Mr P J Webb FRCS, Consultant Orthopaedic Surgeon. The Royal National Orthopaedic Hospital, Stanmore
Control of Spinal Shape
The shape of the spinal joints, strength of ligaments and action of the muscles under the control of the central nervous system maintain spinal shape in the normal person. There is thus a complex of control mechanisms, abnormality in any of which may result in an abnormality of spinal shape.
"Scoliosis" is not a diagnosis in itself, but a description of the spinal shape and implies a lateral curvature, usually with rotation, which may arise from any of a large number of causes.
Scoliosis, it should be noted, is never part of the normal spinal shape pattern, which contrasts of course with kyphosis and lordosis, both of which are angulations in the frontal plane and may be part of the normal shape. They are only considered abnormal if they are increased in size or stiffness.
Development of Spinal Shape
Spinal shape changes with age, the maximum occurring within the first 12 months. A child in-utero is born with a spinal shape which is virtually "C" shaped. At six weeks, control occurs in the neck muscles that result in the foetal kyphos being changed to include a lordosis in the cervical segment.
As the child begins to sit up, lordosis is also encouraged to occur in the lumbar region. Thus, adult shape develops with kyphosis in the dorsal region balanced by a lordosis above and below.
Function of the Spine
The shape of the spine is important for the safe passage of the contents of the spinal canal, attachment of muscles to support the limbs, preservation of function of the spinal cord and an ability to defend itself against increasing load.
Deflection from the normal range results in a loading of the spine which occurs in the direction of the pre-existing curves which, because they are pre-determined by the shape of the joints and ligaments under the control of the muscle are able to resist the increasing loads placed upon the spine by allowing deformation in a controlled manner, which of course contrasts with the buckling which may or may not take place if the spinal column was merely straight.
Types of Spinal Deformity
Spinal deformity exists in the general population in about 5%. Some authors have reported a very much higher level.
Of the overall group with spinal deformity, 80% have scoliosis without an identifiable cause, known as idiopathic. This is likely to occur either in the earlier age group between 0-3 years of age, or at the adolescent growth spurt. The pattern of abnormality is quite typical and although the diagnosis of idiopathic implies 'no known cause’, the particular clinical pattern is easy to identify. There are no other abnormalities associated with this sort of scoliosis.
The majority of the earlier group will spontaneously resolve, whereas the majority of the older group get worse, until the end of the growth spurt, and only those with a curve over a certain degree have problems later on in life. These problems are related to pain arising within the joints and on occasion difficulty with breathing because of the deformation of the shape of the spine supporting the chest with the associated abnormality of rib shape.
It is not true to say that all curves will stop progressing when growth stops. It is unfortunately only true that smaller curves behave this in way.
Approximately 12% of the group with spinal deformity may coexist in association with neuromuscular problems such as muscle dystrophy. The natural history of spinal deformity in this group will depend upon the prognosis of the condition and the progression of the condition with which the deformity is itself associated.
A smaller group of spinal shape abnormalities exist because the spine has developed abnormally. This group is difficult to assess because the deformity, which exists, depends upon the growth potential of the spine itself, which is difficult to assess. Ideally, the rate of progression of the curve needs to be assessed early in the growth period, certainly during the first 2-3 years, in order that logical treatment can be planned.
A very small group of spinal shape abnormalities develop in association with named syndromes, that is, a collection of commonly related abnormalities. The Ehlers-Danlos syndrome is a member of this group that is thus not particularly common in the general population.
As has been implied above, the reason for the shape abnormality in Ehlers-Danlos syndrome almost certainly relates to the lack of support that the soft tissues provide, that is, the fragility of the collagen that is part of the Ehlers-Danlos syndrome.
Modern biochemical analysis of the collagen defects have defined the molecular basis and although it is clear that spinal deformity may exist in the group of patients with Ehlers-Danlos syndrome, it is not clear which of the particular defects carries the greatest risk.
Pattern of Deformity in Ehlers-Danlos Syndrome
Review of Ehlers-Danlos patients with spinal deformity nevertheless demonstrates a similar pattern of spinal shape in all of them, that is, short multiple curves, which exist in comparison with the adolescent idiopathic curve that is usually a longer curve. Furthermore, the rate of progression of the curve is faster than the adolescent idiopathic.
Conservative methods of treatment, that is, exercises and bracing, are likely to affect the smaller curves only. It is to be noted that with the skin problems which exist in Ehlers-Danlos syndrome, bracing may be difficult to maintain because the skin is not tough enough to withstand the continual stress placed upon it by brace wearing.
The shape of the spinal deformities also reduces brace effectiveness, it being very difficult to brace very short, sharp curves. Multiple curves may make it difficult to apply adequate pressures of correction within the brace.
It is the experience of the author of this article that Ehlers-Danlos syndrome patients are unlikely to be successful brace wearers in the long term. Surgical stabilisation is thus likely to be offered if the spinal shape is not controlled by conservative methods.
If it is clear during the course of treatment that the deformity is likely to be greater than a certain degree by the time growth has stopped, then surgical treatment is likely to be required.
Spinal fusions are undertaken to increase the intrinsic strength of the spine by joining together the spinal vertebrae involved in the deformity, by excision of the joints and addition of bone to the joint spaces as well as additional bone on the surface of the vertebrae. This may be undertaken either in front (anteriorly) or behind (posteriorly).
Internal fixation devices such as Harrington Rods or similar devices serve to provide some control and to maintain the spine in the corrected position with as little movement as possible until the fusion has taken place. This process, which is similar to the repair of a fracture, takes approximately 6 months, or longer, during which time the patient needs to wear some form of brace support in the usual case, not so much as a corrective force but merely as a protection against too much movement.
The Ehlers-Danlos syndrome results in softer bones as well as more fragile soft tissues and it is thus advisable to consider a spinal fusion earlier so that the surgical problems are reduced and there is a lesser requirement for firm corrective forces to be applied.
Techniques of spinal fusion vary from patient to patient but, in general, the younger patients, or those with profound curves, are best stabilised from both the front and the back of the spine.
Although a large segment of the spine may need to be treated in this way, the loss of function from this is not profound, but nevertheless needs to be weighted against a tendency for progression of the curve. Although surgical techniques have improved considerably in the last 10 years, nevertheless, Ehlers-Danlos syndrome remains a special problem as a result of the collagen fragility, which needs to be carefully evaluated before surgery can be safely considered.
Ehlers-Danlos syndrome patients have an increased risk of spinal deformity compared with the general population, which results in a typical multiple curved pattern which should be treated early rather than late and may require surgical intervention more commonly than any other types of spinal deformity.
It is important therefore to look for spinal deformity, for example by forward bending positions. If there is asymmetry between the two sides of the spine when viewed from behind, in either the upright or forward bending position, then an explanation should be sought as early as possible. It is all too easy for significant deformity to be missed, particularly since these curves are rather smaller that the usual and can be hidden by corrective or compensatory curves existing above or below.
The views expressed are those of the author(s) and should not be construed to represent the opinions or policy of the Ehlers-Danlos Support UK or its Trustees.