Internal structure stabilization system for spanning three or more structures

A method and system are described for immobilizing three or more vertebrae. The system includes a first bone anchor assembly, a second bone anchor assembly including a connector having a predefined arc, and at least a third bone anchor assembly. The first and second bone anchor assembly are inserted into the pedicles of vertebrae spanning at least a third vertebra. The third bone anchor assembly is positioned into the third vertebra between the first and second bone anchor assemblies using an arc defining instrument which is used to locate the proper position for the third bone anchor assembly based on the predefined arc of the connector. Once the third bone anchor assembly is in place the connector is rotated into position and captured by the first and third bone anchor assemblies.

TECHNICAL FIELD

This invention relates to bone stabilization systems, and more particularly to systems and methods for immobilizing bony structures such as vertebrae, and even more particularly a device designed to span three or more bony structures.

BACKGROUND OF THE INVENTION

The human spine provides a vast array of functions, many of which are mechanical in nature. The spine is constructed to allow nerves from the brain to pass to various portions of the middle and lower body. These nerves, typically called the spinal cord, are located in a region within the spine called the spinal canal. Various nerve bundles emerge from the spine at different locations along the lateral length of the spine. In a healthy spine, these nerves are protected from damage and/or undue pressure thereon by the structure of the spine itself.

The spine has a complex curvature made up of a plurality (24 in all) of individual vertebrae separated by intervertebral discs. These discs hold the vertebrae together in a flexible manner so as to allow a relative movement between the vertebrae from front to back and from side to side. This movement then allows the body to bend forward and backward, to twist from side to side, and to rotate about a vertical axis. Throughout this movement, when the spine is operating properly the nerves are maintained clear of the hard structure of the spine.

Over time, or because of accidents, the intervertebral discs loose height, become cracked, dehydrated, or herniated. The result is that the disc height is reduced leading to compression of the nerve bundles, causing pain and in some cases damage to the nerves.

Currently, there are many systems and methods at the disposal of a physician for reducing, or eliminating, the pain by minimizing the stress on the nerve bundles. In some instances, the existing disk is removed and an artificial disk is substituted therefore. In other instances, two or more vertebrae are fused together to prevent relative movement between the fused discs.

Often there is required a system and method for maintaining, or recreating, proper space for the nerve bundles that emerge from the spine at a certain location. In some cases a cage or bone graft is placed in the disc space to preserve, or restore, height and to cause fusion of the vertebral level. As an aid in stabilizing the vertebrae, one or more rods or braces are placed between the fused vertebrae with the purpose of the rods being to support the vertebrae, usually along the posterior of the spine while fusion takes place. These rods are often held in place by anchors which are fitted into the pedicle of the vertebrae. One type of anchor is a pedicle screw, and such screws come in a variety of lengths, diameters, and thread types.

One problem occurs in systems designed to span three or more vertebrae. It is currently difficult to properly position a rod between two anchors in adjacent vertebrae. This problem is magnified greatly when a rod is fitted across three or more adjacent vertebrae. Problems occur in maintaining each of the anchors in proper alignment to receive the rod and are compounded by imparting a curve in the rod to account for the natural curvature of the spine, in properly positioning the anchors to accept a pre-curved rod.

What is needed is an improved system and method for fitting a curved rod between three or more anchors anchored to associated vertebrae, where the systems and method insures a proper placement of the anchors and each attachment of the curved rod to the anchors.

BRIEF SUMMARY OF THE INVENTION

The present invention, in one embodiment, describes a method for bracing more than two bones. The method begins with the insertion of a first and second bone anchors in a first and second bone, respectively. The first and second bones, which can be vertebrae, can have at least one other bone between them. The method then includes positioning a pre-formed connector having a predefined curvature between the first and second bone anchors, such that the curved portion of the connector is captured by a third bone anchor positioned in the bone between the first and second bones.

In another embodiment, the present invention describes a spine stabilization device utilizing a first bone anchor inserted into a first vertebra, and a second bone anchor inserted into a second vertebra, where there is at least one vertebra between the first and second vertebra. The stabilization device further including a pre-formed connector having a predefined curve, such that the connector spans from the first bone anchor to the second bone anchor and has the curved body of the connector captured by at least a third bone anchor inserted into a vertebra between the first and second vertebra.

The present invention also describes an instrument for positioning a bone anchor in space between a first and second bone anchor assemblies. The instrument includes a mechanism for defining an arc corresponding to the predefined arc of the connector being used. The mechanism for defining an arc is connected to first and second ends which can be removably connected to the first and second bone anchors, and includes a length defining mechanism which allows the spacing between the first and second ends to be matched to the spacing between the first and second bone anchors. A member is movably connected to the arc defining mechanism, which can removably hold an extension used in placing the third bone anchor in the correct position in space.

DETAILED DESCRIPTION OF THE INVENTION

To better understand the devices, assemblies, tools, and methods described below, an understanding is required of the procedure through which the back stabilization of the present invention is placed into the vertebrae of a patient. Reference is made to the figure numbers where specific embodiments of the devices, assemblies, tools and methods are described in greater detail to aid in the understanding of those particular items.

An operation to insert a pedicle screw assembly into a patient's back to immobilize certain vertebrae in order to allow bone grafts to ultimately fuse those vertebrae begins with the surgeon inserting a standard bone biopsy needle into the pedicle of a first vertebra and using the bone biopsy needle to place a guide wire where the first pedicle screw should be inserted. Using the guide wire, progressively larger tissue expanders are inserted into the patient to expand, or dilate, the incision to the size necessary to accommodate the instruments to be used, with the final cannula being left in the incision after the smaller ones are removed. (see,FIGS. 25-27). Next, an awl (FIG. 28) is used to enlarge the hole in the pedicle made by the bone biopsy needle with the awl being inserted over the guide wire to ensure proper placement in the pedicle. A tap (FIG. 29), having a diameter slightly smaller than the pedicle screw to be used, is inserted down the guide wire and used to tap the hole started by the bone biopsy needle and the awl, making it ready to accept the first pedicle screw.

A first pedicle screw (FIG. 5) with a poly-axial rod-capturing head (FIG. 15) attached to form a rod-capturing pedicle screw assembly (FIG. 14) is inserted down the guide wire using the off-axis screw guide of the pedicle screw and into the hole left by the tap. Attached to this pedicle screw assembly are an extension (FIGS. 30-32) and drive mechanism with a torque head attachment (FIGS. 52 and 53). The extension allows access to the pedicle screw assembly once it is in place. The drive mechanism is used to screw the pedicle screw assembly in place and is removed from the extension once the pedicle screw assembly is set to the desired depth.

A tissue separator is used to make a path from the first and second, and potentially additional, vertebra where the second pedicle screw assembly will be inserted. As described above a bone biopsy needle is used to insert a guide wire into the second vertebra where the second pedicle screw assembly is to be placed. Once the guide wire is in place a measurement tool (FIGS. 46 and 47) is used measure the distance between the first pedicle screw assembly and the guide wire, the measurement determining the length of the rod to be used. The second pedicle screw assembly (FIG. 11) is then chosen according to the proper length of the rod. The second pedicle screw assembly is formed by a pedicle screw identical to the pedicle screw of the first assembly, a poly-axial rod-assembly head (FIG. 3), a slide ring (FIG. 8), and a rod (FIGS. 7 and 9) all connected to another extension. A drive mechanism with a head to accept the end of the rod (FIGS. 48 and 49) is used to drive the second pedicle screw assembly into the pedicle of the second vertebra, using the rod to transfer torque from the drive mechanism to the pedicle screw. As before the pedicle screw is sent along the guide wire using the off-axis screw guide in the pedicle screw. The screw is then inserted to the desired depth using the drive mechanism, which is then removed leaving the extension attached to the pedicle screw assembly.

A rod transfer tool (FIGS. 57 and 58) is then inserted into the extension which is attached to the pedicle screw assembly with the poly-axial rod-assembly head until the distal end of the rod transfer tool (FIG. 59) locks with the end of the rod (FIGS. 60 and 61). The rod transfer tool is then used to disengage the rod from the drive mechanism of the pedicle screw, and guide the rod down into the extension holding the pedicle screw assembly with the poly-axial rod-capturing head, the end of rod ultimately being pressed down into the poly-axial rod-capturing head, where it is held in place by a clip ring (FIG. 16) in the rod-capturing head.

After the rod is pressed into the poly-axial rod-capturing head, the rod transfer tool is removed and locking caps (FIG. 18) are screwed into each of the poly-axial heads using a drive tool and counter torque handle assembly (FIG. 65c). The counter torque handle is used to provide a counter torque force to the torque applied by the drive tool, thereby preventing the loading of the rod assembly with torque when the locking caps are tightened into place.

After the locking caps are tightened appropriately, the extensions are removed leaving the stabilization system (FIG. 1) in place. Bone grafts can then be placed between the two stabilized vertebrae which will then grow to fuse the vertebrae together while the stabilization system holds the vertebral segment.

In addition to stabilization systems connecting two bony structures, such as vertebrae, stabilization systems may be employed that rigidly connect three or more vertebrae. (FIG. 73). In a three pedicle stabilization system, the outer poly-axial head assemblies are inserted into the first and second vertebrae, which surround the third vertebra, as described above. To position the third poly-axial head assembly, an arc defining tool (FIG. 74) is required since the rod has a predefined curvature and the third, or middle, poly-axial head assembly must be precisely located to capture the middle of the rod when it is transferred. Additionally, because of the additional length and curvature of the three pedicle rod over the two pedicle rod, the end of the rod with the drive mechanism is formed with an angle to the drive mechanism to minimize the diameter of the extension required. The additional length of the rod also requires a different rod transfer tool to move the rod into position in the poly-axial head assemblies (FIG. 70), and an extension for the middle poly-axial head assembly (FIG. 71).

FIG. 1shows stabilization assembly10which includes poly-axial head assemblies100and200shown interconnected by rod700. Rod700is shown fastened securely to assemblies100and200by locking caps1800. As described above, poly-axial rod capturing assembly100is anchored in the patient's pedicle by anchor500along a guide wire which passes through off axis screw guide504in anchor500. When assembly100is positioned, a measurement is taken to the pedicle where the second assembly is to be positioned. This measurement determines the length of rod700. The poly-axial rod-assembly200with proper size rod700is chosen and assembly200, with anchor500attached to head300, is positioned in the selected other pedicle with torque being applied to anchor500through drive mechanism in distal end702of rod700which, at that point, is in-line with the longitudinal axis of assembly200. From the in-line position, rod700is rotated such that it has an end captured by poly-axial rod-capturing head1500.

While stabilization assembly10is shown connected by rod700, any type of connector for connecting anchor assemblies100and200could be used and is within the scope of the present invention. Such connectors could include any rod, implant, fastener, or brace used for the purpose of connecting anchors mounted in bony structures. Further such connectors may be rigid, as rod700, may be elastic, as bands, cables or artificial ligaments, or may be dynamic such as the dynamic brace described in U.S. patent application Ser. No. 10/914,751 filed Aug. 9, 2004 and entitled SYSTEM AND METHOD FOR DYNAMIC SKELETAL STABILIZATION, which is herein incorporated by reference.

FIG. 2shows assembly200and it has poly-axial head300, anchor500, rod700and slide ring800. Slide ring800allows rod700to translate in position so that proximal end701can be carefully adjusted to fit into poly-axial rod capturing head1500of assembly100as shown inFIG. 1. Rod700includes a distal end702with a drive mechanism, and a proximal end701shaped such that is can be captured by poly-axial rod-capturing head1500shown inFIG. 1.

FIG. 3shows poly-axial rod-assembly head300having main body316and arms318aand318b. Arms318a, bare created by channel320on the center line of poly-axial head300. A bore extends through the longitudinal center line of poly-axial head300and the bore has a spherical portion having threads324cut therein. As will be seen with reference toFIGS. 10aand10b, the spherical portion allows the head to rotate about the top of a bone anchor while threads324allow head300to gain access to, and interconnect to the head of the bone screw.

Head300also has channels326aand326bin opposing arms318a, b, which arms receive slide ring pins of bracket800as will be described. Head300also has machined surfaces328aand328b. These surfaces allow for locking onto a guide tip or extensions to be described hereinafter. Surfaces328a, bhave torquing surfaces330aand330bfor locking purposes, also to be described hereinafter. Arm318balso has cuts332and334, which accept locking member3700, shown inFIG. 37to enable locking of extensions to head300as will be described in greater detail with reference toFIGS. 30-32. Machined surface328aalso includes a recessed area336which is positioned as a keyway to allow an extension to be locked onto head300in only one direction. Therefore surface336is constructed only on surface328aand not on surface328b. Head300also includes screw threads338for receiving locking cap1800ofFIG. 18.

FIG. 4shows a sectional view ofFIG. 3taken along line3-3, and illustrates spherical portion350with threads324, and cylindrical portion352formed by interior wall401. Spherical portion350with threads324allow the threaded portion of anchor500fromFIGS. 1 and 5, to be threaded onto head300. When anchor500is threaded beyond threads324, the threaded portion of anchor500becomes captured in cylindrical portion352, thereby allowing anchor500to move in relation to head300up to a 30° angle from the center line, which translates into 60 degrees of conical freedom. While 60 degrees of conical freedom is described with reference to the preferred embodiment, any amount of poly axial movement is well within the scope of the present invention.

FIG. 5illustrates anchor500, which in this embodiment is a screw having threads506which are inserted into the pedicle or other bony structure. While anchor500is shown as a screw, any other type of anchor that could be inserted into a pedicle of a vertebra is within the scope of the present invention. Anchor500also includes screw threads501which thread in the opposite direction from threads506for attaching anchor500to head300shown inFIG. 4. Anchor500also includes a torque transfer drive mechanism505, which mates with torque transfer drive706shown inFIG. 7, used in driving anchor500into the pedicle of the spine. Anchor500also includes stop limiting collar502, which is slightly larger in diameter then spherical portion350of head300shown inFIG. 4, allowing head510with threads501of anchor500to be movably held by cylindrical portion352of head300, thereby allowing rotation of head300in relation to anchor500.

As discussed, anchor500also includes threads506which are bone threads used to purchase anchor500into a pedicle. Included near the distal end of anchor500is off-axis screw guide504, which is a cylindrical bore passing through the treads506of anchor500and out tip512. This bore is used to pass anchor500down a guide wire to direct the anchor into a pre-tapped hole in the pedicle as discussed.

FIG. 6is a cross-section of anchor500showing off-axis screw guide504. This channel, at its distal end601, receives a guide wire, the end of which is positioned within the tapped hole in the bone. The screw is passed down the guide wire until distal end601enters the tapped hole in the pedicle. Off-axis screw guide504is at angle alpha from the center line of anchor500. Alpha can be any small angle, but is preferably in the range of 10°-15°. As a bore, or cannulation, through the entire screw, as is commonly practiced in the industry, weakens the screw and limits the size of guide wire that can be employed, the off-axis screw guide504, allows for the benefit of placing the screw in the tapped hole using a guide wire, while preserving the strength of a non-cannulated screw. After the screw has been delivered, the guide wire is removed and the screw can then be screwed into the pre-tapped hole in the pedicle.

FIG. 6also illustrates drive mechanism505for engagement by drive surfaces of tightening tools, such as the drive tool shown inFIG. 52or the drive mechanism of rod700shown inFIG. 7, for driving anchor500into the bone. Stop limiting collar502allows a mated head, such as poly-axial rod-assembly head300fromFIG. 3or poly-axial rod-capturing head1500fromFIG. 15, to have a poly-axial motion with respect to anchor500.

As discussed above, to create a tapped hole in a pedicle, the surgeon inserts a bone biopsy needle into the bone. Then the top portion of the bone biopsy needle is removed and pulled out leaving a cannula (an open tube) extending from outside the patient down to the newly created hole in the bone. A guide wire, which can have a diameter on the order of two millimeters, is passed down inside the cannula and over the guide wire and dilators are sent down to create a passageway between the muscle tissue.

Next, the anchor, or bone screw, must be inserted into the hole. Typically, a cannulated screw is used with a hole all the way through the longitudinal axis. Because some of the screws can be as small as 5.5 millimeters on the major diameter, the minor diameter is extremely small. Consequently, only a very small hole will work because otherwise the screw loses strength. Thus, the holes tend to be small, on the order of 1 millimeter. However, even with a cannulation of 1 millimeter the screws may break, either as a result of misplacement, or when they are used on heavy or active patients. Also, a small cannulation diameter requires a small guide wire, which in turn creates several problems for the surgeon. Small wires can kink, or become bent, or get caught when the screw is being advanced.

When a guide wire is caught inside a screw it begins to advance with the screw and can move beyond the plane of the vertebral body thereby puncturing through the anterior portion of the vertebral body causing trauma to the soft tissue and vessels anterior to the vertebral body. The anchor of the present invention, which is formed with the off-axis screw guide, together with a cannula with a groove down its entire length allows the guide wire to remain outside the cannula while the screw is within the cannula. This allows for much thicker guide wires to be used, for example 2 millimeters in diameter, without sacrificing the strength of the screw or having guide wire issues of kinking or wire advancement while the screw is being positioned.

FIG. 7illustrates rod700which has distal end702in which drive mechanism706is positioned. Drive mechanism706mates with drive mechanism505as shown inFIG. 12. Rod700also includes rod curved body portion703in which the rod is partially curved to conform to a patient. Sliding surfaces705are constructed to engage with slide ring800(FIG. 8).

Proximal end701of rod700must accomplish at least two functions, first driving the rod/poly-axial head assembly as an extension of a driver, such as the one shown inFIG. 48, and second being captured by poly-axial rod-capturing assembly1500shown inFIG. 15, which allows for the repositioning of rod700from the in-line position shown inFIG. 11to the “horizontal” position for mating with assembly100as shown inFIG. 1. Specifically, rod700has driving surface710to engage a special head of the driving tool shown as head4901inFIG. 49. Driving surface710engages with the head of the driving tool and allows torque to be transferred from the driving tool through rod700and into anchor500which is then screwed into a pedicle or other bony structure. Opposing drive surface710is locking surface714which is designed to engage with the bottom surface of locking cap1800fromFIG. 18. The locking of rod700using locking caps1800will be discussed in greater detail with reference toFIGS. 22 and 23

Proximal end701of rod700also includes spherical portion711having a diameter larger than the diameter of rod700for the purposes of allowing the cavity of poly-axial rod-capturing head1500(FIG. 15) to capture rod700and to keep the spherical portion711engaged with head1500as will be discussed with greater detail with respect toFIG. 15.

Proximal end of rod700must also be capable of being captured by rod transfer tool5700shown inFIG. 57, such that the rod transfer tool is engaged with rod700until it is nearing the horizontal position at which point rod700must disengage from the rod transfer tool so that it may be engaged with the poly-axial rod-capturing head. Rod transfer tool engagement mechanism720, which is duplicated on the opposing side of spherical portion711includes ramp715which allows tines5905aandbfromFIG. 59of the rod transfer tool to slide up, over lip722, and into recess713, thereby engaging end701with the rod transfer tool until tines5905aandbof rod transfer tool5700are turned to the point that they can slide out of exit ramp716, which controls the release of the tine from end701. While engaged in recess713, tines5905aandbare free to rotate about an axis normal to flats712aand712b.

As the tool pushes on proximal end701, that end rotates toward assembly100(FIG. 1) until end701of rod700is in position to be captured by head1500. At that point, the angle of rod700with the pushing instrument is such that the tines of the instrument are pushed out of cylindrical recess713and out through exit ramp716thereby releasing proximal end701to be engaged into head1500. The operation of rod transfer engagement mechanism, along with the distal end of the rod transfer tool ofFIG. 57will be discussed with greater detail with reference toFIGS. 63 and 65a.

Once engaged with both heads300and1500, locking caps can be inserted into each of heads300and1500, such that the ends of the locking caps are engaged with locking surfaces714and704. Locking surfaces714and704are preferably curved to have locking cap1800, shown inFIG. 18, not force rod700into a position that is normal to the bottom of the locking cap, but rather a position that allows rod700to assume its natural rotation. Thereby allowing for installation of the rod in positions that accounts for variations in anatomical positioning of the vertebral bodies.

FIG. 8illustrates slide ring800which includes main body cylindrical portion805, and extension dog-ear tines802aand802b. Dog-ear tines802a, andballow rod700to register with racetrack openings326a, bof head300as shown inFIG. 3. This facilitates up-down movement of rod700with respect to assembly200(FIG. 1). This then allows for a variation in height of the rod to occur when the rod is in process of being translated from an in-line position to an approximately 90 degree position for engaging rod-capturing assembly100.

Also, as shown inFIG. 8, slide ring800includes a portion having flats803a,803band803cand partial flats806aand806bforming a hexagonal saddle in which sliding surfaces705rest. While a hexagonal saddle is shown, any shape of saddle may be used that captures rod700in a manner that prevents rotation of rod700within the slide ring and allows rod700to slide freely therein. As stated, these surfaces are constructed to allow slide ring800to mate with flats705of rod700and to allow rod700to slide in head300while being held by slide ring800which in turn is held by ears802aand802binside openings326aand326b, respectively, of head300. Surface804is used to contact anchor500fromFIG. 5during the locking of the poly-axial head assembly, which will be discussed in greater detail with reference toFIG. 22a

FIG. 9shows rod700mated with slide ring800which allows rod700to move laterally with respect to slide ring800. The preferred distance of such movement, approximately 1 centimeter of translation, is allowed along track705. For multilevel procedures, discussed with referenceFIGS. 67-77, approximately 15 millimeters of translation is required.

FIGS. 10aandbshow the mating of head300with anchor500, with the following description applying also to the mating of head1500fromFIG. 15with anchor500. Anchor500has stop limiting collar502and threads501. As threads324in spherical portion350of head300advance beyond threads501, spherical portion510of anchor500becomes captured by cylindrical portion352of head300. This allows angulation, shown inFIG. 10b, between head300and anchor500with the preferred angulation to be about 30 degrees from centerline, yielding 60 degrees conical motion. An interesting feature to note is that screw threads501of anchor500and screw threads324of spherical portion350essentially bind creating a cold weld type of mate when pressure is applied from the top in an axial direction through the rod and slide ring to drive505, such as when locking cap1800fromFIG. 18is tightened into head300.

FIG. 11shows a complete poly-axial rod assembly1101formed by anchor500mated with poly-axial rod assembly head300which is in turn holding rod700, where rod700is shown in its in-line orientation with anchor500.

FIG. 12is a cross-sectional view ofFIG. 11showing that in the in-line orientation, drive mechanism706of the rod700is mated with drive mechanism505of anchor500, such that assembly1101is ready to be delivered into the pedicle as discussed above.

FIG. 13shows rod700in the process of being translated from the in-line orientation such as would occur when rod700is being rotated for mating with a rod-capturing head assembly (not shown). The procedure and tool used for this translation will be described hereinafter. Note that during this translation, ears802aand802b(not shown) move upward in opening326awhile rod700is free to move laterally with respect to head300via flats705riding in the slide ring.

FIG. 14shows a poly-axial rod-capturing assembly100having rod-capturing head1500positioned on anchor500. Clip ring1600is shown positioned in groove1510constructed on the inside face of body1401. Ring1600opens by moving backwards as force is applied to it by mating end701of rod700(not shown). Once end701passes into housing1401, ring1600resumes its normal dimensions thereby preventing rod end701from coming out of body1401resulting in rod end701being captured by head1500. The force required to deform ring1600and the returning of ring1600back to its original position yields a tactile as well as audible sensation which can be felt and heard by the surgeon performing the procedure, allowing the surgeon to know that the rod has been placed in the proper position in head1500. Note that the back wall of clip ring groove1510is of a greater diameter than outer diameter1604, shown inFIG. 16, of clip ring1600. Therefore, clip ring groove1510has room to allow for the expansion of clip ring1600into the groove to allow spherical portion711of rod700fromFIG. 7to pass by clip ring1600.

FIG. 15shows head1500having threaded spherical portion1520for mating with anchor500as discussed above with respect to head300. Reduced area1521aand1521bform a groove with ledge1501acting as a stop. This groove accepts an extension, such as the extension shown inFIGS. 30-32. Body1401includes a horseshoe opening1522and interior surfaces1506aand1506b. Horseshoe opening1522is sized to accept body703of rod700fromFIG. 7, while being smaller than spherical portion711of rod700, preventing rod700from pulling out of head1500.

Above surface1501there are two arms,1521aand1521b. Arms1521aand1521binclude torquing surfaces1523aand1523bwhich allow delivery of a counter-torque when held by a tool as will be described with reference toFIG. 66a. When final tightening is given to locking cap1800, surfaces1523aand1523bmate with the tool as will be described. Key way1507allows for uni-directional assembly of head1500on the extension insuring proper orientation of the extension in relation to head1500. Threads1508are designed to receive locking cap1800. On the far side of housing1401channel1509allows for assembly of the extension. Slots1511and1512are positioned on arm1521bto accept a locking slider, described with reference toFIGS. 30 and 37from the extension.

FIG. 16illustrates clip ring1600that mates inside clip ring groove1510of head1500as discussed. Clip ring1600has an outer diameter1604and an inner diameter1603and keeping arms1601aand1601b. These keeping arms have flat surfaces1605a, b for preventing rotation of the clip ring in the groove. Clip ring1600splays apart as the spherical end portion of rod700exerts a force on clip ring1600as it enters head1500. When the spherical portion711of rod700enters head1500the spherical portion contacts inner diameter1603of clip ring1600and requires the expansion of1601aand1601baway from one another to allow the spherical portion to pass. Once that portion has passed, there is a tactile snap that is felt when1601aand1601breturn to their proper position. Holes1602aand1602ballow for installation of clip ring1600into snap ring groove1510of head1500.

Clip ring1600also acts to prevent the spherical portion711of rod700from passing upward out of head1500. As mentioned, rod703cannot pull out of channel1522because channel1522has a smaller diameter than does spherical portion711of rod700. The capturing of rod700in rod-capturing head1500allows the surgeon to then perform other activities that could take many minutes, all while knowing that rod700is captured properly, even though locking cup1800has not yet been either installed or tightened with the final tightening force. Rod end701cannot pull out of head1500laterally, nor can it lift vertically. In addition to allowing the surgeon to perform other procedures before locking the assembly, this system allows the rod to be traversed to adjust for a compression or distraction without worry that the rod will become dislodged from head1500.

FIG. 17is a cross-section of screw assembly100showing threads1508for receiving locking cap1800and also showing threads1520of head1500corresponding to threads501of anchor500. Also the relationship between clip ring1800, spherical portion711of rod700, and drive mechanism505of anchor500are shown when rod700is in the captured position before locking cap1800is installed.

FIG. 18shows details of locking cap1800with threads1803for mating with threads1508of head1500or head300. Cap1800has boss1801for applying force to a captured rod. Driving mechanism1802for tightening the cap is also shown.

FIG. 19is a cross-sectional view of cap1800illustrating threads1803which can be, for example, the type shown in U.S. application Ser. No. 10/805,967, filed Mar. 22, 2004 and entitled CLOSURE MEMBER FOR A MEDICAL IMPLANT DEVICE, hereby incorporated by reference herein. Also shown are extruded appendages1902and1903for the purpose of reducing surface area, therefore increasing pressure when locking cap1800comes to bear on a rod.

FIG. 21illustrates the thread interaction of a helical dovetail interlocking thread2101as described in the above-mentioned application Ser. No. 10/805,967. Thread2101is on cap1800while mating threads2102is on head1500(300). As described in the referenced application, the dovetail threads act to pull the thread of the head inward, instead of acting to place an outward force, causing the walls of the head to splay outwardly as would occur using normally shaped threads.

FIG. 22ashows the relationship between rod700, which is positioned in slide ring800, both positioned in head300, locking cap1800and anchor500. Appendage1903on locking cap1800exerts a force on locking surface704of rod700when locking cap1800is tightened into head300. Surface804of slide ring800in turn exerts a force on drive mechanism505of anchor500. The force of tightening locking cap1800therefore, exerts the necessary forces on the elements of assembly200to hold the elements rigidly in place relative to one another.

FIG. 22bsimilarly shows the relationship between spherical end711of rod700, locking cap1800and anchor500. Appendage1903on locking cap1800exerts a force on locking surface714of rod700when locking cap1800is tightened into head1500. Surface710of rod700in turn exerts a force on drive mechanism505of anchor500. The force of tightening locking cap1800therefore, exerts the necessary forces on the elements of assembly100to hold the elements rigidly in place relative to one another.

FIG. 23is a cross sectional view showing an alternate embodiment of a locking cap1850in relation to rod700, slide800, and poly-axial head300. Where locking cap1800ofFIG. 18is a single body which is threaded into a poly-axial head, such as head300or head1500, and engaged surface704or714on rod700fromFIG. 7as appropriate, locking cap1850is formed by two distinct elements, namely locking ring1852and compression cap1856. Locking ring1852threads into poly-axial head300, which could also be poly-axial head1500, by means of threads1858. Threads1858are described in greater detail with reference toFIG. 21. Locking ring1852also includes drive mechanism1854which accepts a male drive mechanism head such as the one shown inFIG. 66battached to drive shaft6505. Locking ring1852is inserted first, after rod700is properly positioned, and acts to compress guide ring800, through surface1868of the locking ring mating with surface1866of the slide ring, which in turn causes guide ring800to compress anchor500. This results in immobilizing head300relative to anchor500, eliminating the poly-axial movement of head300and anchor500. Locking ring1852locks the head/anchor assembly together but does not compress rod700when it is installed allowing the rod to slide in guide ring800allowing assemblies100and200fromFIG. 1to move relative to one another so that the positioning of the entire assembly can be finalized.

Once the positioning of the assemblies is finalized, and any other tasks needed before the rod is compressed and made rigid, are finished, compression cap1856can be installed in locking ring1852. Compression cap1856is threaded into locking ring1852by means of threads1862and drive mechanism1860. When compression cap is tightened into place, surface1864contacts surface704, or714for assembly100fromFIG. 1, and compresses rod700, causing rod700to lock into place with respect to guide ring800and become rigid, or immobile in the same manner described with reference to locking cap1800inFIGS. 22aandb.

Locking cap1850has advantages over locking cap1800in that it allows assembly100or200to be locked together in two phases instead of the single phase of locking cap1800. The first phase, the insertion of locking ring1852, allows the poly-axial motion of the assembly to removed, holding head300rigid with respect to anchor500, but not compressing rod700so that rod700retains the ability to slide within slide ring800. The second phase, the installation of the compression cap, compresses rod700with slide ring800, thereby causing them to be held rigidly in place and preventing any further motion with respect to rod700and guide ring800. This two phase approach allows for adjustments to be made while the assemblies are held rigidly in place but rod700is still free to slide laterally within guide ring800, allowing for greater flexibility in the delivery of the stabilization system.

FIG. 25shows guide wire2501intended to be positioned in a pedicle (not shown). Dilators2502,2503,2504,2505are positioned over guide wire2501in consecutive larger dimensions, with approximately 1 inch separation in height from each. The first dilator2502has hole2508longitudinally therethrough which allows dilator2502to pass over guide wire2501. Dilator2502has distal end2509which is tapered to allow for ease of assembly and insertion through the tissue. Dilator2503is then passed over dilator2502. Dilator2504is passed over dilator2503and then dilator2505is passed over dilator2504. Note that dilator2505has slot2508down one side to allow for the removal of wire2501and guiding a screw to the bone as discussed above.

FIG. 26is an alternate method for inserting working cannula2505that uses what is called an obturator such as obturator2601, which includes three parts. Part1is handle2602which has a driving surface or palm gripping surfaces2603, and also has a hole2605which goes down the length of the handle for passing over guide wire2501. Handle2602also has hole2604for the purposes of receiving tube2607which is part2. Tube2607has distal end2610which is tapered for passing the obturator through the tissue. Obturator2601acts as the first three dilators and has key way hole2608which allows key2609to be pressed into key way hole2608. The key way acts to center guide wire2505when obturator2601passes over the guide wire. Proximal end of tube2607has radial surface2611which is pressed into hole2604of handle2602. Part3is dilator2505with slot2508therein

FIG. 28shows awl2801. As described above awl2801may be used to enlarge the hole in the pedicle formed by a bone biopsy needle, but it is not required where the bone biopsy needle, is large enough in diameter to make the awl unnecessary. The purpose of an awl is to break through the tough cortical bone that is present at the entrance to the pedicle. This is helpful for patients having high bone density. Awl2801has handle2802that is much like obturator handle2602. Handle2802has opening2803therein for allowing the awl to pass over guide wire2501fromFIG. 25. Awl2801also has tube2804with distal reduced diameter surface2805. The distal end has cutting surfaces2806, typically three but any number will work. These surfaces are serrated around exit opening2807. The awl is passed over the guide wire and then rotated down into the bone until shoulder2808contacts the bone. The awl is then pulled out, leaving a hole in the bone. Awl2801may also be used to create an indentation at the bone entry point, the purpose of which is to facilitate the seating of the tip of anchor500fromFIG. 5at the anchor entry point

FIG. 29shows tap2901for creating threads in the bone using threads2906. The diameter of the tap is typically anywhere from a half of a millimeter to 1 millimeter undersized from the thread size of the screw that will be placed in the bone. The actual size depends on bone density. The greater difference in the tap size to the screw size determines how much fixation and pull-out strength the screw will have. Preferably, one would use a half millimeter undersized tap. Thus, for a 6.5 millimeter screw, a 6 millimeter tap would be used. The tap has indicators2903on main body2905which identify how deep the surgeon has gone. Lines2903typically are in 10 millimeter increments. Body2905has reduced diameter portion2904at the distal end. At the extreme distal end are cutting surfaces and threaded surfaces2906which are in the shape of an acorn. The acorn shape facilitates easier tapping and traveling down the middle of the pedicle rather than using a tap having longer straight threads which tend to follow the trajectory of the guide wire. The acorn tap tends to be more forgiving and finds the center of the pedicle because it seeks the softest bone. The guide wire passes out of awl2901via opening2907.

The tap, as shown, is a fully cannulated tool. At the proximal end, handle2902is typically a straight ratchet handle. This could be a non-ratchet or a T handle and it mounts to tap2901for the purposes of ease of insertion of the tap. The tap has a tapered distal end2904so as to facilitate proper seating within the hole so that the tap is started easily.

After the pedicle has been tapped to the desired depth, the tap is removed and the guide wire remains inside the largest cannula, which is cannula2505shown inFIGS. 25,26, and27. Before the screw can be inserted, an extension must be attached to the head assembly100(200) to create a communication channel from outside the skin to head300or1500as appropriate.

FIG. 30shows an embodiment of an extension used to facilitate the insertion and assembly of the stabilization system and method described in accordance with the present invention. Extension assembly3001includes tube3002which attaches at one end to a poly-axial head, such as poly-axial head300or1506. Over the opposing end of tube3002a locking ring is installed with spring3004. Drive head3006, which is used to tighten the extension to a poly-axial head, and to provide attachment for an anti torque handle, attaches to locking ring3005and tube3002using torque key3007for proper positioning. Extension assembly3001also includes slide3700which fits into a slot on tube3002and engages locking ring3005by means of pin3704.

FIGS. 31 and 32shows extension assembly3001assembled. Starting at the proximal end, thread3603in drive head3006acts as a mechanism for mating the driver guides which are part of the drive assemblies shown inFIGS. 48 through 55, to be described hereafter. Torque flats3602are used with anti-torque handle shown isFIG. 66a, as will be described. Drive head3006mates with locking ring3005. Locking ring3005provides the mechanism for locking the extension to the poly-axial head assembly, such as the ones shown inFIG. 11or14. Locking ring3005includes slot3806which is formed in locking ring at an angle by having the slot begin at one end below the midline of the locking ring and end at the other end above the midline. Slide3700is coupled to slot3806of locking ring3005by means of pin3704and extends down tube3002where it can engage with a poly-axial head connected to the extension.

While slide3700will be shown in greater detail with reference toFIG. 37, its purpose is to lock a poly-axial head with the extension. It accomplishes this by sliding up and down the tube in response to the twisting of the locking ring3005. Twisting locking ring3005causes slot3806to move from its low end to its high end or vise versa. Pin3704coupled to slot3806translates the twisting motion of the locking ring3005into a linear up and down motion by slide3700as pin3704traverses slot3806from low to high or high to low. A locking extension at the end of slide3700proximal to the poly-axial head, shown inFIG. 37as element3701, locks the poly-axial head in place by engaging with slots332and334of head300fromFIG. 3or slots1511and1512of head1500fromFIG. 15. The poly-axial head is unlocked by moving the locking extension of slide3700out of the referenced slots by twisting locking ring3005such that pin3704moves to the high position in slot3806.

Tube3002includes numbers and lines3101positioned in 10 millimeter increments, which are used, if desired, to determine the depth the anchor has been threaded into the bone. Tube3002remains constant and the screw turning tool is inside the tube. If a surgeon desires to go down 40 millimeters then he/she would take a tool with a mark on it and move the mark, for example, from 1 to 5. Tube3002has several openings. The first opening is3103. It is the largest opening with a distance d2. The second opening is opening3104having a reduced distance d1. This change of distance is important during rod transfer (rotation from in-line to horizontal) because the rod proximal end enters tube3001at3103and is guided into the poly-axial head held by tube3002by the reduced opening formed by distance d2.

Protuberance3601a, shown inFIG. 32, interacts with indentions3801aand3801bfromFIG. 38on twist ring3005. These indentions prevent the twist ring from inadvertently twisting thereby raising slider3700causing the assembly to unlock. In operation, to unlock the assembly twist ring3005is pushed down freeing latch3801afrom latch3601a. Spring3004holds the twist ring upward into a latched position. Window3202allows the rod to back out of the attached head during its transfer. Window3102is used for inserting multi-pedicle systems as will be discussed in greater detail with reference toFIGS. 67-77.

FIG. 33describes details of the distal end of tube3002ofFIG. 30. Starting at the top here is dovetail slide groove3503. Opening3202is below the slide groove next to opening3301adapted for receiving head300or1500. Also shown is channel groove3306having top surface3303. Grove3306creates radial surface3305, which is also a surface for keying onto head300(1500). Bottom surface3304is adapted for contacting the head as well. Torquing surface3302connects to the head to allow for torque transfer from the extension to the head when the pedicle screw is being tightened, as will be discussed.

FIG. 34shows openings3103and3202with key3401adapted to engage the head as will be discussed hereinafter. Opposite side torquing surface3402is shown as is surface3405which is a groove similar to groove3306(FIG. 33). Triangular cut3503and surfaces3403and3404are adapted for mating with the head. Reduced diameter portion3404mates to the head as well. These parts are designed to prevent a radial motion between the parts when slider3700is down and mating the groove of the head. Groove3405which mates to a portion on the head functions to prevents separation that could be caused by an upward force on extension3001.

FIG. 35is a top down view looking down at tube3002illustrating dovetail channel3503, as will later be described, for receiving sliding member3700fromFIG. 30. Triangular portion3502receives key3701of slider3700shown inFIG. 37. Also shown inFIG. 35is key way cut3501for receiving torque key3007shown inFIG. 30. Torque key3501mates with slot3605fromFIG. 36, to be described hereinafter, for the purposes of transferring torque so that when counter-torque is applied against flat3602shown inFIG. 30such that transmission of torque is allowed from top proximal member3006fromFIG. 31through torque key3007to the lower portion of extension3002.

FIG. 36shows that the proximal end of head3006has surfaces3602for the transmission of the torque as described. Line3604shown inFIG. 36is an alignment line used to align the extensions relative to one another. Thread3603is used to accept a tool as will be described. Torque key groove3605is where key3007ofFIG. 36mates. The torque goes between groove3605and slot3501, shown inFIG. 35, such that the one side surface is against the back wall of slot3501, and the other surface is against the back wall of slot3605. Protuberances3601aand3601b, as described hereinafter, serve to lock the position of twist ring3005(FIG. 30) in the desired position.

FIG. 37shows slide3700having at its proximal end pin3704. Body3702has three surfaces,3703a,3703band3703c. These surfaces go into the three mating sides of dovetail3503of body3002as shown inFIG. 35. Triangular element3701is positioned at the distal end of slider3700and acts to lock head300onto the extension as has been described.

FIG. 38shows twist ring3005having slots3801aand3801bfor receiving protuberances3601a,3601bof top portion3006fromFIG. 36. Ring3005has central bore3802wherein it is positioned over the top portion of tube3002which is shown inFIGS. 30 and 35. Ring3005also has middle body3805and distal surface3804. Within middle body3805there is slot3806which is a helical pattern with ends3807and3808which are positioned approximately 180 degrees from one another. Slot3806receives pin3704of slider3700. Since slider3700is fixed in rotational position, when the twist ring is rotated it forces slider3700to move up or down as pin3704travels inside slot3806. The down position would be when pin3704is against stop3807and the up position would be when pin3704is against stop3808.

FIGS. 39 and 40show head300with channel320. Key128ais adapted to mate with tube3002. When the parts are mated part3901is locked into extension3002. On the opposite side male surface3401of extension3002is mated with female portion336of head300as well as328band the torquing surface330a. Torquing surface330bis also shown inFIG. 39.FIG. 40shows channel320as well as slider mating surface332of head300. This forces the head into the extension in only one direction.

FIG. 41shows a cross-section when top section328aof the poly-axial head is inserted until it is in contact with surfaces3306and3405of the extension. Opening3103is shown illustrating torquing surface330bthere and330aon the opposite side. Opening3202of the extension is shown at the bottom. One important part of this figure is that portion3401is shown interacting with portion336, and portion3901of head300is mated with portions330band330aof extension3002. This makes this a one-way device that can not go in the other direction, and a clockwise rotation of the head or a counter-clockwise rotation of the extension would bring surfaces330band3302and surfaces330aand surface3402into contact, thereby trapping the head in a vertical position.

FIG. 42shows head300being twisted into locking position with respect to extension3002.

FIG. 43is a cross-section through the midline of the3303groove fromFIG. 33. With rotation,330aand330bare in contact with portions3402and3302respectively. Opening3202is shown as well as opening3103. Channel332of head300is positioned at the same position as channel3503so as to be in position to receive slider3700, tab3701. Portion328ais positioned in its locked position as shown with portion330bstopped against stop3302and with330astopped against stop3402.FIG. 42shows that there is an actual axial trapping by using the male/female key way.

FIG. 44shows slider3700pushed down into locking position by twisting the twist ring (not shown) to reposition the twist ring into its lower position forcing slider3700down so that element3701fromFIG. 37engages in groove332.

FIG. 45shows this operation in cross-section with locking element3701of slider3700engaged with groove332in head300. At this point the head is locked axially and cannot rotate out of its axial position.

FIG. 46shows one embodiment of a measurement tool, such as tool4600, having legs4602and4603and indicator arm4605that moves in relation to arm4604having the actual measurements thereon. Indicator arm4605has indictor4613thereon showing distance between screws displayed in lines of numbers4612. Handle4606is an extension to leg4603and has a bend for finger insertion. Leg4602has handle4607, As the handles move apart so do the legs, pivoting around pin4608. Fixed portion4620pivots around pin4609connected to leg4603while indicator arm4605pivots around pin4610attached to leg4602. Both parts then pivot about pin4611so that as the distal ends4615and4614separate from one another, legs4603and4602pivot about pins4608and4611causing arm4605to move across the path of the radius of the arc between pedicle screws. The radius in this case being the length from pin4611to the numbers on measuring arm4604. This then reads the distance at the distal end of the tool. The numbering on arm4604is adjusted to account for the variance between the implanted pedicle screw and the arm.

Tool4600has two openings4616and4617at the bottom of legs4603and4602, respectively. These openings are to engage whatever features they are to measure the distance between. This measurement tool would be typically used once one screw is positioned. Also, measurements can be taken across two guide wires between pedicles so that a rod length can be selected.

FIG. 47shows tool4600inserted in cannula3001in contact with the head of the first implanted screw such as assembly100, fromFIG. 1. Distal end4617of tool4600comes to rest on top of drive505and mates with drive505. Leg4603is then positioned over guide wire2501and slipped down the guide wire to the base of the pedicle. This then allows the surgeon to read the pedicle to pedicle distance on the tool. The measurement tool can also be used to measure cross connector lengths, or another distance within the limits of the scale of the measurement tool.

FIGS. 48 and 49describe one embodiment of a driver, such as driver4800. Driver4800has three components as shown inFIG. 49. Component4804is the distal end which mates with proximal end701of rod700. This mating is primarily via surface710, but can also be with flats712aand712b, for the purposes of delivering torque from the user's hand down through the driver to the rod and through the rod to the screw.

FIG. 50shows screw assembly200fromFIG. 1inside extension3001with tool4800about to go inside extension3100. Handle2902will mate with tool4800. Portion3001has been latched onto head1500as described above. Tool4800is then passed down inside the extension and mated with the proximal end of rod700. Then threads4907are threaded into threads3603of extension3001forcing distal end4902against rod end711. The threads are used to compress the assembly completely, such that a rigid assembly occurs, allowing the surgeon, using ratchet handle2902on proximal surfaces4913and4911of tool480, to rotate anchor500.

FIG. 51shows spherical surface711captured by distal end4902of tool4800inside extension3001. As portion4802turns, threaded sleeve4803does not turn since portion4802turns inside bore4906of thread sleeve4803. When tool portion4802turns, the rod700turns and turns anchor500. During this time, rod700is effectively part of the anchor driving mechanism. By forming the poly-axial rod-assembly head300in this manner, rod700is part of the anchor assembly and does not need to be inserted after the anchor assembly has been put in place. This means that the rod does not have to be delivered from outside the extension into the patient after the anchor assembly has been set.

FIG. 52shows one example of a tool, such as tool5200, used to drive in the screw associated with assembly100fromFIG. 1. This differs from tool48FIG. 48by replacing drive head4901which is designed to mate rod700with drive head5205which is designed to mate with drive mechanism505of anchor500in assembly100. Tool5200, therefore, is designed to go all the way down and interact with the drive means on the anchor itself. At the distal end there is distal driving member5203and drive head5205ending in driver5204which connects with the drive means of the screw. The upper portions of tool5200operate as does tool4800.

FIG. 53is an exploded view of tool5200, and differs from the tool ofFIG. 49only in the choice of drive heads.

FIG. 54shows screw assembly100fromFIG. 1, extension3001, screwdriver5200which is passed down through extension3001to engage the top of the drive mechanism (not shown) of anchor500inside head1500.

FIG. 55shows the assembly of anchor500, head1500, extension3001, tool5200and handle2902. This assembly is then sent down into the bone after the tap (over the guide wire on the off axis screw guide, if desired) so that anchor500can be embedded in the pedicle. The guide wire is pulled out and retracted and then the screw is able to overtake the axis that the guide wire had and is then turned down into the waiting tapped hole.

FIG. 56illustrates one instrument for the procedural step of separating muscle and fascia tissue between the first and second assemblies100,200. Tool5600has handle5602and blade5603. Blade5603has a sharp cutting portion5604and also has tip5606. On the inside of that tip5606is cutting surface5605. After the pedicle is tapped, tool5600is used to open a channel from the screw to the next pedicle. This is done by working through the tissue and separating the muscle. Tool5600is not intended to be a cutting instrument, but rather a separating instrument. However, if the distal end gets caught on a piece of deep fascia, the surgeon pulls up and the blade tip5606cuts that deep fascia. This allows the surgeon to work over to the second pedicle, creating a separated plane of tissue.

After the second guide wire is inserted and dilation has occurred, an inter-pedicle measurement is taken as discussed above so that a proper length rod can be selected. The rods could be 25, 30, 35, 40 millimeters, or greater, in increments of 5 mm or any other increment that would be appropriate. Once the rod is selected it is added to the assembly discussed with respect toFIG. 11.

FIGS. 57 and 58illustrate one example of a rod transfer tool5700. The handle is a “pistol grip” having elongated portion5702and an elongated portion5703which rotates about pin5704to form a trigger. The trigger pushes sliding member5705which moves along elongated portion5706. Movement of portion5706operates to rotate distal end portion5707about pin5708. As slider5705moves forward, distal arm5707rotates about pin5708as shown inFIG. 58. Pin5709allows for partial pushing motion between slider5705and end portion5707. Distal end5710transcribes on arc as it rotates upward as is shown inFIG. 58.

FIG. 59shows details of arm5707partially rotated about pin5709. Racetrack cut5909allows pin5709in the proximal end of arm5707to move from the up position to the down position and then back up to the top. Flat area5902of arm5707engages slider5705and handle5706. Rod transfer tool5700is designed to grasp rod700at proximal end701and pulls rod700along the path to poly-axial rod capturing assembly1500, at which point rod transfer tool5700, by means of cam5908pushes rod700out of arm5707and toward head1500. At no time does rod transfer tool5700apply pressure to the sides, top or bottom of rod700.

Distal end5710has bore5906which is a pocket having cut5910for purposes of pushing the rod and urging the rod down into poly-axial rod-capturing assembly100fromFIG. 1when the rod is being transferred. End5710also has two tines5905aand5905bin pocket5906. Channel cut5907allows tines5905aand5905bto be sprung away from one another when they are being inserted onto the spherical portion711of rod700. Raised radial surface5908acts as a cam to push the rod away from arm5707when the rod meets the particular exit angle as will be described hereinafter.

FIG. 60shows pocket5906of arm5707as well as spherical portion701of rod700. Note that channels713in the rod end allow tines5905aand5905bto exit from rod end701when the rod is rotated into position. The tines enter via opening715which is sloped to act as a ramp to facilitate entrance of the tines. Tines5905aand5905bhave partially radial surfaces6001, interrupted by flat cut surfaces6002.

FIG. 61shows how instrument5700operates, reference will be made to rod700and its features shown in detail inFIG. 7. Once poly-axial rod assembly200fromFIG. 1is inserted into the bone with extension3001connected to head300, instrument5700is inserted down the bore of extension3001as shown. Distal end5710of tool5700engages proximal end701of rod700causing tines5905aand5905bto splay apart as they engage the ramp at the proximal end of the rod, as discussed above. When the tines get to lip722of ramp715they drop into recess713. The shape of tines5905aand b insure that they remain in recess713until the end of tool5700is rotated into the release position. Tines5805aandbhave a large diameter which is perpendicular to exit ramp716and larger than the transition from recess713to exit ramp716. Tines5905aand b also have a small diameter which becomes perpendicular to exit ramp716upon the rotation of rod700in tool5700. The small diameter of tines5905aandbis smaller than the transition to exit ramp716allowing tines5905aandbto exit their engagement with rod700at the proper orientation.

Once the rod700is engaged with tool5700, upward pulling force is exerted by the surgeon which lifts rod700out of mating relationship with anchor500by disengaging drive mechanism706of rod700from drive505of anchor500as described inFIG. 5. Pulling up moves slide ring800to the top of channel326a, b(FIG. 11) so that the distal end of the rod clears the top of drive mechanism505as it rotates over. By squeezing the trigger5703of tool5700, the surgeon begins the rotation of arm5707which, in turn, causes rod700to pass through open slot3103portion of extension3001fromFIG. 31.

FIG. 62is a section taken through lines62-62ofFIG. 61illustrating ramp715, channel cut5907and arm5707. Tines5905aand5905bare snapped into cylindrical recesses713on rod700. The rod is captured and can be pulled up as discussed above.

FIG. 63is a cut-away view illustrating the orientation of tine5905ain rod hole713. Rod arm5707has pocket5906around rod700. Tines5905aand b (b not being shown) entered via ramp715. Tines5905aand has four surfaces. It has flat surfaces6002aand6002bon the small diameter and curved surfaces6001aand6001bon the large diameter. As stated, once the tines snap into the holes they cannot come out until arm5707is rotated so that the flats on the tines line up with exit slot710. This can only occur when arm5707moves through an arc of approximately 90°.

FIG. 64illustrates tool5700in operation with arm5707rotating rod700from extension3001ainto extension3001b. Note the angle that arm5707of tool5700is making with respect to the proximal end of rod700. The design is such that once the rod end enters wide opening3103of extension3001b, the tine flats will line up with the exit ramps (as discussed with respect toFIG. 63) and with the help of cam5908will release therefrom.

FIG. 65ashows a cross-section through section65a-65aofFIG. 64and illustrates tines5905aand5905bin pocket5906but radial surfaces6001aand6001bcan now pass through exit slots716.FIG. 65bis a cross section through section65b-65bofFIG. 65aand again shows the small diameter of tines5905aand be aligned to pass through the transition between recesses713and exit slots716. Cam5708is also shown which, as it rotates, operates to push the rod end out of pocket5906.

FIG. 66a, shows the assembly for inserting and tightening the locking caps1800fromFIG. 18into the poly axial head assemblies100and200, after rod700is rotated into place. Once rod transfer tool5700fromFIG. 57is removed from extension3001a, rod700needs to be locked into the rigid position shown byFIGS. 22 and 23by the installation of locking caps1800. Locking caps1800are installed by the drive shaft6505attached to handle6506and using drive mechanism head6508. A locking cap is positioned on drive mechanism head6508where drive mechanism head6508is sized to hold locking cap in place until it is tightened into a head assembly. Drive mechanism shaft6505with a locking cap is inserted down the extensions3001aand b in turn and handle6506is twisted to seat locking cap1800into the poly-axial head assembly.

Used alone, drive mechanism shaft6505would not only screw locking cap1800in place but would also tend to place a torque on the poly-axial head assembly due to the friction between the threads of the locking cap1800and the treads of the poly-axial head assembly. This force would load the poly-axial head assembly, with such a load remaining after the end of the procedure potentially leading to problems with the assembly. To prevent this torque from being placed on the poly-axial head assembly, the system of the present invention uses anti-torque handle6501to place an opposing force on the poly-axial head assembly to the force applied by drive mechanism shaft6505. Anti-torque handle6501includes handle6502and ring6503which has flats6504dimensioned to mate with the flats of the drive head of extension3001. As the locking cap is tightened in one direction, for example clockwise, by drive mechanism shaft6505, an equal force to the force applied to the poly-axial head assembly is applied in the opposite direction, for example counter clockwise, preventing any load from being introduced into the poly-axial head assembly.

FIG. 66bshows an embodiment of a drive mechanism shaft6505having a driving end6508and flats6509at the proximal end with quick connect ring6510. As described, a locking cap, such as cap1800(FIG. 18) is placed on drive mechanism head6508of drive mechanism shaft6505. End6508is a tapered surface so it taper locks with the locking cap so that the cap will not fall off. The length of tool6505is such that end6508reaches assembly200as shown inFIG. 66awhich end6509comes out of the patient's skin. Handle6506is connected to the proximal end of tool6505which is rotated using handle6506to tighten locking cap1800thereby locking the assembly together.

Anti-torque handle6501can also be used to disconnect extension3001afrom assembly200by rotating assembly3001a. Once released, assembly3001ais removed from the patient's body and the incision can be closed leaving the assembly ofFIG. 1.

FIGS. 67aandbshow a rod for use in a multi-level procedure where more than two pedicle screws are used. Rod6600has an arched or bent portion,6602, so that rod6600has an arc that best fits the spine curvature. Slide ring surface6603and distal end driving surface6604are the same as discussed for rod700(FIG. 7) except that driving surface6604is at an angle because portion6605is angled with respect to slider6603.

At the proximal end of rod6600there is top surface6606where the locking cap will engage. Entrance ramp6607and spherical portion6611performs exactly as it does for rod700(FIG. 7). Exit ramp surface6609leads away from cylindrical surface (hole)6608that is the same as on rod700. The entire proximal end works exactly as does the proximal end of rod700, except for the use of surface6701to be explained with respect toFIG. 67.

Distal angled portion6605is shown inFIG. 67band illustrates bent or arched portion6602of rod6600. Surface6701gives more purchase for turning the pedicle screw and works in addition to flats6612. Flat surface6610is on spherical end6611. Flat surface6610will connect with the drive features of the driver just like in the single level.

FIG. 68illustrates the relationship of rod6600with extension3001when rod is mated with anchor500and poly-axial head assembly300. Because rod6600is longer than rod700to allow it to span three vertebrae, and has additional curvature to match the natural curvature of the spine, an angle of end6605is required to allow rod6600to fit inside extension3001as shown inFIG. 68. This required angle in end6605allows the drive mechanism in the distal end to match up with the drive mechanism of anchor500. Opening3102allows the rod transfer tool used in multi-pedicle systems, shown inFIG. 69, to enter extension3001. The distal end of the rod transfer tool operates in the same manner as the rod transfer tool ofFIG. 57, and mates with end6701in the same manner as described with reference to the two pedicle system.

Rod transfer tool6900is shown inFIG. 69. Tool6900has shaft6902and handle6903. It has distal arm5707connected to shaft6902by pivots6904, which is the same as discussed above with respect to tool5700fromFIG. 57. Tool6900and shaft6902are designed to span three or more pedicles through three extensions as shown inFIG. 70.

In operation, distal arm5707, which is part of the multi-level rod transfer device6900, is placed through window3102and then tines of arm5707are snapped onto the proximal end of rod6600as discussed above. Then the instrument is lifted to disengage the rod/screw drive mechanism. Next, using handle6903, the rod is pushed out of extension3001via opening3103.

FIG. 70shows, in cut-away, a multi-level setup where assembly7000has been added to a center pedicle between assemblies100and200. Assembly7000is the same as assembly100except that slider800is omitted as it is not required.

FIG. 71shows extension7100in greater detail. Extension7100is used instead of extension3001for the center assembly of the multi-pedicle system. Extension7100includes longitudinal cuts7102and7103on both sides of the body. These cuts allow the rod to pass through extension7100so that end5908can be positioned in assembly100. Referring back toFIG. 70, when end5905is within extension3001of assembly100, the tines come out of the rod, as discussed above, and tool6901can be removed leaving rod6600positioned from assembly200, through assembly7000to assembly100.

FIG. 72shows the entire assembly with extensions. Rod600is in its down position ready to accept locking caps, such as caps1800,FIG. 18, in the manner as discussed above.

FIG. 73shows multi-level system7300locked down. Heads300and1500are not necessarily in line with its respective anchor500because of the axial nature of the connection between the head and the screw. However, once cap1800is tightened, the rod, the poly-axial head, and the anchors are held in a rigid, immovable relationship to one another.

The bend in rod6600is predefined and can be different for rods of different lengths. By way of example, one could have a 65 millimeter rod, a 75 millimeter rod and an 85 millimeter rod, all having different bends. What is presently done in multi-pedicle systems is not to have a rod with a predefined bend, but rather to set all three pedicle screws and then bend a rod, lay it in and take a fluoroscope shot to see how the rod lines up with the three screws. If it is not correct, it is pulled out, re-bent and again put in position and imaged again. If the rod is over-bent, it is often scrapped. If it is under-bent it is re-bent until it is right. However, in order to allow for use of a pre-bent rod, the screws must be installed in the proper arc. Thus, instead of bending the rod to fit the arc defined by the screws, the screws are installed to fit a pre-defined arc. In operation, assembly100is put in first just as with the single level. Then a length is established to the other end pedicles, assembly200inFIG. 1, and rod6600is moved from the in-line position to the horizontal position. In so doing, a center portion of rod6600passes through one or more center extensions (FIG. 70) until end5908becomes engaged within extension3001of assembly100.

FIGS. 74 and 75illustrate an example of an instrument, such as instrument7400, that locates the center poly-axial head assembly in a three dimension space according to the arc defined by rod6600fromFIG. 66between the end point poly-axial head assemblies. Tool7400not only establishes the spacing between the end point assemblies for the center assembly, but also establishes a positional depth setting for the middle poly-axial head assembly. Spherical end7402is designed to be held by a poly-axial rod-capturing head, such as the one shown inFIG. 15, and therefore, includes a spherical portion the same diameter as the spherical portion of rod6600. Thus, end7402can slide down extension3001ato rest in the poly-axial rod-capturing head assembly. End7405is intended to be held in a poly-axial rod assembly head such as is described inFIG. 3and is therefore shaped to fit around rod6600by means of u-shaped groove7417. With the rod in an upright position, end7405slides down inside extension3001bfromFIG. 76to rest on slide ring800inside the poly-axial head. End7402is held to instrument7400by arm7408formed with bend7425which connects to body7403. End7405is connected to rotational member7416which is connected to arm7413and is able to rotate in relation to instrument7400about axis A3. Arm7413is connected to body7404by bend7412and7411.

Extension mounting cylinder7406is connected to body7403by pivot7423which allows extension mounting cylinder7406to pivot in relation to body7403. Extension mounting cylinder7406forms an arc just greater than 180 degrees and is sized such that its inner diameter is equivalent to the outer diameter of an extension such as extension7100ofFIG. 71. This allows extension mounting cylinder to be mounted around an extension and hold the extension in place with respect to instrument7400. Grip7421is formed with extension mounting cylinder7406and includes indention7422which allows grip7421to be held securely. Grip7421allows for the easy manipulation of instrument7400such as the positioning of the instrument over the hole of the center pedicle so that a determination can be made as to the position for the center poly-axial head assembly.

FIG. 75shows the reverse side of instrument7400fromFIG. 74. The relationship of bodies7403and7404can be seen. Bodies7403and7404can move in relation to one another along slot7501. This movement is used to set the distance between end7405and7402so that the instrument can be placed in assemblies100and200which have already be anchored in their respective pedicles.FIG. 75also shows slot7423in which resides pivot7423held in place by shoulder screw7502. Slot7423allows extension mounting cylinder to be moved along the arc defined by slot7423. The arc defined by slot7423corresponds exactly to the arc defined by rod6600ofFIG. 66allowing the center poly-axial assembly to be located in three dimensional space in relation to assemblies100and200.

To set the center poly-axial assembly a guide wire is inserted as described with reference to the setting of assemblies100and200. The hole is tapped and the screw is inserted into the hole attached to its head300as discussed above. This provides an axis for anchor500of assembly7001but there is only one plane that rod6601rod lays in. Instrument7400must position tube7406into that axis.

The hole in the center pedicle is tapped and the new anchor assembly is inserted into the pedicle in the manner discussed above for the other anchors. The anchor is positioned in the pedicle to hold it to get a relative positioning for new (middle) extension7101. Tube7406is attached to the outside of extension7101and connectors7404are positioned on the patients skin surface and ends7405and7402are placed in their respective extensions. At this point, connectors7404can be inserted into the incision between the two extensions and worked down toward the spine. When each end7405and7402reaches its respective rod within its extension the device will stop moving into the body. Since connectors7404are free to adjust to the length and relative heights of each head and since the connector has the same arc as does the rod that will be implanted, top edge7430of extension mounting cylinder7406will be fixed relative to the desired arc which defines the desired location of the center poly-axial assembly.

Once the top edge of extension mounting cylinder7406is fixed with respect to the desired height of the new screw head assembly the screw assembly can be screwed further into the bone. A drive tool as described with reference to the two pedicle assembly, is inserted in side extension7101and middle anchor500is tightened down. This then brings extension7101down until a certain line7701, shown inFIG. 77, on the extension lines up with the top edge of extension mounting cylinder7406. This then positions middle head300at the proper height so that when the pre-bent rod is connected between the end heads the arc of the rod at the point where it passes through the middle head will pass with the head as discussed above.

While only a three pedicle assembly has been shown, the procedure will work for four or more pedicle assemblies in the same manner.

FIG. 76shows instrument7400in relation to all three poly-axial head assemblies100,200, and7001, and their associated extensions3001a,3001band7101.

FIG. 77shows the opposing side of the assembly shown inFIG. 76.