At What Levels Are Freehand Pedicle Screws More Frequently Malpositioned in Children?

Abstract

Study Design

Retrospective case series.

Background

Previous studies report that 5% to 17% of pedicle screws placed in children are malpositioned. Knowledge of the long-term effects of malpositioned screws is limited. We sought to further characterize risk factors for malpositioned pedicle screws in order to establish a more proactive role in limiting future complications.

Objective

We undertook this study to answer the following: 1) Is the rate of freehand pedicle screw malpositioning higher in children with spinal deformity, particularly at the apical concavity? 2) At what vertebral levels do freehand pedicle screws have the highest rates of malpositioning? 3) In which direction (medial or lateral) do freehand pedicle wall violations occur most often?

Methods

Incidental postoperative computed tomographic (CT) exams were retrospectively reviewed in 85 pediatric patients (605 screws) treated with posterior spinal fusion using freehand pedicle screw technique. Of the screws imaged, 355 were in patients without deformity and 250 in patients with deformity. Breaches were categorized as mild (<2 mm), moderate (2–4 mm), or severe (>4 mm).

Results

Screws in pediatric deformity patients were more frequently malpositioned by 2 mm or more than were screws in patients without deformity (26% vs. 19%, p = .02). In patients with deformity, no higher rate of screw malposition was detected at the apical region. Overall, the highest rates of severe screw malposition were between T3 and T8. Pedicle breaches were more commonly in a medial direction compared with lateral (74% vs. 26%, p < .0001). However, severe breaches within the T3–T8 region were more often directed lateral than medial (92% vs. 8%, p ≤ .0001).

Conclusions

The clinical significance of asymptomatic pedicle screw breaches in children has not yet been determined. In this study, screws at the apical concavity were no more likely to be malpositioned than those at other sites. Efforts to reduce pedicle screw malposition would likely be most effective at the T3–T8 levels.

Level of Evidence

Level IV, Therapeutic Study. See the Guidelines for Authors for a complete description of the levels of evidence.

Introduction

Pedicle screw fixation has become the preferred instrumentation for the surgical correction of pediatric spine deformity [1], [2], [3], [4], [5]. Improved fixation, reduced need for anterior surgery, and decreased revision rates are among the advantages of pedicle screws over other forms of posterior spinal instrumentation [2], [6], [7], [8], [9]. Previous clinical success of pedicle screw fixation in the lumbar region has led to further use in the thoracic region, despite the anatomic challenges of placing pedicle screws in the thoracic vertebrae [7], [10]. Children with spinal deformity may have altered anatomy, potentially increasing the difficulty of accurate pedicle screw placement [3], [11]. Vascular or neurologic complications of thoracic pedicle screw malposition are rare, and most pedicle perforations are asymptomatic [1], [3], [6], [10]. Recent data suggest minimal long-term effects of malpositioned pedicle screws [12]. Nevertheless, given the potential complications of such breaches, it is in the interest of the patient to reduce the rate of screw malposition.

A variety of strategies and guidance systems are available to improve the accuracy of pedicle screw positioning [1], [2], [5], [13], [14], [15], [16]. However, barriers of cost, training, time efficiency, and radiation exposure may limit the widespread use of navigation and other guidance techniques [5], [14], [17]. Additionally, guidance may not be necessary for all pediatric surgeries or all spinal levels. Knowledge of what diagnoses and which vertebral levels are at highest risk of screw malposition may allow for the most effective use of such devices and may alert the surgeon when additional precautions may be necessary.

From 5% to 17% of all pedicle screws placed in children are thought to be positioned outside the bony confines of the pedicle [4], [8], [18], [19], [20]. There is limited information regarding the levels and direction at which screws are most frequently malpositioned. Some authors have concluded that pedicle screw malposition is more frequent at the apex of scoliotic curves [18], whereas others have noted more frequent malposition in the midthoracic spine [21]. We previously evaluated the rates of screw-related complications and screw malposition on computed tomography (CT) for children under age 10 [4], [8], [18], [19], [20]. This study seeks to further characterize freehand pedicle screw malposition in patients less than 18 years by posing the following questions: 1) Is the rate of freehand pedicle screw malpositioning higher in children with spinal deformity, particularly at the apical concavity? 2) At what vertebral levels do freehand pedicle screws have the highest rates of malpositioning? 3) In which direction (medial or lateral) do freehand pedicle wall violations occur most often? Given the anatomical complexity of deformity diagnoses, we hypothesized a higher rate of pedicle screw malpositioning in these patients than in patients without deformity. Further, we postulated that malposition rates would be higher at the apical concavity compared with other levels.