Abstract

Background concept: The severity and progression of adolescent idiopathic scoliosis is evaluatd radiologically by measuring Cobbs angle on AP radiographs. Spinal radiographs although invaluable in diagnosis and follow-up evaluation, carry the risk of exposure to ionizing radiation. Development of a valid non-radiologic test for measuring the curve will prevent such exposures.

Study Design: Cross sectional study.

Objective: To evaluate whether the difference in right and left lateral flexion in patients with adolescent idiopathic scoliosis is significantly greater than normal patients and whether it is a valid measure of the magnitude of the scoliotic curve.

Patient Sample: Thirty patients (25 females and 5 males) without any clinical evidence of scoliosis (controls) and 10 patients (9 females and 1 male) with adolescent idiopathic scoliosis formed the study population.

Method: All patients and controls underwent coronal range of motion tests. For the test, the subjects were instructed to start from an upright position and move to full extent of lateral flexion on each side. The distance of the tip of the middle fingers to the floor was measured for both sides. Radiographic measurement of Cobbs angle on an AP radiograph in cases of scoliosis was done.

Statistical Method: In the first part difference in the lateral bending were analyzed for both cases and control group of patients and the mean and standard deviation was calculated for both the groups. The data was analysed using two paired student t test. The next part involved using Pearson’s product - moment correlation coefficients (Pearson’s r) to find out the correlation between the Cobbs angle and difference in lateral bending in the scoliotic group.

Results: Results indicated that the asymmetry in left and right lateral bendings of the scoliosis group was significantly higher than the control group (p=0.000055). The degree of asymmetry was in almost linear correlation with the degree of Cobbs angle as measured on Radiographs with a Pearson’s correlation coefficient (r) of 0.933239.

Conclusion: The asymmetry in coronal range of motion can be used as a valid guide to assess the severity of curves and lacks the usual disadvantage of ionizing radiation exposure and high cost of radiographic measures. The pilot study may be extended to include a longer number and a longer follow-up to evaluate if asymmetry in lateral flexion progresses with progression of the curve and if it does, whether performing this simple test during serial follow ups may potentially obviate the need of serial radiographic follow up of the patient.

Introduction

Scoliosis is a three dimensional deformity that has laterl deviation and axial rotation of vertebrae. Scoliosis assessment in child or adolescent requires radiographic analysis to document the curve pattern and magnitude, and to rule out congenital anomalies or other lesions of the spine. The initial radiographic studies include standing lateral and postero-anterior (PA) views of the thoracic and lumbar spine. The Cobb angle is used as a measure of spinal curvature.1 The angle is used to plan treatment, estimate prognosis and to monitor progression of the curve over time. Although a reliable measure, the method leads to exposure to relatively high dose of ionizing radiation and may have deleterious biologic effect. This is compounded by the fact that most of this exposure occurs during a rapidly growing phase of life and this may potentially amplify these harmful effects.2 A retrospective study has shown a two fold increased risk of breat cancer among scoliosis subjects.3

Development of a non-radiographic method of assessing the severity of the scoliotic curve will help in preventing these side effects. Such methods have been commonly used for measuring the degree of kyphosis.4,5 Electro goniometer angles that had been used as alternative to Cobbs method to measure the scoliotic curve has not shown to provide sufficient clinical precision to substitute for the Cobb angle measured from spinal radiographs.6

Deformities at peripheral joints result in a change of arc of motion across that plane of movement. Simple clinical methods use this change of arc in motion in the plane of deformity to indirectly assess the degree of deformity at the joints where these deformities cannot be directly measured. This principle has traditionally been used to assess the internal rotation component of cubitus varus deformity at the elbow.7 We hypothesized that similar tests should also be applicable to scoliotic spine, which has component of deformity in three planes: frontal, sagittal and rotatory. We further hypothesized that an asymmetry of lateral bending should be a measure of the deformity in coronal plane or the lateral curvature.

External measurements although flawed by the skin movement errors are now accepted as an index of back movement.8 However we are not aware of any study that has established a correlation between the change of arc of motion in coronal plane and the severity of deformity. Change of arc of motion in the coronal plane as a reflection of the severity of lateral curvature may also indirectly reflect the severity of the entire deformity, as the biomechanical studies have shown that the lateral curvature and axial rotation of spine are coupled and that they change in tandem in response to lateral bending.9

The objective of this study was to establish 1) whether a significant asymmetry as compared to normal patients exists in lateral bending in scoliosis patients. 2) And if such an asymmetry exists, does it correlate with severity of deformity as measured by Cobbs angle on radiographs.

Material and Methods

Participants: Thirty patients without any clinical evidence of scoliosis (controls) and 10 patients (9 females and 1 male) patients with adolescent idiopathic scoliosis (all had right-sided thoracic Kings Type III curves) formed the study population. All consecutive patients suffering from right sided Kings Type III curve scoliosis were included in the study group. Patients having neuromuscular, left sided curves, or non-idiopathic scoliosis were excluded. The controls were randomly chosen from the group of patient population who presented for complaints unrelated to spine. The mean age in the case group was 9 years 6 months while in control group was 10 years 2 months. The youngest and eldest patient in both groups was 7 year and 13 years respectively.

Study Location and Duration: The study was carried out at 2000 bedded tertiary referral centre with an indoor orthopaedic strength of 280 beds. The inclusion period began 01/02/2004; all enrollments were finished by 31/07/2005. The data was analyzed at the end of study.

Ethical clearance: The study was carried out in accordance with ‘Ethical principles for medical research involving human subjects: World Medical Association declaration of Helsinki’. No additional prophylactic, diagnostic and therapeutic methods other than routine methods were employed solely for the purpose of study.

Experimental procedure: All patients and controls under went coronal range of motion tests. For the test, the subjects were instructed to start from an upright position and mvoe to full extent of lateral flexion on each side without any noticeable flexion - extension and axial rotation. They were asked to repeat the procedures three times; the third bending were taken for purpose of measurement. The first two bending acted as a warm up stretch exercise and as a teaching session for standardizing the procedure. A demonstration of the movements by the examiner along the instructions was also given. The distance of the tip of the middle fingers to the floor was measured and recorded for both sides. They then returned to their normal upright positions.

Radiographs: Radiographic measurement of Cobbs angle on a PA radiograph was done using standard Cobbs method for only the scoliotic (cases) patients. The films were taken on 15 x 12 cassette and Cobbs angle measurement was done by a blinded second orthopaedic surgeon. The results were tabulated along with the difference in lateral bending of the study group (Table 1). No radiographs were taken solely for the purpose of study.

Table 1 : Statistical analysis of difference in lateral bending of Scoliosis and control groups

Statistical Analysis: In the first part difference in the lateral bending were analyzed for both cases and control group of patients and the mean and standard deviation was calculated for both the groups. The data was analyzed using two paired student t test. The next part involved using Pearson’s product - moment correlation coefficients (Pearson’s r) to find out the correlation between the Cobbs angle and difference in lateral bending in the scoliotic group.

Results

The findings of this study proved that an asymmetry in lateral bending that was significantly greater than normal population existed in scoliosis patients and this asymmetry correlated well with severity of curve as measured on radiographs (Cobbs angle).

The average difference in lateral bending of two sides in the control group was 0.86 cm with a range of 0 cm to 1.9 cm and a standard deviation of 0.555598. The average difference

Table 2: Difference in lateral bending and Cobbs Angle	Table 3: Correlation and regression analysis between clinical asymmetry measurements and Radiographic Cobbs angle.

in lateral bending in the cases group was 3.72 cm with a range of 1.2 to 5.7 cm and a standard deviation of 1.43123 (Table 1). This difference in lateral bending of two groups was statistically significant (p=0.000055).

Correlation: The Pearson’s correlation coefficient between the difference in the lateral bending and the Cobbs angle in scoliosis group measured radiographically was found to be 0.933239 (Tables 2 and 3). This implies a high degree of correlation between the asymmetry and severity of curve as measured radiologically.

Discussion

The spinal radiographs are considered gold standard for evaluating and monitoring progress of Scoliosis.

Fig. 1 : Photo showing the technique of measurement of lateral bending in a scoliotic patient

This method however has obvious disadvantage of exposure to low but not insignificant amount of ionizing radiation.10 Depending on the age at referral and curve size, the total excess lifetime cancer risks were calculated to range from 42 to 238 cases per 100,000 women and 14 to 79 cases per 100,000 men.11 Modern methods and techniques12,13 have reduced the radiation hazards and risk of cancer but despite these improvements in technology it is still important to devise methods that will decrease the need of these radiographs, although it may not completely eliminate their need.

The method used to perform lateral bending and measuring the distance from tip is a standard clinical method and clinically the distances on both sides are equal.14 Like all clinical methods this measurement can also have errors originating because of the observer, the variable measured and the technique. Despite all this lateral flexion has been found to be a good indicator of the degree of back pain and disability.15 Given the reliability in assessing different spinal pathology, evaluating reliability of asymmetrical lateral bending for use as a clinical method for assessing severity of scoliosis holds promise.

Correlation studies in scoliosis, using instruments like electro goniometer angles and radiographic methods have been done in past,16 however we are not aware of any study that correlates the asymmetry in the lateral bending with the degree of scoliosis curve. This study demonstrated a significant difference in amount of asymmetry in lateral bending betweem the control and scoliosis group. Moreover, the asymmetry in scoliosis group was in almost linear correlation with the radiographically measured Cobbs angle. This assumes significance in the wake of concerns that radiographic exposures in growing age group raise.

The study however has its shortcomings : small population group may prevent a meaningful interpretation of results. The study however will serve as an important pilot study for a future larger series, which may also involve a follow-up and study the relationship between the progression of curve and increase in the asymmetry. This finding will be highly significant in wake of its potential ability to circumventing the need of serial radiographs in the follow-up.

Intra tester and inter tester reliability testing must be done before clinical application of any test. Even the measurement of established parameters like Cobbs angle has shown an average of 2.5 degrees of inter reader error and 1.9 degrees of intra reader error.16 The study measurements were taken by a single examiner and no inter and intra tester reliability tests were performed. However the results of the study presented claim only the validity and not reliability, which may be part of a larger study designed on basis of the findings of this study.

Another point of argument against the study could be that all the patients in the study group were having Kings type III adolescent idiopathic scoliosis and these results may not be extrapolated to other form of scoliosis. The kings type III curves are the most frequent type of scoliotic curve, and are the ones that need to be most frequently screened and serially followed up. Thus the test has greatest value in screening this particular subgroup, although a larger cohort consisting of multitude of curves will always remain desirable.

In conclusion we found that asymmetry of lateral bending was significantly greater in the scoliosis group as compared to the control group and that there was good correlation of this asymmetry with radiographic measurement (Cobbs Angle). The method has low cost, lacks the side effects of ionizing radiation and thus has potential of being used as a replacement to radiographic measures in assessing the severity of scoliotic curve.

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*NIIDAAN Orthopaedic Centre, Nagpur, India; +RN Cooper Hospital, Mumbai; #KEM Hospital, Mumbai.