Patent Description:
In the field of spinal fixations there are a plethora of pedicle screw systems available. The screw systems are typically designed for polyaxial, monoaxial, or uniaxial movement lending themselves to certain spinal indications. For example, sagittal uniaxial screws are generally used in a coronal imbalance of the spine whereas a transverse uniaxial screw is used in a sagittal imbalance of the spine. In order to restore, immobilize and stabilize acute and chronic instabilities or deformities of the spine, a spinal surgeon must carry a large amount of stock of pedicle screw options in order to treat the various spinal pathologies. This adds inventory mass into the surgical field and increases the cost of sterilisation, shipping and inventory stock holdings.

The patent literature is replete with pedicle screw systems associated with spinal fixations. Some of these patents are directed to screw systems where an anchor is configured to cooperate with the head of a bone screw to limit movement of the anchor and an associated rod. <CIT> and <CIT> are examples of pedicle screw assemblies of this nature where the rod is locked within the anchor. These assemblies are relatively complicated in construction including an adaptor designed to lock movement of the anchor and the associated rod about the head of the bone screw. Other of prior patents are directed to polyaxial screw systems intended to provide universal movement to capture and anchor a rod. <CIT> discloses one example of a polyaxial screw assembly of this type including a collar which assists in locking of an associated swivel to the bone screw effectively reducing it to a monoaxial screw. <CIT> discloses an example of snap-on multi-planar and mono-planar receiver assemblies having integral and multi-part multipurpose positioners for pivoting and non-pivoting retainers.

In order to achieve a better understanding of the nature of the present invention of a modular pedicle screw assembly will now be described, by way of example only, with reference to the accompanying drawings in which:.

As best seen in <FIG>, there is a modular pedicle screw assembly <NUM> for immobilisation and stabilisation of spinal segments in a patient (not shown). The pedicle screw assembly <NUM> is in the form of a surgical implant configured for the treatment of acute and chronic instabilities or deformities of the spine of the patient. The treatment generally involves the step of: correction of the spinal deformity, spinal fusion using bone grafts to bridge gaps, and spinal fixation, this method/treatment do not form part of the claimed invention.

In the preferred embodiment the modular pedicle screw assembly <NUM> generally comprises a bone screw <NUM>, a uniaxial inner collet <NUM> arranged to cooperate with a head <NUM> of the bone screw <NUM>, a seat <NUM> arranged to provide seating for retention of the inner collet <NUM>, and an inner collet actuator <NUM> designed to engage the seat <NUM> to activate the inner collet <NUM> for clamping about the head <NUM> of the bone screw <NUM>. <FIG> illustrates the modular pedicle screw assembly <NUM> in its exploded view or disassembled condition whereas:.

It will be understood that the bone screw <NUM> having a threaded bone shaft <NUM> is designed for insertion in a vertebrae and more specifically the pedicle of a patient (not shown). The rod <NUM> is shown in part only with each of its ends truncated and in practice may be straight or shaped to substantially match the required spinal alignment with the rod <NUM> being anchored to one or more neighbouring modular pedicle screw assemblies (not shown). The modular pedicle screw assemblies such as <NUM> together with the associated rod such as <NUM> serve as a temporary fixation to hold the spine in its correct position until bone grafts or other instrumented segments fuse as a bone.

The modular pedicle screw assembly <NUM> is configured depending on the required spinal fixation treatment for the instability or deformity in the patient's spine. The modular pedicle screw assembly <NUM> of the preferred embodiment of <FIG> is configured to assist in treating a coronal imbalance in a side-to-side direction of the spine. For this purpose the uniaxial inner collet <NUM> includes a bearing surface <NUM> corresponding to a truncated flat surface <NUM> of the head <NUM> of the bone screw <NUM>. As schematically seen in <FIG>, the bearing surface <NUM> is arranged to permit tilting of the inner collet <NUM> in an inoperative position about a tilt axis <NUM> of the head <NUM> of the bone screw <NUM>. The uniaxial inner collet <NUM> is seated for retention within the seat <NUM> at a fixed angular disposition relative to the rod <NUM>. The modular pedicle screw assembly <NUM> of <FIG> has the tilt axis <NUM> oriented substantially perpendicular to the rod <NUM> which provides uniaxial tilting of the assembly <NUM> in a sagittal plane suitable for a coronal imbalance.

<FIG> illustrates the bone screw <NUM> of the modular pedicle screw assembly <NUM> of the preferred embodiment of <FIG>. Importantly the ball-shaped head <NUM> of the bone screw <NUM> includes the truncated flat surface being one of a pair of opposing truncated flat surfaces 28a and 28b. The pair of truncated flat surfaces 28a and 28b are configured in this embodiment to cooperate with a corresponding pair of bearing surfaces 26a and 26b formed internally of the uniaxial inner collet <NUM>. As seen in <FIG>, this arrangement permits tilting of the inner collet <NUM> in its inoperative position in the sagittal plane about the tilt axis <NUM> of the head <NUM> of the bone screw <NUM>. Otherwise the bone screw <NUM> of this embodiment is cannulated with a longitudinal bore <NUM> and fenestrated with one or more radial apertures such as 36a.

In this embodiment the bone screw <NUM> is provided in a plurality of predetermined lengths and diameters depending on the requirement. Importantly, each of the various sized bone screws <NUM> includes a common-sized and shaped head such as <NUM>. The common head <NUM> having the truncated flat surfaces 28a/b is thus designed to match with the uniaxial inner collet such as <NUM> of the modular pedicle screw assembly <NUM> of the preferred embodiment. The applicant intends to colour the:.

It should be understood that the smaller diameter bone screws may not be of a sufficient size to permit cannulation in which case the threaded bone shaft <NUM> is solid without the elongate bore <NUM> and radial apertures such as 36a/b. Otherwise the head <NUM> of the bone screw <NUM> includes a conventional hexagonal-shaped socket <NUM> for receipt of a tool (not shown) for insertion into the pedicle.

<FIG> shows the uniaxial inner collet <NUM> in more detail taken from the preferred embodiment of <FIG>. In this example the uniaxial inner collet <NUM> includes a plurality of claw elements such as 40a to 40f configured in the inoperative position of the inner collet <NUM> to permit tilting about the head <NUM> of the bone screw <NUM>. This tilting action is enabled by the opposing pair of flat bearing surfaces 26a and 26b formed internally of respective of the opposing pair of claw elements 40a and 40d. In the inoperative position of the inner collet <NUM>, with tilting of the uniaxial inner collet <NUM>, the bearing surfaces 20a/b of the inner collet <NUM> slide about the corresponding truncated surfaces 28a/b of the head <NUM> of the bone screw <NUM>. Clamping of the inner collet <NUM> to the head <NUM> of the bone screw <NUM> in the operative position locks the inner collet <NUM> to the head <NUM>.

<FIG> depicts an alternative uniaxial inner collet <NUM>' which is substantially identical to the inner collet <NUM> of the preceding embodiment except for location of the opposing bearing surfaces 26a' and 26b'. The surfaces 26a'/b' reconfigure the modular pedicle screw assembly <NUM> for uniaxial movement but with the tilt axis <NUM> of the head <NUM> of the bone screw <NUM> substantially aligned with the rod <NUM>, see <FIG>. For ease of reference and in order to avoid repetition, the same reference numerals have been used for corresponding components of the alternative uniaxial inner collets <NUM> and <NUM>'. It will be understood that the modular pedicle screw assembly <NUM> with the substitute uniaxial inner collet <NUM>' is suited to treatment of a sagittal imbalance such as a kyphosis or lordosis being a front-to-back spinal curvature. In this alternative uniaxial configuration, the screw assembly <NUM> is designed to tilt in a transverse plane being approximately orthogonal to the sagittal plane.

<FIG> illustrates a polyaxial inner collet <NUM> configured to substitute for either of the uniaxial inner collets <NUM> or <NUM>' in the modular pedicle screw assembly <NUM>. The polyaxial inner collet <NUM> is substantially identical to the uniaxial inner collets <NUM>/<NUM>' except it does not include the opposing bearing surfaces such as 26a/b but rather each of the plurality of claw elements 400a to 400f is of an identical shape. This means the polyaxial inner collet <NUM> includes a cavity <NUM> defining an internal surface <NUM> configured to permit polyaxial movement of the inner collet <NUM> in the inoperative position about the head <NUM> of the bone screw <NUM>. The polyaxial inner collet <NUM> is otherwise of the same construction as the uniaxial inner collets <NUM>/<NUM>' wherein the claw elements 400a to 400f of the inner collet <NUM> in the operative position clamp about the head <NUM> of the bone screw <NUM> for locking to the bone screw <NUM>.

<FIG> depicts a variation on the polyaxial inner collet <NUM> of <FIG>. In this variation, the polyaxial inner collet <NUM>' includes a pair of inserts 146a' and 146d' frangibly connected to respective of the opposing pair of claw elements 400a' and 400d' of the inner collet <NUM>'. Each of the inserts such as 146a' is in the form of a filler chamfer designed at a predetermined force to release from the respective claw element such 400a' to locate at the truncated flat surface 28a of the head <NUM> of the bone screw <NUM>. The polyaxial inner collet <NUM>' of this variation is thus mobilised in the inoperative position for polyaxial movement about the head <NUM> of the bone screw <NUM>. The polyaxial inner collet <NUM>' in the operative position clamps about the head <NUM> of the bone screw <NUM> with the pair of inserts or filler chamfers such as 146a' increasing the effective clamping surface of the head <NUM> exposed to the plurality of claws such as 400a' to 400f' of the inner collet <NUM>'. This means the polyaxial inner collet <NUM>' is less likely to pull out from the head <NUM> of the associated bone screw <NUM>.

<FIG> illustrates the seat or head <NUM> taken from the modular pedicle screw assembly <NUM> of the preferred embodiment of <FIG>. The seat <NUM> is designed in a general sense to provide seating for retention of the inner collet such as <NUM> which in the inoperative position tilts about the head <NUM> of the bone screw <NUM> in conjunction with the seat <NUM>. In this embodiment the seat <NUM> includes a recess <NUM> within which the inner collet such as <NUM> seats for activation via the inner collet actuator <NUM>. The inner collet <NUM> is thus moveable via the inner collet actuator <NUM> from:.

In this embodiment the seat <NUM> includes an aperture <NUM> formed continuous with the recess <NUM> and arranged for receipt of the head <NUM> of the bone screw <NUM>. The head <NUM> of the bone screw <NUM> is thus received into the inner collet <NUM> which is retained in the inoperative position for seating in the recess <NUM> of the seat <NUM>. The recess <NUM> of the seat <NUM> includes annular rebate <NUM> configured, with the inner collet <NUM> in the inoperative position, to permit the radial separation of the claw elements 40a to 40f into the annular rebate <NUM> on receipt of the head <NUM> of the bone screw <NUM> into the inner collet <NUM>. The seat <NUM> also includes an annular flange <NUM> defining the aperture <NUM> through which the head <NUM> of the bone screw <NUM> is received. The flange <NUM> is configured with the inner collet <NUM> in the operative position to urge the claw elements 40a to 40f of the inner collet <NUM> for clamping about the head <NUM> of the bone screw <NUM>.

<FIG> shows the inner collet actuator <NUM> taken from the preferred embodiment of the modular pedicle screw assembly <NUM> of <FIG>. The inner collet actuator <NUM> is integral with a locking element and together they are provided in the form of a unitary set screw <NUM>. The unitary set screw <NUM> threadably engages the seat <NUM> for both activation of the inner collet <NUM> and locking of the rod <NUM> to the seat <NUM>. The unitary set screw <NUM> includes a hexagonal-shaped socket <NUM> for receipt of a tool (not shown) for applying a torque load to the set screw <NUM>. In an alternative embodiment seen in <FIG>, the locking element functions independent of the inner collet actuator <NUM>'. The inner collet actuator <NUM>' is in the form of an external set screw <NUM> arranged to threadably engage the seat <NUM> for activation of the inner collet <NUM>. The locking element is in the form of an internal set or grub screw <NUM> arranged to threadably engage the external set screw <NUM>. The grub screw <NUM> thus operates independent of the external set screw <NUM> for locking of the rod <NUM> to the seat <NUM>.

Returning to <FIG>, it can be seen that the seat <NUM> includes a pair of legs 60a and 60b defining a pair of opposing and axially oriented channels 62a and 62b. The channels 62a/b are arranged to receipt of the rod <NUM> for locking to the seat <NUM> via the locking element <NUM>. A seen in <FIG>, the inner collet <NUM> includes a pair of radially extending arms 64a and 64b aligned with one another and arranged for seating within the pair of opposing channels 62a and 62b of the seat <NUM>. The rod <NUM> is thus oriented at a fixed angular disposition relative to the tilt axis <NUM> of the head <NUM> of the bone screw <NUM>. It will be appreciated that this angular disposition is determined by the angular position of the flat bearing surfaces 26a/b of the uniaxial inner collet <NUM> relative to the pair of radially extending arms 64a/b.

In the preferred embodiment having the uniaxial inner collet <NUM> of <FIG>, the arms 64a/b are oriented directionally parallel with the bearing surfaces 26a/b of the inner collet <NUM> wherein the rod <NUM> is disposed perpendicular with the tilt axis <NUM> of the head <NUM> of the bone screw <NUM> about which the inner collet <NUM> in the inoperative position is arranged to tilt. This configuration of the modular pedicle screw assembly <NUM> is suited to spinal fixation for treatment of a coronal imbalance where the screw assembly <NUM> tilts in the sagittal plane. Alternatively, the uniaxial inner collet <NUM>' of <FIG> may be fitted to the modular pedicle screw assembly <NUM>. In this case the radial arms 64a'/b' of the uniaxial inner collet <NUM>' are directionally perpendicular with the bearing surface 26a'b' of the inner collet <NUM>' wherein the rod <NUM> is disposed substantially parallel with the tilt axis <NUM> of the head <NUM> of the bone screw <NUM>. In this configuration the modular pedicle screw assembly <NUM> is suited to spinal fixation for treating a sagittal imbalance such as a kyphotic deformity and the screw assembly <NUM> tilts in the transverse plane.

As best seen in the uniaxial inner collets <NUM> and <NUM>' of <FIG> and <FIG> as well as the polyaxial inner collets <NUM> and <NUM>' of <FIG> and <FIG>, the inner collet such as <NUM> includes a pair of legs 70a and 70b disposed either side of the pair of radially extending arms 60a and 60b. The legs 70a/b define a pair of opposing and axially oriented channels 72a/b arranged for receipt of the rod <NUM>. As best seen in <FIG>, the pair of channels 72a/b of the inner collet <NUM> substantially align with the channels 62a/b of the seat <NUM>. Each of the legs such as 70b of the inner collet <NUM> include a protrusion such as 74b for releasable retention within a corresponding opening such as 76b in the corresponding leg 60b of the seat <NUM>. The protrusion 74b is in the form of a nipple designed to retain the inner collet <NUM> within the seat <NUM> in both the inoperative and operative positions.

<FIG> best illustrate the sequence of events for assembly of the modular pedicle screw <NUM> (these methods do not form part of the claimed invention). It will be understood that, although not illustrated, the bone screw <NUM> is typically inserted into the pedicle (not shown) identified for instrumentation prior to assembly of the modular pedicle screw <NUM>. This step is repeated for other pedicles that have been identified for similar instrumentation. The assembly of the remainder of the modular pedicle screw assembly <NUM> involves the following steps:.

The inner collet actuator <NUM> or unitary set screw <NUM> of this embodiment threadably engages the legs such as 60a of the seat <NUM> for contact with the inner collet <NUM> to effect its movement in a sliding action from the inoperative position to the operative position. In the operative position the annular flange <NUM> of the seat <NUM> contacts the claw elements such as 40a to 40f of the inner collet <NUM> for clamping about the head <NUM> of the bone screw <NUM> with increasing pressure. When the inner collet <NUM> is clamped about the head <NUM> of the bone screw <NUM> with sufficient locking pressure, the radially extending arms such as 64a of the inner collet <NUM> are arranged to rest at a base of the respective channels such as 62a of the seat <NUM> within which they are seated. In this example the openings such as 76a of the legs 60a of the seat <NUM> are formed as longitudinal slots so that the protrusion such as 74a of the inner collet <NUM> is retained for sliding movement within the corresponding slots such as 76a during movement of the inner collet <NUM> between the inoperative and operative positions.

In further embodiments of the invention there is provided a uniaxial pedicle screw sub-assembly or assembly. In these embodiments the sub-assembly or assembly need not be of a modular construction. In both embodiments the sub-assembly or assembly is limited to a uniaxial inner collet with uniaxial tilting of the inner collet and the associated seat about a tilt axis of the head of the associated bone screw. The sub-assembly or assembly may take the form of the embodiment of <FIG> but with the inner collet and seat permanently mounted to the head of the bone screw. It will be understood that the uniaxial pedicle screw sub-assembly or assembly may also tilt in an orthogonal plane to that of this embodiment. These other exemples of the nonmodular screw sub-assembly or assembly are inserted into the vertebrae or pedicle with the inner collet and seat in-situ.

Claim 1:
A uniaxial pedicle screw sub-assembly comprising:
a bone screw (<NUM>) having a threaded bone shaft (<NUM>) adapted for insertion in a vertebra;
a uniaxial inner collet (<NUM>) configured in an operative position to clamp about a head (<NUM>) of the bone screw (<NUM>), said head (<NUM>) being substantially ball-shaped with a truncated surface arranged to cooperate with a bearing surface (<NUM>) of the uniaxial inner collet (<NUM>) in an inoperative position to permit tilting of the uniaxial inner collet (<NUM>) about a tilt axis (<NUM>) of the head (<NUM>) of the bone screw (<NUM>);
a seat (<NUM>) arranged to provide seating for retention of the uniaxial inner collet (<NUM>), the seat (<NUM>) designed to tilt in conjunction with the uniaxial inner collet (<NUM>) in the inoperative position about the tilt axis (<NUM>) of the head (<NUM>) of said bone screw (<NUM>);
an inner collet actuator (<NUM>) designed to engage the seat (<NUM>) to activate the uniaxial inner collet (<NUM>) for movement into the operative position for clamping about the head (<NUM>) of the bone screw (<NUM>) to lock the uniaxial inner collet (<NUM>) and the seat (<NUM>) to the head (<NUM>) of said bone screw (<NUM>);
the seat (<NUM>) including a recess (<NUM>) within which the uniaxial inner collet (<NUM>) seats for retention in either the inoperative or operative positions, the uniaxial inner collet (<NUM>) being movable via the inner collet actuator (<NUM>) from i) the inoperative position where the head (<NUM>) of the bone screw (<NUM>) is received within the uniaxial inner collet (<NUM>) with radial separation of the uniaxial inner collet (<NUM>) into the recess (<NUM>) of the seat (<NUM>), to ii) the operative position where the head (<NUM>) of the bone screw (<NUM>) is clamped within the uniaxial inner collet (<NUM>).