ANALYSIS OF THE SECONDARY CURVES IN PATIENTS UNDERGOING SELECTIVE ARTHRODESIS LENKE

Objective: To radiographically evaluate the behavior of the secondary curves in the coronal and sagittal planes in patients with AIS classified as Lenke I, who underwent surgical treatment of selective arthrodesis by posterior approach. Methods: Retrospective study which analyzed 40 patients with AIS, being 33 female. The measurement of the radiographic parameters used followed the recommendations by Cobb. Results: The average correction of the thoracic proximal, primary and lumbar curves was 34.73%, 75.06% and 64.64%, respectively. Conclusion: Surgical treatment by selective arthrodesis in cases of AIS Lenke type I provide correction of compensatory curves in the coronal and maintenance in the sagittal plane.


INTRODUCTION
Adolescent idiopathic scoliosis is the most common form of spinal deformity.2][3] Several theories have been studied, such as changes in collagen, hormonal changes, and more recently, genetic changes, 4 but we still do not have a complete definition of its origin.
The treatment for this type of deformity depends on the degree and the location of the curve, and is based on the degree of potential growth of the patient. 5In curves greater than 45°, measured using the Cobb method, surgery is indicated in patients with growth potential. 6he goals of surgical treatment are to correct the curve, to recover balance in the coronal and sagittal planes, to prevent progression and possible cardiopulmonary complications, and consequently, to provide esthetic improvement.
Several classification systems have been proposed which, depending on the type of deformity, can be used to define the type of proposed treatment.The classification of Lenke et al. 7,8 examines not only deformities in the coronal plane, as suggested by King et al., 9 but also the secondary curves and sagittal balance, since changes in these measurements can directly impact the surgical decision.
The Lenke classification brought great advances to the interpretation of deformities because it clearly defined what would be the main curve, a secondary proximal curve, a secondary distal curve, and the relevant sagittal modifiers, 7,8 criteria that were previously poorly standardized in the literature.Following this standardization, http://dx.doi.org/10.1590/S1808-185120151404152849there was a significant increase in publications using the Lenke classification. 7,8n curves classified as Lenke I, studies show that selective arthrodesis is the appropriate treatment for this type of pathology, as it enables correction of the compensatory curves by performing an arthrodesis involving fewer segments, benefiting the patient. 10,11he objective of this study is to evaluate the behavior of the secondary curves radiographically, both in the coronal and the sagittal planes, by assessing the pre-and postoperative exams of patients with adolescent idiopathic scoliosis classified as Lenke I submitted to posterior approach selective arthrodesis surgery.

CASE SERIES AND METHODS
A retrospective study, conducted following approval of the Institutional Review Board (IRB) -Santa Casa de Misericórdia de Vitória (12041313.0.0000.5065), in which 40 patients with AIS classified as Lenke I were analyzed; 33 female, with an average age of 14.7 years, ranging from a minimum of 11 to a maximum of 22 years of age.
The inclusion criteria were: patients with AIS classified as Lenke type I, between 10 and 22 years of age, indicated for surgery due to spinal deformity, and in follow up at Hospital Santa Casa de Misericórdia.
The exclusion criteria were patients who did not agree to sign the Informed Consent Form, those who did not have the pre-established radiographs taken, and those who refused surgical treatment.
The radiographic parameters used for this study were measured following the recommendations of Cobb, 12 for which panoramic radiographs are taken of the spine in the orthostatic position, in the pre-and immediate postoperative periods and after 4 weeks. 13(Figure 1) The compensatory curves were also measured using the Cobb method 12 as the standard in panoramic pre-and postoperative radiographs of the spine in the orthostatic position, as described.
A descriptive analysis was used to describe or summarize the sample of children and adolescents with scoliosis.
The Student's t test was used to compare the preoperative and postoperative evaluations.A level of significance of 5% was adopted, and a confidence interval of 95%.The statistical program used in the analyses was IBM's SPSS Statistics version 21.

RESULTS
The sample was composed of 40 patients who met the inclusion criteria of the study.We compared the pre-and postoperative spinal radiographs of adolescents and young adults between the ages of 11 and 22 years old with AIS with Lenke type I curves with indication for surgery, and who had no other vertebral deformities.
The averages of the Cobb index in the anteroposterior preoperative radiographic exam were 29.97° for the proximal thoracic curve, 59.08° for the principal thoracic curve, and 35.26° for the lumbar curve.The average postoperative measurements were 19.56º, 14.73º, and 12.5º respectively, with corrections percentages of 34.73%, 75.06%, and 64.64% for their respective curves, as shown in Table 1.Table 2 shows the analysis of the cervical, thoracic, thoracolumbar, and lumbar profiles in the pre-and postoperative periods.tatistical Analysis The Student's t test for paired samples was used to compare the preoperative and postoperative evaluations through the differences in the averages of the degrees.(Table 3)

DISCUSSION
5][16][17] Applying the concept of selective arthrodesis permits us to control and partially correct the main thoracic curve, and to maintain the mobility of the segments, particularly in the lumbar segments.
Lenke et al 18 demonstrated that after selective arthrodesis surgery, the correction of the compensatory lumbar curve is spontaneous and consistent.In a study published by Ritzman et al., 19 a correction of 49% was achieved.Sun et al. 20 conducted a study with 43 patients with adolescent idiopathic scoliosis submitted to selective posterior arthrodesis, and concluded that the restoration of coronal balance was compensated mainly by the non-fused distal segments.
Wong et al. 21reported shorter surgical time in patients submitted to posterior selective arthrodesis and consequently a lower risk of complications.The study published by Fisher and Kim 22 shows that selective arthrodesis in AIS is a way to correct the curve, recover balance, and maintain flexibility by leaving a higher number of segments free.Yu et al. 23 state that this type of treatment is effective and safe, maintaining good balance in the coronal and sagittal planes.
In this study, selective arthrodesis of the principal thoracic curve resulted in a correction of 75%, while for the secondary curves, though not directly targeted in the surgery, significant correction was obtained, with 34.73% correction in the proximal thoracic curve and 64.64% in the lumbar curve.The thoracolumbar profile showed a reduction of 41% in the average angle in the sagittal plane, while the thoracic and lumbar profiles showed reductions of 7.7 and 14.1%, respectively.

CONCLUSION
Surgical treatment of Lenke type I AIS by means of selective arthrodesis provides correction of the compensatory curves in the coronal plane and maintenance of the sagittal plane.
All authors declare no potential conflict of interest concerning this article.

Table 1 .
Comparative analysis between the curves pre-and postoperatively.

Table 2 .
Analysis of the pre-and post-operative profiles.

Table 3 .
Comparison between preoperative and postoperative by the Student's t test.

differences P value Average Stan- dard devia- tion Confidence in- terval of 95% of the difference Lower Upper
Coluna/Columna.2015;14(4):268-70 ANALYSIS OF THE SECONDARY CURVES IN PATIENTS UNDERGOING SELECTIVE ARTHRODESIS LENKE I Figure 1.Cobb method for measuring the principal and secondary curves.