ANATOMICAL STUDY OF THE IDEAL POSITIONING OF THE S2 ILIAC SCREW

ABSTRACT Objective: To evaluate the morphometry of the pelvis to determine the safe trajectory for the insertion of the S2-iliac screw, and to correlate it with studies reported in the literature for other populations. Method: The computed tomography (CT) pelvic exams of 36 Brazilian patients without congenital malformations, tumors, pelvic ring fractures or dysplasias were selected from the database of a radiological clinic. To define the ideal trajectory of the S2-iliac screw, the following variables were measured: 1- maximum sacroiliac screw length; 2- thickness of the iliac dipole for planning the choice of screw dimensions (length and diameter); 3 - distance between the insertion point of the iliac S2 screw and the posterior sacral cortex; 4 - angulation for insertion of the screw in the mediolateral direction, representing the angle formed between the “iliac line” and the anatomical sagittal plane; 5- Angulation for insertion of the screw in the craniocaudal direction. The Pearson's chi squared and student's t tests were used for statistical analysis. Results: The sample consisted of 36 patients, 50% (18/36) of whom were women. The mean age was 63.7 years, ranging from 23 to 96 years. All the pelvic morphometric variables analyzed presented values similar to those described in the literature for other populations. Conclusion: Prior evaluation of the tomography exams was important for preoperative planning, and there was a statistically significant difference between the sexes only in relation to the variables left craniocaudal and length of the left internal table. Level of evidence III; Observational cross-sectional study. RESUMO Objetivo: Avaliar a morfometria da pelve para determinar a trajetória de segurança de introdução do parafuso S2-ilíaco e correlacionar com estudos relatados na literatura para outras populações. Métodos: A partir do banco de dados de uma clínica radiológica, foram selecionados 36 exames de tomografia computadorizada (TC) da pelve de pacientes brasileiros sem achados de malformações congênitas, tumorações, fraturas do anel pélvico ou displasias. Para definição da trajetória ideal do parafuso S2-ilíaco foram mensuradas as seguintes variáveis: 1 - comprimento máximo do parafuso sacro-ilíaco; 2 - espessura da díploe ilíaca para planejar a escolha das dimensões do parafuso (comprimento e diâmetro); 3 - distância entre o ponto de inserção do parafuso S2-ilíaco e a cortical posterior do sacro; 4 - angulação para inserção do parafu