Patent Application
20070066987
The present invention provides self re-directing stylets or, more generally, probes for navigating within cancellous bone enclosed by relatively dense cortical bone. Also provided are methods for using the stylets in helping to retrieve bone marrow aspirate. Methods for using the stylets in procedures involving delivery of material are also provided.
Bone marrow aspiration is a common surgical procedure that involves harvesting of bone marrow from bony structures such as the iliac crest and vertebral body. As will be appreciated, relatively soft, relatively porous, cancellous bone generally resides within relatively hard and less porous cortical bone in areas such as the iliac crest. Access to the cancellous bone permits the harvesting of appreciable amounts of marrow, which is useful in a number of important procedures and in research. Typically, for these procedures, bone marrow aspiration needles are inserted by either tapping or manually advancing into place through the cortical bone and into the cancellous bone area. These needles often include a modular outer cannula and sharp tip stylet assembly, or a one-piece cannulated needle with a sharpened distal tip that is positioned through the cortical wall into the middle cancellous region of the bone, where the marrow is to be harvested. In the case of the assembly, the stylet is removed from the cannula to draw the marrow outside of the body through the cannula, usually into a syringe. In the case of the one piece needle, side ports or fenestrations may be present on the needle to allow for aspiration through the cannula. During the harvesting procedure, the needle is maneuvered within the cancellous bone space to access the marrow.
There are numerous devices in the art that allow for the aspiration of bone marrow from bone. As a class, they suffer from a significant shortcoming in that the sharpened component is capable not only of penetrating a first cortical bone area and into the cancellous bone mass, but also of passing through the cancellous bone and through a further cortical bone wall and out of the bone entirely. The resulting injury can be severe and is clearly to be avoided.
None of the prior devices for marrow harvest, however, have a safety feature for reducing the risk of or preventing damage to tissue external to bone from incorrect or inappropriate employment of the devices. There is a need to provide a device for bone marrow aspiration, which can be used to probe or navigate through cancellous bone safely with little or no risk of unintended puncture to the cortical bone. Further, there is a need in the art to provide a system for bone marrow aspiration that includes a bone navigating probe having improved safety features.
The present invention provides a solid, effectively rigid, self re-directing probe or stylet for navigating cancellous bone. The probe is used as part of an assembly, which is able to pierce cortical bone, such as of the iliac crest, through employment of a sharp stylet. An effectively rigid navigating stylet comprising a proximate mating end and a distal end having a convex geometry is then employed to explore the cancellous bone space within the surrounding cortical bone envelope. The invention thus provides a bone navigation system comprising a cannula, a sharp tip stylet, and a rigid navigating stylet. The cannula has a proximate end and a distal end. The proximate end of the cannula comprises a handle assembly having finger recesses, securing mechanism, such as a Luer to dock a syringe, and preferably a locking arrangement such as a locking recess or notch for receiving a locking tab on a mating stylet. The distal end has fenestrations. The sharp tip stylet has a hub assembly preferably comprising a locking tab and a hammering surface that mates with a handle in an overall assembly. The rigid navigating stylet for navigating trabecular bone may feature a hub assembly, such as one comprising a locking tab on the proximate end of the stylet and a convex geometry, such as a dome, on the distal end.
The cannula and stylets and, indeed, the entire assembly may be formed from any material consistent with the intended functions of the respective parts. Stainless steel is conventional and convenient for medical devices and is one preferred material. A number of plastics, polymers, metals and rubbers which are relatively rigid and can be sterilized may also be employed, especially for the portions of the device which are not intended to enter the bone spaces. The sharp portions of the device, especially the distal portions of the cannula and sharp tip stylet are preferably metal, especially stainless steel. Certain plastics and ceramics can be made to hold a sharp edge and could be employed, however, for these aspects of the invention. In one embodiment, the cannula bears graduated markings over at least a portion of its length to help gauge depth or location. Other portions may also carry geometric landmarks or markings to facilitate navigation in the bone. The landmarks may be at least partially radiopaque so that they may be monitored via fluoroscopy. The several handle and hub assemblies may comprise plastic, metal or other convenient materials.
Also provided are methods of accessing a trabecular site using the rigid navigating stylet. The method comprises piercing cortical bone with the sharp tip stylet preferably having a hub assembly comprising a locking tab and a striking surface that mates with a handle assembly of the cannula, also referred to as a docking cannula. Once the outer cortical bone is pierced, the sharp tip stylet is separated and removed from the cannula. The navigating stylet is then inserted into the lumen of the cannula for navigating the assembly in the cancellous bone. The navigating stylet preferably has a hub assembly comprising a locking tab on the proximate end and a convex geometry, such as a dome, hemi-sphere or spherical portion, on the distal end. The methods disclosed herein may also be used to access the iliac crest, pedicle or other such suitable bone during aspiration of bone marrow. It will be appreciated that further embodiments of the present invention may be developed from this disclosure.
a and 5b show a sharp tip stylet puncturing the cortical bone and a navigating stylet of this invention which has re-directed off the cortical wall back into cancellous space.
The present invention relates to apparatuses for safely probing cancellous bone while avoiding the accidental penetration of surrounding cortical bone. A preferred embodiment of the invention includes a solid, effectively rigid, self re-directing or navigating stylet for probing intraosseous spaces. As used herein, the term intraosseous refers to the bony area between two cortical walls. This navigating stylet comprises a proximate mating end for mating with a cannula, and a distal end in the shape of a convex geometry, such as a dome, hemi-sphere or partial spherical portion. An embodiment of the invention may also be described as an effectively rigid, self re-directing stylet for navigating trabecular bone. After the cortical bone of the iliac crest, pedicle or other such bone is pierced using a cannula- sharp tip stylet assembly, the stylet comprising a proximate mating end and a “blunt” end, one which is convex by reference to the plane normal to the axis of the stylet is inserted and maneuvered via the cannula. In one embodiment, the end is in the shape of a dome. The convex end at least partially enables the stylet to be self-redirecting. As such, this end is a safety feature.
An exemplary, novel device for the aspiration of bone marrow is disclosed in
While selection of dimensions is within the purview of persons skilled in the art, the length of the sharp tip stylet 111 and navigating 112 stylet is generally between about 12 cm and about 18 cm; the diameter can range between about 2 mm and about 12 mm. The length of cannula 110 is generally between about 10 cm and about 15 cm. It should be noted that the respective lengths of the stylets should always be longer than the length of the cannula for best function. The inner diameter of the cannula is slightly larger than the outer diameter of the stylets, allowing the components to operate as a system during the advancement of the assembly into bone in a generally co-axial fashion. The distal end of the cannula 110 preferably has a conical grind 61 that gradually tapers from the outer diameter of the cannula to its inner diameter, which is slightly larger than the outer diameter of the stylet 111 and 112. The materials, structure, design and other aspects of the cannula—and, indeed, the remaining portions of the system provided hereby, will be guided by the functions to be performed thereby. Thus, in the case of the cannula, a metal suitable for surgery, especially stainless steel, is preferably employed. The dimensions of the cannula-sharp tip stylet assembly are selected to permit transmission of appropriate force for penetrating the cortical bone.
The present invention also provides bone marrow aspiration assemblies. These devices allow the user to safely navigate within the cancellous bone regions in order to safely obtain bone marrow aspirate. A cannula interfaces, preferably co-axially, with both a sharp tip stylet and a navigating stylet. A cannula handle, especially one which is ergonomically designed for user comfort and careful control of the stylets is also preferably provided as part of the system. The cannula handle may also be seen to allow for stability and ease of use when applying force to the cannula-sharp tip stylet assembly. It also preferably is adapted, such as via a preferred, threaded Luer connection with an inlet, to provide a docking station for the stylets to be inserted and withdrawn from the cannula and for a surgical syringe to withdraw bone marrow. The stylets preferably have a proximal hub composed of a rigid medical grade plastic. The flat surface of the stylet hub provides a stable platform if hammering is necessary to perforate the cortical bone with the sharp tip stylet. The cannula Luer, shown infra as 160 is preferably protected by a recess 50 that is within the hub assembly 140.
The exemplary cannula handle assembly 115 preferably has finger recesses 100 which provide comfort and handling stability for the user. The placement of the finger recesses 100 allows the user to grip the handle 115 in a variety of configurations. The cannula 110 can be gripped between the index and middle, or middle and ring fingers. The overall size of the handle 115 is designed to fit in the palm of the hand and rounded edges are provided to confer a comfortable grip. In the cannula 110 medical grade stainless steel is insert-molded into the cannula handle assembly 115, which is composed of a rigid medical grade plastic. Laser etched graduations 90 spaced, e.g. 1 cm apart allow for depth measurement within the cancellous bone spaces. The stylets are secured in the assembly by a notch 130 in the cannula handle 115. A standardized Luer 160 is inset within the cannula handle to allow attachment of a surgical syringe for bone marrow aspiration and also to serve as an inlet port for the insertion of the stylets into the lumen of the cannula 110. Fenestrations 80—holes—at the distal end of the cannula 110 allow bone marrow to be aspirated from different directions and depths, even when the cannula is in a stationary position. This feature also allows a relatively large volume of bone marrow to be harvested at each location compared to non-fenestrated designs. There are preferably at least three fenestrations 80 located e.g. within 20 mm from the distal end of the cannula 110 and radially spaced 120° apart on the same cross-sectional plane as shown in
The stylets 111, 112 may comprise exemplary medical grade stainless steel insert-molded into a rigid plastic hub 140. The stylet hubs 140 may be color coded to let the user know which stylet is inserted in the cannula 110. The sharp tip stylet hub 140 may be black or red, indicating danger or caution. The blunt tip navigating stylet hub 140 is preferably green to indicate that the safe “navigation” tip is in place. It should be understood that the sharp tip stylet may be a diamond tip or trocar stylet, or may be beveled. The sharp tip stylet could also be like a cork screw or may even have threads or cutting flutes like a drill bit. When assembled with the cannula handle 115, the hubs 140 provide a stable hammering platform 150 for perforating cortical bone with the trocar stylet 111. The hub 150 is designed to fit securely into the cannula handle 115 through a locking mechanism. When a stylet of the present invention is fully inserted into the lumen of the cannula 110, the tab 120 of the stylet hub 150 locks into a notch 130 in the cannula handle 115 through a twisting motion. This locking mechanism prevents separation of the stylet from the cannula 110 and forms a hammering surface 150. The ergonomic design of this handle assembly 115 provides stability and ease of use when exerting force on the needle 111 to perforate the cortical bone.
The recess 50 in the stylet hub 140, provides a protective housing for the cannula Luer 160. This housing prevents damage to the Luer threads if hammering is necessary to perforate the cortical bone with the trocar stylet 111. Once the trocar stylet 111 has been used to pierce the cortical wall, it is easily removed by rotating the stylet hub 140 to disengage the tab 120 from the recess 130. The trocar stylet 111 can then be withdrawn from the cannula 110 and exchanged with the navigating stylet 112, which is inserted and locked into place using the tab 120 by rotating the stylet hub 140.
The navigating stylet 112 allows the user to safely navigate within the cortical bone boundaries in order to correctly position the cannula 110 within the cancellous bone marrow space. A convex end 60, one which is preferably rounded, chamfered or otherwise blunted is provided on the navigating stylet so that the tip will deflect off of dense, cortical bone walls which surround the softer cancellous bone regions, thus re-directing the cannula assembly within the cancellous bone marrow space. This minimizes the risk for accidental perforation of the cortical bone boundaries, which could result in damage to nerves, vessels, or soft tissue structures.
a depicts the distal tip 60 of a navigating stylet 112 of the invention apart from the cannula. The tip may be seen to be blunt and convex with respect to the plane normal to the axis of the stylet. In
Once the desired depth or location is reached, the navigating stylet 112 can be removed, e.g. by rotating the stylet hub 140 to disengage the tab 120, and withdrawing the stylet 112 out of the cannula 110. To aspirate bone marrow, a surgical syringe (not shown) may conveniently be attached to the cannula Luer 160 and suction applied by withdrawing the syringe plunger. Prior to repositioning or removing the cannula 110, the navigating stylet 112 is preferably reinserted and locked into place via the locking mechanism of the hub 140. If it is necessary to harvest from an additional site, the trocar stylet 111 may be re-inserted to perforate the cortical bone and gain entry into the cancellous bone space at another location.
While one preferred embodiment of the device has been disclosed, the invention is not limited to these specifications. For example, while the preferred length of the stylet is between 12 and 18 centimeters, and the preferred length of the cannula is between 10 and 15 centimeters, any functional length up to and including 25 centimeters may be necessary. Further, while the diameter of the stylet has been disclosed as being between 2 and 12 millimeters, the utility of a smaller or larger device can be useful. In addition, the cannula and stylets have been disclosed as being composed of stainless steel, however these components may be made of any medical grade material that has the strength and rigidity to perforate through cortical bone and navigate within the marrow space. Further, while the cannula handle and stylet hubs have been disclosed as being constructed out of plastic, other rigid medical grade materials could be used for the same purpose. While one locking mechanism for securing the stylet into the cannula handle has been disclosed, any method of mechanically interlocking the stylet to the cannula that allows easy insertion and removal of the stylet is acceptable. The cannula handle has been disclosed as having a Luer as the inlet port to allow for the attachment of a surgical syringe, however other coupling devices such as press fit ports could be used.
In addition, the cannula inlet port may be coupled to devices other than a syringe for use in a variety of procedures involving biopsy or aspiration, and the device assembly is not exclusive to bone marrow aspiration. The navigating stylet has been disclosed as a device that can be used to safely navigate within cortical bone boundaries and safely access cancellous bone marrow spaces. The bone boundaries can be the boundaries of the iliac crest, vertebral body, pedicles or other such bones as desired.
While the present invention has been disclosed for procedures involving the aspiration of bone marrow, the assembly could be used in other procedures in which it is desirable to safely gain access to the interior of bone. The present invention could be utilized in procedures involving the delivery of materials to bone (as opposed to procedures that involve the withdrawal of fluids such as bone marrow aspirate from the bone). For example, the present invention may find utility in procedures such as vertebroplasty or kyphoplasty in which it is necessary to gain access to the interior of vertebral bodies to inject hardenable materials such as bone cements, polymethylmethacrylate (PMMA), calcium phosphate injectables or other hardenable methacrylate based materials such as Cortoss® manufactured by Orthovita, Inc.®.
The sharp tip stylet is inserted into the cannula lumen and is mechanically interlocked by rotating the hub to engage the locking mechanism of the stylet into the notched void of the cannula handle. In
