locking elements which must be screwed onto the locking element for a sufficient length in order to obtain a rigid initial fixing of the bar. The range of laterally moving the bar is thus not particularly large. It is thus the object of the present invention to provide an apparatus for correcting a spinal column having damage vertebrae in which after inserting a distracting or compressing bar, this bar may be initially secured so that it has sufficient play within the locking element, but can be rigidly secured thereafter. The object referred to is solved by the features of the invention according to claim 1. According to the invention, the plate-like locking element is formed to be inserted into opposite grooves triangular in cross section which are provided in the opposing walls of the receiving slot. The grooves are closed at one end to prevent the locking element from falling out. The grooves may be wedge-shaped either alternatively or in addition to coact with the plate-shaped locking element in a clamping relation. Inserting the plate-shaped locking element is relatively simple which facilitates using the apparatus according to the invention for the surgeon. The threaded portion accommodated by the locking element is to rigidly secure the bar within the receiving slot. Prior to such fixation the bar is prevented from being moved out of the receiving slot, however, may move axially in the receiving slot. The invention is hereinafter described in more detail with reference to the drawings which show: Fig. 1 is a sectional view of a pedicle screw including a distracting or compressing bar; Fig. 2 is a sectional view of Fig. 1 along line 2-2; Fig. 3 is an end view of the pedicle screw of Fig. 1; Fig. 4 is a sectional view of the locking elements for a pedicle screw according to Figs. 1 and 2; Fig. 5 is a top view of the elements shown in Fig. 4 in the direction of arrow 5. The pedicle screw 10 comprises a screw shaft 12 and a head 14 which outer periphery is substantially cylindrical and includes a central receiving slot 16 which is open towards the top end. The bottom of the slot has a spherical cross section to closely fit a distracting or compressing bar 18. Above the bar 18 the side walls of the slot 16 are formed with grooves 20, 22 having a triangular cross section. Fig. 1 shows that the upper side of the triangle is perpendicularly oriented with respect to the longitudinal axis of the slot. Fig. 2 shows that the grooves 20, 22 are closed at one end and include a slope. Figs. 4 and 5 show a combination 24 of a threaded portion 26 and a locking element 28. The locking element 28 includes a pair of faces 30, 32 being triangular in cross section which are shaped to fit into the grooves 20, 22. However, there may be provided a slight clamping action in order to fix the element 28 within the grooves 20, 22. The element 28 has a central threaded bore for receiving the threaded portion 26 which is defined by a fixing screw having a tip 34 at the end of the shaft and an opposite head which is provided with an external as well as an internal hexagonal configuration 38. When the combination 24 will be inserted into the grooves 20, 22 after the bar 18 has been inserted in the slot 16, the bar has sufficient play, but is secured from being moved out of the slot 16. After completing the distraction or compression, the threaded portion 26 is actuated until the tip 34 firmly contacts the bar 18 to complete locking the bar to the head of the pedicle screw 10. As mentioned before, the element 28 is inserted into the grooves 20, 22 from one side thereof. However, a plate may be conceived which is placed from above into the slot 16, wherein its length side is oriented toward the length side of the slot 16. Subsequently, the plate is turned about some 90° so that the sides thereof enter the grooves 20, 22. It should be understood that lamina hooks, for example may be provided as anchoring means instead of the pedicle screws, which hooks are then provided with a head similar to that of the pedicle screws shown. It should be further understood that the shanks of the pedicles screws may be separate with respect to the heads which can be shaped to define ball-shaped recesses for receiving balls formed at the upper end of the screw sharks.This similarly applies for lamina hooks having a ball.

Claims: An apparatus for correcting a spinal column having damaged vertebrae, comprising fasteners (10) to be secured to adjacent vertebrae, each of the fasteners (10) including a shaft portion (12) preferably a pedicle screw, and a head (14) at one end of the shaft portion (12), the head (14) having a receiving slot (16) open at one end of the head (14) opposite to the shaft (12) and adapted to receive a distracting or compressing bar (18), the receiving slot (16) having a bottom and opposite inner walls, grooves (20, 22), triangular in cross section formed in the receiving slot (16) above the bottom thereof, a plate-like locking element (24) adapted to be accommodated by the grooves (20, 22), the locking element (24) including a threaded bore to accommodate a threaded portion (26) adapted to engage the bar (18) disposed in the receiving slot (16), characterized in that the triangular grooves (20, 22) are formed and are oppositely located in the opposite walls of the receiving slot (16) in order to hold the locking element (24) against movement towards the shaft portion (12), in that the grooves (20, 22) are closed at one end thereof and in that the grooves (20, 22) are sloped with respect to the axis of the bar (18) within the receiving slot (16). The apparatus of claim 1, characterized in that the locking element (24) is received in the grooves (20, 22) in a clamping manner. The apparatus of claim 1, characterized in that the side of the groove wall facing the bottom extends perpendicular with respect to the longitudinal axis of the slot (16).

Inventors: METZ-STAVENHAGEN PETER DR, ROBIONECK BERND, METZ-STAVENHAGEN, PETER, DR., ROBIONECK, BERND
Applicants: HOWMEDICA GMBH
Application year: 1995
Main classification: A61B17
IPC codes: A61B17