Spinous process fusion plate assembly

Abstract

A spinal implant helps stabilize vertebrae for fusion. The implant includes first and second plates, a brace and a locking mechanism. When installed, the plates extend superiorly-inferiorly along respective lateral sides of the spinous processes. The plates are moved toward one another and relative to the brace by the locking mechanism to clamp the implant to the spinous processes.

Description

BACKGROUND

This invention relates generally to devices for the treatment of spinal conditions, and more particularly, to the treatment of various spinal conditions that cause back pain. Even more particularly, this invention relates to devices that may be placed between adjacent spinous processes to treat various spinal conditions. For example, spinal conditions that may be treated with these devices may include spinal stenosis, degenerative disc disease (DDD), disc herniations and spinal instability, among others.

The clinical syndrome of neurogenic intermittent claudication due to lumbar spinal stenosis is a frequent source of pain in the lower back and extremities, leading to impaired walking, and causing other forms of disability in the elderly. Although the incidence and prevalence of symptomatic lumbar spinal stenosis have not been established, this condition is the most frequent indication of spinal surgery in patients older than 65 years of age.

Lumbar spinal stenosis is a condition of the spine characterized by a narrowing of the lumbar spinal canal. With spinal stenosis, the spinal canal narrows and pinches the spinal cord and nerves, causing pain in the back and legs. It is estimated that approximately 5 in 10,000 people develop lumbar spinal stenosis each year. For patients who seek the aid of a physician for back pain, approximately 12%-15% are diagnosed as having lumbar spinal stenosis.

Common treatments for lumbar spinal stenosis include physical therapy (including changes in posture), medication, and occasionally surgery. Changes in posture and physical therapy may be effective in flexing the spine to decompress and enlarge the space available to the spinal cord and nerves—thus relieving pressure on pinched nerves. Medications such as NSAIDS and other anti-inflammatory medications are often used to alleviate pain, although they are not typically effective at addressing spinal compression, which is the cause of the pain.

Surgical treatments are more aggressive than medication or physical therapy, and in appropriate cases surgery may be the best way to achieve lessening of the symptoms of lumbar spinal stenosis and other spinal conditions. The principal goal of surgery to treat lumbar spinal stenosis is to decompress the central spinal canal and the neural foramina, creating more space and eliminating pressure on the spinal nerve roots. The most common surgery for treatment of lumbar spinal stenosis is direct decompression via a laminectomy and partial facetectomy. In this procedure, the patient is given a general anesthesia and an incision is made in the patient to access the spine. The lamina of one or more vertebrae may be partially or completely removed to create more space for the nerves. The success rate of decompressive laminectomy has been reported to be in excess of 65%. A significant reduction of the symptoms of lumbar spinal stenosis is also achieved in many of these cases.

The failures associated with a decompressive laminectomy may be related to postoperative iatrogenic spinal instability. To limit the effect of iatrogenic instability, fixation and fusion may also be performed in association with the decompression. In such a case, the intervertebral disc may be removed, and the adjacent vertebrae may be fused. A discectomy may also be performed to treat DDD and disc herniations. In such a case, a spinal fusion would be required to treat the resulting vertebral instability. Spinal fusion is also traditionally accepted as the standard surgical treatment for lumbar instability.

A wide variety of spinal fusion devices are used following partial or total discectomies for stabilization of the spine at that site. Many such devices are secured extradiscally, such as to the pedicles or spinous processes. For example, the spinous process fusion plate available from Medtronic, Spinal and Biologics of Memphis, Tenn. under the brand name CD Horizon Spire is typically secured to the spinous processes. See for example the devices and methods disclosed in U.S. Pat. Nos. 7,048,736 and 7,727,233, the entire contents of which are expressly incorporated herein by reference. These devices typically work for there intended purposes. However, with the demands of spinal surgery, the medical device industry is continually looking for ways to improve currently available devices.

SUMMARY

The spinal implant described herein may include first and second plates, a brace extending between the plates and a locking mechanism that moves the two plates toward each other and locks them in an appropriate relative position. When installed in the patient's anatomy, the brace extends laterally through the interspinous space, and the plates extend superiorly-inferiorly along respective lateral sides of the spinous processes.

The first plate and the second plate may each have a generally linear longitudinal axis or may extend along curved longitudinal axes or may have a longitudinal axis that is off-set along its height. Each plate may also have an inner face configured to abut adjacent spinous processes with projections extending therefrom that engage or “bite into” the spinous processes. The brace may be fixed to the first plate and extend through an opening in the second plate. Alternatively, the first plate may include an opening through which the brace extends and the brace may include an enlarged proximal end that can be located on the proximal side of the first plate to prevent that plate from moving proximally with respect to the brace. The opening in the second plate allows the brace to be placed through the opening and allows the second plate to slide along the brace and thus vary the distance between the first and second plate. The axis of the brace is transverse to the longitudinal axes of the first and second plates. The brace may be a hollow tube defining a lumen extending therethrough. The plate to which the brace is affixed may also define an opening to allow a locking element to extend through the first and second plates and through the brace.

The locking element may include an enlarged distal element connected along its proximal portion to a proximal rod. The diameter of the enlarged distal element is chosen so that its maximum diameter is greater than the diameter of the lumen of the brace. The locking element is located within the lumen of the brace so that the enlarged distal element extends distally beyond the distal end of the brace and the rod extends proximally beyond the proximal end of the brace. When the locking element is pulled proximally, the enlarged distal end deforms the distal portion of the brace so the diameter of the distal portion of the brace increases so as to be greater than the diameter of the opening in the second plate, thus preventing the second plate from being moved distally off of the brace. Continued proximal movement of the locking element moves the two plates together so that the projections of each plate engage and “bite into” the spinous processes and lock the implant to the spinous processes. The proximal portion of the rod of the locking element extending from the proximal end of the brace may then be broken or cut off from enlarged distal end or the remainder of the distal portion of the rod.

A method of implanting the spinal implant may include the following steps. After access to the desired spinal motion segment is obtained, a first plate is located adjacent to the proximal lateral sides of adjacent superior and inferior spinous processes. Where the brace is fixed to the first plate, placement of the first plate should be made so that the brace extends in the interspinous space through the sagittal plane. Where the brace is not fixed to the first plate, the brace is inserted through an opening in the first plate so the brace extends in the interspinous space through the sagittal plane and moved distally until an enlarged proximal tab abuts the proximal face of the first plate. The second plate is located over the brace so that the second plate is placed adjacent to the distal lateral sides of the adjacent superior and inferior spinous processes. The locking mechanism is then placed through the brace such that the proximal rod is first inserted through the distal opening to the lumen of the brace and moved proximally until the enlarged distal element abuts the distal opening of the brace. The surgeon may then pull the proximal rod from the proximal side of the brace to enlarge the distal portion of the brace. Continued proximal movement of the locking mechanism forces the enlarged distal element into the distal portion of the brace, enlarging this portion of the brace and forcing the distal plate to move proximally into engagement with the distal lateral faces of the adjacent superior and inferior spinous processes. Once the surgeon is satisfied with the placement of the implant, the surgeon may then break or cut off the proximal rod of the locking element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a spinal motion segment with a spinal implant located therein;

FIG. 2 is a perspective view of the opposite side of the spinal implant shown in FIG. 1;

FIG. 3A is a front elevation view of a spinal implant;

FIG. 3B is a front elevation view of the spinal implant shown in FIG. 3A but with the locking mechanism moved proximally with respect to the spinal implant;

FIG. 3C is a front elevation view of the spinal implant shown in FIG. 3B but with the locking mechanism moved further proximally with respect to the spinal implant;

FIG. 3D is a front elevation view of the spinal implant shown in FIG. 3C but with the proximal end of the locking mechanism removed;

FIG. 4 is a cross-sectional view of the spinal implant shown in FIG. 3A;

FIG. 5 is a cross-sectional view of the spinal implant shown in FIG. 3D; and

FIG. 6 is a cross-sectional view of another embodiment of a spinal implant.

DETAILED DESCRIPTION

As used in this specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, the term “a member” is intended to mean a single member or a combination of members, and “a material” is intended to mean one or more materials, or a combination thereof. Furthermore, the words “proximal” and “distal” refer to directions closer to and away from, respectively, an operator (e.g., surgeon, physician, nurse, technician, etc.) who would insert the medical device into the patient, with the tip-end (i.e., distal end) of the device inserted inside a patient's body first. Thus, for example, the device end first inserted inside the patient's body would be the distal end of the device, while the device end last to enter the patient's body would be the proximal end of the device.

As used in this specification and the appended claims, the terms “up”, “upper”, “top”, “down”, “lower”, “bottom”, “front”, “back”, “rear”, “left”, “right”, “side”, “inner”, “middle” and “center”, and similar terms, refer to portions of or positions in or on the implant when the implant is oriented in its implanted position, such as shown in FIG. 1.

As used in this specification and the appended claims, the term “axial plane” when used in connection with particular relationships between various parts of the implant means a plane that divides the implant into upper and lower parts. As used in this specification and the appended claims, the term “coronal plane” when used in connection with particular relationships between various parts of the implant means a plane that divides the implant into front and back parts. As used in this specification and the appended claims, the term “sagittal plane” when used in connection with particular relationships between various parts of the implant means a plane that divides the implant into left and right parts.

As used in this specification and the appended claims, the term “body” when used in connection with the location where the device of this invention is to be placed, or to teach or practice implantation methods for the device, means a mammalian body. For example, a body can be a patient's body, or a cadaver, or a portion of a patient's body or a portion of a cadaver. A “body” may also refer to a model of a mammalian body for teaching or training purposes.

As used in this specification and the appended claims, the term “parallel” describes a relationship, given normal manufacturing or measurement or similar tolerances, between two geometric constructions (e.g., two lines, two planes, a line and a plane, two curved surfaces, a line and a curved surface or the like) in which the two geometric constructions are substantially non-intersecting as they extend substantially to infinity. For example, as used herein, a line is said to be parallel to a curved surface when the line and the curved surface do not intersect as they extend to infinity. Similarly, when a planar surface (i.e., a two-dimensional surface) is said to be parallel to a line, every point along the line is spaced apart from the nearest portion of the surface by a substantially equal distance. Thus, two geometric constructions are described herein as being “parallel” or “substantially parallel” to each other when they are nominally parallel to each other, such as for example, when they are parallel to each other within a tolerance. Such tolerances can include, for example, manufacturing tolerances, measurement tolerances or the like.

As used in this specification and the appended claims, the terms “normal”, “perpendicular” and “orthogonal” describe a relationship between two geometric constructions (e.g., two lines, two planes, a line and a plane, two curved surfaces, a line and a curved surface or the like) in which the two geometric constructions intersect at an angle of approximately 90 degrees within at least one plane. For example, as used herein, a line is said to be normal, perpendicular or orthogonal to a curved surface when the line and the curved surface intersect at an angle of approximately 90 degrees within a plane. Thus two geometric constructions are described herein as being “normal”, “perpendicular”, “orthogonal” or “substantially normal”, “substantially perpendicular”, “substantially orthogonal” to each other when they are nominally 90 degrees to each other, such as for example, when they are 90 degrees to each other within a tolerance. Such tolerances can include, for example, manufacturing tolerances, measurement tolerances or the like.

A spinal implant 100 for spinal fusion that attaches to adjacent spinous processes to fixate the corresponding vertebrae relative to the other is described herein. Implant 100 may include two fixation plates 10, 20, a brace 30 and a locking element 40. Plates 10, 20 are adapted to be disposed on respective lateral sides of the adjacent superior and inferior spinous processes. Projections 15 may extend from the inner surfaces of plates 10, 20 and are adapted to engage or “bite into” the surfaces of the spinous processes to fix plates 10, 20 with respect to the spinous processes. Brace 30 may be fixed to plate 10 and is adapted to extend through at least plate 20 with distal plate 20 adapted to be moveable proximally with respect to brace 30. Brace 30 may be hollow and may define a lumen 31 extending therethrough that defines a first diameter. Locking element 40 is adapted to be disposed within lumen 31.

Both proximal plate 10 and distal plate 20 may have a generally curved configuration that extends along a curving longitudinal axis. It is to be understood however that plates 10, 20 may be generally rectangular with a straight longitudinal axis or may have an offset configuration where the upper and lower portions of the longitudinal axis are offset from each other. Projections, or teeth, 15 extend inwardly away from the longitudinal axis of the plate on which they are located and toward the spinous process. As mentioned above, projections 15 are adapted to engage or “bite into” the surfaces of the spinous processes to fix plates 10, 20 with respect to the spinous processes. Each plate 10, 20 defines an opening 11, 21, respectively, therein along a medial portion. Opening 21 in distal plate 20 should have a diameter large enough to allow distal plate 20 to slide proximally along brace 30. Opening 11 in proximal plate 10 should have a diameter large enough to allow the proximal rod 42 of locking element 40 to slide proximally past proximal plate 10. As shown in FIG. 6, plates 10, 20 may be substantially mirror images of each other.

Brace 30 may have a generally tubular configuration defining lumen 31 therein. Brace 30 may be fixed to either plate 10, 20. As shown in FIGS. 1-5, brace 30 may be fixed along its proximal end to proximal plate 10 using any suitable means such as welding, brazing, adhesive or mechanical engagement. Distal plate 20 may define an opening 21 to allow brace 30 to extend through plate 20 and thus slide along brace 30 and vary the distance between proximal plate 10 and distal plate 20. The axis of brace 30 is generally transverse to the longitudinal axes of plates 10, 20. Proximal plate 10 may also define an opening 11 to allow proximal rod 42 to extend proximally through plate 10. As shown, in FIG. 6, brace 30′ need not be fixed to plate 10′. Instead, plate 10′ may define an opening 11′ having a diameter to allow brace 30′ to extend through plate 10′. A proximal flange 35 may be located at the proximal end of brace 30′ to prevent plate 10 from moving proximally off of brace 30′. As mention above, the diameter of the proximal portion of brace 30′ and the diameter of opening 11′ may be matched to provide an interference fit therebetween.

Locking element 40 includes an enlarged distal knob 41 and a proximal rod 42 attached to distal knob 41. The maximum diameter of enlarged distal knob 41 is chosen so that it is greater than the diameter of lumen 31. Although knob 41 is shown in the FIGS. as having a generally circular cross-section, it is to be understood that other configurations could be used for knob 41. However, it is desirable that the proximal portion of knob 41 have a tapered proximal configuration that increases in diameter in the distal direction. This taper facilitates proximal movement of locking element 40 with respect to brace 30. Locking element 40 is disposed within lumen 31 of brace 30 so that knob 41 is initially located beyond the distal end of brace 30 and the proximal end of rod 42 extends proximally beyond the proximal end of brace 30 and plate 10. See, e.g. FIG. 4. When locking element 40 is pulled proximally, the tapered portion of knob 41 engages the distal end of brace 30 and forces the distal portion of brace 30 to deform so it increases in diameter such that the enlarged diameter is greater than the diameter of opening 21 in distal plate 20. This increase in diameter for the distal portion of brace 30 prevents plate 20 from being moved distally off of brace 30 and thus locks plate 20 to brace 30 and plate 10. In addition, since the increased diameter of the distal portion of brace 30 caused by knob 41 is larger than the diameter of opening 21, proximal movement of knob 41 forces plate 20 to move proximally. Continued proximal movement of locking element 40 moves plates 10, 20 together so that projections 15 of each plate 10, 20 engage and “bite into” the spinous processes and lock implant 100 to the spinous processes.

Once plates 10, 20 are fixed to the adjacent spinous processes, rod 42 may then be removed from knob 41 so that there is nothing that extends proximally beyond plate 10. See FIG. 5. Rod 42 or a proximal portion of rod 42 can be removed from locking element 40 by any number of mechanisms. For example, the compressive force between plates 10, 20 that is necessary to ensure that plates 10, 20 can be compressed so that projections 15 “bite into” the spinous processes can be determined. Once this force is determined, the cross-sectional area of a segment of rod 42 can be locally decreased so that it fractures after the desired compressive force has been reached. This cross-sectional area can be computed based on the mechanical properties chosen for knob 41 and rod 42 of locking element 40. Alternatively, a mechanical connection, such as a thread located along the distal end of rod 42 and a tapped hole formed in knob 41, may be used. In such an embodiment, the user would be able to manually disengage rod 42 from knob 41 after plates 10, 20 have been fixed to the spinous processes. Also, a cutting device may be used to cut off a proximal portion of rod 42.

A method of implanting the spinal implant may include the following steps. After access to the desired spinal motion segment is obtained, proximal plate 10 is located adjacent to the proximal lateral sides of adjacent superior and inferior spinous processes. Where brace 30 is fixed to plate 20, proper placement of plate 10 ensures that brace 30 extends in the interspinous space through the sagittal plane. Where brace 30′ is not fixed to plate 10′, the distal end of brace 30′ may be inserted through opening 11′ in plate 10′, after plate 10′ is properly located adjacent the proximal lateral sides of the adjacent spinous processes, and moved distally through the interspinous space until flange 35 abuts the proximal medial face of plate 10′ around opening 11′. With proximal plate 10 and brace 30 properly located with respect to the spinal segment, the distal end of brace 30 should extend past the distal lateral sides of the adjacent spinous processes. Distal plate 20 may then be placed over the distal end of brace 30 so that plate 20 is placed adjacent to the distal lateral sides of the adjacent superior and inferior spinous processes. Locking mechanism 40 may then be placed into lumen 31 through brace 30 such that the proximal end of rod 42 is first inserted into the distal end of brace 30 and moved proximally through brace 30 until knob 41 abuts the distal opening of brace 30. Rod 42 may continue to be pulled from the proximal side of brace 30 so knob 41 enlarges the distal portion of brace 30 and locks plate 20 onto brace 30 and with respect to plate 10. Continued proximal movement of locking mechanism 40 forces knob 41 further into the distal portion of brace 30, enlarging this portion of brace 30 and forcing distal plate 20 to move proximally into engagement with the distal lateral faces of the adjacent superior and inferior spinous processes. Once the surgeon is satisfied with the placement of implant 100, rod 42 may be cut or broken off of knob 41. For example, knob 41 may be connected to rod 42 by a frangible connection that may be broken by specific manipulation of rod 42. If desired, the distal portion of brace 30 extending beyond the distal face of distal plate 20 can be removed to minimize the space occupied by implant 100. However, it is contemplated that only a minor length of the distal portion of brace 30 will extend beyond the distal face of distal plate 20 after plates 10, 20 have been compressed into engagement with the spinous processes. Thus it may be unnecessary to remove any portion of the distal portion of brace 30.

Implant 100 may be formed of suitable biocompatible materials. For example, plates 10, 20 may be formed from stainless steel, titanium and its alloys, polymers such as PEEK, carbon fiber and the like. A softer, more ductile material, such as 316 stainless steel, may be used for brace 30. This material would allow brace 30 to deform without fracture and would not require an extremely high force to deform. A harder material, such as a cobalt chrome alloy, may be used for locking element 40. The various materials used for the parts of implant 100 may be considered in combination with the geometry of the various parts to obtain a customized force/implantation profile to facilitate implantation by the surgeon and achieve an optimized function.

While various embodiments of the spinous process fusion device are described herein, it should be understood that they have been presented by way of example only, and not limitation. Many modifications and variations will be apparent to the practitioner skilled in the art. The foregoing description of the spinous process fusion device is not intended to be exhaustive or to limit the scope of the invention. It is intended that the scope of the invention be defined by the following claims and their equivalents.

Claims

1. A spinal implant, comprising: a first plate extending along a first longitudinal axis and having a first inner face configured to abut adjacent spinous processes and having projections extending from the first inner face;a second plate extending along a second longitudinal axis and having a second inner face configured to abut the adjacent spinous processes and having projections extending from the second inner face;a brace extending along a third longitudinal axis, the brace having a first diameter and including a flange fixed to a proximal end of the brace;the first and second plates disposed along the brace such that the first and second longitudinal axes are transverse to the third longitudinal axis and the first inner face and the second inner face are oriented toward each other in spaced relation; anda locking element engaging a distal end of the brace and longitudinally moveable relative to the brace such that longitudinal displacement of the locking element toward a proximal end of the brace modifies the brace such that a distal portion of the brace has a second diameter being greater than the first diameter and configured to prevent the second plate from being moved distally past a distal end of the brace,wherein longitudinal displacement of the locking element toward the proximal end of the brace narrows a distance between the first plate and the second plate.

2. The spinal implant of claim 1 wherein a proximal portion of the brace is fixed to the first plate.

3. The spinal implant of claim 1 wherein the locking element includes a distal end defined by a knob having a tapered proximal portion and a rod extending proximally from the knob.

4. The spinal implant of claim 3 wherein the knob has a circular cross section.

5. The spinal implant of claim 4 wherein the rod is connected to the knob by a frangible connection.

6. The spinal implant of claim 3 wherein the knob has a tapered proximal portion.

7. The spinal implant of claim 3 wherein the knob defines a third diameter that is greater than the second diameter and less than the first diameter.

8. The spinal implant of claim 1 wherein the flange prevents the first plate from being moved proximally past the proximal end of the brace.

9. The spinal implant of claim 1 wherein the brace defines a first configuration wherein the brace has a distal portion with an outer diameter having an initial diameter and a second configuration wherein the outer diameter of the distal portion of the brace has a subsequent diameter and wherein the subsequent diameter is greater than the initial diameter.

10. The spinal implant of claim 9 wherein the initial diameter is less than the first diameter and the subsequent diameter is greater than the first diameter.

11. A spinal implant, comprising: a first plate extending along a first longitudinal axis and having a first inner face configured to abut adjacent spinous processes and having projections extending from the first inner face and having a first opening extending therethrough along a medial portion of the first plate;a second plate extending along a second longitudinal axis and having a second inner face configured to abut the adjacent spinous processes and having projections extending from the second inner face and having a second opening extending therethrough along a medial portion of the second plate, the second opening defining a first diameter;a brace extending along a third longitudinal axis and adapted to be disposed in the second opening and having a proximal portion connected to the first plate adjacent to the first opening, the brace being formed from a deformable material and defining a lumen having a second diameter, the brace including a flange fixed to the proximal portion of the brace and being configured to prevent the first plate from proximally moving off the brace; anda locking element adapted to be moveably disposed at least partially in the brace, the locking element further comprising a distal knob and a proximal rod connected to the distal knob,wherein the brace defines a first configuration wherein the brace has a distal portion with an outer diameter having an initial diameter and a second configuration wherein the outer diameter of the distal portion of the brace has a subsequent diameter and wherein the subsequent diameter is greater than the initial diameter.

12. The spinal implant of claim 11 wherein the distal knob has a tapered proximal portion.

13. The spinal implant of claim 12 wherein the distal knob defines a third diameter that is greater than the second diameter and less than the first diameter.

14. The spinal implant of claim 11 wherein the proximal rod defines a length that is adapted to be shortened.

15. The spinal implant of claim 11 wherein the initial diameter is less than the first diameter and the subsequent diameter is greater than the first diameter.

16. A method for implanting a spinal implant into an interspinous space defined by a superior spinous process and an inferior spinous process, comprising; placing a first plate, having a first opening, adjacent to proximal lateral sides of the adjacent spinous processes;placing a brace into the interspinous space, the brace including a flange fixed to a proximal portion of the brace preventing the first plate from proximally moving off the brace;placing a second plate, having a second opening, adjacent to distal lateral sides of the adjacent spinous processes such that the brace extends through the second opening;inserting a locking mechanism into a distal portion of the brace; andmoving the locking mechanism proximally to change the distance between the first plate and the second plate and to lock the implant with respect to the superior spinous process and the inferior spinous process and to change the diameter of the brace along a distal portion of the brace from a first diameter to a second diameter, wherein the second diameter is larger than the first diameter.

17. The method of claim 16 further comprising changing the length of the locking mechanism from a first length to a second length wherein the second length is shorter than the first length.

18. The method of claim 16 further comprising placing the brace through the first opening.