A Study of Sacral Anthropometry to Determine S1 Sacral Screw Placement for Spinal Lumbosacral Fixation in the Korean Population

Abstract

IntroductionThere are various methods of S1 pedicular screw fixation, and every method has its own advantages and disadvantages. But, anatomical variation of the posterior superior iliac spine (PSIS) was not considered in any method. Therefore, little is known about the safe angle for screw fixation in the Asian population. Material and MethodsWe 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 (CT) 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. ResultsOur 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 Lt. side S1 pedicle insertion angle (SPIA) is 16.00 ± 6.20 (°). The average Korean optimal screw length is 58.35 ± 14.90 (cm) for the Rt. Side and 55.89 ± 16.16 (cm) for the Lt. side. ConclusionWith reference to these parameters, the optimal screw length and angle can be chosen and bicortical anteromedial screw fixation can be easily and safely performed.