Spinal fixation system and method

A spinal fixation system (1) for use in the fixation of a spine having a securing element (18) having a biasing member (21) located on a lower portion (44) of the securing element (18); and a substantially concave surface (25) dimensioned for at least partially circumscribing a fixation rod (15); and a retaining element (22) having: a substantially concave top surface (23) dimensioned for at least partially circumscribing a fixation rod (15); an outwardly extending wing (16); a crimping portion (42), wherein the crimping portion (42) at least partially compresses when a force is exerted on the retaining element (22); and a substantially concave bottom surface (24) dimensioned for at least partially circumscribing a head (11) of a bone fixation element (9).

BACKGROUND OF THE INVENTION

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.

SUMMARY OF THE INVENTION

The present invention is directed to a spinal fixation system having a biasing member located on a lower portion of the securing element; and a substantially concave surface dimensioned for at least partially circumscribing a fixation rod; and a retaining element having: a substantially concave top surface dimensioned for at least partially circumscribing a fixation rod; an outwardly extending wing; a crimping portion, wherein the crimping portion at least partially compresses when a force is exerted on the retaining element; and a substantially concave bottom surface dimensioned for at least partially circumscribing a head of a bone fixation element.

The present invention is also directed to a method for fixating a spine comprising positioning a bottom end of 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 the 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; 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 adjacent 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; inserting a retaining element dimensioned for insertion into the coupling element interior space atop the bone fixation element head, the retaining element for retaining the bone fixation rod within the interior space; admitting a fixation rod into a pair of opposed longitudinal apertures though a wall of the coupling element; inserting a securing element dimensioned for insertion into the coupling element interior space atop the fixation rod, such that a biasing member located on a lower portion of the securing element contacts the retaining element; mating a locking element with a mating element adjacent the top end of the coupling element, for retaining the fixation rod within the interior space; and securing the securing element within the coupling element to prevent rotation of the securing element about a longitudinal axis thereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A description of the preferred embodiments of the present invention will now be presented.

With reference toFIG. 1, an isometric exploded view of a spinal fixation system is shown. The spinal fixation system1includes a coupling element2having walls35and at least one longitudinal aperture17and a securing element18. When used in spinal fixation, a bone fixation element9and a fixation rod15are utilized. The spinal fixation system1may also include an optional locking element20, a washer28, and a retaining element22.

InFIG. 2, an enlarged view of a portion of a partially assembled spinal fixation system is shown. The securing element18includes a concave surface25which may include a raised portion26thereon. The securing element18may also include a biasing member21located on a lower portion44of the securing element18. The biasing member21may be, but is not limited to, a spring.

An upwardly extending arm14may be located on the securing element18so as to be retained within the locking element20. The bone fixation element9includes a head11having a first portion36and a second portion37. The head11, and, as shown, the first portion36, may be secured within the retaining means22. The retaining element22has a generally concave surface with contact areas29. The contact areas29may extend in a linear increasing slope manner from a base section45toward an outwardly extending wing16.

InFIG. 3, a cross sectional view of a spinal fixation system is shown. When assembled, the spinal fixation system1permits rigid fixation of the fixation rod15wherein a constant force is applied on the fixation rod15and rigid fixation of the bone fixation element9wherein a constant force is applied on the bone fixation element9.

When assembled, the bone fixation element9is secured within the coupling element2such that a head11of the bone fixation element9is retained within the coupling element2while a shank10of the bone fixation element9extends through the coupling element2. An optional washer28may be inserted into the coupling element2such that the washer28is located above the head11of the bone fixation element9. A retaining element22is inserted into the coupling element2wherein the retaining element22is located atop the bone fixation element9.

The head11of the bone fixation element9may include a first portion36and a second portion37wherein both the first portion36and second portion37include teeth38located thereon. The teeth38are uniform but asymmetrical, with each tooth having a moderate slope on one edge and a much steeper slope on the other edge. The first portion36and the second portion37may be different sizes. Although shown as concentric circles in circumference (as shown in greater detail inFIG. 15), the first portion36and the second portion37of the head11need not be concentric to one another. If the second portion37is greater in circumference than the first portion36, greater support is provided on the coupling element2.

The fixation rod15, which has a rod diameter12, is admitted through the longitudinal apertures17of the coupling element2. The retaining element22is located between the fixation rod15and the head11of the bone fixation element9. The securing element18is secured within the coupling element2. If a locking element20is utilized, the securing element18is secured thereto and both are ultimately secured within the coupling element2. To secure the securing element18to the locking element20, an upwardly extending arm14may be utilized as described and depicted.

FIG. 4shows a side view of a partially assembled spinal fixation system. The retaining element22may be formed so as to at least partially compress. As shown, the retaining element22includes slits47to permit such compression. However, other means for permitting such compression are envisioned. In one embodiment where the retaining element22may be compressed, the retaining element22holds the bone fixation element9and then compresses, at least partially, when the locking element20is tightened.

When the locking element20is tightened, a force is applied to the securing element18. The force from the securing element18then translates force onto the retaining element22. As the locking element20is tightened, the securing element18moves in a downward direction, first compressing the biasing members21, then applying direct pressure on the fixation rod15. The force applied on the fixation rod15translates force onto the contact area29of the retaining element22. The force applied onto the contact area29causes the wings16to move outwardly, which in turn causes downward and inward movement of a portion of the retaining element22. These forces work together to at least partially compress a crimping portion42of the retaining element22, thereby grasping, crimping, or otherwise securing onto the head11of the bone fixation element9.

FIGS. 5-9show varying views of a coupling element of the spinal fixation system. The coupling element2has an exterior surface4, a bottom end5, a top end6, and a longitudinal axis7. The coupling element2also has a pair of opposed longitudinal apertures17through a wall35thereof extending from a top end6of the coupling element2to an aperture bottom34in spaced relation from a bottom end5of the coupling element2. The apertures17may be substantially U-shaped as shown, but other shapes may also be utilized.

The wall35defines an interior space32dimensioned for admitting a bone fixation element9thereinto and the apertures17are dimensioned for admitting a fixation rod15diametrically through the interior space32of the coupling element2. The coupling element2also includes a hole13through the bottom end5of the coupling element2.

An optional mating element19may be located on an interior surface3of the coupling element2. As shown, the mating element19may be threads; however, other mating elements may also be utilized.

The hole2has a diameter8and is dimensioned for admitting a shank10of the elongated bone fixation element9therethrough (shown inFIG. 3) and smaller than a first portion37of the head11of the bone fixation element9(shown inFIG. 3) for retaining the head11within the interior space32of the coupling element2. As shown, the hole13is dimensioned for housing a bone fixation element head11having at least a partially spherical shape, thereby permitting rotational movement of the bone fixation element9. However, the hole13may be of other dimensions as well, including, but not limited to, planar or convex.

FIGS. 10,11, and12show varying views of a securing element of the spinal fixation system of the present invention. The securing element18may include an upwardly extending arm14dimensioned for insertion into the locking element20. As shown, the arm14is substantially T-shaped; however, other shapes may be utilized. A biasing member21may be located on the lower portion44of the securing element18, and an optional raised portion26may be located on the concave surface25of the securing element18.

FIGS. 13 and 14show varying views of a locking element of the spinal fixation system. The locking element20, which is an optional component of the spinal fixation system1, may include a mating element19A located on an external surface thereon and a downwardly extending wall30. The wall30defines a locking element interior space39dimensioned for housing the arm14of the securing element18and may include at least one groove33located therein. Moreover, the wall30may be sized and shaped so as to prevent the arm14from dislodging, yet permit rotation of the arm14therein. In this manner, the securing element20is rotatingly secured to the locking element18.

Next,FIG. 15shows a perspective view of a bone fixation element of the spinal fixation system. The bone fixation element9may be a bone screw or any other type of fastener that may be utilized for insertion into a bone. The bone fixation element9includes a head11, an elongated shank10which extends downwardly from the bone fixation element9, and a tip43. Bone fixation element threads27may be located on the shank10of the bone fixation element9.

The head11of the bone fixation element9may include a first portion36and a second portion37, with each portion36and37having optional teeth38located thereon. The first portion36and the second portion37each may be of a certain size and shape and may have certain diameters. As depicted, a first portion diameter40is less than a second portion diameter41. These diameters40and41of the bone fixation element9may be of any size; however, the second portion diameter41should be greater than the diameter of the hole13in the coupling element2so as to allow the head11of the bone fixation element9to remain within the coupling element2while the shank10of the bone fixation element9extends through the hole13of the coupling element2. The second portion37of the bone fixation element9may be semi-spherical in shape to permit rotational movement of the bone fixation element9within the coupling means2when the hole13is dimensioned as such, for example, when the hole13is substantially concave. In this manner, when the bone fixation element9is inserted through the hole13of the coupling element2, it still may be rotated and adjusted to a desired angle prior to insertion into a bone. Although the second portion37of the head11of the bone fixation element9is shown having a substantially round shape, other shapes may be utilized.

With respect toFIGS. 16,17, and18, varying views of a retaining element of the spinal fixation system are shown. The retaining element22includes a top surface23and a bottom surface24. The retaining element22may also include at least one outwardly extending wing16. The top surface23of the retaining element22may be concave for at least partially circumscribing the diameter12of the fixation rod15when the fixation rod15is admitted into the apertures17of the coupling element2. Contact areas29are located on the retaining element22such that the fixation rod15makes contact with the contact areas29of the retaining element22. The contact areas29may be sloped. Although a substantially concave top surface23is shown, the top surface23may also be of any other form including, but not limited to, planar or convex.

The bottom surface24of the retaining element22may be generally concave and, as shown, generally spherical, so as to accommodate at least a portion of the first portion36of the head11of the bone fixation element9. As the retaining element22is driven onto the first portion36, the pressure between the retaining element22and the first portion36, and the retaining element22and coupling element2, becomes greater. In this manner, limited motion between the bone fixation element9and the retaining element22is permitted. Although the bottom surface24of the retaining element22is shown having a generally spherical shape, other shapes may also be utilized.

In addition or in the alternative, the bottom surface24may engage the teeth38on the first portion36of the head11. Limited motion between the bone fixation element9and the retaining element22is permitted in this manner as well.

Finally,FIG. 19shows a plan view of the spinal fixation system installed in a bone in a spine. To use the spinal fixation system1, a user positions the bottom end5of the coupling element2adjacent to a bone31of a spine. Then, the user inserts the bone fixation element9into the coupling element2such that a shank10is located within the interior space32and the tip43extends into the hole13and is adjacent to the bone31. The user then drives the bone fixation element9into the bone31such that at least a portion of a shank10extends through the hole13and into the bone31. The bone fixation element9may be driven into the bone31via various methods, such as, but not limited to, rotation or impact of the bone fixation element9.

The retaining element22is then inserted within the coupling element2and positioned on the first portion36of the head11of the bone fixation element9. The fixation rod15is then admitted into the apertures17. The securing element18is then inserted into the coupling element2such that the biasing members21of the securing element18make contact with the retaining element22. The user then rotates the locking element20such that the mating element19of the locking element20mates with the mating element19of the coupling element2.

When the locking element20is tightened, a force is applied to the securing element18. The force from the securing element18then translates force onto the retaining element22. As the locking element20is tightened, the securing element18moves in a downward direction, first compressing the biasing members21, then applying direct pressure on the fixation rod15. The force applied on the fixation rod15translates force onto the contact area29of the retaining element22. Thus, the head11of the bone fixation element9is locked first, then the fixation rod15is locked. These forces work together to compress a crimping portion42of the retaining element22. Additionally, as the locking element20is tightened, the securing element18and the retaining element22are wedged within the coupling element2, thereby providing greater securement.

If threads27are provided on the bone fixation element9, then an additional amount of force may be required when driving the bone fixation element9into the bone31. However, use of bone fixation elements9having threads27thereon provide greater retention of the spinal fixation system1within the bone31.

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.