Lumbosacral Vertebral Angles can Predict Lumbosacral Transitional Vertebrae on Routine Sagittal MRI

Abstract

Objectives: We aimed to measure lumbosacral vertebral angles in routine lumbar sagittal MRIs and assess their association with lumbosacral transitional vertebrae (LSTV).

Methods: We recruited 220 patients referring to our hospital for routine lumbar MRI during 2020-2021. All the participants were subject to routine sagittal lumbar MRI, whole spine localizer scan, and coronal MRI to numerate lumbar vertebrae. Five vertebral angles (A, B, C, D, and delta) and dehydration in L4-L5 and L5-S1 discs were assessed in sagittal MRI scans. Data were analyzed using SPSS 26.

Results: Out of 220 participants (mean age: 44.29 ± 14.14 years), 36 (16.36%) were diagnosed with LSTV. Among those diagnosed with LSTV, L5-S1 dehydration was less frequently observed compared to other participants (P < 0.001). Multivariate regression showed that dehydrated L4-L5 disc, non-dehydrated L5-S1 disc, increased A-angle, and decreased D-angle can independently predict LSTV. The median A-angle was significantly larger in LSTV patients than in non-LSTV participants (P = 0.038), while the medians of C-angle, D-angle, and delta-angle were significantly smaller in the LSTV group (P < 0.05). A C-angle ≤ 35.5˚ could diagnose LSTV with sensitivity and specificity of 72.2% and 57.6%, respectively. A delta angle ≤ 8.5˚ could diagnose type 2 LSTV with 92.3% sensitivity and 87.9% specificity.

Conclusion: Measuring lumbosacral vertebral angles, especially delta-angle, in routine sagittal MRI can potentially alert physicians of a likely LSTV diagnosis.

Keywords: Angle; Diagnosis; Lumbosacral transitional vertebrae; Magnetic resonance imaging.

Figure 1

Sagittal MRI showing the measured angles (a) A-angle and B-angle (Chalian et al.), (b) Lines used to define C-angle, and (c) Lines forming D-angle and D1-angle

Figure 2

The methods used to measure angles in sagittal MRI (a) A-angle is 35.0˚ and the B-angle is 36.1˚; (b) The largest angle formed by the lines is C-angle = 32.2˚

Figure 3

Normal patient with a 24˚ delta angle (calculated as 33˚ minus 9˚). At L5-S1 junction, there is a distinct acute angle, whereas the other levels show a nearly parallel alignment

Figure 4

Axial (a) and coronal (b) T2W images show unilateral pseudoarthrosis of left L5 transverse process with adjacent sacral ala consistent with Castellvi type2a LSTV. In this case, there is a reduced delta angle of 2.8˚, highlighting the influence of two specific levels in shaping the curvature of lumbosacral region (c). Also, note the hydrated L5-S1 disc in the presence of dehydrated L4-L5 disc (d)

Figure 5

ROC curves for the diagnostic value of vertebral angles to diagnose (a) LSTV, and (b) LSTV type 2