Elsevier

The Spine Journal

Volume 8, Issue 6, November–December 2008, Pages 998-1002
The Spine Journal

Clinical Study
Reliability and accuracy of fine-cut computed tomography scans to determine the status of anterior interbody fusions with metallic cages

https://doi.org/10.1016/j.spinee.2007.12.004Get rights and content

Abstract

Background context

Computed tomography (CT) scan has been shown to be more accurate than radiographs in evaluating anterior interbody fusion but may still over-read the extent of fusion.

Purpose

To assess the reliability and accuracy of fine-cut CT scans with reconstructions in evaluating anterior lumbar interbody fusion (ALIF) with metallic cages using surgical exploration as the reference standard.

Study design

Accuracy of a diagnostic test referenced to the gold standard.

Patient sample

A total of 49 patients and 69 surgical levels.

Outcome measures

Evaluation of fine-cut CT scans for evidence of fusion with subsequent surgical exploration as the reference standard.

Methods

Forty-nine patients who underwent ALIF with metallic cages over 69 levels, who had a fine-cut CT scan before revision were included. Five spine surgeons unaware of the findings on surgical exploration evaluated pre-revision CT scans, classified these as fused or not; and determined the presence of a “sentinel sign” and a “posterior sentinel sign.” Kappa coefficients for interobserver reliability, sensitivity, and specificity to detect fusion were determined.

Results

There were 26 males and 23 females with a mean age of 43 years. There were 27 smokers. Average time from index to revision surgery was 22 months. Interobserver kappa for classification as fused or not was 0.25 with 70% to 97% sensitivity and 28% to 85% specificity. The interobserver kappa for the sentinel sign was 0.34 with 13% to 33% sensitivity and 77% to 92% specificity. The interobserver kappa for the posterior sentinel sign was 0.23 with 33% to 87% sensitivity and 56% to 90% specificity.

Conclusions

Raters generally overstated fusion with low specificities across raters and low consensus specificity. Overall accuracy of the posterior sentinel sign (74%) was higher than the sentinel sign (61%). The low kappa value indicates fair reliability. In patients with metallic interbody devices, surgeons should be cautious about interpreting the findings on fine-cut CT scans whether using a general assessment of the fusion, the sentinel sign, or the posterior sentinel sign.

Introduction

Anterior lumbar interbody fusion (ALIF) is a widely used technique for lumbar arthrodesis [1], [2], [3], [4]. Reported rates of fusion vary because of differences in surgical technique and criteria used to determine fusion [5], [6], [7], [8], [9], [10]. Computed tomography (CT) scanning has become the method of choice [11], [12], [13], [14], [15] because it provides osseous detail and allows reformatting to produce images in the sagittal and coronal planes. Studies have shown that CT is superior to plain radiographs in evaluating ALIF, particularly in the presence of metallic interbody devices [14], [16]. However, animal studies suggest that CT scans may overestimate the extent of fusion [14]. This study was done to assess the reliability and accuracy of fine-cut CT with coronal and sagittal reconstruction views in evaluating ALIF with metallic cages using surgical exploration as the reference standard.

Section snippets

Methods

Forty-nine consecutive patients who underwent revision surgery after an anterior interbody fusion with metallic cages and had a fine-cut CT scan before revision were included. Forty-two patients had a preoperative diagnosis of pseudoarthrosis and seven had adjacent level degeneration. Five experienced fellowship-trained spine surgeons who were not aware of the findings on surgical exploration evaluated the pre-revision CT scans and classified the levels as fused or not fused. Fine-cut axial

Results

There were 26 males and 23 females with a mean age of 43 years (range 21–65 years). There were 27 smokers. Average time from the first surgery to the revision surgery was 22 months (range 3–73 months). Thirty-nine of 69 levels were found to have a nonunion on exploration, giving a per-level prevalence of 56.5%. There were 33 single-level fusions, 13 two-level, and 3 three-level fusions. There were 8 previous fusions at L3–L4, 25 at L4–L5, and 36 at L5–S1. Three different cages were used: the

Discussion

Review of literature shows that there are no universally accepted radiological criteria for assessing interbody fusion [19], [20], [21] using either plain radiographs or CT scans. Metallic implants, which are radiopaque and can produce artifacts, add to the difficulty in adequately assessing imaging studies to determine the presence of fusion. McAfee [17] considers bone formation in front of the cage, across the anterior margin of the disc space as the most reliable indicator of a solid

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  • Cited by (0)

    Research support received from the Lumbar Spine Study Group through Medtronic Sofamor Danek and from Norton Healthcare.

    FDA device/drug status: not applicable.

    Authors acknowledge a financial relationship (research support from Medtronic Sofamor Danek [SDG], consultants for Medtronic Sofamor Danek [BRS, JDS, and SDG], stockholder and board member of Pioneer K2 [MFG], other support from Medtronic Sofamor Danek [JDS and SDG] and other support from Stryker [MFG]), which may indirectly relate to the subject of this research.

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