Factors causing deviation of robot-assisted pedicle screw placement for adolescent idiopathic scoliosis: why does deviation still occur even with robotics?

PURPOSE: To clarify the factors that are likely to cause deviation in robot-assisted pedicle screw placement in surgery for adolescent idiopathic scoliosis (AIS).

METHODS

Thirty-two consecutive patients with AIS who underwent posterior spinal fusion using a spine robotics system were included. Robot-assisted pedicle screw placements were evaluated using Gertzbein-Robbins system. Deviation rates for breaches of 2 mm or more (Grade C, D, and E) were calculated. Pedicle channel grade, vertebral level, distance from the reference frame (RF), insertion order of the screws, curve laterality, and use of a navigated high-speed drill were investigated as factors causing deviation.

RESULTS

A total of 465 robot-assisted pedicle screws were placed, and deviations were observed in 13 (2.8%). The deviation rates were significantly different by pedicle channel grade (Grade 1: 0%, Grade 2: 0%, Grade 3: 3.1%, Grade 4: 20.4%, p < 0.001), vertebral level, and use of a high-speed drill. There were no significant differences in deviation rates for distance from the RF, insertion order of the screws, or curve laterality. Logistic regression analysis showed pedicle channel grade 4 was a significant risk factor for deviation.

CONCLUSION

The factor that was most likely to cause deviation in robot-assisted pedicle screw placement in AIS was pedicle channel grade. The most likely situation to cause deviation was a narrow pedicle with an internal diameter of less than one mm. Surgeons should be aware that even with the use of robotics, placing screws into such narrow pedicles is challenging.