Impulsive percussion instruments for endplate preparation

A hand-held instrument, with a rotary power input to a camshaft, has cam and follower arrangement to provide a reciprocating shaft output. A cutter is provided on the output shaft. In one example, rotating cam percussion is transmitted to the cutter by engaging the cutter with the tissue to be cut, and pushing the instrument forward toward the cutter. In another example, rotating cam percussion is transmitted to the cutter by engaging the cutter with the tissue to be cut, and pulling the instrument back toward the user while maintaining engagement of the cutter with the tissue. In both examples, the cutter remains in idle condition until an axially directed load, forward in the one example, or backward on the other example, is placed on the cutter by moving the instrument forward or backward, respectively, while the camshaft is rotating. A distractor with frame is used to spread and maintain space between vertebral bodies, enabling entrance of the cutter.

CROSS REFERENCE TO RELATED APPLICATIONS

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.

BACKGROUND

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

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.

SUMMARY

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.

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.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

Forward Percussion Embodiment

Referring now to the drawings in detail, particularlyFIGS. 1-3,12and13, the instrument has a one-piece elongated body11having a cam housing portion12, a spring chamber portion13, guide barrel portion14, and end cap16. A camshaft17is received in the cam housing portion.

A cutter-shaft21is received in the guide barrel and has a shaft portion with proximal end22and a cutter portion with distal end23. A spring housing26(FIGS. 2,9and10) is received in the bore27of the spring chamber portion of the body11. As best shown inFIGS. 9 and 10, this spring housing has one end wall29with a central aperture31which receives and guides the proximal end portion of the cutter shaft21. Housing26has stop tabs32and33at the end wall and which are received in grooves34and36(FIG. 13, and dashed lines inFIG. 1). These grooves extend longitudinally forward from the proximal end37(FIGS. 1 and 12) of the body, and end at plane35as shown inFIG. 1. They provide abutments to prevent movement of the housing26in the direction of arrow78, beyond the location shown inFIG. 2. Also, the tabs32and33in grooves34and36, respectively, prevent rotational movement of the spring housing within the body11.

The hole31in the proximal end wall29serves as a proximal end bearing for the cutter shaft21. Forward portions of the shaft21are slidably received and guided by contact of the outer wall of the shaft with the inner wall of the guide barrel portion14of the body11.

A spring guide and end stop38(FIGS. 2 and 6) is slidably received on the proximal end portion of the shaft21. Its outer rim39is slidably received in the bore41(FIG. 9) of the housing26. A coil spring42(FIG. 2) is received around the stepped-down portion43of the member38. The shoulder44at the step from the cylindrical surface39to the cylindrical surface43serves as a seat for the distal end of the spring42. The inside face46of the end wall29of the housing26serves as a spring seat for the proximal end of spring42.

The right-hand end portion47of housing26is internally threaded at48and receives end closure ring49(FIG. 11) which is screwed into the housing26. This prevents the member38and 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 screw51(FIGS. 1 and 2) is screwed into the body11and extends through an elongated hole52in the shaft21. This screw normally retains the shaft21in the body. The length of hole52in 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 shaft21can be dropped or pulled out from the distal end53of the guide barrel14followed by installation of the replacement cutter shaft.

Referring now more particularly toFIGS. 4 and 5along withFIG. 2, the camshaft17is generally cylindrical about the axis56and has cylindrical flanges57and58which abut flanged bushings59and61received in upper and lower, rearwardly opening yokes62in the cam housing portion of the body11(FIGS. 1 and 12). Similarly, end cap16(FIGS. 22 and 23) has yoke portions which receive the bushings59and61when the end cap is fastened to the body with the four screws66(FIG. 3). The bushings59and61can be engaged by the outboard faces of the flanges57and58of the camshaft, so they provide location and thrust bearings for the camshaft as well as radial bearings for the smooth cylindrical surfaces67and68(FIG. 4) of the camshaft. It is seen that the yokes62of the body and64of the end cap16, capture the bushings59and61and thereby capture the cam shaft in the assembly for centering the camshaft axis56colinear with the axes of bushings59and61, when the end cap is secured in place by the screws66.

The cam surface itself shown generally at71inFIGS. 4 and 5, is square shaped, having four low areas72and four high points73. Other cam surface profiles may also be used. One example is shown in dotted lines inFIG. 5in the form of a hexagon. It is the square cam shape which is shown inFIG. 2, with the shaft end22(rounded as shown inFIG. 8) engaging a low point on the cam and serving as the cam follower surface. Normally, however, spring42urges the spring seat44on member38(FIG. 6) to the right (in the direction of arrow78). Abutting engagement of the wall76of member38with the annular shoulder77(FIGS. 7 and 8) of the cutter shaft21urges the shaft in the outward direction of arrow78(FIG. 2) to an extent limited by the engagement of the proximal end79of hole52with the stop screw51. Therefore, in this normal rest position of the cutter shaft, the proximal end22thereof will be located, as shown by the dotted line22R (FIG. 2), spaced away from the circular path of the high points of the cam.

Since this is a power operated instrument, converting rotary motion to reciprocating motion, the cam shaft has flat surfaces81for reception of a coupler, and a circular notch82for 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 motor85(FIG. 1A) coupled to the camshaft. Air may be supplied through tubing85A from a compressor85B with speed control pedal85C. Any other available source of air or other gas with pressure and/or volume control may be used.

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 barrel14and install the screw51. 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.

Before or after installation of the cutter shaft, the user may connect the power source to the camshaft. After positioning the distal end23of the cutter at the endplate treatment site and engaging the tissue to be treated, the user may apply force in the forward direction of arrow78, which is the forward cutting direction of the cutters to be used with this embodiment of the invention. The forward force will compress the spring42and 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 inFIG. 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 arrow78, as the spring38is compressed by increasing force and thereby permits the end of the shaft22to project farther into the path of the cam surface as the cam surface moves about the rotational axis56of the camshaft.

From the foregoing discussion, it can be recognized that cutter shafts other than shaft21shown specifically inFIGS. 1,2,7and8, 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 inFIGS. 34,35,36-39,40and41. It is only necessary to remove the screw51and drop or pull cutter shaft21, select a cutter shaft having a different distal end cutter (the shaft portion from the cutter to the proximal end22being of the same configuration as shown inFIGS. 7 and 8), and insert the proximal end of the cutter shaft through the distal end of the barrel14and through the bore and spring seat member38and into the bore31of the housing26. 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 end22struck 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 spring42.

Reverse Percussion Embodiment

This embodiment is discussed with reference toFIGS. 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 inFIGS. 14 through 23, some of the components are very similar to those in the first described embodiment. For example, the body86has a cam housing portion87, a spring housing88and a guide barrel portion89. The body86is very similar to the body11of the first embodiment, and the end cap91is virtually identical to the end cap16of the first embodiment.

Referring particularly toFIGS. 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 edge93in the rearward direction of arrow92. For that purpose, there is a cam shaft94mounted for rotation in the cam housing portion87of the body. It operates a cutter drive shaft96slidably received in the guide barrel portion89. Its proximal end portion97is associated with the camshaft, while its distal end portion98receives a proximal end portion99of a cutter shaft having the cutter93at its distal end.

Referring now toFIGS. 16 and 17along withFIG. 15, the camshaft74is mounted in the body in bushings101and102which are received and located in the housing in essentially the same way as are bushings59and61described above with reference to the first embodiment. The camshaft itself has a smooth cylindrical surface at103receiving radial bearing support by bushing102. It also has a cylindrical flange104having outer face106engaging bushing102for thrust bearing support. The outer end portion of the camshaft has a pair of diametrically opposed flat surfaces108on the otherwise cylindrical surface103which 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 groove109and head111to cooperate with the power source connector and retain it in place. Accordingly, the drive for this camshaft is like that for the first embodiment.

In this embodiment, the cam surface itself is shown at112as a square, having four high points113and four flat surfaces114, the center of each flat114, 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 line116inFIG. 17. At the end face117of the cam112, there is a step inward to a hexagonal post118non-rotatably received in bearing119(FIGS. 20 and 21) and secured to the bearing by a socket head screw121screwed into the end of the camshaft. The hexagonal post118on the camshaft is received in the hexagonal aperture122of the bearing119which is rotatably received in bushing101. Thus, the cylindrical surface123of the bearing119rotating in the bushing101provides radial bearing support for the camshaft, and the circular face124of the bearing119slidingly engaging the lower face of bushing101provides thrust bearing support for the camshaft.

Referring now particularly toFIGS. 15 and 18, the cutter drive shaft96for the cutter shaft has a cam follower end portion97configured for following the cam112. It is illustrated in the form of an elongate hole126with straight parallel sidewalls127and128and a semi-circular end wall129having a radius equal to half the distance between the sidewalls127and128and centered at131. This radius is slightly greater than the distance diametrically across the high points113of the cam and is centered on the cam axis130. The follower end portion97framing the hole126has a shoulder133. A spring134(FIG. 15) is a compression spring having a right-hand end136bearing on wall137of the spring chamber portion of the body86. The left-hand end of the spring abutingly engages the shoulder133of the follower end portion of the shaft96. Therefore, the spring normally pushes the shaft96to the left in the direction of arrow92.

An elongate hole141through shaft96receives travel limit screw142, which is screwed into the instrument body86. When the instrument is idle, the spring134moves the drive shaft96to the left until the right-hand end143of the hole141engages and is stopped by the screw142. This is the normal rest position of the shaft and places it such that the center131of the curved surface129of the cam shaft frame hole126is spaced slightly outboard of the circle defined by the four high points of the cam when the camshaft is rotated.

The left-hand end wall146of the cam follower portion97is provided with extra thickness resulting in a bulge147at the longitudinal axis148of the cutter drive shaft96and serves as the cam follower surface of cutter drive shaft96.

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 shaft99shown in elevation view inFIG. 19and partially shown inFIGS. 14 and 42and shown partially in section inFIG. 15. This cutter shaft99has a cylindrical body portion151slidably received on the inside bore of the barrel89of the instrument. A stem portion152of the tool has less diameter than the body portion151and is slidably received in a bore153in the distal end portion of the cutter drive shaft96. The barrel89of the instrument has an elongate hole154at one location in the wall. A hole156(FIG. 18) in cutter drive shaft96is normally aligned or in registry with the hole154in the housing when the cutter drive shaft is in rest position dictated by the engagement of the stop screw142with the end wall143of hole141in the cutter drive shaft. This is under the urging of the spring134. So when the cutter shaft is installed in the direction of arrow92into the open end157of the instrument body, it can be advanced to the left so that the cutter stem152received in bore153has the threaded hole158of the cutter stem152located in registry or lined up with the hole156in the cutter drive shaft96. Then screw159can be inserted through the hole154in the guide barrel89and screwed into the cutter shaft hole158to fasten the cutter shaft99to the cutter drive shaft96. The screw head is stopped so that it resides in the hole156in the cutter drive shaft, retaining the cutter shaft in place but recessed slightly from the inside wall of the barrel89to avoid interference with reciprocation of the cutter shaft. Besides, the hole154in the wall89is long enough that the screw can move forward and backward in the direction of arrow92within the hole154during reciprocation of the drive shaft96. With this arrangement, the cutter shaft99can be readily removed from the guide barrel by simply removing screw159and 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 end157in the direction of arrow92. When the anchor hole158thereof is lined up with the hole154, the screw159is installed to fix the new cutter shaft to the drive shaft96in preparation for using the new cutter.

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 arrow92with the cutter edge93engaging the surface to be prepared. The force of impact between the cutter edge93and material to be cut, is determined largely by the force with which the instrument is pulled in the direction of arrow92, which thereby compresses the spring134and enables the cam engaging follower surface147of 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.

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 inFIGS. 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 inFIGS. 43 and 44, the cutter will work with the reverse percussion instrument.

Disc Height Maintenance

Referring now toFIGS. 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 toFIGS. 24 and 25, a combination distractor and disc space keeper is shown. As shown specifically inFIGS. 26-28, the illustrated distractor171includes a handle portion172, shaft portion173, head portion174, and wedge portion176. A forwardly opening hook177is fixed atop the shaft portion near the head portion. The wedge portion has a transverse groove178at the tip. Abutments179are provided at the transition from tip portion to head portion and are slightly arcuate in shape, as shown inFIG. 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 axis181of the shaft and handle portions. Referring particularly toFIGS. 29-32, a distractor blade housing186and which serves as the disc space keeper, is made in the form of a frame and includes parallel side members187, a rear cross member188, an intermediate cross member189serving as a hinge pin, and a front cross member191.

In the use of this device, and after the removal of the disc from the space between vertebral bodies shown schematically at191and192inFIGS. 24 and 25, the distractor171is assembled with the blade housing186by inserting the wedge portion between the housing side members and moving it forward to engagement of the groove178of the distractor tip with the front cross member191of the blade housing and simultaneously receiving the hinge pin189in the hook177, as shown inFIG. 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 arrow193, and the handle172is 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 end194, if needed. After the desired disc height is established in this manner, the distractor handle is pulled out in the direction of arrow196, while the blade housing186remains in place and maintains the disc height as desired, thus serving as the disc space keeper. Because of the offset between the plane197(FIG. 30) containing the frame cross member191, and the parallel plane198containing the axis of the rear cross member188, 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 plane197and the pivot pin189and rear cross member188of the keeper frame.

While the views inFIGS. 24 and 25show the combination with the hook177of the distractor and the rear cross member188of the keeper above the axis181of the distractor, the assembly can be used with the orientation inverted relative to that shown inFIG. 25. As with the cutting instruments themselves, the orientation will depend upon the preferences of the surgeon.

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.