Spinal rod system

[0001] The spine is subject to various pathologies that compromise its load bearing and support capabilities. Such pathologies of the spine include, for example, degenerative diseases, the effects of tumors and, of course, fractures and dislocations attributable to physical trauma. In the treatment of diseases, malformations or injuries affecting spinal motion segments (which include two or more adjacent vertebrae and the disc tissue or disc space therebetween), and especially those affecting disc tissue, it has long been known to remove some or all of a degenerated, ruptured or otherwise failing disc. It is also known that artificial discs, fusion implants, or other interbody devices can be placed into the disc space after disc material removal. External stabilization of spinal segments alone or in combination with interbody devices also provides advantages. Elongated rigid plates, rods and other external stabilization devices have been helpful in the stabilization and fixation of a spinal motion segment, in correcting abnormal curvatures and alignments of the spinal column, and for treatment of other conditions.

[0002] While external rod systems have been employed along the vertebrae, the geometric and dimensional features of these rod systems and patient anatomy constrain the surgeon during surgery and prevent optimal placement and attachment along the spinal column. For example, elongated, one-piece rods can be difficult to maneuver into position along the spinal column, and also provide the surgeon with only limited options in sizing and selection of the rod system to be placed during surgery.

[0003] In one aspect, a rod system having a first rod attachable to a second rod in end-to-end fashion allows the surgeon to select from rods having various dimensions and/or other characteristics to construct a rod system that is optimal for pre-operative planning and to address conditions encountered during surgery. The end-to-end attachment minimizes the intrusiveness of the rod system into the anatomy adjacent the connection location.

[0004] In another aspect, a rod system includes a first rod attachable to a second rod in end-to-end fashion includes a coupling mechanism that axially and torsionally constrains the first and second rods to one another.

[0005] In a further aspect, a rod system includes a first rod attachable to a second rod in end-to-end fashion with a coupling mechanism. The coupling mechanism includes a coupling body on one rod that axially receives a coupling member on the other rod and engagement of the coupling member with the coupling body axially constrains the first and second rods to one another.

[0006] In another aspect, a method for assembling a spinal rod system includes: providing a first spinal rod with a first rod portion for attachment to the spinal column, said first rod portion including a first characteristic and a coupling member at an end of the rod portion; providing a second spinal rod with a second rod portion for attachment to the spinal column, said second rod portion including a second characteristic and a coupling body at an end of the rod portion; and axially constraining the first spinal rod to the second spinal rod with the coupling member engaging the coupling body and the first and second spinal rods centered along a longitudinal axis of the spinal rod system.

[0015] For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is hereby intended. Any such alterations and further modifications in the illustrated devices, and any such further applications of the principles of the invention as illustrated herein being contemplated as would normally occur to one skilled in the art to which the invention relates.

[0016] In FIG. 1 there is shown a spinal rod system 10 including a first rod 12 and a second rod 30. First rod 12 and second rod 30 are releasably coupled to one another in end-to-end fashion with a coupling mechanism 28. Coupling mechanism 28 includes a coupling body on one of the first and second rods 12, 30 and a coupling member on the other of the first and second rods 12, 30. The coupling mechanism 28 is configured to secure rods 12, 30 to one another in end-to-end fashion. This minimizes the footprint or intrusiveness of the coupling mechanism into the tissue surrounding the rod system, and maximizes the length of the rod portion of each rod available for positioning and/or attachment along the spinal column.

[0017] First rod 12 includes a first rod portion 14 and coupling member 16 at a first end of first rod portion 14. Rod portion 14 extends from coupling member 16 to an opposite second end 17 (FIG. 5.) Second rod 30 includes coupling body 34 at a first end thereof. Rod portion 32 extends from coupling body 34 to an opposite second end 35 (FIG. 5.) One or both of the second ends 17, 35 of rod portions 14, 32 may include a coupling member, a coupling body, or simply provide a terminal end shaped like the corresponding rod portion 14, 32 as shown. Although only one coupling mechanism 28 is shown, one or more of the rods 12, 30 can be adapted for engagement with another rod at each end thereof so that three or more rods may comprise the rod system. Rod portions 14, 32 can be secured to vertebrae of the spinal column system with any one or combination of hooks, screws, bolts, multi-axial screws, staples, cables or wires, sutures, clamps, interbody fusion devices, an implant between vertebrae, and/or other attachment devices and systems.

[0018] First rod portion 14 can be provided with a characteristic that differs from a characteristic of second rod portion 32. The coupling mechanism 28 allows rods of differing characteristics to be secured to one another in end-to-end fashion to provide a rod system that is adapted for the anatomy, surgical condition, or surgical procedure. In one embodiment, the characteristic includes a cross-sectional dimension of the rod portions 14, 32. Other embodiments contemplate selection criteria for selection and assembly of the rod portion to include any one or combination of characteristics, including length, contouring, flexibility, surface features, shape, section modulus, elasticity, materials and material properties, and coatings, for example.

[0019] As shown in FIGS. 1-2 and 5, rod portion 14 extends along longitudinal axis 11 and includes a first cross-sectional dimension 22 between opposite sides thereof transverse to longitudinal axis 11. Similarly, rod portion 32 extends along longitudinal axis 11 and includes a second cross-sectional dimension 40 between opposite sides thereof transverse to longitudinal axis 11. In the illustrated embodiment, cross-sectional dimension 22 corresponds to a diameter of a cylindrical rod portion 14 that is smaller than a diameter corresponding to cross-sectional dimension 40 of a cylindrical rod portion 32. In one specific application, the diameter of first rod portion 14 is sized to extend along a first portion of the spine, such as the cervical region, and the diameter of second rod portion 32 is sized to extend along a second portion of the spine, such as the thoracic region. Other systems contemplate multiple rod portions coupled to one another in end-to-end fashion with characteristics adapted for positioning along any one or combination of the sacral, lumbar, thoracic and cervical regions of the spinal column.

[0020] Coupling member 16 includes a threaded outer surface extending from rod portion 14 to an end member 20 lacking threads. Coupling member 16 further includes a contact portion 18 along at least one side thereof, as also shown in FIG. 3. Contact portion 18 can be formed by a cutout providing a flat surface extending along coupling member 16. Contact portion 18 can also include a concave surface, a convex surface, a receptacle, or other suitable configuration for contacting an engaging member. As shown in FIG. 5, the thread pattern of coupling member 16 extends completely therearound between the opposite sides of contact portion 18. Other embodiments contemplate that multiple contact portions are provided along coupling member 16 to provide multiple engagement locations for engaging member 42, as discussed further below.

[0021] Coupling body 34 can be enlarged relative to rod portion 32 to provide a flange or hub to which coupling member 16 can be releasably engaged. In the illustrated embodiment, coupling body 34 is a cubic block, although other shapes are also contemplated, such as rectangular and cylindrical shapes. Coupling body 34 includes a first bore 36 formed internally therein that extends along and opens along longitudinal axis 11 at an end of coupling body 34. Coupling body 34 further includes a second bore 38 extending therein transversely to first bore 36. As further shown in FIG. 5, second bore 38 can be internally threaded for receipt of an engagement member. Second bore 38 can also be orthogonal to first bore 36, although other orientations are also contemplated.

[0022] As shown in FIGS. 2 and 5, rods 12, 30 can be assembled in end-to-end fashion and aligned along longitudinal axis 11 with coupling member 16 received in bore 36 and axially constrained by threaded engagement with coupling body 34. End member 20 facilitates positioning and alignment of coupling member 16 in bore 36, preventing or reducing the possibility of cross-threading coupling member 16 with coupling body 34. The axial load between rods 12, 30 is carried by the engagement between coupling member 16 and coupling body 34, which are also aligned along the axis 11 of rod system 10 when engaged. Accordingly, torsional loading of the components of rod system 10 is minimized since the rods 12, 30 are connected to one another in end-to-end fashion along axis 11. Furthermore, the footprint of coupling mechanism 28 both transversely to rods 12, 30 and along rods 12, 30 is minimized, making the procedure for positioning rod system 10 less invasive, providing additional rod length for contouring and attachment of fasteners for engagement with the spinal column, and minimizing the number of components employed in securing the rods 12, 30 to one another.

[0023] Engaging member 42 is positionable in second bore 38 and engageable to coupling member 16 to prevent rod 12 from disengaging from rod 30. In one embodiment, contact portion 18 of coupling member 16 is oriented toward second bore 38, and engaging member 42 is an externally threaded set screw 44 engageable in second bore 38. A tool engaging recess 46 is provided for engagement with a tool, such as a hex driver, to allow the set screw 44 to be driven into second bore 38. Set screw 44 is driven into second bore 38 so that end 48 is in contact with contact portion 18, preventing coupling member 16 from rotating in body 30 and resisting torsional loading between rods 12, 30.

[0024] With contact surface 18 aligned with bore 38, the rod portions 14, 32 are oriented in a predetermined alignment with one another determined by the location of contact surface 18 and bore 38 relative to the respective rod portions 14, 32. For example, if one or both of rod portions 14, 32 are provided with non-circular cross-sections, through-holes, or other characteristic along their respective lengths, the characteristics can be oriented relative to contact surface 18 and/or bore 38 so that when contact surface 18 is engaged by engaging member 42, the characteristic of rod portion 14 is positioned in a desired alignment relative rod portion 32. In this manner, the rod portions 14, 32 can be secured with these characteristics in a predetermined alignment relative to one another, and maintained in this alignment by the engagement of engaging member 42 with contact surface 18.

[0025] Other embodiments contemplate other arrangements for coupling mechanism 28. For example, engaging member 42 can be a pin that is received in a hole or recess in coupling member 16. Coupling body 34 can be a nut rotatably captured on the end of rod portion 32. Coupling mechanism 28 can include a bayonet locking type device, or a spring-biased ball plunger in coupling member 16 that is received in a detent in coupling body 34.

[0026] In FIG. 6, there is shown another embodiment rod system 110 extending along a longitudinal axis 111 and including a first rod 112 having rod portion 114 and coupling member 116. A second rod 130 includes rod portion 132 and a coupling body 134 with an axial bore 136. First and second rod portions 114, 132 can be provided with differing characteristics and axially constrained to one another in end-to-end fashion. Body 130 does not include a second bore for an engaging member, and coupling member 116 can be provided completely threaded therearound. To torsionally constrain coupling member 116 in coupling body 134, coupling member 116 can be provided with locking threads to prevent first and second rods 112, 130 from rotating relative to one another. In another embodiment, a simple threaded engagement is provided to axially constrain rods 112, 130 to one another, and relative rotation of rods 112, 130 is resisted by the engagement of rods 112, 130 to the spinal column.

[0027] In FIG. 7, there is shown another embodiment rod system 210 including a first rod 212 and a second rod 230 extending along a longitudinal axis 211. First rod 212 includes a first rod portion 214 and second rod 230 includes a second rod portion 232. First and second rod portions 214, 232 can be provided with differing characteristics and attached to one another in end-to-end fashion with a coupling mechanism 228. First rod 212 includes a coupling member 216 at an end of rod portion 214. Coupling member 216 is externally tapered toward the first end 220 of rod 212, and forms a lip 218 extending about rod portion 214. Coupling body 234 includes an axial bore that is tapered from a first end 238 of second rod 230 toward rod portion 232. Engaging member 216 is press fit into bore 236 so that the tapered outer surface is received in the flared bore to frictionally engage and axially and torsionally constrain first rod 212 to second rod 230 in end-to-end fashion. It is further contemplated that an engaging member can be provided extending between coupling body 234 and coupling member 216 to provide additional fixation in addition to the friction fit between coupling body 234 and coupling member 216.

[0028] In FIG. 8, there is shown another embodiment rod system 310 including a first rod 312 and a second rod 330 extending along longitudinal axis 311. First rod 312 includes a first rod portion 314 and second rod 330 includes a second rod portion 332. First rod 312 includes a coupling member at an end of rod portion 314 in the form of a flange or hub 316 extending around first rod portion 314. Flange 316 forms a lip 318 extending about rod portion 314. Second rod 330 includes a coupling body at an end thereof that is also in the form of a flange or hub 334. Flange 334 extends around and forms a lip 336 about second rod portion 332. Flanges 316, 334 are positionable in abutting engagement with one another in end-to-end fashion so that rods 312, 330 having differing characteristics can be secured to one another to provide rod system 310.

[0029] Coupling mechanism 328 includes a fastener 340 extendable through aligned bores 320, 338 extending parallel to axis 311 through the flanges 316, 334. A nut 342 is engageable with fastener 340 to axially constrain rods 312, 330 together in end-to-end fashion. It is contemplated that a number of fasteners can be positioned about the flanges to provide additional axial constraint and also torsional constraint to rods 312, 330. Although fastener 340 has been shown as a bolt with a nut, other fasteners are also contemplated, including rivets, screws, and bolts threadingly engaged to the flange bores, for example.

[0030] Another embodiment coupling mechanism 428 is shown in FIG. 8 that includes a clamping member 430 and an engaging member 432. Clamping member 430 includes arms 434, 436 at opposite ends thereof that extend along adjacent ones of the flanges 316, 334. Fastener 432 extends parallel to axis 311 and is engageable to a bore 438 in arm 434. Fastener 432 is positionable in contact with flange 316 to bias arm 436 into contact with flange 334. Flanges 316, 334 are drawn toward one another to position the flanges in end-to-end contact and axially constrain rods 312, 330 relative to one another. It is contemplated that a number of clamping members can be provided about flanges 316, 334 to provide a secure clamping arrangement to prevent rods 312, 330 from pivoting or splaying relative to one another. It is further contemplated that clamping member 430 can be sized to extend along a portion of the perimeter of flanges 316, 334, and a number of fasteners 432 are provided to clamp first and second rods 312, 330 to one another.

[0031] While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character. All changes and modifications that come within the spirit of the invention are desired to be protected.