Adjustable reamer with tip tracker linkage

A positioning tool for a joint socket cutting instrument or a implant is designed for use with a minimally invasive surgical procedure and in conjunction with a computer assisted surgical procedure. The positioning tool has a longitudinally extending drive shaft having a moveable joint at a first end and a drive coupling for connecting to a power source at a second end. A holder for mounting a cutting tool such a drill or as an acetabular cutting instrument or for mounting an acetabular implant is coupled to the moveable joint at the first end of the drive shaft for movement with respect to the drive shaft. The holder is rotatable about a central axis thereof when the drive shaft is rotated. The drive shaft includes a shaft bearing mounted thereon which is pivotally coupled to the shaft at a fixed longitudinal position and is pivotally coupled to a longitudinally extending first arm having a handle. A tracker system which is capable of being utilized by a computer-aided surgical system is mounted on the first arm. A second arm is provided which is pivotally connected to the holder at a first end and pivotally connected to the first arm at a second end. The resulting four bar linkage allows the holder and the cutting instrument/implant to be manipulated in any position while the known geometric relationship between the tracker and the holder allows the location of the holder to be displayed by the computer on a cathode ray tube with respect to a joint.

BACKGROUND OF THE INVENTION

The present invention is directed to the implantation of artificial joint components and in particular to acetabular joint components. More particularly, it is related to instrumentation for reaming the acetabular socket and for locating the prosthetic acetabular cup within the reamed socket. Even more particularly, it is related to an instrument which can be used with computer-assisted minimally invasive surgical implantation of the joint component during joint replacement or revision procedures.

Total hip replacement or orthroplasty operations have been performed to repair the acetabulum and the regions surrounding it and to replace the hip components such as the natural femoral head which has degenerated.

With regard to the acetabulum, many instruments have been designed to locate either the acetabular cup or reamers for repairing the acetabulum to receive such a prosthetic cup. Such instruments are shown in U.S. Pat. Nos. 4,305,394, 4,632,111, 5,037,424, 5,061,270, 5,320,625 and 6,395,005. Many of these instruments require a relatively large incision, i.e., 7–9 inches in the hip area in order to utilize the instruments in preparing the acetabulum and positioning the acetabular cup. There has been a long felt need to develop instrumentation to perform this procedure which can be used with a smaller incision, for example, 2–3 inches.

In addition, computer-assisted surgery has been developed which utilizes a tracking system which can relate positions on the patients and/or instruments to stored X-ray, CT scan and MRI data previously obtained for the patient. Alternately, image free computer-aided surgery has been developed where mechanical relationships can be calculated from anatomical reference points and utilized such as in joint arthroplasty. Such digitized points include the location of the center of the femoral head, the location of the epicondylar ligament attachment points, and the surfaces of the condyles. These systems are used intra-operatively for performing various surgical procedures, including replacement of artificial joints.

It has been especially useful to utilize trackable medical instruments for use in procedures utilizing computer-assisted image guided or image free medical and surgical navigation systems. Systems using body images are shown in U.S. Pat. No. 5,383,454 to Bucholz and U.S. Pat. No. 6,021,343 to Foley et al. In general, these image-guided systems use computer stored digital images of a body part obtained, such as by CT scans taken before surgery, to generate images on a display, such as a CRT monitor screen, during surgery. These images are used in connection with real time information for representing the position of a surgical instrument with respect to the body part. The systems typically include tracking devices such as, for example, an LED array mounted on a surgical instrument as well as a patient body part or parts. A tracker such as an optical tracker is used to track, in real time, the position of the body part and the instrument used during surgery, and a monitor screen to display images representing the body and the position of the instrument relative to the stored images or a vertical image as the surgical procedure is performed.

An image free type system is shown in U.S. Pat. No. 6,385,475 the teachings of which are incorporated herein by reference. Some systems of this type include virtual joint images and relate the tracked anatomic landmarks to the virtual body part images. In such a system, an active or passive marker is attached to bones on opposite sides of a joint and a measuring device such as an optical sensing camera is coupled to a data processing system to which signals corresponding to the positioning data of the optical markers are supplied by the optical camera system. This data is used to correlate the markers on opposite sides of the joint with digitized anatomic landmarks. With a pointer mounted tracker, it is possible to locate various anatomic reference points on the joints to allow the optical/computer system to position a cutting instrument such as a reamer or sawblade having a tracker mounted thereon to shape a joint part for receiving a prosthetic implant.

In utilizing instruments which rotate such as reaming systems, it is important to align the cutting tool in the correct angle as well as locating and controlling the depth of penetration. There has been a long felt need for a tool which can axially align a reamer such as an acetabular reamer and guide the reamer internally of the body to a precise desired location. In addition, in order to perform minimally invasive surgery, reamers have been designed for the acetabulum which, rather than having the standard hemispherical shape, have only a part hemispherical shape but must be rotated through an angle such as 180° to form the hemispherical surface of an acetabular cavity in the pelvis designed to receive a hemispherical prosthetic acetabular component. An expandable reamer such as shown in U.S. Pat. No. 3,702,611 may be used.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an instrument on which a reamer or implant is held which can be manipulated within the body to align the reamer or implant in a desired position.

It is a further object of the invention to provide a holder which can be used with a joint shaper such as an acetabular reamer and/or to position an implant such as an acetabular cup within the body at any angle with respect to the central axis of the cup or reamer.

It is still an additional object of the invention to provide an instrument for positioning a cutting tool or implant on which instrument a tracker, such as an optical tracker, for example, an emitter array, such as a light emitting diode array. The array includes a plurality of light emitters. The tracker can be mounted on an instrument and can interact with an optical tracking system to track the position of the cutting tool, such as a reamer, or an implant, including its axial orientation with respect to a bony target while the instrument is located within the body of a patient.

These and other objects of the invention are achieved by a positioning tool for use in a socket joint such as an acetabular cutting instrument or acetabular implant which tool has a longitudinally extending shaft extending along a longitudinal axis which shaft has a joint capable of movement about at least two axis and preferably three axis at a first end thereof. An implant or tool holder is mounted on the first end of the shaft and is designed to be placed within the body adjacent a socket joint such as the acetabulum. The holder has a central axis and is coupled at a connector to the moveable joint, such as a universal joint, to the first end of the longitudinally extending shaft. The holder is designed to either hold a reaming or cutting tool or to hold an acetabular implant. Since the holder is coupled at a connection point to the moveable joint on the end of the longitudinal shaft, it can be oriented in any angular position or at least a wide range of desired positions with respect to the shaft. The shaft has a shaft bearing mounted on the shaft adjacent an end opposite the holder end. The bearing may be mounted in a fixed position along the length of the shaft. The shaft may be a drive shaft used to rotate within the shaft bearing and drive the reamer or other tool via the universal or flexible joint. The positioner has a longitudinally extending first arm pivotally connected to the shaft bearing at a first pivot point for pivotal movement in a plane parallel or coplanar to the shaft longitudinal axis. The first arm preferably includes a handle portion. The tool includes a second arm pivotally connected to the first arm at a second pivot point and pivotally connected to the holder at a third pivot point. The first arm of the positioning tool has a mounting rod on which the tracker is mounted. In a preferred embodiment, the tracker emitter array includes at least three light emitting diodes to enable the optical tracking system to calculate the position of the arm. The array mounting rod extending from the first arm preferably extends at a point thereon located outwardly of a handle portion on the first arm, which handle is used by the surgeon to manipulate the positioning tool to position the holder at the desired location. The axis of the tracker is oriented at a fixed angle to the holder central axis, and may be parallel thereto to allow the optical tracking system to locate the holder central axis based on tracker data. Mounting the mounting arm parallel to the central axis allows the surgeon to visualize the angle of the holder by the orientation of the tracker mounting rod.

Preferably, the shaft bearing is fixed axially along the longitudinally extending shaft and the first, second and third pivot points are located at distances from one another so as to position the central axis of the holder at an angle with respect to the first end of the longitudinal shaft in fixed relationship to the angle of the tracker mounting rod for all pivotal positions of the first arm with respect to the shaft bearing. This means that the central axis of the holder is located at a fixed angle or parallel to the axis of the tracker mounting rod as the positioning tool first arm is manipulated to any position with respect to the longitudinal shaft. As will be easily understood by one skilled in the art, the structure described is in the form of a four bar linkage with the lengths of the various arms and the locations of the pivot points on the arms connecting the adjacent sides of the linkage chosen to establish a known geometric relationship between the emitter (tracker) array and the reaming tool or implant mounted on the tool. In the preferred embodiment, the four arms form a parallelogram with opposite sides being the same length. Of course as long as the geometry of the tool is programmed into the computer, mathematical algorithms can calculate the position of the cutting head based on inputs of the optical tracking system.

The positioning tool is used by mounting the implant or instrument on the holder and mounting the tracker on the mounting rod attached to the first arm. The surgeon then can manipulate the positioner and the holder about the moveable joints to any desired position. An optical tracking system coupled to the computer-assisted surgical system can calculate the location of the implant or cutting tool from the known relationships of the linkage system and the known angle of the holder central axis which is at a fixed angle or is parallel to the central axis of the rod holding the light emitting diode tracker assembly. The holder, including cutting tool or implant, is placed within the patient and the optical tracking system allows the surgeon to view the joint, such as the acetabulum, on the CRT with the computer generated location of the cutting tool or implant overlayed either on the digital CT images stored in the computer database for the patient or on a vertical acetabulum. The movement (image free) of the holder is tracked in real time and the real or virtual image data is updated to compensate for patient movement, if any, also in real time. The surgeon can then manipulate the holder via the handle on the first arm to cut the proper cavity or locate the implant in its desired position. When used without the optical computer-aided system, the instrument can still be used utilizing the parallel relationship between the mounting rod on the handle and the holder central axis.

DETAILED DESCRIPTION

Referring to the figures, there is shown an acetabular cup or tool positioner of the present invention generally denoted as10. Positioner10is essentially designed as a four bar linkage having a holder at its leading end design either to hold a cutting tool, such as an acetabular reamer or an implant such as a prosthetic acetabular cup. Of course the tool can be used to position other implants within the body.

Referring toFIGS. 1 and 9, there is shown a positioning tool10which includes a drive shaft12extending along a longitudinal axis14. At a first end15, drive shaft12includes a joint16capable of movement about at least two axis such as a flexible shaft or wire or a typical mechanical universal joint which is of a well known design and sized to fit the diameter of the shaft. At a second end17of shaft12, there is a drive connection18adapted to engage a chuck (not shown) of any typical rotary power drive such as an electric drill. Shaft12has a bearing member20mounted thereon. Bearing20is fixed axially on shaft12but allows the shaft12to rotate about axis14of shaft12. Bearing20includes a pivot connection22on an outer surface thereof.

As best seen inFIGS. 2–5and9, pivot connection22is pivotally connected to a first arm24via a pivot pin26and a pair of forks24aand24b. The preferred first arm24includes handle28coupled thereto which has a first end30opposite pivot point22. In the preferred embodiment, a mounting rod32extends at a predetermined angle α with respect to the longitudinal axis31of arm24and handle28. Mounting rod32includes a connector34for connecting an emitter or tracker array36to the first arm24. In the preferred embodiment, tracker array36includes at least three light emitting diodes38located in the same plane which diodes can be tracked by an optical tracking system such as described in U.S. Pat. Nos. 6,021,343 and 6,434,415, the teachings of which are incorporated herein by reference. While in the preferred embodiment, an optical tracking system is used any tracking system such as acoustic system can be used. In addition, while the preferred tracker includes radiation (light), emitting diodes a passive system using light reflectors could also be used.

Moveable joint16attached to first end15of shaft12is coupled to a holder40which includes a mounting system42on which a cutting tool, such as a reamer44is mounted. The preferred universal joint16has a pair of perpendicular pins19and21about which two parts of the joint can pivot in a standard manner. Holding system42can be any suitable system for gripping an acetabular cup implant or acetabular reamer. In the preferred embodiment, the holder is similar to that taught in U.S. Pat. No. 6,264,647. Preferably, the holder can releasably grip both a reaming tool and the prosthetic acetabular cup.

Holder40has a central axis14aand is coupled via a connector43to pin21at one end of the universal joint1650that axis14amay, in the preferred embodiment, be oriented in any angular relationship to axis14of shaft12. In order to effectuate angular movement of holder40, holder40is coupled to a second arm50via a pivot connection52having forks52a and52b. Pivot connection52is similar to the pivot connection22and includes a pivot pin54extending through a bushing56having a flange integrally formed on the outer circumference of holder40. Thus, second arm50has a first end53pivotally coupled to the holder40and a second end55pivotally connected to first arm24at pivot connection60. In the preferred embodiment, the pivot connection60consists of a pivot pin62which extends through a pair of forks64,66formed on second end55of second arm50and, in the preferred embodiment, through a portion of arm24.

The resulting structure can be seen to be a four bar linkage where each of the four bars are pivotally connected. The linkage is thus made up of shaft12, first arm24, holder40and second arm50. In the preferred embodiment, the distances between the pivot points connecting the four bars and the angle α are chosen such that the axis32of mounting rod34always remains parallel to axis44of holder40throughout any location of first arm24and consequently any position of the four bar linkage.

In the preferred embodiment, the linkage forms a parallelogram with the distance between the pivot connection of universal joint16and pivot point22on bearing20along shaft12is approximately 6.6 inches and the length of second arm50between points52,60is also approximately 6.6 inches. In the preferred embodiment, the distance of pivot point54from the center line14aof holder40is approximately 0.79 inches. Likewise, the distance between pivot point22of bearing20from the axis14of shaft12is also approximately 0.79 inches. In the preferred embodiment, the distance between pivot point22and pivot point60a first arm24and second arm50respectively is approximately 1 inch and the distance between pivot point52and pivot point21is also 1 inch. The axis of all the pivot pins (except pin19) are parallel so that movement of handle20takes place in a plane containing axis14of shaft12.

During the preferred surgical procedure and after the optical-aid surgical system has been calibrated to the patient's anatomy, the instrument10, including tracker assembly36mounted on rod32is grasped by the surgeon with one hand on handle28. A cutting element or implant, such as a reamer or acetabular cup, denoted as44would be mounted on holder40. In the case of reaming, a drive source, not shown, would be connected to drive element18on second end17of shaft12for powering the reamer. The positioner10is then inserted into an appropriate incision with the holder being aligned in the desired position via the computer-assisted surgical system. The surgeon may then manipulate handle28by manipulating the four bar linkage such as, for example, by rotating the handle along arrow70ofFIG. 2. The surgeon may also rotate the entire assembly10about axis14of shaft12in the direction of arrow72ofFIG. 2. The simultaneous movement of positioner10in direction72and the handle28and first arm24in direction70causes movement of cutting tool or acetabular cup44about the x, y and z axis of the universal joint16. Such manipulation would be shown on the CRT with respect to either the stored actual images or virtual images of the patient joint by the tracking system. Upon obtaining the correct position adjacent the joint sockets, for example, the acetabulum, the drive shaft12and reamer is activated via drive element18with a suitable drive and rotating the shaft in a direction74about axis14(FIG. 2).

Once the reaming is complete, the instrument is removed from the patient and the reamer is replaced by the acetabular implant which is located in the desired orientation with the computer-aided tracking system. The cup is then implanted in a standard manner. If a tracker system is not used the surgeon can orient the reamer or implant via rod32since, in the preferred embodiment, it is parallel in all orientations to the holder central axis. If visual orientation is not needed, i.e., a computer-aided tracking system will always be used during surgery it may be possible to mount the tool geometry and tracker array in any orientation. The computer can then be programmed with the tracker orientation and calculate the correct holder orientation. Thus, the four-bar linkage need not be parallel as long as the actual geometry of the linkage were correctly programmed into the computer so that the actual holder orientation could be calculated based on the position of tracker38.