Hyperflexion Injuries
Locked Facets

• Normal anatomy
  • Posterior ligamentous complex
    • Supraspinous ligament
    • Interspinous ligament
    • Posterior longitudinal ligament
    • Capsule of the facet joint
  • Normal relationship of facets

Normal relationships of facet joints
Inferior articulating facet of body above (blue arrow) lies posterior to superior facet of body below (red arrow)

• Ligamentous Injuries
  • Mechanism is flexion/distraction
    • Injury is to the posterior spinal ligamentous complex
    • Unstable in flexion; stable in extension
    • If unrecognized, can lead to progressive neurologic damage
  • Imaging Findings
    • Widening of the interspinous distance
    • Slight anterior subluxation of one vertebral body on another
    • Widening of the facet joint
      • Usually the posterior aspect
    • Disk space narrower anteriorly than posteriorly

 

Posterior ligamentous structures involved in flexion injury are
(a) supraspinous ligament (b) interspinous ligament (c) facet joint capsule (d) posterior longitudinal ligament
From Seminars in Roentgenology, Jan 1978 John H. Harris, Jr.

• Sharp angle kyphosis
• Degrees of ligamentous injury
  • Subluxation of vertebral body
  • Perched facet
  • Locked facets
    • At least 50% subluxation
• Unilateral Locked Facet
  • Mechanism is flexion/distraction and rotation
    • Only 30% associated with neurologic defect
  • Most often occurs at C4-5 and C5-6
  • Inferior articular facet of superior vertebral body is locked in front of the superior facet of the more inferior vertebral body but only on one side
  • Imaging Findings
    • Subtle
    • Slight anterior subluxation of one vertebral body on the one below
      • Usually less than 25% of the width
    • On lateral view of cervical spine, some bodies appear true lateral below level of injury and oblique above level of injury
    • “Bow-tie sign”
    • Spinous processes do not align on frontal film
      • Spinous processes of inferior vertebrae displaced toward the locked side
• Bilateral Facet Dislocation
  • Severe flexion injury
  • Both anterior and posterior ligamentous structures are disrupted at site of injury
  • More superior vertebra subluxes forward by 50% or more of the body below
  • Usually occurs in lower cervical spine

Body of C4 is subluxed anteriorly on C5.
The inferior facet of C4(blue arrow) lies anterior to the superior facet of C5 (red arrow).
See normal relationship above

• May have associated fractures of the laminae and vertebral arch
• Quadriplegia frequently develops
  • If there is a fracture through posterior elements, less chance of neurologic injury as cord can decompress
• 85% neurologic deficits with locked facets

  

Seminars in Roentgenology, Jan 1978
Emergency Medicine Clinics of North America, August 1965