Abstract:
Imaging technology may be used to navigate highly innervated tissue, such as the psoas muscle, while maintaining the neural structures intact. An ultrasound transducer may be introduced into the tissue and an image may be consulted to assess the proximity of the transducer to neural structures. Alternate embodiments contemplate an expanded array of surgical applications and alternate imaging technologies.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Application No. 61/222,187, filed Jul. 1, 2009, entitled ULTRASOUND FOR NAVIGATION THROUGH PSOAS MUSCLE, Attorney&#39;s docket no. MLI-76 PROV, which is pending. 
         [0002]    The above-referenced document is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    Open surgical procedures afford surgeons a direct view of the surgical site and the opportunity to manually dissect superficial body structures covering the surgical site, so as to do minimal collateral damage to those structures. However, as minimally invasive surgical procedures become more popular, issues of surgical access and visualization become more critical. There is a need for apparatus and methods that enable surgeons to safely navigate through body structures to a surgical destination along a route at least partially defined by clinically relevant tissues in the vicinity of the route. 
         [0004]    By way of example, surgeons may navigate through muscle while avoiding damage to nerves by using apparatus and methods that electrically stimulate nerves. However, these apparatus and methods do not provide a visual representation of the nerves or muscle, only a proximity warning similar to the “Hot” and “Cold” warnings used in the familiar childhood game. There remains a need for apparatus and methods that let surgeons see where to place their surgical access route. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only exemplary embodiments of the invention and are therefore not to be considered limiting of its scope. 
           [0006]      FIG. 1  is a cephalad view of an intervertebral disc, a vertebra, a psoas muscle, and a straight probe, with the psoas muscle shown in cross section; 
           [0007]      FIG. 2  is a cephalo-lateral perspective view of an intervertebral disc, a vertebra, a psoas muscle, and a curved probe, showing a portion of the psoas muscle adjacent to the vertebral structures; 
           [0008]      FIG. 3  is a transverse section view of a torso, showing a vertebra surrounded by muscles, nerves, blood vessels, and other organs; 
           [0009]      FIG. 4  is a frontal view of a torso, showing the psoas muscle and nerves of the lumbar plexus. 
           [0010]      FIG. 5  is a flow diagram of an exemplary method according to the present invention; 
           [0011]      FIG. 6  is a flow diagram of an alternate method according to the present invention; and 
           [0012]      FIG. 7  is a flow diagram of another alternate method according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Standard medical planes of reference and descriptive terminology are employed in this specification. A sagittal plane divides a body into right and left portions. A mid-sagittal plane divides the body into equal right and left halves. A coronal plane divides a body into anterior and posterior portions. A transverse plane divides a body into superior and inferior portions. Anterior means toward the front of the body. Posterior means toward the back of the body. Cephalad means toward the head. Caudal means toward the feet. Medial means toward the midline of the body. Lateral means away from the midline of the body. Axial means toward a central axis of the body. Abaxial means away from a central axis of the body. 
         [0014]    In this specification, “body” means the physical substance of an animal. “Flesh” means the soft parts of the body of an animal. “Tissue” means an aggregate of cells, usually of a particular kind, together with their intercellular substance, such as connective tissue, epithelium, muscle tissue, and nerve tissue. “Body part” refers to any part of an organism such as an organ or extremity. 
         [0015]    In this specification, “clinically relevant” means having significant and demonstrable bearing on observable or diagnosable symptoms. 
         [0016]    In this specification, “color” means all variations within the visible spectrum including white and black. “Hue” means the attribute of a color produced by a single wavelength of visible light that permits it to be classed as red, yellow, blue, or any intermediate value. “Tint” means a hue altered by the addition of white. “Shade” means a hue altered by the addition of black. “Tone” means a hue altered by the addition of grey. 
         [0017]    Referring to  FIGS. 1-2 , exemplary embodiments of an apparatus according to the invention will be shown and described in detail in the context of a lateral approach spinal intervertebral fusion procedure. While these embodiments are shown and described in the context of a specific surgical application, one of ordinary skill in the art will appreciate that the present invention has utility in other surgical applications in various parts of the body. 
         [0018]    Referring to  FIGS. 1-3 , a vertebra  10  is shown with an adjacent intervertebral disc  20 . A portion of a left psoas muscle  30  is shown laterally adjacent to the vertebra  10  and disc  20 . The disc  20  may be accessed via a lateral approach through the psoas muscle  30 . With specific reference to  FIG. 3 , the vertebra  10  and psoas muscle  30  are shown in a cross sectional view of a torso. 
         [0019]    With continued reference to  FIG. 3 , the psoas muscle  30  incorporates nerves in its substance. In particular, a network of interlacing nerves, or lumbar plexus  40 , is situated in the posterior part of the psoas muscle  30 . The psoas muscle  30  is intimately associated with other anatomical structures, such as left and right ureters  50 , abdominal aorta  60 , inferior vena cava  70 , and intestines  80 . In the context of a lateral approach spinal procedure, these structures in and around the psoas muscle are clinically relevant because collateral damage to any one of these structures may cause undesirable effects, including pain, loss of function, bleeding, or death. In particular, collateral damage to nerves in and around the psoas muscle may cause significant and long lasting pain. Therefore, avoiding intra-operative insult to peri-psoas nerves may improve clinical outcomes, such as post-operative pain scores. 
         [0020]    Referring to  FIG. 4 , a frontal view of the torso is shown. Details of the psoas muscle  30  and the lumbar plexus  40  are shown. Major nerves of the lumbar plexus  40  are shown. An iliohypogastric nerve  41 , an ilioinguinal nerve  42 , and a lateral femoral cutaneous nerve  43  emerge from the lateral border of the psoas muscle  30 . A femoral nerve  44  emerges from a posterolateral aspect of the psoas muscle  30 . A genitofemoral nerve  45  emerges anterior to the psoas muscle  30 . An obturator nerve  46  and a lumbosacral trunk  47  emerge medial to the psoas muscle  30 . 
         [0021]    Returning to  FIG. 1 , an instrument  100  is shown extending mediolaterally through the psoas muscle  30  along a center longitudinal axis  101 . Instrument  100  may have an imaging sensor  102  carried by a proximal working end  104  of a shaft  106 . Sensor  102  may be permanently attached to shaft  106 . In the embodiment of  FIG. 1 , the shaft  106  is straight and rigid. A distal end  108  of the shaft  106  may be physically coupled to an imaging console (not shown), for example, with a cable (not shown) to provide a communication link between sensor  102  and the console. Preferably, an outer diameter of the sensor  102  may be less than or equal to 6 mm. More preferably, an outer diameter of the instrument  100  may be less than or equal to 6 mm. 
         [0022]    Sensor  102  may comprise an ultrasound transducer that may have a radial detection zone extending from a center point within the sensor  102 . Preferably, the detection zone radius may be greater than or equal to 1 cm. The sensor  102  may be adjustable to alter the detection zone or to differentiate between various body structures. Sensor  102  may be a sterilizable reusable item. 
         [0023]    The detection zone of sensor  102  may be planar such that it extends in two dimensions. A two-dimensional radial detection zone may be characterized as a circular segment, if it encompasses less than 360 degrees, or a circle, if it encompasses 360 degrees. The detection zone may lie in a plane that is perpendicular to axis  101 , so that, for example, the detection zone extends around sensor  102 , preferably in a full circle. 
         [0024]    The imaging console (not shown) may comprise a sensor connection, such as a cable connection, a processor, software, a display, and a user interface. The imaging console may display an image acquired with the sensor  102  at a location within the psoas muscle  30 . The imaging console may process data from the sensor to produce a refined image that accentuates differences between various body structures so that, for example, the image visually distinguishes nerves from all other body structures, generically described as flesh. The image may be monochromatic, such as grayscale. Preferably, the image may display different body structures in different hues so that, for example, blood vessels are red, nerves are yellow, muscle is green, and bone is blue. Additional detail about a particular body structure may be indicated in the image by varying the tint, shade, tone, or brightness of at least a portion of the structure. The imaging console may further comprise storage media so that an image may be saved for later retrieval. 
         [0025]    In alternate embodiments of the invention, sensor  102  may be removably coupled to shaft  106 . The alternate embodiment instrument  200  may have a shaft  206  that is bent or curved in at least one plane. The instruments  100 ,  200  may have a shaft that is rigid, flexible, or selectable between rigid and flexible. Distal ends  108 ,  208  may comprise a coupling  110 ,  210  or a handle (not shown). 
         [0026]    In alternate embodiments, sensor  102  may be completely separate from instrument  100 . Furthermore, sensor  102  may be carried by alternate instruments, such as a dilator, a hollow tube or cannula, a retractor, a speculum, or an implant inserter. An alternate embodiment contemplates a set of nesting cannulas and a solid dilator slidingly receivable within a smallest one of the cannulas, with a sensor carried on each component. Multiple sensors may be present on a single instrument. 
         [0027]    The present invention may employ one or more of the following specialized ultrasound technologies: high-frequency, intra-vascular, two-dimensional, three-dimensional, or four-dimensional. Alternate imaging technology is also contemplated within the scope of the present invention. By way of non-limiting example, the invention could employ optical coherence tomography in place of, or in combination with, ultrasound imaging technology. One of ordinary skill in the art will recognize that additional alternate imaging technologies are also within the scope of the present invention to the extent that such imaging technologies are adaptable to the apparatus or methods set forth herein. 
         [0028]    In alternate embodiments, the instrument  100  may wirelessly communicate with the imaging workstation. Sensor  102  may be a single use sterile packaged disposable item. The detection zone of sensor  102  may lie in a plane that is parallel to axis  101 , so that, for example, the detection zone extends in front of sensor  102 , and preferably in a circular segment evenly distributed on either side of axis  101 . The detection zone of sensor  102  may be a three-dimensional spherical segment or full sphere. The image may be two-dimensional to correspond to a two-dimensional detection zone, or as a simplification of a three-dimensional detection zone. Alternatively, the image may be three-dimensional to correspond to a three-dimensional detection zone. The image may display different body structures in different tints, shades, tones, or brightnesses. The user may be able to zoom, pan, rotate, or otherwise manipulate the image or portions of the image through the user interface of the imaging console. 
         [0029]    Referring to  FIGS. 1-3 , exemplary embodiments of methods according to the invention will be shown and described in detail in the context of a lateral approach spinal intervertebral fusion procedure. While these embodiments are shown and described in the context of a specific surgical application, one of ordinary skill in the art will appreciate that the present invention has utility in other surgical applications in various parts of the body. 
         [0030]    The sensor  102  of instrument  100  may be placed against an entry point  90  on a lateral aspect of the body. The entry point may be prepared with a small incision so that the instrument slides easily through the skin. The sensor  102  may be inserted into the body so that the sensor  102  approaches a lateral aspect of the psoas muscle  30 . As the instrument  100  is inserted through the body, the proximal end  104  and thus the sensor  102  may be maneuvered to selectively penetrate or slide past other body structures. Thus, the proximal end  104  and the sensor  102  establish a route  92  through the body, which the shaft  106  of the instrument  100  follows. 
         [0031]    The sensor  102  may then be inserted into the psoas muscle  30  and advanced so that other sensor  102  approaches a lateral aspect of the intervertebral disc  20 , thereby extending the route from the entry point to the disc  20 . A passage is formed along the route  92  through the psoas muscle  30  as the sensor  102  is pushed through the psoas muscle  30 . 
         [0032]    As the sensor  102  is inserted into the body and advanced toward the disc  20 , images may be acquired with the sensor  102 . For example, an image may be acquired with the sensor  102  inserted halfway through the psoas muscle  30 . Upon viewing the image, a surgeon may determine whether any nerve is present in the image. If a nerve, such as a nerve of the lumbar plexus  40 , is present in the image, the surgeon may determine whether the nerve is an acceptable distance away from the sensor  102 . If the nerve is spaced apart from the sensor  102 , the surgeon may advance the sensor  102  closer to the disc  20  along the existing route  92 . If the nerve is unacceptably close to the sensor  102 , the surgeon may choose to move the sensor  102 , and thus the proximal end  104  of the instrument  100 , away from the nerve before advancing the sensor  102  closer to the disc  20  along a revised route  94 . The surgeon may acquire and view images periodically or continuously in order to determine if any nerve is unacceptably close to the sensor  102 . 
         [0033]    Once the sensor  102  is at the lateral aspect of the disc  20 , a surgical access channel may be formed by dilating the body structures surrounding the instrument  100 . For example, a cannula or tube may be pushed over the instrument  100  to force apart surrounding tissues or body structures. Progressively larger cannulas may be added to create a surgical access channel of a desired size. All but the largest cannula may be removed such that the largest cannula holds the surgical access channel open. Alternatively, an adjustable retractor may be inserted around the instrument  100  and opened or spread in order to force apart surrounding tissues and hold the surgical access channel open. The retractor or any of the cannulas may carry an additional sensor so that images may be acquired and viewed during the process of creating the surgical access channel. 
         [0034]    One or more surgical procedures may be performed on the disc  20  or in an intervertebral space created by removal of the disc  20 . In this exemplary embodiment, disc  20  may be excised and the resulting intervertebral disc space may be filled with an intervertebral fusion prosthesis. The prosthesis or any surgical instrument used during the procedure may carry an additional sensor so that images may be acquired and viewed during or after the procedure. 
         [0035]    An image enhancing medium may be introduced around the sensor  102  before or after acquiring an image with the sensor  102 . The medium may acoustically couple the sensor  102  to surrounding body structures. For example, sterile saline or gel may be introduced around the sensor  102  to improve image quality through enhanced acoustic coupling. The image enhancing medium may be reserved for use only when image quality is suboptimal, or it may be introduced routinely, such as by flooding the vicinity with medium prior to introducing the sensor  102 . 
         [0036]    The revised route  94  may take advantage of the flexibility of flesh or the relative motility of organs or other body structures within the body so that it is not necessary to completely withdraw the sensor  102  in order to adopt the revised route  94 . Rather, it may be possible to reorient sensor  102  onto the revised route  94  with minimal or partial withdrawal of sensor  102 . 
         [0037]    Although the exemplary embodiment stresses a route that avoids clinically relevant tissues, in an alternate embodiment, the surgical objective may be best served by a route defined by proximity to, or intersection with, a clinically relevant tissue, such as a nerve, blood vessel, or ligament. 
         [0038]    Referring to  FIGS. 5-7 , exemplary embodiments of methods according to the invention will be shown and described in the context of a lateral approach spinal intervertebral fusion procedure. One of ordinary skill in the art will appreciate that methods according to the present invention also have utility in other surgical applications in various parts of the body. 
         [0039]    Referring to  FIG. 5 , a flow diagram shows a method  300  comprising three basic steps. A first step  302  may comprise inserting an imaging probe to a location within a body part. For example, step  302  may comprise inserting sensor  102  to a mid-substance location within the psoas muscle  30 , adjacent to a portion of the lumbar plexus  40 . A second step  304  may comprise viewing an image acquired with the probe at the location. For example, an image acquired with sensor  102  at the mid-substance location within the psoas muscle  30  may show no nerves proximate the sensor  102 . A third step  306  may comprise identifying a route to a destination. For example, step  306  may comprise identifying a route to intervertebral disc  20 . In this example, the image shows that the sensor  102  is on an acceptable route. 
         [0040]    The method  300  may also comprise certain additional steps which may occur in relation to the steps  302 ,  304 ,  306 . 
         [0041]    A step  308  may comprise securing the probe at a proximal end of a selected one of a straight dilator shaft, a curved dilator shaft, a cannula, and a retractor, before performing step  302 . Step  308  may be performed if, for example, sensor  102  is releasably securable to an instrument. 
         [0042]    A step  310  may comprise introducing an image enhancing medium around the probe oat the location. As  FIG. 5  shows, step  310  may occur at several points in method  300 , since the purpose of step  310  is to enhance the image. 
         [0043]    A step  316  may comprise advancing the probe to the destination along the route. For example, step  316  may comprise advancing sensor  102  along route  92  to disc  20 . Step  316  may be performed when the route is acceptably oriented with regard to a clinically relevant tissue. 
         [0044]    A step  312  may comprise moving the probe to a subsequent location within the body part. Step  312  may be performed when the route appears to be unacceptably oriented with regard to a clinically relevant tissue. For example, step  312  may comprise moving sensor  102  away from the portion of the lumbar plexus  40  so that sensor  102  lies along route  94  instead of route  92 . Alternatively, step  312  may comprise moving sensor  102  toward a clinically relevant tissue, should it be desirable for the route to approach or intersect the clinically relevant tissue. 
         [0045]    As shown in  FIG. 5 , step  312  may be followed by step  310  or step  304 , so that a subsequent image acquired with the probe at the subsequent location may be viewed and a revised route to the destination may be identified. Thus steps  304  and  306  may be construed to pertain to the route or the revised route. 
         [0046]    A decision step  314  may be inherent to the method  300 . Decision step  314  may comprise deciding whether the route is acceptably or unacceptably oriented with respect to a clinically relevant tissue. Decision step  314  may be encountered repeatedly in method  300  until an acceptable route is identified. 
         [0047]    A step  322  may comprise performing a surgical procedure at the destination, such as excising intervertebral disc  20 . Step  322  may be followed by a step  324 , comprising implanting a prosthesis, such as an intervertebral fusion cage. Alternatively, step  324  may be performed without performing step  322 , in the situation where an implant requires no preparation of an implantation site. 
         [0048]    A step  320  may comprise viewing a destination image acquired with the probe at the destination. As shown in  FIG. 5 , step  310  may occur before or after step  320  in order to enhance the image. Step  320  may advantageously confirm that the appropriate surgical destination has been reached, such as confirming the presence of disc degeneration prior to performing the surgical procedure. 
         [0049]    Referring to  FIG. 6 , a flow diagram shows a method  400  comprising four basic steps. A first step  402  may comprise selecting a first route from an entry point to the destination. For example, step  402  may comprise selecting route  94  from entry point  90  to intervertebral disc  20 , as shown in  FIG. 3 . A second step  404  may comprise passing a first end of a dilator along the first route to a first location within the flesh. For example, step  404  may comprise passing proximal end  204  of instrument  100  along route  94  to a location spaced apart from a portion of the lumbar plexus  40 . A third step  406  may comprise viewing an image acquired from an imaging probe at the first location, such as sensor  102  of instrument  100 . A fourth step  408  may comprise passing the dilator along the first route from the first location to the destination. 
         [0050]    The method  400  may also comprise certain additional steps which may occur in relation to the steps  402 ,  404 ,  406 ,  408 . 
         [0051]    A step  410  may comprise selecting a preliminary route from the entry point to the destination, prior to selecting the first route. For example, step  410  may comprise selecting route  92  from entry point  90  to intervertebral disc  20 , as shown in  FIG. 3 . 
         [0052]    As shown in  FIG. 6 , step  410  may be followed by step  404 , so that the dilator may be passed along the preliminary route to a preliminary location within the flesh. Thus steps  404  and  406  may be construed to pertain to the first route or the preliminary route. 
         [0053]    A step  412  may comprise introducing an image enhancing medium around the probe at the location. Step  412  may occur before or after step  406 , since the purpose of step  412  is to enhance the image. 
         [0054]    A decision step  414  may be inherent to the method  400 . Decision step  414  may comprise deciding whether the route is acceptably or unacceptably oriented with respect to a clinically relevant tissue. Decision step  314  may be encountered repeatedly in method  400  until an acceptable route is identified. 
         [0055]    A step  416  may comprise spreading the dilator to form a surgical access channel through the flesh, after passing the dilator along the first route from the first location to the destination. For example, step  416  may comprise spreading movable portions of a retractor from a more compact configuration to a more expanded configuration. Alternatively, step  416  may comprise enlarging a one-piece dilator. 
         [0056]    A step  418  may comprise performing a surgical procedure at the destination. Step  418  may be followed by, or may incorporate, a step  420 , comprising implanting a prosthesis. For example, steps  418  and  420  may comprise excising at least a portion of intervertebral disc  20  and inserting one or more intervertebral fusion spacers into the space previously occupied by disc  20 . 
         [0057]    Referring to  FIG. 7 , a flow diagram shows a method  500  comprising five basic steps. A first step  502  may comprise advancing an imaging probe from an entry point to a first location within the body. For example, step  502  may comprise inserting sensor  102  to a mid-substance location within the psoas muscle  30 , adjacent to a portion of the lumbar plexus  40 . A second step  504  may comprise viewing a first image acquired from the probe at the first location. A third step  506  may comprise moving the probe to a subsequent location within the body. For example, step  506  may comprise moving sensor  102  away from the lumbar plexus  40 . A fourth step  508  may comprise viewing a subsequent image acquired from the probe at the subsequent location. A fifth step  510  may comprise dilating a surgical access channel through the body following a route established by the probe through the entry point, the subsequent location, and the destination. For example, step  510  may comprise dilating a surgical access channel through the psoas muscle  30  and other body structures along route  94  ( FIG. 3 ). 
         [0058]    The method  500  may also comprise certain additional steps which may occur in relation to the steps  502 ,  504 ,  506 ,  508 ,  510 . 
         [0059]    A step  512  may comprise securing the probe at a proximal end of a selected one of a straight dilator shaft, a curved dilator shaft, a cannula, and a retractor blade, before advancing the probe to the first location. 
         [0060]    A step  514  may comprise pushing the probe through the body to create the passage. For example, sensor  102  may be pushed through one or more muscle bellies, i.e., mid-substance, as it passes from the entry point to the first location within the body.  FIGS. 1-2  show that sensor  102  has been pushed through the belly of the psoas muscle  30 . 
         [0061]    A step  516  may comprise introducing an image quality enhancing medium around the probe at the location. Steps  508  and  516  may also be performed in alternation until an acceptable image quality is achieved. 
         [0062]    A step  518  may comprise advancing the probe to the destination along the route, before dilating the surgical access channel. 
         [0063]    A step  520  may comprise inserting a dilator through the body following the route. For example, shaft  106  of instrument  100  may follow sensor  102  along the route. Alternatively, a separate dilator may be inserted along the route, either after removal of instrument  100  or with instrument  100  still in place along the route. The separate dilator may be structurally or functionally similar to a retractor or a speculum. 
         [0064]    A step  522  may comprise spreading apart the body along the route to create the surgical access channel between the entry point and the destination. For example, step  522  may comprise passing a series of sequentially larger dilator cannulas over instrument  100  or a separate dilator in order to spread apart various body structures lying along the route. Alternatively, a collapsed retractor or speculum may be moved to an expanded configuration in order to spread apart a portion of the body in the vicinity of the route. 
         [0065]    A step  524  may comprise performing a surgical procedure at the destination. Step  524  may be followed by, or may comprise, step  526 , implanting a prosthesis. 
         [0066]    While the foregoing disclosure sets forth exemplary embodiments of the present invention, one of ordinary skill in the art will appreciate that the apparatus and method of the present invention may be applicable throughout the body. By way of non-limiting example, the present invention may assist in navigating to surgical destinations near the cervical, brachial, lumbar, sacral, or myenteric plexuses, while avoiding the neural structures comprising these plexuses. The present invention contemplates an application in which posterior access to knee structures is facilitated by accurate visualization of circulatory and neural structures in the popliteal fossa.