Scoliosis is an appreciable lateral deviation from the normally straight vertical line of the spine. It affects females more than males. When viewed from the back the spine should be straight and the shoulders and pelvis should be level. When viewed from the side, the spine has four curves. The cervical and lumbar curves in the neck and low back should gently arch forward toward the chin and belly. The thoracic spine of the ribcage and the sacrum at the pelvis level should gently arch backwards.
The gentle curves of the spine dissipate vertical loads through opposing arches rather than a straight rod. The curves add spring to the spine for running and jumping. The curves of the spine also increase the mechanical advantage of the spine. Twisting about the axis of the spine moves the curves of the spine through their individual arcs. The curves of the spine increase the torque. This adds power to leg and arm action such as running and throwing.
Abnormal sideways curvatures of the spine can be caused by: congenital spinal deformities such as hemi vertebra in which the block shape of the vertebra is distorted; genetic conditions, although no gene has been found; neuromuscular problems usually due to disease or injury; and leg length discrepancy, which can be caused by a congenital defect, disease or injury.
However more than eighty percent are considered idiopathic meaning no known cause. One possibility researchers suspect is that some cases may be due to genetic mismatch, so to speak, between the intended length of the spine versus the length of the spinal cord. In other words, the spinal cord tethers (holds back) the spine not allowing it to fully straighten. The oversize spine relative to the cord then compensates by bending to decrease its length.
Other Abnormal Curvatures of the Spine
There are other abnormal curvatures and these occur in the anterior to posterior plane as opposed to side to side or the lateral deviation of scoliosis.
Normally, as was mentioned above, the cervical spine and lumbar spine have the same lordotic curve, that is the concavity or open part of the curve is toward the rear. The thoracic and sacral spines have kyphotic curves, that is the concavity of the curve is toward the front of the body. Kyphosis (osis means abnormal) is where the spine’s normal lordotic curve becomes kyphotic. This generally occurs in the cervical spine due to it’s lack of stability and, therefore, vulnerability to trauma. Lordosis is where the spine’s normal kyphotic curve becomes lordotic.
There are also instances where the spine loses it’s normal curvature and appears straight or straighter than usual. When this occurs in the cervical spine it is termed a military neck but can occur in all areas of the spine in different degrees.
Affects of Abnormal Curves of the Spine
Abnormal curvatures of the spine affect more than just the vertebra. They also affect the contents of the spinal canal which includes, the arterial blood supply routes, the vertebral venous plexus drainage routes, and the spinal cord.
In addition, abnormal curvatures of the spine affect the level of the hips and shoulders. When the hips and shoulders distort they deform the soft tissue tunnels that contain nerves and blood vessels such as thoracic outlet tunnels where nerves and blood vessels travel to the arms from the vertebral foramen and sciatic tunnels in the pelvis that travel to the legs. Unleveling the pelvis also causes shifts in weight bearing loads on the pelvis.