Screw and rod fixation system

Abstract

A pedicle screw and rod fixation assembly including a pair of opposing tabs having a proximal end and a distal end, the pair of opposing tabs being coupled to one another about the distal end thereof by a screw head member, a decoupling mechanism for decoupling the pair of opposing tabs from the screw head member, a rod receiving slot between the pair of opposing tabs, and a sliding member configured for coupling to the pair of opposing tabs. The sliding member and the pair of opposing tabs are configured for allowing movement of the sliding member distally along the pair of opposing tabs and preventing movement of the sliding member proximally along the pair of opposing tabs.

Description

RELATED APPLICATIONS[0001]This application is a continuation of U.S. patent application Ser. No. 13 / 080,482, filed on Apr. 5, 2011 and titled, “Screw and Rod Fixation System,” the entire contents of which are incorporated herein by reference.FIELD OF THE INVENTION[0002]The present invention relates to spinal implants. More particularly, the present invention relates to screw fixation assemblies for use with bone fixation systems.BACKGROUND OF THE INVENTION[0003]Spinal deformity surgery is a complex technical procedure that can involve numerous implants and techniques to achieve a straightening of the spine in three dimensions. There is a sagital plane that may contain an increased or decreased lordosis or kyphosis, a coronal plane that may contain a left / right curvature of the spine and an axial plane that may contain a rotational deformity. All three planes must be addressed if a result that leaves the patient functional and provides acceptable cosmesis is to be achieved.[0004]Curr...

AI Technical Summary

Benefits of technology

[0010]The screw and rod fixation system of the present invention improves the procedure for correcting defective spines by providing enhanced reduction capabilities without adding the need to drive a set screw the entire length of every extended tab. The reduction mechanism can be made much longer which facilitates rod introduction along the entire length of the spine prior to any forces being applied. Splaying of the extended tabs is not an issue because a collar prevents the tabs from splaying outward and the rod prevents inward splay. This also allows for the simultaneous introduction of two separate rods which reduces the amount of localized force on any given anchor and distributes the corrective load among many of the anchors.

[0012]Reduction of the rods into the bottom of the screw heads is carried out by pushing the collars down toward the base of the screw heads by hand or with an instrument designed for this purpose. As the rods begin to encounter resistance, the spine begins to move in small increments toward the rods. As the collars are pushed farther down, a ratcheting action between the collars and the extended tabs retains the rods in place and prevents them from sliding back up the extended tabs. This allows the physician to sequentially move up and down the spine from screw to screw and on both sides of the spine to push the collars down on the extended tabs with an appropriate amount of force based on the number of anchors, bone quality, anchor quality etc.

[0013]Since this initial reduction is by hand the force applied is 1:1 such that the exact downward force applied by the surgeon is the same force retained by the collar when the surgeon releases pressure. This offers improved tactile feedback in a reduction maneuver over the prior art. The present invention also allows for distribution of the corrective forces over the entire spine thereby reducing the chances of screw pullout.

[0014]As manual reduction continues, instruments that apply more force than can be generated manually can be used to progressively force the collars farther down the extended tabs in a controlled fashion. To continue to distribute the forces, multiple instruments can be used simultaneously such that a single anchor does not receive excessive force. Alternatively, as increased reduction force is applied with an instrument, an assistant can manually advance the collars on the anchors adjacent to the persuader instrument to immediately disperse the force to multiple anchors. Alternatively, a physician can choose to initially place a single rod with this technique and subsequently place the second rod. The benefits are the same except that the corrective forces are not shared by the second rod, therefore increasing the load on the anchors of the first rod placed.

[0016]According to one aspect of the present invention, there is provided a screw and rod fixation assembly including a pair of opposing tabs having a proximal end and a distal end, the pair of opposing tabs being coupled to one another about the distal end thereof by a screw head member. The assembly further includes a decoupling mechanism for decoupling the pair of opposing tabs from the screw head member, a rod receiving slot between the pair of opposing tabs, and a sliding member configured for coupling to the pair of opposing tabs. The sliding member and the pair of opposing tabs are configured for allowing movement of the sliding member distally along the pair of opposing tabs and preventing movement of the sliding member proximally along the pair of opposing tabs.

Problems solved by technology

In certain cases, the physician is unable to introduce the rod into all of the fixation points or bring the rod and fixation points together.

This can occur if the spine is severely deformed which causes the fixation points to be misaligned.

When this occurs, the physician bends the rod in such a way that it can be introduced into the fixation points, but this compromises the correction.

Obviously, the introduction of a rod into a deformed spine can be very challenging to do so there have been many instruments designed to help forcibly bring the spine and the rod together.

Often, when an instrument is used to force the mating of the rod and anchor, the anchor can pull out of the bone because the force is too great.

Also, while reducing the rod into one anchor, it may miss the anchor above or below because the alignment of the rod and the spine do not match.

Further, longer extension tabs are prone to “splay” when reduction forces are applied.

This can cause the set screw to disengage or cross-thread.

Instruments have been designed to control the splaying effect, but they tend to complicate the procedure.

Yet another shortcoming of reduction screws is that the amount of torque they require to drive a rod into the screw seat is difficult to translate into actual downward force by the physician.

This can cause the pedicle screw to pull out of the bone thus causing the loss of a fixation point.

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