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|Classification and external resources|
|It has been suggested that Lumbar hyperlordosis be merged into this article. (Discuss) Proposed since July 2012.|
|Classification and external resources|
Lordosis is the inward curvature of a portion of the lumbar and cervical 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. Excessive or hyperlordosis is commonly referred to as swayback or saddle back, a term that originates from the similar condition that arises in some horses.
A major factor of lordosis is anterior pelvic tilt, when the pelvis tips forward when resting on top of the femurs.
A consequence of the normal lordotic curvatures of the vertebral column, (also known as secondary curvatures) is that there are differences in thickness between the anterior and posterior part of the intervertebral disc. Lordosis may also increase at puberty sometimes not becoming evident until the early or mid-20s. Imbalances in muscle strength and length are also a cause, such as weak hamstrings, or tight hip flexors (psoas).
Other health conditions and disorders can cause lordosis. Achondroplasia (a disorder where bones grow abnormally which can result in short stature as in dwarfism), Spondylolisthesis (a condition in which vertebrae slip forward) and osteoporosis (the most common bone disease in which bone density is lost resulting in bone weakness and increased likelihood of fracture) are some of the most common causes of lordosis. Other causes include obesity, kyphosis (spine curvature disorder in which the thoracic curvature is abnormally rounded), discitits (an inflammation of the intervertebral disc space caused by infection) and benign juvenile lordosis.
Excessive lordotic curvature is also called hyperlordosis, hollow back, saddle back, and swayback. Common causes of excessive lordosis include tight low back muscles, excessive visceral fat, and pregnancy. Although lordosis gives an impression of a stronger back, incongruently it can lead to moderate to severe lower back pain. Rickets, a vitamin D deficiency in children, can cause lumbar lordosis.
Measurement and diagnosis of lumbar lordosis can be difficult. Obliteration of vertebral end-plate landmarks by interbody fusion may make the traditional measurement of segmental lumbar lordosis more difficult. Because the L4-L5 and L5-S1 levels are most commonly involved in fusion procedures, or arthrodesis, and contribute to normal lumbar lordosis, it is helpful to identify a reproducible and accurate means of measuring segmental lordosis at these levels.
A visible sign of lordosis is an abnormally large arch of the lower back and the person appears to be puffing out his or her stomach and buttocks. Precise diagnosis of lordosis is done by looking at a complete medical history, physical examination and other tests of the patient. X-rays are used to measure the lumbar curvature, bone scans are conducted in order to rule out possible fractures and infections, magnetic resonance imaging (MRI) is used to eliminate the possibility of spinal cord or nerve abnormalities, and computed tomography scans (CT scans) are used to get a more detailed image of the bones, muscles and organs of the lumbar region. 
Lordosis of the lower back may be treated by strengthening the hip extensors on the back of the thighs, and by stretching the hip flexors on the front of the thighs.
Too much importance has been attributed to the abdominal muscles in maintaining a neutral spine position. They may help by pushing the internal organs against the spine hence alleviating the lumbar curvature but they can't rotate the pelvis backward while in a standing position. Also the lumbar erector spinae is not able to rotate the pelvis forward while standing, hence its strengthening is not to be avoided during lordosis treatment.
Only the muscles on the front and on the back of the thighs can rotate the pelvis forward or backward while in a standing position because they can discharge the force on the ground through the legs and feet. Abdominal muscles and erector spinae can't discharge force on an anchor point while standing, unless one is holding his hands somewhere, hence their function will be to flex or extend the torso, not the hip. Back hyper-extensions on a Roman chair or inflatable ball will strengthen all the posterior chain and will treat lordosis. So too will stiff legged deadlifts and supine hip lifts and any other similar movement strengthening the posterior chain without involving the hip flexors in the front of the thighs. Abdominal exercises could be avoided altogether if they stimulate too much the psoas and the other hip flexors.
Strengthening of the hip extensors, which are on the back of the thighs, and optionally stretching of the hip flexors, which are on the front of the thighs, will be enough to treat a lordosis in quite a short time. Anti-inflammatory pain relievers may be taken as directed for short-term relief. Physical therapy effectively treats 70% of back pain cases due to scoliosis, kyphosis, lordosis, and bad posture. Hypo-lordosis is more common than hyper-lordosis. Hypo-lordosis can be corrected non-surgically through rehabilitation exercises. Many different techniques exist to accomplish this correction. These exercises, if done correctly, may reduce symptoms in those with the typical presentation in 3-6 months. This type of treatment is typically provided by a chiropractor, though some physical therapists offer it as well.
Controversy regarding the degree to which manipulative therapy can help a patient still exists. If therapeutic measures reduce symptoms, but not the measurable degree of lordotic curvature, this could be viewed as a successful outcome of treatment, though based solely on subjective data. The presence of measurable abnormality does not automatically equate with a level of reported symptoms.
Lordosis can be also seen in animals, in particular horses and other equines. Usually called "swayback," soft back, or low back, it is an undesirable conformation trait. Swayback is caused in part from a loss of muscle tone in both the back and abdominal muscles, plus a weakening and stretching of the ligaments. As in humans, it may be influenced by bearing young; it is sometimes seen in a broodmare that has had multiple foals. However, it is also common in older horses whose age leads to loss of muscle tone and stretched ligaments. It also occurs due to overuse or injury to the muscles and ligaments from excess work or loads, or from premature work placed upon an immature animal. Equines with too long a back are more prone to the condition than those with a short back, but as a longer back is also linked to smoother gaits, the trait is sometimes encouraged by selective breeding. It has been found to have a hereditary basis in the American Saddlebred breed, transmitted via a recessive mode of inheritance. Research into the genetics underlying the condition has several values beyond just the Saddlebred breed as it may "serve as a model for investigating congenital skeletal deformities in horses and other species."
Lordosis behavior refers to the position that some mammalian females (including cats, mice, and rats) display when they are ready to mate ("in heat"). The term is also used to describe mounting behavior in mammalian males.
Lordosis in the human spine makes it easier for humans to bring the bulk of their mass over the pelvis. This allows for a much more efficient walking gait than that of non-human primates, whose inflexible spines cause them to resort to an inefficient forward leaning "bent-knee, bent-waist" gait. As such, lordosis in the human spine is considered one of the primary physiological adaptations of the human skeleton that allows for human gait to be as energetically efficient as it is.