Segmental endplate or segmental kyphosis angles include the monosegmental and bisegmental endplate angle as well as the vertebral compression angle and play a role in the stability assessment after spinal injuries.
The following angles might be used 1-3:
- monosegmental endplate angle or Gardner angle
- bisegmental endplate angle or Cobb angle
- vertebral compression angle (VCA)
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Usage
The measurements are used in the setting of subaxial and thoracolumbar spinal injuries and can help to evaluate spinal instability, predict functional outcomes and determine the respective treatment strategy 1-3.
Incomplete burst fractures (A3 fractures) count as an immediate stable spinal injury as long as the posterior ligament complex is intact and no neurological symptoms are present.
However, they are at risk of instability or progression to kyphosis and thus can cause functional problems 1-3.
Specifically, the monosegmental endplate angle has been recommended for use in a setting of vertebral compression fractures, where only one segment is involvement e.g. incomplete burst fractures (A3 fractures) or posterior tension band injuries with monosegmental vertebral body involvement (B2 fractures with an A3 component) 1.
The bisegmental endplate angle has been recommended for bisegmental pathologies e.g. complete burst fractures (A4 fractures or cervical F3 fractures)
Measurement
Measurements are conducted in a similar fashion as the Cobb angle with lines drawn along the superior and inferior endplates of the respective vertebrae and/or segments. The angle at the intersection point between the two lines is measured 1-3.
- vertebral compression angle: between the superior and inferior endplates of a fractured vertebra
- monosegmental endplate angle: or Gardner angle: between the superior endplate of the upper vertebra and inferior endplate of the lower vertebra of the affected segment
- bisegmental endplate angle: between the superior endplate of the upper vertebra and inferior endplate of the lower vertebra of the affected segments
Interpretation
Ideally the measured monosegmental or bisegmental angle is corrected for the normal kyphotic or lordotic values of the respective vertebral segments. This can be achieved by calculating the difference between the measured segmental endplate angle and the specific normal value for that segment 1.
A mono- or bisegmental endplate angle >15° can be considered as abnormal and especially if corrected for normal kyphosis or lordosis as a sign of instability 1.
History and etymology
Most fracture-related kyphosis measurements on lateral spine radiographs have been derived from the Cobb angle described by John R Cobb in 1948 4.