Tethered Cord and Scoliosis
A tethered spinal cord syndrome is a neurological disorder whereby the spinal cord becomes attached to the spinal column, limiting the movement of the spinal cord. Tethered means to restrict or bind. In normal persons, the spinal cord hangs freely in the spinal canal, allowing it to move, bend and stretch. A tethered cord is caused by tissue attachments such as lipoma, tumor, history of spine surgery, or trauma leaving scar tissues, diastematomyelia (split spinal cord), or dermal sinus tract (a rare congenital deformity). These attachments cause an abnormal stretching of the spinal cord, making it immobile. It is being pulled tightly at the end, reducing blood flow to spinal nerves, thus causing damage to the spinal cord. Tethering most often occurs in the lower lumbar region of the spine causing lower back pain. It can happen before or after birth in both children and adults.
The tethered spinal cord is closely associated with spina bifida (myelomeningocele and meningocele), except for spina bifida occulta. However, a tethered cord can also occur alone or with spina bifida. In a baby with spina bifida, the spinal cord is still attached to the surrounding skin and is prevented from ascending normally. Thus, at birth, the spinal cord is low-lying or tethered. Cases like these are handled by surgeons to surgically separate myelomeningocele from the skin and “sealed” at birth. The spinal cord, which has grown in this position, stays at the same location after the closure, therefore, forming scars at the surgical site. As the spine continues to grow in the affected child, the spinal cord is stretched, allowing symptoms to appear as a result of lack of blood supply to the spinal cord. Read more about spinal growth and Risser Sign.
Symptoms of a Tethered spinal cord syndrome
In adults, the spinal cord will stretch during normal activities such as bending, twisting, and stretching movements. A rough estimation of 50 percent of spina bifida children will require spine surgery at some point to untether the spinal cord. If a symptomatic tethered cord is left untreated, it can lead to progressive, neurological, orthopedic, and urological deterioration.
There are a few apparent symptoms of a tethered spinal cord. These can appear at any stage in life, but more prominent during the growth period. The common symptoms are scoliosis, loss of nerve function, spine pain, and changes in bladder function.
Now, let’s talk about the association between tethered cord and scoliosis. In tethered cord syndrome, in patients with scoliosis, the curvature is typically proximal to the level of the surgical repair site and not associated with vertebral anomalies. They differ from idiopathic curves as they affect boys and girls at an equal ratio; dextro-scoliosis (curvature to the right) and levo-scoliosis (curvature to the left) are equally frequent and occur in preadolescence. Even though it is recognized that tethered cord at the repair site causes neurological deterioration, many have questioned whether tethered cord actually causes scoliosis.
Tethered Cord as a Cause in Scoliotic Spine
A study titled “Tethered Cord as a Cause of Scoliosis in Children with a Myelomeningocele” proved that tethered cord alone was the most common cause of scoliosis proximal to the repair site. In the tethered spinal cord, abnormal function in ascending intersegmental pathways results in ischemic injury at the repair site. This is believed to result in asymmetric tone or imbalance in para-thoracic muscles, leading to scoliosis. Untethering would release the local ischemic effects of tethering and return balance to the ascending system.
If the cause of scoliosis is unknown, a tethered cord may be the cause. And as such, MRI is typically used to rule out or show the tethering site. Surgery to untether the cord should be performed to prevent the curve from getting so severe that it obstructs normal function and movement. After untethering, a follow-up within six months is necessary to show whether untethering has helped stop the progress of the scoliotic curve. If there is an improvement in curvature or non-progression in a curve, a major surgical intervention such as spinal fusion may not be necessary.