Lumbar plain radiograph is not reliable to identify lumbosacral transitional vertebra types according to Castellvi classification principle

Abstract

Background: The anteroposterior view of the lumbar plain radiograph (AP-LPR) was chosen as the original and first radiographic tool to determine and classify lumbosacral transitional vertebra with morphological abnormality (MA-LSTV) according to the Castellvi classification. However, recent studies found that AP-LPR might not be sufficient to detect or classify MA-LSTV correctly. The present study aims to verify the reliability of AP-LPR on detecting and classifying MA-LSTV types, taking coronal reconstructed CT images (CT-CRIs) as the gold criteria.

Methods: Patients with suspected MA-LSTVs determined by AP-LPR were initially enrolled. Among them, those who received CT-CRIs were formally enrolled to verify the sensitivity of AP-LPR on detecting and classifying MA-LSTV types according to the Castellvi classification principle.

Results: A total of 298 cases were initially enrolled as suspected MA-LSTV, among which 91 cases who received CT-CRIs were enrolled into the final study group. All suspected MA-LSTVs were verified to be real MA-LSTVs by CT-CRIs. However, 35.2% of the suspected MA-LSTV types judged by AP-LPR were not consistent with the final types judged by CT-CRIs. Two suspected type IIIa and 20 suspected type IIIb MA-LSTVs were verified to be true, while 9 of 39 suspected type IIa, 9 and 3 of 17 suspected type IIb, and 11 of 13 suspected type IV MA-LSTVs were verified to truly be type IIIa, IIIb, IV and IIIb MA-LSTVs by CT-CRIs, respectively. Incomplete joint-like structure (JLS) or bony union structure (BUS) and remnants of sclerotic band (RSB) between the transverse process (TP) and sacrum were considered to be the main reasons for misclassification.

Conclusion: Although AP-LPR could correctly detect MA-LSTV, it could not give accurate type classification. CT-CRIs could provide detailed information between the TP and sacrum area and could be taken as the gold standard to detect and classify MA-LSTV.

Keywords: Castellvi classification; Coronal reconstructed CT image; Lumbar plain radiograph; Lumbosacral transitional vertebra; Misclassification.

Fig. 1

A suspected type IIb MA-LSTV judged by AP-LPR was verified to be type IV by CT-CRI. a AP-LPR image showing the suspected JLS between the TP of the MA-LSTV and sacrum bilaterally. Arrow indicates the suspected JLS. b CT-CRI showing the JLS was found in most CT-CRIs bilaterally. Arrow indicates the JLS. c CT-CRI showing the detected BUS on left side in only a few CT-CRIs through the posterior vertebral body. Arrow indicates the JLS; arrowhead indicates the BUS. d Transverse CT image verified the JLS on the right side, while the BUS was on the left side. Arrow indicates the JLS; arrowhead indicates the BUS

Fig. 2

A suspected type IIb MA-LSTV judged by AP-LPR was verified to be type IIIb by CT-CRI. a AP-LPR image showing the suspected JLS existed bilaterally, and suspected JLS on the right side was narrower than that on the left side in the craniocaudal direction. Arrow indicates the suspected JLS on the left side; concave arrow indicates the suspected JLS on the right side. b CT-CRI showing the BUS was found in most CT-CRIs, while vague RSB was reserved at the medial region on the right side. Meanwhile, the intermittent JLS and BUS appeared simultaneously on the left side. Arrow, arrowhead and concave arrow indicates the JLS, BUS with RSB on the left side, and the BUS with RSB on the right side, respectively. c CT-CRI showing the detected JLS at the medial region in a few planes on the right side and the intermittent JLS and BUS appearing simultaneously at each plane on the left side. Arrow, arrowhead, concave arrow and concave arrowhead indicates the JLS and BUS on the left side, and the BUS and JLS on the right side, respectively. d Transverse CT images confirmed the JLS and BUS appeared in the same plane on the left side, and the BUS with RSB on the right side. Arrow, arrowhead and concave arrow indicates the JLS and BUS on the left side, and BUS with RSB on the right side, respectively

Fig. 3

A suspected type IV MA-LSTV judged by AP-LPR was verified to be type IIIb by CT-CRI. a AP-LPR image showing the suspected JLS existed on the right side with narrowed connection width and RSB. Arrow indicates the suspected JLS. b CT-CRI showing the right TP of the MA-LSTV separated from the sacrum in some CT-CRIs through the vertebral arch planes. Arrowhead indicates the JLS with vague RSB on the right side. c CT-CRI showing BUS on the right side with RSB. Arrow indicates the BUS with RSB. d Transverse CT image confirmed bony connection bilaterally, while the connection region was much narrower and shorter on the right side compared to the left side

Fig. 4

A suspected type IIa MA-LSTV judged by AP-LPR was verified to be type IIIa by CT-CRI. a AP-LPR image showing the suspected JLS on the left side. Arrow indicates the suspected JLS. b CT-CRI through vertebral body planes showing the suspected JLS to be RSB located at the bony fusion region. Arrow indicates the BUS with RSB. c CT-CRI through vertebral arch showing the suspected JLS to be RSB located at the bony fusion region; no JLS was detected. Arrow indicates the BUS with RSB. d Transverse CT image showing the BUS with RSB on the left side. Arrow indicates the BUS with RSB on the left side

Fig. 5

Variance of the orientation of the JLS seen in type IIa MA-LSTV. a AP-LPR image showing that the orientation of the JLS pointed upward when moving laterally instead of parallel to the horizontal line. Arrow indicates the JLS. b Oblique LPR showing orientation of the JBS was not parallel to the inferior endplate of the MA-LSTV. Arrow indicates the JBS. Arrowhead indicates the inferior endplate of the MA-LSTV. c Transaxial CT images showing the orientation of the JBS was not parallel to the coronal plane. Arrow indicates the JLS