Scoliosis comes generally in two forms “S” or “C” type curve patterns. “S” curves commonly referred to as double majors have a curve in the thoracic spine and a curve in the lumbar spine which are similar in size. The typical pattern for an “S” curve scoliosis is a right thoracic and a left lumbar meaning the concave side in a left lumbar curve is to the right. This would look like an S from the front or a backward S from the back. “S” curves will typically demonstrate a posture presentation that is fairly centered on the midline when viewed from the front or back where their head, torso, and pelvis line up but their eyeline, shoulder line, and hip line will be tilted. The double curve type will lead to two noticeable bumps that form as a “S” scoliosis progresses beyond 30 degrees. When a bending test is performed and the patient is viewed from behind while they bend down to touch their toes the examiner will notice a protrusion by the shoulder blade and a protrusion by in the lower back muscles.
This protrusion is due to the natural adaptation of the postural muscles to the scoliosis and is not causing the scoliosis. The smaller intrinsic or deep smaller muscles that connect each individual bone of the spine are influenced by the brain and the signal from the brain to the deeper smaller muscles is most likely the cause where these protruding muscles along the outside of the curvatures are secondary adaptations. So the brain tells the spine what position to be in and the posture muscle set the tone to stabilize this position as neutral. Since the spine becomes curved the muscles of posture on the outside of the curve will increase in mass,called hypertrophy, due to constant use for stabilization whereas the inside posture muscles will no longer be needed to stabilize the spine and will atrophy, decrease in mass, due to disuse. Think of the posture muscles as a light switch with a dimmer attached, the dimmer switch can be changed to either allow more current or less current to the bulb making it brighter or dimmer where the outside of the scoliosis curvature is given a lot of current and gets brighter (hypertrophy) and the inside of the curvature gets very little current and is dim(atrophy). The larger the scoliosis becomes the more noticeable the difference in brightness or muscle tone. It is not a case of weak or strong but rather how much current is being supplied due to need to remain stable in gravity.
Secondary adaptations to the “S” curve will involve disc wedge deformation and eventually bone wedge deformation. These secondary adaptations occur due to cellular remodeling. Direct pressure on the cartilaginous discs and the individual vertebrae will stimulate or inhibit growth creating an actual difference in the height of the disc or bone. Ribcage deformation will become noticeable with much larger curves in this type of pattern and will be somewhat limited due to the smaller size of thoracic curvature. The ribcage and individual ribs will also deform due to direct pressure since bone remodels based on its stress demands (Heuter- Volkmann principle) when ribs are placed under excessive pressure they will change shape. As the spinal column bends and rotates in the thoracic region this will then create direct forces upon the ribs since they are attached to each individual thoracic vertebrae. The further the spine pushes laterally to the side the more forces will affect the entire cage adding to the ribcage deformation. If we go back to the bending test and notice the two protrusions that appear in an “S” pattern scoliosis the protrusion in the thoracic region will eventually become structural deformation because of the ribs becoming bent. Since the lumbar spine does not have ribs attached the bulging protrusion in this region is limited to the muscle and remains purely soft tissue even in adulthood whereas the individual vertebrae regardless of location will become structural adaptation with time.
“C” curves are a bit misunderstood and can probably be defined differently depending on who you ask. “C” curves generally refer to a scoliosis which has a single major curve in the shape of the letter “C” in either the thoracic spine or the lumbar spine. The real distinguishing factor between “S” pattern and “C” pattern scoliosis is whether or not the compensation curves cross the midline by at least half the distance of the primary curve giving it the S shape. “C” curves generally will demonstrate an awkward posture, meaning the patients neutral stance will appear like they are favoring one leg. “C” curves formed in the thoracic spine will demonstrate much larger ribcage deformity based on the sheer number of thoracic vertebrae involved in this type of curve pattern. C type thoracic curves will have noticeable body disfigurement not easily hidden by clothing especially in curves approaching 40 degrees or higher. The soft tissue adaptations are less prominent and generally deeper due to the structural integrity of the ribcage compared to the lumbar spine where a “C” curve located in this region will demonstrate very large protruding muscle growth.
The ribcage deformity is not corrected by any form of bracing or scoliosis fusion surgery. The only way to reduce or eliminate the larger more angulated rib deformations is to perform a rib resection surgery where they shave it off like a side of beef. The moral of this story is that scoliosis is a very complex organized deformity that presents very young and if not attacked head on in the early stages of the game will lead to an enormous amount of tissue adaptations that become irreversible. So waiting around for this process to unfold is obviously a bad decision.