IDIOPATHIC SCOLIOSIS : EVALUATION OF LOSS OF CORRECTION IN POSTOPERATIVE FOLLOW-UP ESCOLIOSE IDIOPÁTICA

OBJETIVO: Evaluar la perdida de correccion de la escoliosis tratada quirurgicamente, con instrumental de tercera generacion, comparando el postoperatorio inmediato y la ultima consulta de los pacientes operados entre 2002 y 2010. METODOS: Se trata de un estudio transversal, realizado por medio de analisis de fichas medicas, en el cual fueron incluidos 45 pacientes sometidos a la correccion de escoliosis. Las variables fueron evaluadas en el preoperatorio, postoperatorio inmediato y en la ultima consulta de seguimiento. El analisis estadistico de los datos se realizo en el programa PASW, con nivel de significancia de 95%. RESULTADOS: Entre los 45 pacientes estudiados, 88,9% son del sexo femenino y 82,8% estan en el grupo de inmadurez esqueletica. El Cobb promedio fue 57° en el preoperatorio; 6,5° en el postoperatorio y 7,04° en la ultima consulta. En la comparacion del angulo de Cobb, en el postoperatorio y en la ultima consulta, no se encontro diferencia estadisticamente significativa, p = 0,176. CONCLUSION: No hubo perdida importante de la correccion de la escoliosis entre el posoperatorio inmediato y la ultima evaluacion radiografica.


INtrODUctION
Scoliosis has been defined as a deviation of the spine in the coronal and horizontal planes, 1 with idiopathic scoliosis being the most common deviation. 2In its milder forms, scoliosis may only cause changes in the shape of the trunk, but when severe, it can evolve with neurological, cardiac, and pulmonary involvement.
The Scoliosis Research Society recommends that idiopathic scoliosis be classified based on the age at onset due to the difference in evolution of subtypes: infantile scoliosis arises from birth to three years of age; juvenile arises between four and ten years; and adolescent arises between the age of ten and skeletal maturity, which for this study was considered to be eighteen to facilitate statistical interpretation.The prevalence of scoliosis is 1-2% in the general population, and adolescent idiopathic scoliosis (AIS) is its most frequent presentation. 3The correction of scoliosis had a breakthrough with the beginning of the use of the Harrington instrumentation in 1962. 4in August 1978, Luque 5 employed his instrumentation composed of L rods and sublaminar steel wire, which was later combined with Harrington rods, giving them greater accuracy and stability.The innovation arose with the technique described in Paris in 1984 by Cotrel and Dubousset, 6 using multiple hooks with superior and lateral covers, facilitating their assembly, allowing for implants at more levels, and thus better distributing the load between the vertebrae. 7he third generation instrumentation, fixating the three columns with transpedicular screws, provided the possibility of correcting the deformity in the coronal and axial planes.Subsequently, it was modernized with the Colorado instrumentation. 8,9In 1998, a system similar to Colorado was developed in Brazil with long head screws, associated with clamps that offer a greater possibility of successfully correcting highly complex cases. 10he objective of this study is to assess the loss of correction of scoliosis treated surgically, with third generation instrumentation, comparing the immediate postoperative period and the last visit of the patients operated on between 2002 and 2010.

MEtHODs
This is a cross-sectional study, conducted through the analysis of medical records, in which the following variables were assessed: sex, age, the Cobb angle preoperatively, immediately postoperatively, and at the follow-up visit (mean of 7.1 years after surgery), and posterior or combined approach.A radiological study was performed using anteroposterior and lateral panoramic radiographs of the spine in the standing position for the preoperative and postoperative period evaluation.Only the values of the main curve were considered.
Prior to surgery, the fixation points and the direction of the force being applied on the segments and on each side, whether compression or distraction, were planned.
A posterior approach for the fixation and correction of the deformity was employed across the entire sample.Dissection of the spine, facectomy, complete resection of the articular cartilage and the capsule were performed to favor bone fusion and to make the deformity more flexible.Resection of the spinous processes and decortication of the posterior spine were then performed.Fragments were harvested for grafting the area of arthrodesis.
To pierce and pass the pedicle screws, an image intensifier was used for orientation, always focusing on the pedicle, mobilizing the device on three levels according to the degree of rotation; images in the frontal plane were considered with priority.
All patients were instrumented with rods, pedicle screws, and cross-locking devices to correct the approached segments.The intraoperative awakening test was used.
In 15 patients who had more severe and rigid curves, as evidenced by radiographs with a lateral tilt, the anterior approach was combined to improve corrigibility and bone stabilization.(Figure 1) In the immediate postoperative period, cervical-thoracic-lumbosacral or thoracic-lumbosacral bracing was indicated for an average period of four months.
Later, a new radiographic study was performed to measure the deformity using the Cobb method.Measurements were performed in the immediate postoperative period and in the outpatient follow-up.
Initially, exploratory analysis was performed in order to characterize the patient sample; frequency distributions were used for qualitative variables, and descriptive measures (mean, standard deviation) for quantitative variables.
As for the evaluation of differences between pre-and postoperative Cobb variable in the patients studied, the non-parametric Wilcoxon test was used.
The survey data were processed in the PASW statistical software.Statistically significant correlations were those with a p value of less than 0.05.

rEsULts
From 2002 to 2010, 169 records were filed with imaging exams of patients operated for adolescent idiopathic scoliosis.Of these, 45 were recently re-evaluated by the authors and included in the study.We excluded the rest because reassessment was not possible in time for analysis.The patients included are listed in Table 1.
The study sample is comprised of 5 (11.1%) male and 40 (88.9%)female patients.(Table 2) In relation to age, 82.2% of patients surveyed are at the stage of skeletal immaturity.Adult subjects make up the remaining percentage (17.8%).(Table 2) The mean preoperative Cobb was 57° (+/-12.88°),postoperatively it was 6.5° (+/-3.36°),and the last visit was 7.04° (+/-3.55°),considering the total sample.(Table 3) The mean values of the Cobb angle (pre, post, and last visit) showed no significant differences between males and females.The male group had a mean of 7.8° postoperatively, whereas the female group had a mean of 6.33°.(Table 4) By relating age with the Cobb angle, the group of adult patients was found to have Cobb values (pre, post, and last visit) similar to the group of skeletal immaturity.(Table 4) Table 5 presents the pre-and postoperative results for the Cobb variable, which had a p value less than the significance level of 5%.Therefore, we reject the hypothesis that the medians of the Cobb variable are equal in the examined individuals.There is sufficient evidence to affirm that the preoperative Cobb angle in patients is greater than the Cobb angle in the postoperative period, as expected.
In comparing the Cobb angle postoperatively and at the last visit, there was no statistically significant difference found, p = 0.176.(Table 5)

DIscUssION
Over the past 20 years the treatment of idiopathic scoliosis has made great advances.The introduction of the third generation instrumentation and the use of pedicle screws have greatly increased the possibilities of correction and improvement of results.
With 21 patients, 16 women (76.2%) and 5 men (23.8%), with a mean preoperative Cobb angle of 62.38° and a mean postoperative angle of 38.8°, Rodrigues et al. 2 obtained correction of 61.36% of the initial curve.This paper cites no information about the postoperative follow-up.Pratali et al. 12 treated 17 patients, 16 women (94.11%) and one man (5.88%) with a mean preoperative Cobb angle of 53.4° and 15.2° postoperatively.The mean correction achieved was 71% of the initial curve.In their series, two patients (11.76% of total patients) presented complications.
Comparing the efficiency and safety of the surgical treatment of idiopathic scoliosis in skeletally immature patients and adults (closed triradiate cartilage), Yuan et al. 13 reviewed the results of 40 patients (16 skeletally immature and 24 adults), showing good correction and maintenance of results in both groups.However, there were larger corrections and greater loss of correction in the skeletally immature group.In our study, a slightly higher loss of correction was also observed in the follow-up of skeletally immature patients.
After a minimum follow-up of 3 years postoperatively, Lehman et al. 14 showed a 2.14° mean loss of correction of the Cobb angle (a 12.73% loss).
Guanyu et al. 15 published a case series of 27 patients with adolescent idiopathic scoliosis surgically treated with pedicle screws.After 2 years of follow-up, there was an average loss of 2.5° on the final correction of the Cobb angle, corresponding to 19.23%.
Garcia et al. 16 reported a positive experience in the correction of adolescent idiopathic scoliosis of 36 patients, using third generation instrumentation.
In our series, 45 patients were followed up for a mean period of 7.1 years and a minimum of 1 year, with a mean correction of 89.73% and an average loss on follow-up of only 0.54° (average Cobb in the immediate postoperative period: 6.5° and at the last visit: 7.04°).There was no statistically significant difference when comparing the skeletally immature patients with the adults.(Figures 2, 3, 4, and 5) We believe that this loss of only 0.54° of correction is due to a posterior approach with rigid instrumentation, using a greater number of fixation points, large caliber and long screws, covering the three columns, with a combination of anterior approach in the more severe and rigid curves, particularly in cases of younger adolescents with great potential for worsening and risk of the crankshaft phenomenon.We conclude that in this group of patients there was no statistically significant correction loss after surgical treatment of adolescent idiopathic scoliosis, even after long-term follow-up.

Figure 1 .
Figure1.A) Anterior approach to the thoracic spine, thoracotomy with selective intubation, preservation of intercostal arteries and veins, epiphysiodesis of the vertebral body in the young adolescents with great potential for aggravation, vertebral mobilization and arthrodesis.B) Anterior approach of the thoracolumbar spine, with thoraco-phrenectomy, does not require selective intubation.

Figure 2 .
Figure 2. Patient 6, female, radiograph before and after surgery for adolescent idiopathic scoliosis, 1 A N, refused surgery at age 17, at age 24 opted for correction, stiffer curve, anterior and posterior approach was performed.

Figure 4 .
Figure 4. Patient 2, female, 3 B N, 12 years, menarche absent, Risser zero, greatevolutionary potential, we opted for a selective approach of only the medium thoracic curve (more structured), epiphysiodesis and anterior arthrodesis were performed to prevent the crankshaft phenomenon, ending with the correction by posterior approach.From left to right, the preoperative radiographs, those in the immediate postoperative period, and after six years.

Figure 5 .
Figure 5. Patient 2, the case in Figure 4, preoperative photos at age 12, one year later, and at age 18, the correction and trunk balance are observable, and in the picture on the right maintenance of correction after 6 years.Figure 3. Patient 6, A) before surgery on 2/18/06, B) 7/28/09, over 3 years postoperatively, showing good correction and trunk balance.

Table 1 .
Description of the variables for each patient.

Table 2 .
Frequency distribution of patients according to demographic characteristics.

Table 3 .
Cobb angle assessment for the total patient sample.Cobb angle assessment by sex and age.probabilities (p value) refer to the Wilcoxon test.The p values in bold indicate significant differences.The significant results were identified with asterisks according to the level of significance, namely: p value < 0:01 ** (confidence level of 99.0%) and p value < 0.05 * (confidence level of 95.0%).Source: Research data.