Methods and devices for static or dynamic spine stabilization

Methods and devices for static or dynamic spine stabilization include an anterior plating system that allows longitudinal and pivoting motion of the plates and of the stabilized vertebras. In one embodiment a spine fixation assembly for connecting a first vertebra to a second vertebra includes a first plate configured to be attached to one or more locations of the first vertebra and a second plate configured to be attached to one or more locations of the second vertebra. The first plate is pivotally connected to the second plate and may also allow longitudinal and/or horizontal motion of the plates relative to each other.

FIELD OF THE INVENTION

The present invention relates to methods and devices for static or dynamic spine stabilization, and more particularly to methods and devices including an anterior plating system that allows longitudinal and pivoting motion of the plates and therefore of the stabilized vertebras.

BACKGROUND OF THE INVENTION

The human spine consists of individual vertebras (segments) that are connected to each other. Under normal circumstances the structures that make up the spine function to protect the neural structures and to allow us to stand erect, bear axial loads, and be flexible for bending and rotation. However, disorders of the spine occur when one or more of these spine structures are abnormal. In these pathologic circumstances, surgery may be tried to restore the spine to normal, achieve stability, protect the neural structures, or to relief the patient of discomfort. The goal of spine surgery for a multitude of spinal disorders especially those causing compression of the neural structures is often decompression of the neural elements and or fusion of adjacent vertebral segments. Fusion works well because it stops pain due to movement at the facet joints or intervertebral discs, holds the spine in place after correcting deformity, and prevents instability and or deformity of the spine after spine procedures such as laminectomies or corpectomies.

Anterior decompression directly removes anterior compressive structures and is known to have improved results in these cases over indirect decompression afforded by laminectomies. Anterior discectomy and fusion or anterior corpectomy and fusion are most commonly performed in the cervical spine but there is increasing application in the thoracic and lumbar spine.

In recent years, there is an increase in the use of plate fixation to stabilize the cervical spine after anterior decompression and fusion. (U.S. Pat. No. 6,402,756, U.S. Pat. No. 5,616,142, U.S. Pat. No. 5,800,433 and U.S. Publication No. 2002-0111630, U.S. Pat. No. 6,328,738) The goals of plate fixation include increased stability to allow for less reliance on rigid external orthosis such as hard cervical collars and halos for stability. It is thought that plates also increased the rate of fusion and decreased the incidence of graft complications such as graft extrusions and subsidence. One of the disadvantages of current anterior cervical plates includes the lack of graft subsidence and continuous graft loading which is believed to be advantageous for fusion. It is also difficult to place the plate in a straight line longitudinally between adjacent vertebras and plates are therefore often inadvertently placed at an angle. These technical difficulties often lead to a higher rate of complications including failure of the graft to fuse (pseudoarthrosis) and failure of the moveable (dynamic) mechanism to work, or failure of the plate-screw interface due to abnormal angular and rotational forces.

The newest plating systems have been designed to allow motion between the segments to be fused either at the fixation points between the plate and the screws or as a sliding mechanism within the plate with the ends of the plate fixed to screws in the vertebral body. This new “dynamic” plating system is believed to offer superior fusion rates since it allows continuous graft loading and natural graft subsidence while acting as a block to anterior graft displacement.

However, the limitations of dynamic plating systems include, potential failure of the moveable mechanism to work if the plates are placed at an angle between the vertebral bodies to be fused, lack of bidirectional movements during compression (neck flexion) and distraction (extension and lying supine), and lack of variable compression rates during sudden neck movements. Accordingly there is a need for an improved dynamic stabilization system that addresses the above-mentioned limitations.

SUMMARY OF THE INVENTION

Methods and devices for static or dynamic spine stabilization include an anterior plating system that allows longitudinal and pivoting motion of the plates and of the stabilized vertebras.

In general, in one aspect, the invention features a spine fixation assembly for connecting a first vertebra to a second vertebra including one or more guide wires, one or more fixation elements, a plate and one or more locking elements. One or more guide wires are configured to be inserted into one or more locations of the first vertebra and one or more guide wires are configured to be inserted into one or more locations of the second vertebra. One or more fixation elements are configured to be driven into the one or more locations of the first vertebra and one or more fixation elements are configured to be driven into the one or more locations of the second vertebra, respectively. Each of the fixation elements comprises a threaded body, a flange extending from an end of the threaded body, a threaded post extending from the flange and a through bore extending longitudinally through the threaded body the flange and the post, and the corresponding guide wire is dimensioned to pass through the through bore. The plate is configured to be placed over the threaded posts of the one or more fixation elements driven into the one or more locations of the first vertebra and over the threaded posts of the one or more fixation elements driven into the one or more locations of the second vertebra, and to overlay the vertebras. The plate comprises one or more apertures configured to receive the one or more fixation elements. One or more locking elements are configured to attach each of the posts of the one or more fixation elements to the plate, thereby securing the plate to the one or more fixation elements.

Implementations of this aspect of the invention may include one or more of the following features. The plate comprises an hourglass shape and an hourglass central aperture and the hourglass aperture is configured to provide access and line of vision to the under laying first and second vertebras and to an intervertebral space between the first and second vertebras. The apertures are dimensioned to allow the posts to pass through and the flanges not to pass through, so that the plate sits on top of the flanges. The locking elements comprise threads dimensioned to engage threads in the posts. The first vertebra may be adjacent or not adjacent to the second vertebra. The first and second vertebras may be separated by at least a third vertebra and the plate is dimensioned to overlie the first, second and third vertebras. The spine assembly may further include one or more additional fixation elements configured to be driven into one or more locations of the third vertebra and wherein the plate comprises one or more additional apertures configured to receive the one or more additional fixation elements.

In general in another aspect the invention features a spine fixation method for connecting a first vertebra to a second vertebra including the following steps. First, inserting one or more guide wires into one or more locations of the first vertebra and one or more guide wires into one or more locations of the second vertebra. Next, driving one or more fixation elements into the one or more locations of the first vertebra and one or more fixation elements into the one or more locations of the second vertebra, respectively. Each of the fixation elements comprises a threaded body, a flange extending from an end of the threaded body, a threaded post extending from the flange and a through bore extending longitudinally through the threaded body the flange and the post, and the corresponding guide wire passes through the through bore. Next, placing a plate over the threaded posts of the one or more fixation elements driven into the one or more locations of the first vertebra and over the threaded posts of the one or more fixation elements driven into the one or more locations of the second vertebra. The plate is configured to overlay the vertebras and comprises one or more apertures configured to receive the one or more fixation elements. Finally, attaching a locking element to each of the posts of the one or more fixation elements thereby securing the plate to the one or more fixation elements.

In general in another aspect the invention features a spine fixation assembly for connecting a first vertebra to a second vertebra including a first plate configured to be attached to one or more locations of the first vertebra, a second plate configured to be attached to one or more locations of the second vertebra. The first plate is pivotally connected to the second plate.

Implementations of this aspect of the invention may include one or more of the following features. The spine fixation assembly may further include one or more guide wires configured to be inserted into the one or more locations of the first vertebra and one or more guide wires configured to be inserted into the one or more locations of the second vertebra. One or more fixation elements are configured to be driven into the one or more locations of the first vertebra and one or more fixation elements are configured to be driven into the one or more locations of the second vertebra, respectively. Each of the fixation elements comprises a threaded body, a flange extending from an end of the threaded body, a threaded post extending from the flange and a through bore extending longitudinally through the threaded body the flange and the post, and the corresponding guide wire is dimensioned to pass through the through bore. The first plate is configured to be placed over the threaded posts of the one or more fixation elements driven into the one or more locations of the first vertebra and the second plate is configured to be placed over the threaded posts of the one or more fixation elements driven into the one or more locations of the second vertebra. The first and second plates comprise one or more apertures configured to receive the one or more fixation elements. The spine fixation assembly may further include one or more locking elements configured to attach each of the posts of the one or more fixation elements to the plates, thereby securing the plates to the one or more fixation elements. The first plate is also movable relative to the second plate along a longitudinal and/or a horizontal axis of the plates. These motions may be via a ratcheting mechanism. The plates may have triangular shape, rectangular shape, circular shape, semi-circular shape, oval shape, trapezoidal shape or elliptical shape. Each of the plates may comprise a central aperture configured to provide access and line of vision to the under laying first and second vertebras and to an intervertebral space between the first and second vertebras. The apertures are dimensioned to allow the posts to pass through and the flanges not to pass through, so that the plates sit on top of the flanges. The locking elements comprise threads dimensioned to engage threads in the posts. The first vertebra may be adjacent or not adjacent to the second vertebra. The first and second vertebras may be separated by at least a third vertebra and the plates are dimensioned to overlie the first, second and third vertebras. The spine fixation may further include a third plate configured to be attached to one or more locations of a third vertebra and the third plate is pivotally connected to the second plate. The third plate may be also movable relative to the second plate along a longitudinal or horizontal axis of the plates.

In general in another aspect the invention features a spine fixation method for connecting a first vertebra to a second vertebra including attaching a first plate to one or more locations of said first vertebra and then attaching a second plate to one or more locations of said second vertebra. The first plate is pivotally connected to said second plate.

Among the advantages of this invention may be one or more of the following. The improved spine fixation system allows motion between the segments to be fused away from the fixation points. The dynamic fixation system provides bidirectional motion between the fused segments during compression (neck flexion) and distraction (extension and lying supine). The plates are allowed to pivot and/or slide longitudinally and/or horizontally relative to each other at a point between the fused segments. The plates can be placed at an angle relative to each other. This new dynamic plating system offers superior fusion rates since it allows continuous graft loading and natural graft subsidence while acting as a block to anterior graft displacement.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1,FIG. 2andFIG. 3, an anterior one-level fixed cervical fusion system90includes a top loading, one-level fixed cervical plate100that connects two adjacent vertebras82and84. The fixed cervical plate100is attached to the vertebras82and84via four screws130a,130band130c,130d, respectively. The fixed cervical plate100has an hourglass shape and an hourglass shaped aperture102centered in the middle of the plate100. Aperture102provides visibility and access to the vertebras82,84and disc62below the plate100. Plate100also has four holes162a,162b,162cand162dlocated in the four corners of the plate. Holes162a,162b,62c,162dare dimensioned to receive the four screws130a,130b,130c,130d, respectively.

Referring toFIGS. 4A,4B,4C,4D, the process for attaching the plate100to the adjacent vertebras82,84includes the following steps. First, four k-wires140a,140band140c,140dare inserted into the vertebras82and84, respectively (182). Next, four screws130a,130band130c,130dare driven into the vertebras82and84, respectively, using the four k-wires140a,140b, and140c,140d, as guides respectively (184). Each screw has a threaded body131, a flange132on top of the threaded body131and a threaded post133extending upwards from the flange132. The threaded body131is driven into the vertebra while the flange132and the threaded post133remain above the vertebra. Next, the four holes162a,162b,162c,162dof the plate100are aligned with the four threaded posts133a,133b,133c,133d, respectively, and the plate100is top-loaded onto the screws130a,130b,130c,130dand lands onto the screw flanges132a,132b,132c,132d(186). The diameter of the screw flanges132a-132dis larger than the diameter of holes162a-162d, respectively, and the diameter of the screw posts133a-133dis smaller than the diameter of holes162a-162d, respectively. This geometric dimensioning allows the screw posts to pass through the plate holes while the plate stays on top of the flanges. Finally, four locking nuts160a,160b,160c,160dare screwed onto the threaded posts133a,133b,133c,133d, respectively, thereby securing the plate100onto the screws130a,130b,130c,130d(188).

In one example, plate100has a height91of 30 mm, a width93of 17 mm and the aperture102has a height92of 15 mm, as shown inFIG. 5. The plate100may be made of metal such as stainless steel or titanium, plastic, bioabsorbable material and ceramic.

Referring toFIG. 6andFIG. 7, an anterior one-level pivoting cervical fusion system80includes a top loading, one-level pivoting cervical plate100that connects two adjacent vertebras82and84. The pivoting cervical plate100is attached to the vertebras82and84via four screws130a,130band130c,130d, respectively. The pivoting cervical plate100, includes a triangular shaped top subplate110and a triangular shaped bottom subplate120. The top subplate110is closest to the head of the patient and has an apex111facing down toward the bottom subplate120. The bottom subplate110is closest to the patient's feet and has an apex121facing up toward the top subplate110. The apex111of the top subplate110is pivotably connected to the apex121of the bottom subplate120at point150, via a pivoting pin152that protrudes from the top surface of the apex111of the top subplate110. The bottom subplate120has a hole153formed at the apex121for receiving the pivoting pin152. A pivot cap154secures the top subplate120onto the pivot pin152while allowing the two subplates110,120to pivot relative to each other counterclockwise155aand clockwise155bby a few degrees, as shown inFIG. 8A, andFIG. 8B, respectively. Each of the top and bottom subplates110,120, has two holes162a,162band162c,162d, respectively, at the two corners opposite their respective apexes111,121. Holes162a,162b,162c,162dare dimensioned to receive the four screws130a,130b,130c,130d, respectively. The subplates110,120are top loaded onto the posts of the four screws130a,130b,130c,130d, and are secured onto the flanges of the four screws130a,130b,130c,130d, with four locking nuts160a,160b,160c,160d, respectively, as described inFIG. 4D. The triangular subplates110,120have central apertures112,122, that provide visibility and access to the vertebras82,84and disc62below them.

Referring toFIG. 9,FIG. 10andFIG. 11A, an anterior one-level dynamic stabilization system70includes a top loading, one-level dynamic plate100that connects two adjacent vertebras82and84, shown inFIG. 6. The dynamic plate100is attached to the vertebras82and84via four screws130a,130band130c,130d, respectively. The dynamic cervical plate100, includes a triangular shaped top subplate110and a triangular shaped bottom subplate120. The top subplate110slides down and pivots relative to the bottom subplate120via a ratchet and pivot mechanism155, respectively. The top subplate110is closest to the head of the patient and has an apex111facing down toward the bottom subplate120. The bottom subplate110is closest to the patient's feet and has an apex121facing up toward the top subplate110. The apex111of the top subplate110is pivotably connected to the apex121of the bottom subplate120at point155, via a pivoting pin152that protrudes from the top surface of the apex111of the top subplate110, shown inFIG. 7. The bottom subplate120has an elongated hole153formed at the apex121for receiving the pivoting pin152, shown inFIG. 11AandFIG. 11B. The elongated hole153includes a ratchet mechanism for providing the sliding motion of the top subplate110relative to the bottom subplate120. The ratchet mechanism allows for one-way movement156of the top subplate110toward the bottom subplate120, shown inFIG. 11AandFIG. 11B. In one example, the sliding movement has a span of 2 mm at 0.03 mm increments. In this embodiment, the bottom subplate120is not able to slide relative to the top subplate110. A ratchet cap151secures the ratchet mechanism and the top subplate120onto the pivot pin152while allowing the two subplates110,120to pivot relative to each other counterclockwise155aand clockwise155bby a few degrees, as shown inFIG. 12A, andFIG. 12B, respectively. Each of the top and bottom subplates110,120, has two holes162a,162band162c,162d, respectively, at the two corners opposite their respective apexes111,121. Holes162a,162b,62c,162dare dimensioned to receive the four screws130a,130b,130c,130d, respectively. The subplates110,120are top loaded onto the posts of the four screws130a,130b,130c,130d, and are secured onto the flanges of the four screws130a,130b,130c,130d, with four locking nuts160a,160b,160c,160d, respectively. The triangular subplates110,120have central apertures112,122, that provide visibility and access to the vertebras82,84and disc62below them.

Referring toFIG. 13andFIG. 14, an anterior two-level fixed cervical fusion system60includes a top loading, two-level fixed cervical plate100that connects three adjacent vertebras82,84, and86. The fixed cervical plate100is attached to the vertebras82,84and86via six screws130a,130b,130c,130d,130e, and130f. The fixed cervical plate100has a shape of two adjacent hourglasses that are merged together. The plate100has two hourglass shaped apertures105,106centered in the top and bottom of the plate100. Apertures105,106provide visibility and access to the vertebras82,84,86and disc62below the plate100. Plate100also has six holes162a,162b,162c,162d,162eand162flocated in the four corners and center of the plate. Holes162a,162b,62c,162d,162e,162fare dimensioned to receive the six screws130a,130b,130c,130d,130e,130f, respectively. Six locking nuts160a,160b,160c,160d,160e,160gare screwed onto the threaded posts of the screws, thereby securing the plate100onto the screws. The process of attaching the plate100to the adjacent vertebras82,84,86is as described above.

Referring toFIG. 15andFIG. 16, an anterior two-level pivoting cervical fusion system200includes a top loading, two-level pivoting cervical plate100that connects three adjacent vertebras82,84, and86. The pivoting cervical plate100is attached to the vertebras82,84and86via six screws130a,130b,130c,130d,130e, and130f. The pivoting cervical plate100, includes a triangular shaped top plate220a, a diamond shaped middle subplate210and a triangular shaped bottom plate220b. The top subplate220apivots relative to the middle subplate210around pivot point255a. The bottom subplate220bpivots relative to the middle subplate210around pivot point255b. The top subplate220ais closest to the head of the patient and has an apex facing down towards the top apex of the middle subplate210. The bottom subplate220bis closest to the patient's feet and has an apex facing up toward the bottom apex of the middle subplate210. The apex of the top subplate220ais pivotably connected to the top apex of the middle subplate210at point255a. The apex of the bottom subplate220bis pivotably connected to the bottom apex of the middle subplate210at point255b. The pivoting mechanism is similar to the mechanism inFIG. 6and it allows the top and bottom subplates220a,220bto pivot relative to the middle subplate210counterclockwise and clockwise by a few degrees. Each of the top and bottom subplates220a,220b, has two holes262a,262band262e,262f, respectively, at the two corners opposite their respective apexes, and the middle subplate210has two holes262c,262din its middle corners. Holes262a,262b,262c,262d,262e,262fare dimensioned to receive six screws230a,230b,230c,230d,230e,230f, respectively. The subplates220a,220b,210are top loaded onto the posts of the screws and are secured onto the flanges of the screws with locking nuts260a,260b,260c,260d,260e,260f, respectively. The triangular subplates220a,220bhave central apertures213a,213band the middle subplate210has two central apertures212a,212b, that provide visibility and access to the vertebras82,84,86and discs below them. The process of attaching the plate100to the adjacent vertebras82,84,86is as described above.

Referring toFIG. 17andFIG. 18, an anterior two-level dynamic stabilization system205includes a top loading, two-level dynamic cervical plate100that connects three adjacent vertebras82,84, and86. The dynamic cervical plate100is attached to the vertebras82,84and86via six screws230a,230b,230c,230d,230e, and230fThe dynamic cervical plate100, includes a triangular shaped top plate220a, a diamond shaped middle subplate210and a triangular shaped bottom plate220b. The top subplate220aslides and pivots relative to the middle subplate210around pivot point250avia a ratchet and pivot mechanism, as described above inFIG. 9. The bottom subplate220bslides and pivots relative to the middle subplate210around pivot point250bvia a ratchet and pivot mechanism as described for the embodiment ofFIG. 9. The top subplate220ais closest to the head of the patient and has an apex facing down toward the top apex of the middle subplate210. The bottom subplate220bis closest to the patient's feet and has an apex facing up toward the bottom apex of the middle subplate210. The apex of the top subplate220ais slidably and pivotably connected to the top apex of the middle subplate210at point255a. The apex of the bottom subplate220bis slidably and pivotably connected to the bottom apex of the middle subplate210at point255b. The ratchet and pivoting mechanism is similar to the mechanism inFIG. 9and it allows the top and bottom subplates220a,220bto slide by about 2 mm and pivot relative to the middle subplate210counterclockwise and clockwise by a few degrees. Each of the top and bottom subplates220a,220b, has two holes262a,262band262e,162f, respectively, at the two corners opposite their respective apexes, and the middle subplate210has two holes262c,262din its middle corners. Holes262a,262b,262c,162d,262e,262fare dimensioned to receive six screws230a,230b,230c,230d,230e,230f, respectively. The subplates220a,220b,210are top loaded onto the posts of the screws and are secured onto the flanges of the screws with locking nuts260a,260b,260c,260d,260e,260f, respectively. The triangular subplates220a,220bhave central apertures213a,213band the middle subplate210has two central apertures212a,212b, that provide visibility and access to the vertebras82,84,86and discs below them.

In the embodiment ofFIGS. 19A,19B and19C, an anterior two-level dynamic stabilization system205is already in place and the patient needs to have the next level of vertebra stabilized. In this case, the top subplate220a, is removed and is replaced with a diamond shaped sub-plate310, shown inFIG. 19B. Next, the top subplate is re-installed on the top of the diamond subplate310, as shown inFIG. 19C. The attachment of the diamond shaped subplate310to the middle subplate210is not dynamic, i.e., it allows pivoting but not sliding, whereas the connection of the top subplate220ato the diamond shaped subplate310is dynamic.

Other embodiments are within the scope of the following claims. For example, the bottom subplate may be able to slide relative to the top subplate in the dynamic stabilization system ofFIG. 9. The motion of the top subplate110relative to the bottom subplate120may be vertical156, horizontal157, pivoting155and any combinations thereof, as shown inFIG. 21andFIG. 8A-8B. The plate100may be placed onto the cervical bone first and then may be attached to the bone by screwing the screws130a,130b,130c,130dthrough the holes162a,162b,162c,162d, into the bone and then securing the screws onto the plate100with the locking nuts160a,160b,160c,160d, respectively. The screws130a,130b,130c,130dmay be multi-axial screws with locking housings and “starfish” shape locking nuts that locks into the screw housings. Alternatively, the screws may have a spherically shaped head on the screw with textured surface that allows for angular mounting with a concaved spherically shaped hole or chamfered shaped hole with textured surface in the plate. Then a threaded bolt would be screwed onto the top of the spherically shaped head and lock the system together. Alternatively, multi-axial and oversized holes are formed in the plate and “starfish” shaped locking nuts lock the screws onto the plate. The subplates may have other shapes including rectangular (shown inFIG. 20), square, circular, oval or polygonal.