[Learning curve of minimally invasive pedicle screw placement].

Objective: The aim of this study was to estimate the learning curve needed for correct placement of minimally invasive percutaneous pedicle screws (PPS).

Introduction: PPS are the most common system used for instrumentation of spinal lesions that require stabilization.

Methods: We retrospectively assessed the insertion of 422 PPS (T5 to S1) in 75 patients operated between 2013-2016 under two-dimensional fluoroscopic guidance. The surgeon 1 always placed the PPS on the right side and the surgeon 2 on the left side. Screw positioning and pedicle rupture was determined with the Gertzbein tomographic classification. We compared the accuracy of PPS placement in our series with a reference rupture rate of 8.08%, value obtained from a meta-analysis.

Results: Of the 422 TTP, 395 were inserted into the pedicle without violation of its cortical wall (Grade 1 = 93.6%), 27 (6.4%) disrupted the pedicle, of which 3.8% were Grade 2, 1.65% Grade 3 and only 0.9% Grade 4. The Surgeon 1, presented an overall break rate of 6.6% reaching standard values of accuracy by placing 74 PPS, Surgeon 2 showed a disruption rate of 6.1%, reaching baseline values at 64 PPS; the difference between them was not statistically significant ( P = 0.9009).

Conclusion: In our series, it was necessary to place approximately 70 PPS to achieve intrapedicular accuracy comparable to results reported by experienced surgeons in this minimally invasive technique.