Spinal implant fixation assembly

An orthopedic fixation device for securing a rod to a bone is provided. The fixation device includes a receiver with two legs, a pocket defined between the legs, an anchor including a head, and a seat structure that mounts within the receiver. The seat structure includes a top seat for receiving the rod and a bottom seat for receiving the head of the anchor. The top seat includes two legs defining a pocket and first and second raised ridges that are spaced apart from one another. The legs each define a recessed portion extending between the two raised ridges.

TECHNICAL FIELD

This invention pertains to vertebral stabilization. Specifically, the invention provides intervertebral connection systems suited for stabilization of the spine.

BACKGROUND

The spinal column is a highly complex system of bones and connective tissues that provides support for the body and protects the delicate spinal cord and nerves. The spinal column includes a series of vertebrae stacked one atop the other, each vertebral body including an inner or central portion of relatively weak cancellous bone and an outer portion of relatively strong cortical bone. Situated between each vertebral body is an intervertebral disc that cushions and dampens compressive forces experienced by the spinal column. A vertebral canal containing the spinal cord and nerves is located behind the vertebral bodies.

There are many types of spinal column disorders including scoliosis (abnormal lateral curvature of the spine), kyphosis (abnormal forward curvature of the spine, usually in the thoracic spine), excess lordosis (abnormal backward curvature of the spine, usually in the lumbar spine), spondylolisthesis (forward displacement of one vertebra over another, usually in a lumbar or cervical spine) and other disorders caused by abnormalities, disease or trauma, such as ruptured or slipped discs, degenerative disc disease, fractured vertebra, and the like. Patients that suffer from such conditions usually experience extreme and debilitating pain, as well as diminished nerve function.

The present invention generally involves a technique commonly referred to as spinal fixation whereby surgical implants are used for fusing together and/or mechanically immobilizing vertebrae of the spine. Spinal fixation may also be used to alter the alignment of adjacent vertebrae relative to one another so as to change the overall alignment of the spine. Such techniques have been used effectively to treat the above-described conditions and, in most cases, to relieve pain suffered by the patient. However, as will be set forth in more detail below, there are some disadvantages associated with current fixation devices.

One spinal fixation technique involves immobilizing the spine by using orthopedic rods, commonly referred to as spine rods, that run generally parallel to the spine. This may be accomplished by exposing the spine posteriorly and fastening bone screws to the pedicles of the appropriate vertebrae. Clamping elements adapted for receiving a spine rod therethrough are then used to join the spine rods to the screws. The aligning influence of the rods forces the spine to conform to a more desirable shape. In certain instances, the spine rods may be bent to achieve the desired curvature of the spinal column. Some examples of such spinal stabilization systems are disclosed in U.S. Pat. Nos. 6,074,391; 6,488,681; 6,280,442; 5,879,350; 6,371,957 B1; 6,355,040; 5,882,350; 6,248,105; 5,443,467; 6,113,601; 5,129,388; 5,733,286; 5,672,176; and 5,476,464, the entire disclosures of which are incorporated herein by reference.

U.S. Pat. No. 5,129,388 to Vignaud et al. discloses a spinal fixation device including a pedicle screw having a U-shaped head rigidly connected to an upper end of the screw. The U-shaped head includes two arms forming a U-shaped channel for receiving a spine rod therein. The U-shaped head is internally threaded so that a set screw having external threads may be screwed therein. After the pedicle screw has been inserted into bone and a spine rod positioned in the U-shaped channel, the set screw is threaded into the internal threads of the U-shaped channel for securing the spine rod in the channel and blocking relative movement between the spine rod and the pedicle screw.

Surgeons have encountered considerable difficulty when attempting to insert spinal fixation devices such as those disclosed in the above-mentioned '388 patent. This is because the U-shaped heads of adjacent screws are often out of alignment with one another due to curvature in spines and the different orientations of the pedicles receiving the screws. As a result, spine rods must often be bent in multiple planes in order to pass the rods through adjacent U-shaped channels. These problems weaken the strength of the assembly and result in significantly longer operations, thereby increasing the likelihood of complications associated with surgery.

In response to the above-noted problems, U.S. Pat. No. 5,733,286 to Errico et al., U.S. Pat. No. 5,672,176 to Biedermann et al., and U.S. Pat. No. 5,476,464 to Metz-Stavenhagen disclose polyaxial spinal fixation devices wherein the anchoring element fixed to the bone has a spherically-shaped head. The fixation devices in the above-identified patents also have orthopedic rod capturing assemblies for securing orthopedic rods in the capturing assemblies and connecting the rods with the anchoring elements. The spherically shaped heads of the anchoring elements permit movement of the anchoring elements relative to the orthopedic rod capturing assemblies.

There is a need for a screw head securing mechanism or device that provides a strong, effective, and secure lock of the screw head in its desired position. Additionally, there is a need for a screw head securing mechanism or device that is minimal in size and has a reduced amount of components to provide for a simpler, more effective, and less cumbersome device for fixing screws. Moreover, there is a need for a device adapted to more easily receive curved rods.

SUMMARY

One inventive aspect of the disclosure relates to providing orthopedic fixation systems for securing a rod to a bone with means for receiving curved rods.

Another inventive aspect of the disclosure relates to orthopedic fixation systems that secure polyaxial anchors by providing substantially full rings of contact with the heads of the anchors regardless of the angular orientations of the anchors.

Yet another aspect of the disclosure relates to providing orthopedic fixation systems for securing a rod to a bone including receivers and seat structures mounted within the receivers, wherein the receivers and the seat structures include relative anti-rotation features.

It should be noted that, at various locations throughout the specification, guidance is provided through lists of examples. The examples are for illustrative purposes and are not intended to limit the scope of the invention.

DETAILED DESCRIPTION

The invention will now be described by reference to the several drawing figures. The functional features of the invention can be embodied in any number of specific configurations. It will be appreciated, however, that the illustrated embodiments are provided for descriptive purposes and should not be used to limit the invention.

FIG. 1illustrates one embodiment of an orthopedic fixation device10having features that are examples of inventive aspects in accordance with the principles of the present disclosure. The fixation device10includes a receiver30having a top portion32defining a saddle39(i.e., a pocket) for receiving a rod60, and a bottom portion31adapted for receiving a head23of a bone fastener such as a bone screw20. The fixation device10also includes a seat structure40that mounts within the receiver30between the rod60and the head23of the screw20. The seat structure40and the head23of the screw20are bottom loaded into the bottom portion31of the receiver30, and then captured within the receiver30by a retainer50(e.g., a retaining ring) secured to the bottom end of the receiver30. The fixation device10further includes a fastener such as a setscrew70for clamping the rod60within the saddle39of the receiver30.

In general use, a plurality of the fixation devices10are anchored to bones such as vertebral bodies99a,99b(shown atFIG. 2) desired to be stabilized. The fixation devices can be anchored to the vertebral bodies99a,99bby threading the bone screws20into the vertebral bodies99a,99b. Torque for driving the screws20can be provided by a tool (e.g., a torque wrench or screw driver) inserted through the receivers30and into sockets28(e.g., hex-sockets) provided in the heads23of the screws20. By threading the screws20into the vertebral bodies99a,99b, the screws20function to couple the receivers30to the vertebral bodies99a,99bas shown atFIG. 2. After coupling the receivers30to the vertebral bodies99a,99bwith the screws, the vertebral bodies99a,99bcan be distracted apart, compressed together or otherwise moved to a desired relative positioning. Rods60can then be mounted within the receivers30as shown inFIG. 2. The polyaxial configuration of the bone screws20allow the receivers30to pivot relative to the bone screws20to facilitate inserting the rods60in the saddles39of the receivers30. Once the rods60are inserted within the receivers30, the setscrews70are threaded into the saddles39thereby forcing the rods60to seat against the top sides of the seat structures40. Continued tightening of the setscrews70forces the seat structures40downwardly within the receivers30causing the heads23of the bone screws20to be clamped between the bottom sides of the seat structures40and the retainers50, and also causing the rods60to be clamped between the setscrews70and the top sides of the seat structures40. The rods60are preferably clamped with sufficient force to prevent the rods60from sliding relative to the receivers30, and the screw heads23are preferably clamped with sufficient force to prevent the screw heads23from pivoting relative to the receivers30. In this manner, the rods60and the fixation devices10cooperate to form a stabilizing construct or framework that braces the vertebral bodies99a,99bto maintain the desired spatial relationship between the vertebral bodies99a,99b.

Referring toFIG. 1, the screw20of the fixation device10includes a bone engaging end24and a generally spherical head23. The bone-engaging end24preferably includes external threads25adapted to allow the screw20to be screwed into bone material. The spherical head23includes a major diameter26sized such that the spherical head23can be loaded into the receiver30from the bottom end of the receiver30. The spherical head23is shaped to allow a polyaxial freedom of movement for the screw20. In this manner, the screw20can have a range of motion throughout a 360-degree pattern from a longitudinal axis of the receiver30. Polyaxial freedom of movement of the screw20provides the surgeon with a wide range of placement angles, thereby facilitating the rod placement process.

FIGS. 5 and 6are perspective views of the seat structure40of the orthopedic fixation device ofFIG. 1. The seat structure40includes a top seat42for receiving the rod60, a bottom seat44for receiving the head23of the screw20and a through-hole97communicating between the top seat42and the bottom seat44. The seat structure40also includes an exterior surface98and an interior surface99. The seat structure40is shaped and sized to be inserted into the receiver30through the bottom end of the receiver30.

The top seat42of the seat structure40includes two legs43defining a pocket47. The top seat42also includes first and second raised rod contacting structures such as ridges49that are spaced apart from one another. Each of the legs43defines a recessed portion45in the interior surface99extending between the two ridges49.

As illustrated inFIGS. 3 and 4, each of the ridges49provides two contact locations94on the sides of the rod60. Non-contact areas95are defined between the bottom of the rod60and the bottom53of the pocket47. The non-contact areas95are provided by sizing the rod radius of curvature larger than the pocket radius of curvature.

The non-contact area95, the recessed portions45between the ridges49and the location of the through-hole97are configured to facilitate seating of the bent rods by providing open regions for accommodating the curvatures of the rods.FIGS. 7-10show a rod160having an anterior-posterior curvature. Means for accommodating this curvature while maintaining secure contact is provided by the ridges49and the clearance provided by the non-contact areas95and the through hole97between the ridges.FIG. 11shows a rod260having a lateral curvature. Means for accommodating this curvature while maintaining secure contact is provided by the ridges49and the recessed portions45between the ridges49. As shown atFIG. 11, the ridges provide four discrete contact locations94while the recessed portions45provide clearance for accommodating the lateral curvature of the rod.

The rod contacting structures49are adapted to form four separate contact areas94with a rod regardless of which way the rod has been bent. In this manner, the rod contacting structures49provide stability to any rod that has been seated on the top seat42regardless of the rod's curvature. Corrective manipulations may be done to the rod while the rod is at rest on the top seat42.

As shown inFIGS. 5 and 6, the bottom seat44of the seat structure40is adapted to receive the head23of the screw20. After the seat structure40has been inserted within the receiver30, the bottom seat44is adapted to contact the spherical head23of the screw20when the screw20is inserted within the receiver30from the bottom end of the receiver30.

The bottom seat44of the seat structure includes an annular seating surface44ahaving a curvature that generally matches the curvature of the exterior surface of the head23of the screw20. The seating surface44afaces in a generally downward direction and is adapted to provide a full ring of contact80(shown inFIG. 4A) with the head23throughout the range of pivotal movement of the screw20relative to the receiver30. When the fixation device is tightened as shown inFIGS. 3 and 4, the seating surface44apresses down on the screw head23to clamp the screw at the desired angular position. During the clamping process, the surface44amaintains the substantially full ring contact80with the spherical head23of the screw20regardless of the angular orientation of the screw20relative to the receiver30such that the screw is securely clamped at the desired angular orientation relative to the receiver30.

FIG. 12illustrates the receiver30of the orthopedic fixation device10ofFIG. 1. The receiver30includes an outer surface108, and an inner surface109. The receiver30also includes a throughhole34extending vertically from the top portion32to the bottom portion31of the receiver30. As illustrated inFIG. 12, the receiver30may also include grasping features119on the outer surface108that would accommodate instrumentation to facilitate grasping, holding or manipulating of the receiver30.

The receiver30includes two upwardly extending legs38between which the saddle39of the receiver30is defined. The saddle39of the receiver30provides an open region or pocket for receiving the rod60. The legs38also preferably include fastening structure for interconnecting with the setscrew70. For example, the legs38are shown defining interior threads35that mate with corresponding exterior threads72of the setscrew70to allow the setscrew70to be threaded into the saddle39to lock the rod60and screw in place.

The seat structure40is configured to be bottom-loaded into the receiver30. When the seat structure40is bottom-loaded into the receiver30, the seat structure40is prevented from being pushed upwardly through the top end of the receiver30by a stop structure79.

The receiver30may include a keying feature36for aligning the seat structure40in the correct rotational orientation relative to the receiver30during insertion. The keying structure36can also limit rotation of the seat structure40relative to the receiver30once inserted. As used herein, the term “limit” can mean either prevent rotation or limit rotation to a certain range. InFIG. 1, the keying feature36is depicted as opposing internal slots36defined along the inner surface109. The internal slots36have generally rectangular shapes and are configured to complement and receive corresponding rectangular shape structures36′ provided at the exterior98of the seat structure40. The internal slots36are used to align the pockets47of the seat structure40with the saddle39of the receiver30. It will be understood that other types of keying features (e.g., tabs, notches, polygonal shapes, slots, flats, or other structures) can be utilized to correctly align the seat structure relative to the receiver within the spirit of the invention.

Referring toFIG. 13, the retainer50(e.g., a ring) of the orthopedic fixation device10ofFIG. 1is shown. The ring50is adapted to be coupled (e.g., welded, bonded, swaged, snap-fit, threaded, press-fit or otherwise secured) to the bottom of the receiver30after the seat structure40and the head23of the screw20have been inserted within the receiver30. The ring50, once coupled, captures and retains the head23of the screw20within the bottom portion of the receiver30(seeFIGS. 3 and 4). The retainer50includes an annular seating surface50athat faces in a generally upward direction an includes a curvature that generally complements the curvature of the exterior of the screw head23. The seating surface50ais adapted to provide substantially full ring contact82(shown inFIG. 4B) with the head23of the screw20regardless of the angular orientation of the screw20relative to the receiver30. In this manner, when the setscrew70is fully tightened, the seating surface44aof the seat structure40and the seating surface50aof the ring50cooperate to provide two substantially full rings of contact80and82(shown inFIGS. 4A and 4B) between which the spherical head23of the screw20is captured and clamped to lock the head23at a desired angular position relative to the receiver30.

In use, the setscrew70provides an axial locking force on the rod60. When contacted by the setscrew70, the rod60is caused to axially apply a force on the seat structure40. The seat structure40, in turn, moves to create a clamping effect on the spherical head23of the bone screw20against the ring50coupled to the bottom end31of the receiver30. When the setscrew70is fully tightened, the rod60is locked between the setscrew70and the seat structure40, and the screw head23is locked between the seat structure40and the retainer50.

As illustrated inFIGS. 3 and 4, the setscrew70may include a curved bottom surface71. With this configuration, the setscrew70contacts the rod60at a single point of contact73. This feature provides stability to a rod that has been bent upwardly when it is seated on the top seat42of the seat structure40. The threads72of the setscrew70can also be designed with a double lead to allow the setscrew70to start more easily than with a single lead. Torque for driving the setscrew70can be provided by a tool (e.g., a torque wrench) inserted into sockets74(e.g., hex-sockets) provided in the setscrews70.

FIGS. 14 and 15illustrate a second embodiment of orthopedic fixation device110having features that are examples of inventive aspects in accordance with the principles of the present disclosure. The orthopedic fixation device110includes a seat structure140. The seat structure140is similar to the embodiment ofFIG. 1, except that the seat structure140includes an exterior surface198of a hexagonal cross-sectional profile. The device110also includes a receiver130with an internal hexagonal cross-sectional shape136configured to match the shape of the exterior198of the seat structure140. The matching shapes provide a keying function to ensure the seat structure140is inserted into the receiver130at the appropriate rotational orientation, and also limit the rotation of the seat structure140within the receiver130. The device110also includes a setscrew170having a flat bottom surface171for contacting the rod60when the rod is clamped within the device110.

FIGS. 16 and 17illustrate a third embodiment of orthopedic fixation device210having features that are examples of inventive aspects in accordance with the principles of the present disclosure. The device210is similar to the embodiment ofFIG. 1, except has been modified to include a different top locking arrangement. The locking arrangement of the fixation device210includes a fastener in the form of a lock nut270that mounts on a receiver230. The lock nut270is adapted to be threaded about the exterior of legs238of the receiver230. The receiver230includes external threads235adapted to mate with internal threads272of the nut270. The nut270can also be designed with a double lead as previously discussed for the set screw type of a locking mechanism to facilitate start-up.

The embodiments of the locking arrangements disclosed herein (e.g., the set screw70and the nut270) are merely examples of types of locking arrangements that can be used. The locking arrangements can include any mechanism adapted to provide an axial locking force on the rod60to cause it to provide a force on the seat structure40, thereby, causing it to move and create a clamping effect on the spherical head23of the bone screw20against the retainer50. Example structures include lock nuts, screws, collars, plugs, sleeves, tapered sleeves, tapered plugs or other structures. Torque or non-torque locking mechanisms may be utilized for the orthopedic fixation system.

The rod seat42of the seat structure40is preferably generally U-shaped as shown inFIG. 18. However, the shape can be varied. For example,FIG. 19shows a seat structure340having a truncated V-shaped seat342.FIG. 20shows a seat structure440having a rod seat442formed by opposing legs443. The seat structure440also includes provisional retaining tabs400adapted to provisionally retain the rod60between the legs443after the rod60is snapped past the tabs400during insertion. In this embodiment, the legs443are adapted to deflect (e.g. flex apart) to accommodate the rod60and then move inwardly back toward the non-deflected orientation such that the tabs400provisionally retain the rod60within the seat. When provisionally retained, the position of the rod can be readily adjusted. To remove the rod60from the pocket, the rod60is pulled upwardly with sufficient force to cause the legs443to deflect back apart thereby enabling the rod to pass between the tabs400. A fastener such as a lock nut, set screw or other fastener can be used to finally lock the rod within the seat structure once the rod has been adjusted to its final position.

To increase the contact surface and/or to vary the stresses between the bottom seat44of the seat structure40and the head23of the screw20, the seat/spherical head interface may include various cross-sectional shapes. For example, as shown inFIGS. 21-24, the bottom seat may include a cupped cross-sectional shape90, a rounded cross-sectional shape91, a tapered cross-sectional shape92and a squared cross-sectional shape93, respectively, at the seat/head interface. The bottom seat may also include a cross-sectional shape at the seat/head interface that is made up of a combination of the shapes discussed.

The various components of the devices disclosed herein (e.g., the receivers, fasteners, anchors, retainers and seat structures) can be made of any number of different types of biocompatible materials. Example materials include materials such as Titanium, Nitinol, Stainless Steel, Thermoplastic polymers, Thermoset polymers as well as other materials.

As shown in the various embodiments depicted herein, the anchors of the fixation devices have been depicted as bone screws. In other embodiments, the anchors can include hooks, pins, expandable anchors, barbed anchors or other structures.

From the foregoing detailed description, it will be evident that modifications and variations can be made in the devices of the invention without departing from the spirit or scope of the invention. Therefore, it is intended that all modifications and variations not departing from the spirit of the invention come within the scope of the claims and their equivalents.