Posterior Fixation for Odontoid Fractures

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

2. Indications • Oblique Type II fractures • 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

3. Grossly displaced fracture

4. Old Fracture

5. C1 – C2 screw-rod fixation - Goel/Harms technique C1-C2 tansarticular fixation – Magerl’s technique Others Gallie’s, Brook’s, Halifax clamp

7. C2 from above Pars screw Pedicle ?

8. Lateral view of C2 C2 pedicle screw C12 TAS

9. Vertebral artery

10. C1 – C2 fixation Goel/Harms technique • C1 lateral mass • C2 pedicular screw • C2 could be modified and either C2 pars or translaminar screw can be used

11. C1 lateral mass screw The entry point for the C1 screw is above the C2 nerve root, at the junction of the posterior arch of C1 and the centre of the lateral mass of C1, and at the highest point of the C1 mass. The drilling angle is dictated by the arch of C1, and so cannot be angled any more superiorly. A dissector should be used to move the C2 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 C1 screw incorporates a 10 mm unthreaded portion which stays above the bony surface of the lateral mass, minimising the potential for damage to the C2 nerve root and allowing the polyaxial position of the screw to lie above the posterior arch of C1.

12. C2 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.

13. C2 Pedicle Screw

14. Contraindications: • i) high riding vertebral artery • ii) small hypoplastic pedicles (<3.5mm), developmentally or due to a disease process.

15. C2 Pars Screw • It is defined as the portion of the C2 vertebra between the superior and inferior articular surfaces. • Placed in a trajectory similar to that of a C1-C2 transarticular screw so essentially this is a short trans articular screw. • The entry point for the C2 pars screws is 3-4mm cranial to the C2-C3 facet joint and in the midpoint of the pars medio laterally. • Follows a steep trajectory paralleling the C2 pars (Often 40 degrees or more)

16. The trajectory is achieved through an incision extending down to C4 without using a percutaneous stab incision at T1. • Screws are passed with 10 degrees of medial angulation. • Screw length is typically 12-18mm (avg.16 mm) which just stops short of the transverse foramen

17. Advantages of C1-C2 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 C1-C2 reduction • Integrity of posterior arch of C1 is not required • Can be incorporated as part of O-C1-C2 or subaxial spine fusions

18. Translaminar Screws • Translaminar screws serve as a salvage technique for C2 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.

19. C1 Lat mass – C2Trans laminar screws

20. Advantages • Faint chance of vertebral artery injury • Stability similar to that of pedicle screws • Due to large diameter of C2 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 C1 lateral mass screw via interposed rods. • Post operative laminar fractures noted in few cases

21. C1-C2 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 C2-C3 facet joint • Direction is 15 degrees medial with the superior angle visualized by fluoroscopy aiming at the C1 anterior tubercle. The angle can be 40-60% and may reuire a separate small incision at about T1 level to get the right trajectory.

22. Disadvantages of C1-2 transarticular fixation • Need for reduction remains • Needs additional midline fusion • Risk of vertebral artery injury is higher

23. Case 1:

24. Post traction X-ray showing well aligned fracture

26. 3rd day post-operative scan showing loss of reduction with screw cut-through from C2 body.

27. Reason for screw cut through Reassessment of post traction X-ray reveals to us that due to additional chip #, there was inadequate C2 body bone available for screw to have adequate purchase

28. Screw failure salvaged with posterior fixation (Magerls Tech. + C1-C2 wiring) (D) Follow up CT scan at 3 month showing well fused fracture.

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

30. Anterior odontoid screw fixation Anterior odontoid screw fixation was performed

31. Implant failure due to screw cut through

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

33. Post traumatic reducible AAD in a 8 yr old

34. POST OP X-RAY (AP/LATERAL)

35. Post op imaging Post op CT Post op MRI

36. Vertebral Artery Injury due to C2 pedicle screw in C1-C2 fixation

37. 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

38. Conclusion • When indicated C1-C2 fixation is a safe technique • Its surgeon’s preference whether to use a polyaxial screw -rod construct or C1-C2 transarticular though I personally find screw-rod construct easier and also that its not necessary to do midline C1-C2 fixation • Depending upon the anatomy of the patient various choices are available for C2 screw