Introduction:
Sagittal spinal curvatures in children are commonly assessed using isolated parameters, without considering compensatory mechanisms in adjacent anatomical segments. This approach limits diagnostic accuracy and the clinical usefulness of existing postural classifications.

Aim:
The aim of the present study was to develop a nine-type postural classification based on the combined assessment of thoracic kyphosis and lumbar lordosis in school-aged children.

Material and methods:
A cross-sectional observational study was conducted in 303 children aged 10–12 years (47.2% girls). Body posture was assessed under standardized laboratory conditions using the DIERS Formetric III 4D raster stereography system. Thoracic kyphosis and lumbar lordosis angles were used to define nine sagittal posture types, which were subsequently analyzed in relation to compensatory alignment patterns in other body segments.

Results and conclusions:
Normal posture was found in 29.0% of participants, while sagittal postural deviations occurred in 71.0%. The most frequent abnormal patterns were reduced thoracic kyphosis with normal lumbar lordosis (21.8%) and with reduced lumbar lordosis (15.5%). Postures with increased thoracic kyphosis were less common (11.0%). Significant sex-related differences were noted in thoracic and lumbar curvature angles (p < 0.01), with small effect sizes (Cohen’s d < 0.20). Each posture type showed distinct compensatory features involving pelvic alignment, hip extension, knee position, and foot-loading patterns. Sagittal postural disturbances are prevalent in children aged 10–12 years, with reduced thoracic kyphosis—often accompanied by reduced lumbar lordosis—being the dominant pattern. The nine-type classification differentiates sagittal postural phenotypes and identifies characteristic multisegmental compensatory mechanisms, supporting the need for comprehensive, individualized postural assessment and therapy planning.