Adolescent idiopathic scoliosis (AIS) is a lateral deviation of the spine. It is defined as a lateral curvature greater than 10 degrees of unknown cause that progressively distorts the anatomy of the thorax, and with vertebral rotation.1–6 It affects 2–4% of children between 10 and 16 years of age.6 The prevalence of curves greater than 30 degrees is approximately 0.2%, and of curves greater than 40 degrees is approximately 1% of the children between 10 and 16 years of age.1–6 It corresponds to about 80% of the scoliotic deformities of the spine in the adolescent population, and over 50% of the patients present a thoracic curve.1–5 A number of different factors, isolated or combined, have been associated to AIS, such as a deviation in the growth pattern of the spine, neuromuscular or connective tissue abnormalities, asymmetrical growth or lateralization of the sagittal configuration of the spine, as well as hereditary factors.1–5 It is thought to be a multigene dominant condition, with variable phenotypic expression.6

Distortion of the three thoracic dimensions in patients with AIS results in a syndrome with pulmonary function abnormalities, pain and physical deformity.2–4 Pulmonary function testing (PFT) in these patients shows a reduced vital capacity, combining a drop in total pulmonary capacity, reduced arterial oxygenation, and alveolar hypoventilation.2 The pulmonary abnormalities may cause ventilatory restrictions and lead to exercise intolerance, mostly due to a decreased capacity to offer oxygen to the muscles undergoing greater demand.7–9

There are a number of tests designed to assess the inability to perform physical activities. The 6-min walk test (6MWT) has been used to assess physical and cardiorespiratory status of patients presenting with moderate to severe pulmonary and cardiac abnormalities submitted to medical procedures, allowing correlations with morbidity and mortality of specific diseases.7–9 Assessment of the distance walked is an expressive measurement of physiological function and an important component of overall quality of life, since walking is directly related to daily life activities.9 The 6MWT presents a stronger correlation with heart rate (HR), peripheral blood saturation (SpO2), and dyspnea than other physical exertion tests, such as the stationary bicycle and treadmill, both in healthy individuals and in patients with functional respiratory and pulmonary abnormalities.10

The 6MWT significantly correlated to forced expiratory volume in the first second (FEV1) in a study of healthy adolescents aged 12–16 years,11 and in children aged 3–16 years it successfully determined submaximal functional capacity.12 Patients with AIS usually present with reduced aerobic capacity that is possibly related to the ventilatory restriction observed in the reduced forced volume of these patients.13,14 In the first phase of the current study the authors used the 6MWT to evaluate the results of a physical therapy protocol on the pre-operative cardiopulmonary performance of a group of surgical candidates with AIS comparing them to matched controls that did not receive physical rehabilitation, finding that patients submitted to the protocol presented significant reduction in all vital signs and a significant increase in the distance walked when compared to baseline parameters and to controls.7

Considering the improved performance in the 6MWT of patients with AIS submitted to the abovementioned pre-operative rehabilitation protocol,7 the current study was designed to evaluate the long-term results of this regimen following surgical correction of the spinal deformity.

All recruited participants were followed up until the end of this study (there was no loss in follow-up). No patient needed any change in the rehabilitation protocol during the study period. Group I (study) was comprised of 25 patients, with a mean age of 14.12 years (SD+1.83), a mean scoliosis angle of 64.28 degrees (SD+18.62), ranging from 45 to 115 degrees; a mean kyphosis angle of 35.96 degrees (SD+12.36), ranging from 10 to 72 degrees; and a mean Adam's score of 42.04 (SD+14.40). Group II (control) also had 25 patients, with a mean age of 13.56 years (SD+2.02), a mean scoliosis of 65.56 degrees (SD+14.68), ranging from 46 to 110 degrees; a mean kyphosis of 35.52 degrees (SD+14.52), ranging from 8 to 62 degrees; and a mean Adam's score of 41.92 (SD+12.56) ranging from 8 to 67.

At baseline, there were no significant differences between groups for the variables age (p=0.31), scoliosis (p=0.29), kyphosis (p=0.90), and Adam's score (p=0.97).

Comparisons between Groups I and II showed no statistically significant differences on baseline 6MWT results, evidencing homogeneity between groups. There were no statistical differences between baseline and immediate pre-operative 6MWT results in this group of control individuals.

Four months after physical rehabilitation, comparison between baseline and post physical rehabilitation 6MWT results for Group I showed a statistically significant increase in the distance walked (p<0.001).

Tables 1–7 depict the ANOVA multivariate analysis of the repeat measures and confidence intervals of the 6MWT variables: distance walked, heart and respiratory rate, systolic and diastolic blood pressure, peripheral blood oxygen saturation and Borg scale.

It is possible to observe that the pressures SBP and DBP (Tables 3 and 4) behave in a similar way between groups and over time (no interaction effect: p=0.750 and p=0.349, respectively). Incidentally, there is no effect of time (p=0.340 and 0.085, respectively) and no significant difference between groups (p=0.340 and 0.903). For SpO2 (Table 5), the average behavior of the groups over time is equal (p=0.191). Therefore, when comparing the groups, we see that there is no difference between them (p=0.472). There is a time effect (p=0.006), i.e. SpO2 varies over time, but it is similar in both groups.

For the other variables evaluated in the 6MWT (HR, RR, distance and Borg), the interaction between group and time is significant (Tables 1–7, p<0.001).

When checking at which moments the groups are different, we observe that, for all variables described above, on average, the study group has lower values than the control group from the preoperative period on, except for the distance walked, which increases (p<0.001).

Patients with adolescent idiopathic scoliosis (AIS) frequently evolve with reduced vital capacity, and a drop in total pulmonary capacity associated to deficient arterial oxygenation and alveolar hypoventilation as a consequence of the tridimensional physical deformities of the spine.1,2,4,13 This was also observed in the present study, in which the patients with AIS had much lower baseline evaluations than would be expected for their age. This reduced respiratory capacity influences the final distance walked in 6MWT.7 Such deficiencies increase morbidity and are directly related to the severity of the curve.2 Volume changes are also a direct consequence of the decrease in blood oxygen13 and interfere with the capacity to adapt to greater physical challenge, such as that required for walking fast, leading to a progression in restriction to physical activities.19–21 The respiratory changes, however, do not seem to be directly related to the severity of the spinal curve but most likely a consequence of a combination of factors, such as the morphology, the site and the number of vertebra involved in the curve.5 In the first phase of the current study no correlation could be established between the angle of the scoliosis and the distance walked on 6MWT.7

Monitored physical activities in patients with respiratory restrictions have been shown to improve physical performance, endurance and cardiopulmonary function.15,22 The pre-operative physical rehabilitation protocol proposed here revealed a significant drop in RR, HR, and Borg scores, associated to an increase in SpO2 and in the distance walked on the 6MWT that persisted after corrective surgery. Inversely, patients with AIS who did not undergo physical rehabilitation (control group) had an increase in RR, HR and Borg scores, and a drop in SpO2.

An increase in tolerance to dynamic exercise, expressed both by increments in maximum performance and endurance, can be explained by a number of factors, one of which is the real improvement in aerobic power offered by training.23 Unlike other functional tests that are performed during rest the 6MWT does not underestimate the patient's capacity to perform physical activities.10 Thus, by quantifying physiological responses, physical testing via the 6MWT facilitates the design of a personalized physical activity program.20

The pre-operative physical therapy protocol proposed in the current study promoted significant progressive improvement in heart and respiratory rate, peripheral blood oxygen saturation, distance walked in the 6MWT, and level of effort assessed by the BORG scale after surgical correction of AIS. The study group also performed better than controls throughout the post-operative period. Our results suggest an interesting hypothesis to be evaluated: assuming that treated patients have had good performance even after one year after surgery, it is possible that they have felt able to exercise during this year, and this was reflected in the difference compared to controls, which could only walk shorter distances. It is reasonable to assume that the benefit that was obtained by the study group with a four-month exercising protocol before surgery would increase if the exercising was applied also after recovering from surgery – but this would be the subject of another study.

Patients submitted to a pre-operative rehabilitation protocol recovered baseline respiratory and cardiac parameters faster than controls, achieving the same values on the 6MWT one year after surgery as those at completion of the protocol, before surgery.

The authors have no conflicts of interest to declare.

This work was supported by a grant from the São Paulo State Research Foundation [FAPESP# 07/54024-7].