Patent Description:
Certain spinal conditions, including a fracture of a vertebra and a herniated disc, indicate treatment by spinal immobilization. Several methods of spinal joint immobilization are known, including surgical fusion and the attachment of pins and bone plates to the affected vertebras. One known device is a bone interface anchor inserted into at least two spaced-apart vertebras, with a stabilization rod interconnecting the two or more anchors to stabilize the vertebras spanned by the anchors.

Specifically, a bone screw is received within a socket formed in the anchor. The anchor further includes a channel, extending perpendicular to the longitudinal axis of the bone screw, for receiving the stabilization rod. The anchor further comprises a threaded portion above the channel. After the bone screw and anchor have been inserted into the bone material, the rod is placed within the channel and a nut is mated with the external threads of the anchor. The nut applies a compressive force between the rod and the screw head to firmly fix the rod between the spanned vertebras and thus stabilize the spinal vertebrae.

During surgical implantation of these prior art stabilization systems, the surgical site is crowded with tissue masses, sponges and other surgical implements that obstruct access to the anchor threads. Given the difficult access, it is possible for the surgeon to cross-thread the nut with the threads of the anchor after the fixation rod is in place. If the threads of the anchor are cross-threaded, the cross-threaded coupling must be removed and replaced before the surgery can proceed. In addition, the threaded fastener (e.g., the nut) is frequently removed and then reinstalled as the surgeon makes progressive bends to contour the fixation rod. This increases the surgery with each on-off iteration and further increases the chances of cross-threading.

Another problem associated with threaded attachments is the torque exerted on the anchor during the tightening of the threaded fastener about the upper end portion of the fixation device. This torque can inadvertently introduce stress points along the rod, bend the rod, or even loosen the threaded engagement of the anchor in the bone. The elimination of the conventional threaded attachments in the fixation device of the present invention also obviates these problems associated with applying torque.

The angle at which the anchor screws extend from the vertebra pedicle is dictated by the spinal curvature, the orientation of individual vertebra within the spine, and the surgeon's placement of the screw within the pedicle. For example, there is considerable spinal curvature in the region of the S1-L5 vertebra junction and the angle between the longitudinal axis of the screws and the vertebra in that region vary over a wide range. Also, it may be necessary to displace one or more of the anchors from the spin midline to effectuate maximum spinal stabilization. Thus, the rod-receiving channels are typically not collinear or coplanar and, the rod must be shaped or contoured by the surgeon during the implantation procedure to fit within the channels along the spinal column. The prior art systems allow the coupling unit to pivot with respect to the screw over a range of about +/- <NUM>° to +/- <NUM>°, providing some margin for the surgeon to place the rod within the channel.

Current uniplanar screws contain flat features on the screw shank that are engaged by mating flat features on the bushing/load ring component to prevent motion in one plane. Other designs have features on the shank itself that engage the screw body to only allow motion in one plane. None of the existing designs allow the shank to rotate independently of the screw body. Other devices lock rotation of the shank to the body which limits the thread forms that are preferred for pedicle screws. Thus, the present invention addresses these problems as well as others. <CIT> discloses a bone anchor system using a deformable interface between the cap of a bone screw and a stabilization rod to reduce stress concentrations in the rod.

This invention relates to a pivotal screw assembly as set out in claim <NUM> below.

Optional features of the invention are set out in the dependent claims below.

In the accompanying figures, like elements are identified by like reference numerals among the several preferred embodiments of the present invention.

The foregoing and other features and advantages of the invention are apparent from the following detailed description of exemplary embodiments, read in conjunction with the accompanying drawings. The detailed description and drawings are merely illustrative of the invention rather than limiting, the scope of the invention being defined by the appended claims. The invention is thus limited to the subject-matter as defined in the claims. Other described aspects are included for illustrative purposes.

Embodiments of the invention will now be described with reference to the Figures, wherein like numerals reflect like elements throughout. The words proximal and distal are applied herein to denote specific ends of components of the instrument described herein. A proximal end refers to the end of an instrument nearer to an operator of the instrument when the instrument is being used. A distal end refers to the end of a component further from the operator and extending towards the surgical area of a patient and/or the implant.

Reference to the features of the present disclosure may also be described with respect to coronal, sagittal, and transverse axes of the body. The coronal axis refers to an axis running substantially from front (anterior) to back (posterior) of the body and extending through the mid-section. The sagittal axis refers to an axis running substantially from left to right of the body and extending through the mid-section to intersect the coronal axis at a right angle. The transverse axis refers to an axis running substantially from head to toe of the body and crossing the point where the coronal and sagittal axes intersect at a right angle. Furthermore, the coronal, sagittal, and transverse planes refer to the standard definitions associated with each term. Namely, the coronal plane being a plane perpendicular to the coronal axis and formed by the transverse and sagittal axes, the sagittal plane being perpendicular to the sagittal axis and formed by the coronal and transverse axes, and the transverse plane being perpendicular to the transverse axis and formed by the sagittal and coronal axes.

Generally speaking, a screw assembly <NUM> comprises a screw <NUM> operably coupled with a body member <NUM>, a bushing <NUM> employed within the body member <NUM>, and at least one insert <NUM> operably coupled with the screw <NUM>, as shown in <FIG>. Generally, the screw assembly <NUM> includes a longitudinal axis <NUM> running from the proximal end to the distal end of the screw assembly <NUM>, a transverse axis <NUM> running perpendicular to the longitudinal axis <NUM> of the Screw assembly <NUM>, and a lateral axis <NUM> running perpendicular to the transverse axis <NUM> and longitudinal axis <NUM>. Upon insertion into a patient, the longitudinal axis <NUM> may be substantially parallel to a coronal axis of the body, the transverse axis <NUM> may be substantially parallel to a sagittal axis of the body, and the lateral axis may be substantially parallel to a cranial-caudal axis of the body.

The screw assembly <NUM> may be used with at least one other such assembly and a stabilization or fixation rod <NUM> to connect the assemblies and stabilize the vertebras into which the assemblies are inserted. Generally, the body member <NUM> may rotate <NUM> degrees relative to the screw <NUM> about the longitudinal axis <NUM>. In other embodiments, the body member <NUM> may be restricted from rotation about the longitudinal axis <NUM>. The body member <NUM> rotates or pivots relative to the screw <NUM> in only one other direction by operation of the insert <NUM> rotatably coupled with the body member <NUM> and the screw <NUM>. In one embodiment, the body member <NUM> is restricted to rotation about a single other axis, the transverse axis <NUM>, or along the cephalad-caudal plane, and the body member <NUM> is prevented from rotating or pivoting about the lateral axis <NUM> or along the medial-lateral plane. The orientation of the features could be adjusted to limit the motion or rotation in any plane desired (medial / lateral, or cephalad / caudal).

As shown in <FIG>, the screw <NUM> includes a head portion <NUM> on the proximal portion, which defines a slot <NUM> therein used to drive the screw <NUM> into the bone. A threaded shaft portion <NUM> of screw <NUM> extends therefrom through the body member <NUM>, as shown in <FIG>. The head portion <NUM> includes a lipped surface <NUM> defined by the lower portion of head portion <NUM> that rests upon and mates with a rounded interior surface <NUM> formed in the inner or lower end of the insert <NUM>. The lipped surface <NUM> allows the head portion <NUM> to sit within the insert <NUM> while permitting the head portion <NUM> of the screw to rotate about its longitudinal axis. The lipped surface <NUM> may include or form a recessed portion, channel, or groove in a lateral surface of the head portion <NUM>. The channel may be disposed circumerentially about the head portion <NUM>. In one embodiment, the head portion <NUM> includes a height H1. The head portion <NUM> includes a cap <NUM> extending beyond the top portion of the head portion <NUM> that engages a top portion <NUM> of the insert <NUM>.

The top portion <NUM> of the insert <NUM> allows the cap <NUM> and the screw <NUM> to rotate about its longitudinal axis without moving distally. The exterior surface of the cap <NUM> includes a curved surface that substantially aligns with exterior surface <NUM> of the inserts <NUM> as to form a continuous curved exterior surface thereabout, as shown in <FIG>, which permits the body member <NUM> to rotate about exterior surface of the cap <NUM> and exterior surface <NUM> of the insert <NUM>. The insert <NUM> includes at least two extensions <NUM> projecting from an exterior surface <NUM> of the insert <NUM> to operably engage the interior surface of the body member <NUM>, so as to allow the body member <NUM> to rotate relative to the screw <NUM> only in one plane or along the traverse axis <NUM>, while limiting rotation in a plane perpendicular to the transverse axis <NUM>.

The extensions <NUM> may be symmetrical and facing opposite directions or be in substantial parallel alignment about the circumference of the insert <NUM> or head portion <NUM> of the screw <NUM>, which restricts the rotation of the body member only about the transverse axis <NUM> or in a single plane. The insert <NUM> may be a single construction or divided up into a plurality of portions or segments; however, the extensions <NUM> may be symmetrical about the circumference of the insert <NUM>. In one embodiment, the head portion <NUM> includes a Width W1 around the circumference of the head portion <NUM>. The inserts <NUM> allow for operably coupling with any sized head portion <NUM> of the screw, any screw shank design, and any thread pitch. The head portion <NUM> includes a diameter D1, as shown in FIG. IE, wherein the insert <NUM> may be sized to fit around diameter D1 of any size. The inserts <NUM> also can be loaded from the bottom to allow for larger diameter shanks to be used.

In <FIG> , the insert <NUM> is shown integral with the head portion <NUM> of the screw <NUM>. The extensions <NUM> are on opposite sides of the insert <NUM> that is integral with the head portion <NUM>, such that the when the extensions <NUM> are operably coupled with the body member <NUM>, the screw <NUM> is unable to rotate about its longitudinal axis <NUM> relative to the body member <NUM>, but is able to rotate or pivot about the transverse axis <NUM>. In this example, the head portion <NUM> does not include the cap <NUM> and the head portion <NUM> is unable to rotate about the longitudinal axis <NUM> when insert <NUM> and the extension <NUM> are mounted within the body member <NUM>.

As shown in <FIG>, the body member <NUM> includes a side wall <NUM> that defines at least two slots <NUM> axially disposed through the side wall <NUM> thereof, where each slot <NUM> includes a curvilinear surface <NUM> on the distal ends of the slots <NUM>. The two slots <NUM> generally form a U-shape and are sized to receive a fixation rod <NUM> (as shown in <FIG>) within the side walls <NUM>. The side walls defining the slots preferably extend upwardly beyond the midpoint of the rod <NUM> and can be inclined slightly to provide a slight holding force on the rod prior to securing the rod <NUM> with a locking cap <NUM> (as shown in <FIG>). Thus, during assembly, the surgeon exerts a slight downward force on the rod <NUM>, snapping the rod <NUM> into the transverse channel defined by the aligned slots <NUM>.

As shown in <FIG> and 3A-3B, the upper interior surface of side walls <NUM> of the body member <NUM> both have radially projecting serrations formed therein defining a plurality threaded portions <NUM> or axially aligned ratchet teeth <NUM>. The interior distal surface of body member <NUM> has conical section <NUM> formed therein and a pair of concave pockets <NUM>. The conical section <NUM> couples with the exterior surface <NUM> of the inserts <NUM> to allow rotation of the body member <NUM> relative to the insert <NUM>, while the concave pockets <NUM> mates with the extensions <NUM> on the inserts <NUM>, as to provide a rotational motion of the body member <NUM> with respect to the screw <NUM>. The concave pockets <NUM> include a lower opening <NUM> connected to two curved side walls <NUM>, while the two curved side walls <NUM> connect to a top portion <NUM>. Preferably, the top portion <NUM> is substantially straight from the connecting points of the two curved side walls <NUM>. In one embodiment, the concave pocket <NUM> includes a height H3 from the top portion <NUM> to the lower opening <NUM>. In one embodiment, the lower opening <NUM> includes a width W2. In one embodiment, the curved side walls <NUM> and the top portion <NUM> include a thickness T1.

To secure the fixation rod <NUM> within the body member <NUM> of the assembly, a locking cap <NUM> is provided as shown in <FIG>. One exemplary cap, as described in <CIT> defines a top portion, a pair of opposed arcuate depending leg portions and a centrally disposed depending projection equidistantly spaced from leg portions. Central projection preferably defines a planar lower or bottom surface. The leg portions of cap each have a plurality of radially projecting serrations formed therein that define a plurality of axially aligned ratchet teeth adopted to engage teeth <NUM> on the opposed interior side walls <NUM> of the body member <NUM>, as will be described in U. S Patent <NUM>,<NUM>,<NUM>. Alternatively, the cap includes a threaded portion to operably engage the threaded portion <NUM> of the interior side walls <NUM> of the body member <NUM>. For example, in <FIG>, the cap <NUM> may include a setscrew as known in the art.

As shown in <FIG>, each insert <NUM> includes at least one extension <NUM> extending from the curved exterior surface <NUM>. The extension <NUM> includes a top portion <NUM> and a substantially curved bottom portion <NUM>. The curved bottom portion <NUM> includes a radius of curvature R1 that substantially aligns with the two curved side walls <NUM> of the concave pocket <NUM> in the body member <NUM>. The curved bottom portion <NUM> includes a radius of curvature R1 that fits within the lower opening <NUM> with width W2, such that the curved bottom portion <NUM> may rotate within the lower opening <NUM> of the concave pocket <NUM>. The top portion <NUM> includes two angled surfaces 192a and 192b with an angle of decline A2. The angle of decline A2 determines the amount of rotation for the body member <NUM> relative to the screw <NUM>, as rotation will abut one of the angled surfaces 192a, 192b with the top portion <NUM> of the concave pocket <NUM> and cease rotation of the body member <NUM> relative to the screw <NUM>. The insert <NUM> also includes a top portion <NUM> of the exterior surface <NUM>, and the top portion <NUM> of the exterior surface is separated by a distance D2 from the top portion <NUM> of the extension <NUM>.

In one embodiment, the insert <NUM> includes a height H2 from the top portion <NUM> to the bottom of the exterior portion <NUM>, as shown in <FIG>. In one embodiment, the height H2 of the extension <NUM> is substantially equal to the height H1 of the head portion <NUM> of the screw <NUM>. In one embodiment, the extension <NUM> includes a height H4 from the top portion <NUM> to the bottom of the bottom portion <NUM>. In one embodiment, the height H4 of the extension <NUM> allows the extension <NUM> to fit within the concave pocket <NUM> and the height H3 of the concave pocket <NUM>, as to allow the extension <NUM> to rotate within the concave pocket <NUM>. The height H4 of the extension <NUM> may be smaller than the height H3 of the concave pocket. Alternatively, the height H3 of the concave pocket <NUM> relative to the height H4 of the extension <NUM> may be adjusted to allow for increased or decreased rotation of the body member <NUM> relative to the insert <NUM>, whereby an increased height H3 of the concave pocket <NUM> relative to the height H4 of the extension <NUM> provides for an increased rotation, and an decreased height H3 of the concave pocket <NUM> relative to the height H4 of the extension <NUM> provides for a decreased rotation. The increased height H3 of the concave pocket <NUM> relative to the height H4 of the extension <NUM> allows for the top portions 192a, 192b to rotate higher/proximally and engage the top portion <NUM> of the concave pocket <NUM> at an increased angle.

In one embodiment, the range of rotation is about +/- <NUM>° about the transverse axis <NUM> (as measured from the longitudinal axis <NUM> of the screw) alternatively about +/- <NUM>° about the transverse axis, alternatively about +/- <NUM>° about the transverse axis, for a total motion rotational range of between about <NUM>° and <NUM>° about the transverse axis without permitting any rotation about the caudal-cranial axis. This exemplary extended range of motion, while limiting the rotation motional along the axis perpendicular to the transverse axis, allows the surgeon additional freedom in locating the screws and eases the assembly process by reducing the requirement for a rod contouring. In some examples, rotation may be permitted about the caudal-cranial axis and while rotation about the transverse axis may be prohibited.

As shown in <FIG>, in one embodiment, the extension <NUM> includes a thickness T2 that fits within the thickness T1 of the curved side walls <NUM> and top portion <NUM> of the concave pocket <NUM>. In one embodiment, the insert <NUM> includes a width W4 such that the insert fits around at least a portion of the head portion <NUM> of the screw <NUM> and around at least a portion of Width W1 of the head portion <NUM>. As shown in <FIG>, in one embodiment, the extension <NUM> includes a Width W5 such that the extension <NUM> fits within the concave pocket <NUM> and Width W3, while the concave pocket <NUM> is able to rotate about the extension <NUM>.

Alternative embodiments of the insert <NUM> are shown in <FIG>. In one embodiment, as shown in <FIG>, the insert <NUM> may include a plurality of insert portions 180a, 180b, 180c, 180d, whereby the extension <NUM> also includes at least a first extension portion 184a and a second extension portion 184b. The first insert portion 180a includes the first extension portion 184a and the second insert portion 180b includes the second extension portion 184b. Preferably, the first extension portion 184a and the second extension portion 184b each represent half of the extension member <NUM>. The first extension portion 184a may be symmetrical with the second extension portion 184b, or the first extension portion 184a may be asymmetrical with the second extension portion 184b. The asymmetry with the first extension portion 184a and the second extension portion 184b allows for the first curved bottom portion 194a to be different than the second curved bottom portion 194b and include a different radius of curvature R1 if different angles of rotation are desired along the transverse axis. The plurality of insert portions 180a, 180b, 180c, 180d couple with the head portion <NUM> to form the rounded interior surface <NUM> and the curved exterior surface <NUM>.

An alternative embodiment of the insert <NUM> is shown in <FIG>, whereby the insert <NUM> is substantially a single piece including the rounded interior surface <NUM> to fit about the head portion <NUM> of the screw, as to allow rotation of the head portion <NUM> within the rounded interior surface <NUM> of the insert <NUM>. The insert180 may include a cut <NUM> extending through the exterior surface <NUM> to the interior surface <NUM> to enable circumferential expansion of the insert <NUM> to ease assembly with the screw <NUM>, body member <NUM>, and bushing <NUM>. The insert includes a diameter D2, which may be expanded by allowing separate portions or segments of the insert <NUM> to expand around the diameter D1 of the head portion <NUM>. The cut <NUM> may be removed from the exterior surface <NUM> and interior surface <NUM>, as shown in <FIG>, as to form a C-shape insert <NUM> that circumferentially expands diameter D2 to be operably coupled with head portion <NUM> of the screw <NUM>.

An alternative embodiment of the insert <NUM> is shown in <FIG>, whereby the top portion <NUM> includes at least two curved portions <NUM> that are perpendicular to the extensions <NUM>. The curved portions <NUM> are on opposite sides of the insert <NUM> and prevent the insert <NUM> from rotating or pivoting about an axis perpendicular to the transverse axis. Alternatively, the curved portions <NUM> may engage with the bushing <NUM>, as to prevent the head portion <NUM> from rotating about its longitudinal axis.

As shown in <FIG>, the bushing <NUM> is preferably employed within the body member <NUM> of the assembly <NUM> adjacent to side walls <NUM> to better distribute the longitudinal forces exerted on the pedicle screw <NUM> by the cap <NUM> and rod <NUM>. The bushing <NUM> defines a pair of opposed concave surfaces <NUM> formed in the upper end of a circular skirt <NUM> so as to define a seat for the fixation rod <NUM>. The skirt may generally form a U-shape channel that coincides with the curvilinear surface <NUM> of the body member <NUM> and seat therein for the rod <NUM>. The lower portion of bushing <NUM> includes slots <NUM> to provide flexibility therein and defines depending tapered ends <NUM> to form a conical lumen <NUM> adapted to abut opposed sides of the head portion <NUM> and cap <NUM> and allow rotation of the body member <NUM> about the head portion <NUM> and insert <NUM>.

A pair of outwardly projecting opposed resilient tabs <NUM> are provided at the upper ends of the bushing <NUM> between the top ends of the bushing skirt <NUM> that in some embodiments are adapted to be received in a snap fitment within a pair of opposed apertures <NUM> (shown in <FIG>) formed on the inside of the side wall <NUM> of body member <NUM> whereupon the rod seat in bushing <NUM> is aligned with the channel <NUM> in the body member <NUM>. Note that in the illustrated embodiment shown in <FIG> and <FIG>, for example, the resilient tabs <NUM> will engage with the body member <NUM> inner cylindrical surface located below the ratchet teeth <NUM>, the illustrated aperture <NUM> being located in the vicinity of the ratchet teeth <NUM> that cooperate with the locking cap <NUM> and thus at a distance from the bushing <NUM>. In an alternative embodiment, the tabs could be removed from the bushing <NUM> and located on the body member <NUM> for engagement with apertures or other receiving structure or members formed in opposed sides of the bushing.

To provide a basic stability to the system during initial assembly, the bushing <NUM> with its slotted lower skirt portion can be configured to provide a press fitment about the screw head <NUM> so that the pedicle screw <NUM>, body member <NUM> and bushing <NUM> will not move freely prior to the insertion and securement of the fixation rod <NUM>. In other examples, movement may be limited due to partial press fitment. For example, the bushing <NUM> may provide a variable press fitment to provisionally lock the body member <NUM> and pedicle screw <NUM>. In addition, the upper portion of the bushing could be configured such that the wall surfaces <NUM> defining the rod seat therein extend upwardly past the midpoint of the rod and are slightly inwardly inclined. This would provide the same slight holding force when the rod <NUM> is pushed into the bushing seat <NUM> that was above described with reference to the channel walls <NUM> in the body member <NUM> of the assembly <NUM>.

Upon securing the bushing <NUM> in the body member <NUM> and the fixation rod <NUM> in bushing seat <NUM>, the locking cap <NUM>, as shown in <FIG>, is used to rigidly fix the assembly to the rod <NUM> to the screw assembly <NUM>. The locking cap <NUM> includes a screw or threaded portion <NUM> about its exterior surface from the top portion <NUM> of the locking cap <NUM> to the bottom portion <NUM> of the locking cap <NUM>, as shown in <FIG>. The locking cap <NUM> aligns within the side walls <NUM> of the body member <NUM> and the threaded portion <NUM> engages the threaded portion <NUM> of the interior side walls <NUM>, such that the locking cap <NUM> may move distally within the body member <NUM> and lock down on the bushing and apply a distal force on the bushing.

Alternatively, as shown in <FIG>, the cap <NUM> includes depending leg portions <NUM> thereon to aligned with the side walls <NUM> of body member <NUM>. Upon pressing the cap <NUM> downwardly into body member <NUM>, the ratchet teeth <NUM> and <NUM> on the body member <NUM> and cap <NUM> interlock so as to allow the cap to be pressed downwardly but not proximally retracted. As cap <NUM> is pressed downwardly into the body member <NUM> of the assembly, the planar bottom surface <NUM> of the central projection <NUM> thereon abuts the fixation rod and presses the rod into and against the seat <NUM> formed on the upper end of bushing <NUM>. The resulting pressure on the bushing causes the tapered surfaces <NUM> on the lower end of the bushing to press against the rounded surface of the screw head <NUM>, thereby securing the rod in seat <NUM> and providing decentralized and evenly distributed force acting along the longitudinal axis of the screw.

In use, at least two of the pedicle screws <NUM> with the body members <NUM> and attached bushings <NUM> disposed about the screw are inserted into the pedicles of adjacent vertebrae, spanning the vertebral region to be fixated. The surgeon preliminary contours the fixation rod and checks the alignment between the rod and the mating channels formed by the slots in the bushing and body member of the assemblies. Since additional contouring is usually required to improve the alignment, the surgeon incrementally adjusts the rod shape and checks the fit within the channels until the rod properly fits in all channels.

During the contouring process, the body member <NUM> may be rotated in only one plane relative to the insert, as shown in <FIG>. The body member <NUM> is rotated in only one plane when rotated by an operator to allow the concave pocket <NUM> to rotate about the extension <NUM> of the insert <NUM>, where the curved bottom portion <NUM> of the extension <NUM> slides along the two curved side walls <NUM> of the concave pocket <NUM> in the body member <NUM>, as shown in <FIG>. The exterior surface <NUM> of the insert <NUM> slides against the conical section <NUM> of the body member <NUM> while the body member <NUM> rotates about the insert <NUM>, as shown in <FIG>. The top portion 192a of the extension <NUM> engages or abuts the top portion <NUM> of the concave pocket <NUM>, which stops rotation of the body member <NUM> relative to the insert <NUM>.

The bushing <NUM> may be inserted during initial assembly of the screw <NUM> and the body member <NUM>. The bushing applies force to the top of the head portion <NUM> that sits above the insert <NUM> as well as contacts and applies force to the inserts themselves. The force from the bushing <NUM> is then transferred through the insert <NUM> to the screw <NUM> to lock motion in all directions. When the locking cap <NUM> is inserted, it applies force to the bushing <NUM> which then applies force to the screw <NUM> and the insert <NUM>. Then, the locking cap <NUM> can be mated with the body member <NUM> (by pressing the cap axially into the body member to create the interlock between the ratchet teeth on the body member and the cap) to temporarily hold the rod in place, thereby assisting the surgeon in achieving an accurate fit. The locking caps are then easily removable (by rotating the cap a quarter of a turn to disengage the interlocking teeth or disengage the threads), allowing the rod to be further contoured.

Once properly contoured, the rod is inserted into the channels and a locking cap is pressed tightly into each body member and bushing to secure the rod in place. To effect securement of the rod at each of the pedicle screw assemblies, it is solely necessary to drive the locking cap longitudinally into the body member such that the bottom surface <NUM> of the central projection <NUM> on the cap presses against the fixation rod, causing the rod to press downwardly against the bushing <NUM>, which in turn mates with and presses against the head of the pedicle screw.

In another embodiment, the bushing <NUM> is not employed. The opposed axial slots <NUM> in the side wall <NUM> of the body member <NUM> of the assembly define a seat for the fixation rod <NUM>. When the locking cap <NUM> is pressed into the body member <NUM> with the fixation rod extending there-across, the planar bottom surface <NUM> of the central projection <NUM> again abuts the fixation rod and, in this instance, presses the rod against the upper end of the head of the pedicle screw. For such applications, the body member and pedicle screw would be sized such that the upper surface of the screw would project above the bottom of the seat defined by the axially opposed slots <NUM> so as to enable the rod to press against the screw and create a rigid, yet adjustable, securement between the body member and the pedicle screw. In all of these embodiments, the components of the screw assembly are preferably formed of titanium, although any metal, polymer, or composite thereof may be employed.

Claim 1:
A pivotal screw assembly (<NUM>) for securing a fixation rod (<NUM>) to patient bone via a locking cap (<NUM>), the pivotal screw assembly comprising:
a screw (<NUM>) having a longitudinal axis (<NUM>), a proximal end with a head portion (<NUM>), and a distal end with a threaded shaft portion (<NUM>);
an insert (<NUM>) operably coupled with the head portion (<NUM>), the insert having a pair of extensions (<NUM>) projecting radially away from an exterior surface (<NUM>) of the insert (<NUM>); and
a body member (<NUM>) operably coupled with the insert (<NUM>), the body member comprising side walls (<NUM>) having two slots (<NUM>) at an upper end that define a transverse channel sized to receive the fixation rod (<NUM>), the sidewalls having upper interior surfaces with threaded portions (<NUM>) formed therein and an interior distal surface including a pair of pockets (<NUM>) configured to receive a respective extension (<NUM>) of the pair of extensions,
wherein the body member (<NUM>) and insert (<NUM>) are together independently rotatable relative to the screw (<NUM>) about the longitudinal axis (<NUM>) when the head portion (<NUM>) of the screw (<NUM>) and the insert (<NUM>) are disposed within the body member (<NUM>), with the pair of extensions (<NUM>) operably engaging the pair of pockets (<NUM>) so as to allow the body member (<NUM>) to pivot relative to the insert (<NUM>) and the screw (<NUM>) together only about a transverse axis (<NUM>) defined by a line extending between the pair of extensions, prior to the assembly being locked by the locking cap (<NUM>).