DESC:FIELD
The present disclosure relates to apparatus for correcting spinal instability.

DEFINITIONS
The term ‘C1-C2’ used herein is meant to be understood in the general sense of the term and for the purpose of the present disclosure means the joint between the first (C1) and the second (C2) cervical vertebra, also called the atlas and the axis respectively. The term ‘atlantoaxial’ may also be interchangeably used with the term ‘C1-C2’.

BACKGROUND
The atlantoaxial segment acts as a bridge between the occiput and cervical spine. The joint has two-fold functionality (i) providing support and (ii) providing a maximum practicable range of motion and flexibility for the occiput, whilst maintaining stability. The instability in this joint is usually congenital, however, acute traumatic event or degenerative disease may also cause instability in adults.

The existing C1-C2 fixation procedure is performed posteriorly. Meaning, the patient lies face down on the operation table and the surgeon approaches the C1-C2 joint from the patient’s back. Such a procedure is technically very demanding, poses a risk of injury to the spinal cord and the vertebral artery and is known to pose a complication rate of around 10%. Furthermore, fixation of screws to correct the instability is not possible in 22% of the population due to certain anatomic features, when the procedure is carried out posteriorly.

Anterior correction reduces the morbidity related to prone general anesthesia. Further, by the very nature and direction of instability, the anterior approach for correction reduces subluxation, as the added pressure on the spine due to flexion of the neck (observed in the posterior approach) is reduced. Some of the currently prevalent procedures to effect anterior correction, however, entail a mere implantation of screws anteriorly. Consequently, the procedures are associated with numerous technical problems such as inadequate hold on the second cervical vertebra (C2) because of the anterior topography and trajectory of the screws. Further, the difficulty of overlying mandible exists, if the potential infection of an intraoral approach is to be avoided.

The apparatus of the present disclosure facilitates carrying out the C1-C2 instability correction procedure anteriorly, whilst mitigating a majority of the problems associated with the currently prevalent procedures.

OBJECTS
It is an object of the present disclosure to provide an apparatus for effecting C1-C2 stabilization.
It is another object of the present disclosure to provide an apparatus for effecting C1-C2 stabilization by the anterior approach.
It is another object of the present disclosure to provide an apparatus for effecting C1-C2 stabilization which is safer than the conventional.
It is another object of the present disclosure to provide an apparatus for effecting C1-C2 stabilization along with means to increase the stability of the corrected spine.
It is another object of the present disclosure to provide an apparatus for effecting C1-C2 stabilization which is economical.

SUMMARY
The present disclosure provides an apparatus (100) for anterior cervical inter-body fusion based trans-articular C1-C2 stabilization, said apparatus (100) comprising at least one trans-articular fixation element (10) adapted to traverse through the vertebral body of the second cervical vertebra (C2) anteriorly and be affixed to the C1-C2 facet joint, correcting the C1-C2 instability; and at least one inter-body fusion element (20) adapted to be surgically implanted, in the inter-vertebral body disc space between the second (C2) and the third (C3) cervical vertebra to cause fusion thereof; wherein an end of said trans-articular fixation element (10) not affixed to the C1-C2 facet joint, is selectively rotatably engaged in said inter-body fusion element (20); thereby providing support to the corrected C1-C2 facet joint, leading to anterior cervical inter-body fusion based trans-articular C1-C2 stabilization. Typically, said selectively rotatable engagement of the trans-articular fixation element (10), provides a guideline for determining the trajectory of said trans-articular fixation element (10) for affixation to the C1-C2 facet joint anteriorly, while ensuring that said trans-articular fixation element (10) passes through the second cervical vertebra (C2) with enough bony mass there-around, to effect better fixation.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
The present disclosure is illustrated in the accompanying non-limiting drawings, throughout which like reference letters indicate corresponding parts in the various figures.
Figure 1 illustrates a perspective view of one embodiment of the apparatus (100) of the present disclosure and the apparatus (100) after implantation.
Figure 2 illustrates a perspective view of another embodiment of the apparatus (100) of the present disclosure and the apparatus (100) after implantation.
Figure 3 illustrates a perspective view of yet another embodiment of the apparatus (100) of the present disclosure and the apparatus (100) after implantation.
Figure 4 illustrates a perspective view of still another embodiment of the apparatus (100) of the present disclosure and the apparatus (100) after implantation.
Figure 5 illustrates a perspective view of a further embodiment of the apparatus (100) of the present disclosure and the apparatus (100) after implantation.

DESCRIPTION
The present disclosure relates to an apparatus (100) for anterior cervical inter-body fusion based trans-articular C1-C2 stabilization. When the C1-C2 joint is unstable, there develops an exaggerated sliding motion between the two vertebrae during flexion and extension, which causes stenosis in the spinal canal and thus stress on the spinal cord. Typically, the patient is positioned in such a way that the C1-C2 vertebrae attain a neutral position, followed by fixation of the stabilized joint. The apparatus of the present disclosure (100) is used in this procedure to facilitate fixation at the C1-C2 joint.

The apparatus (100) comprises at least one trans-articular fixation element (10) and at least one inter-body fusion element (20). Figures 1 – 3 illustrate three different embodiments of the apparatus (100) of the present disclosure.

The trans-articular fixation element (10) of the present disclosure comprises two ends. One end is adapted to traverse through the vertebral body of the second cervical vertebra (C2) via the superior endplate and be affixed to the C1-C2 facet joint anteriorly. This affixation, besides other surgical maneuvers, results in correction of the C1-C2 instability. The other end of the trans-articular fixation element (10) is selectively rotatably engaged in the inter-body fusion element (20). The trans-articular fixation element (10) is at least one selected from the group consisting of screws, spikes, wires, nails, hooks or any other fixation element suitable for the present application. In one embodiment, the present apparatus has two trans-articular fixation elements (10). In another embodiment, the trans-articular fixation element (10) is a long shank screw.

The inter-body fusion element (20) of the present disclosure is adapted to be surgically implanted anteriorly in the inter-vertebral body disc space between the second (C2) and the third (C3) cervical vertebra to cause fusion of the two vertebrae. In one embodiment, the inter-body fusion element (20) of the present disclosure is an inter-vertebral body spacer. The inter-body fusion element (20) further optionally comprises at least one bone graft cavity (22) to pack bone graft for facilitating fusion of the second (C2) and third (C3) cervical vertebrae (illustrated in Figure 1).

Since one end of the trans-articular fixation element (10) is engaged in the inter-body fusion element (20), the corrected C1-C2 facet joint is given additional support of the fused vertebrae. The resulting C1-C2 stabilization is, therefore, known as anterior cervical inter-body fusion based trans-articular C1-C2 stabilization. It is a further characteristic of the apparatus (100) of the present disclosure, that the trans-articular fixation element (10) is selectively rotatably engaged in the inter-body fusion element (20). The selective rotatable engagement provides a guideline for determining the trajectory of the trans-articular fixation element (10) for affixation to the C1-C2 facet joint anteriorly, along with ensuring that the trans-articular fixation element (10) passes through the second cervical vertebra (C2) with enough bony mass there-around, to effect better fixation.

The inter-body fusion element (20) additionally optionally comprises at least one reinforcing element (24) adapted to interact with the body of at least one vertebra selected from the group consisting of the second cervical vertebra (C2) and the third cervical vertebra (C3). The reinforcing element (24) once in place, imparts additional stability to the C1-C2 facet joint, already stabilized by the apparatus (100) of the present disclosure (illustrated in Figures 2 and 3).

The reinforcing element (24) is at least one selected from the group consisting of screws (24a), plates (24b), locking caps, spikes, wires, nails, mesh or any other reinforcing element suitable for the present application. In one embodiment, as illustrated in Figure 2, a screw (24a) functions as the reinforcing element (24). The screw (24a), originating from the inter-body fusion element (20), traverses through the body of the third (C3) cervical vertebra to reinforce the C1-C2 joint stabilized by the apparatus (100) of the present disclosure.

In another embodiment, as illustrated in Figure 3, two screws (24a) and a plate (24b) function as the reinforcing element. The plate (24b), originating from the inter-body fusion element (20) is implanted along the curved anterior side of the vertebral body of the second (C2) and third (C3) cervical vertebra and the two screws (24a) are inserted into the holes of the plate and made to traverse through the vertebral body of the second (C2) and third (C3) cervical vertebra, respectively.

Figure 4 illustrates yet another embodiment of the apparatus (100) of the present disclosure wherein there are four trans-articular fixation elements (10) that can be inserted across the joint into C1 and C2. The screws are supported by built-in arms that originate from the inter-body fusion element (20), the latter being implanted in between the second (C2) and the third (C3) cervical vertebra. As illustrated in Figure 4, a screw (24a) functions as the reinforcing element (24).

Figure 5 illustrates still another embodiment of the apparatus (100) of the present disclosure wherein there are two trans-articular fixation elements (10), in the form of bent spikes that can be inserted across the joint into C1 and C2. The spikes follow the trajectory of the screws as described in earlier embodiments and are adapted to fix the C1-C2 facet joint. As illustrated in Figure 5, two screws (24a) and a plate (24b) functions as the reinforcing element. The plate (24b), originating from the inter-body fusion element (20), is implanted along the anterior side of the vertebral body of the second (C2) and third (C3) cervical vertebra and the two screws (24a) (not illustrated in the Figure) traverse through the vertebral body of the second (C2) and third (C3) cervical vertebra, respectively.

Conventional anterior trans-articular fixation of C1-C2 has been traditionally associated with technical issues such as inadequate hold on the second cervical vertebra (C2) because of the anterior topography and trajectory of the screws which the present embodiment improves. Further, the difficulty of overlying mandible exists, if the potential infection of an intraoral approach is to be avoided. The point of start and direction of the fixation element (10) - the screw(s), is lower in the present apparatus (100), in addition to the anterior direct plating design which circumvents the difficulties associated with the approach. The present apparatus (100) fixes the C1-C2 facet joint and additionally stabilizes the spine by providing fusion of C2 and C3 vertebrae through the inter-body fusion element (20). Also the presence of a reinforcing element (24) gives additional stabilization to the system. Designing the inter-body fusion element (20) with a right trajectory for the trans-articular fixation elements (10) in the cervical spine anatomical conditions and keeping sufficient strength to the inter-body spacer have been the main challenges in designing the apparatus (100) of the present disclosure. In the anterior approach for C1-C2 stabilization, the trajectory of the fixation element is up to the discretion of the surgeon. In the present apparatus, the seat of the screws i.e. the selective rotatable engagement of the trans-articular fixation element (10) in the inter-body fusion element (20) allows movement of the screws only in a limited direction thereby providing a guideline to the surgeon to fix it in the right trajectory. Furthermore, the screw trajectory is such that it passes through the second cervical vertebrae (C2) with enough bony mass around it, so that the fixation achieved is better than the screw systems available in the prior art. Also a significant advantage associated with the use of the present apparatus (100) is that, the incision required to perform the surgery is smaller.

The embodiments described herein above are non-limiting. The foregoing descriptive matter is to be interpreted merely as an illustration of the concept of the present disclosure and it is in no way to be construed as a limitation. Description of terminologies, concepts and processes known to persons acquainted with technology has been avoided for the sake of brevity.

TECHNICAL ADVANTAGES AND ECONOMIC SIGNIFICANCE
The technical advantages and economic significance of the apparatus (100) of the present disclosure are presented herein after:
• Apparatus for C1-C2 stabilization is provided which enhances the stability of the spine.
• The potential for infections associated with the intraoral approach are avoided.
• The selective rotatable engagement provides a guideline for determining the trajectory of the trans-articular fixation element (10) for affixation to the C1-C2 facet joint anteriorly, along with ensuring that the trans-articular fixation element (10) passes through the second cervical vertebra (C2) with enough bony mass there-around, to effect better fixation.
• The point of start and direction of the fixation element (10) - the screw(s), is lower in the present apparatus (100), in addition to the anterior direct plating design which circumvents the difficulties associated with the conventional anterior approach.
• The incision required to perform the surgery using the present apparatus (100) is smaller.
,CLAIMS:We Claim
1. Apparatus (100) for anterior cervical inter-body fusion based trans-articular C1-C2 stabilization, said apparatus (100) comprising:
a. at least one trans-articular fixation element (10) adapted to traverse through the vertebral body of the second cervical vertebra (C2) anteriorly and be affixed to the C1-C2 facet joint, correcting the C1-C2 instability; and
b. at least one inter-body fusion element (20) adapted to be surgically implanted, in the inter-vertebral body disc space between the second (C2) and the third (C3) cervical vertebra to cause fusion thereof;
wherein an end of said trans-articular fixation element (10) not affixed to the C1-C2 facet joint, is selectively rotatably engaged in said inter-body fusion element (20); thereby providing support to the corrected C1-C2 facet joint, leading to anterior cervical inter-body fusion based trans-articular C1-C2 stabilization.
2. The apparatus (100) as claimed in claim 1, wherein said trans-articular fixation element (10) is at least one selected from the group consisting of screws, spikes, wires, nails, hooks or any other suitable fixation element.
3. The apparatus (100) as claimed in claim 1, wherein said trans-articular fixation element (10) is adapted to traverse through the vertebral body of the second cervical vertebra (C2) via the superior endplate thereof.
4. The apparatus (100) as claimed in claim 1, wherein said inter-body fusion element (20) is an inter-vertebral body spacer.
5. The apparatus (100) as claimed in claim 1, wherein said inter-body fusion element (20) further comprises at least one bone graft cavity (22) to pack bone graft for facilitating fusion of the second (C2) and third (C3) cervical vertebrae.
6. The apparatus (100) as claimed in claim 1, wherein said inter-body fusion element (20) further comprises at least one reinforcing element (24) adapted to interact with the body of at least one vertebra selected from the group consisting of the second cervical vertebra (C2) and the third cervical vertebra (C3) to impart reinforcement to the anterior cervical inter-body fusion based trans-articular C1-C2 stabilization; said reinforcing element (24) being at least one selected from the group consisting of screws (24a), plates (24b), locking caps, spikes, wires, nails, mesh or any other suitable reinforcing element.
7. The apparatus (100) as claimed in claim 6, wherein said plate (24b) is adapted to be implanted anteriorly along the body of the second (C2) and third (C3) cervical vertebra.
8. The apparatus (100) as claimed in claim 6, wherein said screw (24a) is adapted to traverse, anteriorly, through the body of at least one vertebra selected from the group consisting of the second (C2) and third (C3) cervical vertebra.
9. The apparatus (100) as claimed in claim 1, wherein said selectively rotatable engagement of the trans-articular fixation element (10), provides a guideline for determining the trajectory of said trans-articular fixation element (10) for affixation to the C1-C2 facet joint anteriorly, while ensuring that said trans-articular fixation element (10) passes through the second cervical vertebra (C2) with enough bony mass there-around, to effect better fixation.