Study design: Morphology comparisons between the pedicle and pedicle rib unit in the immature spine were conducted through computed tomographic scans.
Objective: To establish reference data concerning the dimensions of the pedicle rib unit for normal children.
Summary of background data: Until recently, studies on extrapedicular fixation were mostly based on adults. No published study has assessed the morphology of the pedicle rib unit in the normal immature population. Establishment of the basic morphometric characteristics may be beneficial in treating immature patients with spinal disorders.
Methods: Measurements were carried out on the chest computed tomography scans of the immature Chinese patients without any spinal disorder findings. The width, chord length, and transverse angle of the pedicle rib unit were obtained and compared with the corresponding pedicle index. Difference between sex groups was measured, and significant statistical correlations were carefully studied to determine potentially important clinical relationships.
Results: The mean values and the standard deviations obtained for each thoracic segment were determined. The width, chord length, and transverse angle of the pedicle rib unit were significantly larger than corresponding pedicle measurements at all levels. Significant difference for measurements between sexes was found at some segments. Compared with the sex, age seemed to have a more significant effect on the measurements. Linear pedicle and pedicle rib unit dimensions had good correlations with age, whereas the transverse angle seemed to change little with age.
Conclusion: Compared with the dimensions of the immature pedicle, the significantly larger size of the corresponding pedicle rib unit provides a more ample space, which accommodates screws with larger diameters. Extrapedicular vertebral body fixation was anatomically feasible for the immature spine. The new procedure should be cautiously applied to avoid potential implant failures or a new deformity because of the growth of the immature spine.