Patent Grant
8236035
1. Field of the Invention
The present invention relates to spinal fixation systems and methods, more specifically, a spinal fixation system that provides retention of a fixation rod wherein lateral and rotational movement of a fixation rod and bone fixation element are significantly reduced.
2. Description of Related Art
Spinal fixation, also referred to as vertebral fixation, is a neurosurgical procedure for reducing movement of a spine so as to decrease damage to the spinal cord and/or spinal roots. Spinal fixation is utilized to treat a wide variety of spinal disorders and deformities which result in vertebral displacement of the spine, including, but not limited to, scoliosis, kyphosis, spondylolisthesis, rotation, tumor diseases, disc degeneration, and congenital defects. In addition, spinal fixation is utilized to treat vertebral fractures, injuries, or other traumas to the spine wherein the spine becomes displaced from such fracture, injury, or trauma.
The procedure utilizes synthetic devices to anchor two or more vertebrae to one another in the spinal column. Such devices may include bone fixation elements, also referred to as bone screws, coupled to a spinal fixation rod via a coupling element. The bone fixation elements are inserted into the pedicle(s) of the desired vertebrae and are secured to or within the coupling element. The spinal fixation rod, in turn, is secured within the coupling element via a securing element. Accordingly, the spinal fixation rod is ultimately secured to the vertebrae such that movement of the stabilized vertebrae is limited. As the ultimate goal of spinal fixation is to limit movement of the spine, it is of great importance that fixation between the bone fixation element, coupling element, and fixation rod be rigid and permanent.
Various structures for securing the fixation rod within the coupling element are currently available. One such structure includes the use of a compression means, such as a compression screw, which exerts a predetermined amount of force on the fixation rod when the compression means is secured within the coupling element. Such compressive force also translates to a compressive force being applied on the coupling element and the bone fixation element as well, thereby reducing movement of the synthetic devices within the vertebra to which such synthetic devices are secured.
However, some synthetic devices require the bone fixation element to be secured within the coupling element at a substantially 90 degree angle thereto, thereby resulting in a substantially 90 degree insertion of the bone fixation element into the pedicle. Thus, use of such synthetic devices limits the ability to secure such devices at an angle customized to a patient, even if a more accurate and secure fixation would result if the bone fixation element were inserted into the pedicle at either an acute or obtuse angle. As such, there exists a need for an improved spinal fixation system that would permit rotational movement of a bone fixation element within the coupling element prior to insertion into a pedicle, but prevent movement thereof after insertion into the pedicle.
Moreover, although the compression means utilized in some synthetic devices results in a reduction of movement of the fixation rod within the coupling element, rotational movement of the fixation rod therein does not always result, as in some cases the compression means is not shaped so as to maximize the surface area contact between the compression means and the fixation rod. As such, there exists a need for an improved spinal fixation system that would limit both lateral and rotational movement of a fixation rod located within a coupling element.
Furthermore, some synthetic devices utilizing compression means may become loose over time due to vibrational forces applied thereto, thereby resulting in pain and discomfort in the patient and a need to perform corrective surgical procedures to re-tighten and re-secure the synthetic devices. As such, there exists a need for an improved spinal fixation system which would limit loosening of the synthetic devices due to vibrational forces.
The present invention is directed to a spinal fixation system having a coupling element having: a pair of opposed longitudinal apertures through a wall thereof extending from a top end of the coupling element to an aperture bottom in spaced relation from a bottom end of the coupling element, the wall defining an interior space dimensioned for admitting a bone fixation element thereinto, the apertures dimensioned for admitting a fixation rod diametrically through the interior space; a longitudinal slot in an interior surface of the coupling element extending from the coupling element top end to a slot bottom in spaced relation from the coupling element bottom end; a hole through the bottom end dimensioned for admitting a shank of the elongated bone fixation element therethrough and smaller than a head of the bone fixation element for retaining the head within the interior space, the shank extending downwardly from the fixation element; and a securing element dimensioned for vertical slidable insertion into the coupling element interior space atop the fixation element head, the securing element having an outwardly extending wing dimensioned for riding in the coupling element slot, for preventing a rotation of the securing element about a longitudinal axis thereof.
The present invention is also directed to a method for fixating a spine comprising positioning a coupling element having: a pair of opposed longitudinal apertures through a wall thereof extending from a top end of the coupling element to an aperture bottom in spaced relation from a bottom end of the coupling element, the wall defining an interior space dimensioned for admitting a bone fixation element thereinto, the apertures dimensioned for admitting a fixation rod diametrically through the interior space; a longitudinal slot in an interior surface of the coupling element extending from the coupling element top end to a slot bottom in spaced relation from the coupling element bottom end; and a hole through the bottom end dimensioned for admitting a shank of the elongated bone fixation element therethrough and smaller than a head of the bone fixation element for retaining the head within the interior space, the shank extending downwardly from the bone fixation element to a bone in a spine; inserting a bone fixation element into the coupling element such that a shank of the bone fixation element is located within the interior space and the tip extends into the hole and is adjacent to the bone; driving the bone fixation element into the bone such that at least a portion of a shank of the bone fixation element extends through the hole and into the bone; admitting a fixation rod into a pair of opposed longitudinal apertures though a wall of the coupling element; inserting an outwardly extending wing of a securing element into the coupling element slot, wherein the outwardly extending wing is dimensioned for riding in the coupling element slot; and securing the securing element within the coupling element to prevent rotation of the securing element about a longitudinal axis thereof.
A description of the preferred embodiments of the present invention will now be presented.
With reference to
In
When assembled, the bone fixation element 9 is secured within the coupling element 2 such that a head 11 of the bone fixation element 9 is retained within the coupling element 2 while a shank 10 of the bone fixation element 9 extends through the coupling element 2. An optional washer 36 may be inserted into the coupling element 2 such that the washer 36 is located above and adjacent to the head 11 of the bone fixation element 9. An optional retaining element 22 may be inserted into the coupling element 2 wherein the retaining element 22 is located atop the washer 36 and bone fixation element 9.
The fixation rod 15, which has a diameter 16, is admitted through the apertures 17 of the coupling element 2. The retaining element 22, if utilized, is located between fixation rod 15 and the head 11 of the bone fixation element 9. The securing element 18 is secured within the coupling element 2. If a locking element 20 is utilized, the securing element 18 is secured thereto and both are ultimately secured within the coupling element 2.
When the spinal fixation system 1 is assembled, a substantially constant force is applied to the fixation rod 15, retaining element 22, and bone fixation element 9. However, if no retaining element 22 is utilized, then the substantially constant force is only applied to the fixation rod 15 and the bone fixation element 9.
The wall 35 defines an interior space 32 dimensioned for admitting a bone fixation element 9 thereinto and the apertures 17 are dimensioned for admitting a fixation rod 15 diametrically through the interior space 32 of the coupling element 2. The coupling element 2 also includes a slot 8 in an interior surface 3 of the coupling element 2 extending from the coupling element 2 top end 6 to a slot bottom 33 in spaced relation from the coupling element 2 bottom end 5. As shown, the apertures 17 are angularly offset with respect to the slots 8. The coupling element 2 also includes a hole 13 through the bottom end 5 of the coupling element 2.
An optional mating element 19 may be located on an interior surface 3 of the coupling element 2. As shown, the mating element 19 may be threads; however, other mating elements may also be utilized.
The hole 13 has a diameter 14 and is dimensioned for admitting a shank 10 of the elongated bone fixation element 9 therethrough (shown in
Next,
The head 11 of the bone fixation element 9 is of a certain size and shape and may have a certain diameter 12. The diameter 12 may be of any size; however, the diameter 12 should be greater than the hole diameter 14 in the coupling element 2 so as to allow the head 11 of the bone fixation element 9 to remain within the coupling element 2 while the shank 10 of the bone fixation element 9 extends through the hole 13 of the coupling element 2. The head 11 of the bone fixation element 9 may be round in shape to permit rotational movement of the bone fixation element 9 within the coupling means 2 when the hole 13 is dimensioned as such, for example, when the hole 13 is substantially concave. In this manner, when the bone fixation element 9 is inserted through the hole 13 of the coupling element 2, it still may be rotated and adjusted to a desired angle prior to insertion into a bone. Although the head 11 of the bone fixation element 9 is shown having a substantially round shape, other shapes may be utilized.
With respect to
The bottom surface 24 of the retaining element 22 may be generally spherically-shaped so as to accommodate at least a portion of the head 11 of the bone fixation element 9. In this manner, limited motion between the bone fixation element 9 and the retaining element 22 is permitted. Although the bottom surface 24 of the retaining element 22 is shown having a generally spherical shape, other shapes may also be utilized.
Finally,
The fixation rod 15 is then admitted into the apertures 17. The wings 27 of the securing element 18 is then inserted into the slots 8 and, finally, the securing element 18 is secured within the coupling element 2 to prevent rotation of the securing element 18 about the longitudinal axis 7 thereof. Additionally, when the securing element 18 is secured within the coupling element 2, a predetermined amount of force is applied on the fixation rod 15 to reduce both rotational and lateral movement thereof within the coupling element 2.
If threads 37 are provided on the bone fixation element 9, then an additional amount of force may be required when driving the bone fixation element 9 into the bone 31. However, use of bone fixation elements 9 having threads 37 thereon provide greater retention of the spinal fixation system 1 within the bone 31.
If the spinal fixation system 1 of the present invention includes both a locking element 20 rotatingly secured to the securing element 18 and a mating element 19 located on the interior surface 3 of the coupling element 2, then, after the user positions the wing 27 on the securing element 18 within at least a portion of the slot 8 of the coupling element 2, the user rotates the locking element 20 such that the mating element 19 of the locking element 20 mates with the mating element 19 of the coupling element 2.
If the spinal fixation system 1 of the present invention includes a retaining element 22, the user inserts the retaining element 22 within the coupling element 2 after insertion of the bone fixation element 9 and prior to insertion of the fixation rod 15 into the coupling element 2 such that the retaining element 22 is located between the bone fixation element 9 and the fixation rod 15. If the retaining element 22 includes wings 26, then the wings 26 are positioned within the slots 8 of the coupling element 2 prior to insertion of the retaining element 22 within the coupling element 9.
If the retaining element 22 is utilized and the diameter 16 of the fixation rod 15 is such that the wings 27 of the securing element 18 either (1) make contact with the wings 26 of the retaining element 22 after the securing element 18 makes contact with the fixation rod 15 or (2) do not make contact with the wings 26 of the retaining element 22 after the securing element 18 makes contact with the fixation rod 15, then a predetermined amount of force is applied on the fixation rod 15, which prevents lateral and rotational movement of the fixation rod 15, and a predetermined amount of force is applied on the retaining element 22 and, in turn, on the head 11 of the bone fixation element 9, thereby resulting in a reduction of movement of the bone fixation element 9.
In the alternative, if the diameter 16 of the fixation rod 15 is such that the wings 27 of the securing element 18 make direct contact with the wings 26 of the retaining element 22 prior to the securing element 18 directly contacting the fixation rod 15, then lateral and rotational movement of the fixation rod 15 is permitted. However, a predetermined amount of force is applied on the retaining element 22 and, in turn, on the head 11 of the bone fixation element 9, thereby resulting in a reduction of movement of the bone fixation element 9.
Having now described the invention, the construction, the operation and use of preferred embodiments thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.
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