General
This study concerns a great number of healthy children and adolescents. This type of analysis in this report enables defining the normal limits of various parameters and gives values of trunk asymmetry. It respects the Bunnell's indications for a critical value of 7 degrees of the angle of trunk rotation in the scoliosis screening [
2]. The results also argue for use of the sitting position in scoliosis screening. This study documents that the relative proportion of a spinal curvature that is caused by a LLI can be detected by a simple method that easily can be incorporated into screening protocols: ATR at forward bending is measured with the subject in a seated position, and the values are compared with those obtained while the subject is standing. The CATR was highly correlated with LLI among patients screened. This particular observation, as far as it could be searched in the available peer-reviewed literature, has not been documented among detailed biomechanical analysis [
6,
20‐
22].
This work has also implications not only for diagnosis and for understanding aetiology and prognosis, as it is inferred here, but also as an avenue to help make targeted decisions regarding referral of patients screened. The report also provides a starting point, potentially, for a new avenue for diagnostic screening, evaluation, and treatment based on simple analysis of the positional dynamics of torso deformity.
Trunk asymmetries (ATR > 0°) are found in normal children with no spinal curves, as it is shown in our study and in other reports [
3,
11]. Thus, scoliometer measurements of 1° – 6° are considered to be associated with nonscoliotic spines. However, children with 5° – 6° of scoliometer measurements are followed up clinically at the Scoliosis Clinic every 4–6 months.
It has been reported, that scoliotic curves of >10° Cobb angle were found in 2% of subjects 12–16 years of age [
2,
4,
12‐
14]. This percentage is closer to that found in the current study of 7 degrees or more asymmetry group, in sitting forward bending position. In other scoliosis screening studies, the reported prevalence generally falls between 2.5 – 4% [
15,
16]. The asymmetries reflecting the percentage of small curves in the current study are similar to other reports from school screening for scoliosis performed by other scoliosis departments in Greece [
8,
17].
In a previous study of a relatively younger sample of children, the more frequently found asymmetries were those to the left, while the right-sided asymmetries were more frequently traced by age [
18]. In the present sample of older children and adolescents, the frequency of asymmetries was always nearly twice larger to the right, for the population studied, except for the male age group of less than 6 years at the thoracic and lumbar area.
In the current study, asymmetries were detected in greater percentages at the standing than in the sitting foreword bending position. If asymmetry detected in the sitting position is considered as the true trunk asymmetry, the most frequent affected part of the spine (ATR > 0°) was the thoracolumbar part in either boys or girls (24.61% of boys, 27.59 % of girls). It has been reported that younger children show most frequently lumbar asymmetry [
18]. In the current study, girls had a higher frequency of total trunk asymmetries than boys in both standing (34.99 % vs. 32.94%) and sitting (24.82% vs. 23.57%) screening position.
In the current study, there was a strong correlation of the CATR and the LLI, which means that the LLI may force the trunk to rotate so the body can maintain its balance. The dynamics of torso deformity have been measured and plotted in a variety of biomechanical approaches [
19‐
22]. However, the level of the spine where this rotatory force mainly occurs and the biomechanical changes, which imposes on the spine, is an issue that will be answered by future studies.
Little information on LLI and scoliosis exists in the peer-review literature [
23‐
28]. In healthy children a physiological shortening of one leg (1 – 2 cm) is associated with a contralateral hump on the back in forward flexion. It has been reported that shortening on the right is less common in boys than in girls [
3]. Ingelmark and Lindstrom [
29] reported that the right leg of adults is usually shorter than the left. Considering that most people preferentially use the left leg, its longer length could perhaps be ascribed to a growth acceleration induced by the greater working load imposed on it [
29]. The left foot supports a significantly higher load than the right in right-handed subjects [
30‐
32]. The typical asymmetric pelvis has also its left half set a little higher and further back than the right [
29,
30]. It has been reported that shortening of one lower limb is associated with contralateral hump on the back not only at L3 but also at T12 and T8 vertebrae [
3]. This finding indicates that the standing forward bending position used as a routine in school screening, while satisfactory for clinical use, should be replaced by a standard sitting forward bending position when measurements are needed [
3].
The differences of frequency of asymmetry in the examination in the two positions are probably expressing the existing small leg length inequalities, or in scoliotics the coupling phenomenon between "hump rotation" and forward flexion in lumbar lateral curves [
33]. The examination of the back trunk shape, with the child placed in sitting forward bending position expresses real trunk asymmetry, which is revealed due to the leveling of the pelvis and elimination of any effect of leg length inequality on back shape. Thus this position is preferred over the standing forward bending position if true trunk asymmetry is the one to be assessed. The results of the current study warrant additional research to explore the hypothesis that the standard sitting forward bending position for examining the rib or loin hump during school screening is the preferred screening position and demonstrates the best correlation with the spinal deformity. However standing forward bending position alone, is inconsiderately appraising both trunk and leg length asymmetry when it is used as the main test in school screening program.
The pattern of scoliosis associated with LLI, (anisomelia), is usually described as being compensatory, non-structural and non-progressive. It has also been reported that anisomelia can produce structural changes in the adult spine with time and many of the patients are experiencing back pain [
34,
35].
Leg asymmetries in normal children are either equalized during growth, or with the contribution of other mechanisms, according to our hypothesis, facilitate the increase of trunk asymmetry and probably aetiological implications on the pathogenesis of scoliosis [
36]. Ingelmark and Lindstrom [
29] reported that the causation of scoliosis is very difficult to establish because it may involve a large number of different mechanisms acting singly or in combination. They suggest that probably the main factor among others is the usually longer right leg in children prior to puberty.
Spinal curvature is "expressed" into surface asymmetry via the rib cage, spinal muscles, viscera, fat, and skin in a manner that is unique to each patient and changes over time as the deformity progresses [
19]. The findings of the current study and the above mentioned hypothesis suggests that trunk asymmetry as measured using the scoliometer could be the surface expression of the asymmetrical action of a "composite muscle trunk rotator", (part of Nottingham AIS theory) for pathogenesis of scoliosis [
37].
Another statement that can be implied from our school-screening program is that asymmetries in the form of thoracic or lumbar hump are earlier traced in the thorax or in the loin, without any apparent deformity in the spine (central axis). This statement was verified in a number of radiographic examinations in our referrals, a study presented elsewhere [
38]. This means that the deforming forces, which begin the asymmetry, do not start within the spine, as it is stated in other reports [
39], but elsewhere.