Imaging the Spine — Systematic Approach
From Alignment Assessment to MRI Cord Evaluation
Spine Imaging Modality Selection
Radiography: Screening tool, alignment assessment, degenerative changes
CT: Gold standard for fracture characterisation, canal compromise, 3D reconstruction
MRI: Gold standard for soft tissue pathology — disc, cord, infection, tumour, ligaments
CT Myelography: Alternative to MRI when contraindicated — shows cord compression
Bone Scan/SPECT-CT: Facet joint disease, spondylolysis activity, metastatic screening
Key: Radiographs screen, CT characterises fractures, MRI evaluates soft tissues and cord
Critical Must-Knows
- Systematic spine radiograph reading follows ABCD: Alignment (3 smooth lines), Bones (vertebral body height/shape), Cartilage/Disc (disc space height), Soft tissues (prevertebral swelling).
- MRI is the gold standard for disc herniation, cord compression, cauda equina syndrome, infection, and tumour assessment.
- CT is the gold standard for fracture characterisation — it reveals fracture lines, posterior column involvement, and canal compromise that radiographs miss.
- Cervical spine clearance: NEXUS criteria or Canadian C-Spine Rule determine the need for imaging after trauma.
- Red flags requiring urgent MRI: cauda equina symptoms, progressive neurological deficit, suspected cord compression, suspected spinal infection, suspected metastatic disease.
Examiner's Pearls
- "Prevertebral soft tissue swelling on lateral cervical radiograph: more than 7mm at C2 or more than 21mm at C6 = significant (suspect fracture/haematoma/abscess).
- "Jefferson fracture (C1 burst): lateral mass overhang of more than 7mm (combined bilateral) on AP open-mouth view = transverse ligament disruption (unstable).
- "Hangman fracture (C2 pars): bilateral C2 pedicle fracture — paradoxically often STABLE because the canal enlarges (spinal cord spared).
- "TLICS score guides management: less than 4 = conservative, 4 = borderline, more than 4 = surgical. Components: morphology + posterior ligamentous complex + neurological status.
- "On MRI: loss of T2 high signal in the spinal cord (cord signal change) indicates myelopathy — this is an ominous finding suggesting compressive myelopathy.
Exam Warning
Spine imaging is tested extensively across all examination formats. You must know: ABCD systematic radiograph reading, the three alignment lines on lateral view, cervical spine clearance rules (NEXUS/CCR), prevertebral soft tissue thresholds, MRI interpretation for disc herniation and cord signal change, CT characterisation of fractures, TLICS scoring, and red flags requiring urgent MRI (CES, myelopathy, infection, metastases). Classic traps: missing C7-T1 junction injury on lateral radiograph and not recognising cord signal change on MRI.
ABCDSystematic Spine Radiograph Reading
Memory Hook:ABCD: the systematic approach for spine radiographs — Alignment, Bones, Cartilage/Discs, Dens/Soft tissues.
CRAMSRed Flags Requiring Urgent Spine MRI
Memory Hook:CRAMS: these five scenarios demand URGENT MRI — delay risks permanent neurological damage.
NSAIDNEXUS Criteria for Cervical Spine Clearance
Memory Hook:NSAID: if ALL five criteria are met, cervical spine can be cleared clinically WITHOUT imaging.
Overview
Systematic spine imaging is fundamental to orthopaedic practice, encompassing acute trauma (fracture/dislocation), degenerative disease (disc herniation, stenosis), infection (discitis/osteomyelitis), and neoplastic conditions (metastases, primary tumours). The imaging approach follows a logical hierarchy: radiographs for screening and alignment, CT for fracture characterisation, and MRI for soft tissue and cord assessment.
Imaging Algorithm
Trauma: (1) Apply NEXUS or CCR to determine need for imaging. (2) If imaging needed: CT is now the primary modality for cervical spine clearance in major trauma (replacing radiographs). (3) If neurological deficit: add MRI for cord, disc, and ligament assessment. Degenerative: radiographs for alignment and deformity, MRI for disc/canal/foraminal assessment if surgical decision-making required. Red flags: urgent MRI for CES, myelopathy, infection, or metastatic disease. Deformity: full-length standing radiographs (scoliosis series) for coronal and sagittal balance.
Critical Interpretation Points
Cervical lateral radiograph must show C7-T1 junction — failure to visualise this level is the most common cause of missed cervical fractures. If C7-T1 is not visible on lateral radiograph, a swimmer's view or CT is required. On MRI: T2 signal change WITHIN the spinal cord (high signal replacing normal cord) indicates myelopathy — this is an ominous finding that often represents irreversible damage and is a stronger predictor of surgical outcome than the degree of anatomical compression alone.
Clinical Imaging
Imaging Gallery
Systematic Approach
Systematic Spine Imaging Assessment
Spine Imaging Selection Guide
| Clinical Scenario | First-Line Imaging | Advanced Imaging |
|---|---|---|
| Cervical spine trauma | CT (primary modality in major trauma). NEXUS/CCR for clinical clearance | MRI if neurological deficit, cord compression suspected, or ligamentous injury assessment |
| Thoracolumbar trauma | AP + lateral radiographs. CT for any suspected fracture | CT for TLICS scoring (morphology, posterior ligament complex). MRI for cord/conus assessment and posterior ligament integrity |
| Disc herniation/radiculopathy | Radiographs (usually normal or degenerative) | MRI: gold standard for disc morphology, nerve root compression, canal stenosis. CT myelography if MRI contraindicated |
| Suspected infection (discitis) | Radiographs (disc space narrowing, endplate irregularity — often delayed) | MRI with contrast: gold standard. Shows disc signal change, endplate destruction, paraspinal/epidural abscess. Blood cultures + CRP/ESR |
| Suspected metastases | Radiographs (may show lytic/blastic lesions, pedicle destruction) | Whole-spine MRI: gold standard for metastatic screening. STIR sequence detects marrow infiltration. CT for stability assessment |
| Cauda equina syndrome | Do NOT delay for radiographs | URGENT MRI (within hours): sagittal and axial T2 for compression identification. This is a surgical emergency |
Clinical Applications
Cervical Spine Imaging
Radiographic assessment (lateral view): Three alignment lines: (1) Anterior vertebral line — follows the anterior cortex of the vertebral bodies. (2) Posterior vertebral line — follows the posterior cortex of the vertebral bodies (the anterior border of the spinal canal). (3) Spinolaminar line — connects the spinolaminar junctions. All three should be smooth lordotic curves. Any step-off suggests subluxation or fracture-dislocation. The atlantodental interval (ADI) should be less than 3mm in adults (less than 5mm in children) — increased ADI suggests transverse ligament disruption or odontoid fracture.
Prevertebral soft tissue width: Measured on the lateral radiograph. At C2: should be less than 7mm (or less than one-third of the vertebral body width). At C6: should be less than 21mm (or less than one full vertebral body width). Widening suggests haematoma from fracture, abscess, or retropharyngeal pathology.
Key cervical fractures: (1) Jefferson fracture (C1 burst): best seen on AP open-mouth view — lateral mass overhang more than 7mm combined (Rule of Spence) = transverse ligament disruption. (2) Hangman fracture (C2 pars): bilateral C2 pedicle fractures — often neurologically intact because canal enlarges. (3) Odontoid fractures (Anderson-D'Alonzo): Type I (tip, rare), Type II (base — most common, highest nonunion risk), Type III (extends into C2 body).
CT for cervical clearance: In major trauma, CT has replaced radiographs as the primary imaging modality for cervical spine clearance. CT sensitivity for cervical fractures is approximately 98% (vs 52-85% for radiographs). MRI is added when there is neurological deficit, suspected ligamentous injury, or persistent clinical concern despite normal CT.
Evidence Base
Canadian C-Spine Rule vs NEXUS
- The Canadian C-Spine Rule (CCR) had higher sensitivity (99.4%) than NEXUS (90.7%) for clinically important cervical spine injury.
- CCR was more specific (45.1% vs 36.8%), reducing unnecessary imaging more effectively.
- Both rules were validated for adult blunt trauma patients with GCS 15.
CT vs Radiography for Cervical Spine Clearance
- CT sensitivity for cervical fractures was 98% compared to 52% for plain radiographs.
- CT was particularly superior for detecting upper cervical (C1-C2) and cervicothoracic junction (C7-T1) injuries.
- Cost-effectiveness analysis supported CT as primary imaging for high-risk trauma patients.
Evidence strongly supports CT over radiographs for cervical spine clearance in major trauma.
Australian Context
In Australia, spine imaging follows evidence-based guidelines consistent with international practice. CT has replaced plain radiographs as the primary imaging modality for cervical spine clearance in major trauma in Australian emergency departments. The NEXUS criteria and Canadian C-Spine Rule are both taught and applied in Australian practice.
MRI is the standard investigation for disc herniation, spinal stenosis, myelopathy, and suspected infection or metastatic disease. Australian guidelines mandate urgent MRI for suspected cauda equina syndrome, with surgical decompression within 48 hours of symptom onset being the target for best neurological outcomes.
RANZCR provides referral guidelines for spine imaging that are aligned with the Royal Australasian College of Surgeons (RACS) and Spine Society of Australia recommendations. These emphasise appropriate imaging selection based on clinical presentation and red flag assessment.
Exam Viva Scenarios
Practice these scenarios to excel in your viva examination
"A 30-year-old man is brought to the emergency department after a motorcycle accident. He is alert, GCS 15, and complains of neck pain. He has no neurological deficit."
"A 45-year-old woman presents with a 4-week history of progressive bilateral leg weakness, urinary retention, and saddle anaesthesia. Back pain has been present for 6 months."
"An examiner shows you an MRI of the lumbar spine and asks you to describe your systematic assessment."
Spine Imaging — Exam Day Reference
High-Yield Exam Summary
ABCD Systematic Reading
- •Alignment: 3 smooth lines on lateral (anterior, posterior vertebral, spinolaminar)
- •Bones: vertebral body height, pedicles (winking owl = metastasis), cortices
- •Cartilage/Disc: disc space height, facet joints, interspinous distance
- •Dens/Soft tissues: odontoid fracture, prevertebral width (C2: less than 7mm, C6: less than 21mm)
Red Flags for Urgent MRI (CRAMS)
- •Cauda equina syndrome (bladder/bowel dysfunction, saddle anaesthesia)
- •Rapidly progressive neurological deficit
- •Abscess/infection (fever + back pain + raised inflammatory markers)
- •Metastatic disease (cancer history + night pain + weight loss)
- •Spinal cord compression/myelopathy (UMN signs)
Key Cervical Fractures
- •Jefferson (C1 burst): lateral mass overhang more than 7mm = transverse ligament torn
- •Hangman (C2 pars): bilateral C2 pedicle fx — often neurologically intact
- •Odontoid: Type II (base) = highest nonunion risk
- •ADI more than 3mm (adults) or more than 5mm (children) = transverse ligament disruption
TLICS Score
- •Morphology: compression(1), burst(2), translational(3), distraction(4)
- •PLC: intact(0), suspected(2), injured(3)
- •Neuro: intact(0), root(2), cord incomplete(3), complete(2), cauda equina(3)
- •Total: less than 4 = conservative, more than 4 = surgical