Istanbul Spine Masters 2017 Posterior Fixation for Odontoid

Istanbul Spine Masters 2017 Posterior Fixation for Odontoid Fractures Sandeep Vaishya Exec. Director Neurosurgery Fortis Memorial Research Institute Delhi and Gurgaon

$Indications Oblique Type II fractures with significant displacement Type II fractures asso. with Jefferson$

Indications Oblique Type II fractures with significant displacement Type II fractures asso. with Jefferson fracture or fracture of atlanto axial joint Fractures associated with ruptured transverse ligament Unstable Type III fractures Old Type II fractures where ant screw may not be a good option Anatomical difficulty in placing the screws – severe thoracic kyphosis or significant barrel chest

$Grossly displaced fracture$

Grossly displaced fracture

Old Fracture

C 1 – C 2 screw-rod fixation - Goel/Harms technique C 1 -C 2 tansarticular fixation – Magerl’s technique Others Gallie’s, Brook’s, Halifax clamp

C 2 from above Pars screw Pedicle ?

Lateral view of C 2 pedicle screw C 12 TAS

Vertebral artery

C 1 – C 2 fixation Goel/Harms technique C 1 lateral mass C 2 pedicular screw C 2 could be modified and either C 2 pars or translaminar screw can be used

C 1 lateral mass screw The entry point for the C 1 screw is above the C 2 nerve root, at the junction of the posterior arch of C 1 and the centre of the lateral mass of C 1, and at the highest point of the C 1 mass. The drilling angle is dictated by the arch of C 1, and so cannot be angled any more superiorly. A dissector should be used to move the C 2 nerve root away from the intended entry point. Using a high speed burr with 1 or 2 mm diamond paste drill tip, perforate to allow access for drilling. Drill the pilot hole using the 2. 4 mm diameter drill and guide. Bi-cortical fixation provides secure screw placement. • NOTE: The C 1 screw incorporates a 10 mm unthreaded portion which stays above the bony surface of the lateral mass, minimising the potential for damage to the C 2 nerve root and allowing the polyaxial position of the screw to lie above the posterior arch of C 1.

C 2 Pedicle Screw The medio-superior border of the dorsal pedicle and the ventral direction of the pedicle are identified using a microdissector. Entry point for pedicle screws is slightly higher and lateral to the entry point of pars interarticularis. 1 to 2 mm below the inferior facet of the cephalad vertebra and is directed about 15 -25 degrees medially and slightly upwards.

C 2 Pedicle Screw

Contraindications: i) high riding vertebral artery ii) small hypoplastic pedicles (<3. 5 mm), developmentally or due to a disease process.

C 2 Pars Screw It is defined as the portion of the C 2 vertebra between the superior and inferior articular surfaces. Placed in a trajectory similar to that of a C 1 -C 2 transarticular screw so essentially this is a short trans articular screw. The entry point for the C 2 pars screws is 3 -4 mm cranial to the C 2 -C 3 facet joint and in the midpoint of the pars medio laterally. Follows a steep trajectory paralleling the C 2 pars (Often 40 degrees or more)

The trajectory is achieved through an incision extending down to C 4 without using a percutaneous stab incision at T 1. Screws are passed with 10 degrees of medial angulation. Screw length is typically 12 -18 mm (avg. 16 mm) which just stops short of the transverse foramen

Advantages of C 1 -C 2 lat mass/pedicle screw fixation Smaller risk of vertebral artery injury as compared to transarticular screws Does not require sublaminar wires Screws can help in C 1 -C 2 reduction Integrity of posterior arch of C 1 is not required Can be incorporated as part of O-C 1 -C 2 or subaxial spine fusions

Translaminar Screws Translaminar screws serve as a salvage technique for C 2 pars screws or pedicle screws in cases of the anomalous high-riding vertebral artery or very thin pedicle. The entry point is at the junction of the spinous process and lamina Offset the entry points craniocaudal to keep the two screw paths from intersecting.

C 1 Lat mass – C 2 Trans laminar screws

Advantages Faint chance of vertebral artery injury Stability similar to that of pedicle screws Due to large diameter of C 2 lamina, can be used where other screw constructs are contraindicated. No fluoroscopy needed Disadvantages: Biomechanically inferior to the pedicle screw Difficulty in connection with the C 1 lateral mass screw via interposed rods. Post operative laminar fractures noted in few cases

C 1 -C 2 transarticular screws • The screw entry point is approximately 3 to 4 mm rostral and 3 to 4 mm lateral to the inferior medial portion of the C 2 -C 3 facet joint Direction is 15 degrees medial with the superior angle visualized by fluoroscopy aiming at the C 1 anterior tubercle. The angle can be 40 -60% and may reuire a separate small incision at about T 1 level to get the right trajectory.

Disadvantages of C 1 -2 transarticular fixation Need for reduction remains Needs additional midline fusion Risk of vertebral artery injury is higher

Case 1:

$Post traction X-ray showing well aligned fracture$

Post traction X-ray showing well aligned fracture

3 rd day post-operative scan showing loss of reduction with screw cut-through from C 2 body.

Reason for screw cut through Reassessment of post traction X-ray reveals to us that due to additional chip #, there was inadequate C 2 body bone available for screw to have adequate purchase

Screw failure salvaged with posterior fixation (Magerls Tech. + C 1 C 2 wiring) (D) Follow up CT scan at 3 month showing well fused fracture.

Case 3 • 25 yr male patient • RTA – bike accident

Anterior odontoid screw fixation was performed

Implant failure due to screw cut through

Redo surgery- removal of odontoid screw and placement posterior transarticular screw

Post traumatic reducible AAD in a 8 yr old

POST OP X-RAY (AP/LATERAL)

Post op imaging Post op CT Post op MRI

Vertebral Artery Injury due to C 2 pedicle screw in C 1 -C 2 fixation

Lesson Learnt Firstly the surgeon should have recognized the vertebral artery injury on the first side. If there was injury on one side then second side should not have been done at all

Conclusion When indicated C 1 -C 2 fixation is a safe technique Its surgeon’s preference whether to use a polyaxial screw -rod construct or C 1 -C 2 transarticular though I personally find screw-rod construct easier and also that its not necessary to do midline C 1 -C 2 fixation Depending upon the anatomy of the patient various choices are available for C 2 screw