A 52-year-old male with ankylosing spondylitis presents for elective lumbar spine fusion. Clinical assessment reveals severe cervical rigidity and limited mouth opening (interincisor distance 2 cm). You anticipate a difficult airway. Which investigation is most appropriate to assess the degree of cervical spine involvement and guide your airway management strategy?

Explanation

## Assessment of Cervical Spine Mobility in Difficult Airway **Key Point:** In patients with ankylosing spondylitis or other conditions causing cervical rigidity, dynamic cervical spine imaging (flexion-extension views) is the investigation of choice to assess residual mobility and guide airway technique selection. ### Why Lateral Cervical Radiographs (Flexion-Extension) Are Optimal 1. **Functional Assessment**: Flexion-extension views demonstrate actual cervical spine mobility, which directly correlates with the feasibility of neck extension during laryngoscopy. 2. **Rapid & Non-invasive**: Plain radiographs are quick, widely available, and do not require sedation or special equipment. 3. **Guides Technique**: Results inform whether awake fiberoptic intubation is necessary or if conventional laryngoscopy might be attempted. 4. **Cost-effective**: Minimal cost compared to CT or MRI. ### Comparison of Investigation Options | Investigation | Utility in Difficult Airway | Limitations | |---|---|---| | **Lateral C-spine X-ray (flexion-extension)** | Assesses dynamic mobility; guides intubation approach | Limited soft-tissue detail; radiation exposure | | Flexible fiberoptic bronchoscopy | Therapeutic (allows awake intubation); visualizes airway | Invasive; requires topical anesthesia; not a diagnostic tool for cervical pathology | | CT cervical spine | Excellent bony detail; 3D reconstruction | Static imaging; does not assess mobility; radiation; cost | | MRI cervical spine | Best soft-tissue detail; no radiation | Expensive; time-consuming; static; not needed for mobility assessment | **Clinical Pearl:** Patients with ankylosing spondylitis often have "bamboo spine" (complete fusion) but may retain some cervical mobility at unfused segments. Flexion-extension X-rays reveal this residual motion and help predict whether awake fiberoptic intubation will be necessary. **High-Yield:** The Difficult Airway Society (DAS) and ASA guidelines recommend cervical spine imaging (preferably dynamic) in patients with known or suspected cervical pathology before attempting intubation. **Tip:** Always obtain flexion-extension views in the awake patient (not under anesthesia) to assess true functional mobility.