Limited Collapse Surgical Screws

A telescopic surgical screw comprising: (a) a first screw section including a distal threaded section and a proximal section; (b) a second screw section including a proximal threaded section and a distal section; and, (c) a reconfigurable bushing configured to be received within at least one of the first screw section and the second screw section to limit travel of the first screw section with respect to the second screw section, where at least one of the first screw section and the second screw section includes an internal cavity sized to receive the reconfigurable bushing and where the first screw section is configured to be repositionable along a length of the second screw section to change an overall length of the surgical screw.

DETAILED DESCRIPTION

The exemplary embodiments of the present disclosure are described and illustrated below to encompass orthopedic devices and processes and, more specifically, to telescopic orthopedic screws including limited collapse sleeves and associated bushings. Of course, it will be apparent to those of ordinary skill in the art that the embodiments discussed below are exemplary in nature and may be reconfigured without departing from the scope and spirit of the present disclosure. However, for clarity and precision, the exemplary embodiments as discussed below may include optional steps, methods, and features that one of ordinary skill should recognize as not being a requisite to fall within the scope of the present disclosure.

ReferencingFIGS. 1-5, a first exemplary telescoping screw100includes a proximal sleeve102and a distal shaft104that are longitudinally repositionable with respect to one another to change the overall longitudinal length of the screw.

In exemplary form, the proximal sleeve102includes a proximal threaded head110that is integral with a distally extending cylindrical housing114. Both the threaded head110and the cylindrical housing114are hollow representative of a through hole that extends between a distal orifice120and a proximal orifice122. More specifically, the proximal orifice122is hexagonal and bounded by six planar walls126that extend distally to a flange130that changes the cross-section from hexagonal to circular. Where the planar walls126intersect the flange130, the diameter of the opening extending through the flange is the same as the distance between opposed planar walls.

Extending distally, the underside of the flange130intersects an inner circumferential wall134of the cylindrical housing114, which operates to increase the diameter of the through opening. This change in cross-sectional area inhibits the proximal portion of the distal shaft104from passing through the circular opening of the flange130. Consequently, the screw100has its shortest length when the proximal portion of the distal shaft104abuts the underside of the flange130. The inner circumferential wall134has a constant diameter until reaching the distal orifice120. The distal orifice120is circular in cross-section, but has a diameter that is less than that of the inner circumferential wall134. The distal orifice120is delineated by an inwardly protruding lip138that is operative to retain a proximal portion of the shaft104within the housing114.

An exterior of the cylindrical housing114includes a tapered surface140having a circular longitudinal profile that decreases in outside diameter slightly from proximal to distal until reaching the protruding lip138. Seamlessly adjoining the tapered surface140is primary outer surface144having a circular longitudinal profile and a constant diameter. The outer surface144extends proximally until reaching threads148that circumscribe the proximal head110. In this exemplary embodiment, the threads140extending circumferentially to increase the diameter of the head110in excess of the diameter of the primary outer surface144.

Referring toFIGS. 1-3and5, the distal shaft104includes a proximal section150that is integrally formed with a column154having a series of helical threads158that extend longitudinally until reaching a distal tip160. The proximal section150is cylindrical in shape and includes an exterior surface166having a substantially circular cross-section with a constant diameter. A proximal end170of the shaft104includes a hexagonal orifice174bounded by six planar walls176that extend distally to a flange180that changes a cross-section of the cavity from hexagonal to circular. Where the planar walls176intersect the flange180, the diameter of the opening extending through the flange is the same as the distance between opposed planar walls. The circular cross-section of the flange180is maintained for a predetermined longitudinal distance, after which the cross-section tapers distally to define a conical end cavity that leads into a central bore cavity182longitudinally extending through to a distal opening at the distal tip160; otherwise, the proximal section150comprises solid material.

Extending distally from the proximal section150is the column154, with a tapered section184therebetween. This tapered section184provides a transition from the larger external diameter of the proximal section150to the slightly smaller external diameter of a smooth portion188of the column. This smooth portion188has a cylindrical shape with a substantially constant external diameter until reaching the helical threads158. Upon reaching the helical threads158, the outside diameter increases and is larger than the outside diameter of the proximal section150.

Referring toFIGS. 6-9, a first exemplary reconfigurable bushing220may comprise a part of the first exemplary telescoping screw100. The bushing220may be fabricated from any number of various materials that include, without limitation, a polymer, a metal, a metal alloy, a composite, or any other material that lends itself to reshaping and has at least a predetermined elasticity. By way of example, the reconfigurable bushing220comprises a metal alloy. In exemplary form, the first reconfigurable bushing220includes a circumferential wall222having a circular outer circumferential surface224extending along a majority of the longitudinal length thereof. A distal end226of the bushing220is flat and delineated by a ring-shaped end surface228perpendicular to the outer circumferential surface224. In exemplary form, the ring-shaped end surface228and the outer circumferential surface224are circumferentially interposed by a tapered ring surface230. The ring-shaped end surface228has a generally uniform radial thickness and includes a through opening232that extends longitudinally along the bushing. An inner circumferential surface234provides a cylindrical boundary for the distal through opening232that is substantially uniform until reaching a series of cut-outs238.

Each cut-out238extends radially through the bushing220and the center of which is equidistantly spaced from an adjacent cut-out. In exemplary form, the bushing220includes four cut-outs238having centers that are circumferentially off-set from one another ninety degrees. It should be noted, however, that fewer than four cut-outs238may be utilized or greater than four cut-outs may be utilized. By way of example, each cut-out238includes a distal circular profile delineated by an arcuate edge242that intersects a pair of parallel edges244partially delineating a rectangular profile. In this exemplary embodiment, the diameter of the arcuate edge242is greater than the distance between the parallel edges244to create a lip246operative to retain a corresponding feature of a inserter (seeFIG. 8). Proximate the proximal end of the parallel edges244, the cut-outs238taper via tapered edges250to increase a circumferential spacing of the cut-outs until reaching a proximal end252of the bushing220, which is adjacent the most proximal portion of the tapered edges.

In exemplary form, the orientation and repetition of the cut-outs238is operative to create a number of circumferentially equidistant fingers260that extend away from the distal end226to delineate a proximal end252. Approximately half way longitudinally along the fingers260, the circumferential wall222begins to gradually increase in radial length embodied in a frustroconical exterior surface264. This gradual circumferential wall222thickness increase is exhibited in the radial thickness of the fingers260increasing in the longitudinal direction. But this increase in outer diameter of the circumferential wall is in contrast to the longitudinal diameter of the inner circumferential surface234, which remains substantially constant but for the cut-outs.

As shown inFIGS. 10 and 11, an exemplary inserter300may be used to selectively engage and move the first exemplary reconfigurable bushing220from outside the proximal sleeve102to seat against the inner circumferential wall134. In exemplary form, the inserter300includes an elongated shaft304that includes a frustroconical outer surface308interposing a first circumferential surface310and a second circumferential surface312. The outside diameter of the second circumferential surface312is less than the outside diameter of the first circumferential surface310.

Along the length of the second circumferential surface312are four generally rectangular projections316that are uniformly circumferentially distributed. Each projection316is oriented radially perpendicular to the second circumferential surface312and includes a block rectangular shape with two tapered surfaces. The height (radial length) of the projections316and the diameter of the second circumferential surface312are selected in order to ensure that the projections extend into and are received by the cut-outs238of the reconfigurable bushing220. In other words, the circumferentially equidistant fingers260interpose the projections316. Extending distally from the projections316, the second circumferential surface312continues its cylindrical exterior until reaching a second set of projections320and a pair of pins322interposing the first and second sets of projections316,320.

The pins322extend radially outward from the second circumferential surface312in opposite directions and are longitudinally aligned with two of the first and second sets of projections316,320. In exemplary form, each projection includes a cylindrical shape having an outer circumferential surface326that terminates at a planar circular surface330that is perpendicular to the outer circumferential surface. As will be discussed in more detail hereafter, each of the pins322is adapted to be received within the cut-outs238of the bushing220to mount the inserter300to the bushing.

The second set of projections320comprise four rectangular blocks that are uniformly circumferentially distributed around the second circumferential surface. Each projection320is oriented radially perpendicular to the second circumferential surface312and includes a block rectangular shape with a single tapered surface. The height (radial length) of the projections320and the diameter of the second circumferential surface312are selected in order to ensure that opposing projections have an outside dimension (i.e., outside diameter) that is less than the inside diameter of the inner circumferential surface234of the bushing220. Extending distally from the projections320, the inserter300includes a substantially flat distal surface324.

Referring back toFIGS. 1-13, assembly of first exemplary telescoping screw100takes place prior to the forming the protruding lip138of the proximal sleeve102. In exemplary form, the proximal portion150of the distal shaft104is inserted through the distal opening120of the proximal sleeve102. It is presumed that the reconfigurable bushing220is not located within the proximal sleeve102and seated against the inner circumferential wall134prior to insertion of the distal shaft104into the proximal sleeve102. The proximal portion150of the distal shaft104is inserted into the proximal sleeve at a depth sufficient for the tapered section184to pass through the distal opening120. After the tapered section184has passed through the distal opening120, a tool (not shown) is used to circumferentially crimp the distal end of the tapered surface140to create the protruding lip138. After the protruding lip138is formed, the tapered section184has a larger diameter than the diameter of the opening delineated by the protruding lip, thereby inhibiting the proximal portion150of the distal shaft104from being removed from the interior of the proximal sleeve102. But at the same time, the longitudinal length of the proximal portion150of the distal shaft104is less than the longitudinal length between the protruding lip138and the flange130, thus allowing for movement of the sleeve102with respect to the shaft104. More specifically, a maximum longitudinal length of the first exemplary telescopic screw100is reached when the tapered section184abuts the protruding lip138. Conversely, the minimum longitudinal length of the first exemplary telescopic screw100is reached when the proximal end170abuts the flange130.

In order to constrain the longitudinal length variance of the first exemplary telescoping screw100, a bushing may be inserted into the proximal sleeve102to occupy a portion of the internal cavity, thereby limiting the longitudinal travel of the shaft104with respect to the sleeve102. More specifically, the first reconfigurable bushing220may be inserted into the proximal sleeve102after the proximal sleeve102and distal shaft104have been mounted to one another.

In exemplary form, the reconfigurable bushing220is first mounted to the exemplary inserter300. To do so, the distal surface324and the second set of projections320are inserted into the proximal end252of the bushing220. In this exemplary embodiment, the second set of projections320are circumferentially aligned and equidistantly spaced apart from one another, as well as each having the same radial height. Accordingly, the outer circumferential surface328of each projection320has an arc of a circle having a diameter slightly smaller than the diameter of the inner circumferential surface234of the bushing220. In this manner, when the second set of projections320are inserted through the proximal end252of the bushing220, continued distal movement of the inserter300with respect to the bushing causes the inserter to penetrate further into the interior of the bushing where a friction fit is formed between the projections and the inner circumferential surface324. At the same time, the pins322and the first set of projections316are aligned with the cut-outs238of the bushing220so that each pin and projection is received within a corresponding one of the cut-outs. In particular, the diameter of each pin322is slightly larger than the distance between opposed parallel edges244partially delineating a cut-out238so that insertion of the pin into a cut-out forces the adjacent fingers260away from one another until the pin reaches the circular profile delineated by the arcuate edge242. Upon reaching the arcuate edge242, each pin322clears the parallel edges244and is secured in the cut-out by the tapered edges250retarding egress of the pin away from the arcuate edge. Nevertheless, the pins322may disengage from the bushing220by applying sufficient force to overcome the force maintaining the fingers260in position and cause the pins to pass beyond the arcuate edges242.

In this exemplary embodiment, the radial height of each projection316is longer than the projections320of the second set. Accordingly, the outer circumferential surface318of each projection316has an arc of a circle having a diameter slightly smaller than the outside diameter of the outer circumferential wall222of the bushing220. As a result, when the distal end of the inserter300is inserted into the proximal end of the bushing220, and the projections316and pins322are aligned with the cut-outs238, the diameter of the pins322inhibits the pins from passing beyond the arcuate edge242, thereby inhibiting further penetration of the inserter into the bushing. But because of the dimensions of the pins322and projections316, the pins and projections extend through a corresponding cut-out238so that rotation of the inserter300will necessarily result in rotation of the bushing220. It should also be noted that an outside diameter of the first and second set of projections316,320, measured from the outer circumferential surfaces318,328of opposing projections, is less an inner diameter of the flange130of the proximal sleeve102in order to allow the projections316,320to pass through the flange in either direction without obstruction. Likewise, the outside diameter of the pins322, measured from the planar circular surfaces330of the pins, is less an inner diameter of the flange130of the proximal sleeve102in order to allow the pins to pass through the flange in either direction without obstruction.

After the bushing220has been mounted to the inserter300, the inserter may be used to position the bushing within the interior of the proximal sleeve102. In exemplary form, the inserter300and bushing220are oriented so that the distal end226of the bushing is longitudinally aligned with the proximal orifice122of the proximal sleeve102. The bushing220and inserter300are repositioned with respect to the proximal sleeve102so that the bushing and inserter pass through the proximal orifice122and through the circular opening delineated by the flange130. It should be noted that the outer circumferential surface224at the distal end226of the bushing220has a diameter that is slightly less than that of the interior diameter of the circular opening delineated by the flange130, thereby allowing the distal end to pass through the flange unimpeded. But the same circumstance is not present with respect to the proximal end252.

When the frustroconical exterior surfaces264of the fingers260reach the flange130, the external diameter of the frustroconical exterior surfaces is larger than the circular opening delineated by the flange. Accordingly, the longitudinal force of the inserter300continuing to move the bushing220distally with respect to the proximal sleeve102causes the fingers260to flex or deform elastically inward (toward the longitudinal axis of the bushing) to allow the fingers to pass through the circular opening of the flange. But after the proximal end252of the bushing220passes distally beyond the flange130, the fingers260flex or deform elastically outward to take on their original dimensions. At the time the fingers260take on their original shape, the diameter at the tapered circumferential surfaces266of opposing fingers is greater than the diameter of the circular opening delineated by the flange130, thereby prohibiting the bushing220from proximally passing through the flange. After the fingers260have completely passed distally beyond the flange130, the inserter300may be disengaged and proximally withdrawn through the flange and through the proximal orifice122of the proximal sleeve102. As can be seen inFIG. 13, the maximum travel of the distal shaft104with respect to the proximal sleeve102has been reduced as a result of the insertion of the bushing220. Moreover, the through opening232of the bushing220allows for through put of a driver (not shown) that is received within the hexagonal orifice174of the distal shaft104in order to rotate the distal shaft with respect to the proximal sleeve102even after the bushing is inserted into the proximal sleeve. It should also be understood, that the driver may engage the hexagonal orifice174of the distal shaft104in order to rotate the distal shaft with respect to the proximal sleeve102prior to insertion of the bushing220into the proximal sleeve.

Referring toFIGS. 14 and 15, a second exemplary reconfigurable bushing400comprises a rectangular-shaped material having a substantially constant length L and thickness T. In exemplary form, the material may comprise a polymer, a metal, a metal alloy, a composite, or any other material that lends itself to reshaping and has at least a predetermined elasticity. By way of example, the reconfigurable bushing400comprises a metal alloy with a thickness T that allows a user to roll the bushing to change its width W. The more the bushing400is rolled over itself, the smaller its width W becomes (compare the smaller width W inFIG. 15with the larger width W inFIG. 14). But when the affirmative pressure that has been applied to roll the bushing400is discontinued, the elasticity of the bushing causes the bushing to at least partially unroll and increase its width W.

This second exemplary reconfigurable bushing may be used in addition to or in lieu of the first reconfigurable bushing220. When used as part of the first exemplary telescoping screw100, the bushing400is able to be rolled so that its width W is smaller than the circular opening delineated by the flange130of the proximal sleeve104in order the distally pass through the flange (such as inFIG. 15). But after the bushing400passes distally beyond the flange130, the bushing400at least partially unrolls to increase its width W so that the width is greater than the diameter of the circular opening delineated by the flange130in order to inhibit passing through the flange (such as inFIG. 14).

It should be noted that the second exemplary reconfigurable bushing400need not include a constant length or thickness. Rather, the length may be non-uniform and the bushing taking on a shape other than rectangular, whether or not the bushing is lying flat. Moreover, the thickness may be non-uniform so that the certain portions of the bushing retard deformation more or less than other portions.

ReferencingFIGS. 16-18, a third exemplary reconfigurable bushing500may be used in lieu of or in addition to the foregoing exemplary bushings220,400as part of the exemplary telescoping screw100. This reconfigurable bushing500is adapted to engage a positioning screw504(FIG. 19) in order to lock or fix the circumferential dimensions of the reconfigurable bushing. More specifically, insertion of the threaded end of the screw504into a proximal end of the bushing500may be operative to increase the circumferential cross-section of the bushing in order to wedge the bushing inside the cylindrical housing114of the proximal sleeve102or at the very least prohibit withdrawal of the bushing through the flange130. In this fashion, by locating the bushing500within the inner circumferential wall134of the proximal sleeve102, the maximum travel of the proximal sleeve with respect to the distal shaft104may be reduced.

The bushing500, when not mounted to the positioning screw504, includes a cylindrical shape having a substantially constant diameter along its longitudinal length. This cylindrical shape is typified by an outer circumferential surface508that is perpendicular to a substantially planar bottom surface510. The bottom surface510is ring-shaped and partially delineates a through hole512that extends longitudinally along the length of the bushing. In exemplary form, the through hole512is bounded by an inner cylindrical surface516having a substantially constant diameter until terminating proximate a proximal end518. The through hole512is axially centered along the longitudinal length of the bushing500and widens at its proximal end typified by cut-outs522that correspondingly form a series of circumferential projections524.

In this exemplary embodiment, there are ten circumferential projections524that are interposed by ten cut-outs522. However, the bushing may include more or fewer than ten projections524. Likewise, while the projections524and cut-outs522are substantially uniform in shape, it is not required that this be the case.

Each projection524includes a tapered proximal surface530that declines from the outside perimeter joining the outer circumferential surface508to the inner perimeter that joins an inner circumferential surface532. In this exemplary embodiment, the arcuate profile of the outer circumferential surface508is representative of a first ring and the arcuate profile of the inner circumferential surface532is representative of a second ring, where the first and second rings are concentric. Interposing the outer circumferential surface508and the inner circumferential surface532for each projection is a pair of planar surfaces536that lie upon a radian extending from a longitudinal axis538. Joining adjacent planar surfaces536of adjacent projections524is a cylindrical surface540that partially defines a partial cylindrical cavity that extends perpendicularly out from the longitudinal axis538. Each projection524includes a triangular plateau544extending radially toward the longitudinal axis538, where each plateau is undercut as a result of the cylindrical surface540. This undercut provides a cavity to receive at least a portion of the threads of the positioning screw504to facilitate longitudinal advancement of the positioning screw with respect to the bushing500.

Referring toFIGS. 19 and 20, the positioning screw504includes a proximal head550from which a threaded shaft554extends perpendicularly. The proximal head550includes a top planar, circular surface556having a depression558formed therein. By way of example, the depression558is bounded by six vertical walls560to define a hexagonal cavity that may receive a hexagonal driver (now shown) to axially rotate the screw504. Adjacent and surrounding the top surface556is a tapered surface564that links the top surface556with a circumferential surface566that is perpendicular to the top surface. Extending distally from the circumferential surface566is a frustroconical surface570that tapers from proximal to distal. Adjacent the frustroconical surface570is a bottom planar, circular surface572from which the threaded shaft554extends perpendicularly. In particular, the bottom surface572is parallel to the top planar surface556and spaced apart therefrom by the longitudinal length of the proximal head550. Extending distally away from the proximal head550is the threaded shaft554, which includes a cylindrical projection576. This cylindrical projection576includes a substantially constant longitudinal diameter and planar bottom surface580. A helical thread582circumscribes the cylindrical projection576and extends from proximate the bottom surface572until reaching the other bottom surface580.

ReferencingFIGS. 21 and 22, usage of the reconfigurable bushing500and the positioning screw504will now be described in the context of the proximal sleeve102and the distal shaft of the first exemplary telescoping screw (seeFIGS. 1-5). Initially, the outside diameter of the bushing500is sized to allow passage into the proximal sleeve102via the circular opening delineated by the flange130. Moreover, the outside diameter of the positioning screw504is also sized to allow passage into the proximal sleeve102via the circular opening delineated by the flange130. While not required, it is envisioned that the bushing500and the positioning screw504will be mounted to one another as shown inFIG. 21prior to insertion through the flange130.

In order to mount the bushing500and positioning screw504to one another, the threaded shaft554is introduced into the through hole512of the bushing where the circumferential projections524are located. In this exemplary embodiment, the substantially constant diameter portion of the through hole512is slightly less than the outside diameter of the threaded shaft554so that the helical thread582engages the inner cylindrical surface516. In this manner, rotation of the positioning screw504with respect to the bushing500causes the screw to longitudinally move proximally or distally with respect to the bushing. In this exemplary combination, clockwise rotation of the screw504causes the screw to move distally with respect to the bushing, while counterclockwise rotation of the screw causes the screw to move proximally with respect to the bushing. Eventually, clockwise rotation draws the threaded shaft554of the screw504deep enough so that at least one of the frustroconical surface570and the bottom surface572contacts the circumferential projections524.

At this point, the screw504and bushing500may be moved through the proximal opening122of the proximal sleeve102and through the circular opening delineated by the flange130. After passing the bushing500and the positioning screw504distally beyond the flange130, while being retained within the interior of the proximal sleeve102, a driver (not shown) may be rotated clockwise to draw the threaded shaft554of the screw504further into the bushing500. By drawing the threaded shaft554of the screw504further into the bushing500, the proximal head550is likewise drawn further into the bushing. In particular, the frustroconical nature of the circumferential surface570acts as a wedge to push against the tapered proximal surfaces530(and eventually against the inner circumferential surfaces532) of the circumferential projections524, thereby pushing the projections524outward away from the longitudinal axis538. In so doing, the outer circumference of the bushing500increases and prohibits passage of the bushing and screw504proximally through the flange130, while at the same time limiting travel of the distal shaft102with respect to the proximal sleeve104.

Referring toFIGS. 23 and 24, a fourth exemplary reconfigurable bushing600may be used in lieu of or in addition to the foregoing exemplary bushings220,400,500as part of the exemplary telescoping screw100. This reconfigurable bushing500is adapted to engage a positioning screw504in order to lock or fix the circumferential dimensions of the reconfigurable bushing. Based upon the prior discussion of the positioning screw504, a detailed discussion of this device has been omitted in furtherance of brevity.

Insertion of the threaded end of the screw504into a proximal end of the bushing600may be operative to increase the circumferential cross-section of the bushing in order to wedge the bushing inside the cylindrical housing114of the proximal sleeve102or at the very least prohibit withdrawal of the bushing through the flange130. In this fashion, by locating the bushing600within the inner circumferential wall134of the proximal sleeve102, the maximum travel of the proximal sleeve with respect to the distal shaft104may be reduced.

The bushing600, when not mounted to the positioning screw504, includes a cylindrical distal end602having a substantially constant diameter along its longitudinal length. This cylindrical distal end602is typified by an outer circumferential surface608that is perpendicular to a substantially planar bottom surface610. The bottom surface610is ring-shaped and partially delineates a through hole612that extends longitudinally along the length of the bushing. In exemplary form, the through hole612is bounded by an inner cylindrical surface616having a substantially constant diameter until terminating proximate a proximal end618of the bushing600. The through hole612is axially centered along the longitudinal length of the bushing600and widens at its proximal end typified by cut-outs622that correspondingly form a series of circumferential projections624.

In this exemplary embodiment, there are ten circumferential projections624that are interposed by ten cut-outs622. However, the bushing600may include more or fewer than ten projections624. Likewise, while the projections624and cut-outs622are substantially uniform in shape, it is not required that this be the case.

Each projection624includes and arcuate exterior transition surface630that transitions from the cylindrical outer circumferential surface608to the outer circumferential surface632. This outer circumferential surface632has a circumferential arc and longitudinal profile the mimics a frustroconical shape. Adjacent the outer circumferential surface632is a pair of planar lateral surfaces636that are also adjacent a proximal arcuate surface638. Opposed lateral surfaces632for adjacent projections624are interposed by a cylindrical surface640that partially defines a partial cylindrical cavity that extends perpendicularly out from a longitudinal axis extending through the bushing600. Each projection624includes a triangular plateau644extending radially toward the longitudinal axis, where each plateau is undercut as a result of the cylindrical surface640. This undercut provides a cavity to receive at least a portion of the threads of the positioning screw504to facilitate longitudinal advancement of the positioning screw with respect to the bushing600. Interconnecting the plateau644and the proximal surface638is an inner circumferential surface646having a circumferential arc and longitudinal profile the mimics a frustroconical shape.

ReferencingFIGS. 23-25, usage of the reconfigurable bushing600and the positioning screw504will now be described in the context of the proximal sleeve102and the distal shaft of the first exemplary telescoping screw (seeFIGS. 1-5). Initially, the outside diameter of the bushing600is sized to allow passage into the proximal sleeve102via the circular opening delineated by the flange130. Moreover, the outside diameter of the positioning screw504is also sized to allow passage into the proximal sleeve102via the circular opening delineated by the flange130.

In order to mount the bushing600and positioning screw504to one another, the threaded shaft554is introduced into the through hole612of the bushing where the circumferential projections624are located. In this exemplary embodiment, the substantially constant diameter portion of the through hole612is slightly less than the outside diameter of the threaded shaft554so that the helical thread582engages the inner cylindrical surface616. In this manner, rotation of the positioning screw504with respect to the bushing600causes the screw to longitudinally move proximally or distally with respect to the bushing. In this exemplary combination, clockwise rotation of the screw504causes the screw to move distally with respect to the bushing, while counterclockwise rotation of the screw causes the screw to move proximally with respect to the bushing. Eventually, clockwise rotation draws the threaded shaft554of the screw504deep enough so that the frustroconical surfaces570contact the circumferential projections624.

Prior to mounting the screw504to the bushing600, the screw504and bushing600are individually moved through the proximal opening122of the proximal sleeve102and through the circular opening delineated by the flange130, with the distal surface610of the bushing passing though the flange first, followed by the screw. When passing the bushing600through the opening delineated by the flange130, the circumferential projections624are deformed in order to decrease the outer circumference of the bushing at the proximal end in order to allow the bushing to completely pass beyond the flange. After passing beyond the flange130, the circumferential projections624elastically reposition back to the position shown inFIGS. 23 and 24. After passing the bushing600and the positioning screw504distally beyond the flange130, while being retained within the interior of the proximal sleeve102, a driver (not shown) may engage the screw and rotate the threaded shaft554of the screw504to engage the bushing500. By drawing the threaded shaft554of the screw504further into the bushing600, the proximal head550is likewise drawn further into the bushing. In particular, the frustroconical nature of the circumferential surface570acts as a wedge to push against the inner circumferential surfaces646of the circumferential projections624, thereby maintaining the position of the projections624outward away from the longitudinal axis. In so doing, the outer circumference of the bushing600prohibits passage of the bushing and screw504proximally through the flange130, while at the same time limiting travel of the distal shaft102with respect to the proximal sleeve104.

Following from the above description and invention summaries, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute exemplary embodiments of the present invention, the invention is not limited to the foregoing and changes may be made to such embodiments without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein are to be incorporated into the interpretation of any claim element unless such limitation or element is explicitly stated. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects of the invention disclosed herein in order to fall within the scope of any claims, since the invention is defined by the claims and since inherent and/or unforeseen advantages of the present invention may exist even though they may not have been explicitly discussed herein.