In this commentary, Dr. M. N. Imrie from Children’s Hospital at Stanford University reviews congenital scoliosis — what it is and how it is treated. In addition, she offers an opinion on a new procedure called a pedicle subtraction osteotomy.
Anything “congenital” means it is present at birth. In the case of congenital scoliosis, there is a curvature of the spine caused by a defect in the vertebral (spinal) bone. There are several different types of spinal defects that can cause this type of congenital scoliosis.
The first is the failure of the vertebrae to form normally. For example, there may be only one half (one side or the other) of the vertebra. This type of defect or anomaly is called a hemivertebra (hemi means half). Or there may be a wedge shape to the normally block-shaped vertebra.
Either of these problems changes the way the vertebrae above and below the hemivertebra stack up. Without a squarish-shaped bone to rest on, the other bones tilt to one side. The effect is like dominoes: each bone shifts in position until the entire spine is listing or curved to one side.
That sounds fairly simple but it does tend to get a bit complicated when other structures are examined. The discs between the hemi- or block vertebra may be fairly normal but sometimes they are only partially there or completely missing.
Without these important supporting structures, the spine (and attached trunk) cannot grow normally. The surgeon must take all of these structural changes into consideration when forming a plan of care. But before we look at treatment options, let’s finish the discussion of types of spinal defects a child can be born with that cause scoliosis.
Besides the formation problems already discussed, there can also be what’s referred to as failures of segmentation. This means instead of each vertebral body being formed separately with discs and endplates in between each adjoining vertebra, two (or sometimes more than two) vertebra are fused together and form one unit.
Segmentation problems are divided further into two groups: block and bar. Block segmentation means both sides of the bone are solid. Bar segmentation refers to just one side (either right or left but not both) being fused. It is possible to have both types if more than two segments are involved.
Now, what about treatment? Any parent, family member, or caretaker of a child with this condition wants to know what can be done? Bracing, casting or doing nothing have not been shown helpful. The curve gets worse.
And bracing has even been shown to keep the chest wall from moving so the trunk cavity doesn’t grow properly. Rib and trunk expansion are essential for proper breathing and growth of all the internal organs. The next likely solution is surgery.
But there’s nothing simple or easy about this problem. There are many different types of surgery that can be done. Fusion-based approaches have been used for a long time with differing results. The deformed vertebra is removed and the remaining vertebrae above and below are fused together with bone graft and hardware fixation (metal plates, rods, screws).
Fusionless surgery has also been developed. The surgeon inserts “growing” rods that can be lengthened as the spine grows. This keeps the child from having stunted growth and makes room for all the organs. Each of these approaches (fusion versus fusionless) has its own advantages and disadvantages based on “indications” (i.e., when to use it). The child’s age and the severity of the deformity are key factors in the decision.
But a new approach has been proposed by a group of Chinese surgeons. The pedicle subtraction osteotomy for the treatment of mild to moderate congenital scoliosis was reportedly safe and “simple.” It’s that word “simple” that Dr. Imrie takes some exception to.
In this procedure, the surgeon removes a pie-shaped piece from the deformed hemivertebra. Along with the piece of vertebral bone, they also remove the transverse process — that’s the bony bump you feel along the back of your spine. The effect is to allow the remaining edges of bone to collapse toward each other.
The surgeon guides either side of the remaining bone fragments to move together — enough to close the gap formed by removing the piece of bone. The end result is correction of the curve. It’s called a subtraction osteotomy because only a portion of the deformed vertebra is removed or taken away (subtracted).
But there are several limitations to this procedure. First, the hemivertebra has to be large enough to allow a chunk of it to be removed. Some are too small for that. Second, since only part of the bone is removed, the curve correction is less than if it were removed completely. And third, this method won’t work if there is a rigid bar of bone present because of a segmentation deformity.
Dr. Imrie agrees that the reduced operative time and smaller blood loss are important advantages of the subtraction osteotomy. But the surgical technique described with this approach is not simple. Highly skilled spine surgeons with the right kind of experience and expertise are needed to perform such procedures.
In addition, the patient must be monitored carefully for any damage to the spinal cord or spinal nerve roots. This type of neural injury could result in sensory and/or motor loss that could even be serious enough to cause permanent paralysis.
Only 12 patients were included in the study. And only those with a defect at the T12 vertebra were operated on with this new technique. Despite the positive outcomes, Dr. Imrie urges caution before adding this procedure as a confirmed, safe treatment option.
Further comparative studies are needed with children of different ages, with different types of deformities, and comparing results to other more tried and true surgical approaches. The first report of pedicle subtraction osteotomy is important but not the final word.