Abstract
Introduction
Axis (C2) pedicle/pars screw fixation has a definite risk of injury to the vertebral artery. An alternative trajectory 3 mm below the midpoint of the C2 facet surface, directed, downwards and medially into the C2 body, bypasses the vertebral artery altogether, and still offers adequate bone stock for rigid fixation of the C2 vertebra.
Material and Methods
Overall, 65 patients, 40 males and 25 females, aged 12 to 82 years, underwent posterior C1–C2 fixation from February 2007 to June 2014. Reducible atlantoaxial instability due to trauma (35), rheumatoid arthritis (20), and infection (tuberculosis) (10), magnetic resonance imaging (MRI), dynamic lateral X-rays of craniovertebral junction (CVJ), 3D CT scan of the craniovertebral region along with dynamic study and CT angiography. The entry point for the C2 screw was 2 to 3 mm below the midpoint of superior facet of the C2 which is also the midpoint C1–C2 joint and directed 10–to 15 degrees medially and downwards into the body of the axis. The same 3-mm drill bit was used incrementally till a depth of 5 mm and, 3.5 mm and 18 to 24mm length self-tapping screw with polyaxial head was used in most cases.
Results
No case of intraoperative vertebral artery injury. No patient required per operative blood transfusion. Follow-up visits were scheduled at 2, 6 to 8 weeks, and 3 months. Dynamic X-ray imaging was done in all patients at 6 to 8 weeks before discontinuing the collar and after 3 months since the operation. All patients followed up for 3 months. Telephonic follow-up of 30 patients was available for 24 months, 12 patients for 6 months, and remaining 7 patients have not reported and are not contactable after the 3 month visit. One postoperative mortality due to myocardial infarction on 7th day. Seven patients complained of occipital numbness and paresthesia which was not disturbing and responded to reassurance and supportive medication (pregabalin). Two patients had superficial wound infection which responded to appropriate antibiotics. There was no case of implant failure or loss of rigidity of fixation up to 3 months.
Conclusion
The new entry point offers rigid fixation and avoids the vertebral artery altogether nullifying the chance of arterial injury. Divergent screws (bridge vs. tension band construct) have a greater pull out strength. The new technique of C2 screw fixation allows rigid immobilization of the C1–C2 joint without any risk of vertebral artery injury.