Patent Description:
Currently, with screw-based constructs for forming bone-to-bone fixation of a joint, surgeons must compromise between obtaining compression and obtaining significant stability. When forming bone-to-bone fixation, compression screws provide optimal compression but not optimal stability. On the other hand, with proper technique, full-threaded constant-pitch screws can provide more stability but not optimal compression. There is a need for a screw construct and a technique for using the screw construct that can accomplish both. In document <CIT> a permanent implant used in orthopedic surgical operations is described.

Disclosed but not claimed is a method for fusing a joint between a first bone and a second bone using a nested screw assembly that comprises: a cannulated outer screw; and an inner screw, wherein: the outer screw comprises: a tubular body having a first end and a second end defining a length between the two ends; and a canal extending through the length of the outer screw. At least a portion of the length of the outer screw is externally threaded and at least a portion of the length of the canal is internally threaded near the first end. The inner screw is externally threaded, and the external thread of the outer screw, the internal thread of the outer screw, and the external thread of the inner screw all have the same thread pitch, whereby the inner screw can be threaded into the first end of the canal of the outer screw to form the nested screw assembly. The method comprises: (a) pre-drilling a hole into the first bone and the second bone through the joint; (b) threading the outer screw into the hole in the first bone up to the joint; (c) threading the inner screw into the hole in the second bone from the opposite side until the inner screw engages with the internally threaded portion of the outer screw from the first end of the outer screw, and tightening to compress the joint while holding the outer screw from turning; and (d) driving the outer screw further into the hole toward and across the joint to maintain compression of the joint.

Also provided is a nested screw assembly comprising: a cannulated outer screw; and an inner screw, wherein, the outer screw comprises a tubular structure having a first end and a second end defining a length between the two ends, and a canal extending through the length of the outer screw, at least a portion of the length of the outer screw is externally threaded and at least a portion of the length of the canal is internally threaded near the first end, the inner screw is externally threaded, and the external thread of the outer screw, the internal thread of the outer screw, and the external thread of the inner screw all have the same thread pitch, whereby the inner screw can be threaded into the first end of the canal of the outer screw to form the nested screw assembly.

These and other features and advantages of the bone fixation implants and methods of implantation described herein will be more fully disclosed in, or rendered obvious by, the following detailed description of the preferred embodiments, which is to be considered together with the accompanying drawings wherein like numbers refer to like parts and further wherein:.

All illustrations shown in the figures are schematic and are not intended to show actual dimensions or proportions.

This description of preferred embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description of this invention. The drawing figures are not necessarily to scale and certain features of the invention may be shown exaggerated in scale or in somewhat schematic form in the interest of clarity and conciseness. In the description, relative terms such as "horizontal," "vertical," "up," "down," "top," and "bottom" as well as derivatives thereof (e.g., "horizontally," "downwardly," "upwardly," etc.) should be construed to refer to the orientation as then described or as shown in the drawing figure under discussion. These relative terms are for convenience of description and normally are not intended to require a particular orientation. Terms including "inwardly" versus "outwardly," "longitudinal" versus "lateral" and the like are to be interpreted relative to one another or relative to an axis of elongation, or an axis or center of rotation, as appropriate. Terms concerning attachments, coupling and the like, such as "connected" and "interconnected," refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.

Disclosed but not claimed is a novel method for fusing a joint between two bones using a nested screw assembly. An example of an application of the disclosed novel method is fusing the first tarsometatarsal (TMT) joint in a Lapidus procedure.

Referring to <FIG>, a nested screw assembly <NUM> is disclosed. The nested screw assembly <NUM> comprises a cannulated outer screw <NUM> and an inner screw <NUM> that is threaded into the cannulated outer screw <NUM>.

Referring to <FIG>, the outer screw <NUM> comprises a body that is a tubular structure having a first end <NUM> and a second end <NUM> defining a length between the two ends, and a canal <NUM> extending through the length of the outer screw <NUM>. At least a portion of the length of the outer screw is externally threaded with threading <NUM> and at least a portion <NUM> of the length of the canal <NUM> is internally threaded with threading <NUM> near the first end <NUM>. In the illustrated example in <FIG>, the whole length of the exterior surface of the outer screw <NUM> is threaded.

Referring to <FIG>, the inner screw <NUM> comprises a body, a substantial portion <NUM> of which is externally threaded with threading <NUM>. The internal thread <NUM> of the outer screw and the external thread <NUM> of the inner screw have the same thread pitch so that the inner screw <NUM> can be threaded into the first end <NUM> of the canal <NUM> of the outer screw <NUM> to form the nested screw assembly <NUM>. The external thread <NUM> of the outer screw <NUM> is also configured to have the same thread pitch and handedness as the internal thread <NUM> of the outer screw and the external thread <NUM> of the inner screw.

Referring to <FIG> and <FIG>, in some embodiments of the nested screw assembly, the inner screw <NUM> comprises an oval head <NUM>. The head <NUM> can be provided with a socket <NUM> for receiving a driver tool bit for screwing/unscrewing the inner screw <NUM>.

Referring to <FIG> and <FIG>, in another embodiment, the inner screw <NUM>' is a headless type and comprises a threaded head portion <NUM>' with a thread pitch that is different from the thread pitch of the external thread <NUM> of the outer screw, the internal thread <NUM> of the outer screw, and the external thread <NUM> of the inner screw <NUM>'. In some embodiments, the thread pitch on the threaded head portion <NUM>' is smaller than the thread pitch of the other threads.

In some embodiments, the outer screw <NUM> further comprises a driving feature <NUM> provided inside the canal <NUM> near the second end <NUM>. The driving feature <NUM> can be a socket, such as a hex socket, star drive socket, etc. The driving feature <NUM> enables the outer screw <NUM> to be screwed into a bone using an appropriate drive bit inserted into the second end opening <NUM> (see <FIG>).

In the embodiment of the nested screw assembly <NUM> where the inner screw <NUM>' has the threaded head portion <NUM>', a compression sleeve <NUM> can be used to drive the inner screw <NUM>' into the outer screw <NUM>. The longitudinal cross-sectional view in <FIG> shows the nested screw assembly <NUM> and the compression sleeve <NUM> engaging the threaded head portion <NUM>' of the inner screw <NUM>'. The compression sleeve <NUM> comprises an internally threaded opening <NUM> at one end for engaging the threaded head portion <NUM>' of the inner screw <NUM>'. The compression sleeve <NUM> can also be provided with a tool receiving socket <NUM> on the opposite end for receiving a driver tool for turning the compression sleeve <NUM>.

Referring to the flowchart <NUM> in <FIG> and the <FIG>, a method for fusing a joint between two bones using the nested screw <NUM> will be described. A method for fusing a joint between a first bone B1 and a second bone B2 using the nested screw assembly <NUM> comprises the following procedures. First, (a) a hole is pre-drilled into the first bone B1 and the second bone B2 through the joint. The joint is indicated by the line J in <FIG>. Then, referring to <FIG>, (b) the outer screw <NUM> is screwed/threaded into the hole in the first bone B1 up to the joint J. The direction of the outer screw's advancement into the first bone B1 is indicated by the arrow A1. Referring to <FIG>, next, (c) the inner screw <NUM>' is screwed/threaded into the hole in the second bone B2 from the opposite side until the inner screw <NUM>' engages with the internally threaded portion <NUM> of the outer screw <NUM> from the first end <NUM> of the outer screw and form a nested screw assembly. The direction of the inner screw's advancement here is indicated by the arrow A2 in <FIG>. Then, to compress the two bones B1, B2 together at the joint, the inner screw <NUM>' is tightened while holding the outer screw <NUM> from turning. The outer screw <NUM> can be held in place from turning using a driver tool that is inserted into the second end <NUM> of the outer screw to engage the driving feature <NUM> in the canal <NUM>. The inner screw <NUM> can be driven using the compression sleeve <NUM>. As illustrated in <FIG>, with the compression sleeve <NUM> engaged to the threaded head portion <NUM>' of the inner screw <NUM>', because the compression sleeve <NUM> has a larger diameter than the inner screw <NUM> and the hole in the second bone B2, as the inner screw <NUM>' is threaded into the outer screw <NUM> and advanced in the direction of the arrow A2 with respect to the first bone B1 and the outer screw <NUM>, the compression sleeve <NUM> comes in contact with the second bone B2 and compresses the second bone B2 toward and against the first bone B1. Once the desired compression of the two bones B1, B2 is achieved, the compression sleeve <NUM> is removed.

If an embodiment of the nested screw assembly <NUM> that comprises the oval headed inner screw <NUM> (see <FIG>) is used, as the inner screw <NUM> is threaded into the outer screw <NUM> and advance in the direction of the arrow A2 with respect to the first bone B1 and the outer screw <NUM>, the head <NUM> of the inner screw <NUM>, rather than the compression sleeve <NUM>, will come into contact with the second bone B2 and compress the second bone B2 toward and against the first bone B1. Thus, when the oval headed inner screw <NUM> is used, the compression sleeve <NUM> is not needed as a standard screwdriver can be used with the oval headed inner screw <NUM>.

Referring to <FIG>, after the compression of the two bones B1, B2 is achieved, (d) the outer screw <NUM> is screwed further into the hole in the first bone B1 in the direction A1, toward and across the joint J to maintain the compression of the joint. This procedure is carried out while the inner screw <NUM> is held in place using a driver bit inserted into the tool socket <NUM> of the inner screw. This procedure is possible because the external thread <NUM> of the outer screw <NUM> has the same thread pitch and handedness as the internal thread <NUM> of the outer screw and the external thread <NUM> of the inner screw. With the inner screw <NUM> in place, the outer screw can be driven across the joint because the outer screw threads across the bone at the same rate it threads over the inner screw <NUM>.

For the embodiment where the headless inner screw <NUM>' with the threaded head portion <NUM>' is used, after the step (c), the threaded head portion <NUM>' of the inner screw <NUM>' is buried into the second bone B2, so that the head portion <NUM>' is not protruding from the bone B2, by driving the inner screw <NUM>' out of the compression sleeve <NUM>. This is illustrated in <FIG>. This step of burying the head portion <NUM>' of the inner screw <NUM>' into the second bone B2 can be done either before or after the outer screw <NUM> is advanced across the joint J. <FIG> shows the position of the headless inner screw <NUM>' after the head portion <NUM>' is buried into the second bone B2.

<FIG> is an illustration showing the nested screw assembly embodiment where the oval headed inner screw <NUM> is used rather than the headless inner screw <NUM>' after the compression of the bones B1, B2 is completed.

Referring to <FIG>, in some embodiments, the outer screw <NUM> comprises a driving feature <NUM> provided inside the canal <NUM> near the second end <NUM>, and the outer screw is threaded into the hole in the procedure (b) by engaging the driving feature <NUM> with a driving tool.

Claim 1:
A nested screw assembly (<NUM>) for forming a bone-to-bone fixation, comprising:
a cannulated outer screw (<NUM>); and
an inner screw (<NUM>),
wherein,
the outer screw (<NUM>) comprises a tubular structure having a first end (<NUM>) and a second end (<NUM>) defining a length between the two ends, and a canal (<NUM>) extending through the length of the outer screw (<NUM>),
at least a portion of the length of the outer screw (<NUM>) is externally threaded and at least a portion (<NUM>) of the length of the canal (<NUM>) is internally threaded near the first end,
the inner screw (<NUM>) is externally threaded, and
the external thread of the outer screw (<NUM>), the internal thread of the outer screw (<NUM>), and the external thread of the inner screw (<NUM>) all have the same thread pitch, whereby the inner screw (<NUM>) can be threaded into the first end of the canal (<NUM>) of the outer screw (<NUM>) to form the nested screw assembly (<NUM>), wherein the inner screw (<NUM>) comprises a threaded head portion with a thread pitch that is different from the thread pitch of the external threads on the outer screw (<NUM>).