Patent Application
20190223917
The bone anchor and methods of use disclosed herein pertain to the field of orthopedic surgery, and more specifically, spinal surgery.
Spinal fusion is a common surgical procedure used to correct numerous disease states including degenerative disorders, trauma, instability, and deformity. A frequent method of fusion entails the use of bone screws placed through various sections of the vertebral body including the body, pedicle, facets, lamina, lateral masses, and/or transverse processes. These screws are then linked rigidly with a spinal rod, plate or other fixation device to immobilize the vertebral segments.
Due to the variation in a patient's anatomy and differences in screw placement technique, screws are often not perfectly aligned which makes securement of a spinal rod more difficult. To solve this, many screws that have a threaded shank portion incorporate an articulating tulip housing or receiver connected to the proximal end of the shank portion, such as in a polyaxial or multi-axial bone screw. Polyaxial bone screws allow for a variation in the angulation of the tulip/receiver relative to the shank portion in order to allow the tulip/receiver to more closely align for receiving a fixation device such as a fixation rod within the tulip/receiver. Some bone screws allow for the lateral translation of the tulip/receiver relative to its point of fixation. Further alignment may be accomplished by contouring of the spinal rod itself to compensate for any remaining misalignment. For example, if a spinal rod is employed, the rod can be bent to conform to the patient anatomy and location of the tulip/receiver to securely attach thereto.
While developments to decrease the overall invasiveness of spinal surgical methods are desirable, conventional surgeries still utilize certain invasive steps, such as tapping or undertapping. A tapping procedure is performed as follows: a bone access needle is used to generate an access hole in the bone. The inner shaft of the bone access needle is removed, and a guidewire is inserted a guidewire thru the inner hole of the bone needle. The remaining portion of the bone access needle is removed while taking care to ensure the guidewire does not move within the bone. A small diameter tap is inserted by rotating the tap into the bone. The smallest diameter tap is removed by turning it outwardly, and a slightly larger size tap is inserted and removed in the same fashion to widen the hole. The taps get progressively larger until the hole is the appropriate for the bone anchor. Undertapping procedures are similar to tapping procedures, except that the last tap used is slightly smaller in diameter than the actual bone anchor. Tapping and undertapping procedures lengthen the duration of the surgery. Conventional spinal surgeries also utilize relatively bulky devices. Developments to decrease the overall invasiveness of spinal surgical methods are therefore needed.
The aforementioned discrepancies in existing orthopedic technology are addressed herein. The bone anchors disclosed herein are smaller in overall diameter, which is less invasive to the patient. The small diameter requires less muscle splitting and results in a smaller incision. Having a smaller diameter tulip housing also allows the screw to be seated closer to the center of rotation of the vertebral body segment within the spinal column.
The bone anchors disclosed herein include a tulip housing comprising a through hole and a distal radially expandable portion, a shank comprising a proximal ball head positioned within the through hole of the distal radially expandable portion, and a pressure cap positioned within the through hole (proximally adjacent to the ball head). The pressure cap includes a bearing surface configured to interface with the ball head. The bone anchors include a retaining ring that limits radial expansion of the distal radially expandable portion when positioned around the distal radially expandable portion, thereby preventing distal movement of the pressure cap and the proximal ball head out of the through hole. In some embodiments, one or more components of the bone anchor can be formed of a metal, such as molybdenum rhenium (MoRe). For example, the tulip housing can be formed of MoRe.
The pressure cap of the bone anchor is positioned within the through hole of the tulip housing. In some embodiments, a proximal surface of the pressure cap comprises a saddle for interfacing with a spinal rod. The saddle can be substantially V-shaped in cross section. The distal bearing surface of the pressure cap can be conical or frustoconical for interfacing with a ball head.
The bone anchors disclosed herein can also include a compression mechanism for forcing the pressure cap into close contact with the ball head. The compression mechanism limits proximal movement of the pressure cap and the proximal ball head within the through hole. The compression mechanism can include a compressing component that exerts a distally oriented force on the pressure cap. In some embodiments, the compression mechanism functions as follows: the pressure cap has a ramped external surface, and a compressing component, such as a pin or screw, extends through a hole in the sidewall of the tulip housing to contact the ramped external surface of the pressure cap. The lateral force placed on the pressure cap by the compressing component is translated to a distally oriented force by the ramped surface.
The radially expandable portion of bone anchor can flex outwardly to permit the passage of the pressure cap and the ball head. In some embodiments, the radially expandable portion can include at least two tabs separated by relief slots. The radially expandable portion can also include a lateral groove for retaining the retaining ring. In some embodiments, the retaining ring includes a first laterally extending locking feature that is configured to mate with a corresponding second laterally extending locking feature on the radially expandable portion.
The bone anchor is configured for a bottom-up assembly, meaning that the pressure cap and the ball head are inserted through the distal end of the tulip housing. The smallest inner diameter of the radially expandable portion is larger than the largest outer diameter of the ball head and pressure cap when the radially expandable portion is in an expanded state, and the same smallest inner diameter is smaller than the largest outer diameter of the ball head and pressure cap when the radially expandable portion is in a contracted state. Furthermore, the smallest inner diameter of the proximal portion of tulip housing is smaller than the largest diameter of the distal threaded portion of the shank, which prevents the shank from being inserted proximally through the through hole of the tulip housing.
One or more attachment features can be located on the tulip housing to facilitate engagement with other devices, such as surgical instruments. In some embodiments, one or more longitudinally extending indentations or protrusions can be included as an attachment feature. The longitudinally extending indentation or protrusion can include angled surfaces. In some embodiments, one or more laterally extending indentations or protrusions can be included as an attachment feature. The laterally extending indentation or protrusion can include angled surfaces.
The shank of the bone anchor can include a threaded region comprising proximal and distal threaded portions for engaging with the bone. The distal threaded portion can, in some embodiments, include a distal set of threads that extends to meet the distal end of the shank. A channel depth of the distal set of threads at the distal end of shank can be greater than zero. In some embodiments, the distal set of threads terminates with cutting edges. Some embodiments include a proximal set of threads with a pitch that is smaller than the pitch of the distal set of threads. The proximal set of threads can be quad lead, and the distal set of threads can be dual lead. In some embodiments, the proximal set of threads extend distally for at least 10 millimeters. In some embodiments, the pitch and lead of the threads is constant throughout the threaded region. In some embodiments, the entire threaded region is dual lead.
Methods of assembling a bone anchor are disclosed herein. The methods include: inserting a pressure cap into a through hole at a distal end of a tulip housing, inserting a proximal ball head of a bone anchor into the through hole at the distal end of the tulip housing, and positioning a retaining ring around a distal radially expandable portion of the tulip housing, thereby preventing distal movement of the pressure cap and the proximal ball head out of the through hole. Inserting the pressure cap and/or inserting the proximal ball head into the through hole can include radially expanding the distal radially expandable portion of the tulip housing. Positioning the retaining ring around the distal radially expandable portion can include limiting the radial expansion of the distal radially expandable portion. Some embodiments of the method further include activating a compression mechanism and forcing the pressure cap into close contact with the ball head. Activating the compression mechanism can include inserting a compressing component through a sidewall of the metal tulip housing.
Methods of inserting bone anchors are also disclosed herein. The methods include inserting a bone access needle into a bone, thereby creating a needle hole space, inserting a guidewire through the bone access needle, removing the bone access needle, screwing a bone anchor into the needle hole space over the guidewire, and removing the guidewire. The method is performed without tapping the bone anchor into the bone. In some embodiments, the bone anchor is screwed into the needle hole space without first widening the needle hole space. In other embodiments, the needle hole space is widened to create a pilot hole prior to screwing a bone anchor into the needle hole space. The bone may be a pedicle, and the bone access needle is a pedicle access needle or a Jamshidi needle. In some embodiments, a minor diameter of the bone anchor approximately matches the outer diameter of the bone access needle. The method can further include inserting a spinal rod into a tulip housing of the bone anchor and locking the spinal rod into place using a set screw.
The following description of certain examples of the inventive concepts should not be used to limit the scope of the claims. Other examples, features, aspects, embodiments, and advantages will become apparent to those skilled in the art from the following description. As will be realized, the device and/or methods are capable of other different and obvious aspects, all without departing from the spirit of the inventive concepts. Accordingly, the drawings and descriptions should be regarded as illustrative in nature and not restrictive.
For purposes of this description, certain aspects, advantages, and novel features of the embodiments of this disclosure are described herein. The described methods, systems, and apparatus should not be construed as limiting in any way. Instead, the present disclosure is directed toward all novel and nonobvious features and aspects of the various disclosed embodiments, alone and in various combinations and sub-combinations with one another. The disclosed methods, systems, and apparatus are not limited to any specific aspect, feature, or combination thereof, nor do the disclosed methods, systems, and apparatus require that any one or more specific advantages be present or problems be solved.
Features, integers, characteristics, compounds, chemical moieties, or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract, and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract, and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.
It should be appreciated that any patent, publication, or other disclosure material, in whole or in part, that is said to be incorporated by reference herein is incorporated herein only to the extent that the incorporated material does not conflict with existing definitions, statements, or other disclosure material set forth in this disclosure. As such, and to the extent necessary, the disclosure as explicitly set forth herein supersedes any conflicting material incorporated herein by reference. Any material, or portion thereof, that is said to be incorporated by reference herein, but which conflicts with existing definitions, statements, or other disclosure material set forth herein will only be incorporated to the extent that no conflict arises between that incorporated material and the existing disclosure material.
As used in the specification and the appended claims, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and/or to “about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent “about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint.
“Optional” or “optionally” means that the subsequently described event or circumstance may or may not occur, and that the description includes instances where said event or circumstance occurs and instances where it does not.
Throughout the description and claims of this specification, the word “comprise” and variations of the word, such as “comprising” and “comprises,” means “including but not limited to,” and is not intended to exclude, for example, other additives, components, integers or steps. “Exemplary” means “an example of” and is not intended to convey an indication of a preferred or ideal aspect. “Such as” is not used in a restrictive sense, but for explanatory purposes.
The terms “proximal” and “distal” are orientations that indicate the positioning of a surgical device. As used herein, the terms “distal” and “distally” indicate a direction farther from a practitioner performing a surgical procedure. “Proximal” and “proximally” indicate a direction closer to a practitioner performing the procedure. For example, the shank of a bone anchor is distal to the ball head of an anchor.
Tulip housing 4 includes a distally located radially expandable portion 6. The radially expandable portion 6 expands to enable the insertion of the pressure cap 16 and the ball head 14 into the through hole 8, despite their larger diameters (discussed in greater detail below). The embodiment shown in
When the radially expandable portion 6 is in an expanded state, the smallest inner diameter of the radially expandable portion 6 is larger than the largest outer diameter of the ball head 14, enabling passage of the ball head 14 for a bottom-up assembly. However, when radially expandable portion 6 is in a contracted state (due to the constriction by the retaining ring 20), the same smallest inner diameter is smaller than the largest outer diameter of the ball head 14, which prevents it from being expelled distally from the tulip housing 4. In other words, retaining ring 20 prevents the radially expandable portion 6 from expanding, and the assembly remains intact. With the ball head 14 captured, for example, having from about a 0.0001 inch to about a 0.04 inch lateral interference, maximum angulation of the threaded shank 10 is achieved. The conical angulation can be, for example, up to 75 degrees (from about 0 degrees to about 75 degrees). Angulation is dependent on the diameter of the ball head 14, the diameter of the neck 50, the diameter of the through hole 8, and the amount of material on the underside of the tulip housing (adjacent the through hole 8).
The proximal portion 52 of the tulip housing 4 has a smallest inner diameter that is smaller than the largest outer diameters of the ball head 14, the pressure cap 16, and the threads of the threaded shank 10, preventing these items from being proximally translated within the through hole 8. The bottom-up assembly (wherein the pressure cap 16 and ball head 14 are inserted into the tulip housing 4 through the distal end of the through hole 8) is advantageous because it allows the tulip housing 4 to be smaller and therefore less invasive. In some embodiments, the tulip housing 4 can be from about 5% to about 15% smaller than conventionally used tulip housings. The diameter of ball head 14 (as well as most major diameter sizes of the bone anchor) is larger than the narrowest path through the tulip housing 4, so it is not possible to assemble from the top as with conventional bone anchors and polyaxial screws. In one embodiment, the largest outer diameter of the tulip housing 4 is from about 9.9 millimeters to about 11.9 millimeters.
The tulip housing 4 can include attachment features that assist with engagement to other devices, such as one or more blades (e.g., blades 66, 68 shown in
Some or all of the components of the bone anchor 2 can be formed of a metal material. For example, in some embodiments the tulip housing 4, shank 10, pressure cap 16, retaining ring 20, and/or pins 24 are formed of molybdenum rhenium (MoRe). The use of MoRe in surgical implants is described elsewhere, for example, in International Patent Application Publication No. WO 2017/003926, published Jan. 5, 2017, and entitled “Molybdenum alloys for medical devices”, U.S. Patent Application Publication No. 2016/0237541, published Aug. 18, 2016, and entitled “Improved Metal Alloy For Medical Devices”, and U.S. Pat. No. 7,488,444 to Furst et al., issued Feb. 10, 2009, and entitled “Metal alloys for medical devices”, which are incorporated by reference in its entirety and for all purposes.
The use of MoRe enables the design of smaller, less invasive components. MoRe as a material is highly resistant to fatigue, which enables the design of thinner walls. MoRe is not notch sensitive, which enables the design of notches and angled surfaces. The notches enable, for example, the inclusion of tabs 40 that lend flexibility of the radially expanding portion 6. Angled surfaces can be advantageous, for example, to prevent sliding between interlocking mechanisms (such as sliding between the interlocking features 46, 48 on the radially expanding portion 6 and retaining ring 20, or sliding between the indentations 56, 58 on tulip housing 4 and their counterparts on engaged instruments). Angled corners also take up less space than rounded corners, which again enables the design of smaller devices.
Various embodiments of the shank 10 are shown in
Instruments for use with a bone anchor are also disclosed herein.
Adjacent pairs of blades define a path between adjacent bone anchors 2 along the spine of the patient during the surgery (not shown). A longitudinal member, such as a spinal rod 3, can be passed or threaded between one pair of blades 66, 68 and an adjacent pair of blades along the spine. The proximal regions 71 of the blades 66, 68 can include fixation features 73, such as through-holes, through-slots, notches, grooves, or cut-outs, for attachment to other surgical instruments. The blades can be made of disposable or reusable materials. Materials used to make blades 66, 68 can include but are not limited to: MoRe, stainless steel, polypropylene, polycarbonate, titanium or a titanium alloy, carbon fiber, and aluminum. In some embodiments, the walls of the blades range from about 1 millimeter to about 4 millimeters.
The curved internal surface 72 can also include an axial locking feature 78, which limits axial movement of the blade with respect to the bone anchor 2. In the embodiment shown in
In some embodiments, a disengagement instrument can, for example, have two handles with two extensions protruding distally from the handles. The handles and both extensions can be held in an open position by springs, for example. One distally protruding extension contains a pin member which mates with a hole located in the sidewall 84 of blade 66, positioned above the skin of the patient during the procedure. The second distally protruding extension is inserted down the length of the interior portion of the elongated blade 66, and has a projecting member. Compressing the handles thrusts the projecting member outward, thus disengaging the elongated member from the bone anchor (for example, by pushing flexing living hinge 82 outwardly and thereby pushing axial locking feature 78 away from the bone anchor 2). With the handles still compressed, the disengagement instrument holds onto the elongated blade 66 during removal from the surgical site to ensure the elongated blade does not fall back into the surgical site for safety to the patient.
Methods of assembling bone anchors are disclosed herein. The bone anchors disclosed herein are assembled by inserting pressure cap 16 into a through hole 8 at a distal end of a tulip housing 4, inserting a proximal ball head 14 of a bone anchor 2 into the through hole 8 at the distal end of the tulip housing 4, and positioning a retaining ring 20 around a distal radially expandable portion 6 of the tulip housing 4 (thereby preventing distal movement of the pressure cap 16 and the proximal ball head 14 out of the through hole 8). The radially expandable distal portion 6 expands to allow for the passage of pressure cap 16 and ball head 14 as they are inserted into the through hole 8. The expansion is possible because tabs 40 of the radially expandable portion 6 flex outwardly during the passage of the ball head 14 and pressure cap 16, which have larger diameters. Positioning the retaining ring 20 limits further expansion of the distal radially expandable portion 6 of tulip housing 4, preventing distal movement of the ball head 14 out of through hole 8. The method of assembling the bone anchor 2 further comprises activating a compression mechanism that forces the pressure cap 16 into close contact with the ball head 14. In some embodiments, activating a compression mechanism includes inserting a compressing component 24 through a sidewall 28 of the metal tulip housing 4.
The bone anchors described herein can be inserted without tapping or undertapping. Methods of inserting the bone anchors include inserting a bone access needle into a bone to create a needle hole space, inserting a guidewire through the bone access needle within the needle hole space, removing the bone access needle, screwing a cannulated bone anchor into the needle hole space over the guidewire, and removing the guidewire. No tapping or undertapping steps are performed, reducing the duration and the invasiveness of the procedure. In some embodiments of the method, the bone anchor is screwed into the needle hole space without first widening the needle hole space. In other embodiments, the needle hole space is widened to create a pilot hole prior to screwing in the bone anchor. The bone can be a pedicle in some embodiments. The bone access needle can be a pedicle access needle, or, in some embodiments, a Jamshidi needle. The minor diameter of the distal threaded portion 12 of the bone anchor 2 can be chosen to approximately match the outer diameter of the bone access needle (and therefore, the needle hole space). The method of inserting the bone anchor can also include inserting a spinal rod 3 between the sidewalls 30 of two adjacent tulip housings 4, and locking the spinal rod 3 into place using set screws 5 (an exploded perspective view of these components is shown in
This application claims the benefit of priority to U.S. Provisional Application No. 62/395,613, filed Sep. 16, 2016, which is hereby incorporated by reference in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US17/51983 | 9/18/2017 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62395613 | Sep 2016 | US |
