BACKGROUND Despite the biomechanical benefits of subaxial cervical pedicle screw (CPS) placement, possible neurovascular complications, including vertebral artery and nerve root injury, are of great concern. We have demonstrated many times the safety and efficacy of CPS deployments, even when using freehand technology. OBJECTIVE To analyze the learning curve of CPS placement to determine the number of cases necessary for assuring safe CPS placement and to identify a reasonable accuracy rate. METHODS From March 2012 to August 2018, a single surgeon performed posterior cervical fusion surgery using CPS placement on 162 consecutive patients. We classified whole surgical periods, 6 years, into 4 periods. We analyzed the screw breach rate, lateral mass screw conversion (LMSC) rate, and reposition rate. We also compared the CPS placement accuracy in the initial 15, 20, and 30 patients with the other 147, 142, and 132 patients, respectively, to assess the number of procedures necessary to reach the learning curve plateau and to identify a reasonable accuracy rate. RESULT The total number of planned CPS placements was 979. Our learning curve showed that the breach rate plateaus at 3% to 4%. The necessary numbers for safe and accurate CPS placement during learning curve were 30 patients and 170 screws. None of the patients undergoing CPS developed a neurologic or vascular complication. CONCLUSION By following our 5 safety steps, the steady state for safety and accuracy can be reached without neurovascular complications even in the initial period of the learning curve.

This paper describes two patients with cervical spondyloptosis with severe spinal cord injury treated with cervical pedicle screw (CPS) through a single-stage operation, posterior approach. A 60-year-old male patient with quadriparesis due to trauma 1 day before visited the emergency room. Cervical spine computed tomography (CT) and magnetic resonance imaging showed complete dislocation of the C7 and T1 vertebrae with severe spinal cord compression, disc injury, and disc herniation at the C7–T1 level. Cervical pedicle screw with freehand technique was done on C6 and T1 vertebrae, and bilateral distraction for a reduction was performed with a screw distractor. After reduction of the C7 vertebra on the surgical field, CPS placement on C7 body was done. After surgery, follow-up X-rays showed near complete reduction. The patient completed a rehabilitation program, and his condition improved. From the third month postoperatively, the patient could ambulate without assistance and perform nearly normal daily activities. A postoperative CT scan 1 year later showed accurate screw position and complete fusion bridges on the C6–C7–T1 vertebrae. The other patient, a 39-year-old male, also showed C7–T1 spondyloptosis with quadriparesis (grade IV). C6–T1–T2 fusion surgery was performed only through a posterior approach. The patient showed nearly normal neurology and reduction. Considering early surgery time followed by open reduction and biomechanical superiority of CPS, single posterior approach and short segment fusion appear to be a great surgical method.