Abstract:
Described herein is one or more implementations for a percutaneous spinal registration-and-access tool for minimally invasive spinal surgery involving lumbar pedicle screw fixation and registration (which is the set-up process for spinal computer navigation). This spinal registration-and-access tool aids registration by allowing more precise targeting of the spinous process (of the vertebrae) and safe working channel for percutaneous placement of a sharp tool (e.g., a bone pin) through the protected subcutaneous tissue.

Description:
BACKGROUND  
       [0001]     In spinal surgery, implant screws or “pedicle screws” are often utilized to stabilize the spine. Typically, these pedicle screws are driven through the pedicles and connected adjacently by rods to manipulate and stabilize the spine during fusion between the bony segments of the spine. Pedicles are two cylindrical or ovoid bones that extend posteriorly from the dorsal surface of the vertebral bodies. Placing these implant screws is typically referred to as “lumbar pedicle screw fixation.” Conventional technique for lumbar pedicle screw fixation involves an open exposure and expanded muscle dissection in order for the surgeon to have a clear and unobstructed access to the spine.  
         [0002]     During a back surgery that targets these lumbar pedicles, the entry point into the back is open and exposed. This exposure may lead to extensive blood loss, muscle disruption, post-operative morbidity, lengthy hospital stays, recovery and/or significant costs. In response to this, spinal surgeons and industry have developed minimally invasive surgical (MIS) techniques and technologies, such as posterior fixation delivery devices that enable percutaneous (i.e., “effected or performed through the skin”) placement of pedicle screws and rods.  
         [0003]     MIS spine techniques do offer significant benefits over traditional spinal approaches. These benefits include reduction in the blood loss, smaller incisions, muscle sparring approaches, shorter hospital stays, and similar to less complications in well experienced institutions. However, MIS techniques also reduce the visibility of the surgical field and thus make it more difficult for the surgeon to directly visualize the anatomy.  
         [0004]     Consequently, when using MIS techniques, surgeons often rely on live fluoroscopic guidance or other equivalent surgical navigation tools. With fluoroscopic X-ray guidance, a surgeon can see the internal structure of opaque objects (such as the living body) by means of the shadow cast by the object examined upon a fluorescent screen when placed between the screen and a source of X-rays. In modern surgery, it&#39;s the use of an intraoperative fluoroscope, commonly referred to as a C-arm for real-time x-ray image updates.  
         [0005]     Dependence on fluoroscopic guidance for MIS techniques may lead to increased fluoroscopic times. This means that the patients, the surgeon (especially his-hands, and OR staff are exposed to increased levels of X-ray radiation). Moreover, in order to produce these two-dimensional or even three-dimensional views of the anatomy in single or multiple planes, “snapshots” or control shots may be frequently used. Doing this also increases the X-ray-exposure time. In addition, there are other ergonomic challenges with a “C-arm” (fluoroscopic guidance) and these challenges increase the X-ray exposure and risks of contamination to the sterile field.  
         [0006]     To enhance and enable these least invasive approaches while minimizing the radiation and sterilization exposure risks, “virtual fluoroscopy” technology can often be employed. Virtual fluoroscopy technology uses calibration and tracking sensor devices that attach to both the C-arm and the patient. The surgeon then prepares to perform a lumbar pedicle screw fusion for target regions of the spine. To prepare for navigation, first a reference “sensor” device is attached to the spinous process via a bone pin or clamp. This is performed through an existing or additional small incision in the back for MIS procedures. The incision in open procedures must be spread wide enough for the surgeon to see, guide, and place both the reference sensor and the implant screws into the pedicles. For MIS pedicle screw procedures, the incision is small and requires x-ray targeting to the spine, but when surgical navigation is deployed, incremental fluoroscopic updates are significantly reduced.  
         [0007]     A transmitter is connected to the previously attached reference bone pin or clamp and the surgeon takes and saves to the computer typically two or more different fluoroscopic X-ray views. The calibration device and navigation computer automatically registers the images to the patient&#39;s anatomy. During the MIS procedure, the surgeon is able to use these saved and calibrated images to plan trajectories, locate difficult anatomy, and determine other surgical parameters in near real-time using virtual instruments superimposed over the previously saved images, with out the need for continuous updated fluoroscopic shots. In addition to improved accuracy in multi-view tracking, one key benefit of virtual fluoroscopy is reduced x-radiation dose for the patient and the surgical team, since the need for continuous fluoroscopy is eliminated.  
         [0008]     Conventional approaches to lumbar pedicle screw fixation often require a significant incision and spreading of the open tissue for the surgeon to see the exposed spine and effectively implant the pedicle screw into the spine. In contrast, less invasive percutaneous approaches for MIS requires small key-hole like incisions through the tissue. The rough or sharp edges of the exposed portions of the specific reference pin or screw for the reference transmitter (sensor), can be difficult to place to the target bone by poor direct visualization and may injure this surrounding subcutaneous tissue during placement. In the end, after the surgery, additional injury may be possible to the surrounding tissue by the removal of the fixated reference screw or pin used to hold the reference transmitter (sensor). It is desirable to make these aspects of a nominally minimally invasive technique to be even less invasive. The patient benefits from doing so are by further reduction in the blood loss, tissue trauma, placement and removal times, medication, quicker discharge, and reduced complications.  
       SUMMARY  
       [0009]     Described herein are one or more implementations for a percutaneous spinal registration-and-access tool for minimally invasive spinal surgery involving lumbar pedicle screw fixation and registration (which is the set-up process for spinal computer navigation). This spinal registration-and-access tool aids registration by allowing more precise targeting of the spinous process (of the vertebrae) and a safe working channel for percutaneous placement of a sharp tool (e.g., a bone pin) through the access tool that protects the surrounding subcutaneous tissue.  
         [0010]     This summary itself is not intended to limit the scope of this patent and the appending claims of this patent. Moreover, the title of this patent is not intended to limit the scope of this patent. For a better understanding of the present invention, please see the following detailed description and appending claims, taken in conjunction with the accompanying drawings. The scope of the present invention is pointed out in the appending claims.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     The same numbers are used throughout the drawings to reference like elements and features.  
         [0012]      FIG. 1 a  top view of a percutaneous spinal registration-and-access tool in accordance with one or more implementations described herein.  
         [0013]      FIG. 2  is an elevation view of a percutaneous spinal registration-and-access tool in accordance with one or more implementations described herein.  
         [0014]      FIG. 3  is an isometric view of a percutaneous spinal registration-and-access tool in accordance with one or more implementations described herein.  
         [0015]      FIG. 4  illustrates an elevation view of a cut-away lower portion of a percutaneous spinal registration-and-access tool in accordance with one or more implementations described herein and a cross-section view of a vertebrae—particularly, the spinous process—and a cross-section of some of the tissue surrounding the spinous process.  
         [0016]      FIG. 5  illustrates the same elements depicted in  FIG. 4 . In accordance with one or more implementations described herein, the tool is shown being inserted through an incision and over the spinous process.  
         [0017]      FIG. 6  illustrates the same elements depicted in  FIGS. 4 and 5 . In accordance with one or more implementations described herein, the tool is shown seated onto and over the spinous process.  
         [0018]      FIG. 7  illustrates the same elements depicted in  FIGS. 4 through 6  and a bone pin. In accordance with one or more implementations described herein, a bone pin is shown inserted through the tubular and conical tool for fixation into the spinous process.  
     
    
     DETAILED DESCRIPTION  
       [0019]     One or more implementations, described herein, is a percutaneous spinal registration-and-access tool for minimally invasive spinal surgery involving lumbar pedicle screw fixation and registration (which is the set-up process for spinal computer navigation). This new tool reduces the existing invasiveness of minimal invasive surgical (MIS) techniques for spinal surgery. Further reducing invasiveness of such MIS techniques benefits the patient by further reduction in the blood loss, tissue trauma, set-up times, hospital stays, and other complications.  
         [0020]     During lumbar pedicle screw fixation (such as for virtual fluoroscopy), a bone pin (i.e., registration pin, screw or clamp) is attached to the spine. More specifically, it is attached to a “spinous process” of one or more vertebra of the spine. The “spinous process” is a projection of bone that extends posteriorly from the lateral margin of the dorsal surface of each vertebra. In conventional approaches, an incision is made for each bone pin and then that incision is spread wide by fingers or tiny retractors. With conventional approaches, the incision must be spread wide enough for the surgeon to see, guide, and attach the reference screw to the spinous process of the vertebral spine.  
         [0021]     However, with one or more implementations of the percutaneous spinal registration-and-access tool, the tool is inserted into a small midline incision (e.g., 1 cm) rather than the incision being manually spread wide by fingers or retractors. This tool is a conically and cylindrically shaped rigid cannula and spreads the tissue apart only as much as is necessary for insertion into the incision. The tool is configured to gently “snap” onto the spinous process. Once inserted and fixed to the spinous process, the tool provides a seamless guide tube for the optimal bone pin placement for the registration process.  
         [0022]     This percutaneous spinal registration-and-access tool replaces the difficulty of spreading the incision with tiny retractors or fingers and the tool provides a barrier between the sharp edges of the bone pin that may tear into the surrounding soft tissue during registration pin implantation and removal as well as a thermal barrier.  
         [0023]     This percutaneous spinal registration-and-access tool is likely to decrease complication rates of a non-securely placed bone pin and instead improve placement for a successful registration. The tool will also assist the surgeon to target the spinous process and guide the bone pin at the optimal angle for a better placement. Additionally, the tool will serve as a protective barrier between the sharp bone pin and surrounding soft tissue. In addition it is radioulcent for clear views of the spinal segments during surgical x-ray updates.  
         [0000]     Exemplary Percutaneous Spinal Registration-and-Access Tool  
         [0024]      FIGS. 1-3  show multiple views of exemplary percutaneous spinal registration-and-access tool  100  for minimally invasive spinal surgery involving lumbar pedicle screw fixation. The same references numbers are used in  FIGS. 1-3  to refer to the same parts of the tool  100 . For discussion purposes, the tool  100  is described with reference to  FIGS. 1-3 .  
         [0025]     As depicted in  FIGS. 1-3 , the exemplary percutaneous spinal registration-and-access tool  100  is a self-retaining conical (and/or cylindrical) and largely rigid hollow tube (e.g., cannula). One or more implementations of tool  100  is constructed from radioulency material, such as a radiolucent polymer. This way the tool  100  will not interfere with fluoroscopy. Also, a low-cost material is desirable so that the tool  100  may be a sterile-packaged single-use disposable medical device. Of course, other material that is radioulency and/or low-cost may be used for other implementations.  
         [0026]     The tool  100  has a proximal end  110  with a tubular opening defined by a circular proximal rim  112 . The tubular opening formed by the circular proximal rim  112  forms an opening which is wide enough to easily accommodate manual insertion of a bone pin driver and reference bone pin there through. As depicted, the opening formed by the circular proximal rim  112  has a diameter of approximately 15 mm. The proximal end  110  has a finger tab  114  to provide a convenient hold for the surgeon to and maneuver the tool  100 .  
         [0027]     The tool  100  has a principal tubular body  120  (or cannula) that has a gentle taper towards an open distal end  130 . As depicted, from one end to the other, the tapered tubular body  120  is approximately 22.5 mm long. While other implementations might have a non-tapered cylindrical shape, the implementation depicted in  FIGS. 1-3  does have a slight taper from the proximal to distal ends and thus a generally conical shape. This shape eases the insertion into and the removal from the tissue.  
         [0028]     Herein, “proximal” refers to the potion of the tool which is typically closest to the surgeon during surgery or, alternatively, the portion of the tool which is protruding from the body during surgery. Thus, the proximal end  110  of the tool  100  is the portion of the tool which protrudes from the body during use. Conversely, “distal” refers to the portion of the tool which is typically furthest away from the surgeon during surgery or, alternatively, the portion of the tool which is typically and primarily inside the body during surgery. Thus, the distal end  130  of the tool  100  is the portion of the tool which is inside the body during use.  
         [0029]     At the open distal end  130 , the open tube flares into two lateral bi-valved flanges  132  and  134 . The term “bi-valved” is used herein in a manner similar to the context of surgical endoscopes or retractor technology when one refers to a split-lumen or a tube that has been separated and can move together or independent of the opposite retractor blade. As described herein, the two blades or flanges  132  and  134  are flexible and are open on the sides.  
         [0030]     These lateral flanges are intended to aid in guiding the tool  100  through the tissue and onto the plateau of the spinous process. These flanges  132  and  134  are spring-biased so as to “grip” the spinous process when in use. In addition to gripping, the spring-biased lateral flanges allow the surgeon to maneuver the tool for better targeting of the spinous process without slipping off the bone. The ends of each flanges  132  and  134  —have blunt lips  136  and  138 . These blunt lips are designed to minimize soft tissue resistance and no injury as the tool is passed down through the fascia (i.e., the flat layers of fibrous tissue that separate different layers of tissue), over the bone and between the paraspinous muscles (that is, those muscles around the spinous process).  
         [0031]     The open distal end  130  of the tool  100  defines a circular cavity  140  which is designed to receive the bulbous-shaped spinous process plateau, while the lateral flanges  132  and  134  grip and stabilize the tool  100  from below.  
         [0000]     Percutaneous Spinal Registration-And-Access Tool in Action  
         [0032]      FIGS. 4-7  shows the exemplary percutaneous spinal registration-and-access tool  100  in action. For discussion purposes, the use of the tool  100  is described with reference to  FIGS. 1-3  and  FIGS. 4-7 . Also for discussion purposes, particular components are indicated as performing particular functions; however, it is possible that other components (or combinations of components) may perform the particular functions.  
         [0033]      FIG. 4  shows the lower portion of the exemplary percutaneous spinal registration-and-access tool  100  and a cross-section view  200  of a vertebra  210 —particularly, its spinous process  220 —and of tissue surrounding the spinous process. This tissue include the skin and fascia  230  and the paraspinous muscles  240 . As depicted in  FIG. 4 , there is an incision  232  in the skin and fascia  230  through which the tool  100  may be inserted.  
         [0034]      FIG. 5  shows the same elements as shown in  FIG. 4 , but the tool  100  is partially inserted into the patient&#39;s body. The blunt lips of the lateral flanges  132  and  134  are inserted through the incision  232  in the skin and fascia  230 . The surgeon aims the tool so that the bulbous end  222  of the spinous process  220  goes in between the flanges  132  and  134 . The flanges are slightly spring-biased and give way to the bulbous end  222  of the spinous process  220 . Also, the spring-biased flanges gently dilate the surrounding tissue (e.g., the skin  230  and the paraspinous muscles  240 ) as the flanges slide over and around the spinous process  220 . Once in position, the spring-biased flanges  132  and  134  capture the spinous process  220  in the area between the flanges.  
         [0035]     As the tool  100  is passed percutaneously (i.e., through the skin/tissue) over the spinous process, the two flanges  132  and  134  flare out from approximately 2.4 mm in the closed position and over 50% of the lateral wall of the spinous process and expands up to approximately 8-10 mm. This action functionally serves to both grip and stabilize the tool  100  over the lateral cortexes of the bone.  
         [0036]      FIG. 6  shows the same elements as shown in  FIGS. 4 and 5 , but the tool  100  is fully inserted into the patient&#39;s body. As depicted, the bulbous end  222  of the spinous process  220  is received by the circular cavity  136  of the tool  100  and the spinous process is gripped by the spring-biased flanges  132  and  134 . The circular cavity  140  is designed to receive the bulbous end  222  of the spinous process  220 . The spring-biased lateral flanges  132  and  134  grip and stabilize the tool  100 . As depicted, the spring-biased lateral flanges  132  and  134  may extend to the base of the spinous process  220 . However, under differing conditions (e.g., variations in human anatomy) and with different embodiments, the spring-biased lateral flanges  132  and  134  might not extend all the way down to the base of the spinous process  220 .  
         [0037]      FIG. 7  shows the same elements as shown in  FIG. 6 . Unlike the previous figures,  FIG. 7  illustrates the use of the tool  100  for one of its primary purpose (with at least one implementation). As depicted, a screw/bone pin  300  is shown inside of the tube formed by the tool  100  itself. The tool allows for seamless passage and access of a screw/bone pin  300  and its driver (not shown) to the spinous process. With this access, the surgeon firmly affixes the screw/bone pin  300  to the bulbous end  222  of the spinous process  220 . Once the screw/bone pin  300  is in place rigidly, a reference array (e.g., navigational transmitter) is attached to the pin for the navigational registration process.  
         [0038]     When the surgeon wishes to remove the tool  100 , she simply manually extracts it. The tool is not affixed to the spinous process  220  in a permanent manner like would be the case for an invasive (e.g., screw, staple, etc.) or chemical (e.g., adhesive) attachment mechanism. Instead, the tool  100  is only “gripping” the spinous process  220 . As such, a gentle tug will flare-out the flanges  132  and  134  and dilate the tissue. Then the tool is easily extracted.  
         [0000]     Other Applications, Implementations, and Details  
         [0039]     The discussion herein focuses on the specifics of minimally invasive spinal surgery involving lumbar pedicle screw fixation. However, the tool may be used in many other surgical techniques. Some of those include (but are not limited to): Percutaneous Pedicle Screw Implantation and Fusion, Kyphoplasty, Vertebroplasty, Bone Marrow Aspiration, Bone Biopsy, Micro-Endoscopic Diskectomy and other MIS spinal implantations for interbody fusions including PLIF, TLIF, Facet screws and future—approaches approaches to the disk-space for various device implants or resection tools.  
         [0040]     Although the one or more above-described implementations have been described in language specific to structural features and/or methodological steps, it is to be understood that other implementations may be practiced without the specific features or steps described. Rather, the specific features and steps are disclosed as preferred forms of one or more implementations.