Postural kyphosis is caused by slouching and other forms of bad posture, which tend to stretch the spinal ligaments. This increases the natural curvature of the spine. It usually develops during adolescence, and is generally more common in girls than boys.
The remaining forms of kyphosis are structural, that is caused by an underlying, structural, problem which may affect the vertebrae, inter-vertebral discs, ligaments and/or muscles.
Congenital kyphosis is present at birth, and is often very severe. It is caused by physical defects in the spine, including abnormal (or misshapen) vertebrae that fail to separate. Neuromuscular kyphosis is typically found in children with primary, neuromuscular conditions, including cerebral palsy; spinal bifida; and muscular dystrophy. Neither form is particularly common.
Scheuermann’s disease is named after the Danish radiologist who first described the condition in 1921. It occurs when the vertebrae in the upper spine begin to grow abnormally (due to a condition called osteochondrosis). The back of each vertebra grows more quickly than the front, leading to a wedge-shaped bone. As a result, the patient displays a pronounced curve in the upper spine (the apex of which is normally around thoracic vertebrae T7 – T9). Scheuermann’s kyphosis usually develops during adolescence, while the spine is still growing.
In the elderly, degenerative changes in the spine can lead to dowager’s hump. For example, an osteoporotic fracture may cause one of the vertebrae to collapse, resulting in a loss of height of some 15-20%. If the collapse is even, the normal curvature of the spine will be maintained. However, if the collapse is uneven (as it often is), a wedge-shaped vertebra is produced. If this happens in the thoracic spine, and the vertebrae slopes from back-to-front (or posterior to anterior), the normal, kyphotic curvature will be increased. Degenerative kyphosis can also be caused by thinning of the inter-vertebral discs, weak muscles and weak ligaments.
How is it diagnosed?
In visual terms, kyphosis is fairly easy to diagnose (a pronounced, dowager’s hump is often very noticeable). In strict, medical terms however, the curvature of the thoracic spine is defined by an angle referred to as the Cobb angle. Normal thoracic curves display an angle of somewhere between 30° and 40° (the mean is 34°). As a result, kyphosis is formally diagnosed for curves > 40°.
Distinguishing between structural and postural kyphosis is also relatively easy. If the increased curvature disappears when the patient lies down, the condition is postural; if not, it is almost certainly structural.
Scheuermann’s kyphosis is defined by three (or more) consecutive vertebrae that display wedging angles in excess of 5° for this reason, Scheuermann’s disease is usually confirmed by the use of X-ray.
Some patients with the condition also display a mild Scoliosis (30%); that is, an additional, lateral (or side-to-side) curvature of the spine.