Pelvic antropometric measurement in 3D CT for placement of two unilateral iliosacral S1 - 7.3 mm screws

Arnold J Suda,Udo Obertacke,Lisa Helm

doi:10.1007/s00264-021-05095-1

Abstract

PurposeStability of the dorsal pelvic ring is important for patient mobilisation and can be restored using several surgical procedures after fracture. Placement of percutaneous iliosacral screws is a reliable and minimal-invasive technique to achieve stabilisation of the dorsal pelvic ring by placement of two screws in the first sacral vertebra. Aim of this study was to evaluate 3D CT scans regarding the anatomical possibility to place two 7.3 mm iliosacral screws for fixation of the dorsal pelvic ring.Methods3D CT datasets of 500 consecutive trauma patients with 1000 hemipelves of a mid-european level I trauma centre with or without pelvic injury were evaluated and measured bilaterally in this retrospective study.ResultsOne thousand hemipelvic datasets of 500 patients (157 females, 343 males) with a mean age of 49.7 years (18 to 95) were included in this study. Only 16 hemipelves (1.6%, 11 in females, 5 in males) in 14 patients (2.8%, 9 females = 5.73%, 5 males = 1.5%) showed too narrow corridors so that 7.3 mm screw placement would not be possible (p = 0.001). In women, too narrow corridors occurred 3.9 times as often as in men. Only two females showed this bilaterally.ConclusionThe evaluation of 3D CT scans of the pelvis showed the importance of planning iliosacral screw placement, especially if two 7.3 mm screws are intended to be placed in the first sacral vertebra.

Highlights

An intact dorsal pelvic ring is mandatory for human’s mobility with upright gait because of force transmission from spine, sacrum, iliosacral joints, and ilium to hip joints and lower extremities
Interruptions of the dorsal pelvic ring caused by fractures lead to severe pain and disability [1]
Unstable dorsal pelvic ring injuries should not be fixed with anterior external fixation only because of insufficient stability [15, 16]

Summary

Introduction

An intact dorsal pelvic ring is mandatory for human’s mobility with upright gait because of force transmission from spine, sacrum, iliosacral joints, and ilium to hip joints and lower extremities. Biomechanical investigations showed that two unilateral screws in S1 generate less cut-out and allow more load cycles in the finite-element model [15, 29] and have less risk of neurological injury compared to screws in S2 [25, 30,31,32,33,34] The aim of this retrospective study was to evaluate sacral S1 corridors in 1000 3D CT datasets to ensure pre-operative planning of unilateral double S1 iliosacral 7.3 mm screws with distance of 5 mm each in all patients independent of gender. 1. The narrowest part of the corridor from ala to corpus between foramen and anterior cortex, 0.4 mm below upper plate of the first sacral vertebral body in axial view (Fig. 1, green line). The length of the corridor crossing the narrowest part and the corridor angle parallel the tangent to both dorsal spinal processes at the level of the sacro-iliac joint in the axial view of both sides (Fig. 3, green line and green angle, respectively)

Methods

Findings

Results