Computed-tomography-based anatomical study to assess feasibility of pedicle screw placement in the lumbar and lower thoracic pediatric spine

Abstract

The anatomy of the pedicle is complex and three-dimensional; however, there are basic dimensions important for possible screw placement. There are relatively few studies examining the pedicle 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. A case illustration is also provided. The CT scans of 102 consecutive children were studied. Patients with abnormal anatomy were excluded. The parameters of the pedicle isthmus width (W), estimation of screw length (L), and axial angle (A) were recorded for 1,632 pedicles from T10 through L5. Patients were divided into four age groups. Statistical analysis was performed evaluating the difference between males and females and of the particular anatomy at the thoracolumbar junction. 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 4.5mm necessary for safe screw placement, we calculate that virtually all pedicles of T12 and L3-L5 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. Most of the pedicles of the lower lumbar spine and T12 are large enough to house the smallest commercially available screw. Understanding of the anatomy at the thoracolumbar junction is important, as the W of L1 is consistently smaller than T12.