Last Updated on December 8, 2023
Rib vertebral angle measurement and its significance were brought in by Dr Mehta. Measurement of this angle has an important implication in infantile idiopathic scoliosis as it differentiates between the progressive and resolving types of scoliosis.
Infantile idiopathic scoliosis is first diagnosed between birth and 3 years of age. This category comprises about 1% of all idiopathic scoliosis in children and 60% of patients are males. The diagnosis of idiopathic infantile scoliosis is based on the age of onset, the absence of any other spinal cord problems, the location of the curve, findings on physical examination, and x-rays.
Relevant Anatomy
The rib cage is part of the thorax. The thoracic spine is connected to the rib cage. The joints between the costovertebral joints and the vertebra are called the costovertebral joints. The normal relationship between rib and its corresponding thoracic vertebra can be affected by spinal deformities.
The rib cage and the costovertebral joints are known to contribute to the stability of the thoracic spine. That is why fractures of the thoracic spine especially T1-T10 are less common as compared to thoracolumbar junction (T10-L2) and lumbar spine.
However, the clear relationship between the rib cage and the thoracic spine is not fully concluded.
Rib vertebral angle was introduced by Dr Min H Mehta in Mehta in 1972.
It was originally described to differentiate between resolving and progressive infantile scoliosis.
Scoliosis is an abnormal curvature of the spine where spine curves laterally making one side convex and other concave. In infantile scoliosis, the spinal curvature appears before the age of 3 years.
The rib vertebral angle method is a valid and reproducible method and has been often used repeatedly. It has been used to analyze the effects of various surgical procedures on the rib cage.
It has also been employed in the studies of the shape of the thorax during growth.
Mehta’s rib vertebral angle degree difference measures the difference between values of rib vertebra angles on either side.
How To Measure The Rib Vertebral Angle?
The angle measurement is done on anteroposterior x-ray
- A line is drawn perpendicular to the apical vertebral endplate [a]
- Another line is drawn from the mid-neck to the mid-head of the corresponding rib [b]
- The angle between [a] and [b] line is called the rib vertebral angle
Rib Vertebral Angle Difference
The rib vertebral angle difference (RVAD) has an important bearing. Rib vertebral angle difference is the difference between the RVA of either side on the same vertebral level.
In scoliosis, the curve has a convex side and an opposite concave side.
The difference between the values of the rib vertebral angles on the concave and convex sides of the curve is rib vertebral angle difference or RVAD.
Significance
If the convex apical rib head does not overlap the apical vertebral body, a curve with an initial RVAD of 20 degrees or more is considered progressive.
If the convex apical rib head overlaps the apical vertebral body on the anteroposterior radiograph, progression is highly likely.
Thus RVAD is an important tool for determining what kind of curve is more likely to progress and accordingly measures can be instituted for aggressive treatment and follow-up.
Though originally intended for use in infantile scoliosis, the RVA has also been used in other types of scoliosis as well.
Recently, this angle has been computed in 3-dimensional form and called RVAD 3D. This measurement has been shown better and more promising by the studies.
3D measurements include apical morphology including axial rotation and apical lordosis which indicates a difference in the severity of the apical deformation.
References
- Mehta MH. The rib-vertebra angle in the early diagnosis between resolving and progressive infantile scoliosis. J Bone Joint Surg Br. 1972 May;54(2):230-43. [Link]
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Brink RC et al. What Is the Actual 3D Representation of the Rib Vertebra Angle Difference (Mehta Angle)? Spine (Phila Pa 1976). 2018 Jan 15;43(2):E92-E97. [Link]
