Lordosis

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Overview
Lordosis (commonly referred to as swayback, saddle back, or hyper-lordosis) is a medical term used to describe an inward curvature of a portion of the vertebral column. Two segments of the vertebral column, namely cervical and lumbar, are normally lordotic, that is, they are set in a curve that has its convexity anteriorly (the front) and concavity posteriorly (behind), in the context of human anatomy. When referring to the anatomy of other mammals, the direction of the curve is termed ventral. Curvature in the opposite direction, that is, apex posteriorly (humans) or dorsally (mammals) is termed kyphosis.

Lordotic curvatures of the vertebral column, also known as secondary curvatures are caused mainly because of the difference of thickness between the anterior and posterior part of the intervertebral disc. Those curvatures start to appear during the fetal period, but don't become evident until infancy.

Excessive lordotic curvature is also called hollow back, saddle back, and swayback. Common causes of excessive lordosis including tight low back muscles, excessive visceral fat, and pregnancy. Loss of lordosis is sometimes seen with painful spinal conditions. If rigid, usually after spinal fusion surgery, it is known as flat-back.

The familiar concave shape of the horse's back is, by extension, described as lordotic.

Lordosis behavior refers to the position that some mammals (cats, mice, rats, etc.) display when they are ready to mate.