Lumbar spine (flexion and extension views)

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The lumbar spine flexion and extension views images the lumbar spine which consists of five vertebrae.

Indications

These views are specialized projections to provide functional tests of lumbar spine instability, often in the context of spondylolisthesis.

Patient position

  • the patient is positioned erect:
    • ideally, spinal imaging should be taken erect in the setting of non-trauma to give a functional overview of the lumbar spine
    • all imaging of patients with suspected spinal injury must occur in the supine position without moving the patient
    • in the lateral decubitus position, position the patient so that the humeri are extended 90 degrees to the thorax, with the elbows flexed so that the forearms are parallel to the thorax. Spinal curvature in the AP projection will determine if a right lateral or a left lateral is performed. 
    • when implementing horizontal beam technique, ensure the distal upper limbs are not overlying the region of interest. Ask the patient to cross their arms over their upper thorax, or to extend them in a similar position to that achieved in the lateral decubitus position
  • flexion
    • at the last possible moment, instruct the patient to 'bend forward' from the lower back, flexing their lower spine
  • extension
    •  at the last possible moment, instruct the patient to 'lean back' from the lower back essentially extending their lower spine

Technical factors

  • lateral projection
  • expiration (to minimize superimposition of the diaphragm over the upper lumbar spine) 
  • centering point
    • the level of the iliac crest 
    • coronal centering point is directly over the lumbar vertebra, which corresponds to the posterior third of the abdomen 
    • the central ray is perpendicular to the image receptor 
  • collimation
    • superiorly to include T12/L1 
    • inferior to include the sacrum 
    • anterior to include the anterior border of the lumbar vertebral bodies 
    • posterior to include all elements of the posterior column, particularly the spinous processes 
  • orientation  
    • portrait
  • detector size
    • 35 cm x 43 cm 
  • exposure
    • 70-80 kVp
    • 60-80 mAs 
  • SID
    • 110 cm
  • grid
    • yes (ensure the correct grid is selected if using focused grids)

Image technical evaluation

  • annotations affixed to demonstrate flexion and extension 
  • the entire lumbar spine should be visible from T12/L1 to L5/S1
  • adequate image penetration and image contrast is evident by clear visualization of lumbar vertebral bodies, with both trabecular and cortical bone demonstrated

Practical points

  • physical demonstration of the projection is often best to ensure patient fully understands the procedure 
  • ensure centering is adjusted when the patient moves into position
  • utilize an erect bucky when performing horizontal beam laterals to utilize oscillating grids, automatic expose control, and CR/IR alignment  
  • if the patient demonstrates spinal scoliosis, ensure that the side with the convexity is closest to the IR. This will utilize the diverging beam and aid in achieving superimposition of the upper and lower endplates
  • try to remove as many possible image artefacts, especially when performing horizontal beam technique in a trauma context 
  • if using a CR system, a smaller cassette 30 x 35 can be used when the sacral region does not need to be demonstrated. When centering, place the height of the CR 2.5 cm above the iliac crests