Convexity, C vs S curves, kyphoscoliosis, Adams test, and Cobb angle staging. One common error ends the confusion permanently.
Most students hear "right rib hump" and guess "left convexity." This game locks the correct reflex in before the board test can punish it.
School screening flagged a spinal asymmetry. You perform the Adams forward-bend test. A posterior rib prominence becomes visible as she bends forward.
The rib prominence is on one side. Tap to name it:
The rib hump is not a hint. It is the answer. The rib hump appears on the convex side because the vertebrae rotate toward the convexity, pushing the convex-side ribs posteriorly. When you see a right rib hump on Adams test, that side is the convexity. Name it right convex. That distinction drives everything that follows.
Every board question about scoliosis description reduces to these three statements. Learn the mechanism, not the memorized list.
A scoliosis is named by the side to which the curve bows outward. If the spine arches to the right, the curve is called right convex (or simply "right scoliosis" or "right thoracic scoliosis"). Never named by the concavity.
Vertebrae rotate toward the convexity. The transverse processes on the convex side swing posteriorly, dragging the attached ribs with them. That posterior protrusion is the rib hump. Spinous processes simultaneously rotate toward the concavity (they move opposite to the vertebral bodies). Right rib hump = right is the convexity. Always.
A single lateral arc makes the spine look like the letter C. When there is a primary structural curve in one direction plus a compensatory curve curving back in the opposite direction, the spine looks like the letter S. The primary curve has the larger Cobb angle.
Think about the physics. The vertebral body rotates right in a right convex curve. The right-side transverse process swings backward, and the ribs pivot with it. The left-side ribs swing forward. From behind, you see a right posterior hump and a left anterior chest prominence. The hump is always the convex side. Know your clues.
The shape tells you whether you're dealing with a simple structural problem or a spine that has developed a compensatory response to stay balanced.
One structural curve. The spine bows in a single direction. Adams test shows one rib hump. Single Cobb angle measured. Most visible on the AP radiograph as one arc. Example: right thoracic C-shaped scoliosis, Cobb 24 degrees.
Two curves: one primary (structural, larger Cobb angle) and one compensatory (flexible, smaller Cobb angle). The compensatory curve develops to keep the head centered over the pelvis. Adams test may show rib humps or paraspinal prominences on both sides. The primary curve is named first, e.g., "right thoracic, left lumbar S-shaped scoliosis."
When you see two curves on the PA radiograph, identify the primary curve by Cobb angle: the larger the Cobb angle, the more structural the curve. The compensatory curve is smaller and tends to be more flexible on bending films. Most boards ask you to name the primary curve. That's the one with the bigger number.