Introduction: The use of C2 pedicle screws in atlantoaxial instrumentation is preferred by many surgeons given their relative technical ease and biomechanical stability compared to translaminar screws, pars screws, and wiring techniques [1,3]. In patients with small C2 pedicles, safe placement of these screws may be challenging or impossible. We present a new quadricortical parapedicular technique for C2 screw placement which allows for instrumentation of the axis in these situations.

Methods: Approximately 5 patients underwent quadricortical parapedicular instrumentation of the axis. The surgical technique is as follows. After the administration of general anesthesia, the patient is positioned prone with the head on a Mayfield horseshoe headrest. The posterior cervical spine is exposed. Both C2 nerve roots are suture ligated. Lateral mass screws are placed bilaterally at C1 and parapedicular screws are placed at C2 (Figures 1 and 2). Lateral masses at C1 and C2 are decorticated and the facet articulations are packed with bone morphogenic protein-soaked sponges and morsellized corticocancellous allograft bone.

Results: No intraoperative or postoperative complications have occurred with this technique. All patients have obtained radiographic fusion and experienced relief of their pre-operative symptoms.

Conclusions: We have demonstrated the feasibility of quadricortical parapedicular C2 screw placement in patients with insufficient C2 pedicles. Although our technique involves transgression of the spinal canal, 4 mm of medial perforation is tolerated in the thoracic spine [2] and expected to be safe at C2 where the canal is more capacious. Quadricortical parapedicular instrumentation of C2 is a viable and effective method for fixation of the axis.

Patient Care: The quadricortical parapedicular C2 screw is a novel technique for instrumenting small C2 pedicles that is safe, technically straight-forward, and biomechanically sound.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the quadricortical parapedicular C2 screw placement technique 2)Understand the relative advantages, disadvantages, and indications for this technique

References: 1. Melcher RP, Puttlitz CM, Kleinstueck FS, Lotz JC, Harms J, Bradford DS: Biomechanical testing of posterior atlantoaxial fixation techniques. Spine (Phila Pa 1976) 27:2435-2440, 2002 2. Polly DW, Jr., Potter BK, Kuklo T, Young S, Johnson C, Klemme WR: Volumetric spinal canal intrusion: a comparison between thoracic pedicle screws and thoracic hooks. Spine (Phila Pa 1976) 29:63-69, 2004 3. Su BW, Shimer AL, Chinthakunta S, et al. Comparison of fatigue strength of C2 pedicle screws, C2 pars screws, and a hybrid construct in C1-C2 fixation. Spine (Phila Pa 1976).39(1): E12-9, 2014