Morphometric Characteristics of Sacral-2 Alar Iliac Screw Fixation in Pediatric Population.

STUDY DESIGN: A computed tomographic assessment.

OBJECTIVE: To establish morphometric data of sacral-2 alar iliac screw fixation in pediatric population.

SUMMARY OF BACKGROUND DATA: Studies on morphometric parameters of sacral-2 alar iliac (S2AI) screw fixation are mostly based on adult population. The pediatric scoliosis also needs the S2AI screw fixation, however, without the previous morphometric information of among pediatric population.

METHODS: Computed tomography (CT) scans of 120 pediatric patients without spinal deformities are obtained and imported to Mimics software for 3D reconstruction. Then, a cylinder (radius of 3.25 mm) is drawn to imitate the screw trajectory of S2AI screw and adjusted to a maximum upward and downward angle to obtain the feasible region. Nine parameters of the S2AI screw are measured. Differences between age groups are compared and significant statistical correlations are carefully studied to determine the potentially important clinical relationships.

RESULTS: The mean values and standard deviations (SD) for nine parameters at the maximum upward and downward angles were determined. With age increased, the S2AI screw trajectory becomes more caudal in the coronal (44.03 ± 4.43° to 53.15 ± 4.68°) and sagittal planes (50.33 ± 5.89° to 57.69 ± 4.21°) and more lateral in the transverse plane (49.40 ± 5.90° to 54.44 ± 2.99°), and all of the distance parameters include max-length, sacral distance, iliac width, S2 midline, iliac wing and skin distance increased. Age has a more significant effect on other parameters than transverse angle and skin distance (p < 0.05).

CONCLUSION: The sacral-2 alar iliac screw fixation could be used on pediatric population too, but the pediatric population had smaller size of pelvis than adults, surgeons should choose the smaller diameters and the shorter length of screws for pediatric population depends on their age.

LEVEL OF EVIDENCE: 4.