Cobb's angle, a measurement used for
evaluation of curves in scoliosis on an AP radiographic projection
of the spine (Fig.1). When assessing a curve the apical vertebra is
first identified; this is the most likely displaced and rotated
vertebra with the least tilted end plate. The end/transitional
vertebra are then identified through the curve above and below. The
end vertebra are the most superior and inferior vertebra which are
least displaced and rotated and have the maximally tilted end plate.
A line is drawn along the superior end plate of the superior end
vertebra and a second line drawn along the inferior end plate of the
inferior end vertebra. If the end plates are indistinct the line may
be drawn through the pedicles. The angle between these two lines (or
lines drawn perpendicular to them) is measured as the Cobb angle. In
S-shaped scoliosis where there are two contiguous curves the lower
end vertebra of the upper curve will represent the upper end
vertebra of the lower curve. Because the Cobb angle reflects
curvature only in a single plane and fails to account for vertebral
rotation it may not accurately demonstrate the severity of three
dimensional spinal deformity. As a general rule a Cobb angle of 10
is regarded as a minimum angulation to define scoliosis.
Measuring Cobb's Angle
 
|
