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In patients with myelomeningocele stable low profile pelvic instrumentation required in spinal deformity surgery may be difficult to obtain due to the variable dysmorphic pelvic anatomy. A number of techniques have been proposed but the superiority of one or another in this challenging population has not been established.


Our aim is to determine the pelvic morphology in patients with myelomeningocele associated scoliosis and its relation to pelvic fixation and deformity correction strategies.


We analyzed the CT scans performed for preoperative planning of scoliosis corrective surgery in 26 individuals with myelomeningocele and the CT scans obtained for the diagnosis of appendicitis in an otherwise healthy age and gender matched cohort. The mean age range was 10.4 years (range 1.9-19.4). Three-dimensional reformatting of the CT scans was performed to permit accurate measurements of bone depth and ideal (best available bone stock) screw trajectories for standard pelvic fixation methods. Segmental anatomic parameters and intersegmental anchor relationships were determined: (1)sacral alar iliac (SAI); (2)posterior superior iliac spine (PSIS); (3)anatomic; (4)sacral-alar; (5) width of sacrum at SAI entry; (6)distance between anchor entry sites.


The cohort of patients with myelomeningocele had greater variation in the angles of their pelvic screws in both the sagittal and axial plane; at least one screw trajectory was impossible in more than half of the myelomeningocele patients compared to only one control patient with an impossible trajectory.

In both groups, the SAI screws (most commonly) had the most harmonious start points compared to L5 screws, however in both groups several patients had L5 start points that lined up better with iliac screws in the horizontal plane. We found that in every patient the sacral ala was at least 1 cm thick and that as a portion of the posterior sacral width, the sacral canal was not wider in the patients with myelomeningocele.


In this cohort of patients with scoliosis and myelomeningocele we found multiplanar pelvic asymmetry that led to wide variation in angles for pelvic fixation and many instances where typical trajectories were not possible due to sacral and pelvic morphology. Three dimensional CT scans are an invaluable aid to the planning of ideal personalized pelvic fixation techniques. Creativity may be necessary with nontraditional screw trajectories or Dunn-McCarthy (or Galveston) techniques to establish a strong pelvic base for spinal fixation and deformity correction.

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Pelvic Asymmetry and Spinal Fixation in Myelomeningocele