An X‑ray of the lumbosacral (LS) spine in lateral flexion is a side‑bending radiograph taken with the patient bending left and right. It evaluates spinal alignment, segmental mobility, and dynamic instability (for example, spondylolisthesis or fusion assessment). It's used for unexplained low back pain or pre/postoperative evaluation. The test is quick, low‑radiation, and often done with neutral and extension views.

The four standard views of the lumbar spine are anteroposterior (AP), lateral, oblique, and flexion–extension (dynamic) views. AP shows vertebral body alignment and disc spaces; lateral demonstrates vertebral height, canal and sagittal alignment; oblique views visualize facet joints; flexion–extension films assess segmental instability, spondylolisthesis or abnormal motion. These views together give a comprehensive assessment for fractures, degenerative disease and instability.

Lateral flexion of the lumbar spine is side‑bending of the lower back in the coronal plane. It occurs through small, segmental movements between lumbar vertebrae and is primarily produced by the quadratus lumborum, internal/external obliques and ipsilateral erector spinae. Motion is limited by facet joint orientation and intervertebral discs; typical active range is roughly 15–20 degrees to each side in healthy adults.

Lumbar flexion is forward bending of the lower spine that decreases the angle between trunk and pelvis, activating abdominal muscles and stretching posterior spinal ligaments and facets; it increases anterior disc pressure. Lumbar extension is backward bending that increases lumbar lordosis, engages paraspinal and gluteal muscles, compresses posterior elements and can relieve anterior disc loading but may irritate facet joints—perform both within pain-free limits.

A true lateral X‑ray of the spine is a lateral projection where vertebral bodies, disc spaces and posterior elements are perfectly superimposed with no rotation. Endplates appear parallel, pedicles aligned, and spinous processes are centered, allowing accurate assessment of alignment and disc height. Proper patient positioning keeps the midsagittal plane perpendicular to the receptor and the X‑ray beam centered over the target level.

A lumbar spine X‑ray is done to assess bone-related causes of low back pain, such as fractures, degenerative changes (arthritis, disc space narrowing), spinal alignment problems (scoliosis, spondylolisthesis), and suspected bony infection or tumor. It helps evaluate trauma, guide further imaging, and screen for red flags when pain is severe or persistent. Limitations: it shows bone structure but not soft tissues or disc herniations.