4 Epidemiology of Idiopathic Scoliosis
Orthopedists who underwent their training three or four decades ago were taught by the scoliosis surgical doyens of the time to treat growing children with idiopathic scoliosis according to a fairly strict protocol ( Table 4.1 ). This was relaxed a bit over the early years thereafter.1
The rationale for this paradigm was that not many small spinal curves progressed, and that most could therefore merely be watched, whereas large curves should not be allowed to go beyond 60 degrees lest patients succumb to cardiopulmonary dysfunction in adulthood. The principal aim of treatment was to prevent progression by bracing moderate curves and by operating on bigger ones. Before the advent of instrumentation for scoliosis, patients underwent preoperative traction and localizer casting,2 a fusion being performed through a window in the back of the cast, which had to be worn for at least 3 months.
With the advent of Harrington instrumentation,3 which provided intraoperative correction and markedly reduced pseudarthrosis rates, surgery for idiopathic scoliosis was enthusiastically prescribed.4,5 Although it was known that not all curves of 20 degrees or more progressed (four-fifths do not), pioneers of brace treatment dictated that braces should be worn (for up to 23 hours a day) because of: (1) unquestioning faith in brace treatment; and (2) because allowing progression to 60 degrees or more would possibly endanger their patients’ lives.6,7
Therefore, the perceived wisdom of the day was to inform patients and families that without bracing, idiopathic scoliosis would worsen, and that without surgery serious heart and lung problems could militate against a healthy adulthood. Moreover, wearing a brace would mitigate the likelihood of having to go through a difficult and dangerous operation not without potentially serious complications (which were real concerns four decades ago). Not surprisingly, both providers and recipients of healthcare happily endorsed this treatment program.
Patients often presented, and still do, with curves of 30 or 40 degrees, and on this premise and those described earlier, it seemed perfectly reasonable to try to identify less severe cases in the community. As a result, school screening programs for idiopathic scoliosis were adopted in many parts of the world. Furthermore, because nothing was known about the natural history of idiopathic scoliosis (and not much more is known today), these screening programs might shed some light on its epidemiology.
Under 20 degrees | – | Observe | → | 25 Degrees |
20–60 degrees | – | Brace | → | 45–50 Degrees |
60+ degrees | – | Operate | → | 50+ Degrees |
These were the rules of the game: bracing is effective, and you might die of idiopathic scoliosis if untreated. Belief in bracing was so strong8–14 that it would have been deemed quite unethical to conduct a trial of it, and indeed, heart and lung dysfunction had been widely reported in particularly severe cases of thoracic idiopathic scoliosis.15–18 As evidence-based medicine has become more fashionable, the past 20 years has seen both of these premises challenged. Clearly, the “retrospectoscope” is a powerful instrument, but looking back, it wasn’t clear from the protagonists how a brace might control this complex three-dimensional deformity from the outside, other than in accord with the simplistic concept of three-point fixation.19
What the designers of the brace did point out, however, was that if it did obliterate the lumbar lordosis (and thus pitch the patient forward), it would hyperextend the spine above the lumber lordosis, and that they observed some degree of improvement when the patient was radiographed with the brace applied. This was because the thoracic lordosis was being encouraged to return toward the sagittal plane: the opposite effect, it might be said, to the forward bend test ( Fig. 4.1 ).20 However, a child with a 30-degree curve without the brace might have a 20-degree curve in the brace and be imprisoned in that position for hours on end, whereas the unbraced patient would be able to move through to 10 degrees or less by the side bending of normal activities of daily living. Not surprisingly, it wasn’t long before evidence of inefficacy of bracing, from the Gothenburg databank, was published by way of a retrospective trial showing no difference between braced patients and unbraced controls.21
Similarly, the evidence for the organic health consequences of untreated idiopathic thoracic scoliosis was seriously misjudged.20 Data on cardiopulmonary dysfunction came from cases of early-onset idiopathic scoliosis, rather than cases of adolescent idiopathic scoliosis (AIS), in which the curves were well in excess of 100 degrees.16,17 Davies and Reid showed that pulmonary alveolar reduplication occurs in the main in the first 2 or 3 years of life and certainly ends by the age of 7 years (see Fig. 2.16).22 If during the early years a significant thoracic deformity is imposed upon this process, it can lead to the hypoplastic lungs encountered in, for example, congenital diaphragmatic hernia, in which the abdominal contents severely compress lung space. This was known as early as 1965 and Reid, the distinguished cardiopulmonary pathologist at the Brompton Hospital in London, presented her findings in this regard at one of the Zorab Scoliosis conferences.15
The benign nature of idiopathic thoracic scoliosis of later onset was confirmed by Branthwaite, who succeeded Philip Zorab at the Brompton Hospital. Her study of untreated idiopathic scoliosis demonstrated that the age of 5 years was the crucial threshold of onset.23 With an onset earlier than this, cardiopulmonary compromise could occur in severe cases; beyond this age idiopathic scoliosis did not have any organic consequences for health.
Notwithstanding this, screening for scoliosis was championed, and the late 1970s and the early 1980s saw reports supporting its use from North America,24–26 Britain,27 Europe,28–30 Australia,31 and Japan.32
Screening for Scoliosis Definitions and Criteria
Screening is defined as the presumptive identification of an unrecognized disease or defect through the application of tests, examinations, or other procedures that can be applied rapidly.33 A number of authorities, including the World Health Organization, have defined several criteria that should be met for effectively informing an unwitting individual that he or she has a problem ( Table 4.2 ).34 One of these prerequisites is that the natural history of the condition for which screening is to be done is adequately understood, which is manifestly not the case with idiopathic scoliosis. Other criteria are that it should be an important health problem, that there should be a recognizable latent stage of the disease to identify, and that an effective treatment for the disease can be applied. If these conditions are met, the screening test for the disease should be valid, meaning that it can sort out those with the disease from those without it. In the case of idiopathic scoliosis, the Adams forward bend test or the scoliometer are clearly far too sensitive in this regard.35 Financial effects should also be taken into consideration, and in the presence of a health service with finite resources, screening for scoliosis should be put on a par with other screening programs, such as for breast or cervical cancer. If the natural history of a disease is not understood, screening may have merit if it is in the nature of an epidemiological survey that elucidates the prevalence and incidence rates and the natural history of the variable being studied.
Screening of selected subgroups of the population selected as being relatively high risk for a disease is called “selective screening,” and the selection process is expected to be based on sound epidemiological research,34 which is clearly not the case with regard to idiopathic scoliosis. That the 10- to 14-year-old age group (the sort of age group most commonly selected) is particularly vulnerable is merely conjectured. There is no doubt that this age selection does produce an enormous harvest, but when the reasons for screening are scrutinized it can be seen that adolescent idiopathic scoliosis is a relatively benign condition.20 When looking at the results of epidemiological surveys it is often impossible to compare these, because the words prevalence and incidence are often used interchangeably, and the class intervals of curve magnitude are not the same. The survey that has class intervals from, for example, 0 degrees to 4 degrees, 5 degrees to 9 degrees of curvature, 10 degrees to 14 degrees, and so forth is clearly not comparable to one that has intervals of 5 degrees or less, 6 degrees to 10 degrees, 11 degrees to 15 degrees, and beyond. This is particularly relevant in that the Scoliosis Research Society defines a scoliosis as being present if it measures at least 11 degrees.36
Screening Methods
The forward-bend test is the most commonly used test for scoliosis ( Fig. 4.2 ). An alternative is the scoliometer, which measures the angle of trunk rotation in the forward-bend position.35 Both of these tests, by using forward bending, compress the lordotic component of the deformity and thus enhance spinal buckling. This has the effect of causing overestimation of the deformity. An alternative is to use surface-shape measurements with the patient in the erect position. This is done with computer-driven surface-shape maps of the back of the child, and although very sophisticated (the Quantec surface-shape measurement generates 250,000 data points in a fraction of a second), poses a problem of quantification ( Fig. 4.3 ).37 Although Cobb angles, rib humps, and lung volumes can be measured, it is not possible to obtain a single figure for overall surface shape.
Bunnell, with his great experience in the use of a scoliometer, originally suggested referral to a clinic for a child with a 5-degree angle, but then increased this to 7 degrees to reduce the number of false-positive results, with 12% of patients being referred for a 5-degree angle and only 3% for a 7-degree angle.38 However, the number of false-negative results is the price for this. When 5 degrees of rotation is used, only 2% of 20-degree curves will be missed, and when this rises to seven degrees of rotation, 12% of 20-degree curves are missed.
Children referred for further assessment and in whom a clinically suspected scoliosis is confirmed then have a frontal radiograph of the spine. It is mandatory that this involve the lowest possible dose of radiation, and the Oxford Scoliosis Study Group devised a technique that reduces the radiation dosage in this procedure to less than 2% of that with a conventional film.39 This is achievable by radiographing the patient in the posteroanterior (PA) direction, so that the full width of the torso will absorb X-rays before they meet the developing breast and thyroid, and by increasing the focus-film distance by a factor of 3 through the incorporation of an air gap ( Fig. 4.4 ).
The Cobb angle is measured on the films obtained in this procedure, preferably by using Whittle’s protractor with a free-hanging needle, which yields an error less than 1 degree,40 rather than by drawing lines on the film with a pencil and dropping perpendiculars, the error of which can be as high as 10% (see Figs. 2.6 and 2.7).
Related posts:
7 The Case for Bracing
6 The Importance of the Sagittal Plane: Spinopelvic Considerations
22 Complications in Surgery for Spinal Deformity
28 The Impact of Genetics Research on Adolescent Idiopathic Scoliosis
17 Surgical Treatment of the Right Thoracic Curve Pattern
10 Biomechanics and Reduction of Scoliosis
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
