Lumbar Spine X-Ray

Lumbar spine radiography images the five lumbar vertebrae, the lumbosacral junction, intervertebral discs, facet joints, pars interarticularis and sacroiliac joints. Standard views are anteroposterior (AP) and lateral. Selected cases add oblique views (to show the pars interarticularis, as the "Scottie dog" outline) and a coned lateral view of the lumbosacral junction.

Flexion and extension lateral views assess instability. The effective dose is about 1 to 1.5 mSv for two views, and higher with obliques, and the gonadal dose is substantial, particularly for the AP view.

Low back pain affects up to 80% of adults at some point, and in 85 to 90% of cases it is non-specific and self-limiting with no benefit from imaging. Plain films do not change outcome in uncomplicated low back pain, expose the gonads to radiation, and show degenerative changes that are equally common in people without pain (disc space narrowing in over half of adults aged 50 or over).

The role of plain films is limited to red flags, suspected fracture, deformity, spondylolisthesis, ankylosing spondylitis, and post-operative review, with MRI preferred for nerve root compression, infection, tumour and cauda equina syndrome, and CT for fracture detail.

Indications. Back pain with red flags: age under 20 or over 50 with new pain, trauma, cancer history, fever or immunosuppression, unexplained weight loss, unremitting night pain, or neurological deficit. Suspected vertebral fracture (osteoporotic or traumatic). Suspected spondylolysis and spondylolisthesis, particularly in young athletes. Suspected ankylosing spondylitis.

Spinal deformity. Suspected metastases or myeloma where MRI is not available. Post-operative assessment of fixation and fusion. Not for acute non-specific low back pain, or for sciatica without red flags in the first 6 weeks.

Contraindications and precautions. Pregnancy: avoid, as the foetal dose is about 1 to 4 mGy, with MRI preferred. Women of childbearing age: ask about the last menstrual period (the 10-day rule or modern equivalent). Trauma patients: spinal immobilisation, log rolling and a cross-table lateral film. Remove clothing with metal, and external devices.

Preparation and technique. Bowel preparation is not required, but bowel gas and faeces reduce quality. The AP film is taken supine with knees flexed to flatten the lumbar lordosis, and the lateral film with the patient on the side and knees flexed. Gonad shielding is used where it does not obscure anatomy. Standing films give functional information in spondylolisthesis.

Normal appearances. Lumbar lordosis (about 40 to 60 degrees between L1 and S1). Rectangular vertebral bodies with parallel endplates, disc spaces that increase in height from L1 to L4 and are smaller at L5-S1 (where the disc is naturally narrower in about half of normal people), and smooth cortical outlines.

On the AP view, pedicles appear as oval rings at the upper outer border of each vertebra, the spinous processes lie midline, and the psoas shadows are visible. On the oblique view, the "Scottie dog" outline shows the transverse process (nose), pedicle (eye), superior articular process (ear), inferior articular process (front leg), and the pars interarticularis (neck).

The sacroiliac joints are symmetric.

Interpretation.

• Degenerative disease: disc space narrowing, osteophytes, endplate sclerosis, vacuum phenomenon (gas in the disc), facet joint arthropathy and sclerosis; frequent in asymptomatic people and poorly correlated with pain.
• Spondylolysis: a defect in the pars interarticularis (a "collar" on the Scottie dog neck on the oblique view), usually L5, commoner in young athletes (fast growing bone and hyperextension).
• Spondylolisthesis: forward slip of one vertebra on the next, graded I (up to 25%), II (25 to 50%), III (50 to 75%), IV (75 to 100%) and V (spondyloptosis, over 100%), measured on the lateral view.
• Degenerative spondylolisthesis is commonest at L4-L5 in older women with an intact pars.
• Fractures: compression (wedge) with loss of anterior height; burst fracture (posterior wall retropulsion, widened interpedicular distance on AP); Chance fracture (horizontal split through body and posterior elements, from seat belt injuries); transverse process fractures (often with renal and visceral injury).
• Malignancy: lytic or sclerotic lesions, loss of the pedicle on the AP view ("winking owl" sign), vertebral collapse and paraspinal mass.
• Infection: disc space narrowing with endplate erosion and paraspinal soft tissue swelling (pyogenic or tuberculous).
• Ankylosing spondylitis: squaring of vertebral bodies, syndesmophytes and fusion ("bamboo spine"), sacroiliitis with erosions, widening, sclerosis and ankylosis on the AP film or pelvis view.
• Transitional vertebra (lumbarisation of S1 or sacralisation of L5, Bertolotti syndrome) with a pseudoarthrosis, and spina bifida occulta (usually L5 or S1, incidental).
• Other: Scheuermann changes, scoliosis, aortic calcification or abdominal aortic aneurysm (calcified wall over 3 cm), renal and ureteric calculi, gallstones, bowel gas and sacral tumours.
• Fusion hardware: pedicle screws, rods and cages checked for position, breakage and loosening (lucency around screws).

Critical values and findings needing immediate action.

• Back pain with cauda equina features (urinary retention or incontinence, saddle numbness, bilateral leg weakness, faecal incontinence): emergency MRI, regardless of the plain film, and urgent neurosurgical review.
• Unstable fracture (burst fracture, Chance fracture, fracture dislocation) or fracture with neurological deficit: immobilise, CT and MRI, and urgent spinal surgical review.
• Vertebral destruction with fever, raised inflammatory markers or an abscess: urgent MRI, blood cultures and biopsy, and antimicrobial treatment directed by cultures.
• Pathological fracture or lytic lesion in a patient with known or suspected cancer: urgent MRI of the whole spine and oncology review.
• High grade spondylolisthesis (grade III or higher) with neurological signs or progressive slip: spinal surgical review.
• Calcified aortic aneurysm over 5 cm or pain with an expanding aneurysm: emergency vascular imaging and review.

Limitations and artefacts.

• Plain films poorly show the soft tissues. They do not show disc herniation, nerve root compression, spinal stenosis (apart from indirect signs), epidural abscess, or cord or cauda equina compression.
• Early metastasis or infection needs 30 to 50% bone loss or about 2 to 3 weeks to show on films.
• Degenerative changes are present in most older adults and may be mistaken as the cause of pain, leading to unnecessary treatment and anxiety.
• Radiation dose is substantial, with a high gonadal dose, and has no benefit in uncomplicated pain; limit repeat films.
• Overlying bowel gas, faeces, barium, calcified lymph nodes and contrast hide lesions, and the L5-S1 level is difficult to show on the lateral view in broad patients.
• Oblique views increase the dose and are used only for suspected spondylolysis.
• Lumbosacral transitional vertebrae cause numbering errors, which matter for surgical planning and level identification.
• Interpretation of the Scottie dog collar requires well positioned obliques; MRI or CT confirms and shows stress reactions that plain films cannot.

Special groups.

• Children and adolescents with back pain: always investigate, because pain is rarely benign (spondylolysis, Scheuermann disease, infection, tumour, disc calcification, and leukaemia); use MRI or SPECT for stress reactions to avoid radiation.
• Pregnancy: MRI without contrast if imaging is needed.
• Older adults and patients on corticosteroids: vertebral compression fractures are common and need bone density assessment.
• Patients with cancer: low threshold for MRI.
• Patients with spondyloarthropathy: AP pelvis or sacroiliac view is a better first film than the lumbar spine.
• Regions: spinal tuberculosis and pyogenic infection occur frequently in many settings, and plain films with high suspicion help early diagnosis where MRI is scarce; heavy manual work is associated with early degenerative disease.

Follow up tests.

• MRI of the lumbar spine for radiculopathy, stenosis, infection, tumour and cauda equina.
• CT for fracture detail and surgical planning.
• Standing flexion extension films for instability.
• Bone scintigraphy or SPECT for stress reaction, and bone density scan.
• Full blood count, erythrocyte sedimentation rate, C-reactive protein, HLA-B27, serum calcium and protein electrophoresis, blood cultures, urinalysis.
• Spinal surgical, rheumatology or physiotherapy review.