Scoliosis

Scoliosis is defined as a lateral curvature of the spine. Viewed from front or back, the spine generally forms a straight vertical line from head to pelvis. Scoliosis represents a deviation from this line, usually defined by a curve. There are several ways to quantify or measure the amount of curvature. The generally accepted, most often used management is the Cobb angle, named for a famous spine surgeon in the early 20th century. This is defined as the angle made by drawing two lines, one perpendicular to the top of the curve, the other perpendicular to the bottom. By definition, scoliosis is said to exist if this angle measures greater than 10˚. (A straight spine would measure 0˚, since the two lines would be parallel, or never intersect to form an angle.)

Scoliosis, when severe, can cause cardiopulmonary or physiologic complications, and result in cosmetic deformity and disability. The treatment of scoliosis is intended to prevent or treat these complications.

Scoliosis is sometimes caused by known conditions such as neuromuscular disease (cerebral palsy, muscular dystrophy, paralysis, etc.), by congenital vertebral abnormalities (misshapen vertebrae, vertebrae that are not separated from each other usually on one side or the other, etc.), by asymmetric disc degeneration and collapse, or by infection, tumor, or other unusual conditions. Most scoliosis occurs for reasons we do not understand, and is referred to as idiopathic (meaning we don’t understand the reason).

Idiopathic scoliosis can occur during childhood and most often is recognized during early adolescence. There is a genetic predisposition and a female-to-male ratio of 10 to 1. The genetic component is not quantifiable. That is, children of parents with scoliosis are more likely to develop the condition, but not to a predictable degree.

The treatment of idiopathic scoliosis is heavily dependent on the age at which the diagnosis is made. In growing patients (children and adolescents), the treatment involves early detection (pediatric visits, school screening programs, etc.), and then treatment to limit the progression of the curve. Small curves (less than 20-25˚) frequently require no more than careful observation. Moderate curves (25-40˚) can be treated by bracing, which is designed to stop the curve from progressing. Various types of braces are used including part-time, full-time, partial or more full-sized braces depending on the type of curve. There are some newer surgical alternatives to bracing that use expanding rods that allow for growth, but surgery is required for this. Beware of claims of non-surgical scoliosis treatment such as exercise, chiropractic, and other unconventional alternatives that have not been proven safe and effective by prospective studies in peer-review journals.

Sometimes bracing is used to treat congenital or neuromuscular scoliosis, but typically these patients do not respond well to braces and are observed until the curve progresses to a point that surgery becomes necessary.

Since bracing is intended to stop the progression of scoliosis rather than to correct it, there are a few important considerations to consider. Sometimes scoliosis in growing children and adolescents does not progress. If a child is braced without first establishing progression (either by observation clinically or by serial x-rays) then during brace treatment, it will be assumed that the brace is effectively stopping the curve progression even though the curve might not be progressive. For this reason we generally like to see evidence that the curve is progressing before prescribing a brace to be sure that the brace is necessary. If a brace is used it is generally continued until skeletal maturity (typically around age 16-17), so it is important to be sure this is necessary treatment at the outset.

Braces work by forcing the spine into a straighter shape. This usually involves lateral pressure on the ribs which exerts a force on the spine. The truth is that the skin is too fragile to hold up to such a force without breaking down, so the actual mechanism by which the brace functions is to put pressure on the skin which causes the patient to move away from the pressure in a direction that straightens the spine. It is for this reason that braces are not used in neuromuscular cases – these kids are not able to move away from the pressure and so develop painful skin breakdown rather than curve correction.

Braces are generally considered to be effective for curves up to 40˚. Sometimes we push the indications to 45 or 50˚ depending on the clinical circumstances. Curves larger than this are:

1. Too large for the brace to be effective and
2. Too large to be considered an acceptable outcome of bracing, since the brace typically doesn’t correct the curve

So bracing is indicated for scoliosis in children with:

1. Progressive curves 20-40˚
2. Further growth anticipated

Since bracing is intended to slow or stop a curve from progressing during growth, there is, generally speaking, no sense in using a brace for an adult with scoliosis.

For those people who have large curves (> 40˚) or for adults with scoliosis, the only effective treatment is surgery. In children the goal of surgery is to prevent the physiologic (cardiopulmonary), painful, cosmetic complications of large untreated curves. For adults, the indications for surgery are either documented curve progression that suggests the possibility of these complications occurring, or the already present complications of pain, disability or disfigurement from the scoliosis.

Surgery for scoliosis has been done for over a century. The goals are to prevent further curve progression and restore spinal balance, leaving as many motion segments as possible free to allow for normal spinal mobility. As of 2016, and for the past century, this involves fusing the curved portion of the spine (i.e. joining together the curved vertebrae with bone). This is the most important surgical consideration. Secondly, we want to correct the curve to as close to normal as possible. Prior to 1960 this was done using external bracing, or casting, similar to non-operative bracing. But following a fusion operation, the ability to correct the curve was obviously limited with this technique, and much like casting an arm or leg fracture, there was a significant percentage of patients with failed fusions.

Around 1960 Harrington developed an internal rod used to augment the fusion and lessen the dependence on the cast or brace for correction. This was a revolution in the surgical treatment of scoliosis. However, there were limitations:

• The rod had only two points of fixation and so was prone to dislodgement and need for revision
• The rod addressed only the “scoliosis,” ignoring the three-dimensional nature of the deformity.

Scoliosis is a lateral deviation of the spine, as defined above. However, it is more complex than that. Viewed from the side, (the sagittal plane), the normal spine is configured like the letter “S.” There is a convex curve behind the lungs and a concave curve in the low back. The curves are essential for normal spinal functioning and health. Frequently these sagittal curves are disfigured in scoliosis or not maintained or corrected in scoliosis surgery. The results can be sometimes worse than the scoliosis in terms of pain and disability.

To complicate the matter still further, scoliosis results in a rotational spinal deformity. This “twisting” of the spine, inherent in the curve, is what makes scoliosis visible. It results in rib prominence on the convex side, best seen when the patient bends forward at the waist.

True surgical correction of scoliosis requires attention to the entire deformity, not just the lateral deviation but the sagittal contouring and the rotational component as well. For an optimal surgical outcome the spinal correction needs to address the deformity in all three planes.

The original Harrington rod was reasonably successful in addressing the lateral curvature. But using the analogy of stretching a string of beads, the sagittal contours were lost in the correction and there was no consideration given to the rotational deformity, or correction in the transverse plane.

These shortcomings were addressed, to some degree, in later surgical scoliosis implants; first Luque contoured rods, then transverse wires connected to Harrington contoured rods, in a variety of iterations. In the early 1980s, two French surgeons, Cotrel and Dubousset, revolutionized the surgery again with multiple points of attachment of paired rods to the spine with attention to “de-rotation.” While a significant improvement, this was not yet the Holy Grail of perfect correction, but certainly a major step in that direction.

Pedicle screws gradually replaced the use of hooks and wires as points of fixation from rods to spine. This meant much more secure fixation to the vertebrae and allowed for potentially much more segment-by-segment correction of the spine. Most scoliosis systems on the market today employ pedicle screws to rods for correction of the curve, maintenance of sagittal balance, and with multiple points of fixation, less reliance on post-op bracing or casting.

I have been fortunate to have witnessed the evolution of scoliosis correction over the course of my career since ~1980. During my training from 1980-1985 I was taught the proper technique of Harrington rods, then Luque rods, and the various hybrids and iterations of these techniques. Then I observed and learned the lessons of Cotrel/Dubousset and finally the implementation and gradual acceptance of the use of pedicle screws. Around 2005 it became obvious to me that combining pedicle screws with the concepts of Harrington, Luque, Cotrel and Dubousset, we had the potential for addressing scoliosis deformity surgery much more comprehensively – true correction of the deformity in all three planes – the Holy Grail. I began to experiment with the concept, partnered with Synthes to develop a working prototype, and patented a technique in 2013 that allows for true correction of the scoliosis in coronal, sagittal and transverse planes, true correction of the rib hump and optimization of sagittal balance, as well as the curve correction. We have since used this on approximately 20 patients with excellent success and are now working with another manufacturer to fine-tune the technique further. The technique is applicable to patients with scoliosis of all ages, young and old.

The ability to correct scoliosis has come a long way in the past 50 years, particularly in the past 30. At the end of the day, though, our ability to correct a spinal deformity is dependent on the amount of force we can reasonably apply to the spine. Curves that are less flexible require more force to correct. Generally scoliosis curves become less flexible with age. The amount of force that can be applied is limited by bone density, which diminishes with age. So, our ability to correct spinal deformities lessens as patients age due to stiffer curves with greater amounts of osteoporosis. Perhaps future techniques will improve on these limitations. For now we continue to learn from the past while always looking to improve in the present, looking for new and better techniques in the future. Perhaps one day we will find a genetic or medical solution to scoliosis rendering bracing and surgery obsolete. Until then we will continue the quest for the surgical Holy Grail of perfect scoliosis correction.