Fluoroscopically assisted computer navigation enables accurate percutaneous screw placement for pelvic and acetabular fracture fixation

Abstract

Percutaneous fixation of pelvic and acetabular fractures are technically demanding procedures, and high rates of screw misplacement and potential neurovascular complications have been reported.

One hundred and sixty two screws from a prospectively collected database were analysed to evaluate the accuracy of a fluoroscopically assisted computer navigated technique to insert a cannulated screw to treat pelvic and acetabular fractures. Actual screw position and trajectory with the intraoperative surgical plan stored in the navigation computer.

The actual screw position differed from the surgical plan by a mean of 3.9 mm, with a mean 1.4 degree difference in screw trajectory. Post operative CT analysis of patients showed 10 screws perforated cortical bone.

Our results show that the use of computer navigation can aid in the accurate placement of percutaneous screws along a predefined plan. It is still possible to incorrectly place a screw and great care needs to be taken with the surgical plan and also to understand the complex anatomy of the bony pelvis.

Introduction

Severe pelvic ring and acetabular fractures are high-energy injuries resulting from significant forces such as motor vehicle and motorcycle crashes and falls from height. Surgical management of these complex fractures has undergone a steady evolution over the past 50 years, with advances in the understanding of pelvic anatomy and concepts of surgical fixation leading to improved operative approaches [1], [2], [3]. The aim of surgery remains the restoration of anatomical integrity and function [4]. The overall goal of treatment and rehabilitation is to return the patient to pre-injury levels of functioning.

Due to the anatomical complexity of the pelvis and intrapelvic structures, internal fixation of pelvic ring and acetabular fractures can be technically demanding, often requiring large operative exposures to allow safe and accurate reduction and fixation. Complication rates as high as 25% have been reported, with the majority of these associated with operative exposure, rather than initial injury [4], [5]. The morbidity associated with extensile surgical approaches has led surgeons to explore alternate means of fixation.

Percutaneous insertion of cannulated sacroiliac, anterior column and supraacetabular screws can be used to manage amenable pelvic and acetabular fractures after closed reduction. This minimally invasive approach has been shown to be a safe alternative to open fixation, with lower rates of bleeding and infection [6], [7], [8].

Percutaneous screw insertion, however, is a demanding procedure requiring adequate reduction of the fracture and accurate screw fixation across narrow safe corridors. In the case of sacroiliac screws, insertion requires repetitive alterations in C-Arm position to acquire inlet, outlet and lateral views whilst drilling or passing guide wires. As corrections in one plane may also cause deviations in others, insertion may require extensive fluoroscopy and multiple passes with a drill or guide wire [9], with potential complications from an erroneous pass.

The narrowest part of the safe corridor for sacroiliac screws, the sacral pedicle, has been measured in 3D CT reconstruction studies with a mean width of only 15.6 mm (range 11.6 to 20.2 mm) [10], [11], with a 4 degree deviation of screw angle being sufficient to perforate the sacral foramina or anterior cortex [11]. This is significantly decreased in the presence of any fracture malreduction [12]. Furthermore, the complexity and variability of the sacral alar shape and slope must be recognised prior to planning a screw. Misplacement of screws and malunion are commonly reported complications [13], [14], [15], [16], with some series reporting neurological complications.

After CT guided navigation systems were shown to improve accuracy of pedicle screw insertion in spinal surgery [17], CT and fluoroscopy based navigation systems were developed to improve the safety and accuracy of sacroiliac screw placement. These systems can also be used to insert percutaneous supraacetabular, anterior column and iliac wing screws.

The aim of this study was to determine the accuracy and safety of pelvic ring and acetabular fracture fixation using a computer navigated cannulated screw technique. We have performed an analysis of our prospectively collected database of intraoperative fluoroscopic images and navigation computer data to assess deviation of the implanted screw from the operative plan.