FRICTION-FIT IMPLANTABLE DEVICES AND ASSEMBLIES

An implantable device may be configured to couple to a bone screw for spinal fixation. The implantable device may include one or more friction-fit features to allow the implantable device to maintain its orientation before being locked into place by a set screw. For example, an implantable device may include a body comprising a sidewall. The sidewall may define a first passage extending within the sidewall and parallel to a vertical axis of the body, and a slot extending through the sidewall and in communication with the first passage. The device may further include a pressure member coupled to the body. The pressure member may include a distal surface for engaging the head of the bone screw. The device may further include a biasing member at least partially within the first passage of the body for applying a downward force on the pressure member.

TECHNICAL FIELD

This disclosure is generally directed to friction-fit implantable devices and assemblies attachable to fixation rods for aligning an anatomy of a patient. For instance, one or more implantable assemblies including a receiver body coupled to a bone screw may be coupled to a connecting rod to retain one or more vertebrae in a desired relationship.

BACKGROUND

Various systems for connecting fasteners (e.g., pedicle screws) to elongated supports (e.g., fixation rods) for the purposes of vertebral fixation have been proposed. Although described with reference to vertebral or spinal fixation, it should be appreciated that the systems described herein may be similarly applicable to other bone structures as well.

Generally, fixation systems include a receiver (or “receiver body,” “body,” or “head”) which is attachable to both a fastener and a fixation rod to retain the rod in fixed relation to the fastener, and in turn, a vertebra into which the fastener is secured. Traditional receiver assemblies include a receiver and a fastener for attachment of fixation rod to a vertebra. A physician may use multiple receiver assemblies and/or multiple rods to secure the vertebrae in a desired spatial relationship. In some installations, a first rod may extend along a first side of a patient's spine and engage a first plurality of fastener assemblies each implanted in a different vertebra, and a second rod may extend along a second side of the patient's spine and engage a second plurality of fastener assemblies.

In some instances, a receiver assembly may come preassembled such that the receiver and fastener are preselected and attached to one another by the manufacturer. The assembly of the fastener and the receiver may involve special tools and trained technicians such that assembly by the physician, nurse, or surgical technician is impractical. Accordingly, the surgeon or technician may select a receiver and fastener assembly from a plurality of receiver and fastener assemblies based on the patient's anatomy and/or indications. Accordingly, the surgeon may be limited based on the variety of selections available at the time of surgery.

During a spinal fixation surgery, the receiver and fastener assemblies may be inserted through the patient's tissue via a surgical opening or ingress. The fasteners of each assembly may be driven into the patient's vertebra at desired locations. A connecting rod is then positioned through each receiver and the receivers and connecting rod are fixed in place by set screws or compression screws in each receiver. In order to position the connecting rod through each receiver, the receivers are oriented in alignment so that the connecting rod can be inserted through a channel or slot of each receiver. The alignment of the receivers can be a complicated part of the procedure. For example, gravity may cause the receivers to droop or slip out of alignment. Accordingly, the procedure may involve repositioning and/or reorienting one or more receivers multiple times before the connecting rod is successfully positioned through each receiver.

SUMMARY

The present disclosure describes implantable devices and assemblies that provide a friction fit between a receiver body and a fastener (e.g., bone screw). For example, an implantable device may be configured to apply a frictional force to a screw head so that an orientation of the receiver body can be maintained relative to the screw head before the position is fixed by a set screw. Further, the implantable devices of the present disclosure may allow for modular assembly before or during a spinal fixation procedure. For example, the implantable device may allow for bottom-side loading of the screw into the receiver body so that various screws having various characteristics (e.g., length, diameter, etc.) can be coupled to the receiver body.

According to one aspect of the present disclosure, an implantable device is configured to couple to a head of a bone screw. The implantable device includes: a body comprising a sidewall defining: a first passage extending within the sidewall and parallel to a vertical axis of the body; and a slot extending through the sidewall and in communication with the first passage; a pressure member coupled to the body such that the sidewall at least partially surrounds the pressure member, the pressure member comprising a distal surface configured to engage the head of the bone screw; a first biasing member positioned at least partially within the first passage of the body and configured to apply a downward force on the pressure member relative to the body.

In some aspects, the pressure member comprises a lateral surface defining an engagement feature, and wherein the first biasing member comprises: a first pin positioned through the slot of the body and in the engagement feature of the pressure member; and a spring positioned within the first passage of the body and configured to apply, via the first pin, a downward force on the pressure member relative to the body. In some aspects, the engagement feature comprises an opening in the lateral surface of the pressure member. In some aspects, the first pin defines a pin opening extending through the first pin in a direction transverse to a longitudinal axis of the first pin, the first biasing member further includes a second pin coupled to the first pin and extending through the pin opening, and at least a portion of the spring is positioned around a proximal portion of the second pin. In some aspects, the first passage comprises first screw threads at a distal opening of the first passage, and the second pin comprises second screw threads at a distal portion of the second pin configured to engage the first screw threads.

In some aspects, the first pin comprises third screw threads at the pin opening, and wherein the second pin comprises fourth screw threads configured to engage the third screw threads. In some aspects, the first pin comprises: a first portion positioned in the engagement feature; and a second portion positioned within the slot. In some aspects, the sidewall of the body further defines a second passage extending within the sidewall and parallel to the vertical axis of the body, and the implantable device further comprises a second biasing member positioned at least partially within the second passage of the body and configured to apply a downward force on the pressure member relative to the body.

In some aspects, the body comprises a first vertical tab extending proximally from a base of the body and a second vertical tab extending proximally from the base of the body, the first passage is defined within the first vertical tab and offset from a center of the first vertical tab, and the second passage is defined within the second vertical tab and offset from a center of the second vertical tab. In some aspects, the pressure member further comprises a proximal surface defining a saddle configured to receive a connecting rod. In some aspects, the spring comprises a coil spring. In some aspects, the device further includes a set screw configured to apply a downward pressure on the pressure member and the head of the bone screw.

According to another aspect of the present disclosure, an implant includes: a body comprising a first arm and a second arm extending vertically from a base of the body, wherein: the first arm defines a first vertical tunnel within a sidewall of the first arm, the first vertical tunnel being offset from a center of the first arm the second arm defines a second vertical tunnel within a sidewall of the second arm; a pressure cap positioned within a cavity of the body between the first arm and the second arm; a first spring positioned within the first vertical tunnel; and a second spring positioned within the second vertical tunnel, wherein the first spring and the second spring are configured to apply a downward force on the pressure cap relative to the body.

In some embodiments, the implant further includes: a first biasing member comprising a first pin attached to a first cross pin such that the first cross pin extends transverse to the first pin, wherein: the pressure cap comprises a lateral surface defining a first pin engagement feature, a first end of the first cross pin engages the first pin engagement feature, a proximal end of the first pin is positioned within the first vertical tunnel, and the first spring is configured to apply the downward force on the pressure cap via the first biasing member.

In some embodiments, the implant further includes: a second biasing member comprising a second pin attached to a second cross pin such that the second cross pin extends transverse to the second pin, wherein: the lateral surface of the pressure cap further defines a second pin engagement feature, a first end of the second cross pin engages the second pin engagement feature, a proximal end of the second pin is positioned within the second vertical tunnel, and the second spring is configured to apply the downward force on the pressure cap via the second biasing member. In some embodiments, the first arm comprises an external surface defining a first tool engagement feature, the first vertical tunnel is offset from the first tool engagement feature, the second arm comprises an external surface defining a second tool engagement feature, and the second vertical tunnel is offset from the second tool engagement feature.

In some embodiments, the implant further includes: an expandable ring positioned within the cavity of the body and adjacent to the base of the body and the pressure cap. In some embodiments, an interior surface of the base of the body is configured to: restrict the expandable ring from expanding when the expandable ring is in a first vertical position relative to the body; and allow the expandable ring to expand to accept a head of a bone screw when the expandable ring is in a second vertical position relative to the body, the second vertical position being proximal to the first vertical position. In some embodiments, the first tunnel and/or the second tunnel may be offset from a center of their respective arms.

According to another embodiment of the present disclosure, a method for assembling an implantable device includes: providing a body comprising a sidewall defining: a passage extending within the sidewall and parallel to a vertical axis of the body; and a slot in communication with the passage; positioning a pressure cap within a cavity of the body, the pressure cap comprising a lateral surface defining a pin engagement hole; positioning a spring within the passage of the body; compressing the spring proximally within the passage; retaining the spring in a compressed state such that the compressed spring is disposed proximal of the pin engagement hole of the pressure cap; inserting a first pin through the slot of the body and in the pin engagement hole of the pressure cap, wherein the first pin defines a bore extending through the first pin and transverse to a central axis of the first pin; and inserting a second pin into the passage of the body, through the bore of the first pin, and into the spring.

It is to be understood that both the foregoing general description and the following drawings and detailed description are exemplary and explanatory in nature and are intended to provide an understanding of the present disclosure without limiting the scope of the present disclosure. In that regard, additional aspects, features, and advantages of the present disclosure will be apparent to one skilled in the art from the following. One or more features of any embodiment or aspect may be combinable with one or more features of other embodiment or aspect.

These figures will be better understood by reference to the following Detailed Description.

DETAILED DESCRIPTION

For the purpose of promoting an understanding of the principles of the present disclosure, reference will now be made to the implementations illustrated in the drawings and specific language will be used to describe them. It will nevertheless be understood that no limitation of the scope of the disclosure is intended. Any alterations and further modifications to the described devices, instruments, methods, and any further application of the principles of the present disclosure are fully contemplated as would normally occur to one skilled in the art to which the disclosure relates. In addition, this disclosure describes some elements or features in detail with respect to one or more implementations or figures, when those same elements or features appear in subsequent figures, without such a high level of detail. It is fully contemplated that the features, components, and/or steps described with respect to one or more implementations or figures may be combined with the features, components, and/or steps described with respect to other implementations or figures of the present disclosure. For simplicity, in some instances the same or similar reference numbers are used throughout the drawings to refer to the same or like parts.

FIG.1is a perspective view of a spinal fixation system100including a plurality of implantable devices102coupled to respective vertebrae of a patient's spine by a plurality of screws120. Each implantable device102inFIG.1includes a receiver body110, a set screw122, and a biasing member140. The implantable devices102are coupled to one another by a rod130positioned in U-shaped slots or saddles of the receiver bodies110. The rod130may be sized, shaped (e.g., bent, curved), and otherwise structurally configured to correct a spinal deformity, and/or to retain the vertebrae in a fixed position. The positions and orientations of the implantable devices102relative to the rod130and the screw120are fixed by the set screws122. For example, the screws120may include spherical, semi-spherical, or otherwise round screw heads seated within the implantable devices102. The implantable devices102may be configured to rotate, tilt, swivel, twist, and/or otherwise move relative to the screw heads of the screws120. With the screws120fixed to the vertebrae, a physician may move the implantable devices102into the orientation shown inFIG.1to receive the rod130. The set screws122can then be tightened down to compress the rod130and the screw heads of the screws120against the base of the receiver bodies110to fix the position and orientation of the receiver bodies110relative to the rod130and screws120.

Each implantable device102further includes at least one biasing member140disposed within a passage, cavity, or chamber in at least one sidewall of the receiver body110. The biasing members140are configured to apply a downward force on a pressure member of the receiver body110. The pressure member will be described further below. The pressure member may include a distal surface configured to engage the screw head of the screw120. In some aspects, the downward force applied to the screw head can cause a base or underside of the screw head to form a friction fit with the base of the receiver body110, or with an inner surface of a split ring disposed within the receiver body110. The frictional force (e.g., static friction) induced by the biasing members140may be sufficient to retain the position and orientation of the implantable devices102relative to the screw heads. For example, the friction may be sufficient to overcome gravitational forces acting on the implantable devices102to keep the implantable devices102from drooping, sagging, or sliding after the physician has positioned the implantable devices102in alignment to receive the rod130. Additionally, as explained below, the implantable devices102may allow for bottom-loading of the screws120into a distal opening of the receiver bodies110. In some aspects, a physician may load the screws120into the implantable devices102to form an implantable assembly prior to inserting and driving the screws120into the patient's bone. The bottom-loading style of the assembly may be referred to as a modular assembly. The bottom-loaded modular assembly may be advantageous, in some aspects. For example, the modular assembly style of the implantable devices102may allow for the physician to choose a type and/or size of screw and assemble the implantable device102and screw120during a spinal fixation procedure, based on the patient's anatomy and indications. The modular style may also allow for quick and efficient assembly with little or no disassembly of the implantable device102.

FIG.2is a perspective view of an implantable device102coupled to a bone screw120. In some aspects, the implantable device102and the coupled bone screw120may be referred to as an implantable assembly or subassembly. The implantable device102includes a receiver body110including opposing sidewalls112,114defining a U-shaped slot or saddle. The sidewalls112,114may be referred to as arms, wings, or any other suitable term. The receiver body110is configured to receive a connecting rod via the U-shaped slot. The implantable device102also includes a biasing member or biasing assembly140. The biasing member140is visible through a slot117in the sidewall114of the receiver body110. The implantable device102also includes a pressure member150, which may also be referred to as a pressure cap. The pressure member150includes a concave upper surface or top surface for receiving the connecting rod, as described above. The pressure member150may also include a concave surface on the bottom side of the pressure member150to contact and engage a top surface of a screw head of the screw120. The biasing member140is configured to apply a downward force on the pressure member150to provide a friction fit of the implantable device102with the screw head of the screw120.

The receiver body110includes a first engagement feature116and a plurality of second engagement features118. The engagement features116,118may provide for releasable engagement with a tool for inserting, positioning, and/or removing the implantable device102. For example, the engagement features116,118may provide for releasable engagement with a tool for inserting the subassembly including the implantable device102and the connected screw120, and driving the screw120into the patient's bone (e.g., vertebra). In the illustrated embodiment, the first engagement feature116is centered with the sidewall114. It will be understood that the other sidewall112may also include an engagement feature similar or identical to the engagement feature116on the sidewall114. The engagement feature on the other sidewall112may also be centered on the sidewall. The centering of the engagement feature116may be beneficial for robust engagement with the insertion tool. For example, the centered placement of the engagement feature116may allow for a deeper groove or impression of the engagement feature116into the sidewall114. The slot117is offset from the center of the sidewall114. In this regard, the slot117may avoid at least part of the area of the first engagement feature116, which may be a relatively thinner portion of the sidewall114. In some aspects, the off-center position of the slot117and the biasing member140may avoid a potential weak point or failure point of the receiver body110. In this regard, the slot117is in communication with a vertical passage, channel, or tunnel, which may extend from a bottom or distal opening119to an upper region of the sidewall114, which is above the slot117. The vertical passage will be described further below with respect toFIGS.7A and7B. Because the upper portion of the sidewall114is thinner in the region of the first engagement feature116, a centered position of the slot117and the vertical channel in which the biasing member140is placed would potentially result in an area of thin material near the engagement feature116. The area of thin material may be a potential failure point of the receive body110. Accordingly, the offset position of the slot117and biasing member140advantageously maintains the structural integrity of the receiver body110.

Further, the offset position of the slot117and passageway for the biasing member140may allow the passageway to extend further proximally in the sidewall114. For example, because the offset position of the slot117and passageway may not result in the potential weak point described above, the passageway can extend further up the sidewall114beside the engagement feature116, as will be shown inFIGS.7A and7Bbelow. The greater length of the passageway may allow for springs with desirable characteristics (e.g., spring constant, stress-strain profile, etc.) to be used for the friction fit mechanism. However, in other embodiments of the present disclosure, the passageways and biasing members140are aligned with the centers of the corresponding sidewalls112,114.

The receiver body110further includes internal threads115on the interior surfaces of the sidewalls112,114. The threads115may be configured to engage corresponding threads on a set screw (e.g.,122,FIG.1). The set screw may be tightened down into the receiver body110to compress the connecting rod onto the pressure member150. Compressing the pressure member150may also cause the pressure member150to put additional pressure onto the screw head of the screw120to fix the implantable device102in a desired position and orientation.

The biasing member140, or biasing assembly, includes a cross pin142, a pin144, and a spring146. The cross pin142extends horizontally through the sidewall114of the receiver body110. An outer surface of the cross pin142is shown inFIG.2. The cross pin142also includes a second side or distal side, which may engage in engagement feature of the pressure member150. In this regard, the spring146may be configured to apply a downward force on the cross pin142, such that the cross pin142applies the downward force to the pressure member150. It will be understood that the opposing side of the implantable device102may include a second biasing member or biasing assembly similar or identical to the biasing member140. Accordingly, the biasing members on each side of the implantable device102may be configured to apply a balanced, or substantially balanced, downward force on the pressure member150.

The spring146is positioned around the pin144. The pin144may be inserted through the bottom or distal opening119, and through an opening or bore of the cross pin142. In some embodiments, the cross pin142includes inner threads configured to engage outer threads of the second and144. Accordingly, the cross pin142and the pin144may be coupled, connected, and/or fixed to one another via the threads. In some embodiments, the cross pin142and the pin144are connected to each other by a weld and/or an adhesive, instead of or in addition to the threads. For example, the cross pin142may first be coupled to the pin144by the threads, and then fixed to one another by a weld. The welding may be accomplished through a hole in the external side or surface of the cross pin142. For example, the cross pin142may be configured to form a press fit with the pin144. The press fit may be followed by a weld or an adhesive, in some embodiments. In the illustrated embodiment, the cross pin142and the pin144are coupled to one another in a perpendicular fashion. However, it will be understood that the angle formed by the cross pin142and the pin144may not be 90°. For example, the angle formed by the cross pin142in the pin144may be acute (e.g., 80°, 85°, 88°, 89°, etc.) or obtuse (e.g., 91°, 92°, 95°, 100°, etc.). The cross pin142and the pin144may be configured to translate vertically within the passage in the sidewall114. In some aspects, the amount of travel allowed for the first biasing member140may be associated with or defined by the slot117, and/or the spring146. The amount of travel allowed for the cross pin142, and by association the pressure member150, may allow for bottom loading of the screw120. For example, as explained further below, bottom loading of the screw120may include inserting the screw head of the screw120through a bottom or distal opening of the receiver body110to a first vertical position at which the head of the screw can fit within a split ring. The screw120may then be moved downward or distally to a second vertical position where in the split ring closes around a base of the screw head due to a tapered base of the receiver body110. Accordingly, the screw120may be locked within the implantable device102by the split ring.

The spring146may be configured and/or selected to provide sufficient downward force to provide for the friction fit described above. For example, the spring146may be configured and/or selected to provide sufficient downward force to the pressure member150in combination with a similar or identical biasing member and spring in the other sidewall112.

In some embodiments, the spring146may be sized, shaped, and otherwise structurally configured to operate in a plastic region. Accordingly, during assembly, the spring146may experience some permanent deformation. After assembly, the spring146may remain functional to induce the frictional forces for the friction fit with the screw head. In some aspects, the spring146may be formed of a biocompatible titanium or titanium alloy. In some aspects, the downward force applied by each spring on the cross pin142ranges between 0.3-0.8 Newtons at maximum compression. In some aspects, the combined downward force of two biasing members, one in each of the sidewalls112,114, ranges between 0.6-1.6 Newtons at maximum compression. Further, the spring146may be configured and/or selected to provide sufficient travel to allow for bottom loading of the screw120. In some embodiments, the spring146may comprise a metal, such as titanium, titanium alloy, nitinol, stainless steel, and/or any other suitable metal.

The materials of the implantable device102may be biocompatible, and may have other structural characteristics appropriate for use in spinal fixation. For example, the receiver body110, pressure member150, cross pin142, pin144, spring146, and/or the screw may include a biocompatible metal, such as stainless steel, titanium, and/or alloys thereof. In other embodiments, one or more components of the implantable device102may include a polymer material, such as DELRIN, polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE), polysulfone (PS), polycarbonate, and/or any other suitable polymeric material. One or more components of the implantable device102may be manufactured by milling, machining, casting, molding, laser sintering, 3D printing, and/or any other suitable process. The components of the implantable device102may be formed of the same materials or of different materials.

FIG.3is an exploded view of an implantable assembly104including the implantable device102and the screw120shown inFIG.2, according to an embodiment of the present disclosure. It will be understood that the ordering or arrangement of the components of the assembly104shown inFIG.3may not represent the order of assembly of the implantable assembly104. For example, the components of the assembly104shown inFIG.3may be arranged based on the relative positions and/or their relationship with the other components of the assembly104. The assembly includes pins144positioned within channels or passageways within the receiver body110. The channels or passageways of the receiver body110may be accessible by distal or bottom openings119. Springs146are positioned around distal shaft portions of the pins144. The distal shaft portions may have a relatively smaller diameter than a base portion of the pins144. The pins144include threads145between the distal shaft portions and the base portions. The threads145are external threads, and may be configured to mate with and/or engage corresponding internal threads on the cross pins142. In some embodiments, the threaded connection between the cross pin142and the pin144may include a runout, meaning that the threads145and/or the threads of the cross pin142include a transition section where the depth of the threads decreases. The runout may provide a stop for the threaded connection to facilitate consistent dimensions and relative positions of the pins142,144during assembly.

The receiver body110includes or defines a slot117and a distal or bottom opening119. The slot117and the bottom opening119are offset from a center of the sidewall of the receiver body, as explained above. The other sidewall of the receiver body110may also include a corresponding slot and/or bottom opening or distal opening. The corresponding slot and bottom opening of the other sidewall may also be offset from the center of the other sidewall. Accordingly, the slot and/or bottom opening on the other sidewall are not visible inFIG.3. In some embodiments, the slot117and bottom opening119are positioned approximately 180° from the other slot and bottom opening on the other sidewall of the receiver body110. However, in other embodiments, the slots and/or bottom openings in the receiver body110may be positioned less than 180° from each other.

The assembly104further includes the pressure member150. The pressure member150includes a concave surface123configured to receive a connecting rod. The pressure member150includes or defines at least one engagement feature125. In some embodiments, the engagement feature125includes a slot or hole extending through a sidewall of the pressure member150. In other embodiments, the engagement feature125includes a recess, groove, protrusion, detent, and/or any other suitable engagement feature configured to engage a surface of at least one cross pin142. Although only one engagement feature125is visible inFIG.3, it will be understood that the pressure member150may include one or more additional engagement features125on one or more other sides of the pressure member150. For example, the pressure member150may include an additional engagement feature125positioned 180°, or approximately 180°, from the visible engagement feature125. The engagement feature125includes a slot or aperture configured to receive and engage a distal portion of the cross pin142. Accordingly, the cross pin142is configured to apply a downward force on the engagement feature125of the pressure member150.

The pressure member150may also include a bottom concave surface configured to engage an upper surface of a screw head126of the screw120. The upper surface of the screw head126may include a spherical, aspherical, or otherwise curved shape configured to engage the bottom surface of the pressure member150. In other embodiments, the screw head126may include a conic section shape. Accordingly, the screw head126may be curved about at least one axis to allow the screw head126to continuously rotate relative to the pressure member150. In other embodiments, the screw head126may include a polygonal shape having a plurality of flat surfaces arranged around an axis of the screw120. For example, the screw head126may include, on the upper surface,10,20,25,30, or any other suitable number of flat surfaces arranged around the axis of the screw120. The number of flat surfaces on the upper surface of the screw head126may correspond to the number of possible orientations of the implantable device102about the longitudinal axis of the screw120. In some embodiments, the pressure member150may include corresponding polygonal surfaces on the bottom side or surface of the pressure member150.

The assembly104further includes a split ring124. The split ring124may include a discontinuous annular shape configured to expand and/or retract to enlarge and/or reduce an inner diameter of the split ring124. The split ring124may be configured to lock the screw120into the implantable device102once the screw head126has been inserted through a bottom opening of the split ring124. For example, the upper surface of the screw head126may be configured to cause the split ring124to expand and allow the screw head126to pass through the split ring124. Once the screw head126has passed through the split ring124, the split ring124may relax and contract to lock against a bottom curved surface of the screw head126. In some embodiments, an inner surface of the split ring124includes a ridge or seating feature configured to engage the bottom surface of the screw head126.

The screw120includes a distal threaded shaft comprising screw threads configured to drive into and engage the patient's bone. In the illustrated embodiment, the threads are right-handed threads. In other embodiments, the threads may be left-handed threads. The threads may have any suitable pitch, depth, and/or other geometric characteristics based on the target bone or tissue and application for the assembly104. The screw120may be machined, laser sintered, 3D printed, or otherwise manufactured by any suitable manufacturing process. It will be understood that the threaded portion of the shaft of the screw120may extend a greater or lesser portion of the shaft than what is shown inFIG.3.

FIG.4is a side elevation view of the implantable device102, according to an embodiment of the present disclosure.FIG.4shows a sidewall of the receiver body, including an engagement feature116, and a slot117. The sidewall shown inFIG.4may be either of the sidewalls112,114shown inFIG.2. The biasing member140, including the cross pin142, the pin144, and the spring146, are positioned within the vertical channel of the sidewall of the receiver body110. An outer portion of the cross pin142is positioned to translate vertically within the slot117. Accordingly, the slot117may at least partially define the travel allowed for the cross pin142. The pin144includes a bottom portion143. The bottom portion143is positioned within the distal opening119of the sidewall. The bottom portion143may include a coupling feature to rotate the pin144within the channel and engage the threads of the cross pin142. For example, the bottom portion143may include a feature for a flat head screwdriver head, Phillips screwdriver head, hex key, TORX screwdriver head, square screwdriver bit, or any other suitable coupling feature. The receiver body110further includes a flat surface or milled surface111centered with the sidewall and extending vertically down the receiver body110. The flat surface111may reduce the outer profile of the receiver body110, in some aspects.

FIGS.5and6illustrate the relative orientations of the passageways or channels of an implantable device102for receiving the biasing members140, according to an embodiment of the present disclosure.FIG.5is a top plan view of the implantable device102, andFIG.6is a bottom plan view of the implantable device102. Referring toFIG.5, the receiver body110includes a first horizontal axis101extending through the centers of the sidewalls112,114. The receiver body110includes an opening129. The opening129may be at or near a center of the receiver body110. The opening129may be configured to receive a screw head and/or a screw shaft of a bone screw. The opening129may be further configured to provide access for a screwdriver or other tool to drive the screw into the patient's bone and/or tissue. A pressure member150is positioned within the receiver body such that the saddle of the pressure member150is aligned with the U-shaped slot of the receiver body110.

As illustrated above, the receiver body110may include or define an engagement features (e.g.,116,FIG.2) to engage with a positioning tool. The engagement feature(s) may be aligned with the axis101. The receiver body110further includes a second axis103of three intersecting with the first axis101. The second axis103is non-parallel with the first axis101. The second axis103may represent the orientation of the passageways or channels for receiving the biasing members140. For example, referring toFIG.6, the receiver body110includes or defines distal openings119centered on the second axis103. The distal openings119may provide access to insert one or more components of the biasing members140. For example, the springs146and pins144of biasing assemblies may be inserted into their respective passageways or channels in the receiver body110through the distal openings119. In some embodiments, the second axis103may be offset from the first axis101by 20°, 25°, 30°, 35°, 40°, or any other suitable amount, both greater or smaller.

FIGS.7A and7Bare cross-sectional views of an implantable device102before and during a modular assembly, according to an embodiment of the present disclosure. In some embodiments, the implantable device102may be configured for assembly before or during a surgical procedure. For example, the physician may select the screw120based on the patient's anatomy and indications. In some embodiments, the screw120may be selected after the surgery has begun and after the surgeon has created an access through the patient's tissue to the bone. In other instances, the physician and/or surgeon may select the screw120before the surgery based on medical images of the patient's anatomy (e.g., x-ray, computed tomography, magnetic resonance imaging).

The cross-sectional views ofFIGS.7A and7Bare taken along the second axis103shown inFIGS.5and6. Accordingly, the cross-sectional views ofFIGS.7A and7Bshow the access channels or passageways141in both sidewalls112,114of the receiver body110. Referring toFIG.7A, the biasing members140are shown in a first position prior to insertion of the screw120. In the first position, the biasing members140are fully extended such that the outer portions of the cross pins142are seated on the bottoms of the openings119. Accordingly, the springs146are in a relatively uncompressed or extended state. The pins144are coupled to the cross pins142such that the threads145of the pins144engage corresponding threads147of the cross pins142. In the first position shown inFIG.7A, the bottom portions143of the pins144are shown at or near the distal openings119. The split ring124is seated within a conical base of the receiver body110. InFIG.7A, the split ring124is in an unexpanded state.

The passageways141in the sidewalls112,114of the receiver body110extend from the distal openings119to proximal ends149. Accordingly, in the illustrated embodiment, the passageways141do not extend completely through the sidewalls to the top surface or proximal surface of the receiver body110. However, in other embodiments, the passageways141may extend completely through the sidewalls112,114to the top surface of the receiver body. Accordingly, there may be multiple access points for assembling and/or adjusting the biasing members140. In some aspects, the passageways141may be referred to as tunnels, channels, or cavities, for example. The length of the passageways141may allow for springs with desirable characteristics to be used. For example, the larger passageways may allow for titanium springs to operate in a plastic region while applying an amount of force suitable to create a friction fit (e.g., 0.3-0.8 Newtons for each spring at maximum compression). Titanium may have beneficial biocompatibility characteristics for use in implants.

In the first state shown inFIG.7A, the split ring124may be limited in vertical motion by the pressure member150. In some embodiments, there may be some clearance between the split ring124and the pressure member150. In other embodiments, there may be no clearance between the split ring124and the pressure member150.

Referring toFIG.7B, the implantable device102is shown during a modular assembly with the biasing members140and a second vertical position. By inserting the screw head126through the bottom opening of the receiver body110, the screw head moves the split ring124and the pressure member150upward by a distance105. As a result, the pins144and cross pins142are translated upward to a second vertical position to compress the springs146within the passageways141. With the split ring124translated upward within the receiver body110, the split ring124has room to expand to allow the screw head126to pass through the split ring124. With the split ring124around the screw head126, the bottom surface of the pressure member150engages a top surface of the screw head126. If the physician or technician removes the upward force on the screw120, the biasing members140can apply a downward force on the pressure member150, and as a result to the screw head126and the split ring124. The downward force may result in the frictional force between the pressure member150and the screw head126. The screw head126and split ring124may translate downward until the outer tapered surfaces of the split ring124contact the inner tapered surface of the receiver body110. In some embodiments, the modular assembly shown inFIGS.7A and7Bmay be non-reversible, such that the screw120may not be removed after it has been inserted into the implantable device102, as shown inFIG.7B. In other embodiments, the modular assembly shown inFIGS.7A and7Bmay be reversible, such that the screw120may be removed after assembly.

FIGS.8A-8Fillustrate an assembly process for an implantable device, such as the implantable device102shown inFIGS.1-7B. The assembly process shown inFIGS.8A-8Fincludes or involves an assembly device200or assembly jig. The assembly device200includes a first mandrel212having a first control piece202, and a second mandrel214having a second control piece204. The first control piece202includes a first through hole206. The second control piece204includes a second through hole208. The mandrels212,214may support and retain components of the implantable device in place during assembly.FIG.8Ais a perspective view of the receiver body110positioned within the assembly device200. The receiver body110is positioned with in the assembly device200such that the slot117is facing upward and centered between the lateral sides of the assembly device200. The engagement feature116is also facing upward and off of center.

FIGS.8B-8Fare top plan views of the receiver body110in the assembly device200during various stages of the assembly process. Referring toFIG.8B, the implantable device102is shown in a first stage of the assembly process. A split ring and a pressure member, such as the split ring124and the pressure member150shown inFIG.3, may be positioned within the receiver body110. Accordingly, the first stage of the assembly process may include providing the receiver body110, where the receiver body includes a passage extending with in a side wall. The passage may extend parallel to a vertical axis of the body the side wall of the receiver body110may further define the slot117in communication with the passage. The first stage of the assembly process may further include positioning the pressure member or pressure within a cavity of the receiver body110. The pressure member may include a lateral surface defining a pin engagement hole. With the receiver body110positioned within the assembly device200such that the distal opening119and slot117are centered and aligned with the mandrels212,214, a first tool220can be used to insert a spring146into a chamber of the receiver body110through the distal opening119. For example, the first tool220may be inserted through the first through hole206shown inFIG.8a.

Referring toFIG.8C, the implantable device102is shown during a second stage of the assembly procedure. The first tool220is advanced into the passageway of the receiver body110to compress the spring146against a proximal end of the passageway. The compressed spring146is seen through the slot117. The first tool220may be advanced through the opening119by sliding the first control piece202over the mandrel212toward the receiver body110.

Referring toFIG.8D, the implantable device102is shown during a third stage of the assembly procedure. A second tool222is inserted into the slot117to retain the spring146in the compressed state. The second tool222may include a pick, hook, or any other suitable type of tool to retain the spring146in the compressed state, as shown inFIG.8D. In some embodiments, the second tool222is coupled to the assembly device200so that the second tool222can keep the spring146in the compressed state in a hands-free fashion. The spring146is compressed such that the entirety of the spring146is proximal of a pin engagement hole152of the pressure member.

Referring toFIG.8E, the implantable device102is shown during a fourth stage of the assembly procedure. While the second tool222keeps the spring146in the compressed state, a cross pin142is inserted through the slot117such that a distal portion of the cross pin142is inserted into the pin engagement hole152shown inFIG.8D. The cross pin142includes a bore extending laterally through the cross pin142. The bore is transverse to a central axis of the cross pin142. The bore includes internal threads147configured to engage corresponding external threads145of a pin144, as explained below.

Referring toFIG.8F, the implantable device102is shown during a fifth stage of the assembly procedure. A pin144is inserted through the opening119into the passageway of the receiver body110. The pin144may be inserted by the tool220, in some embodiments. In other embodiments, the pin144may be inserted using a screwdriver. Once the pin144has been inserted into the passageway, the pin144may be coupled to the cross pin142by inserting at least a distal portion of the pin144through the bore of the cross pin142and rotating the first pin144to engage the threads145with the threads147. The screwdriver may then be removed, and the device102may be removed from the assembly device200. The implantable device102may then be ready for use and/or assembly by a physician for a spinal fixation procedure.

It will be understood that one or more embodiments described above may be modified in one or more ways without departing from the scope of the present disclosure. For example, although the embodiments described above may include a coil spring146, it will be understood that any type of biasing device or spring may be used, including a wave spring, elastomeric Bushing, elastomeric band, and/or any other suitable type of biasing device. Further, it will be understood that fewer or more than two biasing members140may be used for the implantable device102. For example, an implantable device may include two, three, four, and/or any other suitable number of biasing members. In some aspects, the cross pin142may be coupled are attached to the pin144by welding, adhesive, detents, and/or any other suitable type of attachment. In some embodiments, a receiver body110may include fewer or more engagement features than the engagement features116,118shown above. In some embodiments, an implantable device102may not allow for modular assembly. For example, an implantable device102may not include the split ring124illustrated above. In this regard, an implantable assembly may be configured such that a bottom surface of the screw head directly contacts a seating surface of the receiver body110. In some embodiments, the implantable device102may include protrusions extending from the pressure member150, instead of the cross pins142. For example, the pressure member150may include projections extending outward and positionable within the slots117. The pins144may be configured to mate with and/or engage with the projections of the pressure member150.

Aspects, components, and features described above may be used in a variety of skeletal stabilization and/or fixation systems. For example, although the biasing members140described above are shown low-profile, singular receiver body implants, the present disclosure contemplate other types of receiver bodies and spinal implant devices. For example, the biasing members140described above, or components of the biasing member140, may be incorporated into reduction screw receiver bodies, sliding double bodies, closed receiver bodies, and/or any other suitable type of spinal implant or receiver body. Further, although embodiments of the present disclosure may be described as spinal implants or spinal fixation devices, it will be understood that the devices described above may be used for a variety of skeletal stabilization and/or fixation procedures.

Persons of ordinary skill in the art will appreciate that the implementations encompassed by the present disclosure are not limited to the particular exemplary implementations described above. In that regard, although illustrative implementations have been shown and described, a wide range of modification, change, combination, and substitution is contemplated in the foregoing disclosure. It is understood that such variations may be made to the foregoing without departing from the scope of the present disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the present disclosure.