US 20100241123 A1
A percutaneous surgical device and method for creating a cavity within tissue during a minimally invasive procedure. A cavitation device includes a shaft interconnected to a flexible cutting element. A flexible cutting element has a first shape suitable for minimally invasive passage into tissue. The flexible cutting element has a means to move toward a second shape suitable for forming a cavity in tissue. When used in bone, the resulting cavity is usually filled with bone cement or suitable bone replacement material that is injectable and hardens in situ. The disclosed cavitation device and methods can be used for the following applications: (1) treatment or prevention of bone fracture, (2) joint fusion, (3) implant fixation, (4) tissue harvesting (especially bone), (5) removal of diseased tissue (hard or soft tissue), and (6) general tissue removal (hard or soft tissue).
1. A method for treating bone comprising the steps of:
forming a passage in bone;
creating a cavity by cutting bone, wherein the cavity formed by cutting bone is generally spherical and has a larger diameter than the passage; and
expanding the volume of the cavity by expanding a device within the cavity, thereby reducing a fracture.
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9. A method of reducing a fracture comprising the steps of:
forming a passage in bone;
providing a tissue cavitation device, wherein the tissue cavitation device comprises a deformable cutting element;
separating a portion of bone about the passage with by rotating the deformable cutting element of the tissue cavitation device to create a cavity, wherein the diameter of the cavity is larger than the diameter of the passage; and
expanding the volume of the cavity, thereby reducing the fracture.
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16. A method of reducing a fracture comprising the steps of:
forming a passage in bone using a first device along a linear axis;
separating a portion of bone using by rotating a second device to create a cavity, wherein the cavity is substantially coincident with the linear axis and has a non-uniform diameter; and
expanding the volume of the cavity with a third device, thereby reducing the fracture.
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The application claims priority to and is a continuation of U.S. Non-Provisional patent application Ser. No. 10/818,452, entitled “Tissue Cavitation Device and Method,” filed Apr. 5, 2004, which is a continuation of U.S. Non-Provisional patent application Ser. No. 09/872,042, entitled “Tissue Cavitation Device and Method”, filed Jun. 1, 2001, now U.S. Pat. No. 6,746,451, the disclosures of which are herein incorporated by reference in their entirety.
The present invention relates generally to surgical devices and methods and, more particularly, to minimally invasive surgical devices and methods for creating a cavity within hard or soft tissue.
Surgeons are using minimally invasive surgical techniques on an increasing basis for the treatment of a wide variety of medical conditions. Such techniques typically involve the insertion of a surgical device through a natural body orifice or through a relatively small incision using a tube or cannula. In contrast, conventional surgical techniques, typically involve a significantly larger incision and are therefore sometimes referred to as open surgery. Thus, as compared with conventional techniques, minimally invasive surgical techniques offer the advantages of minimizing trauma to healthy tissue, minimizing blood loss, reducing the risk of complications such as infection, and reducing recovery time. Further, certain minimally invasive surgical techniques can be performed under local anesthesia or even, in some cases, without anesthesia, and therefore enable surgeons to treat patients who would not tolerate the general anesthesia required by conventional techniques.
Surgical procedures often require the formation of a cavity within either soft or hard tissue, including bone. Tissue cavities are formed for a wide variety of reasons, such as for the removal of diseased tissue, for harvesting tissue in connection with a biopsy or autogenous transplant, and for implant fixation. To achieve the benefits associated with minimally invasive techniques, tissue cavities should be formed by creating only a relatively small access opening in the target tissue. An instrument or device can then be inserted through the opening and used to form a hollow cavity that is significantly larger than the access opening. Depending on the specific application, the shape of the desired cavity can be spherical, hemispherical, cylindrical, or any number of different combinations or variations of such shapes.
One important surgical application requiring the formation of a cavity within tissue is the surgical treatment and prevention of skeletal fractures associated with osteoporosis, which is a metabolic disease characterized by a decrease in bone mass and strength. The disease leads to skeletal fractures under light to moderate trauma and, in its advanced state, can lead to fractures under normal physiologic loading conditions. It is estimated that osteoporosis affects approximately 15-20 million people in the United States and that approximately 1.3 million new fractures each year are associated with osteoporosis, with the most common fracture sites being the hip, wrist and vertebrae.
An emerging prophylactic treatment for osteoporosis involves replacing weakened bone with a stronger synthetic bone substitute using minimally invasive surgical procedures. The weakened bone is first surgically removed from the affected site, thereby forming a cavity. The cavity is then filled with an injectable synthetic bone substitute and allowed to harden. The synthetic bone substitute provides structural reinforcement and thus lessens the risk of fracture of the affected bone. Without the availability of minimally invasive surgical procedures, however, the prophylactic fixation of osteoporosis-weakened bone in this manner would not be practical because of the increased morbidity, blood loss and risk of complications associated with conventional procedures. Moreover, minimally invasive techniques tend to preserve more of the remaining structural integrity of the bone because they minimize surgical trama to healthy tissue.
Other less common conditions in which structural reinforcement of bone can be appropriate include bone cancer and avascular necrosis. Surgical treatment for each of these conditions can involve removal of the diseased tissue by creating a tissue cavity and filling the cavity with a stronger synthetic bone substitute to provide structural reinforcement to the affected bone.
Existing devices for forming a cavity within soft or hard tissue are relatively complex assemblies consisting of multiple components. U.S. Pat. No. 5,445,639 to Kuslich et al. discloses an intervertebral reamer for use in fusing contiguous vertebra. The Kuslich et al. device comprises a cylindrical shaft containing a mechanical mechanism that causes cutting blades to extend axially from the shaft to cut a tissue cavity as the shaft is rotated. The shaft of the Kuslich et al. device, however, has a relatively large diameter in order to house the blade extension mechanism, and therefore it is necessary to create a relatively large access opening to insert the device into the body. The complexity of the device leads to increased manufacturing costs and may also raise concerns regarding the potential for malfunction.
U.S. Pat. No. 5,928,239 to Mirza discloses a percutaneous surgical cavitation device and method useful for forming a tissue cavity in minimally invasive surgery. The Mirza device comprises an elongated shaft and a separate cutting tip that is connected to one end of the shaft by a freely-rotating hinge, as shown in
U.S. Pat. No. 6,066,154 to Reiley et al. discloses an inflatable, balloon-like device for forming a cavity within tissue. The Reiley et al. device is inserted into the tissue and then inflated to form the cavity by compressing surrounding tissue, rather than by cutting away tissue. The Reiley et al. device, however, is not intended to cut tissue, and at least a small cavity must therefore be cut or otherwise formed in the tissue in order to initially insert the Reiley et al. device.
Thus, a need continues to exist for a tissue cavitation device and method that can form tissue cavities of various shapes that are significantly larger than the access opening in the target tissue. A need also exists for a cavitation device that is of relatively simple construction and inexpensive to manufacture, that can be operated either manually or by a powered surgical drill, and that, in the case of manual operation, provides the surgeon with increased control over the size and shape of the cavity formed.
The present invention comprises an improved tissue cavitation device and method that utilizes shape-changing behavior to form cavities in either hard or soft tissue. The shape-changing behavior enables the device to be inserted into tissue through a relatively small access opening, yet also enables the device to form a tissue cavity having a diameter larger than the diameter of the access opening. Thus, the invention is particularly useful in minimally invasive surgery, and can be used for at least the following specific applications, among others: (1) treatment or prevention of bone fracture, (2) joint fusion, (3) implant fixation, (4) tissue harvesting (especially bone), (5) removal of diseased tissue (hard or soft tissue), and (6) general tissue removal (hard or soft tissue).
The cavitation device of the present invention comprises a rotatable shaft having a flexible cutting element that is adapted to move between a first shape and a second shape during the process of forming an internal cavity within tissue. The process of forming the cavity primarily involves cutting tissue as the shaft is rotated about its longitudinal axis, but those skilled in the art will appreciate that the device also can form a cavity by impacting tissue or displacing tissue as the shaft is either partially or completely rotated. The internal cavity formed by the device has a significantly larger diameter than the diameter of the initial opening used to insert the device into the tissue. The present invention also comprises flexing means for biasing the flexible cutting element to move from its first shape to its second shape. One such means comprises spring bias arising from elastic deformation of the flexible cutting element. A second such means comprises bias arising from the behavior of a thermal shape-memory alloy. A third such means comprises bias arising from centrifugal force generated as the shaft is rotated. A fourth such means comprises a tension cable that forcefully actuates the shape change of the flexible cutting element. The device of the invention can be operated by conventional surgical drills, and some embodiments also can be manually operated using a conventional T-handle. When a T-handle is used to operate the device, the T-handle also can be adapted to apply tension to the tension cable.
During minimally invasive surgery, the flexible cutting element of the cavitation device can be adapted to assume a first shape for insertion of the device into tissue through a tube placed percutaneously, thereby creating only a relatively small access opening in the tissue. Depending on the application and size, the insertion tube can be a trochar, a cannula, or a needle. As the device is inserted beyond the distal end of the insertion tube, the flexible cutting element is adapted to assume a second shape for forming a cavity in tissue upon rotation of the shaft. When it assumes the second shape, the flexible cutting element extends or projects away from the longitudinal axis of the shaft. Thus, the diameter of the cavity is greater than the diameter of the initial access opening or pilot hole. In addition to cutting, a flexible cutting element is capable of displacing and impacting tissue away from the axis of the shaft.
According to one method of the present invention, the periphery of the target tissue, such as bone, can be accessed with an insertion tube placed percutaneously, and a pilot hole can be formed in the bone with a standard surgical drill and drill bit. Next, the cavitation device of the present invention is inserted to the depth of the pilot hole and rotated. As the flexible cutting element of the device moves from its first shape to its second shape, portions of the cutting element forcefully extend away from the longitudinal axis of the shaft, thereby forming a tissue cavity. Emulsified bone can be removed through known irrigation and suction methods. In the case of bone harvesting, the abated bone is used at another surgical site to promote healing of a bony deficit or to promote joint fusion. The cavity can then be filled with a suitable bone substitute that is injectable and hardens in situ. In the case of removing and replacing osteoporotic bone, the cavity is filled with structural synthetic bone or bone cement. Since the device and methods of the present invention are minimally invasive, they can be used for the prevention of osteoporosis related fractures in individuals at high risk. Skeletal structures where osteoporosis related fractures are common include the radius, femur, and vertebral bodies.
Surgeons can create cavities of various shapes and sizes with the device and methods of the present invention. For example, cavities of various shapes and sizes can be formed by moving the cavitation device along its axis of rotation or transverse to its axis of rotation. The size and shape of the cavity also can be modified by adjusting the insertion angle of the shaft (or the insertion tube, if one is used) with respect to the tissue angle. Tissue cavities of various shapes and sizes also can be interconnected to form more complex shapes.
The objects and advantages of the present invention include simplicity, wherein a flexible cutting element eliminates the need for complex assemblies with numerous moving parts. The shape-changing behavior of the flexible cutting element enables the device to be adapted to a shape suitable for minimally invasive placement in tissue. The inherent outward forces associated with the shape change of the flexible cutting element assist in the cutting and displacement of tissue during the process of forming a cavity.
Throughout the following description and the drawings, like reference numerals are used to identify like parts of the present invention.
As shown in
Cavitation device 100 can be constructed from a wide spectrum of surgical-grade stainless steels capable of elastic behavior. Consistent with spring mechanics, it is preferred to have the shape change of flexible cutting element 120 operate within the elastic range of the material. Stainless steels are strong, relatively inexpensive, and their manufacturing processes are well understood. Another suitable material is the metal alloy Nitinol (TiNi), a biomaterial capable of superelastic mechanical behavior, meaning that it can recover from significantly greater deformation compared to most other metal alloys. The Nitinol metal alloy contains almost equal parts of titanium and nickel. Nitinol has a “spring-back” potential ten times greater than stainless steels and is capable of nearly full recovery from 8% strain levels. Suppliers of Nitinol include Shape Memory Applications, Inc. and Nitinol Devices & Components. Alternatively, cavitation device 100 can be constructed from a polymer, such as nylon or ultra high molecular weight polyethylene.
A thermal shape-memory alloy can also be used as a flexing means for biasing a flexible cutting element to move from a first shape to a second shape. The most commonly used biomaterial with thermal shape-memory properties is the Nitinol metal alloy. A flexible cutting element made from Nitinol can be deformed below a transformation temperature to a shape suitable for percutaneous placement into tissue. The reversal of deformation is observed when the flexible cutting element is heated through the transformation temperature. The applied heat can be from the surrounding tissue, or associated with frictional heat generated during operation. Nitinol is capable of a wide range of shape-memory transformation temperatures appropriate for the clinical setting, including a transformation temperature at body temperature of 37° C. Heat may also be applied by passing electrical current through the material to cause resistive heating.
It may be advantageous to add additional features to enhance the performance of a cavitation device of the present invention and to enhance the process of cavity creation or tissue removal. Numerous secondary features to aid in tissue cutting include serrated edges, threads, cutting flutes, abrasive surfaces, and beveled edges. Variations and different combinations are possible without departing from the spirit of the present invention. Referring now to
Geometric variations, within the spirit of the present invention, may be developed to enhance or alter the performance of the dynamic shape behavior. Examples of such variations include the cross-sectional shape and the length of a flexible cutting element. For example, the cross-sectional shape of the flexible cutting element can form a quadrilateral so that the edges formed from the acute angles of the quadrilateral are adapted to aid in cutting. A quadrilateral cross-section with a particularly acute angle can form a knife-edge. Persons skilled in the art will understand that a flexible cutting element with a quadrilateral cross-section and a beveled edge would have a substantially quadrilateral cross-section and that a rectangular cross-section is a substantially quadrilateral cross-section. Further, the curvature of a flexible cutting element in the extended position may take a specific shape; therefore the shape of the tissue cavity need not be limited to combinations of cylindrical and hemispherical tissue cavities. Different tissue cavity shapes may be desirable for interfacing with an implant or to create a region of synthetic bone to match complex anatomical structures. In addition, a plurality of flexible cutting elements can be used, rather than a single flexible cutting element. As an example,
Another flexing means for biasing a flexible cutting element to move from a first shape toward a second shape is centrifugal force arising from rotational velocity of the shaft. Centrifugal force is the force that tends to impel a thing or parts of a thing outward from a center of rotation.
A sixth embodiment of the present invention, cavitation device 700, is shown in
Additional components may be added to enhance performance in circumstances requiring a more forceful change in shape of a flexible cutting element. For example, more force is appropriate for moving fractured bone to form a tissue cavity and restore the shape of bone structures, as in the case of treating compression fractures of vertebral bodies. A cavitation device of the present invention can be adapted to provide the operator with a means to directly apply a flexing force to a flexible cutting element.
A cavitation device of the present invention is shown in
Referring specifically to
Polymethylmethacrylate (PMMA), commonly referred to as bone cement, is a well-known bone synthetic substitute that has been in use for several decades. Although PMMA has been used effectively, there continue to be concerns regarding high exothermic temperatures and potentially toxic fumes produced by PMMA during curing. Other synthetic bone substitutes have been introduced in recent years, including resorbable and non-resorbable materials. An example of a recently introduced resorbable bone substitute is injectable calcium phosphate, such as the material offered by Synthes-Stratec, Inc. under the Norian Skeletal Repair System™ brand name. An example of a non-resorbable bone substitute is injectable terpolymer resin with combeite glass-ceramic reinforcing particles, such as the material offered by Orthovita, Inc. under the Cortoss™ brand name, which is said to have strength comparable to human cortical bone.
Osteoporosis can be a contributing factor to fractures of bone, especially the femur, radius, and vertebral bodies. There are several non-invasive methods for determining bone mineral density, and patients at high risk for fracture can be identified. Patients with previous fractures related to osteoporosis are at high risk for re-fracture or initial fractures of other bone structures. Minimally invasive devices and methods, combined with synthetic bone substitutes, allow for the strengthening of bone to be practiced as a preventive treatment for patients at high risk of fracture.
The proximal end of the femur, particularly the neck region, is a common location for osteoporosis-related fractures. Referring now to
There are numerous situations in orthopaedics where surgical treatment of a painful joint involves immobilization of the joint through a process called joint arthrodesis, or joint fusion. The device and method of the present invention can be used for fusion of numerous joints, including the spine or sacroiliac joint.
A spinal motion segment has numerous structures, including two vertebral bodies 58/58′ and an intervertebral disc 62, as shown schematically in
Implants, such as bone screws, anchors, pins and intramedullary nails are widely used in the orthopaedics. However, the effectiveness of such implants can be greatly diminished if their attachment to bone is not secure. Osteoporosis can lead to excessive porosity that compromises the integrity of the bone/implant interface. Loose implants are less effective and can cause additional problems if they migrate from their intended position. Local strengthening of the bone at the attachment site would be of tremendous benefit, and the present invention combined with synthetic bone substitutes addresses this problem.
Referring now to
To repair or fuse bone, surgeons often harvest bone from a second surgical site. Compared to allograft and current bone substitutes, autogenous bone graft provides all the cells, proteins, and matrix required to form new bone. Because of the morbidity associated with open procedures for harvesting bone, the trend is toward minimally invasive techniques associated with percutaneous instrumentation. The present invention allows for minimally invasive access to bone for harvesting. The dynamic shape behavior of the present invention will allow the technology to move toward less invasive instruments with smaller working diameters. Referring now to the
From the description above, a number of advantages of our invention become evident. The flexible cutting element of the invention eliminates the need for complex assemblies with numerous moving parts. Additionally, the shape-changing behavior of the flexible cutting element enables percutaneous passage through an insertion tube. The shape change behavior also improves cutting efficiency by providing a forceful press of a flexible cutting element against the tissue during formation of a cavity. The cavitation device of the present invention can be further adapted in multi-component configurations to provide the operator with a means for forcefully actuating a flexible cutting element on demand. The device and methods of the present invention are minimally invasive and have many applications, especially in orthopaedics.
The preferred embodiments presented in this disclosure are examples. Those skilled in the art can develop modifications and variants that do not depart from the spirit and scope of the disclosed cavitation devices and methods. For example, there are instances where an insertion tube is not required and a pilot hole in bone tissue is appropriate for passage to the cavitation site. Disclosed flexing means for biasing the flexible cuffing elements to move from a first shape to a second shape include elastic deformation, thermal shape-memory, centrifugal force, and force applied through a tension cable. Although these means are considered in the examples separately, cavitation devices of the present invention can comprise a combination of two or more of these means. Those skilled in the art will understand that markings on the shaft of a cavitation device of the invention can be used for indicating depth of insertion and that an additional fitting on the shaft can be used to limit the depth of insertion. Additional variants, also with the spirit and scope of the invention, include flexible cutting elements slidably connected to the shaft, such that the length of a flexible cutting element can be adjusted. Thus the scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given.