The human spine has natural curvatures. When you look at a back from behind, the spine should be straight and centered over the pelvis. However, when you look at the spine from the side, the curves are designed to maintain balance as the spine is behind organs in the chest and abdomen. The spine has two alternating curves to create an “S” like shape. In the neck and low back there is normally an inward curvature or sway back known as lordosis. In the thoracic spine and sacrum there is an outward curvature known has kyphosis or hunchback. These curves normally balance out each other so that when the patient stands they are well balanced with their head straight above their hips when viewed from the side. Standing in this position minimizes the effect of gravity and allows the patient to stand with the best posture and use the least energy when moving or walking.
Flat back syndrome is an abnormal condition where the spine loses its natural low back curve to become flat. The spine becomes imbalanced and the patient leans forward. Patients with flat back syndrome typically notice troubles standing upright or have ongoing back or leg pain. Symptoms usually worsen as the day goes on and the patient feels they lean further and further forward the longer they try to stand upright. The severity of the symptoms usually depends on the amount of curvature present and difficulties with standing erect.
Here is a lesson from Dr. Jarl Kleinman!