The current invention is directed to a bone fastener system; and more specifically to a bone fastener system having a stabilizing member connector that is offset from the axis of the fastener.
A multitude of orthopedic and neurological procedures use fasteners of one kind or another to connect one bone, or bone fragment, to another. Among these the most common use is in the connection of one vertebra of the human spine to another vertebra. In particular, the vertebrae of the human spine are positioned in a delicate arrangement that evenly distributes the force between the adjacent vertebrae and allows the spine to flex and twist with remarkable freedom. However, this delicate arrangement can be easily disrupted by a number of external stresses such as age, trauma, disease or general malformation.
Most conventional fastener systems operate through a plurality of bone fasteners interconnected by stabilizing rods. Although the specific design of these fasteners and rods have taken a number of different forms, in the vast majority of these systems the rod is held by a rod engagement seat that is positioned along the axis of the fastener. While this arrangement provides excellent support in helping fuse adjacent vertebrae in most cases, particularly in relatively simple deformities where the spine is still in a conventional conformation, these fasteners are not well engineered in complex cases where spinal fusion is combined with neurological decompression.
Specifically, it is often the case that there are several goals in performing an operation on an individual. For example, sometimes it is necessary to both decompress the nerves around a particular vertebral body and perform a fusion on a badly deformed spine. In this case, it is important that the rods interconnecting the vertebral bodies not encroach over the top of the spinal decompression because with the twists and bends found in some badly deformed spines it is possible that the metal of the rods can come close enough to impinge on the nearby nerves causing chronic pain and in some cases failure to fuse. However, in conventional systems, because the rod's position in relation to the vertebral fastener cannot be adjusted, it is necessary to radically bend and twist the rod to avoid this encroachment. Unfortunately, it is known that such radical bending and twisting can damage the crystalline structure of the metal in the rods, which in turn can lead to pre-stressing of the material and premature failure of the rods.
Accordingly, a need exists for an improved fastener system that allows for more flexibility in the positioning of the rod in relation to the vertebral fastener itself.
The current invention is directed to a bone fastener system incorporating an axially offset stabilizing member assembly.
In one embodiment of the invention the bone fastener is screw shaft having a head that interconnects with connector seat.
In another embodiment of the invention the connector seat is designed to secure a rod assembly therein.
In still another embodiment of the invention the connector seat is hingedly interconnected with the fastener through an armature such that the connector seat may be adjusted after fixation on either side of the fastener axis.
In yet another embodiment of the invention the length of the armature interconnecting the connector seat to the fastener may be adjusted radially such that the distance of the connector seat relative to the fastener may be changed.
In still yet another embodiment of the invention the connector seat is rotatably connected to the fastener such that the angle of the rod relative to the fastener may be adjusted.
Various examples of the present invention will be discussed with reference to the appended drawings. These drawings depict only illustrative examples of the invention and are not to be considered limiting of its scope.
a is a perspective view of one embodiment of a bone fastener assembly according to the present invention;
b is a side view of the bone fastener shown in
c is a top view of the bone fastener shown in
d is an exploded view showing the interconnection between the rod connector and the fastener body of the bone fastener shown in
Embodiments of a bone fastener assembly according to the present invention include a bone fastener and a connecting member for holding a stabilizing member, such as a rod or plate, mounted together via an armature that allows the connecting member to be offset from the longitudinal axis of the bone fastener and optionally also permits the bone fastener to pivot relative to a longitudinal axis of the assembly and the connecting member swivel about the longitudinal axis of the assembly. By allowing the connecting member to be offset and independently swivel about the longitudinal axis of the assembly, the bone fastener assembly provides an unprecedented degree of freedom in positioning an interconnecting rod to that assembly.
Bone Fastener: For the purposes of this invention, a bone fastener is defined as any device suitable for engaging a bone, including, a screw, pin, nail, bolt, staple, hook, etc.
Stabilizing Member: For the purposes of this invention, a stabilizing member is defined as any device suitable for interconnecting and stabilizing bone, including, plates, rods, etc.
Connecting Member: For the purposes of this invention, a connecting member may include any suitable member for assembling a construct for stabilizing bones of a patient such as a plate engaging stud, rod holder, etc.
The bone fastener assembly of the current invention is comprised of three fundamental parts: a bone fastener for anchoring the assembly to a bone, a rotatable connecting member for holding a stabilizing member such as a plate rod, etc., and an offset linkage interconnecting the bone fastener to the connecting member. The following description details exemplary embodiments of these bone fastener assembly of the current invention.
a to 1d illustrate a bone fastener assembly in the form of a pedicle screw assembly 10 coupled to a spinal rod 12. As shown, each pedicle screw assembly 10 includes a bone fastener in the form of a screw 14 having a “T” shaped head, a connecting member in the form of a rod holder 16, and a offset linkage in the form of a hinged armature 18 (
As best seen in
First, with regard to the exemplary embodiment shown in
As discussed above, although any suitable bone fastener may be used, in one embodiment the screw 14 includes an elongated shank 21 having a tip 22 at a distal end, a head 24 at a proximal end, and a longitudinal axis 20 extending therebetween. A thread 26 spirals around the shank such that the screw 14 may be threaded into a bone. As shown in
Likewise, although
To secure the rod within the passageway 30 any suitable securing means may be used. As shown in
Finally, interconnecting the connecting member 16 and the bone fastener 14 is an offset linkage 18. As shown in
Turning to the rod attachment end 42 of the offset linkage, as shown in
Although the engaging or tightening screw 48 engages the rod 12 between the arms 44 and 46 to prevent the rod from slipping from between the armatures, because the armatures are aligned parallel, absent some inner retaining means it would still be possible for the rod to move along the arms 44 and 46 inward toward the screw 14. Accordingly, some inner retaining means is required to ensure stable fixation of the rod 12 within the rod attachment end 42 of the offset Linkage 18. A number of exemplary alternatives are shown in
Finally, although all of the embodiments of the offset bone fastener system shown thus far have had a fixed offset distance, that is the offset distance is predetermined by the length of the offset linkage, it should be understood that the current invention also contemplates variable offset systems. First, in the embodiments shown in
Although the above has only focused on the construction of the bone fastener assembly and system of the current invention, it should be understood that the invention is also directed to a method of stabilizing a bone using the system described herein. For example using the embodiment shown in
Regardless of the specific embodiment, the screw 14, the connecting member/rod holder 16 and offset linkage 18 may be assembled intraoperatively by the surgical team or they may be preassembled. Preferably, the components are preassembled and locked in place to prevent disassembly in order to simplify their use in surgery.
While the specific embodiments used to illustrate the invention show the bone fastener assembly in the form of a pedicle screw useful to attach a rod to a vertebrae, the bone fastener assembly may connect to a bone in any of the variety of ways known in the art and may be utilized in any of the variety of constructs known in the art to stabilize bones at any location within the body.
Although examples of a bone fastener assembly and its use have been described and illustrated in detail, it is to be understood that the same is intended by way of illustration and example only and is not to be taken by way of limitation. The invention has been illustrated in the form of a pedicle screw assembly for use in assembling stabilizing constructs to connect vertebrae of the human spine. However, the bone fastener assembly may be configured with other kinds of fasteners and connecting members to assemble other kinds of constructs to stabilize bones and bone fragments at any location in the body. Accordingly, variations in and modifications to the bone fastener assembly and its use will be apparent to those of ordinary skill in the art. The various illustrative embodiments illustrate alternative configurations of various component parts such as screw seats, screws, pivot mechanisms, swivel mechanisms, and inserts among others. In most cases, and as will be readily understood by one skilled in the art, the alternative configuration of a component part in one embodiment may be substituted for a similar component part in another embodiment. Likewise, the various mechanisms illustrated for attaching the screw seat to the rod holder may be interchanged. Furthermore, throughout the exemplary embodiments, where component part mating relationships are illustrated, the gender of the component parts may be reversed as is known in the art within the scope of the invention. The following claims are intended to cover all such modifications and equivalents
The present application claims priority to U.S. Provisional Patent No. 60/024,629, filed Jan. 30, 2008, the disclosure of which is incorporated herein by reference.