The normal spine, when viewed from behind, appears straight throughout its entire length. However, when one looks at the spine from the side, there are two visible curvatures. There is a gentle rounding of the upper back from the shoulders to the bottom of the ribcage known as thoracic kyphosis and an opposite curve in the lower back known as lumbar lordosis. These two opposite curvatures of the spine are necessary in the normal spine to balance the trunk and head over the pelvis. A normal thoracic spine extends from the 1st to the 12th vertebra and should have a slight kyphosis ranging from 20o to 45o. When the “roundness” of the upper spine increases past 45o it is called “hyperkyphosis”. Scheuermann’s kyphosis is the most classic form of hyperkyphosis and is the result of wedged vertebrae that develop during adolescence. The cause is not currently known and the condition appears to be multi-factorial and is seen more frequently in males than females.
Definition and Classification
In the first six to eight weeks of embryonic life, a genetic mistake occurs that results in the failure of formation or failure of segmentation on the front part of one or more vertebral bodies and disc. This defect causes the spine to develop a sharp forward angle as it grows. The forward bend of the spine is called kyphosis and is considered to be congenital as it occurred prior to birth. Congenital kyphosis is not passed through families but rather something that happened for no known reason. The spine may appear straight when viewed from the front, or there may be congenital scoliosis as well. There are two basic types of congenital kyphosis: failure of formation and failure of segmentation. The failure of formation (Type I deformity) of a portion of one or more vertebral bodies results in kyphosis that usually worsens with growth (Figure 1). The deformity is usually visible at birth as a lump or bump on the infant’s spine. The failure of segmentation deformity (Type II deformity) occurs as two or more vertebrae fail to separate and to form normal discs and rectangular bones. This type of congenital kyphosis is often more likely to be diagnosed later, after the child is walking.
On X-Ray, normal vertebrae are close to rectangular in size when viewed from the side. Thoracic vertebrae are somewhat smaller in the front than the back (to create kyphosis), while lumbar vertebrae are the opposite to create lordosis. Congenital kyphosis creates more kyphosis than expected for the particular region of the spine. As with congenital scoliosis, there is potential for defects in other organ systems. After X-rays confirm the diagnosis, the physician may order additional tests to determine if occult abnormalities are present in the spinal cord, kidneys, cardiac or gastrointestinal system. The MRI provides additional information regarding the abnormal growth potential and may assist in predicting progression of the spinal deformity (see Figure 1). From a clinical perspective, it is important to monitor the child’s leg strength and ability to walk. More severe kyphosis can place significant pressure on the spinal cord causing myelopathy (spinal cord compression). Young children may be perceived as being late walkers when they actually have spinal cord compression. In most instances, however, there is not significant pressure on the nerves.
Failure of formation deformity can present with 30o – 60o degree deformities. With the rapid growth of the skeleton in the first year of life, progression is highly likely. Failure of separation (segmentation) deformity has a slower rate of worsening and may not become a surgical curve until adolescence.
Observation is usually the first method of treatment for a young child with a spinal deformity. The visits to the physician will be spaced according to the likelihood of measuring a significant change in the X-ray between each visit. Type I deformities are more likely to have several visits per year. Severe or progressive congenital kyphosis deformities greater than 45o or kyphosis associated with neurologic weakness are usually treated surgically. Early surgical intervention generally produces the best results and can halt progression of the curve. The type of surgical procedure will depend on the nature of the abnormality.
Bracing Unfortunately, bracing is not recommended when treating congenital scoliosis. Clinical studies fail to demonstrate improved patient outcomes with this method of treatment.
In Situ Fusion
The surgical choice for a progressive kyphotic deformity is a solid fusion or arthrodesis of the deformed vertebrae. The fusion may also include one normal vertebra above and one normal vertebra below this area. Bone graft from the patient or tissue bank is placed posteriorly, on the back of the spine, along the area of the abnormality. In severely angulated curves, additional bone graft may be placed anteriorly, on the front of the spine, as well as from behind. The fusion may be performed with or without the use of instrumentation. In situ fusion is a non-instrumented fusion without correction of the angulation. The bone graft will require 4-6 months to mature into a solid fusion mass. During the postoperative period the fusion must be protected with a cast or brace until X-rays demonstrate a solid fusion.
Instrumented Fusion and Osteotomy
With progressive kyphotic curves in older children, surgery may include instrumentation (rods, hooks, and screws) that helps to correct the deformity. If the spinal cord is unable to tolerate the manipulative techniques that “straighten” the spine, the surgeon may consider the removal of the mis-shapened vertebrae to realign the spine. The postoperative course remains the same until the fusion mass is determined by X-ray to be solid. Your surgeon may recommend an osteotomy (bone-cutting procedure) to re-align the spine. Pedicle subtraction osteotomies work by removing the bone in the back of the vertebra so the bone can be collapsed backwards. Vertebral column resections allow resection of the front and the back of the spine from a posterior procedure. The surgeon may also recommend separate approaches from the front and the back of the spine.