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Section I: SYMPOSIUM: Tribute to Dr. G. Dean MacEwen

Selective Screening for Scoliosis

Bunnell, William P MD

Editor(s): Guille, James T MD, Guest Editor; Kumar, S Jay MD, Guest Editor

Author Information
Clinical Orthopaedics and Related Research: May 2005 - Volume 434 - Issue - p 40-45
doi: 10.1097/01.blo.0000163242.92733.66
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Abstract

School screening for scoliosis has been practiced widely in the United States and throughout the world for nearly 50 years. A large body of literature has been established during this time describing techniques9 and the outcome of clinical experience.9,12,28,33,35,55 The orthopaedic community views the beneficial results of spinal screening, most notably a reduced need for spinal fusion, but epidemiologists and public policymakers consider screening unjustified for several reasons, mainly cost.13,22,45,46 Recent publications by the United States Preventive Services Task Force recommend against spinal screening66,67 but may not fully recognize data answering some of their objections.18,29,38,42,43,48,51,58,68,72

The major factors fueling this controversy include the low prevalence rate of significant spinal deformity, the high sensitivity but low specificity of available screening techniques, and the high but hidden cost of managing large numbers of false positive referrals.9 Orthopaedic surgeons view spinal screening as beneficial and cite the effectiveness of nonoperative treatment as evidence48,58 whereas epidemiologists and public policymakers argue that the total health care burden of scoliosis is low and the cost of screening excessive.13,22,45,46,66,67

My purpose in doing this study is to review briefly this collective experience, to review newer knowledge about scoliosis having direct implications for screening, and to make recommendations for increasing screening effectiveness.

Scoliosis Screening

G. Dean MacEwen, MD played an important role in the early development of school screening by implementing programs in all schools in the state of Delaware in the 1960s.26 A large body of literature has been established since that time that reports a great deal of clinical experience.9,12,28,33,35,55

Scoliosis is a lateral curvature of the spine measuring at least 10° on an xray as determined by the Cobb method. Structural scoliosis is characterized by vertebral and trunk rotation.

Screening is the presumptive identification of unrecognized disease or defect by the application of tests, examinations, or other procedures that can be applied rapidly.

The goal of screening is to detect scoliosis at an early stage when deformity is likely to go unnoticed and when there is opportunity for a less invasive method of treatment than would otherwise be the case.14

All screening techniques depend on surface topography. The Adams forward bending test is well known to school and primary health care personnel and widely used to provide a subjective or qualitative evaluation of spinal deformity.

The application of physical measurements provides a quantitative evaluation of deformity and the basis for objective referral criteria for screening, which substantially increases its effectiveness.3 Many devices and techniques have been used, including measurement of the rib hump height using a level and ruler, stereophotogrammetry, flexicurve, ultrasound, thermography, back contour devices, etc.9

Moiré topography, a photographic method, and computerized surface mapping systems such as Integrated Shape Imaging Systems (ISIS) have been studied extensively and provide the most complete description of surface topography. The time and expense required to do these studies make them impractical for mass screening.1,15

Inclinometry [measurement of the angle of trunk rotation (ATR) observed with the patient in the forward bent position] seems to be the simplest, quickest, most reliable, and least expensive objective measurement of trunk deformity.9,24,31 One useful device, the scoliometer (Orthopaedic Systems, Inc., Union City, CA), has achieved widespread usage with numerous reports of its reliability.2,9,29,47,60,65

None of these techniques is diagnostic. Radiographs are required to establish the diagnosis, etiology, and severity of spinal deformity.

Organization, public information, and documentation are important aspects of screening programs. Many articles have appeared primarily in the school health literature regarding these issues.55

From an orthopaedic standpoint, screening is beneficial. It provides an individual opportunity for early diagnosis and nonsurgical treatment, which is often missed in the absence of screening.

This view is not shared by epidemiologists and public policymakers who view the problem at a macro level. They consider the total health care burden of scoliosis to be low, the prevalence low, the specificity of the screening test low, the false-positive rate high, and the cost of screening excessive. For them, screening for scoliosis is not indicated.13,22,45,46,66,67

The Scoliosis Research Society and the American Academy of Orthopaedic Surgeons have endorsed scoliosis screening. It is mandated by law in 22 states, recommended in 14, and practiced at some volunteer level in most other states in the United States and in many other countries.5 All programs use the Adams forward bending test and most now use objective criteria for referral. The National Scoliosis Foundation (Stoughton, MA) has long been a leader, promoter and coordinator of this effort.

Outcome of Spinal Screening Programs

There was widespread enthusiasm for these programs in the early years of their implementation and in the absence of objective criteria for referral, a “contest” mentality developed in which the de facto goal was to identify every student with even the slightest deformity. Many series were reported from different communities with referral rates as high as 21%.8,9,20,21,23,25,39

Recognition of the problem of overreferral led to the practice of re-screening done presumably by more experienced personnel in an attempt to be more selective.18 The introduction of objective deformity measurements and referral criteria provided some standardization to the referral process.9 Authors of many studies reported on the screening of hundreds of thousands of school children and began to show remarkably consistent referral rates of 2% to 5%.16,24,27,32,40,41,49,50,52,62,63,68,72 Referral rates have been reduced by as much as 90% by the use of objective criteria.9,29,54 Nearly all authors now agree that the referral rate should be in the 2% to 3% range.9,29,53,68

Authors of long-term studies of well-controlled populations have shown a notable change in the demographics of scoliosis treatment. In general, the average degree of curvature at diagnosis decreased greatly with screening, the number of braces prescribed increased because of earlier detection, and the number of spinal fusions required decreased because of effective brace treatment.38,42,43

Conditions most suitable for screening have a high prevalence rate.45,46 Although the prevalence of small degrees of scoliosis is quite high, the prevalence of scoliosis requiring treatment (greater than 25 to 30°) is quite low (2 to 3 in 1000). This makes the predictive value of any positive screening test low.44

Unfortunately, lack of general standards and the resultant disparity among programs with respect to screening education, procedures, referral criteria, data retrieval and management, followup methods, etc, have limited the informational benefits of scoliosis screening programs. This has been a great missed opportunity to learn even more about the prevalence and natural history of scoliosis.

All screening techniques rely on back surface topography and clinical deformity for recognition of scoliosis. The Adams test is quick, sensitive (able to identify the condition), and acceptable to patients. Objective measurements increase the specificity (ability to exclude those who do not have the condition) of the screening process.29,54

It has become apparent from many reports that although there is a significant correlation between clinical deformity and radiographic measurement, the standard deviation is so high that it is not possible to reliably predict the degree of curvature from surface topography in any given patient by any technique.9,29,31,35,59,60 In general, clinical deformity is disproportionately greater than expected for the degree of Cobb angle in the early stages of the development of scoliosis. This discrepancy makes the screening test more sensitive in detecting small degrees of curvature, but less specific in excluding those of no clinical importance. This inverse relationship between sensitivity and specificity creates a conundrum: specificity can be achieved only by compromising sensitivity and vice versa.

Other problems with the examination process include failure to provide reliable mechanisms to identify students absent on the day of screening or to provide screening for private or home-schooled children. Failure of families to obtain medical followup is another problem reported to be more than 50% in one study.68

Early cost estimates for school screening were artificially low because of failure to include all proper expenses created by the conversion of a “student” into a “patient.” These must include not only the costs of the screening process itself (about 6 cents per student),38 but also those for medical examinations and xrays of all students referred (including false positives) and all followup examinations and xrays. It must also include all costs for those treated in braces with all their subsequent medical evaluations and xrays plus the costs for surgical treatment for any who fail brace treatment.6,12,41 Hidden costs include productivity loss by the parents, travel expenses, etc. Comparison costs in the absence of screening must include those for children referred by primary care physicians for examination and treatment including braces or surgery and those patients in whom the condition was discovered late who require surgical treatment. Most agree that the total cost of screening programs is equal to or greater than the cost of not screening.12,41,44 The problem of over-referral dramatically escalates the total cost of screening.

One of the great contributions of school screening programs has been a new appreciation of the widespread prevalence of small degrees of deformity and curvature and the opportunity to study the natural history of these curvatures.

Shands and Eisberg61 reported the first mass screening exercise for scoliosis by reviewing 50,000 chest mini-films done in the state of Delaware for tuberculosis screening in the general population and determined the prevalence of scoliosis greater than 10° to be 19 in 1000. Many other clinical and radiographic studies have been done since then on large populations11,33 with remarkably similar findings. More importantly, authors of many of these studies report a dramatic decrease in prevalence for larger curves.4,11,12,32,33,49,52,56,62,63,72 The prevalence of 20° curves decreases to 5 in 1000 and further drops to 2 in 1000 for 30° curves and 1 in 1000 for curves of 40° or more. The prevalence of 5° scoliosis is estimated at 77 in 1000. This information has clear implications for scoliosis screening and points to the need to reconsider the degree of curvature required to be of significance for diagnostic and screening purposes.

Authors of all studies report the prevalence of scoliosis nearly equal despite gender for small curves but increased three to 10 times in girls for curves greater than 30°. Curves less than 20° typically present in preadolescent children and many resolve spontaneously or remain nonprogressive.

The health burden for adolescents is almost entirely related to the deformity itself including the risk of increasing deformity. The health burden for adults also includes the deformity, but the risk of progression is generally limited to those with curves exceeding 50°. Severe thoracic curves (greater than 80°) cause cardiopulmonary compromise and curves found in the lower spine seem to increase the incidence and severity of back pain.69 The health burden imposed by scoliosis is well known but is considered low by public health experts.

Prevention of curve progression is the main treatment concern for adolescents. If it is to occur, it always does so during the time of peak growth velocity, typically during the year just prior to menarche.12 Determining which curves will become progressive and will require treatment remains elusive for individual patients, but several risk factors have proven to be predictive. The most important of these factors include gender (female risk 3–10 times greater than male risk), chronologic age (those younger than 12 years have three times the risk of progression), menarche (risk is reduced by ⅔ after menarche), curve pattern (thoracic and double-major curves have a threefold increased risk of progression over nonthoracic curves), growth potential (greatest risk of progression during peak growth velocity), curve magnitude (risk of progression is 20% for 20° curves, 60% for 30° curves, and 90% for 50° curves), and Risser stage (risk reduced by ⅔ if iliac crest more than 50% capped).10,11,34,36,71 Because all except curve magnitude and Risser stage can be known at the time of the screening examination, individuals clearly at low risk for curve progression could be excluded from the referral process.

It has been observed that all scoliosis eventually requiring treatment can be identified by rib deformity at age 10.7,70 In these well-controlled studies, no case of progressive scoliosis was found in patients who had no rib deformity at age 10.

A substantial number of patients will have nonstandard rotation, ie, it is either in the opposite direction or at a different level of the spine than expected.3 These most certainly are nonstructural curves and none are progressive.

Comparing the outcome for treated and untreated scoliosis patients provides the basis for evaluating the effectiveness of nonsurgical treatment. Many reports show success in preventing curve progression with orthotic treatment.19,34,48 Authors of a meta-analysis of the effectiveness of nonoperative treatment for idiopathic scoliosis showed that 51% of untreated patients had curve progression whereas only 7% had progression while wearing a brace 23 hours per day.58 It was shown in an important prospective study of the effectiveness of brace treatment for scoliosis sponsored by the Scoliosis Research Society that progression occurred in 66% of those patients not offered brace treatment whereas progression occurred in only 26% of those treated with a brace. The predicted risk of progression for this group of patients if untreated was greater than 50%.48

The effectiveness of surgical treatment has increased dramatically in the past 25 years because of advances in anesthesia, blood management, and instrumentation and fusion techniques. A review of surgical treatment is not relevant to the screening discussion.

DISCUSSION

Much has been learned about the prevalence and natural history of scoliosis over the past 25 years. Scoliosis screening has proven effective in many ways, but a number of problems prevent it from being universally accepted. The de facto goal of early screening programs was to find every child with even the slightest degree of scoliosis and the result was overreferral on a grand scale. The new goal should be to identify only those children who have significant curves likely to require treatment.14 This would require selective screening of high-risk students, primarily preadolescent females.

Using a Cobb angle of 10° as the minimum significant curvature to establish a diagnosis of scoliosis includes a great many that are truly insignificant. Because most curvatures less than 40° are left untreated if discovered after skeletal maturity, one might consider using 40° as the minimum requirement for a truly significant curvature when evaluating the outcome of screening, natural history, or treatment studies. Therefore, only those curves more than 40°, or those predicted to become so, are truly significant because lesser curves predicted to be stable would no longer be of interest for screening or treatment purposes.

Most authors agree that the Cobb angle is subject to at least 5° measurement error. Most authors also consider that curve progression has occurred if there is a change of 6° or more. The clinical significance of such small increases is doubtful and furthermore falsely inflates the risk of progression in the natural history data and the failure rate for brace treatment. It would seem more appropriate to consider significant progression to have occurred only in those curves that exceed 40°. This would more accurately and realistically state the outcome of natural history and brace treatment. Therefore, any stable curvature less than 40° at skeletal maturity would be considered a satisfactory outcome (whether by natural history or brace treatment), and only those curves more than 40° would be considered unsatisfactory.

It seems that nearly all significant curvatures can be found on physical examination by age 10. Screening only 10-year-olds would reduce the screening burden by 50% compared with the present recommendation for screenings at ages 10 and 12.3,71 This typically would be fourth or fifth grades in schools in the United States.

The risk of some curve progression is nearly 10 times greater in females than in males and the risk of requiring spinal correction and fusion is nearly 10 times greater for females.10 Screening females only would further reduce the screening burden by 50%.

Because the risk of curve progression decreases dramatically after onset of menses, only premenarchal females need be screened.

It seems that there is an ideal window of time for scoliosis screening because those who develop the condition show clinical signs by age 10 years and are no longer at risk of significant progression after menarche (average age, 12.5 years). Selective screening would dramatically increase the value of screening by reducing the total number screened and eliminating those presumed to be at very low risk of developing a significant scoliosis.

Objective criteria for referral must be established for each technique used in the screening examination. A scoliometer reading of greater than 7°, a rib height difference greater than 10 mm, and two or more fringe differences on Moiré topography have been suggested.9,27,29,53,54

Re-screening was an integral part of early programs and should be reinstituted using objective measurements and criteria to reduce the referral rate of borderline cases.

A patient with a scoliometer angle of trunk rotation measurement of 5° or less should be dismissed without re-screening with reasonable confidence that a significant scoliosis is not present or likely to develop. Patients with scoliometer angle of trunk rotation measurements greater than 10° should be referred immediately for medical evaluation and xray. Patients with scoliometer angle of trunk rotation readings of 5° to 9° should be re-screened every 6 months until 1 year after the occurrence of menarche. Documentation and followup by school health personnel are essential.

The obvious benefit of spinal screening is that it creates the opportunity to institute early nonsurgical treatment of spinal deformity and thereby reduces the need for spinal fusions. Reducing overreferral of curvatures not likely to require treatment by selective screening of high-risk students using objective criteria and re-screening rather than referring patients who have borderline cases greatly can enhance the effectiveness of spinal screening programs.

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