Patent Description:
A bone defect may be repaired by inserting a permanent nail or rod into the medullary canal of the bone. A connecting screw may be attached at one end to the intramedullary (IM) nail and a force applied to the opposing end of the connecting screw to insert the IM nail into the medullary canal. The connecting screw may loosen during the nail insertion procedure as a result of the applied force and require retightening. Document <CIT> discloses an intramedullary nail insertion assembly according to the preamble of claim <NUM>.

The present disclosure relates to a system and method for inserting an intramedullary (IM) nail. The method does not form part of the invention as claimed. An IM nail insertion assembly includes an IM nail extending longitudinally from a proximal end to a distal end. A proximal portion of the IM nail has an internal threading. The IM nail insertion assembly also includes a connecting screw extending longitudinally from a proximal end to a distal end. A distal portion of the connecting screw has an external threading for engaging the internal threading of the IM nail. One of the proximal portion of the IM nail and the distal portion of the connecting screw has a feature to resist a disengagement of the proximal portion from the distal portion.

In an embodiment, the feature is a portion of the external threading of the connecting screw having a first pitch different from a remainder of the external threading having a second pitch.

In an embodiment, the first pitch is greater than the second pitch.

In an embodiment, the second pitch is greater than the first pitch.

In an embodiment, the feature is a portion of the internal threading of the IM nail having a first pitch different from a remainder of the internal threading having a second pitch.

In an embodiment, the feature is a portion of the external threading of the connecting screw forming a plurality of detents different from one another.

In an embodiment, each of the detents extends radially from a middle portion of the external threading.

In an embodiment, the portion of the external threading forms two detents.

In an embodiment, the feature is a portion of the internal threading of the IM nail forming a plurality of detents different from one another.

In an embodiment, each of the detents extends radially from a middle portion of the internal threading.

In an embodiment, the portion of the internal threading forms one detent.

In an embodiment, the connecting screw is cannulated.

In an embodiment, the IM nail insertion assembly further includes an insertion handle extending from a proximal end to a distal end; and a sleeve extending longitudinally from a proximal end to a distal end, the proximal end of the sleeve sized and shaped to receive the proximal end of the connecting screw therein. The proximal end of the sleeve is rigidly fixed to the distal end of the insertion handle.

In an embodiment, the sleeve further includes a lumen sized and shaped to receive a shaft of the connecting screw.

In an embodiment, the IM nail insertion assembly further includes a screwdriver extending from a proximal end to a distal end, the screwdriver having a tip at the distal end and a handle at the proximal end. The tip is sized and shaped to engage a recess in the proximal end of the connecting screw.

In an embodiment, the tip is hexagonal for engaging a correspondingly shaped hexagonal recess in the proximal end of the connecting screw.

In an embodiment, the IM nail insertion assembly further includes a tab extending radially from the proximal end of the connecting screw, the tab biased toward a non-deformed state engaging the proximal end of the sleeve.

In an embodiment, the IM nail is made of a titanium alloy.

In an embodiment, the connecting screw is made of a stainless-steel alloy.

Also described herein although not falling within the scope of the claims is a method which includes inserting an IM nail insertion assembly into a medullary canal, the IM nail insertion assembly including an IM nail, a proximal portion of the IM nail having an internal threading, a connecting screw, a distal portion of the connecting screw having an external threading for engaging the internal threading of the IM nail, and one of the proximal portion of the IM nail and the distal portion of the connecting screw having a feature to resist a disengagement of the proximal portion from the distal portion; inserting a tip of a screwdriver into a recessed portion of a head of the connecting screw; and rotating the screwdriver in a first direction to engage the external threading of the connecting screw with the internal threading of the IM nail.

In an embodiment, the method further includes rotating the screwdriver in a second direction opposite of the first direction; removing the connecting screw; and placing an end cap on a proximal end of the IM nail.

The present disclosure may be further understood with reference to the following description and the appended drawings, wherein like elements are referred to with the same reference numerals. The exemplary embodiments describe connecting screws and/or intramedullary (IM) nails having features to resist disengagement or loosening therebetween during nail insertion. The connecting screws and IM nails described herein may be implemented in a system for inserting an IM nail. It should be noted that the terms "proximal" and "distal," as used herein are intended to refer to a direction toward (proximal) and away from (distal) a user of the device.

<FIG> show a system <NUM> for performing an intramedullary (IM) nail insertion procedure according to various exemplary embodiments of the present disclosure. The system <NUM> includes an intramedullary (IM) nail <NUM> according to a first embodiment sized and shaped to be inserted into a medullary canal to repair a bone defect. The IM nail <NUM> insertion is implemented with a connecting screw <NUM> according to a first embodiment that is coupled to the IM nail <NUM> during insertion and detached therefrom when the IM nail <NUM> is fully inserted. During the insertion procedure the connecting screw <NUM> is further coupled to an insertion handle <NUM> that is gripped by the operating physician. Forces, e.g., hammering forces, are applied to the insertion handle <NUM> to push the attached IM nail <NUM> into the medullary canal as would be understood by those skilled in the art. The applied forces may be significant and can stress the connection between the IM nail <NUM> and the connecting screw <NUM>.

Due to the magnitude of the forces applied to the system <NUM> and to facilitate the set-up of the various components, various elements involved are connected in multiple ways in part to maintain a secure connection during the insertion procedure. An initial connection is made between the insertion handle <NUM> and the IM nail <NUM> via a sleeve <NUM> extending from a distal end of the insertion handle <NUM>. The sleeve <NUM> has a proximal end <NUM> rigidly connected to the distal end of the insertion handle <NUM>. The sleeve <NUM> is part of the insertion handle <NUM> and is rigidly fixed at its proximal end <NUM>, thus the sleeve <NUM> cannot be disassembled from the handle <NUM>. In the present embodiment, a distal end <NUM> of the sleeve <NUM> has a feature shaped to snap-lock into a correspondingly shaped feature at a proximal end <NUM> of the IM nail <NUM>. For example, the proximal end <NUM> of the IM nail <NUM> may have a protrusion extending radially inward that engages a correspondingly sized and shaped recess in the distal end <NUM> of the sleeve <NUM>. However, other attachment mechanisms between the sleeve <NUM> and the IM nail <NUM> may be used.

The sleeve <NUM> has a hollow interior sized and shaped to receive a longitudinal shaft <NUM> of the connecting screw <NUM>. Thus, once the sleeve <NUM> and the IM nail <NUM> are initially attached to one another, the distal end <NUM> of the connecting screw <NUM> is inserted into the proximal end <NUM> of the sleeve <NUM> and extended through the length of the sleeve <NUM> to engage the proximal end <NUM> of the IM nail <NUM>, as described below, to more securely connect the IM nail <NUM> to the sleeve <NUM>. The proximal end <NUM> of the sleeve <NUM> has an increased diameter relative to the remainder of the sleeve <NUM>, the proximal end <NUM> having a recessed portion <NUM> to receive a head <NUM> of the connecting screw <NUM> so that the head <NUM> is seated in the recessed portion <NUM> when the connecting screw <NUM> and the IM nail <NUM> are coupled.

The connecting screw <NUM> is cannulated, to enable the insertion of the IM nail <NUM> and the insertion handle <NUM> over a reaming rod. The connecting screw <NUM> has a channel extending throughout the length of the connecting screw <NUM> from a proximal end <NUM> to a distal end <NUM>. The distal end <NUM> has an external threaded portion <NUM> for engaging a correspondingly threaded inner surface <NUM> on the proximal end <NUM> of the cannulated IM nail <NUM>, as seen in <FIG>.

The connecting screw <NUM> is inserted through the sleeve <NUM> and a T-arm screwdriver <NUM> is used to thread the distal end <NUM> of the connecting screw <NUM> into the proximal end <NUM> of the IM nail <NUM>. The T-arm <NUM> has a longitudinal shaft <NUM> extending from a proximal handle <NUM> to a distal tip <NUM>, the tip <NUM> sized and shaped to engage the countersunk head <NUM> of the connecting screw <NUM>. In this embodiment, the tip <NUM> is hexagonal for engaging a correspondingly shaped hexagonal recess in the head <NUM> of the connecting screw <NUM>, however, other shapes for the tip <NUM> of the T-arm <NUM> and the head <NUM> may be used. The T-arm screwdriver <NUM> is used to tighten the connecting screw <NUM> until a distal face <NUM> of the head <NUM> of the connecting screw <NUM>, i.e., the portion of the head <NUM> extending radially between the outer surface of the head <NUM> and the shaft <NUM>, engages a proximal shoulder <NUM> of the recessed portion <NUM> of the sleeve <NUM>, i.e., the portion of the sleeve <NUM> extending radially between the inner surface of the recessed portion <NUM> and the inner surface of the sleeve <NUM>, as shown in <FIG>. This tightening may cause a compressive force between the connecting screw <NUM> and the sleeve <NUM> that coincides with the engagement of the connecting screw <NUM> and the IM nail <NUM> via the threaded portions <NUM>, <NUM>, further strengthening the connections between the components.

When the connecting screw <NUM> and the IM nail <NUM> have been joined, the operating physician may proceed to drive the distal end <NUM> of the IM nail <NUM> into the medullary canal. As would be understood by those skilled in the art, the connection between the distal end <NUM> of the connecting screw <NUM> and the proximal end <NUM> of the IM nail <NUM> may be stressed during this procedure. To prevent a loosening of the connection, which would typically require a retightening of the connection with the T-arm <NUM> in the middle of the insertion procedure, the system <NUM> according to various exemplary embodiments includes features to provide a more secure connection that resists such a loosening effect during the insertion procedure. The IM nail <NUM> in the exemplary embodiments may be made of a titanium alloy, for example, TAN or TAV. The connecting screw <NUM> in the above embodiment, as well as connecting screws in the following embodiments, may be made of a stainless steel alloy.

<FIG> shows a distal end <NUM> of a connecting screw <NUM> according to a second embodiment. The connecting screw <NUM> may be substantially similar to the connecting screw <NUM> described above, with the exception of the distal end <NUM>. In this second embodiment, the distal end <NUM> has a threaded portion <NUM> with a variable pitch, including a first thread <NUM> extending from the distal-most point of the threaded portion <NUM> to a transition approximately midway through the threaded portion <NUM> and a second thread <NUM> extending from the transition to the proximal-most point of the threaded portion <NUM>. Those skilled in the art will understand that the pitch of a thread relates to the angle of the helix along which the thread extends (i.e., an angle between the axial progression of the helix and the axis of the cylinder around which it wraps) and that a smaller pitch represents a larger helical angle so that the threads of a smaller pitch are closer to one another than are the threads of a larger pitch.

The first thread <NUM> has a first pitch that corresponds to the pitch of the interior threaded portion <NUM> of the IM nail <NUM>, while the second thread <NUM> has a second pitch that is smaller than that of the first thread <NUM> and interior threaded portion <NUM> so that the second thread <NUM> generates interference with the interior threaded portion <NUM>. A ratio between the first pitch of the first thread <NUM> and the second pitch of the second thread <NUM> being from <NUM> to <NUM>. As the threaded portion <NUM> of the connecting screw <NUM> is advanced along the threaded portion <NUM> of the IM nail <NUM> the second (smaller) thread <NUM> engages the threaded portion <NUM> of the IM nail <NUM>.

Due to the differing pitches, one or both of the engaging threads will deform causing the distal end <NUM> of the connecting screw <NUM> and the proximal end <NUM> of the IM nail <NUM> to become more tightly joined to one another in a manner that resists loosening during the insertion procedure. Despite the deformation caused by the tightening, once the IM nail <NUM> has been fully inserted, the engaging threads may be subsequently disengaged by rotating the connecting screw <NUM> in the direction opposite the tightening direction.

If the threaded portion <NUM> of the IM nail <NUM> is deformed during the advancement of the connecting screw <NUM>, the first thread <NUM> of the connecting screw <NUM> will engage the deformed threaded portion <NUM> and may substantially counteract the deformation - that is, the engagement of the first thread <NUM> with the interior threaded portion <NUM> will retap and correct the threading of the interior portion <NUM>. Thus, if and when further elements are attached to the threaded portion <NUM> of the IM nail <NUM>, e.g. an end cap, the end cap will not encounter significant resistance when tightened thereon. Accordingly, if the first thread <NUM> matches with the threaded portion <NUM> of the IM nail <NUM>, the threaded portion <NUM> of the IM nail <NUM> will not deform and thus, the endcap will have a tight fit within the IM nail <NUM>.

<FIG> shows a distal end <NUM> of a connecting screw <NUM> according to a third embodiment. The connecting screw <NUM> may be substantially similar to either of the connecting screws <NUM>, <NUM> described above with the exception of the distal end <NUM>. In this third embodiment, the distal end <NUM> has a threaded portion <NUM> with a variable pitch, including a first thread <NUM> extending from the distal-most point of the threaded portion <NUM> to a transition approximately midway through the threaded portion <NUM> and a second thread <NUM> extending from the transition to the proximal-most point of the threaded portion <NUM>, similar to the connecting screw <NUM> of the first embodiment.

However, in the third embodiment, the first thread <NUM> has a first pitch that corresponds to the pitch of the interior threaded portion <NUM> of the IM nail <NUM>, while the second thread <NUM> has a pitch that is larger than that of the first thread <NUM> and interior threaded portion <NUM>. In a manner similar to that of the connecting screw <NUM> described above, as the threaded portion <NUM> of the connecting screw <NUM> is advanced along the threaded portion <NUM> of the IM nail <NUM> the second thread <NUM> engages the threaded portion <NUM> of the IM nail <NUM>. A ratio between the first pitch of the first thread <NUM> and the second pitch of the second thread <NUM> being from <NUM> to <NUM>.

Due to the differing pitches, one or both of the engaging threads will deform, the deformation causing the distal end <NUM> of the connecting screw <NUM> and the proximal end <NUM> of the IM nail <NUM> to become tightly joined together and resist loosening during the insertion procedure. If the threaded portion <NUM> of the IM nail <NUM> was deformed during the advancement of the connecting screw <NUM>, the first thread <NUM> of the connecting screw <NUM> will engage the deformed threaded portion <NUM> and substantially correct the deformation. Thus, if and when further elements are attached to the threading <NUM> of the IM nail <NUM>, e.g. an end cap, the end cap will not encounter significant resistance when tightened thereon.

By adjusting the pitch on the proximal end of the threading, rather than the distal end, only a proximal portion of the corresponding threading of the IM nail <NUM> will potentially deform when the connecting screw is advanced, rather than the entirety of the threading. In alternate embodiments, connecting screws are provided having the smaller/larger pitches of connecting screws <NUM>, <NUM>, but without the distal threading corresponding to the threading of the IM nail <NUM>. Thus, when the connecting screws are threaded into the IM nail <NUM>, only the smaller/larger pitched thread of the connecting screws engages the threaded portion <NUM> of the IM nail <NUM> and the distal portion of the threaded portion <NUM> remains unengaged.

The principle described above with respect to connecting screws <NUM>, <NUM> may be implemented instead at the IM nail <NUM>. Specifically, the connecting screw <NUM>, having a uniform pitch for its threaded portion <NUM>, may be used with an IM nail having a variable pitch for its threaded portion. In these embodiments, a distal portion of the IM nail threading has the smaller or larger pitch, causing either the threading <NUM> of the connecting screw <NUM> or the distal threading of the IM nail to deform as the connecting screw <NUM> is advanced.

<FIG> shows a proximal end <NUM> of an IM nail <NUM> according to a second embodiment. The IM nail <NUM> may be substantially similar to the IM nail <NUM> described above with the exception of the proximal end <NUM>. The IM nail <NUM> has a threaded portion <NUM> with a variable pitch, including a first thread <NUM> extending from the distal-most point of the threaded portion <NUM> to a transition approximately midway through the threaded portion <NUM> and a second thread <NUM> extending from the transition to the proximal-most point of the threaded portion <NUM>. The first thread <NUM> has a first pitch that is smaller than that of the second thread <NUM>, the second thread <NUM> having a second pitch that corresponds to the pitch of the exterior threaded portion <NUM> of the connecting screw <NUM>.

<FIG> shows a proximal end <NUM> of an IM nail <NUM> according to a third embodiment for use in the system <NUM> of <FIG>. The IM nail <NUM> may be substantially similar to the IM nails <NUM> or <NUM> described above with the exception of the proximal end <NUM>. The IM nail <NUM>, similar to the IM nail <NUM>, has a threaded portion <NUM> with a variable pitch, including a first thread <NUM> extending from the distal-most point of the threaded portion <NUM> to a transition approximately midway through the threaded portion <NUM> and a second thread <NUM> extending from the transition to the proximal-most point of the threaded portion <NUM>. The first thread <NUM> has a first pitch that is larger than that of the second thread <NUM>, the second thread <NUM> having a second pitch that corresponds to the pitch of the exterior threaded portion <NUM> of the connecting screw <NUM>.

<FIG> shows a distal end <NUM> of a connecting screw <NUM> according to a fourth embodiment. The connecting screw <NUM> may be substantially similar to any of the connecting screws <NUM>, <NUM>, <NUM> described above, with the exception of the distal end <NUM>. In this fourth embodiment, the distal end <NUM> has a threaded portion <NUM> including a detent <NUM> at two locations on the threaded portion <NUM>, as shown in <FIG>. The two detents <NUM> extend radially from a middle portion of the threading and are shaped differently from the remainder of the threading.

Specifically, the threading is deformed axially so that gaps between adjacent portions of the threading are either narrower or wider. Thus, the detents <NUM> will cause mechanical interference with the threaded portion <NUM> of the IM nail <NUM> when the IM nail <NUM> and the connecting screw <NUM> are screwed together. Although the threaded portion <NUM> shown in <FIG> has two detents <NUM>, more or fewer detents may be used. In a similar manner to the connecting screws <NUM>, <NUM> described above, when the distal end <NUM> is threaded into the proximal end <NUM> of the IM nail <NUM>, the detents <NUM> engage the threaded portion <NUM> of the IM nail <NUM> so that the mechanical interference between more tightly locks the connecting screw <NUM> and the IM nail <NUM> to one another. The detents <NUM> may be on a proximal portion of the threaded portion of <NUM> in order to interfere only with a proximal portion of the threaded portion <NUM> of the IM nail, thus, if and when further elements are attached to the threaded portion <NUM> of the IM nail <NUM>, e.g. an end cap, the end cap will have a tight fit with the IM nail <NUM>.

<FIG> shows a proximal end <NUM> of an IM nail <NUM> according to a fourth embodiment. The IM nail <NUM> may be substantially similar to the IM nails <NUM>, <NUM>, <NUM> described above with the exception of the proximal end <NUM>. In this fourth embodiment, the IM nail <NUM> has a threaded portion <NUM> including a detent <NUM> extending laterally from a middle portion of the threading. The detent <NUM> is a portion of the threading that is deformed relative to the remainder of the threading. Thus, due to the detent <NUM>, the shape of the threading of the threaded portion <NUM> differs from the shape of the gaps between the turns of the threading of the threaded portion <NUM> and, as these parts are screwed together, this difference in shape generates a mechanical interference between the threaded portion <NUM> of the connecting screw <NUM> and the IM nail <NUM> that resists loosening during the implantation of the IM nail <NUM>. Although the threaded portion <NUM> has a single detent, as shown in <FIG>, more detents may be used.

In addition to the mechanisms described above at either the distal end of a connecting screw or the proximal end of an IM nail, a further mechanism may be implemented at the proximal end of a connecting screw to resist disengagement of the tight connection between the connecting screw and an IM nail.

<FIG> shows a proximal end <NUM> of a connecting screw <NUM> according to a fifth embodiment. The connecting screw <NUM> may be substantially similar to the connecting screw <NUM> described above with the exception of the proximal end <NUM>. In this embodiment, the countersunk head <NUM> of the proximal end <NUM> has a deformable tab <NUM> extending radially through the head <NUM>. In a natural, i.e., non-deformed state, the tab <NUM> is oriented so that an outer portion <NUM> of the tab <NUM>, e.g. a corner, projects radially outward relative to the outer surface of the head <NUM>, as shown in <FIG>. Thus, when the connecting screw <NUM> is inserted in the sleeve <NUM> of the insertion handle <NUM>, the outer portion <NUM> engages the proximal end <NUM> of the sleeve <NUM>.

This engagement acts to prevent movement, e.g. rotation, of the connecting screw <NUM> relative to the sleeve <NUM>. For example, during the insertion procedure, stresses generated by the insertion forces may act to dislodge the connecting screw <NUM> from the IM nail <NUM> or the sleeve <NUM>. The tab <NUM>, in its non-deformed state, provides a force resisting relative movement, e.g. rotation, between the connecting screw <NUM> and the sleeve <NUM>, which further resists movement between the connecting screw <NUM> and the IM nail <NUM>, considering the rigid connection between the sleeve <NUM> and the IM nail <NUM> described above.

In its non-deformed state, the tab <NUM> also has an inner portion <NUM>, i.e. the opposing corner of the outer portion <NUM>, projecting radially inward relative to the inner surface of the head <NUM>. However, when the tip <NUM> of the T-arm <NUM> is engaged in the recess of the countersunk head <NUM> of the connecting screw <NUM>, the tip <NUM> forces the inner portion <NUM> radially outward and the tab <NUM> deforms under the pressure from the tip <NUM>. The deformation causes the tab <NUM> to straighten out, such that the outer portion <NUM> no longer engages the proximal end <NUM> of the sleeve <NUM>, as shown in <FIG>. Thus, the connecting screw <NUM> may be rotated relative to the sleeve <NUM> when the tip <NUM> of the T-arm <NUM> is inserted in the countersunk head <NUM>. This allows the connecting screw <NUM> to be threaded into the IM nail <NUM> at the outset of the nail insertion procedure and unthreaded from the IM nail <NUM> at the end of the insertion procedure without the tab <NUM> causing interference with the sleeve <NUM>. In other words, the connecting screw <NUM> is rotatable relative to the sleeve <NUM> when the tip <NUM> of the T-arm <NUM> is inserted in countersunk head <NUM>, and when the T-arm <NUM> is withdrawn the tab <NUM> resists rotation, providing a more secure connection between the connecting screw <NUM> and the IM nail <NUM>.

Claim 1:
An intramedullary (IM) nail insertion assembly, comprising:
an IM nail (<NUM>) extending longitudinally from a proximal end (<NUM>) to a distal end (<NUM>), a proximal portion of the IM nail (<NUM>) having an internal threading (<NUM>): and
a connecting screw (<NUM>) extending longitudinally from a proximal end (<NUM>) to a distal end (<NUM>), a distal portion of the connecting screw (<NUM>) having an external threading (<NUM>) for engaging the internal threading (<NUM>) of the IM nail (<NUM>),
wherein one of the proximal portion of the IM nail (<NUM>) and the distal portion of the connecting screw (<NUM>) has a feature to resist a disengagement of the proximal portion from the distal portion, characterized in that
the feature is a portion of the external threading (<NUM>) of the connecting screw (<NUM>) having a first pitch different from a remainder of the external threading (<NUM>) having a second pitch or
the feature is a portion of the internal threading (<NUM>) of the IM nail (<NUM>) having a first pitch different from a remainder of the internal threading (<NUM>) having a second pitch or
the feature is a portion of the external threading of the connecting screw (<NUM>) forming a plurality of detents (<NUM>) different from one another or
the feature is a portion of the internal threading (<NUM>) of the IM nail (<NUM>) forming a plurality of detents (<NUM>) different from one another.