Surgery – Instruments – Orthopedic instrumentation
Reexamination Certificate
1999-03-19
2001-10-16
Buiz, Michael (Department: 3732)
Surgery
Instruments
Orthopedic instrumentation
C606S064000, C411S005000, C411S393000, C411S405000, C411S910000
Reexamination Certificate
active
06302888
ABSTRACT:
FIELD OF THE INVENTION
The invention relates generally to an implant assembly for a manipulation and/or stabilization of a spine and generally comprises an anchor for an elongated stabilizer such as a rod, a sliding locking member which cooperates with the anchor so as to capture the stabilizer within the anchor and a shear off set screw having removal means.
BACKGROUND OF THE INVENTION
It has become accepted for certain medical indications to stabilize the relative position of vertebrae for at least some limited period of time. Anchor members are attached onto vertebral bodies, such as in the case of laminar hooks, or are implanted into the bodies using screw members. The anchors generally include means to hold a rod such as a clamping means which forms an integral part of the anchor. Adjacent anchors customarily hold respective vertebrae relative to a stabilizer, i.e. a plate or a rod.
In reciting the objectives of an assembly, it is critical to keep the biological context in mind. Thus, it is important not only to achieve the desired load limitations and stabilization characteristics, but also to design a series of components and respective instrumentation which is as easily manipulated and as quickly assembled as possible, which is as non-obtrusive into the biological environment as possible, and which is designed with the goal of avoiding failure. A surgeon may have limited physical access to the surgical site as well as obscured surgical visibility. It is critical to avoid the pieces or filings which could fall into a wound site. It is also important to design a system which can be manipulated by a gloved surgeon.
It is also desirable to have a system designed to allow as much flexibility for the surgeon as possible and yet to include some self-limiting features in order to maintain ease of application.
It is therefore an object of the current invention to provide a stabilizer anchor member having a closure means, which slides into position to capture an elongated stabilizer within the anchor member. The sliding closure means is designed to provide increased resistance to spreading of the anchor member.
It is a further object of the invention to provide a novel set screw which is self limiting and can achieve a higher torque. Moreover, the set screw allows for a gradual transition shear rather than a sudden snapping.
In addition, the set screw includes external prongs to mate with a removal instrument for removal of the set screw after shear.
SUMMARY OF THE INVENTION
The invention relates to a spinal implant assembly including an elongated stabilizer which is preferably a rod but could include a plate or cable, and anchor means which are secured relative to a spinal bone member and which include clamping means which secure the stabilizer relative to the anchor means. More specifically, the anchor means includes a U-shaped channel which receives a stabilizer rod. A closure member slides into position in the channel so as to capture the rod circumferentially in the channel. The channel has at least one, preferably a plurality and most preferably two undercut surfaces in each one of the two side walls of the U-shaped channels. These undercut surfaces formed for example as part of groove, define an oblique angle with respect to the side wall surface. The closure member includes multiple mating flange-like projections on each side or “dovetails” which have a corresponding configuration. These mating dovetails inhibit the spreading or splaying of the side walls of the channel in response to forces executed on the anchor assembly by the locking set screw acting on the stabilizer rod.
The closure member includes a detent means which cooperates with the anchor member. This causes the closure member to “snap” into place as it is slid into position in the channel. In particular, the closure member has a ridge, and preferably has two ridges on opposing sides, and the anchor includes a recess to receive the ridges. In particular, the anchor member includes a central bore at the top of the U-shaped channel to define opposing C-shaped areas. Correspondingly, the anchor includes integral opposing radiused recessed areas in the section of each side wall adjacent the top opening of the channel. These areas interact with the ridges so that the closure member is slid longitudinally and subsequently locked into position.
Additionally, the anchor assembly includes a self-limiting set screw received in a screw hole in the closure member. The set screw has a threaded portion with a beveled end distal to an external hexagonal head for tightening the screw. The hex head is joined to the rest of the screw by a necked area which is designed to shear at a preselected torque so that after tightening the screw does not extend beyond the anchor assembly. The screw further includes a plurality of radially projecting prongs which form a collar which fits into the recessed central bore in the top opening of the rod channel. The prongs include undercut areas designed to allow the screw to be removed after the hexagonal head has sheared off.
These undercuts provide for the screw to be self-tightening with regard to the removal instrument. The prongs of the set screw nest into a recessed central bore in the top opening of the rod channel. This prevents the closure member from disengaging the bone anchor once the set screw is tightened. Thus, the detent means, or interference fit acts as a temporary locking mechanism which will hold during manipulation such as rod rotation or distraction. In accordance with the invention, the anchor member is open, i.e. includes a top loading rod channel but can be closed to allow for considerable forces during manipulation. Thus, the invention allows the rod to be installed in the rod anchor and subsequently closed rather than requiring the anchor to be threaded on to the rod and surgically implanted while in place on the rod. The implant assembly is subsequently locked by tightening the set screw. First, the set screw is loosely positioned to hold the components together during intermediate tweaking of the assembly to achieve the desired vertebral alignment. When this has been achieved, the set screw can be tightened to lock the assembly and more specifically to lock the rod in the anchor. The set screw is subsequently sheered. During tightening of the set screw, a large force is applied to the bone anchor. Multiple dovetails of the present invention inhibits the anchor from spreading in response to the applied force. Further, the nesting fit between the shoulder of the set screw and the recess of the anchor inhibits longitudinal sliding of the closure member.
An additional key advantage of the design is that the closure member can be slid into the anchor from either side. Again, the nesting of the set screw relative to the bone anchor inhibits disengagement. The additional aspect of allowing top loading of the closure member in the bone anchor provides that the closure member has to be slid only a minimum distance, i.e. three or four millimeters, and from either direction. Consequently, the systems provide many assembly options to the surgeon.
The anchor or assembly includes means to fasten it to bone such as a hook or screw. The fastener can be integral with the anchor or assembly or can be a separate and cooperating member. For example, the anchor can include a through bore extending substantially perpendicular to the rod channel. The bore includes a rimmed bottom portion such that a screw or hook can be received in the anchor. Preferably the screw has a hemispherical or spherical head so as to form a ball and socket joint with the anchor.
As a further aspect of the invention, the screw head is at least substantially spherical. The screw head has multiple offset holes, preferably three or four to permit the screw to be implanted into the vertebrae and easily removed. The screw socket includes a high friction mating surface and the rod channel is spaced at a distance less than the diameter of the screw head from the bone contact surface so that the rod forces the screw h
Knoth Donald B.
Mellinger Philip A.
Buiz Michael
Hudak & Shunk Co. L.P.A.
Interpore Cross International
Reip David O.
Shunk Laura F.
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