Bone plate system

In one aspect, a bone plate system is provided that includes a bone plate body having a throughbore and a bone screw. The bone plate system includes a slider slidably connected to the bone plate body to slide between a clearance position wherein the slider permits a bone screw head portion to be advanced into the throughbore and seated against the bone plate body and an interference position wherein the slider inhibits bone screw back out from the throughbore. The bone plate system includes a resilient pin and the slider has a surface configured to deflect the resilient pin as the bone screw head portion shifts the slider from the interference position toward the clearance position. The deflected resilient pin urges the slider from the clearance position toward the interference position upon the bone anchor head portion seating against the bone plate body in the throughbore.

FIELD

This disclosure relates to bone plate systems and, more specifically, to bone plate systems having devices to limit back-out of bone screws of the bone plate systems.

BACKGROUND

Bone plate systems are often used to stabilize adjacent bones or portions of a bone. For convenience, the term “bone” as used herein is intended to encompass a bone or a portion of a bone. Bone plate systems often include a bone plate which is placed against the bones and bone screws that are driven into throughbores of the bone plate and into the bone to secure the bone plate to the bones. Bone plate systems often include devices to inhibit back-out of the bone screws to ensure the bone plate and bone screw construct remains secured with the bones. The devices also limit back-out of the bone screw to keep the bone screws from projecting outward from the bone plate and irritating surrounding tissues.

Bone plates are often used to stabilize vertebrae to address an injury, intervertebral disc replacement, or other situation. Some bone plate systems for the cervical region of the spine utilize a spring retainer in each throughbore of the bone plate that deflects out of the way of the bone screw to permit a bone screw to advance into the throughbore and returns to its initial position in the throughbore to inhibit back-out the bone screw. The spring retainer may be made of a wire that extends across an upper surface of the bone screw head to limit back-out once the bone screw head is seated in the throughbore. One issue with these spring retainers is that the wire material is very thin which may make it difficult for a surgeon to visually ascertain whether the retainer is positioned above the bone screw head to limit back-out.

Some bone plate systems have a multiple-stage bone screw installation process. In a first stage, a bone screw is driven into a throughbore. In a subsequent stage, the surgeon moves a rigid member into an overlapping position with the bone screw head to limit back-out of the bone screw. This multiple-stage process may complete installation of a bone plate system.

DETAILED DESCRIPTION

RegardingFIG.1, a bone plate system10is provided that includes a bone plate12and bone screws14. The bone plate12includes a body16having throughbores18formed therein for receiving the bone screws14. The throughbores18each have a central, longitudinal axis19. The bone plate12includes retainers, such as one or more sliders20, and resilient members, such as pins22, urging the sliders20laterally to an interference position. The bone screws14each include a head portion24(seeFIG.16) having a tapered surface260configured to urge the respective slider20from the interference position to a clearance position and permit the head portion24to advance beyond the slider20and be seated in the throughbore18. The pin22resiliently returns the slider20to the interference position above the bone screw head portion24to inhibit back-out of the bone screw14from the throughbore18.

RegardingFIG.2, the bone plate body16includes one or more windows30to permit bones or an implant therebetween to be observed by a surgeon. The bone plate body16may be elongated and have a longitudinal axis32and each slider20may be slidable along a path34. In one embodiment, the path34is straight and extends at an angle36relative to the longitudinal axis32. The one plate body16may include a receptacle for each slider20that includes an undercut42and an opening48. The slider20may be constrained to sliding movement in the bone plate body16by way of a lower level40(seeFIG.6) received in the undercut42of the bone plate body16. The slider20has a narrower, upper level44with an upper face46visible through the opening48in an upper surface50of the bone plate body16. The opening48opens to the undercut42and permits the upper level44of the slider20to be visible whether the slider20is in the interference position (seeFIG.2) or the clearance position (seeFIG.9). In this manner, a surgeon may readily visually ascertain whether the slider20has been shifted back by the pin22to the interference position upon seating of the bone screw14in the throughbore18. Further, the pin22snaps the slider20back to the interference position once the bone screw head portion24is advanced beyond the slider20which provide a tactile indication that the slider20has returned to the interference position.

RegardingFIGS.2and3, the slider20is shown in the interference position. The pin22is under a preload with the pin22and slider20mounted to the bone plate body16. Regarding momentarily toFIG.11, the pin22has an underformed configuration wherein the pin22is straight. Returning toFIG.3, the pin22has opposite end portions50,52, and an intermediate portion54therebetween. The pin22has ends56,58and a longitudinal axis59(seeFIG.11) extending between the ends56,58. The pin22is loaded upon assembly of pin22and slider20with the bone plate body16as discussed in greater detail below. The pin22is bent when the slider20is in the interference position and is bent further with the slider20in the clearance portion. The pin may have a cross-section transverse to the length80that is uniform for at least a majority of the length80. The cross-section may be, for example, circular or rectangular.

RegardingFIG.3, the bone plate body16has pockets60,62that include recesses64,66which open to the undercut42. The pockets60,62include surfaces70,72against which the ends56,58are tightly engaged by the preloaded pin22. The pin22is biased to straighten out to its unloaded configuration (seeFIG.11); however, the distance between the surfaces70,72is less than the length80of the pin22in the unloaded configuration. In other words, the pocket60,62are too close together to permit the pin22to straighten out. The engagement between the ends56,58of the pin22and the surfaces70,72of pockets60,62inhibits the pin22from shifting radially inward in direction82.

The slider20has a bending member, such as a wall86having a curved surface88configured to contact the intermediate portion54of the pin22. As shown inFIG.3, the slider20is in the initial, interference position wherein the intermediate portion54of the pin contacts the wall86to bias the slider20toward the interference position. The slider20further includes a foot portion90spaced from the wall86to form a channel92therebetween. The pin22extends in the channel92with the end portions50,52of the pin projecting laterally outward from the slider20and into the pockets60,62. The wall86supports the intermediate portion54of the pin22as a fulcrum about which the pin22may bend with shifting of the slider20in direction100toward the clearance position thereof.

RegardingFIG.3, the bone plate body16includes supports102,104on opposite sides of the slider20configured to support the end portions50,52and provide a base for the end portions50,52to contact and urge the slider20back toward the interference position. Opposite the supports102,104, the bone plate body16includes retainer portions110,112that are spaced apart a distance smaller than the length80of the pin22to inhibit the pin22from straightening out and exiting the bone plate body16.

With the slider20in the interference position, the foot portion90of the slider20is spaced a distance114from a wall116of the bone plate body16. Further, the intermediate portion54of the pin22is in contact with the curved surface88a length120. The curved surface88provides a gradual transition for the pin22that limits stress risers in the pin22.

RegardingFIG.4, the slider20has been shifted in radial or lateral outward direction100by a bone screw head portion (not shown inFIG.4) as the bone screw head portion is being advanced into the throughbore18. The shifting of the slider20in direction100causes the wall86and curved surface88thereof to press against a center portion, such as the intermediate portion54, of the pin22. The wall86shifts the intermediate portion54in direction100with the slider20and shifts the ends56,58of the pin22away from the surfaces70,72of the pockets60,62. This forms gaps130,132between the ends56,58and the surfaces70,72. With the slider20in this intermediate position, the ends56,58of the pin22are no longer pressed against the surfaces70,72. Further, the end portions50,52have opposite side portions, such as outer side surface portions140,142, contacting portions of the support102,104such as edges144,146. The intermediate portion54of the pin22is bent more in the intermediate position ofFIG.4than with the slider20in the interference position ofFIG.3. Further, the end portions50,52are closer together when the slider20is in the intermediate position than when the slider20is in the interference position. As shown inFIG.4, the supports102,104include support surfaces150,152that are spaced from the end portions50,52of the pin22by gaps154,156when the slider20is in the intermediate position.

RegardingFIG.5, the bone screw head portion has shifted to the slider20radially outward in direction100to the clearance position thereof. This causes the wall surface88of the slider20to further shift the intermediate portion54away from the throughbore18so that the pin22extends a length120A along the wall surface88that is greater than the length120as shown inFIG.3. The support surfaces150,152of the bone plate body16may be curved to compliment the curving of the pin22caused by the shifting of the slider20to the clearance position. The support surfaces150,152may generally extend along axes170,172that are each oriented at an angle174relative to the path34of the slider20. As shown inFIG.5, the ends56,58of the pin22are spaced from the pocket surfaces70,72by larger gaps180,182than in the intermediate position of the slider20shown inFIG.4. The ends56,58have at least been partially withdrawn from the recesses64,66of the pockets60,62when the slider20is in the clearance position.

As shown inFIG.5, the pin22generally has three points of contact including the support surface150, the support surface152, and the surface88. The pin22is resiliently deformed in this configuration and is biased to straighten out and urge the slider20back radially inward in direction82toward the interference position once the bone head portion24has seated against a seating surface200of the bone plate body16. Once the bone head portion24is seated against the seating surface200, the pin22straightens out which causes the intermediate portion54to urge the wall86of the slider20back laterally inward in direction82and permits the end portions50,52of the pin22to snap back into the pockets60,62and press against the surfaces70,72.

RegardingFIG.6, the bone plate body16has a lower surface210opposite the upper surface50. The undercut42includes a floor212that supports a bottom face214of the lower level40of the slider20. The lower level40has a width215that is wider than a width216of the opening48and a width218of the upper level44of the slider20. The bone plate body16includes overhangs, such as upper walls220, that at least in part define the opening48and have lower surfaces222facing upper faces224of the lower level40. The bone plate body16further includes lower side walls226facing side wall portions228of the lower level40. At the upper level44, the slider20includes upper side wall portions230that face upper side walls232of the upper walls220. In this manner, the sliders20have notched profiles on the opposite sides thereof and the bone plate body16has narrow sections that extend into the notched profiles and form an example of a slide connection between the bone plate body16and the slider20.

RegardingFIG.7, a throughbore18at an end portion250of the bone plate body16is shown. The throughbore18has a central, longitudinal bore axis252that may be at an angle254from an axis256generally normal to the upper surface250of the bone plate body16. The throughbore18may be configured to permit the surgeon to toe out the bone screws14in the throughbores18at the end portions250,251of the bone plate body16. The head portion24of the bone screw14includes a tapered surface260that performs multiple functions. One function is to engage a tapered surface262of a lip portion264of the slider20and cammingly shift the slider20in lateral or radial direction100as the bone head portion24is advanced into the throughbore18. Another function of the surface260is to seat against the seating surface200of the bone plate body16. The seating surface200may be generally concave, including an upper portion270having an inner diameter and a lower portion272having a smaller inner diameter. The seating surface200permits polyaxial insertion of the bone screw14into the throughbore18. Further, the surfaces200,260may be configured to permit controlled pivoting of the bone screw14relative to the bone plate body16such as due to subsidence of the bones to which the bone plate12is secured.

The head portion24of the bone screw14includes a rotary drive structure280for receiving a driving tool. The head portion24may include an opening282that opens to the rotary drive structure280, a collar portion284, and an undercut286. The driver may have a portion that extends into the undercut286to retain the bone screw14on the driver tool as the driver tool is used to advance the bone screw14into the throughbore18. The rotary drive structure280may have a Torx configuration as one example.

RegardingFIG.8, the bone screw14is shown and driven in direction290into the throughbore18with a lower edge292of the bone screw head portion24contacting the tapered surface262of the slider20. RegardingFIG.9, continued advancing of the bone screw14in direction290brings the tapered surface260of the bone screw head portion24into camming engagement with the tapered surface262of the slider20such that the camming engagement between surfaces260,262shifts the slider20outward laterally in direction100to the clearance position thereof so that the head portion24may be advanced into the throughbore18. As the head portion24is advanced in direction290, the pin22is deflected and biases the slider20back toward the interference position in direction82. RegardingFIG.10, the head portion24of the bone screw14shown seated against the seating surface200of the bone plate body16. The pin22has urged the slider20in direction82back to the interference position. The slider20has the lip portion264thereof with a lower surface310overlapping upper surface312of the bone screw head portion24. Thus, the lower surface310of the slider20is positioned to contact the upper surface312and inhibit back-out of the bone screw14in direction290A. The lip portion264of the slider20provides a gap314between the lower surface310and the upper surface312. The gap314permits controlled pivoting or angulation of the bone screw14. Specifically, the gap314permits the bone screw14to turn in direction320with subsidence of the bones stabilized by the bone plate system10.

RegardingFIGS.12and14, the slider20has an inboard end340, an outboard end342, and an axis346extending therebetween. The narrower upper level44forms a step profile348with a notch350on opposite sides of the slider20for receiving the upper walls of the bone plate body16. The upper side wall portions230may be parallel to the lower side wall portions228and the upper face224of the lower level40extends therebetween.

RegardingFIGS.12and13, the slider20includes a through opening for receiving the pin22such as the channel92. The channel92may include a flared portion360at sides362,364of the slider20. The flared portions360provide clearance for the intermediate portion54of the pin22to deflect as the slider20is moved between the clearance and interference positions.

RegardingFIGS.13and15, the wall86and the foot portion90of the slider20include lower surfaces380,382configured to slide along a floor surface212(seeFIG.6) of the bone plate body16. The surfaces380,382and212may be flat or have other shapes, e.g. protrusions, or textures.

RegardingFIG.16, the bone screw14includes the head portion24having a cylindrical surface390. The bone screw14further includes a shank portion392depending from the head portion24that may include threads394. Threads394may be single lead or multiple lead threads as some examples.

RegardingFIGS.17-20, a method of assembling the slider20, pin22, and the bone plate body16is shown. RegardingFIG.17, the slider20is positioned in the throughbore18with the pin22in a straight, undeflected configuration extending in the channel92. The end portions50,52of the pin22extend outward from the side wall portions228of the slider20. The retainer portions110,112of the bone plate body16include tapered guide surfaces400,402that are inclined and extend toward each other as the surfaces400,402extend away from the throughbore18and end at edges404,406. The edges404,406are separated by a width or distance410that is less than a distance412of the widest portions412,414of the tapered guide surfaces400,402. The distance410may be less than a maximum width of the pin22such as the length80.

RegardingFIG.18, the slider20has been shifted in direction100such that the outer side surface portions140,142of the pin22slide along the tapered guide surfaces400,402. Because the length80of the pin22in the undeflected configuration is larger than the distance410, shifting the slider20in direction100causes the pin22to bend as the intermediate portion54of the pin22is bent and moves with the slider20while the end portions50,52are engaging and sliding along the tapered guide surfaces400,402. The tapered guide surfaces400,402cause the end portions50,52to be urged together as the slider20shifts in direction100.

RegardingFIG.19, the slider20is continued to be shifted in direction100and the outer side surface portions140,142of the pin22are engaged with the edges404,406of the bone plate body16. The pin22is bent and is resiliently urging the end portions50,52apart in directions420,422. RegardingFIG.20, the slider20has been shifted in direction100to a position where the end portions50,52of the pin22have shifted radially beyond edges404,406such that the end portions50,52may snap apart and into the pockets60,62. Once the end portions50,52have snapped into the pockets60,62, the slider20may be released and the pin22urges the end portions50,52in directions420,422against the surfaces70,72of the pockets60,62. As noted above, the edges404,406are separated by the distance410which is less than the length80of the unloaded pin22such that the retainer portions110,112of the bone plate inhibit the pin22from fully unloading and urging the slider in direction100A. In this manner, the pin22may be assembled with the slider20and the bone plate body16and the preload applied to the pin22. The preload in the pin22keeps the pin22in a bent configuration in the bone plate body16so that the pin22resists movement of the slider20in direction82A and positions the pin22to be shifted with the slider20in direction100upon the advancing of the bone screw into the throughbore18.

RegardingFIG.21, a bone screw remover tool500is provided that permits a surgeon to connect the bone screw remover tool500to a bone screw14in a throughbore18, shift the slider20out of the way of the bone screw14, and then turn the bone screw14to remove the bone screw14from the throughbore18. More specifically, the bone screw remover tool500includes a driver502having a handle504and a shaft506. The bone screw remover tool500has a sleeve508with a cannula509through which the shaft506extends until protruding at a driving member, such as a driving tip514having a rotary drive structure516(seeFIG.22). The sleeve508has a knob518and is rotatably connected to the shaft506of the driver502. In this manner, the surgeon may turn the knob518in direction520to cause the sleeve508and a cam portion522thereof to shift the slider20from the interference position to the clearance position and then may turn the handle504and driving tip514connected thereto to remove the associated bone screw14. As shown inFIG.21, the bone screw remover tool500has a distal end portion512and a proximal end portion524, and a longitudinal axis526extending therebetween. As noted above, the sleeve508may be rotated relative to the driver502in direction520. Conversely, the driver502may be rotated in direction530relative to the sleeve508to loosen the bone screw14while the sleeve508keeps the slider20in the clearance position thereof. In some embodiments, a surgeon may connect the driving tip514to a bone screw14, turn the sleeve508in direction530to shift the slider20to the clearance position, and then turn the driver502in direction530to remove the bone screw14from the throughbore18.

RegardingFIG.22, the driving tip514extends out from the cannula509of the sleeve508to expose the rotary drive structure516, such as projections that fit into recesses of the rotary drive structure280of the bone screw14. The rotary drive structure516may be, for example, a Torx driver. The driving tip514extends out of a distal surface544of the sleeve508. The surface544may be adapted to seat against the upper surface312(see FIG.24) of the bone screw head portion24. The cam portion522of the sleeve508has a recess550that is axially aligned with the slider20before the driving tip514is advanced into the throughbore18. The recess550provides clearance for the sleeve508to be advanced without contacting the lip portion264of the slider20. The surface544may have a general circular periphery with a center that is eccentric to a center556of the driving tip514. The cam portion522includes a cam surface560having radii562,564,566from the center556of the driving tip514that increase as the cam surface560extends clockwise (inFIG.22) about the driving tip514from the approximate twelve o'clock position to the proximate six o'clock position. Once the driving tip514has been advanced into engagement with the rotary drive structure280of the bone screw head portion24, the surgeon may turn the sleeve508in direction520about the shaft506to cause a radially enlarged portion570of the sleeve508to rotate into contact with the slider20and shift the slider20in direction100from the interference position to the clearance position.

RegardingFIG.23, a cross section of the bone screw remover tool500is provided. The handle504may be secured using adhesive, welds, or fastener(s) to a collar580. The collar580may be threadingly engaged with a threaded portion582of the shaft506. The shaft506extends through the cannula509of the sleeve508to project outward of the driving tip514.

RegardingFIG.24, the bone screw remover tool500has been connected to the bone screw14by aligning the recess550of the sleeve508with the slider20and advancing the driving tip514in direction600into the rotary drive structure280of the bone screw head portion24. A radially narrow portion569of the sleeve508is positioned radially intermediate the slider20and the shaft506. Next, the surgeon turns the sleeve508around the shaft506and cammingly engage the cam surface560of the sleeve508with the surface610of the slider20to shift the slider20from the interference position to the clearance position. The surgeon turns the sleeve508in direction520until the radially enlarged portion570of the sleeve508is radially intermediate the slider20and the shaft506. The presence of the thicker, radially enlarged portion570against the slider20keeps the slider20in the clearance position. With the slider20in the clearance position, the surgeon may turn the handle504in direction530which causes the corresponding turning of the driving tip514in direction530and removes the bone screw14from the bone and the throughbore518. The radially enlarged portion570of the sleeve508is sized to have an outer radius that is similar to a maximum outer radius of the bone screw head portion24, such as a corner620(seeFIG.16), so that the radially enlarged portion570of the sleeve508may hold the slider20in the clearance position as the head portion24is removed in direction601until the slider20can transition into contact with the tapered surface260of the bone screw head portion24. The slider20may slide along the tapered surface26as the bone screw head portion24is removed from the throughbore18.

Uses of singular terms such as “a,” “an,” are intended to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms. It is intended that the phrase “at least one of” as used herein be interpreted in the disjunctive sense. For example, the phrase “at least one of A and B” is intended to encompass A, B, or both A and B.

While there have been illustrated and described particular embodiments of the present invention, it will be appreciated that numerous changes and modifications will occur to those skilled in the art, and it is intended for the present invention to cover all those changes and modifications which fall within the scope of the appended claims.