Increased medial pedicle angulation of the lumbar spine as a function of the posterior osseous defect in patients with myelomeningocele

Purpose Bony anatomy in patients with immature spines has been previously characterized. Alterations in lumbosacral morphology in patients with myelodysplasia, demonstrating increasing medial pedicle angulation (MPA) from L1-S1, have been examined; however, MPA related to size of the defect in myelomeningocele patients has not been defined. We aimed to establish that magnitude of posterior vertebral arch defects determines the extent of MPA in the lumbar spine, with larger posterior defects associated with increased MPA. Methods This retrospective case-control study compared lumbar morphometric measurements of patients with and without myelomeningocele. Eighteen patients with myelomeningocele underwent computed tomography with three-dimensional reconstruction; there was no concurrent pathology. Advanced imaging software was utilized to manipulate the axial, sagittal, and coronal axes at each lumbar level, and obtain accurate measurements of pedicle width, height, length, MPA, and posterior laminar defect. Results In lumbar vertebrae with a posterior arch defect (PAD), increased magnitude was associated with a concurrent increase in MPA between 16.2 degrees (43.4%) and 28.1 degrees (299.4%) depending on lumbar level. At levels without a PAD, increases in MPA were between 0.8 degrees (4.3%) and 5.7 degrees (60.6%) depending on lumbar level. Although the actual degree of medial angulation increases from cephalad to caudal levels, the percentage of deviation from normal is higher at the more cephalad levels compared with controls. Conclusion In patients with myelomeningocele, larger posterior vertebral arch defects were associated with increased MPA in the lumbar spine. Lumbar levels without a PAD also demonstrated increases in MPA compared with normal values.