Age-period-cohort analysis of the need of surgery in patients with adolescent idiopathic scoliosis

Abstract

Background

The use of school scoliosis screening for early detection of adolescent idiopathic scoliosis (AIS) in order to avoid the need of invasive surgery remains controversial. In an internationally large population-based cohort of students, the Hong Kong scoliosis screening programme has been shown to have low referral rate of students for radiographic diagnosis and high accuracy in identifying AIS patients requiring clinical follow-up. However, before school scoliosis screening is considered worth implementing, its direct effect on the need of surgery should also be assessed as stipulated in the literature. Therefore, we aimed to examine the temporal change of the rate of AIS patients in need of surgery since the inception of the Hong Kong screening programme in 1995, and assess the change of the rate across age and birth year of adolescents.

Methods

A large scale data collection was made from the Duchess of Kent Children Hospital (DKCH), the Prince of Wales Hospital (PWH) and the Department of Health. We obtained the screening history, spinal curvature, surgical status and demographics of AIS patients aged between 10 and 19 years who visited either of the DKCH or PWH, the only two public specialist hospitals in Hong Kong that managed AIS patients, during 1996 to 2009. The data have been carefully collated and cleaned before data analysis. Age-period-cohort model estimated by the modern intrinsic estimator was used to delineate the effects due to age, period taken as calendar year, and cohort taken as birth year on the rate of reaching an indication for surgery, taken as a Cobb angle ? 45° or operated for AIS.

Results

During 1996 and 2009, a total of 1,117,182 students participated in the Hong Kong scoliosis screening programme. Of which, 16,780 visited either DKCH or PWH, and had AIS detected. The incidence rate of AIS in Hong Kong adolescents generally increased over years. The proportion of AIS patients who previously participated in screening for scoliosis was 43% in 1996 and increased to over 90% after 2001. A total of 636 AIS patients received spinal fusion surgery. The mean curvature at operation in patients who were previously screened for scoliosis was 2.48 (95% CI = 11.35 to 12.65; p-value = 0.031) smaller than that in those who were not screened. The relative risk of indication for surgery was the maximal at the age of 14-15 years. Since the start of the programme, the risk of reaching indication for surgery generally increased but the rate was reduced by 2004-2005 onwards. However, the risk was fairly stable across birth cohorts.

Conclusions

This was the largest study that examined the temporal trend of the rate of requiring surgery for AIS in adolescents. The risk of requiring surgery for AIS increased due to changes in the incidence of AIS and exercise pattern. The Hong Kong scoliosis screening programme has provided important information on the annual trends about AIS, a disorder with unfortunately poor knowledge of its aetiology.