Learning curve of thoracic pedicle screw placement using the free-hand technique in scoliosis: how many screws needed for an apprentice?

PURPOSE: The purpose of this study is to evaluate the learning curve of thoracic pedicle screw (TPS) placement of an inexperienced apprentice in scoliosis with the free-hand technique. METHODS: The patients with scoliosis who underwent TPS inserted with the free-hand technique by the apprentice under the direction of a chief surgeon were included in this study. The TPS placement by the apprentice was evaluated by examining the assessed position in chronological subgroups of 30 screws. The TPS position was assessed on the postoperative computed tomography (CT) scan images using Zdichavsky grading evaluation system and pedicle breach. The rates of good and dangerous screw placement and the rates of pedicle breaches in each apprentice subgroup were compared with those in the chief surgeon group. RESULTS: Thirty-eight patients with 311 TPS were retrospectively analyzed in our study. Of all screws, 154 pedicle screws were inserted by the apprentice, and were divided chronologically into five subgroups. The rates of dangerous placement performed by the apprentice in the first two subgroups were 26.7 and 23.3%, respectively, and were significantly higher than 9.1% by the chief surgeon (P < 0.05). Meanwhile, the breach rate was 46.6% in subgroup 1 and 50.0% in subgroup 2, and was significantly higher than 29.3% in chief surgeon (P < 0.05). Furthermore, after the first 60 TPS placements, the assessed rates in apprentice reached to a stable level, and no significant difference could be found among the subgroups (subgroup 3, 4 and 5) and the chief surgeon group (P > 0.05). CONCLUSIONS: For an apprentice, an experience of at least 60 screw placements under the direction of an experienced surgeon is needed for inserting the TPS in scoliosis using the free-hand technique independently.