Impulsive percussion instruments for endplate preparation

[0001] The present Application claims foreign priority benefits of European Patent Application Number 03292241.1, filed Sep. 11, 2003, the contents of which are hereby incorporated by reference.

[0002] This invention relates generally to surgery tools and more particularly to power cutting instruments for vertebral endplate preparation in spinal surgery.

[0003] Following removal of some disc materials during spinal surgery, it is important to prepare the endplates of the vertebral bodies for reception of inter-body implant materials. It is desirable to provide devices and procedures for safer, more controlled and more efficient disc space cleaning and endplate preparation. The present invention is directed to providing an additional option for surgeons for improvement in these regards.

[0004] In general, the present invention provides power-operated, hand-held instruments adapted to reception of different types of tissue treatment tools, and drives them in a reciprocating motion.

[0005] Further, the invention provides for conversion from a rotary input power source to a reciprocating source, and percussion action in the forward direction in one embodiment, and percussion action in the reverse direction in another embodiment. More specifically, in one embodiment the invention enables use with treatment tools expected to perform more effectively during a forward motion and, in another embodiment, the invention enables use with treatment tools expected to perform more effectively during a reverse motion. Such tools have preferred performance directions, forward or reverse. The invention further comprises treatment tool configurations particularly suitable to the direction and type of cutting action sought. For tools that perform well in either direction, either of the embodiments of the invention may be used. The invention further provides a distractor and keeper arrangement for maintaining distracted disc space height during endplate preparation, the keeper being shaped for convenient use with the powered instruments according to the present invention.

[0053] 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, such alterations and further modifications in the illustrated devices, and 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.

[0054] Referring now to the drawings in detail, particularly FIGS. 1-3, 12 and 13, the instrument has a one-piece elongated body 11 having a cam housing portion 12, a spring chamber portion 13, guide barrel portion 14, and end cap 16. A camshaft 17 is received in the cam housing portion.

[0055] A cutter-shaft 21 is received in the guide barrel and has a shaft portion with proximal end 22 and a cutter portion with distal end 23. A spring housing 26 (FIGS. 2, 9 and 10) is received in the bore 27 of the spring chamber portion of the body 11. As best shown in FIGS. 9 and 10, this spring housing has one end wall 29 with a central aperture 31 which receives and guides the proximal end portion of the cutter shaft 21. Housing 26 has stop tabs 32 and 33 at the end wall and which are received in grooves 34 and 36 (FIG. 13, and dashed lines in FIG. 1). These grooves extend longitudinally forward from the proximal end 37 (FIGS. 1 and 12) of the body, and end at plane 35 as shown in FIG. 1. They provide abutments to prevent movement of the housing 26 in the direction of arrow 78, beyond the location shown in FIG. 2. Also, the tabs 32 and 33 in grooves 34 and 36, respectively, prevent rotational movement of the spring housing within the body 11.

[0056] The hole 31 in the proximal end wall 29 serves as a proximal end bearing for the cutter shaft 21. Forward portions of the shaft 21 are slidably received and guided by contact of the outer wall of the shaft with the inner wall of the guide barrel portion 14 of the body 11.

[0057] A spring guide and end stop 38 (FIGS. 2 and 6) is slidably received on the proximal end portion of the shaft 21. Its outer rim 39 is slidably received in the bore 41 (FIG. 9) of the housing 26. A coil spring 42 (FIG. 2) is received around the stepped-down portion 43 of the member 38. The shoulder 44 at the step from the cylindrical surface 39 to the cylindrical surface 43 serves as a seat for the distal end of the spring 42. The inside face 46 of the end wall 29 of the housing 26 serves as a spring seat for the proximal end of spring 42.

[0058] The right-hand end portion 47 of housing 26 is internally threaded at 48 and receives end closure ring 49 (FIG. 11) which is screwed into the housing 26. This prevents the member 38 and spring therewith, from sliding out of the assembly when one cutter shaft is removed and replaced by another one having a different type of cutter. Normally, however, a screw 51 (FIGS. 1 and 2) is screwed into the body 11 and extends through an elongated hole 52 in the shaft 21. This screw normally retains the shaft 21 in the body. The length of hole 52 in the axial direction permits a range of shaft reciprocation from engagement with low points on the cam surface to slightly beyond the maximum height of the cam surface. To change cutters, the screw must be removed and then the shaft 21 can be dropped or pulled out from the distal end 53 of the guide barrel 14 followed by installation of the replacement cutter shaft.

[0059] Referring now more particularly to FIGS. 4 and 5 along with FIG. 2, the camshaft 17 is generally cylindrical about the axis 56 and has cylindrical flanges 57 and 58 which abut flanged bushings 59 and 61 received in upper and lower, rearwardly opening yokes 62 in the cam housing portion of the body 11 (FIGS. 1 and 12). Similarly, end cap 16 (FIGS. 22 and 23) has yoke portions which receive the bushings 59 and 61 when the end cap is fastened to the body with the four screws 66 (FIG. 3). The bushings 59 and 61 can be engaged by the outboard faces of the flanges 57 and 58 of the camshaft, so they provide location and thrust bearings for the camshaft as well as radial bearings for the smooth cylindrical surfaces 67 and 68 (FIG. 4) of the camshaft. It is seen that the yokes 62 of the body and 64 of the end cap 16, capture the bushings 59 and 61 and thereby capture the cam shaft in the assembly for centering the camshaft axis 56 colinear with the axes of bushings 59 and 61, when the end cap is secured in place by the screws 66.

[0060] The cam surface itself shown generally at 71 in FIGS. 4 and 5, is square shaped, having four low areas 72 and four high points 73. Other cam surface profiles may also be used. One example is shown in dotted lines in FIG. 5 in the form of a hexagon. It is the square cam shape which is shown in FIG. 2, with the shaft end 22 (rounded as shown in FIG. 8) engaging a low point on the cam and serving as the cam follower surface. Normally, however, spring 42 urges the spring seat 44 on member 38 (FIG. 6) to the right (in the direction of arrow 78). Abutting engagement of the wall 76 of member 38 with the annular shoulder 77 (FIGS. 7 and 8) of the cutter shaft 21 urges the shaft in the outward direction of arrow 78 (FIG. 2) to an extent limited by the engagement of the proximal end 79 of hole 52 with the stop screw 51. Therefore, in this normal rest position of the cutter shaft, the proximal end 22 thereof will be located, as shown by the dotted line 22R (FIG. 2), spaced away from the circular path of the high points of the cam.

[0061] Since this is a power operated instrument, converting rotary motion to reciprocating motion, the cam shaft has flat surfaces 81 for reception of a coupler, and a circular notch 82 for reception of a spring clip or clamp of a coupler from an external rotary power source. This may be any of a variety of power sources such as, electric, hydraulic or more likely an air or nitrogen powered turbine motor 85 (FIG. 1A) coupled to the camshaft. Air may be supplied through tubing 85A from a compressor 85B with speed control pedal 85C. Any other available source of air or other gas with pressure and/or volume control may be used.

[0062] As an example of the operation of this embodiment of the invention, the user may select the treatment tool to be used, insert it in the barrel 14 and install the screw 51. The tissue treatment tool referred to above and hereinafter is referred to broadly hereinafter as a cutter, and this term is intended to include tools which chisel, file, shape, rasp, polish, broach or otherwise perform the intended effect on or with the body tissue treated.

[0063] Before or after installation of the cutter shaft, the user may connect the power source to the camshaft. After positioning the distal end 23 of the cutter at the endplate treatment site and engaging the tissue to be treated, the user may apply force in the forward direction of arrow 78, which is the forward cutting direction of the cutters to be used with this embodiment of the invention. The forward force will compress the spring 42 and move the cam surface toward the shaft end (the cam follower surface) 22. If the camshaft is rotating, percussion action will begin as soon as the shaft end is touched by the high points of the rotating cam, and reciprocating action of the cutter will begin. The speed of such action can be controlled by speed control of the power source, whether by a motor at the instrument (as shown in FIG. 1A), or through a cable or hose and foot control or whatever speed control is desired or available. The percussion impact will depend on how much force the user applies in the direction of arrow 78, as the spring 38 is compressed by increasing force and thereby permits the end of the shaft 22 to project farther into the path of the cam surface as the cam surface moves about the rotational axis 56 of the camshaft.

[0064] From the foregoing discussion, it can be recognized that cutter shafts other than shaft 21 shown specifically in FIGS. 1, 2, 7 and 8, may be used in the practice of the present invention. Examples are different types of chisels, shavers and rasps to decorticate the endplate from the disc materials and the cartilage layer. Some are shown in FIGS. 34, 35, 36-39, 40 and 41. It is only necessary to remove the screw 51 and drop or pull cutter shaft 21, select a cutter shaft having a different distal end cutter (the shaft portion from the cutter to the proximal end 22 being of the same configuration as shown in FIGS. 7 and 8), and insert the proximal end of the cutter shaft through the distal end of the barrel 14 and through the bore and spring seat member 38 and into the bore 31 of the housing 26. Of course, it is preferable to have the power source turned off or disconnected from the camshaft during the cutter shaft installation to avoid the risk of having the proximal end 22 struck by the cam and driving the tool back out of the barrel before the limit screw has been installed. Such event might otherwise occur, depending upon whether the cutter shaft is pushed in with enough force to compress the spring 42.

[0065] This embodiment is discussed with reference to FIGS. 14 through 23, although it will be seen that several of the components described above with reference to the first (forward percussion) embodiment also are used in the reversed percussion embodiment. In this second embodiment of the invention illustrated in FIGS. 14 through 23, some of the components are very similar to those in the first described embodiment. For example, the body 86 has a cam housing portion 87, a spring housing 88 and a guide barrel portion 89. The body 86 is very similar to the body 11 of the first embodiment, and the end cap 91 is virtually identical to the end cap 16 of the first embodiment.

[0066] Referring particularly to FIGS. 14-23, and in contrast to the direction of percussion impulse from the cam in the first embodiment, the direction of impulse from the cam in this second embodiment is in the reverse direction so that it pulls the cutter edge 93 in the rearward direction of arrow 92. For that purpose, there is a cam shaft 94 mounted for rotation in the cam housing portion 87 of the body. It operates a cutter drive shaft 96 slidably received in the guide barrel portion 89. Its proximal end portion 97 is associated with the camshaft, while its distal end portion 98 receives a proximal end portion 99 of a cutter shaft having the cutter 93 at its distal end.

[0067] Referring now to FIGS. 16 and 17 along with FIG. 15, the camshaft 74 is mounted in the body in bushings 101 and 102 which are received and located in the housing in essentially the same way as are bushings 59 and 61 described above with reference to the first embodiment. The camshaft itself has a smooth cylindrical surface at 103 receiving radial bearing support by bushing 102. It also has a cylindrical flange 104 having outer face 106 engaging bushing 102 for thrust bearing support. The outer end portion of the camshaft has a pair of diametrically opposed flat surfaces 108 on the otherwise cylindrical surface 103 which provide anti-rotation cooperation with a connector of a rotary power source in the same manner as for the first described embodiment. Likewise, it has a stem with annular groove 109 and head 111 to cooperate with the power source connector and retain it in place. Accordingly, the drive for this camshaft is like that for the first embodiment.

[0068] In this embodiment, the cam surface itself is shown at 112 as a square, having four high points 113 and four flat surfaces 114, the center of each flat 114, as in the square cam of the first embodiment, being a low point in the cam travel. The cam can have other cross sectional shapes as mentioned above. One of several possible shapes could be hexagonal as designated by the dash line 116 in FIG. 17. At the end face 117 of the cam 112, there is a step inward to a hexagonal post 118 non-rotatably received in bearing 119 (FIGS. 20 and 21) and secured to the bearing by a socket head screw 121 screwed into the end of the camshaft. The hexagonal post 118 on the camshaft is received in the hexagonal aperture 122 of the bearing 119 which is rotatably received in bushing 101. Thus, the cylindrical surface 123 of the bearing 119 rotating in the bushing 101 provides radial bearing support for the camshaft, and the circular face 124 of the bearing 119 slidingly engaging the lower face of bushing 101 provides thrust bearing support for the camshaft.

[0069] Referring now particularly to FIGS. 15 and 18, the cutter drive shaft 96 for the cutter shaft has a cam follower end portion 97 configured for following the cam 112. It is illustrated in the form of an elongate hole 126 with straight parallel sidewalls 127 and 128 and a semi-circular end wall 129 having a radius equal to half the distance between the sidewalls 127 and 128 and centered at 131. This radius is slightly greater than the distance diametrically across the high points 113 of the cam and is centered on the cam axis 130. The follower end portion 97 framing the hole 126 has a shoulder 133. A spring 134 (FIG. 15) is a compression spring having a right-hand end 136 bearing on wall 137 of the spring chamber portion of the body 86. The left-hand end of the spring abutingly engages the shoulder 133 of the follower end portion of the shaft 96. Therefore, the spring normally pushes the shaft 96 to the left in the direction of arrow 92.

[0070] An elongate hole 141 through shaft 96 receives travel limit screw 142, which is screwed into the instrument body 86. When the instrument is idle, the spring 134 moves the drive shaft 96 to the left until the right-hand end 143 of the hole 141 engages and is stopped by the screw 142. This is the normal rest position of the shaft and places it such that the center 131 of the curved surface 129 of the cam shaft frame hole 126 is spaced slightly outboard of the circle defined by the four high points of the cam when the camshaft is rotated.

[0071] The left-hand end wall 146 of the cam follower portion 97 is provided with extra thickness resulting in a bulge 147 at the longitudinal axis 148 of the cutter drive shaft 96 and serves as the cam follower surface of cutter drive shaft 96.

[0072] This embodiment of the invention can be provided with a variety of cutters of various configurations and types useful, particularly when pulled toward the surgeon. Some examples are different types of curettes, scrapers and pull shavers. One example is the cutter shaft 99 shown in elevation view in FIG. 19 and partially shown in FIGS. 14 and 42 and shown partially in section in FIG. 15. This cutter shaft 99 has a cylindrical body portion 151 slidably received on the inside bore of the barrel 89 of the instrument. A stem portion 152 of the tool has less diameter than the body portion 151 and is slidably received in a bore 153 in the distal end portion of the cutter drive shaft 96. The barrel 89 of the instrument has an elongate hole 154 at one location in the wall. A hole 156 (FIG. 18) in cutter drive shaft 96 is normally aligned or in registry with the hole 154 in the housing when the cutter drive shaft is in rest position dictated by the engagement of the stop screw 142 with the end wall 143 of hole 141 in the cutter drive shaft. This is under the urging of the spring 134. So when the cutter shaft is installed in the direction of arrow 92 into the open end 157 of the instrument body, it can be advanced to the left so that the cutter stem 152 received in bore 153 has the threaded hole 158 of the cutter stem 152 located in registry or lined up with the hole 156 in the cutter drive shaft 96. Then screw 159 can be inserted through the hole 154 in the guide barrel 89 and screwed into the cutter shaft hole 158 to fasten the cutter shaft 99 to the cutter drive shaft 96. The screw head is stopped so that it resides in the hole 156 in the cutter drive shaft, retaining the cutter shaft in place but recessed slightly from the inside wall of the barrel 89 to avoid interference with reciprocation of the cutter shaft. Besides, the hole 154 in the wall 89 is long enough that the screw can move forward and backward in the direction of arrow 92 within the hole 154 during reciprocation of the drive shaft 96. With this arrangement, the cutter shaft 99 can be readily removed from the guide barrel by simply removing screw 159 and pulling the cutter shaft out of the barrel. Another cutter shaft with a different configuration of the cutter portion but with the same configuration otherwise, can then be inserted through the end 157 in the direction of arrow 92. When the anchor hole 158 thereof is lined up with the hole 154, the screw 159 is installed to fix the new cutter shaft to the drive shaft 96 in preparation for using the new cutter.

[0073] As mentioned above, the surgeon can run the cam constantly if desired, or can start it and stop it at the beginning and end of a cutting operation. Depending upon the power source available, the speed of rotation may be varied and thus, the speed of the cutter strokes would vary. A reciprocating action begins when the surgeon has engaged the cutter with the surface to be treated and pulls the instrument in the direction of arrow 92 with the cutter edge 93 engaging the surface to be prepared. The force of impact between the cutter edge 93 and material to be cut, is determined largely by the force with which the instrument is pulled in the direction of arrow 92, which thereby compresses the spring 134 and enables the cam engaging follower surface 147 of the cam follower to impinge on the path of rotation of the high points of the cam. The rate of impulses depends upon the speed of the camshaft as determined by the surgeon.

[0074] It can be understood that some cutters may be useful and which can treat the tissue in a useful way regardless of whether the cutter is driven in the forward or reverse direction. Such cutters can be used in either the forward or reverse percussion type instrument described above, if the proximal end portion of the cutter shaft is shaped and located to work with the cam and follower arrangement provided in the instrument. One example is a cutter as shown in FIGS. 34 and 35. With the shaft as shown in those figures, the cutter will work with the forward percussion instrument. If the shaft is made as shown in FIGS. 43 and 44, the cutter will work with the reverse percussion instrument.

[0075] Referring now to FIGS. 24-30, there is shown apparatus used according to the present invention to facilitate use of either of the two previously described embodiments. Referring first to FIGS. 24 and 25, a combination distractor and disc space keeper is shown. As shown specifically in FIGS. 26-28, the illustrated distractor 171 includes a handle portion 172, shaft portion 173, head portion 174, and wedge portion 176. A forwardly opening hook 177 is fixed atop the shaft portion near the head portion. The wedge portion has a transverse groove 178 at the tip. Abutments 179 are provided at the transition from tip portion to head portion and are slightly arcuate in shape, as shown in FIG. 26. The upper and lower surfaces of the tip portion converge at a five degree total angle, half above and half below a plane containing the axis 181 of the shaft and handle portions. Referring particularly to FIGS. 29-32, a distractor blade housing 186 and which serves as the disc space keeper, is made in the form of a frame and includes parallel side members 187, a rear cross member 188, an intermediate cross member 189 serving as a hinge pin, and a front cross member 191.

[0076] In the use of this device, and after the removal of the disc from the space between vertebral bodies shown schematically at 191 and 192 in FIGS. 24 and 25, the distractor 171 is assembled with the blade housing 186 by inserting the wedge portion between the housing side members and moving it forward to engagement of the groove 178 of the distractor tip with the front cross member 191 of the blade housing and simultaneously receiving the hinge pin 189 in the hook 177, as shown in FIG. 25. Then, approaching from the anterior side of the spine, the space from which the disc material has been previously removed is approached in the direction of the arrow 193, and the handle 172 is pushed in that direction to open up the space to approximately eight or ten millimeters, or to such other extent as desired, and by hammer or other impulses on the handle end 194, if needed. After the desired disc height is established in this manner, the distractor handle is pulled out in the direction of arrow 196, while the blade housing 186 remains in place and maintains the disc height as desired, thus serving as the disc space keeper. Because of the offset between the plane 197 (FIG. 30) containing the frame cross member 191, and the parallel plane 198 containing the axis of the rear cross member 188, there is ample room for entry and manipulation of a cutter in the space between the vertebral bodies and entry of the percussion instrument in the space between the plane 197 and the pivot pin 189 and rear cross member 188 of the keeper frame.

[0077] While the views in FIGS. 24 and 25 show the combination with the hook 177 of the distractor and the rear cross member 188 of the keeper above the axis 181 of the distractor, the assembly can be used with the orientation inverted relative to that shown in FIG. 25. As with the cutting instruments themselves, the orientation will depend upon the preferences of the surgeon.

[0078] The preferred material for the larger components is stainless steel; however, the used of other materials suitable for the intended functions are also contemplated as falling within the scope of the invention.

[0079] 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 all changes and modifications that come within the spirit of the invention are desired to be protected.