Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
2000-02-08
2001-07-17
Philogene, Pedro (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S075000
Reexamination Certificate
active
06261288
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to an implant and a configuration for implantation of the implant into the human body, especially along the spine, having improved stabilization and locking with respect to desired position of the overall implant, as well as improved resistence to torsion during use.
The art of correcting back deformities, injuries and the like has advanced dramatically in recent years. Surgeons who perform operations on the spine and related bones of the body are constantly developing new procedures and techniques that require implants which are capable of being stable in the body after implantation and which firmly lock in place so as to resist the substantial pressures and forces developed by the body on the implant. Such implants must often also resist twisting or torsion applied to parts of the implant and prior art implants have not always been successful at resisting twisting or torsion.
Such implants often involve rods which are placed along the spinal column or various bones of the living body and, once secured to the bones, such rods may be bent and shaped to force the bones to align with the rods and, in this manner, either provide correction to the bones caused by deformity, injury or the like. That is, one or more rods are placed in the correct curvature for the spine and the spinal bones are joined to the rod or rods, before or after bending the rods, in such a manner as to thereafter force the bones to follow the same configuration as the rods. Once the rods are bent, forces created by the muscles of the patient, or by sudden movement, or by accident, or the like often act to try to rotate or apply torque to the implant as a whole or a rod individually. That is such forces generally apply torsion to the apparatus. Such torsion may act to loosen or even dislodge the implant or to turn or rotate one or more rods to a less effective support position. It is desirable that the apparatus be able to resist such forces acting upon it.
Historically, the rods used as implants in the manner described above, are typically joined with various bones along the length of the rod by use of bone screws or other implants that are joined with the rod. It has been found that conventionally available implants have systems that join rods to bone screws or intermediate connectors in such a manner that the rods are often held against axial movement relative to the bone screws or intermediate connector. That is, the rods are not likely to move substantially with respect to the other implants in a direction that is along the central axis of the rod. However, because of the substantial forces exerted on the rod during use, certain forces act to try to rotate the rod within bone screws and connectors, such that the spinal corrective configuration and positioning of the rod can slip due to rotation of the rod from an optimal position to one that is less suited for the patient. This can occur when substantial forces are applied to the back during exercise, accident or the like.
Consequently, it is desirable to have an implant that not only effectively resists axial movement of the rod relative to the other implants, but also effectively resists torque or torsion that produce turning of the rod or rotation of the rod relative to the implants. One use of the present invention is especially suited for the locking and stabilizing an anterior spinal implant. In particular, the installation of anterior spinal rods is often utilized to reposition the spine and correct deformities and the like. Such a rod is typically anchored at opposite ends to vertebrae and is likewise joined with vertebrae along the length of the rod by bone screws or the like. Such a system is typically installed by curving the rod to fit the malformed spine of the patient and then securing the anchors at both ends and various intermediate bone screws to the rod. The rod is thereafter bent by rod benders to assume the desired configuration of the spine and the rod in this manner translates the various bones of the spine along with it to the correct configuration.
Once the rod is bent, the body exerts a substantial amount of rotational force or torsion on the rod, especially should the patient be struck on the back, during exercising, or the like. It is also noted that the rod can first be bent and then the bone moved to the rod and secured to the rod. In either case, it is important that the anchors at opposite ends of the rod resist rotation of the rod therein and that the anchors themselves remain stable and securely attached to an associated bone. Furthermore, it is important to both lock the rod against rotation in or relative to the bone screw and to secure the anchors of the rod against rotation relative to the spine.
An implant system is therefore desirable that provides a strong anchor at opposite ends of the rod that resists rotation of the rod both relative to the bone screws and relative to the spine during procedures at the time of implantation and later during use.
SUMMARY OF THE INVENTION
A medical implant apparatus is provided which includes an anchor for operatively resisting rotation or dislodgement of the implant apparatus and also operatively resists rotation of a spinal implant rod associated with the apparatus relative to bone screws and other elements of an implant system. The invention is especially useful in conjunction with rods that are utilized to correct deformities, injuries or the like in the spine, but has related applications in other types of implants.
In particular, an anchor is provided for securing a rod to bone in a living person, especially near the end of the rod. The anchor has a first bone screw to which the rod is attached. The rod may be attached to the first bone screw either directly or indirectly through another implant. The bone screw may be an open bone screw that has a yoke that is closed by a cap once the rod is placed in the yoke, or may be a closed bone screw where the rod is received through an opening in the top of the bone screw.
The anchor further includes a second bone screw which is positioned radially out or laterally with respect to the first bone screw. The second bone screw is also connected either directly or indirectly to the rod and is typically joined by an offset or lateral implant to the rod. In this manner, the first and second bone screws are positioned laterally with respect to each other or generally in a line that is perpendicular or radially outward with respect to the axis of the rod and thus cooperate to provide greater resistance to rotation of the rod, both because there are multiple bone screws secured to the rod at this location and because there is a lever arm that is provided between the two bone screws to resist rotation or torsion of the rod due to action of the body or outside forces.
Secondly, a set screw in conjunction with optimal positioning and configuration for the set screw is likewise provided to resist rotation of the rod. In particular, the rod is positioned and secured in a bore or other opening that receives the rod by a set screw that resists both axial movement of the rod and rotational movement of the rod within the opening. This is accomplished by effective positioning of the set screw relative to the rod and the opening. In particular, the set screw is positioned such that as the set screw is installed, the set screw first urges the rod against an opposed wall of the bore or opening in such a manner that the rod is held against that wall and secured between the set screw and the wall. In this manner, the rod is frictionally secured in the opening, especially where the opening is not fully enclosed; for example, in the situation where the implant has a hook connection with the rod. Thus, in part, the set screw and friction against the wall of the bore resist axial movement of the rod relative to the remainder of the implant.
The implant may include additional set screws that secure the rod against axial movement and this is especially true in the situation where the implant includes t
McMahon John C.
Philogene Pedro
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