Fastener assembly including contact pin

A bone fastener assembly including a bone screw, a receiver, a crown, a seat, and a contact pin is provided. The contact pin is formed as a leaf spring resiliently biased in a first position that affords generation of spring force via deformation thereof, and the contact pin acts as a tensioner to ultimately press against a head portion of the screw to aid movement prevention of the head portion relative to the receiver.

FIELD

The present technology is generally related to a fastener assembly including a contact pin.

BACKGROUND

Multi-axial screw assemblies are used to facilitate placement and attachment of spinal rods relative to the spine. The spinal rods can be used in correcting spinal abnormalities. Typically, such multi-axial screw assemblies include at least a bone screw portion and a receiver portion attached to one another. The bone screw portions are attached to vertebrae, and the receiver portions receive portions of the spinal rods. Furthermore, the receiver portions of typical pedicle screw assemblies are angularly and fixedly positionable with respect to the screw portions to afford attachment of the spinal rods between vertebrae. The receiver portion is angularly/pivotally positionable relative to a screw portion prior to being fastened to a rod. However, without some friction between those components, the receiver portion would potentially flop freely relative to the screw portion. Therefore, there is a need for a contact pin portion receivable within the receiver portion that can provide enough friction between the components so that the receiver portion can be adjusted to approximately the final position and the components will stay in that position.

SUMMARY

The techniques of this disclosure generally relate to a contact pin used in fastener assemblies to aid in maintaining the angular/pivotal position of a screw and a receiver relative to one another.

In one aspect, the present disclosure provides a bone fastener assembly including a bone screw including a head portion, a threaded shaft portion, and a central axis, the head portion including an exterior surface; a receiver including a body portion, a first arm portion, and a second arm portion, the body portion having a first end, an opposite second end, and an interior surface defining a first cavity extending between the first end and the second end, the first arm portion including a first interior arm surface and the second arm portion including a second interior arm surface, the first interior arm surface and the second interior arm surface defining a second cavity therebetween, the first cavity and the second cavity communicating with one another; a crown including a first end, an opposite second, an exterior surface, and an interior surface defining at least a first interior cavity portion extending from the first end of the crown to a position intermediate the first end and the second end of the crown; a seat included in the receiver; and a contact pin having a first end, a second end, and a length between the first end and the second end, the contact pin being resiliently biased in a first configuration; where, when the bone fastener assembly is assembled, at least a portion of the crown is positioned within the first cavity of the receiver at a position at and adjacent the second end of the body portion, the contact pin is positioned within the first cavity of the receiver at a position between the crown and the seat; at least a portion of the head portion is receivable between the crown and the seat and positionable adjacent the contact pin, and the exterior surface of the head portion contacts at least the seat and the contact pin; and where the contact pin contacts the head portion of the screw and presses the exterior surface of the head portion of the screw against the interior surface of the first cavity of the receiver.

In another aspect, the disclosure provides a bone fastener assembly including a bone screw including a head portion, a threaded shaft portion, and a central axis, the head portion including an exterior surface; a receiver including a body portion having a first end, an opposite second end, and an interior surface defining a first cavity extending between the first end and the second end; a crown including a first end, an opposite second, an exterior surface, and an interior surface defining at least a first interior cavity portion extending inwardly from the first end of the crown; a seat included in the receiver; and a contact pin having a first end, a second end, and a length between the first end and the second end, the contact pin being resiliently biased in a first configuration; where, when the bone fastener assembly is assembled, at least a portion of the crown is positioned within the first cavity of the receiver at a position at and adjacent the second end of the body portion, at least a portion of the head portion is receivable between the crown and the seat, and at least a portion of the contact pin contacts the exterior surface the head portion.

In yet another aspect, the disclosure provides a bone fastener assembly including a bone screw including a head portion, a threaded shaft portion, and a central axis, the head portion including an exterior surface; a receiver including a body portion having a first end, an opposite second end, and an interior surface defining a first cavity extending between the first end and the second end; a seat included in the receiver; and a contact pin having a first end, a second end, and a length between the first end and the second end, the contact pin being resiliently biased in a first configuration; where, when the bone fastener assembly is assembled, at least a portion of the head portion is receivable between the seat and the second end of the body portion, and at least a portion of the contact pin extends into the first cavity of the receiver and contacts the exterior surface of the head portion to press the exterior surface of the head portion of the screw against the interior surface of the first cavity of the receiver.

DETAILED DESCRIPTION

A fastener assembly according to an embodiment of the present disclosure is generally indicated by the numeral10inFIGS. 1-3. The fastener assembly10can be a multi-axial screw assembly, and includes a bone screw12, a receiver14, a crown16, an expansion (or retaining) ring18, and a contact pin P. As depicted inFIG. 3, when the fastener assembly10is assembled, the crown16, the expansion ring18, and the contact pin P are positioned within the receiver14, and a portion of the screw12is receivable within receiver14between the crown16and the expansion ring18and adjacent the contact pin P to attach the screw12and the receiver14to one another. The fastener assembly10is configured to afford angular/pivotal adjustment of the screw12and the receiver14relative to one another into a selected angular/pivotal position.

The fastener assembly10is used in facilitating attachment of a spinal construct such as a spinal rod (not shown) to the spine. A portion of the spinal rod is ultimately received within the receiver14, and a threaded cover (not shown) engaging the receiver14is positioned over the portion of the spinal rod to retain the portion of the spinal rod within the receiver14. Ultimately, the threaded cover pushes the portion of the surgical rod received in the receiver14against the crown16to force the crown16against the screw12and force the screw12against the expansion ring18. As depicted inFIG. 3, such contact of the crown16against the screw12and the screw12against the expansion ring18, along with the engagement of the screw12with the contact pin P as well as the receiver14, ultimately serves in fixedly attaching the screw12and the receiver14to one another in a selected angular/pivotal position with respect to one another. Moreover, before the fixed attachment of the screw12and the receiver14, the contact pin P can be used to hold the screw12and the receiver14in position relative to one another during adjustment as the angular/pivotal position of the screw14and the receiver14is being selected.

The screw12can be used to facilitate fixed attachment of the receiver14and the crown16to tissue such as, for example, bone. For example, the screw12can be a pedicle screw, or as depicted inFIGS. 1-3, a lateral mass screw. Furthermore, the screw12includes a head portion20, a neck portion22, a shaft portion24, and a central axis. As depicted inFIGS. 2 and 3, the head portion20can be generally spherical, the neck portion22joins the shaft portion24to the head portion20, and the shaft portion24is configured to penetrate tissue such as, for example, bone. The shaft portion24can include one or more thread forms30having a continuous turn or discrete turns and/or different pitches around a shank32to facilitate such bone penetration. Besides facilitating bone penetration, the thread form30is used in securing the screw12and the receiver14to the bone. Furthermore, the shank32can have a smaller or a larger diameter than the neck portion22, and can include portion(s) having tapered and/or cylindrical configurations.

The head portion20includes a tool-engaging portion34configured to engage a surgical tool or instrument for rotating the screw12to facilitate penetration of the screw12into tissue such as, for example, bone. The tool-engaging portion34includes six (6) lobes arranged in a generally hexagonal cross-sectional configuration. In some embodiments, the tool-engaging portion34can have, for example, alternative cross-sectional configurations such as being generally polygonal (including generally triangular, rectangular, hexagonal, etc. configurations), oval, or irregular.

Furthermore, the head portion20includes an exterior surface36, and, as depicted inFIGS. 2 and 3, the exterior surface36can be generally spherical. The receiver14can be angularly/pivotally adjustable on the exterior surface36of the head portion20. Thus, after penetration of the screw12into tissue such as, for example, bone, the angular/pivotal position of the receiver14on the exterior surface36of the head portion20can be adjusted into the selected angular/pivotal position of the screw14and the receiver14. Friction caused by the ultimate engagement, as depicted inFIG. 3, of the exterior surface36with the contact pin P, the receiver14, the crown16, and the expansion ring18serves in maintaining the position of the receiver14relative to the head portion20of the screw12.

As depicted inFIGS. 1, 2, and 4, the receiver14includes a body portion40, a first arm42extending upwardly from the body portion40, and a second arm44extending upwardly from the body portion40. The receiver14includes a first cavity46and a second cavity48that together extend between a first end50and a second end52of the receiver14. The first cavity46is internal to the body portion40, and extends between a first opening54and a second opening56in the body portion40. The first opening54is at the first end50of the receiver14, and the second opening56is intermediate the first end50and the second end52of the receiver14. Furthermore, the second cavity48is formed between the first arm42and the second arm44. As discussed below, the crown16is initially received in portions of the first cavity46and the second cavity48and then ultimately received in the first cavity46, at least portions of the head portion20and the neck portion22are received in the first cavity46, and a portion of the spinal rod is ultimately received in the second cavity48.

As depicted inFIGS. 2-4, the crown16includes a wall portion60having a first end62and a second end64and an internal cavity66extending through the wall portion60between a first opening70formed at the first end62of the crown16, and a second opening72formed at the second end64of the crown16.

The wall portion60includes a first interior surface74, a second interior surface76, a first exterior surface80, and a second exterior surface82. The first interior surface74and the second interior surface76define the internal cavity66, the first interior surface74can be spherical or generally spherical to facilitate engagement with the generally-spherical shape of the exterior surface36of the head portion20, and the second interior surface76can be generally cylindrical to afford passage of a surgical tool or instrument. Friction caused by the ultimate engagement, as depicted inFIG. 3, of the exterior surface36with the interior surface74(along with the ultimate engagement of the exterior surface36with the contact pin P, the receiver14, and the expansion ring18) serves in maintaining the position of the head portion20relative to the receiver14. Furthermore, as depicted inFIG. 2, the first exterior surface80can be generally cylindrical, and the second exterior surface82can be generally flat. The generally cylindrical shape of the first exterior surface80can facilitate engagement with similarly contoured portions of the receiver14in the first cavity46, and a portion of the spinal rod received in the second cavity48is ultimately contacted to the exterior surface82.

As depicted inFIGS. 3 and 4, the first cavity46formed in the body portion40of the receiver14is defined by an interior surface90, the first opening54, and the second opening56. The interior surface90can be sized to receive the crown16. The interior surface90includes a generally cylindrical portion92and at least one shoulder portion94. Upon insertion of the crown16into the first cavity46, the first exterior surface80of the crown16interfaces with the portion92of the interior surface90, and the at least one shoulder portion94prevents the crown16from exiting the first cavity46. Furthermore, upon insertion of a portion of the head portion20into the first cavity46, the exterior surface36contacts the portion92of the interior surface90. Friction caused by the ultimate engagement, as depicted inFIG. 3, of the exterior surface36of the head portion20with the portion92of the interior surface90(along with the ultimate engagement of the exterior surface36with the contact pin P, the crown16, and the expansion ring18) serves in maintaining the position of the head portion20relative to the receiver14.

As depicted inFIG. 4, the second cavity48is formed between the first arm42and the second arm44by a first interior surface100formed on the first arm42and a second interior surface102formed on the second arm44. The second cavity48includes first threads104and second threads106formed on the first interior surface100of the first arm42and the second interior surface102of the second arm44, respectively, for engaging the threaded cover. When a portion of the spinal rod is received in the second cavity48, the threaded cover can be engaged to the first threads104and the second threads106to facilitate attachment of the portion of the spinal rod received in the second cavity48to the fastener assembly10.

The expansion ring18serves as a seat for seating a portion of the head portion20, and the expansion ring18is formed as an incomplete generally annular structure that affords expansion and contraction thereof. As depicted inFIG. 2, the expansion ring18includes a first end110, an opposite second end112, and an aperture114extending between the first end110and the second end112. Furthermore, the expansion ring18is incomplete, and includes a first circumferential end portion120, a second circumferential end portion122, and a gap124between the first circumferential end portion120and the second circumferential end portion122. The expansion ring18defines the aperture114, and the aperture114is configured to receive a portion of the screw12.

The expansion ring18is ultimately received at least partially in the space defined by a recess126formed in the portion92of the interior surface90adjacent the first opening54in the body portion40. To that end, the expansion ring18is compressible between at least an expanded first position and a compressed second position to decrease the size of the gap124, and hence, decrease the size of the aperture114. The expansion ring18can be initially be threaded onto the screw12to be received around the neck portion22. When received around the neck portion22, and upon insertion of a portion of the head portion20into the first cavity46, the expansion ring18can be compressed to fit through the first opening54. Thereafter, the expansion ring18can be moved along the portion92of the interior surface90until it reaches the recess126, where the expansion ring18expands into the space defined by the recess126. Friction caused by the ultimate engagement, as depicted inFIG. 3, of the exterior surface36of the head portion20with the expansion ring18(along with the ultimate engagement of the exterior surface36with the contact pin P, the receiver14, and the crown16) serves in maintaining the position of the head portion20relative to the receiver14.

The contact pin P can be formed as a leaf spring resiliently biased in a first position that affords generation of spring force via deformation thereof, and, as depicted inFIG. 3, the contact pin P acts as a tensioner to ultimately press against the head portion20of the screw12to aid movement prevention of the head portion20relative to the receiver14.

As depicted inFIG. 2, the contact pin P includes a first end130, a second end132, and a length134between the first end130and the second end132. The contact pin P can be substantially straight or curved along its length, and the contact pin P is at least partially received in at least one groove136formed in the portion92of the interior surface90intermediate the first opening54and the second opening56in the body portion40. The groove136is configured in shape and size to at least partially receive the contact pin P.

When portions of the contact pin P, as depicted inFIG. 4, are received in the groove136, a portion of the length134extends into the first cavity46. More specifically, at least a portion of the contact pin P adjacent the first end130can be received in the groove136, at least portion of the contact pin P adjacent the second end132can be received in the groove136, and at least a portion of the length134extending between the portions received in the groove136is positioned in the first cavity46.

The contact pin P, as discussed above, is a leaf spring, and, given that a portion thereof extends into the cavity, the contact pin P ultimately forms an interference fit with a portion of the head portion20received in the first cavity46. When a portion of the head portion20is received in the first cavity46, as depicted inFIG. 3, the contact pin P contacts the exterior surface36of the head portion20, and the spring force thereof presses portions of the exterior surface36(generally opposite from the contact of the contact pin P) against the portion92of the interior surface90of the first cavity46. The contact pin P can deform via deflection to generate the spring force for pressing against the exterior surface36of the head portion20. Friction created by the ultimate engagement, as depicted inFIG. 3, of the contact pin P with the exterior surface36and of the exterior surface36with the portion92of the interior surface90generally opposite from the contact of the contact pin P (along with the ultimate engagement of the exterior surface36with the crown16and the expansion ring18) serves in maintaining the position of the head portion20in the first cavity46. Furthermore, the friction created by use of the contact pin P can be used to somewhat loosely hold the screw12and the receiver14in position relative to one another during adjustment as the angular/pivotal position of the screw12and the receiver14is being selected.

The fastener assembly10can be assembled with the crown16, then the contact pin P, and then the head portion20of the screw12, then the expansion ring18inserted through the first opening54and into the first cavity46of the receiver14. To illustrate, the crown16is initially inserted through the first opening54, into the first cavity46, and positioned in a first position within the cavity. In the first position, the crown16is somewhat loose in the first cavity46. The contact pin P is then inserted through the first opening54, into the first cavity46, and into the groove136. Thereafter, a portion of the head portion20is inserted through the first opening54and into the first cavity46, and the expansion ring18is inserted through the first opening54, into the first cavity46, and positioned in the recess126. Upon initial installation, the head portion20is somewhat loosely held within the first cavity46between the interior surface74of the crown16and the expansion ring18by the contact of the contact pin P with the exterior surface36of the head portion20and the corresponding contact of the exterior surface36of the head portion20with the portion92of the interior surface90of the first cavity46. The spring force of the contact pin P can hold the screw12and the receiver14in position relative to one another during adjustment as the angular/pivotal position of the screw12and the receiver14is being selected.

After the angular/pivotal position of the screw12and the receiver14is selected, a portion of the surgical rod is positioned in the second cavity48, and threads of the threaded cover are threadably engaged to the first threads104and the second threads106. Continued threadable engagement of the threaded cover with the first threads104and the second threads106pushes the portion of the surgical rod received in the receiver14against the crown16. When the threaded cover pushes the portion of the surgical rod against the crown16, the crown16is moved downwardly within the receiver14. Such movement of the crown16pushes the interior surface74against the exterior surface36and the exterior surface36against the expansion ring18to trap at least a portion of the head portion20firmly in position between the crown16and the expansion ring18. In doing so, a portion of the head portion20adjacent the neck portion22is seated against the expansion ring18. Friction between the screw12and the expansion ring18, and friction between the screw12and the crown16ultimately fixedly attaches the screw12and the receiver14and serves in maintaining the selected angular/pivotal position of the head portion20of the screw12in the cavity46relative to the receiver14.

Furthermore, when at least a portion of the head portion20is positioned relative to the receiver14, the crown16, and the expansion ring18, the contact pin P, as discussed above, contacts the exterior surface36of the head portion20, and the spring force thereof presses portions of the exterior surface36(generally opposite from the contact of the contact pin P) against the portion92of the interior surface90of the cavity46. The friction created by the contact of the contact pin P with the exterior surface36of the head portion20and the corresponding contact of the exterior surface36of the head portion20with the portion92of the interior surface90further serves in maintaining the selected angular/pivotal position of the head portion20of the screw12in the cavity46relative to the receiver14.