What is a cervical spine x-ray with extension and flexion used for in patients with suspected ligamentous injury, fracture, or conditions that may compromise cervical spine stability, such as osteoarthritis or rheumatoid arthritis?

Cervical Spine Flexion-Extension X-rays: Primary Clinical Applications

Cervical spine flexion-extension radiographs are primarily used to assess the clinical significance of equivocal MRI findings showing abnormal ligament signal without definite disruption, and as a complementary tool in the outpatient setting for patients with persistent neck pain after negative MRI. 1

Primary Indication: Clarifying Equivocal MRI Findings

The most appropriate use of flexion-extension radiographs is when MRI demonstrates abnormal signal in spinal ligaments without definite disruption. 1 In this specific scenario:

• The level and nature of the suspected lesion are already known from MRI 1
• Flexion-extension views help determine whether the MRI findings correlate with pathologic motion 1
• This addresses MRI's tendency to overestimate injury severity, with specificity as low as 64-77% and false-positive rates of 25-40% 1

Secondary Role: Outpatient Follow-up

Flexion-extension radiographs may be useful in the outpatient setting for patients with persistent neck pain and negative MRI. 1

• These studies are more likely to provide adequate visualization when patients can tolerate upright imaging and have fewer distracting injuries 1
• They are considered complementary to MRI rather than a replacement 1
• At least 30° of excursion for both flexion and extension must be achieved, as instability may only become apparent near terminal points of motion 1

Critical Limitations and Contraindications

Acute Trauma Setting

Flexion-extension radiographs should NOT be used as a primary tool for detecting ligamentous injury in acute trauma. 1 The evidence is uniformly negative:

• 28-97% of flexion-extension studies are inadequate for evaluating ligament injury due to limited motion and inadequate visualization 1, 2, 3
• Even when technically adequate, they rarely demonstrate evidence of ligament instability 1
• They carry real danger of producing neurologic injury 1
• They fail to reveal most ligament injuries identified on MRI 1
• In one study, 80% of films either failed to demonstrate C7/T1 junction or had less than 30° range of motion 2
• Sensitivity of 0% with 95.5% inadequate studies in one trauma center series 3

Degenerative Conditions

Flexion-extension radiographs have minimal utility in evaluating degenerative cervical spine conditions. 4

• Only 1% of patients had spondylolisthesis noted only on flexion-extension images 4
• None led to changes in clinical management 4
• The extra cost and radiation exposure are not justified 4

Proper Imaging Algorithm

For Suspected Ligamentous Injury:

1. Start with CT cervical spine - the gold standard for bony injury with 88.6-100% sensitivity 5, 6

2. Proceed to MRI if ligamentous injury suspected - MRI is the most sensitive test for ligament injury with 88.5% sensitivity and 96.9% specificity 7, 6

3. Consider flexion-extension radiographs ONLY if:

   • MRI shows abnormal ligament signal without definite disruption 1
   • Patient is in outpatient setting with persistent symptoms and negative MRI 1
   • Patient can achieve adequate motion (≥30° excursion) 1

For Acute Trauma:

Do NOT obtain flexion-extension radiographs in the acute setting. 1, 8, 3

• If CT is negative but clinical suspicion remains, proceed directly to MRI 7
• Approximately 1% of patients with unreliable examination and negative CT will have unstable injury requiring surgery identified on MRI 1, 7

Common Pitfalls to Avoid

• Never use flexion-extension radiographs as a primary screening tool - they have poor sensitivity and high inadequacy rates 1, 2, 3
• Do not obtain these studies in patients with limited motion - 30% of acute examinations are inadequate due to muscle spasm, and this group has higher injury rates (12.5%) requiring cross-sectional imaging 9
• Do not delay MRI while waiting for flexion-extension studies - this prolongs cervical collar use and hospital stay without diagnostic benefit 3
• Do not rely on these studies to "clear" the cervical spine - they should be removed from cervical spine clearance protocols 3
• Avoid in acute whiplash-associated disorders (WAD) - flexion-extension radiographs are unlikely to yield positive results in the presence of acute neck pain and loss of lordosis 8