Objective. To assess efficacy and safety of using a three-level navigation template in the surgical treatment of congenital spinal deformities. Material and Methods. Three-level navigation templates were used in surgical treatment of four consecutively operated 10-17-year-old patients with congenital scoliosis associated with thoracic hemivertebrae. The correctness of screw position was evaluated according to CT data using a 2-mm increment method: class 0-intraosseous screw position; class 1-the screw extends beyond the pedicle cortex by less than 2 mm; class 2-by 2-4 mm; and class 3-by more than 4 mm. Preoperative DICOM data were processed with free software. The model of target zone and navigation template were 3D printed and used in surgery. Results. Four of 16 (25 %) pedicles were narrower than 4.35 mm and were estimated as difficult for implantation with a planned violation of the integrity of the endplate. Perforation of the outer cortical layer took place in all these cases, and screw position corresponded to class 2 only in pedicle width of 1.9 mm. In pedicles wider than 4.35 mm, 11 of 12 (91.7 %) screws were implanted intraosseously. One screw extended beyond the pedicle cortex by 0.8 mm (class 1). Conclusion. Three-level navigation template can be considered as an effective means of positioning transpedicular screws in secondarily changed segments adjacent to anomalous one and confounding implantation. Free software is sufficient for preparing 3D-model of target zone and navigation template, and such a model is a highly informative reference object that is convenient to use during the operation.

Objective. To assess the correctness of transpedicular screw insertion in thoracic and lumbar vertebrae using two-level navigation templates for narrow pedicles.Material and Methods. Two-level navigation templates were used in surgical treatment of four patients aged 14–17 years with scoliotic deformity and multiple pedicles of small width (less than 4.35 mm). In each patient, the least favorable zones were selected for implantation using navigation templates. The rest of planned pedicle screws were inserted using free-hand technique. All patients underwent CT scanning postoperatively. Screws inserted to pedicles less than 4.35 mm in width  were classified as correctly placed if they did not extend beyond the medial cortical layer by more than 2 mm.Results. Out of 68 pedicles planned for screw placement, 42 were narrower than 4.35 mm. In the pedicles difficult for implantation, 29 screws were inserted using navigation templates and 13 by free-hand technique. Screws classified as correctly placed were 28 from those inserted with navigation templates and 9 from those implanted by free-hand technique. Difference in results of screw placement in narrow pedicles with navigation templates and by free-hand technique was statistically significant (exact Fisher test, p < 0.05).Conclusion. Transpedicular screw placement with two-level navigation templates in narrow pedicles is more correct than insertion by free hand technique.

Objective. To evaluate short-term result of selective navigation templates application in idiopathic scoliosis surgery.Material and Methods. A total of 12 patients aged 14–17 years with idiopathic scoliosis were included in the study. Group A included 6 patients treated with selective application of navigation templates for pedicle screws insertion in the most difficult zones. Group B (control) included 6 patients in whom all the pedicle screws were placed with free-hand technique. Number of screws inserted was 16–20 per patient. There was no significant difference between the groups in sex, age, Cobb angle, number of vertebrae instrumented, number of pedicle screws and laminar hooks. Surgery duration, blood loss, absolute and relative correction were compared. In Group A, duration of the 3D-objects fabrication and printing, as well as pedicle screw accuracy based on 2-mm increment grading system were evaluated.Results. Selective application of navigation templates as compared with total free hand screws placement significantly reduced surgery duration. Difference in blood loss and deformity correction was not significant. A total of 107 pedicle screws were placed in Group A, 48 of them with navigation templates and 59 by free-hand technique. Average pedicle width in screw installation with navigation templates was 4.28 ± 1.43 mm, and in that with free-hand technique 6.53 ± 1.72 mm, with significant difference. Accurate screw placement with navigation templates and by free-hand technique were 93.7 % and 88.0 %, respectively, with no significant difference. Duration of 3D-objects manufacturing was 1419 ± 190 minutes. Active operator’s involvement was required in about 10 % of the while.Conclusion. Selective application of a pair of two-level navigation templates for most difficult pedicles in idiopathic scoliosis significantly reduces surgery duration. Difference in blood loss and deformity correction is insignificant. Refusal of total templates usage for combination of navigation templates for selected difficult pedicles and free-hand technique for the rest is an option for shortening the preoperative preparation, but provides screw placement accuracy comparable with total templates usage (92.5–97.6 % as reported).

Introduction. Correlation between pedicle screw malposition and small values of pedicle morphometric parameters has been confirmed in numerous studies. Definition of critical pedicle size for screw insertion is an actual problem for pediatric spinal surgery.Material and methods. 29 patients, aged 3-17, with congenital or acquired spinal deformities were included in the study. All the patients had posterior surgery with pedicle screw implantation. All the screws were inserted by free hand technique. On preoperative CT, external pedicle width, internal pedicle width, and spongiosa proportion were measured. On postoperative CT, pedicle screw accuracy was evaluated. The binomial logistic regression was used to define dependence of pedicle screw accuracy on pedicle morphometric parameter values. ROC-curves were graphed, and AUC were calculated.Results. 233 pedicle screws were implanted to 29 patients by free hand technique. On postoperative CT, 191 (82%) screws were confirmed to be accurately inserted. The logistic model confirmed significance of all the examined morphometric parameters (p<0.001). The external pedicle width possessed the maximal predictive value. Statistical indices for the prognostic model (sensitivity, specificity, and accuracy) were calculated for pedicle width 3.5; 6.0; 7.5 mm.In the cut-off value of external pedicle width 3.5 mm, probability of accurate screw insertion is about 50%; this technique has been highly sensitive and maximally accurate. This morphometric feature is a technical limit of free hand pedicle screw insertion. Recommendations for selecting an implantation technique in different pedicle width are proposed.Conclusion. The external pedicle width 3.5 mm is a critical one for pedicle screw insertion by the free hand technique.