Scoliosis is a common medical condition defined by an abnormal lateral curvature of the spine. Determining the severity of this curvature is a fundamental step in medical management, as the “level” of scoliosis directly dictates the subsequent treatment plan. The assessment process provides a standardized way for healthcare providers to track the condition’s progression over time and make informed decisions about observation, bracing, or surgery. This system of measurement and classification is essential for achieving the best possible outcome for the patient.
Defining the Condition
Scoliosis is a three-dimensional spinal disorder, meaning the spine does not simply bend sideways but also involves a rotation and twisting of the vertebrae. This complex deformity is most often diagnosed during adolescence, known as Adolescent Idiopathic Scoliosis, where the cause remains unknown in approximately 80% of cases. Common visible signs include uneven shoulders or hips, a visible prominence of the rib cage when bending forward, and an overall uneven posture. While the spine normally has natural front-to-back curves, scoliosis is defined by an S- or C-shaped curve when viewed from the back.
The condition involves structural changes to the vertebrae, which is why it is considered a progressive deformation. The twisting motion within the spine pulls the ribs along, which creates a rib hump or a rotational asymmetry noticeable in the torso. A diagnosis is made when the lateral curvature measures 10 degrees or more.
Measuring Spinal Curvature
The standard method used by healthcare professionals to measure the degree of spinal curvature is the Cobb angle, determined from a standing X-ray of the spine. This measurement provides an objective, two-dimensional quantification of the curve, used to diagnose and monitor the condition. To calculate the Cobb angle, the physician first identifies the “end vertebrae,” which are the most tilted vertebrae at the top and bottom of the curve.
A line is drawn along the superior endplate of the uppermost tilted vertebra and a second line is drawn along the inferior endplate of the lowest tilted vertebra. Perpendicular lines are then drawn from these two endplate lines. The angle created where these two perpendicular lines intersect is the Cobb angle, expressed in degrees. Although scoliosis is a three-dimensional problem, the Cobb angle is the standard for quantifying the magnitude of the curve in the coronal (side-to-side) plane. Consistent positioning during X-rays is necessary for accurate comparison over time, as a measurement error margin of about five degrees is established.
Classification of Severity
The Cobb angle is the foundation for classifying scoliosis into mild, moderate, and severe groups.
Mild Scoliosis
Mild scoliosis is defined by a Cobb angle measuring between 10 and 25 degrees. Curves in this range are typically monitored closely with regular X-rays, often every four to six months, especially in patients who are still growing. Mild cases are usually asymptomatic and may only cause minimal cosmetic concerns.
Moderate Scoliosis
Moderate scoliosis corresponds to a Cobb angle between 25 and 40 degrees. At this level, the curve becomes more significant, and there is a higher risk of progression, particularly during growth spurts.
Severe Scoliosis
Severe scoliosis is generally classified as a curve measuring 40 degrees or more, though some surgical thresholds begin at 45 or 50 degrees. Curves in the severe range carry a high risk of continued progression, even after skeletal maturity, and may lead to functional impairments or cardiopulmonary complications.
Treatment Based on Severity
The classification of the Cobb angle serves as a roadmap for determining the appropriate treatment strategy.
Observation (10–25 Degrees)
For mild curves, the typical protocol is observation, often referred to as “watchful waiting,” to ensure the curve does not worsen. This approach is combined with periodic physical examinations and X-rays to track any curve progression.
Bracing (25–40 Degrees)
When the curve progresses into the moderate range in a patient who is still growing, bracing is recommended to halt the curve’s progression and prevent the need for surgery. Braces are custom-fitted devices designed to apply pressure to the outside of the curve, holding it in place. Success with bracing is directly related to the number of hours the brace is worn daily, with full-time wear often defined as 13 to 18 hours.
Surgery (40+ Degrees)
Surgical intervention, most often spinal fusion, is reserved for severe curves, generally those exceeding 40 to 50 degrees. The goal of surgery is to correct the spinal deformity and prevent further progression by permanently fusing the affected vertebrae together using bone grafts and metal rods. This procedure is necessary when the curve magnitude threatens to compromise physical function or when the curve progresses despite bracing.