Elsevier

The Spine Journal

Volume 14, Issue 8, 1 August 2014, Pages 1470-1475
The Spine Journal

Clinical Study
Interreader and intermodality reliability of standard anteroposterior radiograph and magnetic resonance imaging in detection and classification of lumbosacral transitional vertebra

https://doi.org/10.1016/j.spinee.2013.08.048Get rights and content

Abstract

Background context

Different types of lumbosacral transitional vertebra (LSTV) are classified based on the relationship of the transverse process of the last lumbar vertebra to the sacrum. The Ferguson view (30° angled anteroposterior [AP] radiograph) is supposed to have a sufficient interreader reliability in classification of LSTV, but is not routinely available. Standard AP radiographs and magnetic resonance imaging (MRI) are often available, but their reliability in detection and classification of LSTV is unknown.

Purpose

The purpose of this study was to evaluate the interreader reliability of detection and classification of LSTV with standard AP radiographs and report its accuracy by use of intermodality statistics compared with MRI as the gold standard.

Study design/setting

Retrospective case control study.

Patient sample

A total of 155 subjects (93 cases: LSTV type 2 or higher; 62 controls).

Outcome measures

Interreader reliability in detection and classification of LSTV using standard AP radiographs and coronal MRI as well as accuracy of radiographs compared with MRI.

Methods

After institutional review board approval, coronal MRI scans and conventional AP radiographs of 155 subjects (93 LSTV type 2 or higher and 62 controls) were retrospectively reviewed by two independent, blinded readers and classified according to the Castellvi classification. Interreader reliability was assessed using kappa statistics for detection of an LSTV and identification of all subtypes (six variants; 1: no LSTV or type I, 2: LSTV type 2a, 3: LSTV type 2b, 4: LSTV type 3a, 5: LSTV type 3b, 6: LSTV type 4) for MRI scans and standard AP radiographs. Further, accuracy and positive and negative predictive values were calculated for standard AP radiographs to detect and classify LSTV using MRI as the gold standard.

Results

The interreader reliability was at most moderate for the detection (k=0.53) and fair for classification (wk=0.39) of LSTV in standard AP radiograph. However, the interreader reliability was very good for detection (k=0.93) and classification (wk=0.83) of LSTV in MRI. The accuracy and positive and negative predictive values of standard AP radiograph were 76% to 84%, 72% to 86%, and 79% to 81% for the detection and 53% to 58%, 51% to 76%, and 49% to 55% for the classification of LSTV, respectively.

Conclusion

Standard AP radiographs are insufficient to detect or classify LSTV. Coronal MRI scans, however, are highly reliable for classification of LSTV.

Introduction

A lumbosacral transitional vertebra (LSTV) was initially defined as the last lumbar vertebra with an additional connection between the transverse process to the sacrum [1]. Castellvi et al. [2] suggested a classification of LSTV in 1984. The classification, widely used today, is based on the assessment of a unilateral or bilateral hypertrophied transverse process of the last lumbar vertebra and its relationship to the sacrum (no connection, articulation, or osseous bridging) (Fig. 1). This classification was introduced using conventional radiographs—not with standard anteroposterior (AP) lumbar spine radiographs, but a 30° angled AP view of the lumbosacral joint (Ferguson view) with the aim to decrease the radiographic overlap effect of the transverse process of the last lumbar vertebra on the sacrum [2]. A high interreader reliability in LSTV classification has been reported (kappa=0.77–1) [3], [4] with the Ferguson view. However, Ferguson view radiographs are not routinely performed as part of the standard radiographic assessment of the lumbar spine, which typically includes standing AP and lateral radiographs. The interreader reliability and accuracy for the standard AP radiograph for detection and classification of different LSTV types is not known. Coronal magnetic resonance imaging (MRI) scans are anecdotally accepted as highly reliable in detection and classification of LSTV, but to the best knowledge of the authors, there are no reports on interreader reliability of coronal MRI to classify LSTV.

The first hypothesis of this study was that standard AP radiograph of the lumbar spine was unable to provide a sufficient interreader reliability and accuracy in detection and classification of LSTV. The second hypothesis was that coronal MRI was highly reliable in classification of LSTV.

Section snippets

Subjects

After institutional review board approval, 93 subjects with LSTV (type 2 or higher) (mean age±standard deviation: 56.7±16.4 years) from a database of 770 patients diagnosed with LSTV, retrieved from a picture archiving and communication system search, were randomly added and defined as the case group. Sixty-two subjects (58.2±16.4 years of age) without a connection between their transverse process of the last lumbar vertebra and the sacrum were added as the control group (imaged between

Detection

The interreader reliability for the detection of a connection between the transverse process of the last lumbar vertebral body to the sacrum was moderate (k=0.53) in standard AP radiograph, but almost perfect (k=0.93) with coronal MRI.

Classification

The interreader reliability for classification of LSTV was at best fair (wk=0.39) in standard AP radiograph, but very good (k=0.83) with coronal MRI (Fig. 4).

One hundred and twenty-nine of 155 subjects were classified correctly by both readers using MRI. However,

Discussion

The purpose of this investigation was to determine the reliability and accuracy of standard AP radiographs of the lumbar spine to detect and classify LSTV. In addition, the reliability of coronal MRI was assessed. Our data suggest that standard AP radiographs are insufficient to detect or classify LSTV because the interreader reliability was at best moderate (k=0.53) to detect and only fair (wk=0.39) to classify an LSTV. Second, the accuracy for standard AP radiographs, using MRI as the gold

References (6)

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FDA device/drug status: Not applicable.

Author disclosures: NAF-A: Grants: Individual funding of Swiss National Foundation (PBYHP3_143674) (D). BL: Nothing to disclose. RJH: Nothing to disclose. MF: Nothing to disclose.

The disclosure key can be found on the Table of Contents and at www.TheSpineJournalOnline.com.

Supported by the departmental fund of the MRI Department, Hospital for Special Surgery, New York, NY, USA and individual funding of Swiss National Foundation (NAF-A PBZHP3_143674).

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