There is a relationship of the thoracic spine to sacroiliac functioning. The thoracic region does manifest itself with many varieties of kyphosis.
Some thoracic regions are flat, some are mildly kyphotic and some are moderately kyphotic.
Beyond this, we witness the hyperkyphotic thoracic curves. There is a principle which should be applied to the thoracic kyphotic curvature, and which may include the upper lumbar spine. The more thoracic kyphotic curvature, the more lumbar and cervical lordosis or tendency for such. Severe thoracic kyphosis could involve more lumbar levels in hyperlordosis. An effective alternative is to contact the sacral region about midway or caudally and traction the sacrum inferiorly and anteriorly.