FIELD OF THE INVENTION 
     The invention relates to a system and method for performing a surgical procedure, and in particular, to a minimally invasive surgical system that includes a restraining mechanism to ensure positional stability of a bone filler device without requiring manual support of that device. 
     BACKGROUND OF THE INVENTION 
     A minimally invasive procedure is a medical procedure that is performed through the skin or an anatomical opening. In contrast to an open procedure for the same purpose, a minimally invasive procedure will generally be less traumatic to the patient and result in a shortened recovery period. 
     However, there are numerous challenges that minimally invasive procedures present. For example, minimally invasive procedures are typically more time-consuming than their open procedure analogues due to the challenges of working within a constrained operative pathway. In addition, as minimally invasive procedures have evolved, unique challenges have arisen that require new solutions. 
     For example, for many individuals in our aging world population, undiagnosed and/or untreatable bone strength losses have weakened these individuals&#39; bones to a point that even normal daily activities pose a significant threat of fracture. In one common scenario, when the bones of the spine are sufficiently weakened, the compressive forces in the spine can cause fracture and/or deformation of the vertebral bodies. For sufficiently weakened bone, even normal daily activities like walking down steps or carrying groceries can cause a collapse of one or more spinal bones. A fracture of the vertebral body in this manner is typically referred to as a vertebral compression fracture. Other commonly occurring fractures resulting from weakened bones can include hip, wrist, knee and ankle fractures, to name a few. 
     Fractures such as vertebral compression fractures often result in episodes of pain that are chronic and intense. Aside from the pain caused by the fracture itself, the involvement of the spinal column can result in pinched and/or damaged nerves, causing paralysis, loss of function, and intense pain which radiates throughout the patient&#39;s body. Even where nerves are not affected, however, the intense pain associated with all types of fractures is debilitating, resulting in a great deal of stress, impaired mobility and other long-term consequences. For example, progressive spinal fractures can, over time, cause serious deformation of the spine (“kyphosis”), giving an individual a hunched-back appearance, and can also result in significantly reduced lung capacity and increased mortality. 
     Until recently, treatment options for vertebral compression fractures, as well as other serious fractures and/or losses in bone strength, were extremely limited—mainly pain management with strong oral or intravenous medications, reduced activity, bracing and/or radiation therapy, all with mediocre results. Because patients with these problems are typically older, and often suffer from various other significant health complications, many of these individuals are unable to tolerate invasive surgery. In addition, to curb further loss of bone strength, many patients are given hormones and/or vitamin/mineral supplements—again with mediocre results and often with significant side effects. 
     In an effort to more effectively and directly treat vertebral compression fractures, minimally invasive techniques such as vertebroplasty and, subsequently, kyphoplasty, have been developed. Vertebroplasty involves the injection of a flowable reinforcing material, usually polymethylmethacrylate (PMMA—commonly known as bone cement), into a fractured, weakened, or diseased vertebral body. Shortly after injection, the liquid filling material hardens or polymerizes, beneficially supporting the vertebral body internally, alleviating pain and preventing further collapse of the injected vertebral body. 
     Because the liquid bone cement naturally follows the path of least resistance within bone, and because the small-diameter needles used to deliver bone cement in vertebroplasty procedure require either high delivery pressures and/or less viscous bone cements, ensuring that the bone cement remains within the already compromised vertebral body is a significant concern in vertebroplasty procedures. Kyphoplasty addresses this issue by first creating a cavity within the vertebral body (e.g., with an inflatable balloon) and then filling that cavity with bone filler material. The cavity provides a natural containment region that minimizes the risk of bone filler material escape from the vertebral body. An additional benefit of kyphoplasty is that the creation of the cavity can also restore the original height of the vertebral body, further enhancing the benefit of the procedure. 
     In both vertebroplasty and kyphoplasty, as with most minimally invasive procedures, x-ray fluoroscopy is used to allow the surgeon to visualize the procedural actions being performed within the patient. Unfortunately, efforts to move the physician out of the fluoroscopic field are often hampered by the nature of traditional minimally invasive instruments. Specifically, the devices used to deliver bone filler material during minimally invasive procedures have typically been designed to be manipulated and held from just outside the working cannula (or plunged directly into the vertebral body without the use of a cannula). Therefore, adding remote operation capabilities (e.g., via flexible tubing or hydraulic lines) can be difficult due to the tendencies of the tubing or other connection/control lines to cause unintended movement of the instrument within the working cannula. 
     Accordingly, it is desirable to provide surgical tools and techniques that enable the stable and secure operation of a bone filler material delivery device through a cannula. 
     SUMMARY OF THE INVENTION 
     By providing a releasable retainer for coupling a bone filler material delivery nozzle and a working cannula, a minimally invasive surgical procedure can be performed from outside the fluoroscopic radiation field used for visualization. The retainer ensures that the delivery nozzle remains properly positioned with respect to the cannula during the procedure, yet allows simple disengagement/removal of the delivery nozzle to minimize procedure duration. 
     In one embodiment, a minimally invasive surgical system or kit can include a cannula, a bone filler material delivery nozzle for use in a minimally invasive surgical procedure (e.g., kyphoplasty) through the cannula, and a retainer. In various embodiments, the system can include additional tools and instructions for use that specify how the system is to be used. The retainer attaches to the cannula and maintains the position of the delivery nozzle relative to the cannula during the surgical procedure. Because the cannula is typically firmly anchored in the patient (e.g., within cortical bone) during the procedure, the retainer ensures that the delivery nozzle remains properly positioned as well. 
     In one embodiment, the retainer can comprise a gripping mechanism that exerts a constant gripping force on the delivery nozzle once it is placed within the cannula. In various embodiments, the gripping mechanism can include o-rings, gaskets, flexible arms or linkages, or any other mechanism that can provide a gripping force sufficient to hold the delivery nozzle in place during the surgical procedure. Once the procedure is complete, the delivery nozzle can be pulled from the gripping mechanism. In one embodiment, the delivery nozzle can include mating features (e.g., detents) that positively mate with the gripping mechanism and thereby define one or more distinct positions for the delivery nozzle relative to the cannula. 
     In various other embodiments, the retainer can comprise a gripping mechanism that only exerts a gripping force on the delivery nozzle when a clamping mechanism is actuated. In one embodiment, the gripping mechanism can include multiple arms having a default spacing that allows the delivery nozzle to pass through freely, and a clamping element that selectably forces the arms together to grip the delivery nozzle. In one embodiment, the clamping element is a cap that threads over the arms and includes an internal taper that forces the arms together as the cap is tightened down. 
     In one embodiment, the retainer includes a latching mechanism to connect to the cannula. In various other embodiments, the connection between the retainer and the cannula can include one or more clips, pins, hooks, snaps, magnets, or any other mechanism or combination of mechanisms for temporarily securing the retainer to the cannula. 
     In another embodiment, a method for performing a minimally invasive surgical procedure includes placing a cannula in a patient, attaching a retainer to the cannula, placing a delivery nozzle in the cannula, securing the delivery nozzle relative to the cannula using the retainer, and performing the procedure using the delivery nozzle. In one embodiment, securing the delivery nozzle relative to the cannula includes placing the cannula in the retainer and moving the delivery nozzle through the retainer until a desired position is achieved, wherein the retainer applies a constant gripping force to the delivery nozzle as it is moved through the retainer. 
     In another embodiment, securing the delivery nozzle relative to the cannula involves placing the cannula in the retainer, and then applying a clamping force to the retainer to cause the retainer to grip the delivery nozzle. In one embodiment, applying the clamping force includes threading a cap with an internal taper over multiple arms that surround the delivery nozzle, such that the internal taper forces the multiple arms inward and into contact with the delivery nozzle. 
     In one embodiment, delivering bone filler material can include remotely causing the bone filler material to be dispensed from the delivery nozzle into bone (e.g., via hydraulic pressure or material delivery via flexible tubing) as part of a kyphoplasty or vertebroplasty procedure. 
     As will be realized by those of skilled in the art, many different embodiments of an introducer/guide pin device, systems, kits, and/or methods of using an introducer/guide pin device according to the present invention are possible. Additional uses, advantages, and features of the invention are set forth in the illustrative embodiments discussed in the detailed description herein and will become more apparent to those skilled in the art upon examination of the following. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a minimally invasive surgical system that includes a cannula, a bone filler material delivery nozzle, and a retainer for selectively securing the delivery nozzle to the cannula. 
         FIGS. 2A-2G  show an exemplary use of the system of  FIG. 1  to perform a surgical procedure. 
         FIG. 3  is a flow diagram for a surgical procedure using the system of  FIG. 1 . 
         FIGS. 4A-4D  show exemplary embodiments of the retainer of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     By providing a releasable retainer for coupling a bone filler material delivery nozzle and a working cannula, a minimally invasive surgical procedure can be performed from outside the fluoroscopic radiation field used for visualization. The retainer ensures that the delivery nozzle remains properly positioned with respect to the cannula during the procedure, yet allows simple disengagement/removal of the delivery nozzle to minimize procedure duration. 
       FIG. 1  shows a system  100  for use in a minimally invasive surgical procedure. System  100  includes a cannula  110 , a bone filler material delivery nozzle  120  sized to fit through a lumen  111  of cannula  110 , and a retainer  130  for securing delivery nozzle  120  with respect to cannula  110  during the surgical procedure. In various embodiments, system  100  can be a kit providing a prepackaged collection of items for performing the surgical procedure, including optional instructions for use  180  for describing the proper application of system  100 , and optional additional tools  190 . 
     In various embodiments, retainer  130  can be a discrete element that attaches to a proximal end  112  of cannula  110  during the surgical procedure, and can be used to hold or clamp delivery nozzle  120  while delivery nozzle  120  is positioned within lumen  111  of cannula  110 . Note that in various other embodiments, retainer  130  can be integrated with cannula  110  (e.g., optional retainer  130 - 1 ) or can be integrated with delivery nozzle  120  (e.g., optional retainer  130 - 2 ). 
     Retainer  130  can include any type of mechanism that can secure delivery nozzle  120  and prevent unwanted motion relative to cannula  110  during the surgical procedure. For example,  FIG. 4A  shows an exemplary retainer  130  that includes a base structure  131  having (or coupled to) gripping arms  132  with gripping surfaces  132 -S that are spaced by a default spacing D 2  (i.e., normal spacing, when not in contact with the delivery nozzle) that is less than a dimension D 1  at a gripping region of delivery nozzle  120 . Retainer  130  further includes a securing element  135 , such as a latch, clip, pin, hook, snap, magnet, or any other mechanism that can secure retainer  130  to cannula  110  via a mating securing element  115   
     Therefore, when securing elements  135  and  115  are engaged, as shown in  FIG. 4B , retainer  130  is fixedly coupled to cannula  110 . When delivery nozzle  120  is placed into cannula  110  past retainer  130 , gripping arms  132  press gripping surfaces  132 -S against the sides of a section of delivery nozzle  120  (in this case, shaft  121 ) to hold delivery nozzle  120  in place relative to cannula  110 . In one embodiment, delivery nozzle  120  can include optional features  125  (e.g., detents, grooves, ridges, bumps, indentations, or other features) that positively mate with gripping surfaces  132 -S (i.e., interlock or fit together) to provide one or more discrete positions for delivery nozzle  120  relative to cannula  110 . 
     In various other embodiments, gripping arms  132  can be articulating arms that are biased inward (i.e., towards the centerline of retainer  130 ), thereby providing a natural clamping effect to hold delivery nozzle  120 . The articulation can be provided by material flexibility, spring loading, or any other mechanism. In other embodiments, gripping arms  132  can be substantially rigid, but gripping surfaces  132 -S can include a resilient or compressible element (e.g., an elastomer, an o-ring, a gasket, or a spring-loaded tip) that provides an elastic or frictional gripping force on delivery nozzle  120 . 
     In various other embodiments, the gripping action provided by retainer  130  can be generated by a compression mechanism, such as shown in  FIG. 4C .  FIG. 4C  shows another exemplary retainer  130  that is similar to the embodiment shown in  FIGS. 4A and 4B , and includes a base structure  131  having (or coupled) to gripping elements  132  and a securing element  135 . As described above with respect to  FIGS. 4A and 4B , securing element  135  can be a latch, clip, pin, hook, snap, magnet, or any other mechanism that can secure retainer  130  to cannula  110  via a mating securing element  115 . 
     However, unlike the embodiment shown in  FIGS. 4A and 4B , the gripping surfaces  132 -S in retainer  130  of  FIG. 4C  have a default spacing distance D 3  that is greater than dimension D 1  of the gripping region of delivery nozzle  120 . Therefore, retainer  130  also includes a cap  136  having internal threads  137  to mate with the threads  133  of gripping arms  132 , and an internal taper  138 . When cap  136  is screwed down on to gripping arms  132 , as shown in  FIG. 4D , internal taper  138  forces the gripping arms  132  inward, thereby clamping gripping surfaces  132 -S onto delivery nozzle  120 . 
     In some embodiments, gripping surfaces  132 -S can mate with optional mating features  125  (e.g., detents, grooves, ridges, bumps, indentations, or features) on delivery nozzle  120  that provide distinct gripping locations for gripping surfaces  132 -S. In various other embodiments, the compressive loading provided by threaded cap  136  could be provided by a ratcheting mechanism, a spring-loaded mechanism, a cammed mechanism, or any other mechanism capable of selectively forcing gripping surfaces  132 -S towards inward. 
       FIGS. 2B-2G  show an exemplary use of retainer  130  in the performance of a minimally invasive surgical procedure.  FIG. 2A  shows a portion of a human vertebral column having vertebrae  201 ,  202 , and  203 . Vertebra  202  has collapsed due to a vertebral compression fracture (VCF)  202 -F that could be the result of osteoporosis or cancer-related weakening of the bone. The abnormal curvature of the spine caused by VCF  202 -F can lead to severe pain and further fracturing of adjacent vertebral bodies. 
     One treatment for this type of fracture is to perform a minimally invasive procedure in which a reinforcing bone filler material is injected into the fractured vertebra, either directly into the fractured region (vertebroplasty) or into a cavity created beforehand in the cancellous bone structure (kyphoplasty). Kyphoplasty is often a preferred technique due to the enhanced cement placement control provided versus vertebroplasty, along with the potential height restoration that can be achieved during the cavity creation phase of a kyphoplasty procedure. 
       FIG. 2B  shows a cannula  110  being positioned next to the target surgical location, which in this case is the cancellous bone structure within fractured vertebra  202 . In this manner, a percutaneous path to vertebra  202  is provided via an interior lumen  111  of cannula  110 . Typically, cannula  110  is docked into the exterior wall of the vertebral body (using either a transpedicular or extrapedicular approach) using a guide needle and/or dissector, after which a drill or other access tool (not shown) is used to create a path further into the cancellous bone  202 -C of vertebra  202 . However, any other method of cannula placement can be used to position cannula  110 . Once docked, the distal end  113  of cannula  110  is substantially secured by the hard cortical (outer) bone of vertebra  202 . 
     Then in  FIG. 2C , an inflatable bone tamp  220  is placed into cannula  110 . Inflatable bone tamp  220  includes a shaft  221  (e.g., a catheter), an expandable structure  223  (e.g., a balloon) at the distal end of shaft  221 , and a connector  222  (e.g., a Luer Lock fitting) at the proximal end of shaft  221 . Inflatable bone tamp  220  is coupled by flexible tubing  295  to an inflation syringe  291 . 
     Syringe  291  includes a reservoir  292  and a plunger  293 . Plunger  293  includes a plunger tip  294  that is slidably disposed in reservoir  292 . To inflate expandable structure  223 , a force is applied to plunger  291  that drives plunger tip  294  through reservoir  292 , thereby expressing flowable material  209  through tubing  295 , connector  222 , and shaft  221 , and into expandable structure  223 . The resulting expansion of expandable structure  223  compresses the surrounding cancellous bone  202 -C to create a well-defined cavity within fractured vertebra  202 , and can also restore some or all of the original height of the vertebral body, as shown in  FIG. 2D . 
     Once expandable structure  223  has been expanded to a desired volume, it is contracted and removed from vertebra  202  through cannula  110 . As shown in  FIG. 2E , the result of the previously described expansion procedure is a well-defined cavity  207  in cancellous bone  202 -C. Cavity  207  can then be filled with bone filler material  209  (e.g., PMMA), as shown in  FIG. 2F . A delivery nozzle  120  is inserted through cannula  110  and into cavity  207 , and is fed bone filler material  209  from a cartridge  196  that it then directs into cavity  207 . Cartridge  196  is coupled to a hydraulic actuator  191  by a hydraulic line  195  that drives bone filler material  209  from cartridge  196  using hydraulic pressure (e.g., by driving a piston inside cartridge  196  via the hydraulic pressure). 
     To prevent delivery nozzle  120  from moving or twisting within cannula  110  due to the loading from hydraulic line  195 , a retainer  130  secures nozzle  120  to cannula  110 . Retainer  130  can have any construction (e.g., as described with above with respect to FIGS.  1  and  4 A- 4 D) that enables the securing of delivery nozzle  120  to cannula  110 . Retainer  130  therefore allows the bone filler material delivery process to be performed consistently and reliably, even as high pressures generated within hydraulic line  195  increase the loading on delivery nozzle  120 , and permits the physician to remain outside the fluoroscopic radiation field used to visualize the target site. 
     Once the filling operation is complete, delivery nozzle  120 , retainer  130 , and cannula  110  are removed from vertebra  202  as shown in  FIG. 2G . Upon hardening, bone filler material  209  provides structural support for vertebra  202 , thereby substantially restoring the structural integrity of the bone and the proper musculoskeletal alignment of the spine. In this manner, the pain and attendant side effects of a vertebral compression fracture can be addressed by a minimally invasive kyphoplasty procedure. 
     Note that the kyphoplasty procedure described with respect to  FIGS. 2A-2G  incorporates an inflatable bone tamp for cavity creation and a hydraulically-operated cement delivery system for explanatory purposes only. In various other embodiments, cavity creation can be performed using other types/combinations of mechanical systems (e.g., an expandable mechanism, a stent, a cutting tool, a coring tool, etc.), and bone filler delivery can be accomplished via other types of flow control mechanisms (e.g., a syringe coupled directly to the nozzle, a syringe coupled directly to the nozzle that is remotely controlled via a cable, a high pressure pumping system for pumping bone filler material from a remote location to the nozzle, etc.). 
       FIG. 3  shows a flow diagram of a process for performing a surgical procedure using a delivery nozzle and retainer as described with respect to FIGS.  1  and  2 A- 2 G. In a PLACE CANNULA step  310 , a cannula (e.g., cannula  110  shown in  FIG. 2B ) is docked next to a surgical target (e.g., docked into the cortical bone of a vertebra  202 , as shown in  FIG. 2B ). As noted above, this placement operation can be performed using any necessary accessory tools, such as a needle, a guidewire, a drill, an obturator, or a mallet, among others. 
     Then, in a PLACE RETAINER step  315 , a delivery nozzle retainer (e.g., retainer  130  shown in  FIG. 2F ) is affixed to the cannula (e.g., as described with respect to  FIGS. 4A-4D  using a latch, clip, pin, hook, snap, magnet, or any other securing mechanism). A bone filler material delivery nozzle (e.g., delivery nozzle  120  as described with respect to  FIG. 2F ) is then inserted into the cannula in a PLACE DELIVERY NOZZLE step  320 . Note that in various embodiments, the retainer could be preassembled with either the cannula or delivery nozzle, in which case step  315  can be eliminated. 
     Note that any number of additional procedure steps can be performed between the placement of the cannula in step  310  and the steps  315  and/or  320 . For example, as described above with respect to  FIGS. 2C-2E , a cavity could be formed in a vertebral body prior to the delivery nozzle being placed into the vertebral body. 
     Next, in an ENGAGE RETAINER step  325 , the delivery nozzle retainer is engaged with the delivery nozzle to establish a fixed position for the delivery nozzle with respect to the cannula (e.g., as described with respect to  FIGS. 2C ,  2 F, and  4 A- 4 D). Note that in some embodiments, the retainer can be engaged with the delivery nozzle continuously once the delivery nozzle is placed within the retainer (i.e., the delivery nozzle is held securely but not fixedly (i.e., sufficient force can cause movement), such as described with respect to  FIGS. 4A-4B ). In various other embodiments, the retainer can be engaged with the delivery nozzle once the desired positioning of the delivery nozzle has been established (i.e., the delivery nozzle moves freely in the cannula until the retainer is actuated, such as described with respect to  FIGS. 4C-4D ). 
     A minimally invasive surgical procedure (e.g., cavity creation within bone, such as described with respect to  FIG. 2D , or bone filler material delivery within bone, such as described with respect to  FIG. 2F ) is then performed using the delivery nozzle in a DELIVER BONE FILLER MATERIAL step  330 . In one embodiment, step  330  can involve dispensing the material through the delivery nozzle remotely via a flexible coupling (e.g., delivering cement to a target location using a remotely actuated hydraulic pumping system coupled to a cement cartridge/delivery nozzle via a hydraulic line as described with respect to  FIG. 2F ). 
     Upon completion of the bone filler material delivery, the retainer can be disengaged from the delivery nozzle in a DISENGAGE RETAINER step  335 , and the delivery nozzle removed from the cannula in a REMOVE DELIVERY NOZZLE step  340 . Note that in various embodiments, steps  335  and  340  can be performed substantially simultaneously (e.g., if the retainer applies a continuous gripping force to the delivery nozzle). 
     The retainer can be removed in a REMOVE RETAINER step  345 , and the cannula can be removed in a REMOVE CANNULA step  350  to complete the surgical procedure. Note once again that various additional procedure steps can be performed between steps  345  and  350 . Note further that in various embodiments, multiple different bone filler material delivery operations can be performed through the same cannula (e.g., delivering a first quantity of material, and then delivering a second quantity of the same or different material), in which case, after step  345 , the process could return to steps  315 , as indicated by the dashed line. Note that in various other embodiments, the same retainer could be used for multiple delivery nozzles, in which case, after step  340 , the process could return to step  320 , as indicated by the dotted line. Various other sequences of steps will be readily apparent. 
     While various embodiments of the invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. Where methods and steps described above indicate certain events occurring in certain order, those of ordinary skill in the art having the benefit of this disclosure would recognize that the ordering of certain steps may be modified and that such modifications are in accordance with the variations of the invention. Additionally, certain steps may be performed concurrently in a parallel process when possible, as well as performed sequentially as described above. Thus, the breadth and scope of the invention should not be limited by any of the above-described embodiments, but should be defined only in accordance with the following claims and their equivalents. While the invention has been particularly shown and described with reference to specific embodiments thereof, it will be understood that various changes in form and details may be made.
A system for performing a minimally invasive surgical procedure comprises a cannula, a bone filler material delivery nozzle for performing the procedure through the cannula, and a retainer for securing the delivery nozzle relative to the cannula. The retainer eliminates the need to manually stabilize and position the delivery nozzle during the procedure, thereby allowing the physician to perform the procedure outside of the fluoroscopic radiation field used to visualize the procedure location. The retainer can be attached to the cannula, and can provide either selective or constant clamping force onto the delivery nozzle.