Spinal fixation device with rotatable connector

Abstract

A spinal fixation device for securing two stabilizing rods to a bone has a threaded shaft and a first rod coupling and a second rod coupling. The first rod coupling is connected to the threaded shaft. The first rod coupling has a cavity that is open toward a top of the first rod coupling. In a neutral position of the first rod coupling, the first rod coupling extends symmetrically about a longitudinal axis of the threaded shaft. The second rod coupling is rotatably connected to the first rod coupling about a rotational axis. In the neutral position of the first rod coupling, the rotational axis is at an angle that is not perpendicular to the longitudinal axis of the threaded shaft. This allows independent manipulation of the two rods through different axial planes at any single bone fixation point.

Description

TECHNICAL FIELD

[0001] The present invention relates to a spinal fixation device, such as a pedicle screw, for use in spinal surgery, including cervical, thoracic, lumbar, pelvic and posterior cranial surgery. In particular, the present invention relates to a fixation device, such as a pedicle screw, transpedicular screw, pelvic bolt, cranial fixation device, having a primary rod fastening element that is rotatably connected to a secondary rod fastening element having an aperture, such that two rods can be mounted to a single device and the position of the rods relative to each other can be adjusted.

[0002] This allows the primary rod to be fastened in a polyaxial plane and the secondary rod to be fastened in a uniaxial plane. This arrangement allows the highest degree of biomechanical stability while providing the necessary level of patient safety and surgeon preference. The arrangement of the present invention allows the primary and secondary rods to be attached to a single bone fixation point via the device.

[0003] In this specification, the terms pedicle screw, fixation device, spinal implant are used interchangeably in order to illustrate the invention. The invention can be used throughout the spine, pelvis and cranium, and can also be used to modify the size of the implant. BACKGROUND

[0004] Pedicle screws and fastening rods are used for spinal fusion and spinal fixation to add additional support and strength to the fusion as the spine heals. It is also used for various reasons and surgeon preference, i.e. whenever rigid fixation in the spine is required. Depending on the diagnosis and surgeon preference, the pedicle screw can be placed in the spinal segment that needs to be fused or stabilized. In more modern times, this usage has been extended to include pelvic and cranial instrumentation. The screw is used with a rod that prevents movement and achieves fixation, whether it is for bone fusion, trauma, or tumor. The etiology behind the diagnosis can be degenerative disease, deformity, trauma, or tumor.

[0005] The head of a typical pedicle screw (connection member) can be formed as a U-shaped or tulip element, in which the rod is placed. A set screw is then tightened on top of the tulip element to fasten the rod to the pedicle screw. It is often beneficial to use two parallel rods to additionally support the vertebrae. In modern spinal surgery, i.e. in orthopedic, tumor, trauma, or revision surgery, there are multiple reasons to require additional fixation rods.

[0006] Furthermore, the rigidity / stability in the traditional pedicle screw arrangement is insufficient, resulting in non-union of the bone fusion (pseudoarthrosis), requiring revision surgery, patient discomfort, or hardware failure. Various attempts have been made to construct a pedicle screw that can connect to two rods simultaneously. For example, Picetti, U.S. Patent Application Publication No. 2004 / 0111088, discloses a double-ended pedicle screw having a single head with multiple channels for connecting multiple rods. The problem with this and other similar solutions is that, depending on the shape of the head, the two rods must always be in a fixed position relative to each other. Since the channels in the head are fixed, there is no room for adjustment of the position or angle of the rods relative to each other. Furthermore, the fixed position of the screw does not allow the screw and rods to move during flexion and extension of the spine. This can cause patient discomfort. It can also be a problem in surgery, as it reduces the surgeon's choice of implant and can be incompatible with the patient's surgical anatomy.

[0007] Pedicle screws with adjustable pivotable heads have also been developed, such as the pedicle screw shown in Erbulut et al., U.S. Patent No. 10,188,431. But the head in this device pivots only about a horizontal axis defined by the post that fastens the head to the screw. This angle is not ideal because the superior corner of the screw head, by its protruding nature, can cause irritation to the patient during movement. Furthermore, depending on the surgeon and the position of the screw, it can be difficult for the surgeon to reach the angle at which the second head is located. That is, because of the angle (or lack thereof) of the second head relative to the primary head, this can create a problem in which the superior corner can impinge on important neural elements.

[0008] In both of the above examples, there are design features that are inconvenient to use and do not guarantee intraoperative safety. The chances of the fixation device conforming to the surgical anatomy of different patients are at best very low. At the same time, in addition to the problem of the orientation angle of the primary and secondary rod tulip elements, there is a high possibility of nerve injury.

[0009] The connection assembly disclosed in Simonson, U.S. Patent No. 5,643,263, has been used to connect rods to pedicle screws with adjustable angles. This has proven to be very useful in practical applications, and it would be desirable to have a system that has this angle adjustability as well as the ability to connect two rods at once. SUMMARY

[0010] Accordingly, it is an object of the present invention to provide a pedicle screw that allows two rods to be connected to a single screw, where the connectors for the rods are rotatable relative to each other, and the connectors are set at optimal angles that ensure surgical efficiency, patient comfort, and safety.

[0011] These and other objects are achieved by a pedicle screw for fastening a stabilizing rod to a spinal segment or pelvis / skull, the pedicle screw comprising a threaded shaft configured for fastening to a bone and a first rod coupling connected to the threaded shaft, the first rod coupling having a sidewall and a cavity for receiving a rod. The threaded shaft has a longitudinal axis and, in a neutral position of the first rod coupling, the first rod coupling extends symmetrically around the longitudinal axis. The cavity opens towards a top of the first rod coupling and has a thread at the top into which a set screw is screwed to cover the cavity and secure the rod in the cavity. A second rod coupling is rotatably connected to the first rod coupling around a rotation axis. In the neutral position of the first rod coupling, the rotation axis of the second rod coupling is at an angle a that is not perpendicular to the longitudinal axis of the screw, so that the second rod coupling is tilted towards the first rod coupling rather than being disposed completely parallel. The optimal tilt angle is preferably 5 to 15 degrees from perpendicular, or 70 to 85 degrees from the longitudinal axis. By tilting the second rod coupling towards the first rod coupling, the surgeon has easier access to the second rod coupling during surgery. The surgeon has easier access to the tilted rod coupling when it reaches above the spine compared to a parallel arrangement. This results in a more efficient, effective and safer surgery.

[0012] Furthermore, the present invention allows the primary rod to be fastened by a conventional polyaxial top-loading tulip (connector) and allows the secondary rod to be fastened by an attached rotatable closed uni-axial orifice style connector. In this preferred embodiment, the first rod coupling is connected to the threaded shaft so as to be polyaxially movable at least while the rod is being arranged. A locking plate can be provided in the first rod coupling so that inserting the rod in the cavity and tightening the set screw into the rod pushes the rod against the locking plate and prevents any axial movement of the first rod coupling after the screw is tightened, thereby locking the first coupling in the neutral position. To achieve this, the threaded shaft has a ball connector and the first rod coupling has a recess for receiving the ball connector to polyaxially connect the first rod coupling to the threaded shaft. Upon tightening the set screw down on the rod, the locking plate then presses against the ball connector to prevent any movement of the first rod coupling around the ball connector when the set screw is fully tightened. An example of a suitable ball connector / locking plate arrangement is disclosed in U.S. Patent Application Publication No. 2017 / 0020573, the disclosure of which is incorporated herein by reference.

[0013] In one embodiment, the second rod coupling is formed from a connecting plate and a C-shaped rod retaining element having a cavity for the rod and an aperture for a set screw. The C-shaped rod retaining element is fixedly attached to the connecting plate. The connecting plate is rotatably connected to one side of the first rod coupling and has a grooved or textured surface that mates with a grooved or textured surface on the first rod coupling so that when the rod is inserted through the C-shaped retaining element and the set screw is tightened in the aperture, the rod will press the grooved surface of the connecting plate against the grooved surface of the first rod coupling to prevent the second rod coupling from rotating relative to the first rod coupling and secure the rod couplings in place.

[0014] One advantage of the present invention is that the primary polyaxial coupling can be used to sequentially secure the first rod to all other fixed points head-to-tail. The secondary monoaxial coupling can then be manipulated by rotating about the fixed axis to safely "thread" the secondary rod around important neural elements, one screw at a time. This would be a standard technique used by spine surgeons to augment the support of the secondary rod device; it is currently not possible to do this because two rods need to be laid down simultaneously in a polyaxial manner.

[0015] An advantage of the present invention is that both rod couplings are adjustable during the placement of the rods and remain immobile after the set screws are tightened. The present invention allows the use of a single screw shaft with two adjustable connectors, whereas in the past a second connector had to be attached separately along the rod at a distance. The specific angle of the second rod coupling relative to the first rod coupling allows for safer and more efficient placement of the rods and tightening of the set screws because the surgeon has easier access to them. BRIEF DESCRIPTION OF DRAWINGS

[0016] Other objects and features of the present invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. However, it is to be understood that the drawings are designed solely for purposes of illustration and not as a definition of the limits of the invention.

[0017] In all of the drawings, like reference numerals refer to like parts throughout the several views:

[0018] Figure 1 A spinal fixation device of the present invention is shown;

[0019] Figure 2 A side view of a connecting plate connecting a first rod coupling and a second rod coupling is shown;

[0020] Figure 3 A front view of the connecting plate is shown;

[0021] Figure 4 A rear view of the connecting plate is shown; and

[0022] Figure 5A cross-sectional view of a spinal fixation device in use is shown with a rod passing through the device. DETAILED DESCRIPTION

[0023] Reference will now be made in detail to the drawings, Figure 1 A pedicle screw 10 of the present invention is shown. The pedicle screw 10 is comprised of a shaft 11 having a helical thread 12 for attachment to a bone, a first rod coupling head 20, and a second rod coupling head 50. The first rod coupling head 20 is in the form of an open connector having a sidewall 22, a cavity 21 for receiving a rod, and a thread 23 near the top for receiving a set screw. The shaft 11 has a longitudinal axis A passing therethrough. The second rod coupling head 50 is connected to the first rod coupling head 20, the second rod coupling head 50 being connected to a connecting segment 27 of the first rod coupling head 50 by a connecting plate 60. The connecting plate 60 is connected so as to be free to rotate about a rotational axis R relative to the connecting segment 27. The rotational axis R is not perpendicular to the longitudinal axis A, but is disposed at an angle a of about 83 degrees to the axis A, or preferably 70-85 degrees to the axis A. A C-shaped rod holder 51 is fixedly connected to the connecting plate 60 and forms the second rod coupling head 50 with the connecting plate 60 so that the second rod coupling head 50 is rotatable relative to the first rod coupling head 20. The second rod coupling head 50 has a cavity 52 in which a second rod can be fastened and a hole for a set screw to fasten the second rod to the second rod coupling head 50.

[0024] Figures 2-4 The internal structure of the connecting plate 60 is shown. This structure is identical to that used in U.S. Patent No. 5,643,263, the disclosure of which is incorporated herein by reference.

[0025] The connecting plate 60 has a front side 62 having an engagement groove 64 for receiving a rod and a rear side 66 having a variable angled slotted surface 72. An opening 68 is provided in the middle of the connecting plate 60 for connecting the connecting plate 60 to the first rod coupling head. The first rod coupling head 20 has a connecting segment 27 having a variable angled slotted surface 28 facing the variable angled slotted surface 72 so that when the two surfaces 28, 72 are pressed against each other, rotation of one part relative to the other is prevented due to the frictional contact of the surfaces against each other.

[0026] In Figure 5The fully assembled pedicle screw 10 is shown in cross-section. Here, the interior of the first rod coupling shows a locking plate 25 provided in the bottom of the cavity 21. The locking plate 25 abuts the ball head 13 of the shaft 11 provided in the recess 29 and allows polyaxial movement of the first coupling 20 relative to the shaft 11. The locking plate 25 can be held in place by a spring (not shown). When the set screw 40 is tightened in the thread 23 of the first rod coupling 20, the rod 48 is pressed down onto the locking plate 25, which then presses against the ball head 13 and prevents any axial movement of the first rod coupling 20 relative to the shaft 11. Upon full tightening of the set screw 40, the first rod coupling 20 is locked in a neutral position on the shaft 11, in which the first rod coupling 20 extends symmetrically around the longitudinal axis of the shaft 11.

[0027] The second rod coupling 50 is connected to the connecting segment 27 of the first rod coupling 20 via a shaft element 29 through an opening 68 in the connecting plate 60 and allows the connecting plate 60 to rotate freely around a rotation axis R relative to the connecting segment 27 when not stressed. In the neutral position of the first rod coupling 20, the rotation axis R of the second rod coupling 50 does not run perpendicular to the longitudinal axis A of the shaft 11, but rather extends obliquely at an angle a of between 70 and 85 degrees to the axis A. The preferred angle a of the rotation axis R relative to the longitudinal axis A is approximately 83 degrees, or 7 degrees off perpendicular.

[0028] A second rod 55 is provided in the cavity 52 of the second rod coupling 50 and is held in place by a set screw 58 through a hole 56 in the holding element 51. Upon tightening of the set screw 58, the connecting plate 60 with the variably angled slotted surface 72 presses against the connecting segment 27 and prevents any further rotation of the second rod coupling 50 relative to the first rod coupling 20. Thus, upon tightening of both set screws, the rod couplings are fixed in place and no relative movement is allowed. Like the primary set screw (set screw 40), the set screw 58 is loaded in a top-down manner. The set screw 58 is also slightly tilted back towards the primary set screw to allow safe fastening to the second rod 55. This makes the pressure required in this action safe and directed away from important neural elements.

[0029] While in the foregoing only some specific embodiments of the application have been illustrated and described, it will be evident that various modifications and changes can be made without departing from the spirit and scope of the application.

Claims

1. A spinal fixation device for fastening a stabilizer bar to a bone, comprising: A threaded shaft configured to be fastened to the bone, the threaded shaft having a longitudinal axis, a proximal end, and a distal end; A first rod connector, connected to the proximal end of a threaded shaft and configured to rotate multi-axis relative to the threaded shaft, has sidewalls and a first cavity for receiving a first rod, the first cavity opening toward the top of the first rod connector, wherein a midpoint position of the first rod connector is defined when the first rod connector extends symmetrically about the longitudinal axis of the threaded shaft; and The second rod connector has a first end rotatably connected to one of the sidewalls of the first rod connector about a rotation axis so as to rotate uniaxially relative to the first rod connector, and has a second end opposite to the first end, and a second cavity between the first end and the second end, the second cavity being configured to receive the second rod. When the first rod connector is in the neutral position, the rotation axis is set at an angle of 70 to 85 degrees to the longitudinal axis of the thread shaft away from the far end of the thread shaft, and the rotation axis passes through the first cavity and extends through the center of the second cavity, so that the second rod connector rotates symmetrically about the rotation axis.

2. The spinal fixation device as claimed in claim 1 further includes a locking plate disposed in the first rod connector, such that inserting the first rod into the first cavity and tightening the stop screw into the first rod will push the first rod against the locking plate and prevent any axial movement of the first rod connector, thereby locking the first rod connector in the neutral position.

3. The spinal fixation device of claim 2, wherein the threaded shaft has a ball connector, and the first rod connector has a recess for receiving the ball connector to connect the first rod connector to the threaded shaft.

4. The spinal fixation device of claim 1, wherein the second rod connector is formed by a connecting plate and a C-shaped retaining element, the second rod connector having a second cavity and the C-shaped retaining element having a closed orifice formed together with the connecting plate for the second rod, the C-shaped retaining element having an orifice for receiving a stop screw, the C-shaped retaining element being attached to the connecting plate, wherein the connecting plate is connected to one of the sidewalls of the first rod connector and has a first variable surface that mates with a second variable surface on the first rod connector, such that when the second rod is inserted through the C-shaped retaining element and the stop screw is tightened in the orifice, the second rod presses the first variable surface of the connecting plate against the second variable surface on the first rod connector to prevent the second rod connector from rotating relative to the first rod connector.

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