Abstract:
Disclosed are methods for performing a surgical procedure at a surgical site utilizing a surgical robot. Other embodiments are also disclosed.

Description:
[0001]    This application is a continuation of co-pending application Ser. No. 10/965,100, filed October, 15, 2004, which is a continuation of application Ser. No. 09/912,687, filed Jul. 24, 2001, now U.S. Pat. No. 6,837,892, which claims priority from Provisional Application Ser. No. 60/220,155, filed Jul. 24, 2000. The contents of all of the above-listed applications are incorporated herein by reference. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to a robotic device. Particularly, this invention relates to a robotic device that attaches to a bone of the patient and aids or performs surgical procedures. 
       BACKGROUND OF THE INVENTION 
       [0003]    Generally, robots are used in many different industries for many different applications. One industry, for example, is the medical industry that uses robots in applications including assisting the surgeon during surgical procedures. Robots are especially suited for some surgical tasks because they can be constructed to be very steady, computer controlled, and precise in their movements. Characteristics such as these can be especially helpful during surgery on sensitive areas, such as, for example, the vertebral column but are applicable throughout the body. 
         [0004]    Typical vertebral column surgical procedures include vertebral fusion, insertion of medical devices such as pedicle screws, discography, percutaneous discectomy, or the like. These procedures typically require a large invasive operation that exposes the patient to a high risk of infection, excessive trauma, fluid loss, post operative pain, scarring, and a lengthy recovery time. Some difficulties relating to surgery on the vertebral column include micro-movement of the vertebral column during the operation, inherently small target objects of the procedure such as the pedicles, extremely delicate nearby nerve tissue, and limited operating room space because large equipment is needed to aid in the procedure, such as C-arm X-ray devices. Furthermore, the patient and operating room staff are exposed to large doses of radiation because these procedures require repeated X-raying and/or fluoroscoping of the surgical site so the surgeon can view the position of surgical tools or implants relative to non-visible body parts. 
         [0005]    A need exists for a device that can assist minimally invasive surgery with low radiation exposure while allowing the surgeon to precisely align and control or monitor the surgical procedure. Some prior art devices have attempted to accomplish this however, these devices are either too complicated, not sufficiently accurate, or consume too much operating room space. 
         [0006]    One such device is disclosed in U.S. Pat. No. 6,226,548. This device combines a navigation system, a bone mounted apparatus, and surgical tools that communicate with the navigation system. This apparatus primarily consists of a clamp that attaches to the patient&#39;s spine and extends outward forming a reference arc bearing emitters or a tracking means. All the surgical tools used in this procedure are fitted with emitters or a tracking means similar to the reference arc. The surgical suite is fitted with a navigation system capable of recognizing the emitters or tracking means of the reference arc and surgical tools, a computer system for interpreting the location of the tools, and a video display for the surgeon. After surgically placing the clamp and reference arc on the patient a CT or MRI is taken creating a three-dimensional image of the patient with the attached device. When the patient is in place in the surgical suite with the attached reference arc the navigation system locates the arc and the surgical tools and displays them, relative to each other, on the three-dimensional CT scan. 
         [0007]    While the device disclosed in the &#39;548 patent offers some advantages in terms of accuracy and reduced trauma, the advantages of this type of prior art device are limited. The critical part of a surgical tool that must be monitored is the working end of the tool, whether that be a screwdriver or a drill bit or the like. These cannot be tracked with such prior art systems. Transmitters or emitters cannot be attached to the working ends of tools so the computer must estimate the location of the working end by locating the tool generally and extrapolating. This causes inaccuracy and errors that cannot be tolerated in spinal surgery or other high accuracy procedures where the smallest error can result in a serious and permanent outcome. Also, prior art devices such as these are hand held by the surgeon and thus, limited in accuracy to the surgeon&#39;s ability to hold and align the tool. 
         [0008]    Furthermore, when using this system, the user must be cautious to not block the line-or-sight between the tool mounted emitters or receivers, the reference arc bearing emitters or receivers, and the navigation system. This can severely limit the ability of the surgeon or surgical team as the tool may actually limit their ability to aid the patient. Also, while such prior art systems do reduce the incision size, they complicate the surgical procedure. Usually a patient is brought into a surgical suite ready for a procedure, the procedure is performed, completed, and the patient leaves. However, the &#39;548 patent system requires the patient to be put through a surgical procedure to affix the clamp and referencing arc, then the patient is transported to a CT or MRI, then transported back to the surgical suite in a non-sterile condition for the substantial portion of the procedure to commence. Finally, this system has many components, such as the navigation system and the computer output unit, that clutter up the already limited space in the surgical suite. 
         [0009]    Therefore, there is a need in the art for a device with high precision and accuracy that can assist the surgeon in aligning the working end of the surgical tool such that delicate procedures can be preformed percutaneously with minimal radiation exposure to both the patient and the surgical staff. 
       SUMMARY OF THE INVENTION 
       [0010]    The present invention is directed to a device and method for assisting in surgical procedures. According to the invention, a robot is disclosed that precisely positions a surgical tool with respect to a surgical site. The robot attaches to the bone of a patient with a clamp or with wires such as K-wires. Actuators extend from the robot base and move away from and toward the base member. This manipulates balls that rotate within spherical swivel joints that in turn align a sleeve. A surgical tool such as a screw driver or a drill bit is inserted through the sleeve and thus is precisely aligned with a site requiring surgery. 
         [0011]    The present invention also includes a method for using the robot to assist in surgical procedures. Initially, three dimensional images are taken of the patient and the surgeon performs pre-operative planning of the procedure to be done on the images. This creates parameters that will later be used to direct the robot to the location where the surgical procedure is required. The robot is then attached to the patient by the clamp or the k-wire. C-arm images are taken of the patient with the attached clamp and these images are co-registered and calibrated such that a precise image of the bone with the robot attached is generated. This image is then registered, or matched, with the three dimensional image. This is accomplished in a highly efficient and accurate manner by taking small windows of the images where the surgery is to take place and registering these small portions. The small windows are chosen off the images by locating the bone attached clamp and selecting a window according to pre-operative calculation of the bone-robot attachment location. After these windows are chosen and registered, the remaining bone is registered by aligning the registered windows. At this point the robot is located precisely on the bone of the patient in the three dimensional image and can be manipulated by the surgeon to a pre-operative planned location for percutaneous insertion of surgical tools, medical devices, or implants. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    For a better understanding of the nature, objects, and function of the present invention, reference should be made to the following detailed description in conjunction with the accompanying drawings, in which: 
           [0013]      FIG. 1  is an overview of an embodiment of a surgical system showing a control unit with a display, C-arm with a calibration phantom attached, and a robot used for aligning surgical tools attached to the patient according to the present invention; 
           [0014]      FIG. 2  is a perspective view showing a miniature surgical robot attached to a bone and aligning a surgical tool in an embodiment of the invention; 
           [0015]      FIG. 3  is a perspective view showing a clamp for attaching to a bone and adaptor for receiving a robot in an embodiment of the invention; 
           [0016]      FIG. 4  is a cross-sectional view of  FIG. 3 ; 
           [0017]      FIG. 5  is a flow chart of an embodiment of the method of using the present invention; 
           [0018]      FIG. 6  is a perspective view of an image referencing plate with three referencing markers attached; 
           [0019]      FIG. 7  is a perspective view of a spacer used to extend the clamp; and 
           [0020]      FIG. 8  is a perspective view showing a miniature surgical robot for aligning a surgical tool attached to a bone by K-wires in an embodiment of the invention. 
       
    
    
       [0021]    Like reference numerals refer to corresponding elements throughout the several drawings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0022]    Referring to the illustrations and particularly to  FIG. 1  it can be seen that a preferred embodiment of the present invention generally includes an image guided, robot assisted, surgical system. Included in this system generally, as shown in  FIG. 1 , is a bone attached surgical robot  30 ; a control unit  10  that matches data from CT scans and C-arm images to locate robot  30  on the patient&#39;s bone and allows a surgeon to control robot  30 , through the use of a mouse, joystick, touch screen, or the like; and video display  20 . Control unit  10  generally includes a cpu and user interface communicating with display  20  and robot  30 . 
         [0023]      FIG. 2  illustrates robot  30  according to one embodiment of the present invention attached with clamp  40  to vertebra  50 . Robot  30  aligns sleeve  60  through which surgical tool  70  such as a screwdriver, drill bit, Kirschner wire (K-wire), or the like can be inserted and precisely aligned with a site requiring a surgical procedure and thus, the operation can be conducted percutaneously or in traditional open procedures. 
         [0024]    In a preferred embodiment of the invention, robot  30  includes base  35  that sits vertically on clamp adaptor  45 . At least two pairs of actuators  80  extend from base  35 . The actuators  80  extend from the base  35  forming a fixed angle  85  between base  35  and actuator  80 . This angle is generally between about 15-90 degrees and more preferably about 45 degrees. In one preferred embodiment, the points of attachment of actuators  80  are spaced apart by about 50 mm in the Z direction and about 50 mm in the Y direction. Each actuator  80  is capable of operating independently from the other actuators  80 . Actuator  80  is similar to known linear actuators and includes a housing, a motor, a lead screw, an electrical connection, and a position sensor such as an optical encoder, an LVDT, or the like. In a preferred embodiment each actuator is approximately 5 mm in diameter and approximately 35 mm in length. 
         [0025]    The end of actuator  80  that is not fixedly attached to base  35  contains hinge joint  90 . Hinge joint  90  links actuator  80  to rigid member  100 . In a preferred embodiment member  100  is about 4 mm in diameter and 40 mm in length. Hinge joint  90  permits member  100  to freely rotate through about 270 degrees on an axis that runs parallel to base  35 . The other end of the rigid member  100  is fixed with solid connection  105  to ring member  110 . There is no movement between rigid member  100  and ring member  110  at solid connection  105 . 
         [0026]    Upper ring member  110 A and lower ring member  110 B, solidly connected to individual rigid members  100 , come together at spherical swivel joint  120 . Each ring member  110  forms one half of an outer race of spherical swivel joint  120 . Ring members  110  are free to rotate with respect to one another, but are held fixedly from separating in the Z axis direction. Contained between upper ring member  110 A and lower ring member  110 B, and free to swivel, is ball  130 . Passing through ball  130  is sleeve  60 . Sleeve  60  passes through both upper and lower balls  130 , forming an aligning axis through which surgical tool  70  is passed. As actuators  80  extend and retract, hinge joints  90  freely rotate about the Z axis and balls  130  swivel in the spherical swivel joints  120  formed by upper and lower ring members  110 . A hollow axis is formed by the sleeve passing through each of upper and lower balls  130  such that a surgical tool  70  can be inserted through and be accurately aligned with the working location. 
         [0027]    According to the present invention the above described robot  30  is just one example of a robot configured for surgical assistance that may be utilized with the system according to the present invention. Other robot configurations that could satisfy the same tasks include, for example, a parallel robot constructed to the required dimensions, such as that described in Simaan, N., Glozman, D., and Shoham, M.: “Design Considerations of new types of Six-Degrees-of-Freedom Parallel Manipulators,” IEEE International Conference on Robotics and Automation, Belgium, 1998, which is incorporated by reference herein. 
         [0028]    In a preferred embodiment of the invention, robot  30  is attached with the bone of a patient by clamp  40 . As shown in  FIGS. 3 and 4 , clamp  40  comprises bone clamping portion  42  and clamp adaptor  45 . Initially, handles  210  extend from clamp  40  and allow a user to hold, align, and affix clamp  40  onto a bone of the patient. The base of the handles  210  fit over nuts  220 , shown in  FIG. 4 , located on clamp  40 . When clamp  40  is in place, the user pushes handles  210  toward each other to close jaws  230  onto the selected bone. When handles  210  are fully closed, or pushed together, a first locking (described below) occurs and clamp  40  is locked in place on the bone. The user then rotates handles  210  in a clockwise direction, turning and tightening nuts  220 . Nuts  220  tighten down on threaded studs  250  and pinch clamp adaptor  45  onto bone clamping portion  42 . This causes a second locking of clamp  40  into place on the bone. The base of each threaded stud  250  has a spherical mating surface  255  so that when clamp adaptor  45  is tightened down onto bone clamping portion  42  the clamp adaptor can self align itself on spherical mating surface  255  of stud  250 . This allows the top surface of clamp adaptor  45  to maintain a horizontal surface for receiving the robot base  35 . The handles,  210 , are then removed by pulling straight up and away from the clamp  40 . Protruding from the top surface of clamp adaptor  45  are connection pins  200 . Connection pins  200  align with receiving holes in robot base  35  and when inserted lock robot  30  into place by some type of a snap ring or spring and ball bearing or plunger ball/pin. 
         [0029]    With reference specifically to  FIG. 4 , it can be seen that threaded studs  250  are embedded in levers  260 . Left and right levers  260  are connected together by upper center hinge  280 . The other end of levers  260  connect with respective jaws  230  through side axis hinge  270 . Left and right jaws  230  are connected together by main pivot  290  around which the jaws rotate. When a user pushes handles  210  together to close jaws  230 , upper center hinge  280  is pushed downward and at the same time side axis hinges  270  rotate around the main pivot  290 . The first locking occurs when upper center hinge  280  is pushed below the center line formed between left and right side axis hinges  270 , and clamp  40  locks onto the bone. When clamp  40  is in the fully closed and locked position, jaws  230  are parallel to each other and separated by a set distance. The set closing distance between jaws  230  can be altered for different bone attachment applications by exchanging re-moveable jaw inserts  240  with the same of a different thickness. 
         [0030]      FIG. 7  illustrates spacer  900  that can be attached to the top surface of clamp adaptor  45  to ensure that robot  30  remains above the working area and out of any tissue that might occur when a patient has unusual body proportions. Spacer  900  attaches to connector pins  200  of clamp adaptor  45  and provides connector pins  910 , similar to connector pins  200 , for robot  30  attachment to the top surface of the spacer  900 . 
         [0031]    Above described clamp  40  is an example of one embodiment according to the invention by which a robot may be attached to a bone for assisting in a surgical procedure. Other attachment devices can also be incorporated with a robot such as, for example, K-wire connections.  FIG. 8  illustrates such a K-wire connection. K-wires  950  are inserted into the bone by standard surgical procedures. Robot base  35  contains an elongated slot through which K-wires  950  are inserted. Screw  960  can then be turned and tighten pinch plate  970  against robot base  35  pinching K-wires  950  between pinch plate  970  and robot base  35  holding robot  30  tight with respect to K-wires  950  and bone  50 . 
         [0032]      FIG. 5  illustrates the registration system used to establish the position of the robot on the bone. Initially there is a pre-operative step  400 . This step  400  consists of taking a three-dimensional scan  410  of the patient, such as a CT or MRI scan. A surgeon then performs pre-operative planning  420  on the three-dimensional scan. For example, if the procedure to be done is a fracture fixation, the surgeon will study the three-dimensional image and the condition of the bone, choose the proper implant from a database containing implants of all types and sizes based on the present application, and electronically position and insert the implant, the screw, or the like. This is known in the art, for example, as described in “Marching Cubes: a high resolution 3D surface reconstruction algorithm”, W. E. Lorensen, H. E. Cline, Computer Graphics 21 (1987) 163-169 which is incorporated by reference. The parameters generated by the pre-operative planning  420  are stored in the control unit  10  for positioning the robot  30  during the actual surgical procedure. 
         [0033]    With reference now to  FIGS. 1 ,  5 , and  6  the next step is initial calibration of the C-arm  450 . A phantom  320  ( FIG. 1 ) is attached to the lens of the C-arm device  300  and a blank C-arm image is taken, step  460 ,  FIG. 5 . The phantom  320  is used to correct for the distortion associated with the C-arm image. The phantom contains several reference objects and a large number of small reference objects. The control unit automatically recognizes the reference objects and creates distortion correction maps and calibration intrinsic parameters to correct for the imprecise C-arm image. Systems such as these are known in the art and described, for example, in Brack et al., “Accurate X-ray Navigation in Computer-Assisted Surgery”, Proc. Of the 12th Int. Symp On Computer Assisted Radiology and Surgery, H. Lemke, et al., eds., Springer, 1998; Yaniv et al., “Fluoroscopic Image Processing for Computer-Aided Orthopaedic Surgery”, Proc. 1st Int. Conf. On Medical Computing and Computer-Assisted Intervention, Lecture Notes in Computer Science  1496 , Elsevier, et al., eds., 1998; Hofstetteret al., “Fluoroscopy Based Surgical Navigation—Concept and Clinical Applications”, Proc. 11th Int. Symp. on Computer Assisted Radiology and Surgery, H. U. Lemke, et al., eds., Springer 1997; Tsai, R., “A Versatile Camera Calibration Technique for High-Accuracy 3D Machine Vision Metrology Using Off-the-Shelf TV Cameras and Lenses”, IEEE Journal of Robotics and Automation, Vol. RA-3, No. 4, August 1987, which are incorporated by reference. 
         [0034]    Next, the patient is brought into the operating room, a small incision is made according to standard surgical practice at the site where clamp  40  is to be attached, and the clamp is attached to the selected bone using handles as described above, step  462 ,  FIG. 5 . Handles  210  are then removed from the clamp  40 . An image referencing plate  800  ( FIG. 6 ) is attached to clamp  40 , step  465 ,  FIG. 5 , by receiving holes that receive connector pins  200 . The image referencing plate  800  ( FIG. 6 ) has three referencing markers  810  on it that show up very clear and precise in the C-arm image. The distance and angle between the referencing markers  810  are known such that the C-arm image can be calibrated in a secondary calibration step, step  465 , to accurately represent actual size of the image. At least two, but preferably three C-arm images are taken of the patient with the attached clamp  40  and image referencing plate  800 . These C-arm images are taken from different angles, preferably 0, 45, and 90 degrees, step  470 ,  FIG. 5 . 
         [0035]    In another embodiment of the present invention the secondary calibration step, step  465 B, can be accomplished by attaching the robot  30  to the clamp and taking multiple C-arm images. By knowing the dimensions, or by placing referencing markers on robot  30  and knowing the distance and angle between the referencing markers the C-arm images can be calibrated in a secondary calibration step, step  465 B. 
         [0036]    The next step of the process is co-registration, step  500 . The C-arm images are transferred into the control unit  10  as data, step  502 . At each location an image is taken from, the position of the C-arm is recorded, step  504 , into the control unit  10 . The data of the images, step  502 , and the position of the C-arm, step  504 , are correlated by knowing the position from which each images was taken, step  504 , and by aligning the referencing markers  810  ( FIG. 6 ) from the image referencing plate  800  ( FIG. 6 ). Thus, an accurate, pseudo three-dimensional image of the surgical site with the clamp  40  attached to the bone is generated. This stage can be referred to as robot to bone registration or co-registration. 
         [0037]    According to a preferred embodiment of the invention, bone to bone registration next occurs in step  600 . Step  600  is a process of estimating and matching the true surface contours or the objects in the images. Registration methods are either based on geometry or intensity of the image. Geometric based registration is achieved by finding features in the 2D fluoroscopic images and matching these features with corresponding features in the 3D image, acquired, for example, from a CT scan dataset, MRI image, ultrasound image or from a CAD model. The features can be known landmarks (anatomical landmarks or implanted fiducials), or contour points in the fluoroscopic image, matched with the registered object&#39;s surface. An algorithm that may be used to compute the transformation is the Iterative Closest Point (ICP) algorithm. This algorithm is described, for example in Besl, P. J. and McKay, N. D., “A Method for Registration of 3D Shapes”, IEEE Trans. on Pattern Analysis and Machine Intelligence, 1992, 14(2), 239-255, which is incorporated herein by reference. The input to the algorithm are sets of back-projected rays from the fluoroscopic images, and a model of the registered object. The algorithm iteratively computes a transformation that approximates the ray sets to the model. For landmark registration, a match between each ray and the corresponding landmark is defined before searching for the transformation. Contour registration selects a new surface point to match with each ray on every iteration. 
         [0038]    Preferably, the registration process uses two or more fluoroscopic images, as described in greater detail, for example, in Hamadeh, et al., “Towards automatic registration between CT and X-ray images: cooperation between 3D/2D registration and 2D edge detection”, Medical robotics and computer assisted surgery, 1995, Wiley 39-46, and Hamadeh, et al., “Automated 3-Dimensional Computed Tomographic and Fluoroscopic Image Registration”, Computer Aided Surgery, 1998, 3, which are incorporated herein by reference. According to this method, anatomical landmarks in the images are detected and matched manually. Based on this match, an approximated initial guess is computed, with ray intersections, which are 3D points in the registration environment, being matched with the model&#39;s landmarks. Then, the object&#39;s contour in the 2D image is registered with the model&#39;s surface. A likelihood estimator is used to remove outliers, or pixels not in the contour, from the sample point set. A signed distance function is defined to overcome any internal contours problems. The overall in-vitro accuracy of this method can be better than 2 mm. 
         [0039]    In one alternative, a single fluoroscopic image may be used for registration, achieving an accuracy of about 3 mm. This technique is based on a combinatorial search among matches of three points and three rays. The match with minimal average distance for the registration is then selected. This alternative is described in Tang, “Method for Intensity-based Registration with CT Images,” Masters Thesis: Department of Computer Science, Queen University, Ontario Canada, 1999, which is incorporated herein by reference. 
         [0040]    In a further alternative according to the invention, intensity-based registration is achieved by comparing fluoroscopic images with simulated X-rays (digitally reconstructed radiographs, or DRR&#39;s) from an estimated position. Such a technique is generally described in Lemieux et al., “Patient-to computed-tomography image registration method based digitally reconstructed radiographs”, Medical Physics, 21, 1994, 1749-1760 and Murphy, M. “An automatic six-degree-of freedom image registration algorithm for image-guided frameless stereotactic surgery”, Medical Physics, 24(6), June 1997, which are incorporated by reference herein. 
         [0041]    When the camera position guess and the actual position are very close, the original and reconstructed image are very similar. Pixel intensity information is used to define a measure of similarity between the datasets. The similarity measure can include intensity values, cross-correlation, histogram correlation, and mutual information. The algorithm proceeds in three steps. The input is a CT data set, intrinsic camera parameters, one or more fluoroscopic images and an initial camera position estimate for each image. In the first step, the algorithm generates one DRR for each given camera position. In the second step, a dissimilarity measure is computed between the real and reconstructed image. In the third step, new camera poses are computed that best reduce the dissimilarity between the images. The process is repeated until convergence is reached. The parametric space of camera positions in then searched incrementally from an initial configuration. The space is six-dimensional (three rotations and three translations). The advantages of this technique is that no segmentation is necessary. However, the search space is six-dimensional, and can contain many local minima. 
         [0042]    A benefit of the present invention is that it can utilize either of the above described registration methods. By utilizing the dimensions of the bone attached robot and its attachment location, the initial location of the window is a very good guess of the location and therefore the intensity based method can be utilized. Thus, according to the present invention, a faster and more accurate registration process is accomplished as between the fluorscopic and 3D images. This is done in step  600 , and occurs very quickly and with a high degree of accuracy because the registration process is performed on small windows of the images, rather than the images as a whole. Preferably windows are selected that specifically relate to the known location of the robot and/or its support member. Windows of about 20 mm by 20 mm located approximately adjacent to the clamp location, according to pre-operative calculation of the bone-robot attachment location, are selected from the C-arm (fluoroscopic) image data, step  610 . For example, these windows may be selected as the area above the attached clamp  40  in the C-arm image and the tip of the transverse process of the vertebra covering the area where the surgical procedure is to take place. Generally, the same windows are chosen from both the pseudo three-dimensional hybrid C-arm image, step  510 , and also from the CT image (3D image), step  410 . The small windows chosen from the C-arm images and the CT scan image are then laid over each other and matched or registered by the control unit, step  620 , as described above. Focusing only on a small window of the C-arm image rather than looking for a matching anatomical landmark in the entire image, makes the process occur very fast and with the high degree of accuracy needed for precise procedures such as vertebra surgery. 
         [0043]    Next, the remaining portion of the CT and C-arm image of the bones are overlaid, the registration windows are aligned, and the remaining bone is registered, step  630 . Since the windows have already been accurately registered this step occurs quickly and also with a high degree of accuracy. Now clamp  40  is located precisely on the bone, step  640 , of the CT image. Next, the user attaches robot  30  to clamp  40  and thus, robot  30  is located precisely with respect to the bone, step  645 . 
         [0044]    After robot  30  is co-registered  500  and registered  600 , its position is known relative to the patient&#39;s bone and therefore can move to align with the pre-operatively picked location such that the operation can virtually take place on the control unit. The user selects a pre-operatively planned location and task from step  420  by use of a joystick, mouse, touch screen, or the like, step  710 . The Robot  30  responds and moves sleeve  60  into position, step  720 , such that when the user inserts a surgical tool  70  through the opening in the sleeve  60  the surgical tool  70  will be precisely aligned with the location requiring the surgical procedure, step  730 . The surgeon can then insert a selected surgical tool  70  and operate without opening the surgical site to see the placement of the surgical tool because the surgeon can verify the positioning of the surgical tool  70  on the control unit  10  and display  20 . Thus operating percutaneously or in general open procedures, with a high degree of accuracy, low trauma, small incisions, low chance of infection, and minimal exposure to radiation. A further benefit of this system is that because the robot is miniature it can be freely attached to the bone of a patient and move with the body. Therefore, the robot system does not need a dynamic referencing device to maintain orientation with the body once it is registered. This creates a more precise and less complicated system that is versatile and user friendly as the surgeon can manipulate the patient into different surgical positions without disturbing the robot system. 
         [0045]    The present invention is illustrated herein by reference to a spinal vertebra attachment. However, it will be appreciated by those in the art that the teachings of the present invention are equally applicable to other bone attachments.