Anatomical Feasibility and Morphometric Analysis of Cortical Bone Trajectory Screw Fixation in the Pediatric Lumbar...

The cortical bone trajectory (CBT) screw fixation technique has been widely adopted in adult spinal surgery due to its minimally invasive nature and biomechanical advantages. However, systematic research on its anatomical feasibility and morphometric parameters in the pediatric lumbar spine remains lacking. This study aimed to evaluate the anatomical feasibility of CBT screw fixation in the pediatric lumbar spine, and to characterize the variations in screw dimensions and insertion angles across different age groups and lumbar levels, providing an individualized reference for pediatric lumbar surgery.

This retrospective study included 80 pediatric patients aged 5-16 years without lumbar pathologies. Participants were stratified into four age groups (5-7, 8-10, 11-13, and 14-16 years, denoted as Groups 1, 2, 3, and 4, respectively), with 20 patients per group and sex-matched distribution (10 males and 10 females per group). Multiplanar reconstruction based on computed tomography (CT) images with 1 mm reconstruction was performed to measure the following parameters at each lumbar level (L1-L5): maximum screw length (MSL), maximum screw diameter (MSD), lateral angle (LA), and cephalad angle (CA). Statistical analysis was conducted using a mixed linear effects model to assess the influence of age, sex, lumbar level, and their interactions on each parameter, supplemented by analysis of variance (ANOVA) and post hoc multiple comparisons with Bonferroni correction.

MSL increased significantly with age and showed a level-specific pattern, generally rising from L1 to L3 and declining at L5. In the mixed-effects model, age group and lumbar level had significant effects on MSL, and a significant Group 4 × female interaction was observed. MSD increased progressively from L1 to L5 and was significantly affected by age group, sex, lumbar level, and age × sex interaction, with a particularly significant Group 2 × female interaction (estimate = 0.459, p < 0.001). LA generally increased with age and caudal progression of the lumbar level and was significantly influenced by age group, sex, and lumbar level. In contrast, CA decreased progressively from L1 to L5 within each age group and was significantly influenced by age group and lumbar level, whereas the age × sex interaction was not significant. Anatomical feasibility was assessed using a screw diameter threshold of ≥ 4.5 mm. The applicability rate of CBT fixation increased with both age and caudal lumbar level, with lower feasibility mainly observed at upper lumbar levels in younger children. At L1, applicability rates were 50% in Group 1, 70% in Group 2, and 100% in Groups 3 and 4; at L5, applicability reached 100% in all groups.

The anatomical parameters for CBT screw placement in the pediatric lumbar spine are significantly influenced by age, lumbar level, and sex. This study provides a systematic anatomical reference for CBT screw dimensions and trajectory angles across pediatric age groups. Anatomical feasibility, defined by a ≥4.5 mm screw diameter threshold, was higher in older children, whereas the use in younger children requires careful individual evaluation due to limited space and increased risk of cortical disruption, especially at upper lumbar levels. These findings offer supportive evidence for guiding patient selection and preoperative planning, though clinical applicability requires further biomechanical and outcome validation.