WO1997015231A1

WO1997015231A1 - A spinal implant device having a single central rod and plow and/or claw hooks

Info

Publication number: WO1997015231A1
Application number: PCT/US1996/011391
Authority: WO
Inventors: Joseph P. Errico; Thomas J. Errico; James D. Ralph
Original assignee: Fastenetix, L.L.C.
Priority date: 1995-10-23
Filing date: 1996-07-10
Publication date: 1997-05-01
Also published as: AU6636296A

Abstract

A hook and rod apparatus for fixation to the central posterior axis of the spine includes hood elements (110a) (130b) which are mounted beneath the arched portion of the lamina. In a first plow-shaped (110a) variation, the blade portion (115a) of the hook is an arched surface which seats under the arch surface of the lamina. In a second claw-shaped variation (130b), the blade portion (136b) (137b) includes a bifurcated conformation having a pair of offset flat extending members which are angled relative to one another so as to seat under the angled portions of the lamina which are lateral to the arched center of the lamina. The rod coupling features of the hooks (122b) may be poly-axial by virtue of separate coupling elements which may be mounted to the blade portion, for example, on a semi-spherical head portion (201) thereof.

Description

A SPINAL IMPLANT DEVICE HAVING A SINGLE CENTRAL

ROD AND PLOW AND/OR CLAW HOOKS

BACKGROUND OF THE INVENTION

1.Field ofthe Invention This invention relates generally to a hook and rod implant apparatus for immobilization of the spinal column. More particularly, the present invention relates to an implant apparatus comprising hook devices for attaching to the posterior lamina at a central position thereon, and a single support rod, securely held by the hooks to form a single central axis implantation apparatus.

2. Discussion ofthe Prior Art

The bones and connective tissue of an adult human spinal column consist of an upper portion having more than 20 discrete bones, and a lower portion which consists of the sacral bone and the coccygeal bodies. The bones of the upper portion are generally similar in shape, as will be more fully described hereinbelow with respect to Figures 1, 2 and 3. Despite their similar shape, however, they do vary substantially in size in accordance with their individual position along the column and are, therefore, anatomically categorized as being members of one of three classifications: cervical, thoracic, or lumbar. The cervical portion, which comprises the top ofthe spine, up to the base ofthe skull, includes the first 7 vertebrae. The intermediate 12 bones are the thoracic vertebrae, and connect to the 5 lumbar vertebrae.

The lower portion of the spinal column, which extends into the hip region is primarily comprised of the sacral bone. This bone is unlike the other bones of the spinal column, in both shape and size. In fact, at birth humans have five distinct sacral bones which begin to fuse together during childhood, and by adulthood have fully combined. For the purpose of describing this invention, however, the sacral bone shall be referred to as distinct from the spinal column; the spinal column, therefore, comprising for the purposes of this description, only the cervical, thoracic, and lumbar vertebrae. The bones ofthe upper portion vary in size, but are each similarly coupled to the next by a tri-joint complex. The tri-joint complex consists of an anterior disc and the two posterior facet joints, the anterior discs of adjacent bones being cushioned by cartilage spacers referred to as intervertebral discs. Referring now to Figures 1, 2 and 3, top, lateral, and posterior views of a typical vertebral bones ofthe spinal column are shown. The spinal cord is housed in the central canal 10, protected from the posterior side by a shell of bone called the lamina 12. The lamina 12 has three large protrusions, two of these extend laterally from the side ends thereof and are referred to as the transverse processes 14. The third extends back and down from the center of the lamina and is called the spinous process 16. The lamina 12 defines an arched shape about the posterior of the spinal cord, the arched shape having lateral portions 13a, 13b which are generally straight, and which meet beneath the spinous process at a curved surface 15.

The anterior portion of the spine comprises a set of generally cylindrically shaped bones which are stacked one on top of the other. These portions of the vertebrae are referred to as the vertebral bodies 20, and are each separated from the other by the intervertebral discs 22. Pedicles 24 are bone bridges which couple the anterior vertebral body 20 to the corresponding lamina 12 and posterior elements 14,16.

Referring specifically to Figure 3, the stacking of vertebrae is shown from the posterior. From the posterior, each vertebra is coupled to the one above and below via facet joints 19 on either side of an opening into the spinal canal 10. In its entirety, the spinal column is highly complex in that it houses and protects critical elements of the nervous system which have innumerable peripheral nerves and arterial and venous bodies in close proximity. In spite of these complexities, the spine is a highly flexible structure, capable of a high degree of curvature and twist through a wide range of motion. Genetic or developmental irregularities, trauma, chronic stress, tumors, and disease, however, can result in spinal pathologies which either limit this range of motion, or which threaten the critical elements ofthe nervous system housed within the spinal column. A variety of systems have been disclosed in the art which achieve this immobilization by implanting artificial assemblies in or on the spinal column.

These assemblies may be classified as anterior, posterior, or lateral implants. As the classification suggests, lateral and anterior assemblies are coupled to the anterior portion of the spine, which is the sequence of vertebral bodies. Posterior implants are attached to the back of the spinal column, generally by coupling to the pedicles via screws, or by means of hooks which attach under the lamina, and entering into the central canal. In either case, the implants generally comprise at least one (and usually a pair thereof) elongate support rod element which is coupled to the screws or hooks to immobilize several sequential vertebrae, for example to hold them stable so that the adjacent bones may be fused with bone graft. The prior co-pending application, U.S.S.N. 08/502,285, of which this application is a continuation-in-part, discloses novel devices which provide significantly superior performance for such implants which comprise screws for coupling to the pedicles. Inasmuch as the pedicles are disposed laterally with respect to the posterior profile ofthe column of vertebrae, the rods of such screw systems have universally been disposed to the sides of the central axis of the spine, lateral to the axis formed by the spinous processes. As set forth more fully hereinbelow, the disposition of the rods in the natural site for desired bone fusion, limited bone graft can be achieved. Maximal posterior bone fusion is desired for all immobilizations of such portions of the spine, and therefore, the placement ofthe rod in the best site for such bone growth is a drawback of lateral systems. Hook and rod assemblies however, have not provided any superior access to the lateral portions ofthe posterior surfaces ofthe spine. Generally hook and rod assemblies ofthe prior art have included a plurality of hooks having rounded blade portions which are inserted posteriorly under the straight portion of the lamina between the transverse process and the spinous process (off the center line of the spine). The hooks include upper body portions to which the support rod is coupled.

Referring now to Figures 4 and 5, U.S. Patent 5,005,562 to Cotrel teaches such a hook and rod apparatus which includes a pair of rods 30a,30b, which are coupled to hooks 32a,32b and 34a,34b. Upper hooks 32a,32b are disposed such that the blade portions are directed downward, hooking the straight (side) portion 13a,13b of the lamina 12 which is sequentially below them. Lower hooks 34a,34b are disposed in the opposite orientation, so that the blade portions thereof are directed upward relative to the axis of the spine. It is understood that the rods 30a,30b are also coupled to pedicle screws 36a-36d. The rods 30a,30b hold the hooks 32a-b,34a-b to the lamina 12, preventing their movement out from beneath their respective lamina 12 by virtue of tensile rigidity in the rod. In addition, the rods 30a,30b are further stabilized by cross link devices 38a,38b. It is clear from Figure 4 that there is little free space to place bone graft material, and in fact where such bone graft may ultimately grow is precisely where the implant is positioned, thereby risking difficulty of removal if long term post-operative problems necessitate removal of repair of the apparatus.

Figure 5 illustrates one specific type of hook, the ones disclosed by U.S. Patent 5,005,562. These hooks have a blade portion, including a flat extending member 51 which is designed to fit snugly to the undersides of the flat portions 13a, 13b of the lamina 12 which is next to the transverse processes (on either side of the spinous process). This hook further includes an integrally formed rod receiving body 52, which extends upwardly from the top of the blade portion 55. The rod receiving body 52 comprises a generally cylindrically shaped portion 54 having a vertical slot 58 formed in the top thereof for receiving the rod 30a or 30b. This rod is secured in the slot 58 by a threaded plug 56.

In addition to the disadvantages of the laterally disposed rod apparatuses, with respect to the availability of free space in which to introduce bone graft material, it has been identified that hooks having flat extending members which are disposed under the flat portion of the lamina 13a, 13b may cause undue stress concentrations in the laminar bone. This is in part due to the location of the blade, the narrowness of the blade, as well as the torquing which the lateral offset implies. In addition, it is a function of the relative thinness of the lamina 12 at these sites.

Further, it has been found that considerable difficulty may be associated with inserting hooks under sequential lamina along a misaligned curvature while simultaneously exactly positioning their rod receiving portions thereof such that they are aligned so that the rod can be passed therethrough without distorting, tilting, rotating, or exerting undesired translational forces on the hooks. Correction of this difficulty requires the time consuming and difficult task of reshaping the rods or repositioning the hooks, each of which is understood to require considerably longer operating time, which is known to increase the incidence of complications associated with surgery. Often such alignments with such fixed body hooks cannot be satisfactorily achieved, and the entire instrumentationing effort has to be altered to utilizing screws. Any such time consuming efforts which afflict the implantation of a single rod assembly is understandably amplified with the necessity of implanting a parallel apparatus on the opposing lateral extent ofthe posterior ofthe spinal column. It is, therefore, the principal object of the present invention to provide a single center axis hook and rod implant system to maximize desirable area for bone grafting purposes.

It is also a principal object of the present invention to eliminate the need for a second parallel apparatus to be implanted to stabilize and immobilize sequential vertebrae.

It is, relatedly, an object of the present invention to provide a simplified implantation apparatus which reduces the amount of operative time necessary for proper introduction thereof.

It is still further an object of the present invention to provide an implant apparatus which reduces the point stress loads on the laminar bones ofthe spine.

It is another principal object of the present invention to provide a lamina hook which may be utilized in accordance with the above objects.

It is relatedly an object ofthe present invention to provide a lamina hook having a rod coupling body which provides a polyaxial freedom of implantation angulation with respect to rod reception.

Accordingly it is also an object of the present invention to provide an assembly which is reliable, durable, and provides long term fixation support. Other objects of the present invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter.

SUMMARY OF THE INVENTION The preceding objects of the invention are achieved by the present invention which is a single axis, centerline, lamina hook and rod apparatus. The hook devices of this system may further include polyaxial and/or extending rod coupling bodies. More particularly, the hooks of this apparatus may comprise a blade portion having an extending member, or members, which seat under the lamina and are designed to fit snugly under the arched portion 15 thereof. The hooks are therefore designed to be seated beneath the thickest portion of the lamina, ensuring significant strength enhancement, and correspondingly reduced concern for laminar bone breakage at the hook-bone interface. These blades further provide self alignment to the hook relative to rotational forces which may be applied thereto.

In a first variation, this blade portion comprises a curved shape, herein referred to as the plow hook, having a single extending member which has a curved surface. The curve is approximated to the arch 15 at the center of the lamina. In a second variation, the blade portion includes a pair of extending members, each flat, but angled relative to one another so as to mutually seat against the undersides ofthe lamina on either side of the curved portion of the laminar arch 15. This second variation shall be herein referred to as the claw hook variation. The implantation of such a device may require the removal of the spinous process, inasmuch as a preferred position of the rod receiving body portion of the hook is directly along the centerline of the spine (often defined by the sequence of spinous processes). It shall be understood that embodiments of this apparatus may be contemplated, some of which are herein disclosed, which do not require the removal of the spinous process, and which do include the capacity for a parallel rod to be implanted. It is, however, herein noted that the spinous process is not a structurally significant feature providing direct support to the spinal column. In fact, the spinous processes is often removed for use as bone graft material, or to provide increased potential bone graft sites in instances wherein there is such a reduction in alternative bone graft site due to the apparatuses implanted (which is precisely an advantage of the present invention).

In addition, a number of additional embodiments (the hooks) of this invention achieve the objects set forth above with respect to ease of alignment by providing polyaxial and/or extending rod coupling body portions. More specifically, in a first of these additional embodiments, the hook comprises a ball shaped head. The body of the device comprises a separate coupling element mounted on the ball shaped (semi-spherical) head so that it is rotationally free prior to secure fixation of the rod thereto, and which is securely locked in a given angulation once the rod is received by the coupling element. The coupling element has a generally cylindrical main body portion, a locking collar, and a top locking nut. In certain embodiments, the coupling element further includes a rod locking sleeve.

The coupling element may be conceptually divided into a lower socket portion, and an upper rod and top nut receiving portion. In embodiments which receive the rod into a channel formed in the top of the device, the conceptual division of the coupling element into lower and upper portions is sufficiently precise for description. However, in embodiments in which the rod is received into a side channel in the coupling element, the upper portion may be conceptually subdivided into an intermediate and top sections. In either case, the lower socket portion is designed with an interior chamber having an opening at the bottom of the coupling element. The interior chamber is provided for receiving therein the head of the blade portion such that the blade and the coupling element are held together, but prior to the securing of the rod to the intermediate portion, the blade and coupling element remain free to swing and rotate freely with respect to one another. The external surface of the socket portion includes at least one vertical slot which is provided so that the curvate head, which has a major diameter which is larger than the opening in the bottom ofthe element may be received within the open volume therein. The at least one slot resiliently expands to receive the head and contracts into position once the head is fully inserted, therein inhibiting the head from being retracted. The exterior ofthe lower portion ofthe coupling element, into which the head is inserted, tapers outward slightly toward the bottom of the element, therein having a slightly wider bottom diameter than at the top ofthe lower portion. A locking collar, having a diameter equal to or greater than the top ofthe lower portion, but less than the diameter of the bottom of the lower portion, is disposed initially about the top ofthe lower portion. Subsequent to proper positioning of the blade portion of the hook under the corresponding arch ofthe desired lamina, the coupling ofthe rod to the coupling element (as set forth in more detail hereinbelow), and the setting of the proper angulation of the coupling element relative to the hook, the locking collar may be forced by a sufficient application of pressure downward along the exterior ofthe lower portion ofthe coupling element. The locking collar therein applies an inward force against the walls of the interior chamber, and the corresponding narrowing of the vertical slots thereof. Once fully driven downward the locking collar causes the coupling element to be securely locked relative to the blade portion of the hook.

In the embodiment of the present invention which receives the rod into the side thereof, the intermediate portion ofthe coupling element comprises a recess in the side thereof, wherein the rod is retained. More particularly, at a position above the lower portion, a channel is formed in the side of the cylindrical body for receiving the rod. An external rod securing sleeve is also provided for holding the rod in the side channel and preventing it from moving relative thereto. The external rod securing sleeve is generally cylindrical in shape, having a hollow center for sliding over the top of the coupling element. The bottom of the sleeve includes two opposing downwardly extending members; forming therebetween a second channel. The sleeve, therefore, has a conformation which resembles an upside down U-shape and cups the rod from above. Subsequent to the placement of the rod in the channel, the rod securing sleeve is deposited on the coupling element such that the rod is positioned within the vertically aligned slots therein. In top loading variations, the rod is positioned between two upwardly extending members which form, therebetween, the channel. The upwardly extending members comprise the upper portion ofthe cpoupling element.

In either variation, the locking collar on the lower portion is initially positioned so that the upper annular surface thereof extends vertically above the bottom ledge of the channel, so that in its initial disposition in the channel, the rod seats on the locking collar.

The upper portion of both variations of the coupling element comprises a threading onto which a top locking nut may be inserted. The bottom surface of the nut is designed to mate with the top of the rod or the rod securing sleeve (depending on the embodiment). Engagement of the nut with the upper portion of the coupling element, and driving of the nut downward onto the upper portion of the coupling element causes the rod securing sleeve and/or the rod to be driven downward. Thise downward movement,in turn, drives the rod downward within the recess on the locking collar. Ultimately the inward radial force applied to the lower portion ofthe coupling element causes the at least one slot therein to close and for the head ofthe hook to be locked therewith. The rod, too, is then securely locked between the top of the locking collar and the sleeve and/or nut, and is thereby prevented from axial or rotational movement.

In a second set of embodiments, the hook has a variable height extending body portion and a blade portion to which the variable height body portion may be coupled. More particularly, the blade portion comprises a body coupling end having a cylindrically shaped recess in the top thereof. The cylindrical recess is oriented to be generally peφendicular to the axis ofthe spine. The top ofthe cylindrically shaped recess comprises a slotted opening so as to be selectively contractible by an inwardly directed radial force. The external surface ofthe body coupling end, which includes the slots also includes a taper, for example a narrower top. This tapered portion further comprises an external threading so that a nut may be introduced onto the threading; the tightening of which causes the selective contraction of the top of the cylindrical recess. In this second set of embodiments, the body of the device comprises a rod coupling structure and an otherwise elongate lower shaft portion. The shaft portion is designed to be slidably and rotationally mounted within the cylindrical recess so that prior to being locked into place by tightening the top of the recess to the shaft, the coupling element may be rotationally varied relative to the blade portion, and raised or lowered within the cylindrical recess and relative to the blade. In a preferred variation of this embodiment, the shaft portion is restrained against full removal from the recess in the blade portion by means of a mutual track feature, guide rails, or equivalent means. The coupling element of this embodiment may be fixed to the shaft portion, or may be equivalent to the coupling element set forth hereinabove with respect to the fixed height hooks (and be mounted to a curvate head at the end ofthe shaft portion).

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a top view of a vertebral bone characteristic of those of the cervical, thoracic, and lumbar spine; Figure 2 is a side view of sequentially aligned vertebral bones, such as are found in the cervical, thoracic, or lumbar spine;

Figure 3 is a posterior view of a sequence of vertebrae;

Figure 4 is a posterior view of a hook, screw and rod system ofthe prior art;

Figure 5 is a side cross-sectional view of the hook device of the prior art apparatus of Figure 4;

Figure 6 is a posterior view of the hook and central rod apparatus of the present invention;

Figures 7a, 7b, 7c, and 7d are side perspective views of variations of hook devices of the present invention illustrating the plow and claw, and the side and top loading variations ofthe blade portions thereof;

Figure 8 is a side cross-section view of a top locking nut which is an aspect of the present invention; Figure 9 is a side view of a rod securing sleeve which is an aspect ofthe present invention;

Figures 10a and 10b are, respectively, a side perspective view of the hook of Figure 7a, having a support rod secured therein with the rod securing sleeve and top locking nut of Figures 8 and 9, and a side perspective view of the hook of Figure 7c, having a support rod secured therein with the top locking nut of Figure 8;

Figure 11 is side perspective view of a blade portion of a polyaxial embodiment ofthe hook device ofthe present invention having a plow conformation;

Figures 12a and 12b are, respectively, side views of the side and top loading polyaxial coupling elements ofthe present invention; Figure 13a and 13b are, respectively, a side view of the coupling element of

Figure 12a shown mounted to the semi-spherical ball head of the blade portion as shown in Figure 11, and a side view of the coupling element of Figure 12b shown mounted to the semi¬ spherical ball head ofthe blade portion as shown in Figure 11 ;

Figure 14 is a side view of the locking collar which is an aspect of the present invention;

Figures 15a and 15b are, respectively, a side perspective view of the fully assembled hook ofthe embodiment ofthe present invention as shown in Figure 13a, and a side perspective view of the fully assembled hook of the embodiment of the present invention as shown in Figure 13b; Figure 16 is a side perspective view ofthe blade portion of an other embodiment ofthe present invention having a contractible cylindrical recess therein;

Figure 17 is a side cross-section view of the tightening nut which is an aspect of the present invention;

Figures 18a and 18b are, respectively, side views of the side and top loading body portions which are aspects of embodiments ofthe present invention; Figures 19a and 19b are side perspective views of fully assembled hook devices ofthe present invention, wherein the blade element of Figure 16 and the body element of Figure 18a and 18b are utilized, respectively;

Figure 20 is a side view of a body portion of an aspect of the present invention, wherein the body portion includes a curvate head; Figures 21a and 21 b are side views of fully assembled embodiments of the body portion of an aspect ofthe present invention, wherein the curvate head portion is received in the socket portion ofthe coupling element of Figures 12a and 12b, respectively; and

Figures 22a and 22b are, respectively, side perspective views of hook devices of the present invention wherein the blade portion is a plow shape and there are a pair of side and top looading rod receiving bodies extending upwardly and outwardly from the top of the blade portion.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

While the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which particular embodiments and methods of implantation are shown, it is to be understood at the outset that persons skilled in the art may modify the invention herein described while achieving the functions and results of this invention. Accordingly, the descriptions which follow are to be understood as illustrative and exemplary of specific structures, aspects and features within the broad scope of the present invention and not as limiting of such broad scope.

Referring now to Figure 6, a posterior view of the centerline unitary rod and hook apparatus ofthe present invention is provided. As in Figure 4, which illustrated a dual rod apparatus of the prior art, the present invention may be generally categorized as one which utilizes hooks to provide coupling of a rod to the spine, and which does so by being anchored under the lamina. More specifically, with respect to the present invention however, the hooks

102 are designed to be inserted under the arch 15 of the lamina 12, wherein the undersurface of the bone forms a shallow inverted- V shape. Inasmuch as the rod 104 of this embodiment ofthe present invention is intended to extend downward along the centerline of the spine, it may be necessary to remove the spinous processes ofthe sequence of vertebrae along which the rod 104 is to extend. This includes vertebrae 106 to which the hooks 102 are not mounted, but which are disposed between vertebrae which are coupled by the apparatus, or which are adjacent to the sequence which is to be instrumented, and may therefore be effected by the presence ofthe rod. The removal of the spinous processes may be avoided if the disposition of the rod is to be above their profile, or if the rod receiving part of the hook is offset sufficiently for the rod to extend along them (see Figures 22a and 22b).

Referring now to Figures 7a and 7c, the simple plowhook embodiments 110a, 110c of the present invention are provided in perspective views. Each of the plowhooks 11 Oa, 110c comprises a blade 112a, 112c and a rod receiving portion 120a, 120c. More specifically, the rod receiving portions 120a, 120c, which are integrally formed at the top of the blade portion (described more fully hereinafter), comprise a side channel 122a in the side loading embodiment 1 10a, and a vertical channel 122c in the top loading embodiment 110c.

In the side loading embodiment 110a shown in Figure 7a, the rod receiving channel 122a comprises a curvate inner wall 123a which is ideally suited for receiving a cylindrical rod. The lateral depth ofthe channel 122 is sufficiently deep such that a cylindrical rod, for example the support rod of a spinal implant apparatus, may be fully inserted thereinto without the rod extending beyond the lateral extent of the channel and interfering with the engagement of the rod by external rod securing means. The portion 124a of the rod receiving portion 120a which extends upwardly from the rod receiving channel 122a includes a surface threading 126a, which is ideally suited for receiving thereon a nut, such as a top locking nut (as described more fully with respect to Figure 8 et al.)

Referring specifically to Figure 7c, the rod receiving portion 120c, which is integrally formed at the top of the blade portion (described more fully hereinafter), comprises a pair of upwardly extending members 111c, defining therebetween a channel 122c for receiving a support rod therein. The rod receiving channel 122c comprises a curvate lower wall 123c which is ideally suited for receiving a cylindrical rod. The depth of the channel 122c is sufficient such that a cylindrical rod, for example the support rod of the present invention, may be fully inserted thereinto without the rod extending above the height ofthe upwardly extending members 111c and interfering with the engagement ofthe rod by external rod securing means. The uppermost portions 124c of the upwardly extending members 111c include a surface threading 126c, which is ideally suited for receiving thereon a nut, such as a top locking nut (as described more fully with respect to Figure 8 et al.)

In both embodiments, the blade 112a, 112c comprises a C-shaped portion 114a, 114c having a lower branch extending member 116a, 116c, and an upper branch 118a, 118c which extends into, and integrally forms the base of the rod receiving portion 120a, 120c. The lower branch extending member 116a, 116c of this embodiment has a curvate conformation, such that it forms an arched surface 115a, 115c. The arched surface 115a,l 15c is so formed to be approximately fitted to the arched undersurface of the center of the lamina of the patient's spine. This arched surface 115a, 115c, therefore, is defined by a surface maximum 117a, 117c extending along the center line of the lower branch extending member 116a, 116c; the surface 115a, 115c sloping off to the edges 119a,119c thereof, at an angle which is equal to the approximate angle of the lamina along the underside portions 13 a, 13b thereof which are adjacent to the centerline 15.

Referring now to Figures 7b and 7d, second variations 130b,130d ofthe hook of the present invention are shown, wherein the blade portion 132b, 132d of each comprises a pair of angularly offset extending members 136b,137b, 136d,137d which form a claw conformation. The rod receiving upper portions 120b,120d of these clawhook embodiments comprise the same features as the, respective plowhook 110a, 110c as set forth with respect to Figures 7a and 7c. More specifically, the upper portion of hook 130b is equivalent to that of hook 110a, including a side channel 122b for receiving therein a cylindrical support rod, and an upper portion 124b which comprises a threading 126b. Similarly, the upper portion of hook 130d is equivalent to that of hook 110c, including a top channel for receiving the rod, and upwardly extending members H id which define therebetween the channel 122d. Threading 126d, for receiving thereon the locking nut is also provided in a similar manner as with respect to hook 110c.

With respect to the blade portions 132b,132d of each of these clawhooks 130b,130d, as introduced above, the blade portions 132b,132d each comprise a pair of extending members 136b,137b, 136d,137d. The lower branch of the C-shaped portion 114b,114d is bifurcated so that a pair of angularly offset, but planar, members 136b, 137b, 136d,136d are produced. Although it is understood that each may have a surface conformation which is more suited to the particular undersurface of the lamina, as shown in Figures 7b and 7d, a substantially flat conformation is sufficient to provide stable and secure seating against the underside of the lamina. More specifically, each of the offset members 136b, 137b and 136d,137d is ideally suited to being seated against the undersurface of a corresponding portion 13a or 13b thereof which is adjacent to the centerline 15.

Referring now to Figures 8 and 9, a top locking nut 170 and the rod securing sleeve 164 of the first embodiments are shown in side cross-section views. Referring specifically to Figure 9, the rod securing sleeve 164 comprises a hollow cylindrical body having a flat annular top surface 163 and a curved bottom surface 169. In fact, the bottom surface 169 is so curved as to have an upside-down U-shape defined by a pair of downwardly extending members 168a, 168b formed of the cylindrical body. These downwardly extending members 168a, 168b in turn, define diametrically opposing vertical slots 161, which together provide a passage through the bottom of the sleeve for cupping a rod placed therethrough. The interior surface 166 of the sleeve 164 has a diameter which is equal to the outer diameter of the rod receiving portion 120, so that it may be placed thereover to engage the rod which may be disposed in the channel 122 thereof, and secure same therein.

Referring now to Figure 8, the nut 170 comprises an inner threading 171 which is intended to mate with the threading 126 on the upper portion 124 ofthe rod receiving portion 120 of the hook 110 or 130. The bottom surface 174 of the nut 170 is intended to seat against the top surface 163 ofthe rod securing sleeve 164 or the rod (in the top loading embodiments), but is permitted to rotate relative to the sleeve or rod, therein providing a means for driving the sleeve or rod downward (as more fully described hereinbelow with respect to the full assembly of each device, and with respect to Figures 10a and 10b).

Referring now to Figures 10a and 10b, fully assembled plowhook 11 Oa, 11 Oc and attending elements, such as described with respect to Figures 7a and 7c, are provided in perspective views, wherein support rods 150a, 150c ofthe apparatus are mounted and secured in the, respective, channels 122a, 122c thereof. The implantation procedure which is associated with such an assembly is described hereinalso. It shall further be noted that all alternative embodiments of the rod receiving portions ofthe present invention are set forth hereinafter and described exclusively with respect to the plow shaped blade originally described with respect to Figures 7a and 7c. All of such rod receiving features, however, are equivalently contemplated in conjunction with the offset bifurcated blade portion as described with respect to Figures 7b and 7d.

More specifically with respect to the assembled hook 110a, 110c of Figures 10a and 10b, the implantation thereof generally begins with the removal ofthe spinous process from the upper surface of the lamina. Once this has been removed, the plow shaped extending member 116a, 116c is positioned against the lamina such that the C-shaped portion 114a, 114c of the blade portion 112a, 112c is seated to the lamina and the arched surface 115a, 115c of the blade securely engages the arched undersurface 15 of the lamina.

Referring specifically to Figure 10a, once a sequence of the hooks 110a are so positioned, the support rod 150a is placed in the side channel 122a of the rod receiving body portion 120a. The rod securing sleeve 164, as set forth more fully with respect to Figure 9, is then dropped over the top 124a ofthe body portion 120a, such that the curvate undersurface 169 thereof seats against the top of the rod 150a, with the U-shaped slots 161 formed thereby receiving therethrough, and securely holding the rod 150a. Subsequent to the disposition ofthe rod securing sleeve 164 on the body portion 120a, the top locking nut 170 is rotationally engaged on the threading 126a of the top 124a of the body portion 120a, such that the bottom annular surface 174 of the nut 170 seats against the top annular surface 163 of the sleeve 164. Continued rotation of the nut 170 so that it descends along the threading 126a causes a downward force to be applied against the sleeve 164, which is in turn applied to the rod 150a. The rod is thereby locked in the channel 122a and prevented from both axial, translational, and rotational motion by the engagement thereof between the lower ledge portion of the inner surface 123a ofthe channel 122a from below, and the curved bottom 169 ofthe sleeve 164.

Alternatively, with respect to Figure 10b, once a sequence ofthe hooks 110c are so positioned, the support rod 150c is placed in the channel 122c of the rod receiving body portion 120c. The top locking nut 170 is rotationally engaged on the threading 126c of the upwardly extending members 111c such that the bottom annular surface 174 of the nut 170 seats against the top ofthe rod 150c. Continued rotation ofthe nut 170 so that it descends along the threading 126c causes a downward force to be applied against the rod. The rod is thereby locked in the channel 122c and prevented from both axial, translational, and rotational motion by the engagement thereof between the lower surface 123 c ofthe channel 122c from below, and the bottom surface 174 ofthe nut 170.

Referring now to Figure 11, a side view of the blade portion 199 of the first embodiment ofthe present invention having a polyaxial and/or extending body is provided. As previously described, this embodiment comprises a plow shaped blade portion, having a lower extending member 116, branching from the lower end of the C-shaped section 114, which has an arched surface 1 15. In this embodiment, however, a semi-spherical head portion 201 is integrally formed to the end of the upper extending branch of the C-shaped portion 114 at a neck portion 203. It is understood that the semi-spherical shape is a section of a sphere. In the embodiment shown, the section is greater in extent than a hemisphere, and it correspondingly exhibits an external contour which is equidistant from a center point ofthe head. In a preferred embodiment, the major cross-section of the semi-spherical head 201 includes at least 270 degrees of a circle.

Referring now to Figures 12a and 12b, alternative embodiments of the coupling elements 200a,200c of the present invention are shown in side views, wherein critical features of the interior of each element is shown in phantom. Each coupling element 200a,200c comprises a generally cylindrical body which may be conceptually separated into a lower portion 202a,202c and an upper portion 206a,206c, each of which shall be described more fully hereinbelow. The upper portion 206a of the side loading embodiment 200a may be further conceptually subdivided to include an intermediate portion 204a.

First, with respect to the lower portions 202a,202c (which are equivalent in each embodiment), the exterior surface 208a,208c of the body is tapered in the elongate direction such that the body is wider at the bottom 210a,210c of the lower portion 202a,202c than at the top 212a,212c thereof. The bottom 210a,210c of the element includes an expandable and contractible opening 214a,214c, defined by annular lip 213a,213c, which forms the mouth of an expandable and contractible interior chamber 216a,216c. The diameter of the opening 214a,214c, when otherwise unaffected by external deflecting forces, is more narrow than the maximum diameter A-A of the interior chamber 216a,216c. The interior chamber 216a,216c has a generally curvate inner surface 218a,218c which is correspondingly shaped to receive the semi-spherical head 201 ofthe blade portion 199.

The exterior surface of the lower portion 202a,202c includes a series of slots 220a,220c which extend vertically upward from the bottom 210a,210c ofthe element to a point which is closer to the top 212a,212c of the lower portion 202a,202c than the maximum horizontal diameter A-A ofthe interior chamber. The slots 220a,220c are provided in order that the application of an extemal deflecting force may widen or narrow the opening 214a,214c therein permitting the insertion of an object, such as the head 201 ofthe blade portion, which is larger than the undeflected diameter of the opening 214a,214, or conversely, providing for the retention of an object such as the same.

Referring now specifically to the embodiment of Figure 12a, the intermediate portion 204a of the generally cylindrical body of the coupling element 200a includes a large removed section which forms a horizontal channel 222a in the side of the coupling element 200a. The rod receiving channel 222a comprises a curvate inner wall 224a. As is the case with the first embodiment described with respect to Figures 7a and 7b, the horizontal depth of the inner wall 224a is established such that a circular support rod which is positioned in the rod receiving channel 222a may nests fully within the coupling element 200a, and does not extend beyond the lateral extent of the element, which would prevent a rod securing sleeve (such as was described with reference to Figure 9) from sliding over the intermediate portion 204a ofthe element 200a to retain the rod within the channel 222a. In the embodiment shown in Figure 12a, the vertical distance between the interior opposing surfaces of the channel 222a (the distance being represented in Figure 12a by line B-B) is greater than the anticipated diameter of the support rod to be positioned therein, such that the rod may be translated vertically within the channel 222a (the purpose for which is set forth hereinbelow with respect to Figure 15a).

The upper portion 206a of the coupling element 200a comprises a slightly narrower cylindrical core 225a, having a threading 226a thereon. The upper portion 206a, and the threading 226a thereon, is ideally suited for receiving the top locking nut 170 described with respect to Figure 8.

With reference now to the alternative top loading coupling element 200c as illustrated in Figure 12b, the upper portion 206c of the generally cylindrical body of the coupling element 200c includes a pair of upwardly extending members 221c which define therebetween a vertical channel 222c in the top ofthe coupling element 200c. The rod receiving channel 222c comprises a curvate bottom 223 c. As is the case with the similarly loading fixed hooks described with respect to Figures 7c and 7d, the depth of the bottom 223c is established such that a circular support rod which is positioned in the rod receiving channel 222c may nests fully within the coupling element 200c, and does not extend beyond the vertical extent of the upwardly extending members 221c, which would prevent a top locking nut 170 from sliding thereover to retain the rod within the channel 222c. The vertical extent of the channel 222c is large enough so that the rod may be translated vertically within the channel 222c (the purpose for which is set forth hereinbelow with respect to Figure 15b).

The uppermost portions of the upwardly extending members 221c comprise a threading 226c thereon which is ideally suited for receiving the top locking nut 170 described with respect to Figure 8.

Referring now to Figures 13a and 13b, the coupling elements 200a,200c and the blade portion 199, as described more fully with respect to Figures 1 1, 12a and 12b, are shown in perspective views, wherein the head 201 of the blade portion 199 has been received within the interior chamber 216a,216c, and the head 201 is rotationally free to move relative to the coupling element 200a,200c. In each case, the coupling element 200a,200c is prevented from fully separating from the blade 199 by the mutual engagement of the annular lip 213a,213c at the bottom 210a,210c of the lower portion 202a,202c and the diameter of the head 201. The head 201 may be placed in the socket ofthe coupling element 200a,200c prior to the use by the surgeon in the operating room, or, if desired, the head 201 may be inserted into the socket at the time the surgeon desires it.

Referring now to Figure 14 the locking collar 250 of the present embodiment is shown in a side view. The locking collar 250 comprises a contiguous annular element having an inner diameter which is equal to the outer diameter of the lower portion 202a,200c at the top 212a,212c thereof. The inner surface 251 of the locking collar may be tapered slightly at the bottom thereof to match the upper portion of the taper of the lower portion 202a,202c. In its initial disposition, about the coupling element 200a,200c, the collar 250 is positioned so that the upper annular surface 252 thereof is above the lower ledge of the recess 222a,222c. In this disposition, the bottom 254 of the collar 250 extends to a point below the uppermost part 212a,212c of the lower portion 202a,202c, the point being determined by the diameters of the tapered lower portion 202a,202c and the tapered inner surface 251 ofthe collar 250.

The upper surface 252 of the locking collar comprises a notch 253 which is ideally suited and shaped for supporting thereon the rod. The locking ring is, therefore, designed to be positioned at the top 212a,212c of the lower portion of the coupling element 200a,200c and for the rod to seat in the notch 253 thereof. Application of pressure downward by the rod causes the ring 250 to crush the inner surface of the interior volume 216a,216c against the curvate head 201.

It shall be understood that a dowel, protuberance, or other suitable means may be provided at or above the top 212a,212c of the lower portion 202a,202c so that the collar 250 may not be easily moved upward, and thereby preventing separation ofthe locking collar during handling prior to use. With reference now to Figures 15a and 15b, which show side perspective views of the fully locked coupling elements, rods, and plow hook systems, the alternate preferred methods of implantation and assembly are described hereinbelow. As with the previous embodiments, the lower extending member 116, and the arched surface 115 thereof, is positioned under the arched underportion ofthe lamina. The head 201 ofthe blade portion 199 is then inserted into the interior chamber 216a,216c of the corresponding coupling element 200a,200c. (As stated above, as well, this step may, of course, be taken prior to the positioning of the blade portion relative to the lamina.) At this point in the assembly process, the locking collar 250 has been positioned about, but not yet forced downward along, the outwardly tapered lower portion 202a,202c, so that the coupling element 200a,200c may still rotate and angulate relative to the positioned blade portion 199.

Specifically with respect to the side loading embodiment shown in Figure 15a, the rod securing sleeve 164 is placed over the upper portion 206a ofthe coupling element 200a, such that the rod 150 extends through the slots 161 defined in the curved bottom surface 169 thereof. The rod securing sleeve 164 is prevented from fully descending onto the coupling element 200a by the top surface of the support rod 150, the bottom surface thereof being initially prevented from translating downward by the locking collar 250.

Once the proper angulation of the coupling element 200a to the blade portion 199, and the secure nesting of the rod 150 within the receiving channel 222a, have been established, the top locking nut 170 is threaded onto the upper portion 206a of the coupling element 200a. The lower surface 174 ofthe nut 170 seats against the top surface 163 ofthe rod securing sleeve 164. As the nut 170 rotates, and descends along the threading 226a relative to the coupling element, the rod securing sleeve 164 is driven downward. This motion forces the support rod 150 to translate downward in the channel 222a, causing the locking collar 250 to translate downward along the lower portion 202a of the coupling element 200a. (It shall be understood that one or both of the downwardly extending members 168a, 168b of the rod securing sleeve 164 may contact the top of the locking collar 250 to additionally apply a downward force directly to the collar.) By descending along the tapered lower portion 202a of the element, the locking collar 250 provides an inwardly directed deflecting force which causes the slots 220a in the lower portion 202a ofthe element to narrow so that the collar may proceed downward. This deflection inward causes the inner surface 218a ofthe interior chamber 216a to crush lock against the head 201 of the blade portion 199. This clamping force locks the angulation ofthe coupling element 200a relative to the blade portion 199. Ultimately, once the locking collar 250 cannot be translated down any further, the downward force of the nut 170 against the rod securing sleeve 164 causes the bottom cupping surface 163 of the sleeve 164 to lock the rod 150 between itself and the top surface of the locking collar 250. This locking prevents the rod 150 from sliding relative to the assembled structure. The full insertion of the top locking nut 170, therefore, locks the rod 150 to the coupling element 200a, as well as the blade portion 199 to the coupling element 200a.

Referring alternatively to the top loading variation illustrated in Figure 15b, once support rod 150 is positioned in the channel 222c, the top locking nut 170 is introduced on the threading 226c of the upwardly extending members 221c. As above, the rod 150 is prevented from fully descending into the channel 222c by the top surface ofthe locking collar 250. Once the proper angulation of the coupling element 200c to the blade portion

199, and the secure nesting of the rod 150 within the receiving channel 222c, have been established, the top locking nut 170 is tightened down onto the rod 150. The lower surface 174 of the nut 170 seats against the top surface of the rod. As the nut 170 rotates, and descends along the threading 226c relative to the coupling element, the support rod 150 is forced to translate downward in the channel 222c, causing the locking collar 250 to translate downward along the lower portion 202c of the coupling element 200c. By descending along the tapered lower portion 202c of the element, the locking collar 250 provides an inwardly directed deflecting force which causes the slots 220c in the lower portion 202c of the element to narrow so that the collar 250 may proceed downward. This deflection inward causes the inner surface 218c of the interior chamber 216c to crush lock against the head 201 of the blade portion 199.

This clamping force locks the angulation of the coupling element 200c relative to the blade portion 199. Ultimately, once the locking collar 250 cannot be translated down any further, the downward force ofthe nut 170 against the rod 150 causes it to be fully locked between the top locking nut 170 and the top surface of the locking collar 250. The full insertion of the top locking nut 170, therefore, locks the rod 150 to the coupling element 200c, as well as the blade portion 199 to the coupling element 200c.

Referring now to Figure 16, the blade portion 300 of the third embodiment of the present invention is shown wherein it comprises a body receiving portion 302 and a C- shaped portion 314. As in the above described embodiments, the lower extending branch ofthe C-shaped portion 314 comprises an extending member 116 which has an arched surface 115 which is understood to be the portion which is inserted under the center of the lamina of the patient's spine. The body receiving portion 302 is positioned at the upper extending branch of the C-shaped portion 314 at the end 318 thereof.

The body receiving portion 302 comprises a cylindrically shaped recess 310 being defined by an inner tubular surface 311. The axis of the cylindrical recess 310 is oriented to be generally peφendicular to the axis of the spine, and transverse to the axis of the support rod of the implant apparatus. The top of the cylindrically shaped recess 310 comprises an opening 312 defined by the upper annular portion of the inner surface 31 1 and an outer annular surface 313. The opening further includes slots 304 so that the opening may be selectively narrowed by an inwardly directed radial force. The outer surface 313 of this opening 312 is tapered such that it widens as a function of distance from the opening. This tapered outer surface 313 further comprises an external threading 315 so that a nut may be introduced thereonto; the downward translation of which provides an inward radial force to contract the opening 312 of the cylindrical recess 310.

Referring now to Figure 17, the tightening nut 380 comprises an interior threading 382 which is designed to engage the outer upper surface 313 of the recess 310 and be rotationally translated downward on the threading 315 thereof. This downward translation causes the nut 380 to apply the inwardly directed radial force necessary for the slots 314 to be closed, thereby narrowing the opening 312 and crush locking the inner surface 311 of the opening against any properly fitted cylindrically shaped object which may be placed therein and thereby locking it within the recess 310.

Referring now to Figures 18a and 18b, alternate side and top loading body portions 320a,320c of an extending rod coupling subassembly of the present invention, which are equivalently engaged by and mounted in the recess 310 of blade portion 300 are shown in side views. Each body 320a,320c comprises a generally cylindrical shape which may be conceptually separated into a shaft portion 322a,322c, and an upper portion 326a,326c, each of which shall be described more fully hereinbelow. As previously set forth, in the side loading variation 320a, an intermediate portion 324a is further subdivided from the upper portion 326a.

First, with respect to the shaft portions 322a,322c which are otherwise equivalent, the body portion 320a,320c is designed to be slidably mounted in the cylindrical recess 310 of the blade portion 310 (see Figure 16) and as such has a generally cylindrical shape. This shaft 322a,322c must be long enough to provide a sufficiently large stroke within the recess 310 so that the height of the upper portion 326a,326c (and the intermediate portion 324a) of the body 320a,320c may be varied enough to compensate for misalignments of the support rod relative to the entire assembly. The shaft 322a,322c is cylindrical in shape for the additional puφose of permitting the body 320a,320c to be rotated within the recess 310, so that the rod receiving means, as described more fully hereinbelow with respect to the intermediate portion, may be positioned to receive the rod independent of normal deviations from the standard axial disposition ofthe rod. Specifically with respect to the side loading version shown in Figure 18a, the intermediate portion 324a of the generally cylindrical body 320a is similar to the equivalent portions ofthe coupling element 200a shown in Figure 12a as well as the rod receiving portions of Figures 7a and 7b, and therefore includes a large removed section which forms a horizontal channel 332a in the side thereof. The rod receiving channel 332a comprises a curvate inner wall 334a. The horizontal depth ofthe inner wall 334a is established such that a circular support rod which is positioned in the rod receiving channel 332a may nests fully within the body 320a, and does not extend beyond the lateral extent thereof, which would prevent a rod securing sleeve from sliding over the intermediate portion 324a of the body 320a to retain the rod within the channel 332a. The radius of curvature ofthe inner wall 334a is ideally matched to the radius of the support rod so that the rod is rigidly held in the channel 332a, and cannot move vertically once positioned therein.

The upper portion 326a ofthe body portion 320a comprises a slightly narrower cylindrical core 335a, having a threading 336a thereon. The upper portion 326a, and the threading 336a thereon, is ideally suited for receiving a top locking nut.

Alternatively, with reference to Figure 18b, in which the top loading version is illustrated, the upper portion 324c of the generally cylindrical body 320c is similar to the equivalent portions of the coupling element 200c shown in Figure 12b as well as the rod receiving portions of Figures 7c and 7d, and therefore includes a pair of upwardly extending members 324c defining therebetween a channel 332c in the top thereof. The rod receiving channel 332c comprises a curvate bottom 334c. The depth of the bottom 334c is established such that a circular support rod which is positioned in the channel 332c may nests fully within the body 320c, and does not extend above the extent of the upwardly extending members 324c which would prevent a top locking nut 170 from sliding thereover to retain the rod within the channel 332c. The radius of curvature ofthe bottom 334c is ideally matched to the radius ofthe support rod so that the rod is rigidly held in the channel 332c, and cannot move vertically once positioned therein.

The uppermost portions of the upwardly extending members 324c comprises a threading 336c thereon, which is ideally suited for receiving a top locking nut.

With reference now to Figures 19a and 19b, which illustrate fully assembled alternative side and top loading hook devices, including the support rod 150, step by step methods of implantation are described. As with the previous embodiments, first the blade portion 300 is mounted to the lamina, such that the flat extending member 116 thereof is disposed beneath the lamina and the body receiving portion 302 is disposed above the lamina.

The shaft portion 322a,322c of the body 320a,320c is then positioned in the cylindrical recess 310 at the proper height and rotational orientation. It may be desirable for the shaft to be coupled within the recess 310 so that it may not be fully removed therefrom, but may be raised and rotated as necessary.

Once properly set, the tightening nut 380 is introduced onto the threading 315 of the blade portion 300. It is understood that the tightening nut 380 may have been placed on the outer tapered surface 313 prior to the introduction of the shaft 322 in the recess 310, or the tightening nut may be dropped over the body 300 to engage the threading 315. Tightening of the nut 380 on the outer threading causes the nut 380 to translate downward on the outer tapered surface 313, thereby applying an inward force against it, and closing the slots 304. The inner surface 311 of the recess 310 is then locked to the shaft 322 preventing further movement thereof relative to the blade portion 300. Referring specifically to the side loading embodiment of Figure 19a, once the shaft portion 322a is locked in position, the support rod 150 may be positioned in the rod receiving channel 332a. The rod securing sleeve 164 is placed over the upper portion 326a of the body 320a, the bottom surface 169 thereof cupping the top of the rod 150 and pressing it against the bottom surface of the channel 332a. The top locking nut 170 is then threadably mated to the threading 336a of the upper portion 326a, the downward translation of which causes the bottom surface 174 of the nut 170 to seat against the top surface 163 of the sleeve 164. The nut 170, thereby, supplies the necessary force through the sleeve 164 and the bottom surface ofthe channel 332a to hold the rod securely in the channel.

Alternatively, and with respect to Figure 19b, once the shaft is 322c is locked in position, the support rod 150 being positioned between the upwardly extending members 324c, in the channel 332c. The top locking nut 170 is then threadably mated to the threading 336c of the upper portion 326c, the downward translation of which causes the bottom surface 174 ofthe nut 170 to seat against the top surface of the rod. The nut 170, thereby, supplies the necessary force to hold the rod securely in the channel 322c, locking the rod against the bottom 334c. Referring now to Figure 20, the body portion 400 of a variation of the present invention, wherein the rod receiving portion ofthe hook device comprises the coupling element 200a,200c as described hereinabove with respect to Figures 12a and 12b, so that the rod receiving channel 222a,222c may be angulated relative to the blade portion 300 (and the body portion 400), is shown. The body comprises a shaft portion 402, which is similar in all respects to the shaft portion 322a,322c of the body 320a,320c of the previous embodiment. The body 400, however, has a curvate head 404 at the distal end ofthe shaft 402. This curvate head 404 further comprises a recess 406 in the top thereof for coupling to a post (not shown) so that the surgeon using the present device may raise and lower the body portion 400 relative to the blade portion 300 more easily. It is preferable that this recess 406 be threaded so that the post may engage the head 404 via a threaded end.

With reference now to Figures 21a and 21b, which show side views of the coupling element 200a,200c locked to the semi-spherical head 404 ofthe body portion 400, the preferred method of implantation and assembly is described hereinbelow. As above, the blade portion 300 is first positioned in contact with the lamina (not shown) such that the extending member 116 thereof is positioned under the lamina and in the spinal canal. It is critical that the arched surface 115 be positioned as close to flush against the arched underside of the center of the lamina as possible. Then the body portion 400 is locked in place relative to the blade 300, in a manner identical to the way described with respect to each of the previously described embodiments; the tightening nut 380 being used to crush lock the cylindrical recess 310 of the blade portion 300 to the shaft portion 322a,322c ofthe body 320a,320c.

Once the base of the assembly is rigidly positioned relative to the lamina, the head 404 thereof is inserted into the interior chamber 216a,216c of the coupling element 200a,200c. (This step may, of course, be taken prior to the locking of the shaft 402 to the blade portion 300, however, in such a case, the surgeon may need to rotate the polyaxial coupling element such that a threaded post may be inserted down the axial passageway of the coupling element 200a,200c, into the interior chamber 216a,216c, and couple with the recess 406 in the semi-spherical head 404, so that the shaft 402 may be raised and lowered relative to the blade portion 300 to attain the proper height adjustment.)

At this point in the assembly process, the locking collar 250 has not yet been forced downward along the outwardly tapered lower portion 202a,202c, thereby providing the coupling element 200a,202c with the capacity to rotate and angulate relative to the shaft 402 (and the blade portion 300). This permits the support rod 150 to be properly nested within the rod receiving channel 222a,222c in spite of small misalignments ofthe rod. The securing ofthe rod and the coupling element, by means ofthe rod securing sleeve and/or the top locking nut are carried out as set forth above, for each respective and corresponding embodiment. Referring now to Figurea 22a and 22b, alternate variations of the fixed embodiments, originally set forth with respect to Figures 7a-7d, are shown wherein the rod receiving portion comprises a pair of cylindrical body portions, each having a side or top recess therein for receiving a support rod. In such a conformation, it may be possible for the surgeon to leave the spinous process intact, however, such a device would be primarily useful in providing a second rod alignment axis of channels by which a de-curving force may be applied to the spine prior to final fixation via the first axis of channels.

While there have been described and illustrated a variety of embodiments of a single rod and hook apparatus which is provided for immobilization of the spine via fixation of specifically formed hooks, both plow and claw shaped, to the arched portion of the lamina; as well as a variety of different hooks having polyaxial and or extending rod receiving portions, it will be apparent to those skilled in the art that further variations and modifications are possible without deviating from the broad spirit and principle of the present invention. The present invention shall, therefore, be limited solely by the scope ofthe claims appended hereto.

Claims

We claim:

1. A hook and rod apparatus for immobilization of sequences of bones in a spinal column via fixation to posterior lamina elements at a central posterior axis thereof, comprising: a support rod; at least one blade element, including a curved section for attaching to the central vertical axis portion of the lamina, a lower extending member for disposition beneath the lamina, and an upper portion disposed above the lamina along the central vertical axis thereof; a body, coupled to the upper portion ofthe blade, said body including a channel therein for receiving therein said support rod; means for locking said support rod in said channel.

2. The apparatus as set forth in claim 1, wherein said lower extending member further comprises an arched surface such that it is plow shaped and seats against the arched conformation ofthe central vertical axis ofthe corresponding lamina.

3. The apparatus as set forth in claim 1, wherein said lower extending member further comprises a bifurcated conformation including a pair of angularly offset extending elements each of which seats against opposing underside portions of the lamina which are laterally adjacent to the arched central vertical axis ofthe corresponding lamina.

4. The apparatus as set forth in claim 1, wherein said channel is formed in a side of said body.

5. The apparatus as set forth in claim 1, wherein said channel is formed in a top of said body.

6. The apparatus as set forth in claim 1 , wherein said means for locking the rod in the channel comprises a nut.

7. A hook for use with central vertical axis orthopaedic rod implantation apparatus, comprising: a blade portion, including a curved section for attaching to the central vertical axis portion ofthe lamina, a lower extending member for disposition beneath the lamina, and an upper section for disposition above the lamina along the central vertical axis thereof; a body portion, coupled to the upper portion of the blade, said body including a channel therein for receiving therein a support rod of said central vertical axis orthopaedic rod implantation apparatus; means for locking said support rod in said channel.

8. The apparatus as set forth in claim 7, wherein the upper section of said blade portion comprises a curvate head, and wherein said body portion comprises a separate rod coupling element which is polyaxially coupled to said curvate head.

9. The apparatus as set forth in claim 8, wherein said rod coupling element has lower and upper portions thereof, said upper portion having said channel formed therein, and further having said surface threading, and said lower portion including: a taper wherein the bottom of the lower portion is wider than the top thereof; at least one vertical slot extending upward from the bottom; and an opening in said bottom, for receiving therethrough said curvate head, said opening being expandable and contractible by via radially inward forces applied to lower portion; an interior chamber for receiving therein said curvate head; a locking collar mounted around the lower portion, said locking collar being translatable downward along said tapered outer surface of said lower portion via a downward force applied to said locking collar, whereby the locking collar provides said radially inward force; and means for applying a downward force on said locking collar.

10. The hook as set forth in claim 9, further comprising a rod securing sleeve positioned around the upper portion for securing the rod in the channel.

11. The hook as set forth in claim 10, wherein the means for applying a downward force on said locking collar comprises a nut.

12. The hook as set forth in claim 11, wherein a bottom surface of said nut seats against a top surface of said rod securing sleeve, and the rod seats against a top surface of said locking collar, the downward translation of said nut thereby causing said support rod to be crush locked between said rod securing sleeve and said locking ring.

13. The coupling assembly as set forth in claim 12, wherein said downward translation of said nut on said surface threading of said upper portion of said coupling element causes the sleeve to translate downward, which causes the rod to translate downward, which causes the locking collar to translate downward and apply a radially inward force against the lower portion of the coupling element, which causes the at least one slot to narrow and the opening in said bottom of said coupling element and said interior chamber to crush lock the semi-spherical head within said interior chamber.

14. A hook for use with central vertical axis orthopaedic rod implantation apparatus, comprising: a blade portion, including a curved section for attaching to the central vertical axis portion of the lamina, a lower extending member for disposition beneath the lamina, and an upper section disposed above the lamina along the central vertical axis thereof, said upper section including a cylindrical recess having a contractible opening, said opening having a taper, at least one slot extending down therefrom, and a surface threading; a tightening nut which is engageable with said surface threading for the puφoses of narrowing said at least one slot, thereby contracting said opening; a body portion having a shaft initially slidably mounted within the cylindrical recess of said upper section of the blade portion, said shaft being lockable in said cylindrical recess by engagement of said tightening nut with said surface threading of said opening; said body including a channel therein for receiving therein a support rod of said central vertical axis orthopaedic rod implantation apparatus; means for locking said support rod in said channel.

15. The hook as set forth in claim 14, wherein said lower extending member comprises an arched surface such that it is plow shaped and seats against an arched undersurface portion of said lamina along the central vertical axis ofthe corresponding lamina.

16. The apparatus as set forth in claim 14, wherein said lower extending member comprises a bifurcated conformation including a pair of angularly offset extending elements each of which seats against opposing underside portions of the lamina which are laterally adjacent to the arched central vertical axis ofthe corresponding lamina.

17. The apparatus as set forth in claim 14, wherein said body portion further comprises a surface threading disposed on an outer surface thereof, and wherein the means for locking the support rod in said side channel comprises a rod securing sleeve, positionable about, and in rod securing relationship with, said channel for securing said rod therein and a top locking nut, mateable with said surface threading.

18. A hook for use with central vertical axis orthopaedic rod implantation apparatus, comprising: a blade portion, including a curved section for attaching to the central vertical axis portion of the lamina, a lower extending member for disposition beneath the lamina, and an upper section disposed above the lamina along the central vertical axis thereof, said upper section including a cylindrical recess having a contractible opening, said opening having a taper, at least one slot extending down therefrom, and a surface threading; a tightening nut which is engageable with said surface threading for the purposes of narrowing said at least one slot and thereby contracting said opening; a cylindrical shaft having a curvate head integrally formed at one end thereof, the other end of said thereof being initially slidably mounted within the cylindrical recess of said upper section of the blade portion, said shaft being lockable in said cylindrical recess by engagement of said tightening nut with said surface threading of said opening; a body, said body being initially polyaxially mounted on said semi-spherical head and including a channel therein for receiving therein a support rod of said central vertical axis orthopaedic rod implantation apparatus; means for locking said support rod in said channel.

19. The hook as set forth in claim 18, wherein said lower extending member comprises an arched surface such that it is plow shaped and seats against an arched undersurface portion of said lamina along the central vertical axis ofthe corresponding lamina.

20. The apparatus as set forth in claim 20, wherein said lower extending member comprises a bifurcated conformation including a pair of angularly offset extending elements each of which seats against opposing underside portions of the lamina which are laterally adjacent to the arched central vertical axis ofthe coπesponding lamina.

21. The apparatus as set forth in claim 18, wherein said body comprises a coupling element having lower, intermediate, and upper portions thereof, said intermediate portion having said channel formed therein, said upper portion having a surface threading, and said lower portion including: a taper wherein the bottom of the lower portion is wider than the top thereof; at least one vertical slot extending upward from the bottom; and an opening in said bottom, for receiving therethrough said curvate head, said opening being expandable and contractible by via radially inward forces applied to lower portion; an interior chamber for receiving therein said curvate head.

22. The hook as set forth in claim 21, wherein the means for locking the support rod in said channel comprises a rod securing sleeve, positionable about, and in rod securing relationship with, said channel for securing said rod therein and a top locking nut, mateable with said surface threading of said upper portion.

23. The hook as set forth in claim 22, further comprising a locking collar, disposed about said coupling element, an upper surface of said collar extending up to a position above a lower surface of said channel so that the support may seat thereon upon introduction of the support rod into said side channel; said locking collar being translatable downward along said tapered outer surface of said lower portion via a downward force applied to said upper surface ofthe locking collar, whereby the locking collar provides said radially inward force.

24. The hook as set forth in claim 22, wherein a bottom surface of said top locking nut seats against a top surface of said rod securing sleeve, and the support rod seats against a top surface of said locking collar, the downward translation of said top locking nut thereby causing said support rod to be crush locked between said rod securing sleeve and said locking collar.

25. The coupling assembly as set forth in claim 22, wherein said downward translation of said nut on said surface threading of said upper portion of said coupling element causes the sleeve to translate downward, which causes the rod to translate downward, which causes the locking collar to translate downward and apply a radially inward force against the lower portion of the coupling element, which causes the at least one slot of the coupling element to narrow and the opening in said bottom of said coupling element and said interior chamber to crush lock the curvate head of said shaft within said interior chamber.

26. A hook and rod apparatus for immobilization of sequences of bones in a spinal column via fixation to posterior lamina elements along a central vertical axis thereof, comprising: at least one support rod; at least one blade element, including a curved section for attaching to the central vertical axis portion of the lamina, a lower extending member for disposition beneath the lamina, and an upper portion for disposition above the lamina along the central vertical axis thereof; at least one body, coupled to the upper portion of the blade, said at least one body including a channel therein for receiving therein said corresponding at least one support rod; means for locking said coπesponding support rod in said channel.

27. The apparatus as set forth in claim 26, wherein said lower extending member further comprises an arched surface such that it is plow shaped and seats against the arched conformation ofthe central vertical axis ofthe coπesponding lamina.

28. The apparatus as set forth in claim 26, wherein said lower extending member further comprises a bifurcated conformation including a pair of angularly offset extending elements each of which seats against opposing underside portions of the lamina which are laterally adjacent to the arched central vertical axis ofthe corresponding lamina.

29. The apparatus as set forth in claim 26, wherein said at least one body portion is integrally formed with the upper portion of blade.

30. The apparatus as set forth in claim 29, wherein said at least one body further includes a surface threading disposed on an outer surface thereof, between a top thereof and the side channel, and wherein the means for locking the support rod in said side channel comprises a rod securing sleeve, positionable about, and in rod securing relationship with, said side channel for securing said rod therein and a top locking nut, mateable with said surface threading.

31. The apparatus as set forth in claim 29, wherein said at least one body comprises a pair of bodies.

32. A central axis spine hook having a polyaxial colleted taper locking mechanism, comprising: a blade portion having a curved lower extending member for disposition beneath the lamina, and an upper portion for disposition above the lamina along the central vertical axis thereof, said upper portion including a curvate head; a coupling element, a lower portion of said coupling element having a tapered and colleted exterior surface and a curvate interior volume for receiving therein said curvate head; and a locking collar mounted around said tapered colleted portion, selected translation of said locking collar relative to said lower portion causing said curvate interior volume to crush lock to said curvate head.