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OSTEOPENIA IN ADOLESCENT IDIOPATHIC SCOLIOSIS (AIS) IS PERSISTENT THROUGHOUT PERIPUBERTY – LONGITUDINAL TRACKING OF BONE MINERAL DENSITY TRAJECTORY AND ITS ASSOCIATION WITH CURVE SEVERITY IN 318 GIRLS

¹ Department of Orthopaedics & Traumatology , ³ Centre for Epidemiology and Biostatistics, Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong. ² Centre of Nutrition and Food safety, School of Biomedical and Molecular Sciences, University of Surrey, Guildford, Surrey, GU2 7XH, U.K.

Background: Low bone mass in patients with adolescent idiopathic-scoliosis has been well reported in cross-sectional studies. No large-scale longitudinal-study has been conducted to track bone-mineral-density (BMD) trajectory in peripubertal AIS with varying scoliosis-severity.

Aim: We evaluated the BMD trajectory and factors determining BMD accretion in AIS during peripubertal period.

Method: One hundred and ninety-six newly diagnosed AIS girls with Cobb-angle >100 and 122 healthy girls, aged 12–15 years were followed-up for two years. Weight, height, leg length, menarche and Cobb-angle were determined. Areal lumbar-spinal BMD (LSBMD) and femoral-neck BMD (FNBMD), and volumetric distal-tibial BMD (TiBMD) were evaluated by dual-energy-x-ray-absorptiometry and peripheral QCT respectively. BMD growth-models were fitted by multilevel modelling (mixed longitudinal design).

Results: At baseline, 93% participants were pre-menarchial or within three years of menarche. Average Cobb-angles at baseline and subsequent follow-ups were 260, 230 and 260 respectively. TiBMD of AIS (moderate- and severe-severity) was significantly lower than the controls from 13–16 years (ANOVA, P<0.05). Posthoc-test showed that TiBMD of severe-AIS was lower than moderate-AIS at 15–16 years (P<0.05). LSBMD accrual was significantly lower among AIS (moderate- and severe-severity) than the controls from age 13–17 years (ANOVA, P<0.05). FNBMD of AIS (moderate- and severe-severity) was lower than the controls at 15 years (ANOVA, P<0.05). BMD trajectories of individuals differed inter-personally and intra-personally over time and that BMD growth followed a curvilinear pattern. The rates of BMD accretion reduced with retarded growth across peripubertal-period. Weight and height were significant time-varying predictors on BMD growth. BMD of AIS was persistently lower than the healthy girls throughout the study (P<0.05).

Conclusions: This large-scale longitudinal study in AIS girls with moderate to severe-curve-severity showed for the first time that both the volumetric and areal BMD were persistently lower when compared to the age-matched healthy girls throughout 12–17 years. AIS with more severe curve-severity were found to have much lower BMD throughout the peripubertal period. Promotion of a higher bone-mass is important for AIS to modify scoliosis-progression and to achieve peak bone mass in order to reduce the risk of osteoporosis later in life.

Correspondence should be addressed to Jeremy C T Fairbank at The Nuffield Orthopaedic Centre, Windmill Road, Headington, Oxford OX7 7LD, UK