Scoliosis is the curvature of the spine to the side, out of the normal plane. This curvature in spinal muscular atrophy most likely develops because of a lack of muscular support of the bones of the spinal column or muscular imbalance. The bones, discs and ligaments of the spinal column only have so much rigidity and are meant to be quite pliable. Because of this, when they lack normal muscular support, there’s a tendency for them to bend further; either to the side, forward or backward. In spinal muscular atrophy, as the muscular weakness progresses along with growth, there is a tendency for the curvature to develop and, over time, for it to become more severe.
The spine can curve in several directions. A bend to the side is described as "scoliosis". Usually, when looking from front to back, the spine should appear essentially straight. Although any curve to the side technically is scoliosis, usually this term is reserved for curves of significant magnitude. A bending of the spine more backward (or hunchback) is kyphosis. This is a common type of curvature for the upper spine. When looking from the side there is a normal amount of kyphosis, but when it exceeds a certain magnitude, it becomes abnormal. Finally, a curve forward, or inward, is lordosis. Again, this is normal in the lower spine when looking from the side, but can become abnormal at certain degrees. These may be described in combination, such as kypho-scoliosis (backward and to the side). In addition, descriptive terms are used for the curvature. These describe the flexibility (flexible, rigid or stiff), the cause (neuromuscular), and the balance (compensated or balanced, or uncompensated).
While the numbers vary, a very high percentage of people with spinal muscular atrophy will develop scoliosis. Since spinal muscular atrophy is a diverse disorder, so is this development. In children who develop spinal muscular atrophy at a very young age, the curvature will almost always occur by the age of ten. Scoliosis can start as early as eight or nine months of age, but in most studies was identified between six and eight years of age. It appears that the longer and later that you watch for curvature, the more often it will be identified. The occurrence ranges from 57 to 95 percent in the orthopedic literature. Whether scoliosis is inevitable over time is uncertain, but seems probable. There appears to be a relationship between the residual motor function and the development of scoliosis. If left untreated, the scoliosis will most often be progressive.
The spinal curvature of scoliosis or kyphosis may cause some difficulties with already compromised pulmonary function. Since the curve is relatively flexible, these can often be compensated for by adjusting seating or external support. The curve can also cause greater difficulty with seating position. The child may lean to the side, requiring support with the arms, which can lead to decreased freedom for the upper extremities for function or other daily activities. The question of whether scoliosis has an adverse effect on life expectancy remains controversial.
In attempting to treat the scoliosis, one can utilize conservative or non-operative methods to help support the spine. These will almost certainly not prevent development nor halt the progression of the deformity, but will lend support to the trunk and spine of the child to better perform activities of daily living. Care must be taken in judging the tolerance of these measures, including the tendency toward skin breakdown. A brace or body jacket is meant to support the trunk to allow for better activities of daily living and better seating. It is hoped that it will delay the progression of the curvature, allowing the child to grow more, but almost certainly has no effect on the early development or eventual progression of the curvature.
Special seating devices, such as supports or molds, can be helpful in this regard also. There is no study showing whether a brace or seating is more effective in the long-term delay of progression. The literature supports the use of a brace after a curve reaches about 20 degrees, but the brace may be helpful for these same aspects well beyond that. Again, one has to watch for the child’s tolerance of the brace, which may become somewhat worse as muscular weakness worsens. In summary, bracing or special seating is really used to improve the functional performance of the children, and not to prevent long term development of scoliosis.
The need and the timing of an operation for scoliosis in spinal muscular atrophy is somewhat controversial. Because almost all cases of spinal deformity in spinal muscular atrophy will progress despite conservative measures, and the progression of this leads to poorer sitting posture with pulmonary and functional limitations increasing, the early treatment of the spine with fusion is often considered necessary. Other authors have argued that spinal fusion will affect only quality of life and therefore remains a choice. In my hands, I tend to discuss these aspects at great length, as I would suggest all families do with their doctors. Certainly, if one has chosen to proceed with surgical intervention "at some point", it remains optimal to proceed while the spine is still flexible, while pulmonary function is still adequate, but once sufficient height has been gained. Often times, these three criteria do not occur at the same time.
Some very severely involved children at early ages have very marked curvature which interfere with their sitting or pulmonary functions. Several options remain for these children. Initially, conservative treatment such as seating changes, support, or even brace wear would be probably warranted. Failing this, more conservative surgical treatments, such as limited fusion (surgery just at the apex of the curvature), subcutaneous rodding (a supporting rod without a fusion, with hooks only at the top and the bottom), or a "growing construct" (a rod with cables around the spine but no fusion, with the idea that the spine can grow along the rod like a trolley). None of these options is perfect, and each has its own difficulties. As such, they should be discussed at length with the physician relying both on the literature and the doctor’s and family’s own judgment and experience.
Surgery in neuromuscular scoliosis really has two aspects to it. The final goal of the surgery is to prevent progression and maintain balance. This is achieved by bony fusion. Fusion of the bone takes place between the individual segments or parts of the spine, much as it would between the two ends of a broken bone in one’s forearm. This takes time, and in the spine, it usually requires many months. Just as a cast would hold the arm in place to allow healing (fusion) of the broken arm, instrumentation and/or bracing is used to hold the spine in place as the bony fusion takes place. Many combinations of fusion with and without instrumentation can be undertaken. As noted in the above paragraph, in small children, limited use of instrumentation or limited areas of fusion can be used to allow for further growth despite having undergone surgery. When contemplating surgery in somewhat older children, a more standard posterior (from the back) fusion with instrumentation (rods, hooks, screws and wires) is usually undertaken. The most significant concerns with this surgery include pulmonary or ventilation concerns, blood loss, infection, and the impact on nerves. This is almost always undertaken in children who are now wheelchair bound but still, their neurologic function is quite important to their daily activities and care.
The most commonly held indications for spinal fusion in SMA are curves which have progressed to greater than 40 degrees (measured from the upper edge of one vertebrae to the lower edge of another vertebrae, demonstrating the maximum amount of curvature). There are still some authors who feel that surgery should not be undertaken unless there is a very significant curvature (85 degrees or so) because of the risks and benefits involved. It’s usually optimal to undertake the surgery after the age of ten, because the child has achieved sufficient growth, and there’s less concern about future growth causing difficulties with progression or deformity. The greatest concerns during spinal surgery in SMA are pulmonary. These need to be discussed at length with both the surgeon and the anesthesiologist, along with the pulmonary care specialist. Certainly the risks of more long-term ventilation or tracheostomy persist and should be discussed openly.
The time in the hospital varies anywhere from four days to two weeks, depending upon the extent of surgery and the recovery (largely the pulmonary recovery). Most of the children stay home anywhere from two to five weeks following this to regain their strength. Gradual progression of activities is warranted. Certain activities, such as bending and lifting, must be done in a cautionary manner until the bone has fused in completely around the metal rods (six to twelve months). Sometimes a post-operative brace may be helpful to protect this area also. The operation itself should have no effect on future interventions other than those along the spine. Adjustments in the chair will be necessary and certainly further interventions may be needed if there is significant growth remaining.
In general, this is obviously a very big step for any of the children and their families. I suggest that they have prolonged discussions beginning early on so that the course can be mapped out and the benefits and risks discussed at length. If questions remain, I would advise seeking further insight from the pulmonary doctors, the neurologists, and anesthesiologist. One can always seek a second opinion, and the family should have a good relationship and confidence in the involved parties.