IMPLANT INTERCONNECTION MECHANISM
BACKGROUND OF THE INVENTION
Field of the Invention:
This invention relates generally to spinal osteosynthesis and more particularly, to a system for making connections from various types of anchors to the spinal rods themselves. Description of the Prior Art:
Many types of hooks and screws and rods and connectors have been devised for use in connection with spinal osteosynthesis. U. S. Patent No. 5,005,562 issued April 9, 1991 to Yves Cotrel shows examples of all of these devices. It shows screws 19 including the "threaded rod" portion 21 anchored in bone, and hooks 18 including the curved blade portion 1 hooked around bone. It also includes transverse rods 22 with hooks 23 on them and set screws for clamping the hooks 20 and 23 to the spinal rods. Some such devices use screws and hooks which must be slided onto the end of the spinal rod for installation. In the Cotrel patent, the hooks and screws are "top opening" and have, for example, a body 2 with two "side branches" 4 and defining between them a channel 6 with a rounded bottom 7 to receive the spinal rod 3 between them. A plug 8 is screwed into the thread 11 formed in the inner walls of the branches 4, thereby closing the channel after insertion of the spinal rod from the top, and having either a center point 12 or peripheral ring 13 or both projecting downward from the face of the plug to penetrate and lock on the spinal rod when the plug is tightened in the channel. A sawtooth thread pitch on the screw is used to avoid spreading the branches as the plug is tightened. The type of hook and screw head shown in and described in
the Cotrel patent, where the spinal rod can be inserted directly from above into the receiving channel is in a category referred to as an "open system", in contrast to the necessity in certain other systems for introducing the spinal rod to the hook or screw axially or endwise of the rod through an aperture in the hook or screw and then clamping them. U. S. Patent No. 5,261,907 issued November 16, 1993 to Vignaud et al. is another example of spinal rods anchored in open-headed pedicular screws secured to the rod by a locking screw 6, with annular element 9 around the diapason-shaped cylindrical head 5 and element 9 locked in place around the "branches" 5a and 5b of head 5 by the tendency of the branches to spread as the screw 6 tends to spread the branches. There has remained a need for a system using open screws and hooks secured to the spinal rods, easily fixable in position by the use of a set screw, but without the need for some kind of special threads for the set screw or some ring or other arrangement capturing the branches of the screw head. The present invention is addressed to that need.
SUMMARY OF THE INVENTION
Described briefly, in a typical embodiment of the present invention, implants are provided for osteosynthesis, and have features for anchorage in or onto bone or to connectors. As applied to spinal osteosynthesis, the implants have a body with an upwardly opening channel receiving a spinal rod therein. The channel has sidewalls with a curved slot in each of the sidewalls. A cap is mounted on the implant body and has a central portion received in the channel and has tongue portions at each side of the central portion, the tongue portions being received in the curved slots in the sidewalls. A fastener mounted in the body or cap clamps the rod, the body and cap together. The curved slots enable installation of the cap in minimal space measured lengthwise of the rod. The implant body has an integral bone screw, or bone hook, or lateral connector rod or parallel spinal rod receiving body thereon.
BRIEF DESCRIPTION OF THE DRAWINGS
Fig. 1 is a schematic view of a portion of the spine with an osteosynthesis system applied thereto incorporating implants according to the present invention.
Fig. 2 is a perspective view of three parts of a screw and cap type of implant assembly according to the present invention.
Fig. 3 is a top plan view of the screw itself.
Fig. 4 is a front elevational view thereof.
Fig. 5 is a side view thereof.
Fig. 6 is a section through the top portion of the screw taken at line 6-6 in Fig. 3 and viewed in the direction of the arrows.
Fig. 7 is a section therethrough taken at line 7-7 in Fig. 6 and viewed in the direction of the arrows.
Fig. 8 is a top plan view of one embodiment of a cap for the screw of Fig. 2.
Fig. 9 is a rear elevational view thereof.
Fig. 10 is a side elevational view thereof.
Fig. 11 shows a section of the cap taken at line 11-11 in Fig. 9 and viewed in the direction of the arrows but installed with a spinal rod and pedicle screw shown in section.
Fig. 12 shows a section taken at line 12-12 in Fig. 11 and viewed in the direction of the arrows.
Fig. 13 is a top plan view of a hook incorporating the present invention.
Fig. 14 is a front elevational view thereof.
Fig. 15 is a side elevational view thereof.
Fig. 16 is a section through the top portion thereof taken at line 16-16 in Fig. 13 and viewed in the direction of the arrows.
Fig. 17 is a section therethrough taken at line 17-17 in Fig. 16 and viewed in the direction of the arrows.
Fig. 18 is a view of a lateral connector taken at line 18-18 in Fig. 1 and viewed in the direction of the arrows.
Fig. 19 is a front elevational view of that connector.
Fig. 20 is a front elevational view of a lateral connector similar to that of Figs. 18 and 19 but having two rod-receiving channels therein.
Fig. 21 is a front elevational view of a lateral connector like that in Fig. 20, except that there is no transverse rod between the channels.
Fig. 22 is a top plan view of a preferred embodiment of a cap for the screw of Fig. 2.
Fig. 23 is a rear elevational view thereof.
Fig. 24 is a side elevational view thereof.
Fig. 25 is a section taken through the cap on lines 25-25 in Fig. 24 and viewed in the direction of the arrows.
Fig. 26 shows a section of the cap taken at line 26-26 in Fig. 23 and viewed in the direction of the arrows, but installed with a spinal rod and with a pedicle screw shown fragmentarily and in section.
Fig. 27 is a view like Fig. 26 but showing the manner of insertion of the cap into the pedicle screw before securing the set screw in the cap.
DESCRIPTION OF THE PREFERRED EMBODIMENT
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiment 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 thereby intended, such alterations and further modifications in the illustrated device, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates .
Referring now to the drawings in detail, in Fig. 1 there is a spinal column shown generally at 11 with an osteosynthesis system including two spinal rods 12 and 13 and, for purposes of illustration, two suprala inar hook assemblies 14 and 16, two infralaminar hook assemblies 17 and 18 and four screw assemblies 19, 21, 22 and 23. There is also a lateral connector assembly 26 and associated connectors 27 and 28. The screws and hooks are used for the same types of purposes as described in the above-mentioned Cotrel patent, but have some advantages.
Figs. 2 through 7 show one of the screw assemblies such as 19. It includes a body portion 31, having an upwardly opening U-shaped slot 32 therein which serves as a spinal rod receiver channel. Each of the channel sidewalls 33 and 34 has a curved slot such as 36 and 37, respectively, therein. The slot is L-shaped, with the "leg" portion 36L of slot 36 cooperating with the channel wall 33 to form a downwardly extending flange whose lower edge 33B cooperates with the bottom 36B of slot 36 to form the "foot" of the L-shape.
The bottom 39 of the rod receiver channel is curved about a longitudinal axis 41 of the channel and has ridges therein parallel to the axis 41.
The body of the screw has parallel flat front and rear faces such as 42F and 42R being in planes at a spacing of about 7.00 mm and perpendicular to the channel axis 41. As best seen in Figs. 2 and 3, the upper portions of the body at the sides 43 of the flat faces 42F and 42R are curved, the maximum outside dimension being about 13 mm, for example. The sides 43 blend into a conical portion 44 providing the transition from the faces and sides of the body to the threaded stem whose longitudinal axis 45 is perpendicular to axis 41 and centered between faces 42F and 42R. The screw is threaded for anchoring in bone and has a self-tapping point. The cap 46 Figs. 2 and 8-12 has a central portion 47 and outwardly extending curved flange or tongue portions 48 at each side of the central portion. These flange or tongue portions are generally L-shaped in having a foot portion 49 and leg portion 51. The bottom of the central portion of the cap has a downwardly opening rod-receiving channel 52. Threaded aperture 54 receives the threads 56 of the socket head cap screw 57 which serves as a set screw in the assembly, fastening the rod to the pedicle screw and cap assembly.
Referring again specifically to Figs. 4, 6 and 7, the L-shaped slots face each other and, as best shown in Fig. 7, the bottom 36B of the foot portion of the slot is curved about an axis 61 which is above the channel bottom cylindrical axis 41 and lies in a plane that is perpendicular to the channel bottom cylindrical axis 41 and lies in a second plane that is perpendicular to the screw axis 45. Similarly, the bottom 33B of the downwardly projecting flange of channel face 33 is curved about the axis 61. So is the top 36T of the downwardly opening leg portion 36L of the channel formed by the flange. For a pedicle screw in which the radius from the axis 41 to the rod-engaging channel bottom grooves is about 3.25 mm, the radius from axis 61 to the flange bottom 33B is about 5.8 mm and to the bottom 36B
of the slot 36 is about 8.9 mm, for example.
Referring again to Figs. 8-12, these show that the top 48T of each of the tongues is curved about an axis 62 which is in a plane that is centered between the front and rear faces 46F and 46R of the cap and perpendicular to the center line 63 of the cap which is also the center line of the rod receiving channel 52 therein. The bottom 46B of the cap is also curved about the same center. So is the bottom 48B of the slot formed by the tongue 48. These features are slidingly fittable in the mating features of the screw in a tongue-in-groove relationship. An abutment stop ear 66 is provided on each side of the central portion of the cap at the rear face 46R thereof and near the top of the cap. Chamfers 67 are provided at all outside edges of the front face of the cap. These features facilitate insertion of the cap into the top of the bone screw in the direction of arrow 68 in Figs. 1, 2, 8 and 10, for example. Engagement of the stop ears 66 with the rear face 42R of the screw, will prevent the cap from sliding all the way through the channel and out.
Referring now to Fig. 11, note that the axis 71 of the threaded aperture 54 is at a 10° angle with respect to the vertical center line 72 of the cap. This enables not only the point 56P at the bottom of the set screw to bite into and anchor the rod 12, but enables also the edge 56E of the set screw to bite into and lock against the rod. This not only drives the rod tightly against the grooves in the bottom of the channel in the pedicle screw, but also drives the cap up to snug engagement of the tongue top portions 48T with the tops such as 36T of the grooves or L-shaped slots in the screw. At the same time, the top 46T of the cap is at the same essentially flush level as the top 31T of the screw body, thus minimizing the overall height of the system.
Figs. 13-17 show an infralaminar hook such as 18 in Fig. 1 and in which all features are the same as for the screw in
Figs. 1-7 except that, instead of having the threaded stem, the hook 18 has a curved blade 76 extending down from the rod receiving channel body portion 74 thereof. The center line 77 of the curve of the channel bottom lies in a vertical plane that is the center of the part, being equi-distant from the channel side flanges 78 and 79. The blade 76 is also centered with respect to this plane. The blade extends generally in this plane in the direction of the center line 77 and the particular shape of the channel 82 in the blade may be dictated by the application such as whether it is to be an infralaminar hook, a supralaminar hook, a pedicular hook, or a thoracic hook, for example. For the infralaminar hook, a pad 83 is provided in vertically spaced relation to the lower portion of the blade to provide a distinct U-shaped channel for reception on bone.
The configuration of the curved, L-shaped slots, the channel bottom grooves and other features of the hook which receive the spinal rod and the cap, are the same as for the pedicular screw described above and the rod is assembled into the hook or vice-versa in the same manner from the top as for the screw, followed by installation of the cap in the same manner as described above with reference to the pedicular screw.
Referring now to Figs. 18 and 19, a part of the lateral connector assembly 26 of Fig. 1 is shown. It includes the body portion 86 and lateral rod portion 87. The body portion has the U-shaped upwardly-opening spinal rod receiver channel 88, with the curved bottom portion 89 having its longitudinal center line 91 which, in the assembly, is the center of the spinal rod 12. The channel sides have the curved L-shaped slots 92 and 93 formed by the downwardly projecting flanges 94 and 96 which are the sides of the channel 88. These features are the same as described above with reference to the pedicle screw and receive the cap 26C and set screw 26S (Fig. 1) in the same manner as described above for the
pedicle screw and cap and set screw assembly 19. The rod 87 extending laterally from the body portion is useful for making a connection to the other spinal rod through a swivel base clamp 27 and U-clamp 28, or other types of clamps to the respective rod 87 and spinal rod 13, but which are not parts of the present invention and need not be further described. The rod portion 87 of the assembly 18 can be made of any length (long as in Fig. 1, to short as in Fig. 18) desired for the intended purpose, as well as having the longitudinal ridges or teeth in the number, nature and extent desired to inhibit rotation of the clamp such as 27 attached to it.
Fig. 20 shows a lateral connector of the same nature as in Fig. 19. For example, the body portion 97 thereof is exactly the same as body portion 86 of Fig. 19. But instead of a rod such as 87 being used to receive a clamp on it, the integral rod 98 can be a smooth rod with an integral body portion 99 at the right-hand end thereof, having exactly the same features as the body portion 97. Consequently, where the spinal rods can be spaced a known desired dimension apart, or where there is a need to space a couple of rods a predetermined known distance apart, this particular embodiment of the invention can be used with the rods, caps and set screws mounted and secured in the same manner as described above with reference to the other embodiments. Fig. 21 shows an embodiment of the invention in which there are two body portions joined together in a Siamese twin arrangement without the intermediate lateral rod portion 98 of the Fig. 20 embodiment. The rod receiver channel and curved slot portions are the same in size and configuration as described above with reference to the Figs. 3-7 embodiment, and the spinal rod or other rods can be installed therein in the same manner as described above.
Referring now to Figs. 22 through 27, these show a preferred embodiment of the cap for use with the pedicle screw of Figs. 2-7, 11-12 and with the various other
rod-receiving implants of Figs. 1 and 13-21. In this case, instead of the cap having the stop ears 66, the cap 101 has other features that prevent it from being pushed too far into or entirely through the upwardly-opening channel in the body portion of the implant. Referring specifically to Fig. 22, which is the top view, the cap has a front or leading edge 101F and a rear or trailing edge 101R. It has the sides 101S which diverge slightly so that the overall width W at the leading edge is slightly less than the overall width W„ at the trailing edge. For example, if the overall width at the leading edge is 10.1 rnm, the overall width at the trailing edge can be 10.4 mm. In this example, where the overall length between the leading edge 101F and trailing edge 101R is 7.00 mm, the width increases from the leading edge to 10.4 mm at a vertical line S at each side and located 5.75 mm back of the leading edge. Therefore, there is no taper in the sides 101S from line S to the trailing edge 101R.
With the slots in the sides of the U-shaped channel having straight walls from the front to the rear, the cap will become snug in the slots when it is installed in the direction of arrow 102 (engraved in the top of the cap) to the point where the center 103C of the set screw thread aperture 103 is 1.25 mm away from colinearity with the center line 45 of the screw. A pliers or crimping tool can be used to advance the cap the rest of the way to colinearity of the set screw aperture axis with the pedicle screw axis. In this embodiment of the cap, the shapes of the intersections of the downwardly opening channel 104 with the leading and trailing edges of the cap, are different from each other. Note in Fig. 23, for example, that the shape 104R at the trailing edge is basically the same as for the cap in Fig. 9. But in the section shown in Fig. 25, it is apparent that the shape at the leading edge as defined by the high arched edge 104F is different from the shape 104R at the trailing edge in Fig. 23. The reason for the change in
contour of the channel from the rear edge 104R to the front edge 104F can be best understood by referring to Figs. 26 and 27. In Fig. 27, the spinal rod 12 is in place on the bottom 39 of the rod receiver channel. Installation of the cap is achieved by first installing the threaded lower end of a manipulating tool 105 into the set screw thread aperture 103. Then the cap is tilted so that the leading edge 101F is down near the top of the spinal rod 12 so that the groove bottoms 101B (Figs. 22 and 23) of the cap will be received under the f-lange edges 33B, 34B (Figs. 6 & 7) , and the tongue rail tops 101T (Fig. 25) at the front of the cap will be received in the grooves such as 36L (Fig. 6) immediately under the top 36T of the groove in the slots 36 at both sides of the channel 32, whereupon the cap can be moved into position through the arcuate path 102P (Fig. 27) into the position shown in Fig. 26. When the cap has reached the position shown in Fig. 26, where the leading and trailing faces 101F and 101R of the cap are co-planar with the faces of the screw body 31, the sides 101S of the cap, particularly behind the lines S, will have become wedged against the vertically extending walls 36W and 37W of slots 36 and 37 at the front face 42F of the body portion of the screw. When the cap is in this attitude as shown in Fig. 26, the installation tool 105 is removed and the set screw 107 is installed and can be turned down so that the point thereof 107P engages and embeds to the extent desired or needed in the top of the rod 12. As the screw is tightened, the bottoms 101B of the grooves and tops 101T of the rails in the cap will abuttingly engage the bottoms of the flanges 33 and 34 of the body portion of the screw and the tops 36T and 37T of the slots 36 and 37, respectively, in the mounting screw 31. Consequently, the assembly of the spinal rod, mounting screw 31, cap 101 and set screw 107 will remain permanently and securely in place thereafter. The rear edge 104R of the channel 104 will be closely spaced to the top of the rod as
shown in Fig. 26. It may be recognized that, even if the wedging function did not occur, as the cap is turned into place in the direction of arrow 102P, rear edge 104R and the top of the downwardly opening rod receiving channel 104 behind the set screw aperture will come down onto the spinal rod and prevent further advance of the cap in the rod receiving channel 32 of the screw, as the cap is confined by the curved bottoms such as 33B of the side flanges cooperating with the upwardly opening curved grooves in the cap, and the tops 101T of the curved rails in the cap cooperating with the curved tops 36T of the slots 36, dictating the arcuate movement of the cap as it is installed.
All of the components for the various embodiments of the invention can be made of a material such as 316L ASTM F138 Grade 2 Cold Rolled 900/1050 MPa material. Other materials may also be found suitable. Also, although some specific dimensions were given above with respect to examples, the invention is not limited to those particular sizes. The devices can be used with smooth surface rods or rods having knurled or diamond embossed surfaces. The present invention has significant advantages over known prior art. Among these are minimal volume requirements, but convenience in use. The tongue-in-groove relationship of cap to slot avoids concern about spreading of branches of a diapason-type head and avoids the need for any bulky girdling closure to control such spreading. The tongue-in-groove arrangement with curved slots enables installation of the cap in less space between implants situated along a spinal rod than is possible with other arrangements which require caps to be installed by motion precisely parallel to the rod axis and thus require more space between implants along the rod. The lateral stop ears on the Fig. 8-12 embodiment prevent loss of control of the cap during installation, and facilitate initial location of it in place. The angled set screw axis enables at least
two-point engagement of the set screw with the spinal rod and in a direction tending to push the cap tight against the slots in the screw or hook or lateral connector, as the case may be, while, at the same time, urging the cap stop ears in a direction tending to pull the cap tight against the implant body portion in a direction lengthwise of the rod receiver channel axis. In the Figs. 22-27 embodiment, the taper at the sides and the curved slots and channel opening shape at front and rear facilitate installation of the cap in one direction and appropriately limit its travel. The construction of both embodiments avoids the need for some over-cap arrangement which would not only be bulky, but also would tend to interfere with the use of other features or accessories in an osteosynthesis system, the lateral connector rod being just one example.
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, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.