A study of sacral anthropometry to determine S1 screw placement for spinal lumbosacral fixation in the Korean population

Purpose To investigate the incidence of closed-type PSIS in the Korean population. To categorize the morphological features of Korean sacrum. To measure the safe marginal length and angle for screw fixation considering the PSIS and course of the external iliac vein, using a Korean sacrum model. Methods We performed our study in 160 sacra including the pelvic ring obtained from 80 Korean cadavers. The bony measurements were obtained by performing 1-mm computed tomography cuts from the L5 lumbar vertebra to the pelvic ring and excluding other structures. We evaluated the incidence of anatomic variation of the PSIS and measured the safe marginal length and angle for screw fixation considering the PSIS and course of the external iliac vein, using a Korean sacrum model. Results Our study showed that the closed type of PSIS is more frequent in males than in females. The optimal angle for screw fixation is 16.91 ± 6.85 (°), while the left side S1 pedicle insertion angle is 16.00 ± 6.20 (°). The average Korean optimal screw length is 58.35 ± 14.90 (cm) for the right side and 55.89 ± 16.16 (cm) for the left side. Conclusion With reference to these parameters, the optimal screw length and angle can be chosen and bicortical anteromedial screw fixation can be easily and safely performed.