Back mobility and interincisor distance ranges in racially diverse North American healthy children and relationship to generalized hypermobility

BACKGROUND Given the dearth of normal values, we conducted a cross-sectional study of North American racially diverse children to determine normal values of interincisor distance and lower spine flexion. METHODS Demographs of 307 children aged 5-17 seeking treatment emergency care were obtained along with interincisor distance measured by incisor tooth-to-tooth gap, lower spine flexion measured by the Schober and modified Schober measurements, popliteal extension, hypermobility (Beighton) score, weight and height. RESULTS Normal range of motion values for the Schober was a mean of 14.3 cm (95% confidence interval (CI) was 11.2 to 17. cm) and the mean modified Schober's was 21.6 cm (95% CI 18.4 cm to 24.8 cm). Retained lumbar lordosis on forward flexion was observed in 33%. Back mobility was associated with body mass index (BMI), popliteal angle, and Beighton score but not sex, race or retained lordosis. The mean interincisor distance measurement was 47 mm (95% CI 35 mm to 60 mm) and was associated with height and BMI but not sex, race, or Beighton score. CONCLUSION Normal values for lower back range of motion and interincisor distance were obtained which are needed in pediatric rheumatologic clinics and do not significantly vary as to race or sex. Retained lordosis on forward flexion is a normal variant. Hamstring tightness, hypermobility and BMI need to be considered when ascertaining back mobility.