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Scoliosis in Spinal Muscular Atrophy

Summary

This article looks at recent research into different aspects of spinal surgery, in the treatment of scoliosis in Spinal Muscular Atrophy.

Background

Scoliosis is the medical term for the progressive curvature of the spine to one side: it is easiest to think of the shape the spine forms as an ‘S’. You may also hear about ‘kyphosis’, which refers to how the spine bends forward in shape, as this is the most likely back shape problem to need treatment – but for simplicity, this article will only refer to scoliosis when talking about both. Scoliosis is one of the main health-related problems that individuals with SMA may encounter. Scoliosis in SMA is directly linked to the severity of the type of SMA, individuals with SMA Type 1 or Type 2 are all likely to be affected, as are about 50% of individuals with SMA Type 31,2. Scoliosis is caused by weakness of the back muscles, which usually help to keep the back in the correct position, but which also allow bending and movement. As scoliosis develops in SMA over a period of years, individuals will naturally stop growing as they reach adulthood; however scoliosis can continue to worsen even after growth has stopped3.

Development of scoliosis is known to cause several problems:

  • The shape of the back affects how easy it is for the lungs to expand and allow full deep breathing; a case of severe scoliosis means that the lungs have less room to do their job.
  • Scoliosis also reduces mobility, and therefore encourages stiffening of the joints coming from the spine. This includes the hip joints, which may be held at an angle (also called subluxation).

The most common treatment for scoliosis caused by SMA is surgery. This is not a new intervention and there are many studies which discuss the treatment of scoliosis that have been published over the last 30 years3-5. There have, however, been several advances in treatments and several aspects of management that differ between countries or regions; some of these are discussed below.

What evidence is there of the benefits of spinal surgery?

Several studies have investigated what effects spinal surgery can have on breathing function; mainly trying to decide whether the change in the shape of the back and chest following surgery immediately leads to improvements in measurements of breathing. Chou and colleagues in 2016 followed up individuals with SMA Type 2 who had spinal surgery, over a period of 12 years. They showed that breathing function was relatively maintained over this long period6. Several other studies have looked at mixed groups of individuals with SMA Type 2 and SMA Type 3 before and after surgery. Some of these have shown improved results of breathing tests, and others have shown a reduction in measurements of breathing over a longer period (i.e. ten years)6-10. It is worth remembering that measurements of breathing do reduce over time in individuals with some types of SMA and this is not just due to the development of scoliosis but also due to the increased weakness of breathing muscles over time. Comparing the rate at which measurements of breathing decline before and after surgery suggests that decline happens more slowly after surgery4,8,11. There appears to be support for spinal surgery in improving breathing function in the short term, but over longer periods such as ten years, this is less certain6. One potential benefit may be to reduce how often individuals get chest infections6. To add further support, looking at other conditions which make breathing muscles weak and which also require spinal surgery, the majority of studies have found that spinal surgery can improve breathing function12-15.  

Several studies have looked at other aspects that may be improved by having spinal surgery in SMA. These include better tolerance of sitting still for long periods (i.e. in school)6,16, how the individual feels they look to others4,16, and quality of life4,16. These aspects were measured by questionnaires after surgery - all showed positive results.

When to perform spinal surgery?

The Standards of Care for SMA (a document developed by a large number of experts and patient groups, which says how treatment and care should be provided to individuals with SMA – these guidelines are in the process of being updated) suggest that surgery should be performed in any individuals who have scoliosis that is contributing to breathing problems or is preventing comfortable sitting17. This means that the age at which spinal surgery takes place varies and isn’t necessarily fixed; some authors argue that the timing of spinal surgery could be based on physiotherapy assessments of how well individuals perform daily tasks (functional assessment)18. The idea is that after surgery, there is a decline in how well individuals do on these tests. To some (those who were less able already) this may make no difference, but those who were better at doing these tests prior to surgery may become less able to perform the same tasks afterwards18. Other studies have, however, suggested that activities of stronger individuals are not changed by surgery19. No studies have yet been done to compare those with better function before and after surgery to see what happens to ability in the long term.

As children with SMA are still growing, surgeons will also take into account how mature the spine is, and will wait for as long as possible to minimise the effect on growth. In light of new treatments which may become available and that are introduced into the spine via lumbar puncture (procedure of putting a small needle into the space between the bones in the back) there have been some concerns that older forms of spinal surgery may prevent the giving of medication via this method. This may not always prevent this technique but this should be discussed with the surgeon who performed the procedure or someone from the medical team.

It is worth mentioning that modern spinal surgery should not stop lumbar puncture from being possible although it will make it more complicated and may require to guide the needle. Untreated scoliosis may also make it difficult to find the right place to introduce such medication. If this is a concern, individuals and their families should talk to their surgeon about it before deciding whether to proceed with surgery.

Advances in surgery

A description of the surgical treatment of scoliosis was first published in the 1970s20; over the decades, advances in surgical technique and materials have reduced complication rates. The most commonly performed surgical procedure is based on a technique called ‘sub-laminar band technique’. This is a process by which the surgeon inserts rods on either side of the spine and attaches plastic or acrylic bands between the bones of the spine (vertebrae). In the past the bands were made of titanium or other metals. Modern plastic bands have a similar strength and allow the surgeon to progressively tighten up the bands and therefore reduce the scoliosis during the surgery. If the patient is still growing these may need to be regularly adjusted further to allow for growth; this is a more minor surgery than the first operation and may be required 6-12 monthly until growth stops. There is a lot of evidence that use of this technique reduces complications, operating time, and infections, and gives a better overall result 21-23.

In individuals who are not growing, this procedure can be performed as a ‘one off spinal fusion’ as adjustments aren’t usually needed after the first major operation, unless there are complications. There is another surgery which is also referred to by some as a ‘one off spinal fusion’ but this is used less commonly and only in individuals who are not growing. The procedure involves joining (or fusing) the individual bones of the spine together in a similar way to the method described above, but using pieces of bone taken from the bone around the hip (pelvis) instead of metal or plastic bands.    

Most recently, magnetic control rods have been trialled in patients with scoliosis. These have been used to allow the spine to grow, and potentially to allow adjustments to be made without further surgery. So far these have shown good results in spinal correction in both children with scoliosis of other causes and children with SMA24,25

Non-surgical options

Before surgery is considered, scoliosis is monitored in clinic and with spinal X-rays. Early management of scoliosis is with physiotherapy exercises. Physiotherapy aims to slow the progress of scoliosis through the relaxing of the joints and the strengthening of specific muscles26. According to studies of similar conditions, standing frames, leg splints and regular standing exercises may help to maintain bone thickness, and to slow the progression of scoliosis11,27,28.

Spinal bracing (sometimes called ‘spinal orthoses’) have been used for many years in the treatment of scoliosis caused by different conditions. Many regions and countries have different views on this. At the very least spinal braces have a place in assisting individuals who find it hard to remain in the sitting position for long periods of time, and in those with SMA who don’t want to, or can’t, have spinal surgery. There have been mixed views as to whether spinal bracing works to slow the progression of scoliosis29. Other studies have looked at how spinal bracing may restrict breathing, and have shown that although they help to maintain a sitting posture, which on the whole is good for breathing, restriction of the chest means that the braces cause breathing measurements to be significantly lower compared to those without a brace30. There are several types of brace, and it has been suggested that some which are designed to not restrict breathing could be of benefit to slowing progression of scoliosis. French studies looking at individuals with SMA Type 2 and a sub group of those with SMA Type 1 using a specific type of brace have suggested that there may be a significant benefit if this brace is used before scoliosis begins, compared to those who have the same brace after scoliosis has progressed11, 31.

Complications of surgery

Like all treatments and surgeries, there are complications to be aware of. Spinal surgery is, understandably, classed as ‘major surgery’ and takes several hours to perform. Compared to other causes of scoliosis, spinal surgery in individuals with SMA (and other conditions affecting muscles) is more complicated. In order, the most common complications of spinal surgery in muscle-related conditions are: breathing problems, implant-related problems (issues with the bands or rods not staying in place) and infection32-34. The authors of one paper which looked at lots of studies and analysed them said that although there was a large variation between studies in their rates of how often a complication occurred, overall risk was lower for those who had the surgery over the age of 13 years old. Other studies have also put forward suggestions of factors that can help to assess the risk of complications. These include nutritional status (i.e. whether the individual is a healthy weight) and measurements of breathing ability before surgery.

Conclusions

Spinal surgery in the treatment of scoliosis caused by SMA has come a long way since it was first performed. Although spinal surgery is now well established as part of SMA management for scoliosis in some individuals with SMA, it is still considered a major operation with accompanying potential complications. The best time to perform spinal surgery is much discussed and, in spite of the number of studies that have looked into this, it is always likely to depend on the individual as to when they feel ready and are well enough to proceed. The timing of the surgery remains important, as being too early or too late can have ramifications. As discussed, there are non-surgical options for scoliosis management which have benefits in terms of reducing pain; however surgery remains the definitive treatment. It is important to contact your medical team to have a discussion about scoliosis and the options open to you / your child.  

 

References

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