Patent Publication Number: US-2021177526-A1

Title: Method and system for spine tracking in computer-assisted surgery

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the priority of U.S. Patent Application No. 62/948,494, filed on Dec. 16, 2019 and incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure relates generally to computer-assisted surgery, and, more particularly, to methods, systems, and devices for spine tracking in computer assisted surgery. 
     BACKGROUND OF THE ART 
     Traditional spinal surgical operations are invasive, often requiring large incisions which, while necessary to achieve sufficient spinal exposure, result in extended patient trauma and post-operative pain. Computer-assisted image guided surgical instrument navigation is typically used wherever possible in an effort to reduce the invasiveness of spinal surgery. Nevertheless, it is still desirable to reduce the invasiveness of spinal surgery. 
     As such, there is a need for improved methods, systems and devices for spine tracking in computer-assisted surgery. 
     SUMMARY 
     The present disclosure is generally drawn to methods, systems, and devices for spine tracking in computer-assisted surgery. 
     In one aspect, there is provided a method for spine tracking in computer-assisted surgery, the method comprising: obtaining, at a computer-assisted surgical system, at least one image of at least part of the spine and at least one surgical device; determining, at the computer-assisted surgical system, a three-dimensional position and orientation of the at least one surgical device relative to the spine from the at least one image to create a referential system; tracking, at the computer-assisted surgical system, the at least one surgical device altering a first vertebra of the spine for attachment of a spinal screw to the first vertebra, in the referential system; and tracking, at the computer-assisted surgical system, the spine in the referential system with a trackable reference attached to the spinal screw of the first vertebra. 
     In another aspect, there is provided a system for spine tracking in computer-assisted surgery, the system comprising: a processing unit; and a non-transitory computer-readable memory having stored thereon program instructions executable by the processing unit for: obtaining at least one image of at least part of the spine and at least one surgical device; automatically registering a three-dimensional position and orientation of the at least one surgical device relative to the spine from the at least one image to create a referential system; tracking the at least one surgical device altering a first vertebra of the spine for attachment of a spinal screw to the first vertebra, in the referential system; and tracking the spine in the referential system with a trackable reference attached to the spinal screw of the first vertebra. 
     In another aspect, there is provided an assembly for spine tracking in computer-assisted surgery, the assembly comprising: a spinal screw having a connector; a surgical device including an attachment member for coupling to the spinal screw, and a trackable member coupled to the attachment member, the trackable member including at least one detectable element for being tracked in three-dimensional space by a computer-assisted surgical system, thereby allowing tracking position and orientation of a spine by the computer-assisted surgical system when the attachment member is coupled to the spinal screw implanted in a vertebra of the spine. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       Reference is now made to the accompanying figures in which: 
         FIG. 1A  is a perspective view of a surgical device comprising a trackable member, in accordance with an embodiment; 
         FIG. 1B  is a perspective view of the surgical device of  FIG. 1A  with a variant of the trackable member, in accordance with an embodiment; 
         FIG. 1C  is a cross-sectional view of the surgical device of  FIG. 1B  from a first perspective, in accordance with an embodiment; 
         FIG. 1D  is a cross-sectional view of the surgical device of  FIG. 1B  from a second perspective, in accordance with an embodiment; 
         FIG. 1E  is a perspective view of exemplary spinal screws, in accordance with an embodiment; 
         FIG. 2  is a schematic diagram of a computer-assisted surgical system, in accordance with an embodiment; 
         FIG. 3  is a flow diagram illustrating an example of a computer-assisted surgical process, in accordance with an embodiment; 
         FIG. 4  is a flowchart illustrating an example method for spine tracking in computer-assisted surgery, in accordance with an embodiment; and 
         FIG. 5  is a schematic diagram of an example computing system for implementing at least in part the system of  FIG. 2 , the process of  FIG. 3 , and/or the method of  FIG. 4 , in accordance with an embodiment. 
     
    
    
     It will be noted that throughout the appended drawings, like features are identified by like reference numerals. 
     DETAILED DESCRIPTION 
     The present disclosure is generally drawn to methods, systems, and devices for spine tracking in computer-assisted surgery (CAS). Imaging of a spine and a reference (e.g., a spinal screw and/or a surgical device having a trackable member) may be obtained and used by a CAS system to determine a three-dimensional (3D) position and orientation of the reference relative to the spine. The reference may be used by the CAS system to determine the position and orientation of the spine and/or to track the position and orientation of the spine during the spinal surgery. The reference may be used by the CAS system to track one or more surgical tools and/or implants relative to the spine during the spinal surgery. 
     With reference to  FIG. 1A , there is illustrated a surgical device  100  for use in a CAS. The surgical device  100  includes an attachment member  110  and may optionally have a trackable member  120 . The attachment member  110  is adapted for coupling to a spinal screw  130 . More specifically, the attachment member  110  is adapted for being removably attached to a vertebra of a spine via the spinal screw  130  when the spinal screw  130  is implanted in the vertebra. The attachment member  110  may be adapted for removably coupling the screw  130 , and preserve its position relative to the screw  130 . The attachment member  110  can be decoupled from the screw  130  when not needed. The attachment member  110  may be a cannulated tube, a support rod (e.g., hollow or not) for mounting the trackable member  120  thereon, as shown in  FIG. 1 . The shape and/or configuration of the attachment member  110  may vary depending on practical implementations. 
     The trackable member  120  is coupled to the attachment member  110 . The trackable member  120  may be removably coupled to the attachment member  110 . In other words, the trackable member  120  may be attached to the attachment member  110  when needed during surgery and subsequently removed when not needed. In some embodiments, the trackable member  120  is not removable from the attachment member  110 . The trackable member  120  may comprise a plurality of branches  124  each comprising a plurality of detectable elements  122 , e.g., circular tokens of retroreflective material. As shown in  FIG. 1A , the trackable member  120  may comprise three branches  124 , each comprising three detectable elements  122 . The number of branches  124  and/or the number of detectable elements  122  of the trackable member  120  may vary depending on practical implementations, and any suitable number of branches and/or detectable elements may be used. In some embodiments, the trackable member  120  is the NavitrackER™ reference marker device provided by Zimmer Biomet. With additional reference to  FIG. 1B , the surgical device  100  of  FIG. 1A  is illustrated with a variant of the trackable member  120  having three detectable elements  122 . The shape and/or configuration of the trackable member  120  may vary depending on practical implementations. For instance, instead of the circular tokens shown in  FIG. 1A , the detectable elements  122  may be spheres, disks, may have polygonal shapes, etc. 
     In some embodiments, the surgical device  100  comprises a handle  140 . The handle  140  may or may not be removable from the surgical device  100 . The handle  140  may be used for turning the surgical device  100  in order to implant the spinal screw  130  into a vertebra. The handle  140  may be connected to a screw driver mechanism  150  adapted for turning (e.g., screwing) the spinal screw  130  coupled to the attachment member  110 . With additional reference to  FIGS. 10 and 1D , cross-sectional views of the surgical device  100  are illustrated. As shown, the attachment member  110  may be adapted for receiving at least in part the spinal screw  130  therein. More specifically, the attachment member  110  may be hollow so as to have a cavity  112  for receiving tabs of the spinal screw  130  in order to couple the spinal screw  130  to the surgical device  110 . Inside the cavity  112 , the attachment member  110  may have an elongated rotor component  114 . The rotor component  114  is coupled to the screw driver mechanism  150  such that a rotation of the handle  140  causes a rotation of the rotor component  114  relative to the tubular body of the attachment member  110 . Therefore, in an embodiment, a user may hold the tubular body of the attachment member  110  or part of the screw driver mechanism  150  while imparting a rotation to the handle  140 , such that the rotor component  114  screws the spinal screw  130  into a vertebra, for example. 
     With additional reference to  FIG. 1E , and for being coupled to the rotor component  114 , the spinal screw  130  may include a connector such as a bracket that may be defined by two tabs  132  and a screw  134  attached to tabs  132 , being elongated in shape. Although the expression tabs is used, other expressions could be used to describe the elongated features that couple to the attachment member  110 . The number of tabs  132  may vary depending on practical implementations, and any suitable number of tabs may be used. The spinal screw  130  may vary depending on practical implementations. Some anti-rotation feature may be present between the rotor component  114  and the tabs  132 , such as complementary flat surfaces, as one of numerous possibilities. In an embodiment, an inner surface of the attachment member  110  is cylindrical, and the rotor component  114  is a shaft having such complementary flat surfaces. The tabs  132  may be shaped to be snuggly received between the rotor component  114  and space in the inner cavity  112 . Therefore, when coupled together as in  FIG. 1B , the attachment member  110  and the spinal screw  130  are coaxial. Central axes of the attachment member  110  and the spinal screw  130  have the same orientation, and a trajectory of the spinal screw  130  may be known from a tracking of the longitudinal central axis of the attachment member  110 . Other coupling arrangements could be used, for instance with the spinal screw  130  having a socket, and the attachment member  110  having a complementary tool end. Moreover, the attachment member  110  is shown as having an open ended tube housing the rotor component  114 . However, the rotor component  114  could be exposed, with the attachment portion of the spinal screw  130 , such as the tabs  132 , connected to the rotor component  114  for concurrent rotation. A ring could for instance be slid onto the assembly of the rotor component  114  and tabs  132 , as a possibility. 
     With reference to  FIG. 2 , there is illustrated a CAS system  200  for use with the surgical device  100 . In the illustrated embodiment, the computer-assisted surgical system  200  includes a computing device  210 , a tracking camera such as at least one optical sensor  220  for tracking the trackable member  120  and connected to the computing device  210 , and a display device  230  connected to the computing device  210 . The computing device  210  may be any suitable computing device, such as a desktop computer, a workstation, a laptop computer, a mainframe, a server, a distributed computing system, a cloud computing system, a portable computing device, a mobile phone, a tablet, or the like. The display device  230  may be any suitable display device, for example, such as a cathode ray tube display screen, a light-emitting diode display screen, a liquid crystal display screen, a touch screen, a tablet or any other suitable display device. One or more input device(s) such as a keyboard, a mouse, a touch pad, a joy stick, a light pen, a track ball, a touch screen, and/or any other suitable input device may be connected to the computing device  210  for interacting with a GUI displayed on the display device  230 . In embodiments where the display device  230  is a touch screen device, the input device(s) may include the display device  230 . In some embodiments, the optical sensor(s)  220  and/or display device  230  may be provided separate from the CAS system  200 . The configuration of the CAS system  200  may vary depending on practical implementations. 
     The optical sensor(s)  220  are for tracking the surgical device  100 , and in particular the trackable member  120  if present. The optical sensor(s)  220  may be used to track any other surgical tools and/or implants used during the surgery. Any suitable optical sensor(s) may be used. The optical sensor(s) may be provided as part of an optical system connectable to computing device  210 . In some embodiments, the optical sensor(s)  220  are infrared sensors. The sensor(s)  220  may be provided as part of one or more cameras for capturing images of the trackable member  120 . In some embodiments, the optical sensor(s)  220  are structured light cameras and/or motion sensing input devices. The optical sensor(s)  220  may be configured to identify and/or track the position and/or orientation of the detectable element(s)  122  of the trackable member  120 . With some other tracking modalities, the trackable member  120  may not be required, or may take another form. For example, structured light cameras and/or motion sensing input devices used as the optical sensor(s)  220  may track the surgical device  100  without additional trackable member. The trackable members may be other recognizable features, including patterned labels, etc. Alternatively, the computing device  210  may be able to identify and/or track the detectable element(s)  122  from the data (e.g., images) acquired by the optical sensor(s)  220 . Accordingly, the CAS system  200  is able to detect the position and/or orientation of the surgical device  100 , such as via the trackable member  120  if present through its movement (e.g., the position of each of the detectable element(s)  122 ), to then compute a position and/or orientation of the surgical device  100  and/or of the spinal screw  130  using the tracking of the surgical device  100 , such as via the trackable member  120 , and the geometrical relation between the trackable member  120  (if present), the surgical device  100  and spinal screw  130 . Similarly, the CAS system  200  may be able to detect the position and/or orientation any other surgical tools and/or implants used during the surgery. The computing device  210  may obtain the images of the trackable member  120  or any other surgical tools and/or implants from the optical sensor(s)  220  or generate images based on data received from the sensor(s)  220 . The images depicting the trackable member  120  or any other surgical tools and/or implants may be displayed on the display device  230  via the GUI. 
     In some embodiments, the CAS system  200  comprises a robotic arm  240  for controlling the position and orientation of the surgical device  100 , though the tracking may also be done in free hand mode as well. Alternatively, the CAS system  200  may be connected to an external robotic arm  240  via the computing device  210 . The robotic arm  240  is adapted for holding the surgical device  100 . The robotic arm  240  of  FIG. 2  is an example of an arm that may be used with the surgical device  100  being connected to an effector end of the robotic arm  240 . In an embodiment, the robotic arm  240  may provide 6 DOFs (position and orientation) of movement to the effector end, though fewer or more may be possible. In an embodiment, the robotic arm  240  is used in a collaborative mode, as manipulated by a user, with the possibility to provide some movement constraints, such as blocking the joints of the robotic arm. The robotic arm  240  of  FIG. 2  may for example be as described in United States Patent Application Publication No. 2018/0116758, incorporated herein by reference. In such a configuration, the robotic arm  240  may automatically lock in a collaborative mode, once a user is satisfied with the orientation of the surgical device  100 . 
     The position of the robotic arm  240  and the position of the surgical device  100  may also be controlled by interacting with the GUI displayed on the display device  230  via the input device(s). The computing device  210  may accordingly control movements of the robotic arm  240  and the surgical device  100  during the surgery, as requested by the surgeon via the computing device  210  and/or according to an preprogrammed process. In alternative embodiments, the robotic arm  240  may be omitted and the surgeon may manual control the position and orientation of the surgical device  100 . 
     In some embodiments, the CAS system  200  includes an imaging system  250  for obtaining images of anatomy of a patient, for example intra-operatively. Alternatively, the CAS system  200  may be connected to an external imaging system  250  via the computing device  210 . As shown in  FIG. 2 , the anatomy being imaged comprises a spinal column  10 , and in particular, a spinal column  10  comprising vertebrae  12 , where each vertebra  12  has two pedicles  14 . The imaging system  250  may be an X-ray imaging system for providing X-ray images. The X-ray images may be fluoroscope x-ray shots. The imaging system  250  may be a computed tomography (CT) imaging system for providing CT scans. The imaging system  250  may also be an ultrasound imaging system for providing ultrasound images. Any other suitable imaging system may be used. The imaging system  250  may be configured to provide images from different perspectives. For example, the imaging system  250  may provide images from two perspectives, such as a lateral perspective and a posterior perspective. The images may be taken with a C-arm in order to obtain lateral and posterior or anterior images. The images may obtained prior to the spinal surgery and/or intra-operatively during the spinal surgery. For example, images of the spine  10  and of the surgical device  100  may be obtained before alterations to vertebrae. By way of an example, images of the spine  10  and of the surgical device  100  may be obtained intraoperatively with the spinal screw  130  implanted in a vertebra  12 . The computing device  210  may obtain the images from the imaging system  250  and the images may be displayed on the display device  230  via the GUI. 
     The CAS system  200  may be configured to determine the 3D orientation and optionally position of the surgical device  100  relative to the spine  10 . Determining the 3D position and/or orientation of the surgical device  100  may include any one or more of the following: determining the position and/or orientation of the attachment member  110 , determining the position and orientation of the trackable member  120  and determining the position and orientation of the spinal screw  130 , for example relative to a vertebra(e). The images from the imaging system  250  may be processed at the computing device  210  in order to determine the 3D position and/or orientation of the surgical device  100  relative to the spine  10 . 
     The CAS system  200  may determine the position and/or orientation of the surgical device  100  relative to the spine  10  prior to incision of soft tissue, or with a minimally invasive incision that exposes only a part of a vertebra, for example. For example, the robotic arm  240  may be used to hold the surgical device  100  in place for the spinal surgery, at an approximate position and orientation of a desired trajectory of the spinal screw  130 . Images from the imaging system  250  may be processed at the computing device  210  to determine the 3D position and orientation of the surgical device  100  relative to the spine  10  at that approximate position and orientation, prior to bone alteration. Assuming that the patient is still, as expected during such surgery, and using appropriate imaging modality so as not to have to move the patient (e.g., C-arm), images of the spine  10  and of the surgical device  100  may be obtained, and correlated to tracking data from the computing device  210  at the instant of the imaging. This may be achieved by appropriate synchronization techniques (e.g., using internal clock or time stamps). This allows the CAS system  200  to locate the surgical device  100  and the spine  10  in the same coordinate system (a.k.a., referential system, frame of reference, etc), for subsequently tracking the surgical device  110  relative to the spine  10 , in position and orientation, with the movements of the surgical device  110  being tracked by the sensor  220 . The above may require some additional steps by the computing device  210 , some of which may include obtaining or generating 3D models of the spine  10  using for example a bone atlas, or preoperative models of the spine  10  specific to the patient, merging existing models of the spine to the images, etc. In some embodiments, the images from the imaging system  250  may be processed at the computing device  210  to determine the anticipated 3D position and orientation of the spinal screw  130  relative to the spine  10 , using geometrical relations described above. The 3D position and orientation of the surgical device  100  may thus be determined based on the known configuration of the surgical device  100  (e.g., the length of the attachment member  110 , the position of the trackable member  120  on the attachment member  110  if present, and/or the configuration of the trackable member  120 , the coupling configuration between the attachment member  110  and the screw  130 , etc.), whereby it is possible to determine the position and trajectory of the screw  130 . This may be done during the placement of the screw  130  into a vertebra. Consequently, data from the optical sensor(s)  220  may be processed by the computing device  210  to obtain position information of the attachment member  110 , for example via the trackable member  120 . Based on the position information of the trackable member  120  and the 3D position of the surgical device  100  as determined from the images, the 3D position of the surgical device  100  relative to the spine  10  may be tracked by the CAS system  200  throughout surgery. Assuming that the patient does not move, the position of the surgical device  100  relative to the spine  10  may be determined at the CAS system  200  based on the data from the optical sensor(s)  220 . The surgical device  100  may then be used to implant the spinal screw  130  into a vertebra  14  of the spine  10 . This arrangement may cause the surgery to be less invasive, notably because an operator does not need to physically see the trajectory of the screw  130 , relying instead on the combination of imaging and tracking. For this purpose, the surgical device  100  may be coated with radiopaque material to have a high contrast definition when imaged by the imaging system  250 . 
     The CAS system  200  may thus determine the position and orientation of the surgical device  100  relative to the spine  10  as the spinal screw  130  is implanted in a vertebra  12 . As another possibility, once the spinal screw  130  is inserted in a pedicle  14  of a vertebra  12  with the surgical device  100 , the position and orientation of the surgical device  100  relative to the spine  10  may be determined using the geometrical relations described above. 
     The 3D position and orientation of the surgical device  100  relative to the spine  10  may be registered (e.g., stored at the computing device  210 ) in order to create a position and orientation reference of the surgical device  100 . The registration of the 3D position and orientation may occur prior to or after implantation of the spinal screw  130  in a vertebra  12  of the spine  10 . The registered 3D position and orientation of the surgical device  100 , and/or the spinal screw  130 , may provide a position and orientation reference used during subsequent steps of the surgery. For example, the screw  130  may be a first inserted screw for the surgery and using the position and orientation reference of the screw  130 , the position and orientation of subsequent implants (e.g., screws, other devices, etc.) may be determined and displayed on the display device  230 . 
     The CAS system  200  may be configured to generate a 3D coordinate system X-Y-Z relative to the spine  10 . Data from the optical sensor(s)  220  may be processed by the computing device  210  to obtain the position and orientation information of the surgical device  100 , for example via the trackable member  120 . Based on the 3D position and orientation of the surgical device  100  relative to the spine  10  as determined from the images of the imaging system  250 , a 3D coordinate system X-Y-Z relative to the spine  10  may be generated at the computing device  210 . 
     The CAS system  200  may be configured to track the spine  10  once the spinal screw  130  is implanted in a vertebra  12  of the spine  10 . Accordingly, the CAS system  200  may be configured to track the spine  10  once the surgical device  100  is coupled to the spine  10  via the spinal screw  130 . The CAS system  200  may be configured to identify and/or track the position and orientation of the spine  10  based on the position and orientation reference of the surgical device  100  (or spinal screw  130 ) for example via the position information of the trackable member  120  and. In some embodiments, the position and orientation of the spine  10  may be identified and tracked by the CAS system  200  in the 3D coordinate system X-Y-Z. More specifically, data from the optical sensor(s)  220  may be processed by the computing device  210  to identify the position and orientation of the surgical device  100  and hence the spine  10  in the 3D coordinate system X-Y-Z. This may provide the surgeon with an accurate representation of the position and orientation of the spine  10  during the surgery. 
     The CAS system  200  may be configured to identify and/or track one or more surgical tools and/or implants. The surgical tool(s) and/or implant(s) may be identified and/or track based on the position and orientation reference of the surgical device  100  (or spinal screw  130 ). For example, the surgical tool(s) and/or implant(s) may be identified and tracked by the CAS system  200  in the 3D coordinate system X-Y-Z. More specifically, data from the optical sensor(s)  220  may be processed by the computing device  210  to identify a surgical tool (or an implant) and the 3D position and orientation of the surgical tool (or the implant) in the 3D coordinate system X-Y-Z may be determined. The position and orientation of the surgical tool (or the implant) relative to the images of the spine  10  may be displayed on the display device  230 . This may provide the surgeon with an accurate representation of the position and orientation of the surgical tool (or the implant) relative to the spine  10 . 
     In some embodiments, the surgical device  100  may be moved along the vertebrae as multiple surgical screws are implanted, while performing the identification and/or tracking described herein. The attachment member  110  may be configured to decouple from an implanted surgical screw in order to be used for implanting another surgical screw. Accordingly, multiple surgical screws may be implanted in multiple pedicles of the vertebrae with the surgical device  100 . The surgical device  100  may have a release mechanism adapted to cause the attachment member  110  to decouple for an implanted surgical screw. The surgical device  100  may be slid off of the screw  130 , for example. The surgical device  100  may then be used to implant another surgical screw. The surgical device  100  may be used with one or more implants used for interconnecting one or more vertebrae, for example, such as one or more of the implants described in U.S. Pat. No. 7,107,091, the contents of which are hereby incorporated by reference. The imaging of the patient&#39;s spine may be updated each time a new surgical screw is implanted, may occur continuously during the surgery, or may be updated at any regular interval or irregularly. Based on the updated imaging, the CAS system  200  may be able to update the 3D position and orientation of the surgical device  100  relative to the spine  10  and continue the identification and/or tracking described herein. Imaging may not need to be updated when multiple spinal screws are implanted with the surgical device  100 , for example, when the patient does not move. 
     In some embodiments, the CAS system  200  may be configured to create an anatomical model with either pre-operative images and/or with intra-operative images of the patient, which is displayed on the display device  230  during the surgery. The anatomical model may be used in place or in conjunction with the images from the imaging system  250  to determine the position and orientation reference. The anatomical model of the spine  10 , the intra-operative images of the spine  10 , the position and orientation of the surgical device  100  and/or the position and orientation of the surgical tool(s) and/or implant(s) may be displayed on the display device  230  during the surgery. 
     With additional reference to  FIG. 3 , there is shown a flow diagram illustrating an example of a computer-assisted surgical process  300  performed with the surgical device  100  and the CAS system  200 . At step  302 , a surgeon makes an initial incision for spinal surgery on a patient. This initial incision may be a minimally invasive incision. At step  304 , the surgeon estimates a position and/or orientation of the pedicle  14  of a given vertebra  12  of the spine  10  of the patient using the surgical device  100 , and uses a tool, just as the surgical device  100 , in an approximate desired position and trajectory of a spinal screw. It may be possible to have a robotic arm, such as robotic arm  240 , hold the surgical device  100  in place in the desired position and orientation. At step  306 , images of the patient are obtained at the CAS system  200 . The images of the patient may be obtained with the image system  250 . The obtained images may include X-ray images obtained with a C-arm. In some embodiments, the registration of the 3D position and orientation of the surgical device  100  relative to spine  10  and/or any planning (e.g., an anatomical model generated with pre-operative images) may occur at step  306 . The registration may be automatic and entails a combination of the instant images and tracking output from the CAS system  200 , to locate the spine  10  and the surgical device  100  in a 3D common coordinate system, as explained above. 
     In an embodiment, the automatic registration includes using the anatomical model generated with pre-operative images and/or modelling techniques, such as a 3D model of the spine  10 , and registering the 3D model of the spine  10  with the images from the image system  250 . For example, U.S. Pat. No. 9,826,919, incorporated herein by reference, describes a method and system for generating a display of a tracked object relative to a vertebra, and includes the combination of radiographic images with models. As another possibility, the automatic registration includes a Digitally Rendered Radiographs (DRR) technique, by which a 3D pre-operative model is matched to the 2D images from the image system  250 . As part of the image processing performed by the registration, the geometry of the surgical device  100 , or like pointer tool, may be taken into consideration. The geometry of the surgical device  100  or like pointer tool may be known pre-operatively, and the geometry of the device  100  is additional data that may be used in the sizing and scaling computations. Other steps may be required, though optionally, such as the registration of prominent features of vertebrae, such as the spinous process, by the operator or robotic arm  420 , to contribute to or confirm the registration of the spine  10  in the referential system. Consequently, the registration may not be fully automatic, as some verification steps or additional data gathering steps may be required. Upon completion, the registration provides the known position and orientation of the spine  10  in the virtual referential system tracked by the CAS system  200 , such that subsequent tracking of devices by the CAS system  200  is relative to the spine  10 . 
     Once the 3D position and orientation of the surgical device  100  relative to spine  10  is registered, the position and orientation of surgical device  100  may be tracked by the CAS system  200  with additional use of the optical sensor(s)  220 , the tracking being for instance continuous and in real-time. The position and orientation of surgical device  100 , or any other instrument may thus be tracked during movement of the surgical device  100  using the tracking of the trackable member  120  and the geometrical relation between the trackable member  120 , if present, the surgical device  100  and spinal screw  130 . At step  308 , the surgical device  100  is used to insert into the patient the spinal screw  130 . This may involve the tracking of a drilling tool  308 A or any other tool to make a hole at a desired trajectory in the vertebra  12 . This may entail that the patient has not moved from registration to positioning of the screw  130 . For instance, at step  308 , the surgical device  100  may be navigated by controlling the robotic arm  240  to move the position and orientation of the surgical device  100  or drilling tool  308 A into a position for inserting the spinal screw  130 . This may occur in collaborative mode as well, with a user manipulating the surgical device  100  and spinal screw  130 , with navigation data provided via the GUI  230 , for example. The robotic arm  240  may then lock the surgical device  100  in a desired trajectory for the spinal screw  130 . At step  312 , the spinal screw  130  is inserted. For example, after the drilling tool  308 A is navigated into the desired position and orientation as per a pre-operative plan or based on operator decisions, a hole for the spinal screw  130  may be drilled and tapped in a vertebra  12 , and in particular a pedicle  14 , per the pre-operative plan. The spinal screw  130  may then be implanted in the hole. At step  312 , one or more dilators  310 A are placed over the surgical device  100 . The dilator  310 A may be a tube, such as with a tapered end, that may be used to push or pull soft tissue away from the hole in the vertebra. The dilator  310 A may be slid onto a drill bit, drill pin of the drilling tool  308 A as a possibility. The surgical device  100  may be used to drill and/or implant the spinal screw  130  into the vertebra  12 . This may occur with the dilator  310 A in place. Once the surgical device  100  is attached to the vertebra  12  via the spinal screw  130 , the position and orientation of the spine  10  may be tracked by the CAS system  200 , with reference to the surgical device  100  remaining connected to the vertebra  12 . The position and orientation of the spine  10  may be tracked using the tracking of the trackable member  120  and the geometrical relation between the trackable member  120 , the surgical device  100  and spinal screw  130 , or directly by tracking the surgical device  100  if tracking modality permits. Similarly, once the surgical device  100  is attached to the vertebra  12  via the spinal screw  130 , the position and orientation of one or more surgical tools and/or implants may be tracked by the CAS system  200 . For example, additional spinal screws  130  are added to other vertebrae  14 , along some of the actions taken in steps  302 - 312  described above, but with or without imaging as per step  304 , as the tracking of the surgical device  100  anchored to a vertebra  14  may provide the tracking accuracy for the subsequent alterations steps to be performed. The steps of the process  300  may vary depending on practical implementations, as the order of the steps may vary and/or some steps may be omitted and/or combined. For example, the images of patent at step  306  may occur at one or more different steps of the process  300 . By way of another example, the other of step  302  and  304  may be reversed. Other modifications are possible. Hence, in a variant, the surgical device  100  as connected to a vertebra  14  via a spinal screw  130  may serve as tracking reference for the tracking of other tools (e.g., the drilling tool  308 A) performing alterations on other vertebrae  14 . 
     With reference to  FIG. 4 , there is shown a flowchart illustrating an example method  400  for a computer-assisted surgical process. The method  400  may be at least in part implemented by the computing device  210  associated with the CAS system  200 . It should be appreciated that aspects of the process  300  and the method  400  may be combined, as one or more the steps of the method  400  may occurring during one or more steps of the process  300 . 
     Step  402  of the method  400  includes obtaining a surgical device  100  including an attachment member  110  adapted for coupling to a spinal screw  130 . The attachment member  110  may have a trackable member  120  coupled to the attachment member  110 , or may be trackable without a trackable member  120 . The surgical device  100  may configured as described elsewhere in this document. Other tools may be obtained such as a registration pointer-like tool or drilling tool having a configuration similar to that of the surgical device  100 . For example, such tool may have an elongated shape with a central axis that emulates the surgical device  100  with the screw  130 . The tool may be the surgical device  100  without screw  130 . 
     Step  404  of the method  400  includes obtaining, at a CAS system  200 , images of the spine  10  and the surgical device  100  or like tool. The images may be obtained from the imaging system  250 . The images of the spine  10  may be X-ray images providing both a lateral and posterior or anterior perspective of the spine  10 , such as those provided by a C-arm. In the image, the spine  10  is spatially correlated to the surgical device  100  or like tool. In a variant, the surgical device  100  or like tool is positioned and oriented at an estimated drilling trajectory within a given vertebra. 
     Step  406  of the method  400  includes determining, at the CAS system  200 , a 3D position and orientation of the surgical device  100  or like tool relative to the spine  10  from the images of the spine  10  and the surgical device  100 , in a referential system (e.g., a X,Y,Z coordinate system). This may include a determination of the 3D position and orientation of the attachment member  110 , the trackable member  120 , and/or the spinal screw  130  relative to the spine  10 . The 3D position and orientation of the surgical device  100  may be used to provide a position and orientation reference of the surgical service  100 , i.e., to set the position and orientation of a trackable tool relative to the spine  10  in the referential system. The 3D position and orientation of the attachment member  110 , the trackable member  120  (if present), and/or the spinal screw  130  may be used to provide a position and orientation reference. From that point on, real-time tracking of any tool, including the surgical device  100 , may be performed, for instance by the CAS system  200 . 
     Step  408  of the method  400  includes obtaining, at the CAS system  200 , position and orientation information of the surgical device  100 , as the surgical device  100  moves relative to the spine  10 , or of other surgical devices such as a drill. Stated differently, devices such as the surgical device  100  may be moved relative to the spine  10 , and the position and orientation of the tool may be output relative to the spine  10 . Obtaining the position and orientation information of the surgical device  100  may include obtaining position information of the trackable member  120 . The position and orientation information of the surgical device  100  may be determined from the obtaining position information of the trackable member  120 . The position information may be provided by an optical system including the one or more optical sensors  220  or may be determined at the CAS system  200  based on data obtained by one or more optical sensors  220 . In some embodiments, the method  400  includes tracking the position and orientation of the surgical device  100  based on the position and orientation information of the surgical device  100  and the 3D position and orientation of the surgical device  100  as determined per step  406 . The position and orientation of the surgical device  100  may be tracked using the tracking of the trackable member  120 —or the tracking of the attachment member  110  directly—and the geometrical relation between the trackable member  120  if present, the surgical device  100  and spinal screw  130 . The tracking may be continuous, or may be in continuous periods. 
     Step  410  of the method  400  includes attaching the surgical device  100  to a vertebra  12  of a spine  10  via the spinal screw  130  implanted in the vertebra  12 . In some embodiments, the surgical device  100  is attached to the spinal screw  130  after the spinal screw  130  is implanted in the vertebra  12 . In some embodiments, the spinal screw  130  is implanted in the vertebra  12  with the surgical device  100  having the spinal screw  130  coupled thereto. In an embodiment, step  410  includes tracking tool tapping a hole in the vertebra  12  using trajectory angles obtained by the tracking of step  408 , prior to securing the surgical device  100  to the vertebra  14  via the spinal screw  130 . Step  408  may occur continuously during step  410 , with step  410  being guided by the data provided in step  408 . A drilling tool  308 A ( FIG. 3 ) may be used and tracked for drilling the vertebra on the desired trajectory. The robotic arm  240  may be controlled to preserve a desired trajectory. The trajectory may be as planned, or as decided by an operator (e.g., surgeon) based on the navigation output of step  408 . Once the hole is drilled, a dilator (e.g.,  310 A,  FIG. 3 ) may space surrounding soft tissue away from the hole, for the spinal screw  130  to then be screwed in via the surgical device  100 . The surgical device  100  may then remain anchored during surgery to define a trackable reference of the spine  14 . 
     Step  412  of the method includes tracking, at the CAS system  200 , the spine  10  based on the position and orientation information of the surgical device  100  (e.g., position information of trackable member  120 ) and the 3D position and orientation of the surgical device  100 . The optical sensor(s)  220  (or the optical system) may be used to sense the position and orientation of the surgical device  100  and the spine  10  may be tracked based on this information of the surgical device  100 . The position and orientation of the spine  10  may be tracked using the tracking of the trackable member  120  and the geometrical relation between the trackable member  120 , the surgical device  100  and spinal screw  130 , and the known position and orientation of the spinal screw  130  implanted in the spine  10 . 
     In some embodiments, the method  400  includes tracking, at the CAS system  200 , one or more surgical tools or implants relative to the spine  10  based on the 3D position and orientation of the surgical device  100  (e.g., the position and orientation reference) and the position and orientation information of the surgical device  100  (e.g., the position information of trackable member  120 ). The optical sensor(s)  220  (or optical system) may be used to sense the surgical tool(s) or implant(s) and the position of the surgical tool(s) or implant(s) relative to the spine  10  may accordingly be determined. For example, additional spinal screws  130  are added to other vertebrae  14 , but with or without imaging as per step  404 , as the tracking of the surgical device  100  anchored to a vertebra  14  may provide the tracking accuracy for the subsequent alterations steps to be performed. The surgical device  100  as connected to a vertebra  14  via a spinal screw  130  may serve as tracking reference for the tracking of other tools (e.g., the drilling tool  308 A) performing alterations on other vertebrae  14 . The robotic arm  240  may assist in holding the surgical device  100  during such other alterations. In an embodiment, the tracking steps of  408  and  412  are performed by the continuous operation of the sensor(s)  220 . 
     In an embodiment, the devices and methods described herein may render the spinal surgery less invasive, as the use of the spinal screw(s)  130  as an attachment for a trackable device (e.g., the surgical device  100  via its attachment member  110 , with or without the trackable member  120 ) may limit the incision to the vertebra (with dilators optionally present to assist). Moreover, because of the accuracy of the surgical device  100  remaining on the spinal screw  130 , smaller incisions may be made at other vertebra(e)  14  for alterations and installation of other spinal screws  130 . The surgical device  100 , or other tool, with or without the trackable member  120 , becomes a trackable reference. 
     The method  400  may further comprise generating a 3D coordinate system X-Y-Z relative to the spine  10  in a manner as described elsewhere in this document. Accordingly, the tracking of the spine  10  and/or of the surgical tool(s) or implant(s) may occur in the 3D coordinate system X-Y-Z. The tracking information may be output for display on the display device  230 . For example, the position and orientation of the spine  10  and/or the position and orientation of the surgical tool(s) or implant(s) relative to the spine  10  may be displayed. The steps of the method  400  may vary depending on practical implementations, as the order of the steps may vary and/or some steps may be omitted and/or combined. 
     It should be appreciated that by performing the surgery with the surgical device  100  and/or the CAS system  200  that the invasiveness of the surgery may be reduced or minimized as additional surgical openings for a reference and/or tracking device may be omitted. 
     While the embodiments and examples described above relate to use of the surgical device  100  and the CAS system  200  in a spinal surgery, the device  100 , the CAS system  200 , the process  300  and the method  400  may be adapted for any other suitable surgery where a screw is inserted into a bone and tracking of a bone, surgical tools and/or implants are desired. 
     With reference to  FIG. 5 , at least in part, the process  300  and/or the method  400  may be implemented by a computing device  210 , comprising a processing unit  512  and a memory  514  which has stored therein computer-executable instructions  516 . The processing unit  512  may comprise any suitable devices configured to implement at least in part the process  300  or the method  400  such that instructions  516 , when executed by the computing device  210  and/or other programmable apparatus, may cause the functions/acts/steps performed as part of the process  300  and/or the method  400  as described herein to be executed. The processing unit  512  may comprise, for example, any type of general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, a central processing unit (CPU), a graphical processing unit (GPU), an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, other suitably programmed or programmable logic circuits, or any combination thereof. 
     The memory  514  may comprise any suitable known or other machine-readable storage medium. The memory  514  may comprise non-transitory computer readable storage medium, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. The memory  514  may include a suitable combination of any type of computer memory that is located either internally or externally to device, for example random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like. Memory  514  may comprise any storage means (e.g., devices) suitable for retrievably storing machine-readable instructions  516  executable by processing unit  512 . 
     The methods and systems described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device  210 . Alternatively, the methods and systems described herein may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods and systems may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or special-purpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the methods and systems may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or in some embodiments the processing unit  512  of the computing device  210 , to operate in a specific and predefined manner to perform the functions described herein. 
     Computer-executable instructions may be in many forms, including program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types. Typically the functionality of the program modules may be combined or distributed as desired in various embodiments. 
     Examples 
     The following examples can each stand on their own, or can be combined in different permutations, combinations, with one or more of other examples. 
     Example 1 is a method for spine tracking in computer-assisted surgery, the method comprising: obtaining, at a computer-assisted surgical system, at least one image of at least part of the spine and at least one surgical device; determining, at the computer-assisted surgical system, a three-dimensional position and orientation of the at least one surgical device relative to the spine from the at least one image to create a referential system; tracking, at the computer-assisted surgical system, the at least one surgical device altering a first vertebra of the spine for attachment of a spinal screw to the first vertebra, in the referential system; and tracking, at the computer-assisted surgical system, the spine in the referential system with a trackable reference attached to the spinal screw of the first vertebra. 
     In Example 2, the subject matter of Example 1 includes, wherein tracking the spine in the referential system includes tracking the at least one surgical device altering at least a second vertebra of the spine. 
     In Example 3, the subject matter of Example 2 includes, wherein tracking the at least one surgical device altering at least the second vertebra of the spine is performed without additional obtaining at least one image. 
     In Example 4, the subject matter of Examples 1 to 3 includes, wherein tracking the spine in the referential system includes tracking the trackable reference being a surgical device used to screw the spinal screw in the first vertebra. 
     In Example 5, the subject matter of Examples 1 to 4, including controlling a robotic arm to hold the trackable reference fixed. 
     In Example 6, the subject matter of Examples 1 to 5 includes, wherein obtaining at least one image includes obtaining at least one image with a C-arm. 
     In Example 7, the subject matter of Examples 1 to 6 includes, wherein obtaining at least one image includes generating a model of the spine using the at least one image. 
     In Example 8, the subject matter of Example 7 includes, wherein generating the model includes using an existing bone model with the at least one image. 
     In Example 9, the subject matter of Examples 1 to 8 includes, wherein tracking the at least one surgical device includes outputting a GUI display of the at least one surgical device relative to the spine. 
     Example 10 is a system for spine tracking in computer-assisted surgery, the system comprising: a processing unit; and a non-transitory computer-readable memory having stored thereon program instructions executable by the processing unit for: obtaining at least one image of at least part of the spine and at least one surgical device; automatically registering a three-dimensional position and orientation of the at least one surgical device relative to the spine from the at least one image to create a referential system; tracking the at least one surgical device altering a first vertebra of the spine for attachment of a spinal screw to the first vertebra, in the referential system; and tracking the spine in the referential system with a trackable reference attached to the spinal screw of the first vertebra. 
     In Example 11, the subject matter of Example 10 includes, wherein tracking the spine in the referential system includes tracking the at least one surgical device altering at least a second vertebra of the spine. 
     In Example 12, the subject matter of Example 11 includes, wherein tracking the at least one surgical device altering at least the second vertebra of the spine is performed without additional obtaining at least one image. 
     In Example 13, the subject matter of Examples 10 to 12 includes, wherein tracking the spine in the referential system includes tracking the trackable reference being a surgical device used to screw the spinal screw in the first vertebra. 
     In Example 14, the subject matter of Examples 10 to 13, including controlling a robotic arm to hold the trackable reference fixed. 
     In Example 15, the subject matter of Examples 10 to 14 includes, wherein obtaining at least one image includes obtaining at least one image with a C-arm. 
     In Example 16, the subject matter of Examples 10 to 15 includes, wherein obtaining at least one image includes generating a model of the spine using the at least one image. 
     In Example 17, the subject matter of Example 16 includes, wherein generating the model includes using an existing bone model with the at least one image. 
     In Example 18, the subject matter of Examples 10 to 17 includes, wherein tracking the at least one surgical device includes outputting a GUI display of the at least one surgical device relative to the spine. 
     In Example 19, the subject matter of Examples 10-18, including the at least one surgical device. 
     In Example 20, the subject matter of Example 19 includes, wherein the at least one surgical device includes a drilling tool. 
     In Example 21, the subject matter of Examples 19 to 20 includes, wherein the at least one surgical device includes a surgical device having an attachment tool for connection to the spinal screw. 
     In Example 22, the subject matter of Example 21 includes, wherein the attachment tool includes a rotor in a hollow tube for rotatably receiving a connector on the spinal screw. 
     In Example 23, the subject matter of Examples 10-22, further including at least one sensor device for tracking the at least one surgical device. 
     In Example 24, the subject matter of Example 23, further including at least one trackable member secured to the at least one surgical device and trackable by the at least one sensor device. 
     In Example 25, the subject matter of Examples 10-24, further including at least one imaging system for obtaining the image. 
     In Example 26, the subject matter of Example 14, further including the robotic arm. 
     Example 27 is an assembly for spine tracking in computer-assisted surgery, the assembly comprising: a spinal screw having a connector; a surgical device including an attachment member for coupling to the spinal screw, and a trackable member coupled to the attachment member, the trackable member including at least one detectable element for being tracked in three-dimensional space by a computer-assisted surgical system, thereby allowing tracking position and orientation of a spine by the computer-assisted surgical system when the attachment member is coupled to the spinal screw implanted in a vertebra of the spine. 
     In Example 28, the subject matter of Example 27 includes, wherein the connector has a pair of elongated tabs. 
     In Example 29, the subject matter of Examples 27 and 28 includes, wherein the attachment member includes a tube for housing the pair of elongated tabs. 
     In Example 30, the subject matter of Example 29 includes, wherein the attachment member includes a rotor within the tube. 
     In Example 31, the subject matter of Example 30 includes, wherein the rotor has flats for coupling engagement with the elongated tabs. 
     In Example 32, the subject matter of Examples 30 and 31 including a handle for rotating the rotor. 
     The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Still other modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure. 
     Various aspects of the methods, systems and devices described herein may be used alone, in combination, or in a variety of arrangements not specifically discussed in the embodiments described in the foregoing and is therefore not limited in its application to the details and arrangement of components set forth in the foregoing description or illustrated in the drawings. For example, aspects described in one embodiment may be combined in any manner with aspects described in other embodiments. Although particular embodiments have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from this invention in its broader aspects. The scope of the following claims should not be limited by the embodiments set forth in the examples, but should be given the broadest reasonable interpretation consistent with the description as a whole.