Variations in the sagittal plane precede the development of scoliosis: a proof of concept.

Idiopathic scoliosis in man is believed to be related to the unique human sagittal profile. Patients with a thoracic scoliosis have a longer, more proximal, posteriorly inclined segment of the spine as compared to lumbar scoliosis and controls, whereas patients with a lumbar scoliosis have a more caudal, shorter and steeper posteriorly inclined segment. In 22q11.2 deletion syndrome, half of the patients develop a scoliosis that is very similar to idiopathic scoliosis and may serve as a model for the general population. In our center, all patients with 22q11.2 deletion syndrome older than 6 years receive standardized radiographic spine imaging every 2 years to screen for scoliosis. In this prospective proof-of-principle study the goal was to determine whether there are differences in sagittal alignment between patients that develop scoliosis vs. controls before the onset of scoliosis, and obtain data to perform a power calculation for future studies. To capture the sagittal shape of the spine into one risk factor for development for scoliosis, we combined relative length and magnitude of dorsal inclination into a new parameter: the posterior inclined triangle surface (PITS). We included 31 patients with initially straight spines, five developed a thoracic scoliosis and seven developed a (thoraco)lumbar scoliosis after a mean follow-up of 3.4 years. The PITS was considerably higher in the group that developed scoliosis as compared to the controls (59 vs 43). Based on this pilot study, we have identified a potential overall sagittal profile risk parameter for the development of idiopathic scoliosis.

Anterior lengthening in scoliosis occurs only in the disc and is similar in different types of scoliosis.

Relative anterior spinal overgrowth (RASO) was proposed as a generalized growth disturbance and a potential initiator of adolescent idiopathic scoliosis (AIS). However, anterior lengthening was also observed in neuromuscular (NM) scoliosis, was shown to be restricted to the apical areas and to be located in the intervertebral discs, not in the bone. In this study the goal was to determine if other scoliotic curves of known origin exhibit the similar mechanism of anterior lengthening without changes in the vertebral body. Therefore CT-scans of 18 patients in whom a short segment congenital malformation had led to a long thoracic compensatory curve without bony abnormality were included. Of each vertebral body and intervertebral disc in the compensatory curve, the anterior and posterior length was measured on CT-scans in the exact mid-sagittal plane, corrected for deformity in all three planes. The total AP% of the compensatory curve in congenital scoliosis showed a lordosis (+1.8%) that differed from the kyphosis in non-scoliotic controls (-3.0%; p<0.001), and was comparable to AIS (+1.2%) and NM scoliosis (+0.5%). This anterior lengthening was not located in the bone; the vertebral body AP% showed a kyphosis (-3.2%), similar to non-scoliotic controls (-3.4%), as well as AIS (-2.5%) and NM scoliosis (-4.5%; p=1.000). However, the disc AP% showed a lordosis (+24.3%), which sharply contrasts to the kyphotic discs of controls (-1.5%; p<0.001), but was similar to AIS (+17.5%) and NM scoliosis (+20.5%). The results demonstrate that anterior lengthening is part of the three-dimensional deformity in different types of scoliosis and is exclusively located in the intervertebral discs. The bony vertebral bodies maintain their kyphotic shape, which indicates that there is no active bony overgrowth. Anterior lengthening appears to be a passive result of any scoliotic deformity, rather than being related to the specific cause of AIS.