Normal Lumbosacral Disc Angle Size on X-ray, CT & MRI
The lumbosacral disc angle (LSDA) describes the angular relationship between the inferior endplate of L5 and the superior endplate of S1, measured on a lateral projection. It serves as a reliable geometric indicator of lumbosacral lordosis and sagittal alignment. Accurate assessment of this angle is important when evaluating low back pain, degenerative disc disease, and spinal instability.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Lateral | 10-15¡ |
Clinical Significance
A normal lumbosacral disc angle of 10–15° reflects balanced sagittal alignment at the L5–S1 junction. An angle exceeding this range indicates increased lumbosacral lordosis, which is commonly associated with anterior pelvic tilt, hyperlordotic posture, and increased shear stress at the L5–S1 disc. Conversely, a reduced or negative angle may suggest segmental kyphosis, disc collapse, or compensatory flattening of lumbar lordosis.
Clinically significant deviations in the lumbosacral disc angle should prompt correlation with symptomatology and additional functional or dynamic imaging. The angle is particularly useful in preoperative planning for lumbar fusion, where restoration of segmental lordosis is a surgical goal. Pitfalls include patient positioning errors and pelvic obliquity, both of which can artificially alter the measured angle.
- Degenerative disc disease with disc height loss at L5–S1
- Isthmic or degenerative spondylolisthesis at L5–S1
- Lumbar hyperlordosis secondary to anterior pelvic tilt
- Post-traumatic deformity or endplate fracture
- Iatrogenic malalignment following lumbar fusion surgery
Reference: Yochum TR, Rowe LJ. Essentials of Skeletal Radiology. (2005).
Imaging Notes
On lateral radiography, the lumbosacral disc angle is measured by drawing one line along the inferior endplate of L5 and a second line along the superior endplate of S1; the acute angle formed anteriorly between these lines is recorded. A true lateral projection with the patient standing is preferred to minimize rotational error and allow weight-bearing assessment. CT multiplanar reconstructions in the sagittal plane permit precise endplate identification, especially when osteophytes or endplate irregularity obscure plain-film landmarks. MRI sagittal sequences (T1 or T2-weighted) provide excellent soft-tissue contrast and allow simultaneous evaluation of disc signal, height, and nerve root involvement alongside angle measurement, making it the preferred modality for comprehensive L5–S1 assessment.