[Learning curve of minimally invasive pedicle screw placement]

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

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

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.

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).

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.