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Adolescent Idiopathic Scoliosis

Adolescent Idiopathic Scoliosis: 5-Year to 20-Year Evidence-based Surgical Results

Westrick, Edward R. MD; Ward, W. Timothy MD

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doi: 10.1097/BPO.0b013e3181fd87d5
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Abstract

Adolescent idiopathic scoliosis (AIS), a structural 3-dimensional deformity of the spine that occurs in otherwise healthy children during puberty, is the most common form of scoliosis. The diagnosis is one of exclusion, and is made only when other causes of scoliosis, such as vertebral malformations, neuromuscular disorders, and other syndromes have been ruled out. Curvatures <10 degrees are considered a variation of normal, and those curves have little potential for progression.1 When AIS is defined as a Cobb angle of at least 10 degrees, epidemiologic studies estimate that 1% to 3% of children aged 10 to 16 years will have some degree of spinal curvature, although most curves will not require surgical intervention.2,3 Significant controversy exists with regard to the natural history of untreated AIS, the value of surgical correction,4,5 and the ideal surgical instrumentation.6–9

The primary objectives of surgical treatment for AIS are to (1) arrest progression by achieving a solid fusion, (2) achieve permanent deformity correction, (3) improve appearance, (4) improve perceived functional outcomes of cosmetic appearance, physical, and psychosocial health, and (5) diminish the development of low back pain (LBP), degenerative changes, functional impairment, and cardiopulmonary compromise in adulthood. The generally quoted indication for surgery in adolescents is a primary curve with a Cobb angle greater than 45 to 50 degrees. A thorough understanding of the natural history of untreated AIS is essential to properly evaluate the results of surgical treatment and to determine whether the benefits outweigh the risks.

NATURAL HISTORY

Early long-term studies of AIS presented a bleak prognosis, suggesting that the condition inevitably caused poor general health and disability from back pain and cardiopulmonary compromise. These studies showed increased mortality, higher percentage of unmarried women, and higher rates of disability, back pain, poor general health, and cardiopulmonary compromise. However, many studies were fraught with flaws,10–17 making the conclusions from these studies questionable. Examples of shortcomings from these studies are:

  • Inclusion of patients with other causes of scoliosis
  • Retrospective studies with small numbers and small inclusion percentage
  • No follow-up radiographs or clinical examination
  • No validated patient outcomes instruments used.

Later studies18–25 examining the natural history of AIS did not show significant disability, and disproved many of the conclusions of earlier studies.10–17 Although spinal deformity can be significant with AIS, these later studies did not show significant disability. Back pain was similar to controls,18,19,23,24 and although slightly more prevalent, it was not found to be more disabling, and had no impact on functional activities18,21–24 or perception of general health. Cardiopulmonary compromise was rare and almost never clinically significant.18,23,25 Mortality rate was equal to controls,18,19,23,25 and at middle age, patients led healthy, productive lives, with no difference in disability compared with controls.18,19,21–24 Other significant findings from these studies commonly quoted to patients regarding the risk of AIS progression are (1) curves between 50 and 75 degrees at skeletal maturity progress an average of 1 degree/y,20 and (2) thoracic curves carry the greatest risk, followed by lumbar, thoracolumbar, and double major, in descending order.24

As with any medical treatment, surgical intervention for AIS should be proven to alter the natural history in a positive manner without introducing iatrogenic complications, such as infection, pseudoarthrosis, hardware failure, and reoperation. The risks of surgery should be substantiated by a body of scientific research, which should show a clear superiority of surgery over observation, both in the short term and the long term. The purpose of this review was to conduct a systematic search of the MedLine literature to critically evaluate the scientific evidence on the long-term outcomes and complications of surgical intervention for AIS.

METHODS

A MedLine search of all the English language medical literature, American and foreign, published from 1950 to 2008 was conducted pertaining to the surgical treatment of AIS. More than 7500 articles were generated and screened by the authors, with all pertinent articles further evaluated for eligibility. Earlier investigators6,26–28 have used a similar approach.

Inclusion criteria were study of the publications between 1950 and 2008, publications in the English language, patients treated surgically with a minimum 5-year average follow-up, and patients with the diagnosis of AIS. If duplicate publications of the same data, or expanded numbers from same institution existed, the data were included only once. In eligible articles studying patients with different etiologies, only those patients with AIS were considered.

Studies were omitted if only nonsurgical treatments were undertaken, average postoperative follow-up was less than 5 years, and if only etiologies other than AIS were included in the study population. Selected articles were excluded if the data could not be interpreted, and abstract presentation data were not included.

Data Analysis

This study is a true English language literature review of the long-term surgical results of AIS, not a meta-analysis. This analysis includes descriptive measures of populations, such as mean values, rather than inferential statistics. After discussion with our departmental statisticians and University of Pittsburgh meta-analytic experts, we believe it is inappropriate to assign inferential statistics to aggregate, retrospective case series data, as there is no assurance that the patient populations of different series are identical. As there were no estimates of variability (ie, standard deviation) reported for the continuous outcomes (ie, final Cobb angle correction), it is not possible to compare the different treatment options for these variables across studies. For the dichotomous outcomes (ie, percentage of pseudoarthrosis, percentage of metal failure), it is only appropriate to combine those studies, which compare 2 or more treatment approaches in the same study. This analysis highlights the limitations of the current literature as it exists.

RESULTS

Our search identified 39 distinct patient populations from 47 articles,16,29–74 with a minimum average follow-up of 5 years. No level I or II studies were found, and all the included studies are level III or IV.75 There were 3401 patients identified between 1950 and 2008, representing 35 different cities (10 US cities) and 18 different countries. The surgical study sizes ranged from 5 to 535 patients (both outliers), and the average was 77±60 surgical patients per study when the outliers were excluded.

Although 47 articles met our criteria for analysis, articles by Cochran et al,32 Pehrsson et al,56 Danielsson and Nachemson,51,52 and Danielsson et al50,53 (total 6 articles) report on the same surgical cohort. Similarly, articles by Helenius et al59,61,72 and Remes et al76 (total 4 articles) report on the same or an expanded surgical cohort. As these articles were duplicate publications of the same data or expanded numbers from same institution, each data set was included only once. The article by Pecina and Dapic71 is an expanded letter to the editor regarding Harrington rods (HRs), but was included as 1 of the 39 independent surgical cohorts owing to the substantial amount of valid clinical information provided.

The 39 patient populations identified in these articles spanned the years 1959 to 2008, with a total of 3401 patients. Twenty-seven patients in 2 studies29,31 were noninstrumented, 113 patients in 4 studies39,46,57,73 underwent anterior fixation; 1 of these studies compared 14 anterior fixation cases with 14 posterior pedicle screw cases.57 HRs were used in 2040 patients in 19 studies, with 17 studies comprising HR only16,30,33–38,40,42,43,52,54,58,59,63,64,71 and 2 studies compared HR and segmental hooks.44,61 Segmental hooks were used in 608 patients in 10 studies, with 6 studies confined to Cotrel-Duboussett (CD),45,48,49,68–70 1 study to Texas Scottish Rite Hospital,67 1 study combined CD and Universal Spine System,47 and 2 studies combined with HR as mentioned above.44,61 Alternative fixation systems included 35 Wisconsin patients in 1 study,41 34 patients not specified in 1 study,55 179 Isola hybrid patients in 1 study,62 99 Harri-Luque patients in 1 study,66 217 all pedicle screw patients in 2 studies,57,65 and 49 mixed anterior and posterior patients with unspecified posterior fixation in 1 study.74 These patient populations are described in Table 1.

TABLE 1
TABLE 1:
Patient Information

Looking at the Cobb angle correction (Table 2), anterior systems gave an overall average correction of 62.4%, HRs gave a 34.1% average correction, and segmental hooks gave a 51.2% average Cobb angle correction. Schlenzka et al77 and Behensky et al78 each compared HR with CD with long-term HR follow-up, but with a less than 5-year follow-up for CD, and both reported little radiographic difference between the 2 systems (these were not included in the 5-y to 20-y surgical results). The study using Wisconsin fixation reported 39% correction, whereas the highest percent correction was obtained in the pedicle screw and Isola hybrid patients, at 69.5% and 63% respectively.

TABLE 2
TABLE 2:
Cobb Angle Correction

Loss of Cobb angle correction (Table 3) averaged 11% for anterior constructs, 17.5% for HRs, 6.5% for segmental hooks, 3.4% for pedicle screw fixation, 3% for Isola hybrid, and 7% for Wisconsin fixation.

TABLE 3
TABLE 3:
Loss of Cobb Angle Correction

There were no studies that reported information regarding infection (Table 4) in patients fused without instrumentation. The infection rate averaged 0% for patients treated with anterior fixation, 6.5% for HRs, 2.2% for segmental hooks and Isola hybrid, and 5.7% for Wisconsin fixation. The lowest reported infection rate was 1.4% in pedicle screw patients.

TABLE 4
TABLE 4:
Infection Rate

The rate of pseudoarthrosis (Table 5) was 22.7% in the study without instrumentation that reported results, 15.1% for anterior constructs, 3.6% for HRs, 2.8% for segmental hooks, 2.2% in Isola hybrid patients, 0% in Wisconsin, and 7.1% in the 14 pedicle screw patients who were reported.

TABLE 5
TABLE 5:
Pseudoarthrosis Rate

The rate of hardware failure (Table 6) was 12.3% for anterior constructs, 15.8% for HRs, 3.9% for segmental hooks, 0% for Isola hybrid, 8.6% in Wisconsin patients, and 7.1% in pedicle screw patients.

TABLE 6
TABLE 6:
Hardware Failure Rate

The reoperation rate (Table 7) was 10.2% for anterior constructs, 11.9% for HRs, 7.6% for segmental hooks, 7.1% for pedicle screws, 9.5% for Isola hybrid, and 5.7% for Wisconsin patients.

TABLE 7
TABLE 7:
Reoperation Rate

Health-related quality of life (HRQL) is a subjective multidimensional construct that captures the impact of health status, including disease and treatment, on physical, psychological, and social functioning. The Scoliosis Research Society (SRS) domains include pain, self-image, function, activity level, postoperative self-image, postoperative function, and satisfaction. Only 40% of the studies used HRQL outcome instruments, such as SF-36 or SRS-24/22. Typically, the questionnaires were only used postoperatively and were almost always equivalent to scores of normal age-matched nonscoliotic controls (Table 8).

TABLE 8
TABLE 8:
Health-related Quality of Life Outcome Measures

Table 9 addresses the correlation between length of lumbar fusion, lordosis, and degenerative disc disease in relation to Low back pain (LBP). Only 61% of the studies commented on the relationship between the lowest instrumented vertebra and LBP. When reported, 80% found no correlation. Only 45% of the studies reported on the relationship between lordosis and LBP, and when reported, 100% found no correlation with LBP. Only 55% of the studies commented on the relationship between degenerative disc disease and LBP, and when reported, 83% found no correlation.

TABLE 9
TABLE 9:
Correlation Between Back Pain, Fusion Length, Lordosis, and Degenerative Disc Disease

Table 10 addresses the correlation between patient satisfaction and back pain. Only 45% of the combined HR and segmental hook studies examined whether patients were satisfied with their results. Approximately 86.6% of the HR patients and 96.2% of the segmental hook patients were satisfied. Only 38% of the combined HR and segmental hook studies examined the relationship between the percentage of Cobb angle correction and patient satisfaction, and when reported, 91% found no correlation. Although pedicle screw fixation yielded the highest percentage of Cobb angle correction at 69.5%, no information was provided on patient satisfaction or percentage of Cobb angle correction related to patient satisfaction. Isola hybrid fixation, which yielded a 63% Cobb angle correction, resulted in 88% patient satisfaction, but no further information.

TABLE 10
TABLE 10:
Patient Satisfaction and Back Pain

DISCUSSION

As healthcare costs continue to rise, proving the effectiveness of surgical treatment for AIS with high-quality, evidence-based outcomes are essential. This comprehensive English language literature review showed no prospective, randomized controlled studies examining surgical intervention for the treatment of AIS. As highlighted earlier,4,79 the signs and symptoms of AIS may not be significantly altered by surgery, and this was again evidenced by this review of the long-term literature. This review calls attention to the need for prospective, randomized studies with long-term follow-up and rigorous scientific analysis of the surgical treatment for AIS.

Bridwell et al80 reported that the highest expectation and primary reason for having AIS surgery is to reduce future pain and disability as an adult. However, the 5-year to 20-year results do not provide evidence that these expectations are met, and there is no conclusive evidence that improved radiographic outcomes result in enhanced function, self-image, or health.22,81 Although adolescents with AIS may experience significant psychological distress, body image issues, and other HRQL issues, these typically decrease into adulthood.82

Smith et al83 reported that the radiographic and physical measures of deformity do not correlate well with the perceptions of appearance of patients or parents, and they do not strongly agree with the cosmetic outcome of scoliosis surgery. The surgeons advised that the assessments of patients should have more influence on the need for surgery compared with the assessment of parents or radiographic measures. Similarly, based on SRS-24, parents typically scored higher than their children in the operative treatment of AIS in total score, self-image, and overall satisfaction.84 Using Oswestry Disability Index, Visual Analog Scale, and McGill Pain Questionnaires, parents rated scoliosis problems more severely than patients, but by 2 years after surgery, both thought that the problems had decreased.85

There are several other important points to consider when examining the literature to decide on surgical strategy. Only 8 literature reports73,74,86–91 have preoperative and postoperative SRS-24 scores, but 7 of these studies report on either the same or overlapping surgical cohorts, and 6 of the articles have less than 5-year follow-up. The normative values of SRS-24/22 for significant untreated AIS patients and for normal teenagers are not known,7 and there is no standardized method for reporting the SRS-24/22, making comparisons difficult. Upasani et al74 showed that SRS pain score statistically worsened from 2 to 5 years postoperatively and trended toward statistical significance in 4 other domains, but the patient satisfaction domain remained unchanged. The minimal clinically important difference is not defined for AIS making the interpretation of studies with preoperative and postoperative scores difficult.7,92

The controversy with regard to the ideal surgical instrumentation was recently highlighted in 2 interesting commentary papers. Winter et al8 argued that competition among some surgeons has led to a “My gizmo works better than your gizmo” mentality, and the investigators urged surgeons to “avoid the rush to the latest fad.” The counter argument was made by Lenke et al9 in their response to Winter et al's paper in which they stated: “We believe the current expanded use of pedicle screw constructs for spinal deformity correction has not been driven by a modest improvement in coronal correction, but by many other noted benefits that continue our strive for optimal patient care.”

The extended use of pedicle screws, originally pioneered by Suk et al,93 allows stronger mechanical fixation, multiplanar correction, and sparing of fusion levels compared with standard constructs.65,94 The disadvantages of thoracic pedicle screws include increased cost, steep learning curve, and difficulties associated with placing pedicle screws within dysplastic pedicles.95–97 On the basis of this literature review and others,81 there is no conclusive evidence that improved radiographic outcomes correlate with enhanced function, self-image, or overall health.

CONCLUSIONS

The natural history of untreated AIS is relatively benign, and studies have not shown a significant increase in disability, back pain, cardiopulmonary compromise, or mortality; therefore, the indications for surgery remain largely for cosmetic and psychological reasons. Surgery clearly reduces deformity and prevents further progression, but its role in the prevention of other negative long-term effects of scoliosis is unknown, based on the current literature. The existing literature on long-term surgical results has many limitations, making definitive statements impossible, but the senior author continues to support and perform surgical instrumentation and fusion in adolescents with significant curves and cosmetic concerns to prevent late progression and avoid increased risk and less satisfactory correction associated with surgical intervention in the adult.

Segmental hook systems have improved Cobb angle correction over HRs and pedicle screw systems, and similarly, over segmental hooks. The loss of Cobb angle correction is less with all systems compared with HRs. Alternative instrumentation systems, such as Isola hybrid and pedicle screw fixation, have very little 5-year to 20-year average follow-up data, and further studies with long-term follow-up are necessary. Although the available information suggests that Cobb angle correction is better and loss of Cobb angle correction is less, the significance of additional marginal correction is not clear and the satisfaction rate has not clearly improved. The reported infection, hardware failure, pseudoarthrosis, and reoperation rates are low for all instrumentation systems, but these complications remain significant issues for patients.

Finally, controversy persists from an evidence-based standpoint with regard to the optimal instrumentation system, and more importantly, over the value of surgery in the treatment of AIS. No long-term, prospective controlled studies exist to support the hypothesis that surgical intervention for AIS is superior to natural history. However, surgery reliably arrests the progression of deformity, achieves permanent deformity correction, and improves appearance. Although there may be no medical necessity for surgery based on the current body of literature, the surgeon must not underestimate the psychological indication that occurs when a patient is no longer able to cope with the deformity.

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Keywords:

adolescent idiopathic scoliosis; evidence-based; optimal instrumentation

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