Introduction: Pedicle screw fixation has a number of advantages over other methods of spine instrumentation. The anatomy of the pedicle is complex, however there are basic dimensions important for planning screw placement. Pedicle anatomy has been studied extensively in adults; however, there are only a few small studies examining the anatomy in children. This study was performed to evaluate the feasibility of pedicle screw placement in children aged 5-16, based on key anatomic dimensions.

Methods: The CT scans of 102 consecutive children evaluated at Riley Hospital for Children were studied. The parameters of the pedicle isthmus width (W), estimation of screw length (L) and axial angle (A) were recorded for 1632 pedicles from T10 through L5. Patients were divided into four age groups: Group A (5-7 years old), B (8-10 years), C (11-13 years), and D (14-16 years). Statistical analysis was performed evaluating the difference between genders and of the particular anatomy at the thoracolumbar junction (T12 to L1).

Results: The pedicles increase in both L and W from T10-T12 and from L1-L5. L1 has a consistently smaller W compared to T12 in both genders over all age ranges. Estimating a W of 4.5 mm necessary for safe screw placement, we calculate that virtually all pedicles of T12 and L3-5 are large enough for screw placement in both genders after age 8. L4 and L5 are large enough for screw placement in both genders in the youngest age range. The pedicle dimensions increase with age, with the largest percentage of growth between Group A and B.

Conclusions: Most of the pedicles of the lower lumbar spine and T12 are large enough to house the smallest commercially available screw, estimating a necessary W of 4.5 mm. Understanding the anatomy at the thoracolumbar junction is important, as the W of L1 is consistently smaller than T12.

Patient Care: Pedicle screw fixation has a number of advantages over other methods of instrumentation, however the placement of screws in a smaller pedicle may be challenging. While thoracolumbar pedicle morphology has been well studied in adults, such studies are lacking in pediatric patients. We feel a thorough understanding of the anatomy in the growing pediatric spine is vital for the effective application of pedicle screw fixation to the pediatric patient population.

Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the importance of pedicle anatomy in assessing the feasibility of pedicle screw fixation. 2) Discuss pedicle morphology of the pediatric lumbar and lower thoracic spine. 3) Understand the anatomy of the pediatric thoracolumbar junction and its implications for screw placement.

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