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Scoliosis generally experiences it's most rapid curve progression during a patients adolescents until they reach skeletal maturity.  Often parents and patients are told that curvature won't continue to progress after that point.  Unfortunately, that generally isn't the case and many adolescent idiopathic scoliosis patients do experience continued curve progression throughout life (average 1-3 degrees per year).  This is particularly true in cases in which the curvature was over 25 degrees when the patient reached skeletal maturity (as discussed in the following study).  It is absolutely imperative that a patient engaged in an effective early stage scoliosis intervention program that works to keep the spinal curvature under 20 degrees while the patient is still growing and allows them to reach skeletal maturity with the curvature measuring less than 25 degrees.

 

Curve Progression in Idiopathic Scoliosis

Follow-up Study to Skeletal Maturity

 

Ken-Jin Tan, MBBS, MMed, MRCS,* Maung Maung Moe, MBBS,*

Rose Vaithinathan, MBBS, MMed,† and Hee-Kit Wong, MBBS, FRCS*

Study Design. This is a follow-up study to skeletal maturity

on a cohort of students screened for a 1-year prospective

epidemiological prevalence study for scoliosis.

 

Objectives. This study aims to identify the prognostic

factors for curve progression to a magnitude of 30° at

skeletal maturity in skeletally immature patients with adolescent

idiopathic scoliosis.

 

Summary of Background Data. The natural history of

idiopathic scoliosis is not well understood. Previous reports

have focused on the characteristics of curve progression

where progression has been predefined at specific angles of

5° to 6°. However, the absolute curve magnitude at skeletal

maturity is more predictive of long-term curve behavior

rather than curve progression of a defined magnitude over

shorter periods of skeletal growth. It is generally agreed that

curves less than 30° are highly unlikely to progress after

skeletal maturity. Hence, defining the factors that influence

curve progression to an absolute magnitude of more than

30° at skeletal maturity would more significantly aid clinical

practice.

 

Methods. One hundred eighty-six patients who fulfilled

the study criteria were selected from an initial 279 patients

with idiopathic scoliosis detected by school screening, and

who were followed-up till skeletal maturity. The initial age,

gender, pubertal status, and initial curve magnitude were

used as risk factors to predict the probability of curve progression

to more than 30° at skeletal maturity.

 

Results. Curve magnitude at first presentation was the

most important predictive factor for curve progression to a

magnitude of more than 30° at skeletal maturity. An initial

Cobb angle of 25° had the best receiver-operating characteristic

of 0.80 with a positive predictive value of 68.4% and

a negative predictive value of 91.9% for curve progression

to 30° or more at skeletal maturity.

 

Conclusion. Initial Cobb angle magnitude is the most

important predictor of long-term curve progression and behavior

past skeletal maturity. We suggest an initial Cobb

angle of 25° as an important threshold magnitude for longterm

curve progression. Initial age, gender, and pubertal

status were less important prognostic factors in our study.

Key words: adolescent idiopathic scoliosis, natural

history, Cobb angle, curve progression, skeletal maturity.

Spine 2009;34:697–700

Knowledge of the natural history and factors that influence

curve behavior over time is critical in the evaluation,

prognostication, and management of patients with scoliosis.

Particularly, in the case of school-based screening

programs, the surgeon is often faced with the management

of a large number of patients many of whom have

relatively small curves at presentation.

There have been relatively few studies on the natural

history of adolescent idiopathic scoliosis, and these have

largely been limited to the analysis of defined units of

curve progression.1–3 Some factors that have been identified

to be related to progression include the magnitude

of the curve, the patient's age at presentation, the Risser

sign, and the patient's menarchal status.1–3

Although previous authors have identified the risk of

curve progression by a stipulated magnitude of usually

5° and the associated factors, this does not allow the

physician to predict the longer-term behavior of the

curve at skeletal maturity and into adulthood.

An understanding of curve behavior into skeletal maturity

and adulthood is important as it is now established

that curves because of idiopathic scoliosis do not necessarily

stop progressing after skeletal maturity. In a longterm

follow-up study of patients with idiopathic scoliosis,

Collis and Ponseti4 found that curves of larger degree

did increase after skeletal maturity. In a separate study

with an average follow-up of 40 years, Weinstein and

Ponseti5,6 also found that a significant number of idiopathic

curves increased after skeletal maturity. They reported

that in thoracic curves, the Cobb angle, apical

vertebral rotation, and the Mehta angle were important

prognostic factors. For lumbar curves, the degree of apical

vertebral rotation, the Cobb angle, the direction of

the curve, and the relationship of the fifth lumbar vertebra

to the intercrest line were of prognostic value. However,

they also observed that curves that were less than

30° at skeletal maturity tended not to progress regardless

of curve pattern.

In this study, we report on a group of 279 patients

with idiopathic scoliosis detected by school screening,

and who were followed-up until skeletal maturity. One

hundred eighty-six patients fulfilled the study criteria

and for these adolescents, the initial age, gender, pubertal

status, and initial curve magnitude were used as risk

factors to predict the probability of curve progression to

more than 30° at skeletal maturity.

 

Materials and Methods

Our study population was derived from a cohort of school

children screened for scoliosis in 1997 the results of which were

From the *Department of Orthopaedic Surgery, National University

Hospital, National University of Singapore, Singapore; and †Health

Promotion Board, School Health Service, Singapore.

Acknowledgment date: May 12, 2008. Acceptance date: October 21,

2008.

The manuscript submitted does not contain information about medical

device(s)/drug(s).

No funds were received in support of this work. No benefits in any

form have been or will be received from a commercial party related

directly or indirectly to the subject of this manuscript.

Address correspondence and reprint requests to Ken-Jin Tan, MBBS,

MMed, MRCS, Department of Orthopaedic Surgery, National University

Hospital, 5 Lower Kent Ridge Road, Main Building 1, Singapore

119074, Singapore; E-mail: This e-mail address is being protected from spambots. You need JavaScript enabled to view it

697

previously reported.7 In this study, 72,699 children aged 6 to

14 years out of a total enrolment of 152,000 schoolchildren

were screened for a 1-year prospective epidemiological prevalence

study for scoliosis. Of the 72,699 screened, 279 were

diagnosed to have idiopathic scoliosis on the basis of a single

standing radiograph, which showed a Cobb angle equal to or

greater than 10°. Of the 279, 17 were either uncontactable or

did not attend more than once.

The selection criteria for the present study on curve progression

were that the adolescent must be skeletally immature at the

beginning of the study and be skeletally mature at the last

follow-up appointment. Skeletal maturity was defined as an

age of 15 years or a Risser grade of 4 or 5.5 Patients with

incomplete data on maturity or on factors studied were also

excluded.

Of the 262 patients, 36 patients were skeletally mature at

presentation and excluded from the study. The remaining 226

patients were observed-up at regular intervals ranging from 3

to 6 months over the following years. The follow-up period

ranged from 1 to 8 years. During the period of follow-up, some

patients were referred for bracing or surgical fusion of the

curve. Their final Cobb angle at the last follow-up appointment

was used for the study.

At the end of the study, 9 patients had not attained skeletal

maturity and 31 patients had incomplete data or were lost to

follow-up. These patients were excluded from the study. The

remaining 186 patients formed the study group.

84.9% of the patients were girls, with 37.3% being of prepubertal

status. The initial age of the patients ranged from 7 to

14 years of age. The median age was 12 years with a mean

(standard deviation) of 12 (1.50) years with 34.9% less than 12

years of age. Of the 186 patients, 38 (20.4%) progressed to a

Cobb angle of 30° or more at skeletal maturity.

The study parameters analyzed were the age at first appointment,

gender, initial or presentation Cobb angle and

initial pubertal status. Both univariate and multivariate

analyses were performed. The
2 test was used for univariate

analysis and a logistic regression model was used for multivariate

analysis. Receiver operating characteristic (ROC)

analysis was used to determine the optimal cut-off for Cobb

angle at presentation.

 

Results

ROC analysis demonstrated that the Cobb angle at

presentation was the single most important factor that

predicted further curve progression to a Cobb angle of

30° or more at skeletal maturity. Age, pubertal status,

and gender were not found to be of predictive value

(Figure 1).

Furthermore, a Cobb angle of 25° at presentation had

the best overall predictive value for curve progression to

a Cobb angle of 30° or more at skeletal maturity. The

ROC value for a Cobb angle of 25° at presentation was

0.80. This was associated with a positive predictive value

of 68.4% and a negative predictive value of 91.9%for

curve progression to 30° or more at skeletal maturity

(Figure 2). These findings on ROC analysis closely

agreed with the results of univariate and multivariate

analysis.

Using a cut-off presentation Cobb angle of 25° as

determined by ROC analysis, 68.4% of patients with a

Cobb angle of 25° or more at presentation progressed

to a final Cobb angle of 30° or more. This compared

with 8.1% of patients with a Cobb angle of less than

25° at presentation. This difference was highly significant

on both univariate and multivariate analyses

(P
0.001).

Patients who had an initial age less than 12 years

(26.2%) compared with patients aged 12 years and

above (17.4%) had a final Cobb angle of 30° or more.

This difference was not found to be of significance

(P 0.158).

Relatively similar percentages, 23.0% (17 patients)

who were prepubertal initially and, 18.8% (21 patients)

who had attained puberty initially, progressed to a final

Cobb angle of 30° or more (P 0.485).

The difference in gender between the patients that

progressed and did not progress to a final Cobb angle

of 30° was slightly more pronounced than that for age

Figure 1. ROC plots for the various factors analyzed. The Cobb

angle at presentation was the single factor that had an ROC curve

that was significantly different from the reference line. The ROC

plots for age, pubertal status, and gender all lie close to the

reference line.

Figure 2. The ROC plots for 16° to 29° cut-offs for the presentation

Cobb angle are presented here. The 25° cut-off had the

highest ROC.

698 Spine • Volume 34 • Number 7 • 2009

and pubertal status. 22.8% of girls compared with

7.1% of boys progressed to a final Cobb angle of 30°

or more. This difference was close to statistical significance

(P 0.076). Table 1 shows the univariate and

multivariate analyses of age being less than 12 years,

gender, pubertal status, and Cobb angle at presentation

on curve magnitude of 30° or more at skeletal

maturity.

When factors were combined and analyzed by logistic

regression, we found that a prepubertal girl less than 12

years of age with a Cobb angle of 25° or more at presentation

had the highest chance of progression (82.23%) to

a Cobb angle of 30° or more (Table 2).

On the other hand, a boy who was postpubertal

with an age of 12 years or more and an initial Cobb

angle of less than 25° was least likely to progress to a

Cobb angle of 30°. This probability was only 2.39%.

Conversely, the same male patient would have a

97.61% probability of his curve not progressing to a

Cobb angle of 30° or more (Table 2).

For logistic regression analysis, the probability of progression

to a final Cobb angle of 30° or more was calculated

by the following equation.

Probability of final Cobb angle  30 1/

(1 exp (z))

where z 3.709  0.931 (gender)  0.825 (pubertal

status)  3.314 (initial Cobb angle)  0.171 (age at

presentation).

Where girl 1, boy 0; before puberty 1, after

puberty 0, initial Cobb angle
25 0, initial Cobb

angle 25 1; age at presentation 12 0, age at

presentation
12 1.

 

Discussion

The care of adolescents with mild curves because of idiopathic

scoliosis is a constant clinical dilemma. Management

decisions should ideally be based on accurate

prediction of long-term curve behavior and not on risk

for curve progression of a defined magnitude over

shorter durations of skeletal growth.

Studies on curve progression include those by Lonstein

and Carlson and Soucacos et al, which examined

for curve progression as defined by a limited increase in

curve magnitude of 5 to 6°.1,2 Lonstein and Carlson1

found that the strongest predictive factors for curve progression

were the curve magnitude, the Risser sign and

the chronological age. Similarly, Soucacos et al observed

a strong association between the incidence of curve progression

and sex of the child, curve pattern, maturity

(pubertal status), age, and curve magnitude.2

In addition, a recent French study, which retrospectively

reviewed 205 patients with idiopathic scoliosis,

found that curve pattern, Cobb angle at onset of puberty

and curve progression velocity to be strong prognostic

factors of curve progression during pubertal growth.3 In

the above study, the authors found that juvenile scoliosis

with magnitude more than 30° increased rapidly during

pubertal growth and had a 100% prognosis for surgery.3

Weinstein and Ponseti, after following-up 102 patients

over more than 4 decades, reported that curves

that were less than 30° at skeletal maturity tended not to

progress regardless of curve pattern. This was unlike

curves with a magnitude above 30°, which had a higher

Final Cobb refers to the Cobb angle at skeletal maturity.

Curve Progression in Idiopathic Scoliosis • Tan et al 699

tendency to progress, even after skeletal maturity. In this

study, skeletal maturity was defined as a Risser grade of

4 or 5.7

Hence, it would be more useful to have data on the

risk of curve progression to a magnitude of 30° or more

and the factors associated with this. This information

would enable a more accurate prediction of curve behavior

in the long-term and at the same time reducing the

number of patients requiring follow-up. Available data

suggests that curves with a magnitude of less than 30° at

skeletal maturity do not continue to progress, whereas

those of magnitude 30° or more behave differently and

have a propensity for further progression. Our study

aims to address this need by following-up adolescents

with idiopathic scoliosis detected in our national screening

program to skeletal maturity and analyzing the progression

risk and associated risk factors.

The main prognostic factor that we identified in our

study was curve magnitude at presentation. Age, gender,

and pubertal status had much less prognostic

value than curve magnitude. There has been no agreement

as to the most important factors that influence

curve progression in previous studies. However, age,

gender, and pubertal status have previously been

found to be important factors.

A possible reason why age, gender, and pubertal status

were much less important in our study could be the

different aspect of curve behavior studied. Therefore, it is

likely that the factors involved would reflect the growth

potential of the patient during the likely shorter period of

curve progression of 5° to 6°. However, we followed-up

the patients' curves to skeletal maturity regardless of the

magnitude of curve progression. Hence, prognostic factors

in our study may be less dependent on shorter periods

of curve progression but instead be more reflective of

the risk of final curve progression to a defined threshold

magnitude of 30°.

Our findings of a critical Cobb angle of 25° at first

presentation suggests that regardless of previous curve

magnitude or curve progression during skeletal growth,

the absolute value of the curve at presentation is the most

important factor in long-term prognostication. Our logistic

regression model also identified that a Cobb angle

at presentation of 25° or more when combined with a

girl less than 12 years of age and prepubertal status gave

the highest risk for curve progression to a Cobb angle of

30° or more at skeletal maturity. This was in contrast to

a boy who was postpubertal with an age of 12 years or

more and a Cobb angle at presentation of less than 25°.

This profile was associated with only a 2.39% probability

of the curve progressing to 30° or more at skeletal

maturity.

 

Key Points

● Cobb angle on initial presentation is the most

important predictor of long-term curve progression.

● Curves with a Cobb angle of 25° or more have a

68.4% probability of progressing to 30° or more at

skeletal maturity. On the other hand, curves with a

Cobb angle of less than 25° have a 91.9% probability

of not progressing to 30° or more at skeletal

maturity.

● A prepubertal girl less than 12 years of age with

a Cobb angle of 25° or more at presentation had an

82.23% chance of progression to a Cobb angle of

30° or more.

● Conversely, a postpubertal boy, 12 years old or

older, with a Cobb angle of less than 25° at presentation

had only a 2.39% chance of progression to a

Cobb angle of 30° or more.

 

References

1. Lonstein JE, Carlson JM. The prediction of curve progression in untreated

idiopathic scoliosis during growth. J Bone Joint Surg Am 1984;66:1061–71.

2. Soucacos PN, Zacharis K, Gelalis J, et al. Assessment of curve progression in

idiopathic scoliosis. Eur Spine J 1998;7:270–77.

3. Charles YP, Daures JP, Rosa VD, et al. Progression risk of idiopathic juvenile

scoliosis during pubertal growth. Spine 2006;31:1933–42.

4. Collis DK, Ponseti IV. Long-term follow-up of patients with idiopathic scoliosis

not treated surgically. J Bone Joint Surg Am 1969;51:425–45.

5. Weinstein SL, Ponseti IV. Curve progression in idiopathic scoliosis. J Bone

Joint Surg Am 1983;65:447–55.

6. Weinstein SL, DC Zavala, Ponseti IV. Idiopathic scoliosis: long-term follow-

up and prognosis in untreated patients. J Bone Joint Surg Am 1981;63:

702–12.

7. Wong HK, Hui JH, Rajan U, et al. Idiopathic scoliosis in Singapore schoolchildren:

a prevalence study 15 years into the screening program. Spine 2005;

30:1188–96.

700 Spine • Volume 34 • Number 7 • 2009