Measurement error associated with spinal mobility measures in children with and without low-back pain

Evidence of the reliability of measurements in children is scarce, particularly in children with low-back pain. The aim of this investigation was to evaluate the measurement error associated with repeated measures of spinal mobility measures in children with and without low-back pain by establishing 95% limits of agreement.

A repeated measures study was performed involving 119 children aged 11-16 y. Of this sample 30 subjects reported recurrent low-back pain and were classified as symptomatic, the remaining 89 subjects were asymptomatic. Standardized measures were taken, including the sit-and-reach test, hip range of motion (Leighton flexometer), lumbar flexibility (modified Schöber test) and lateral flexion of the spine. The same experimenter performed all testing, with 1 wk between the repeated measures.

Correlation coefficients suggested that all measures exhibited good reliability in both the symptomatic (r = 0.80-0.95) and asymptomatic groups (r = 0.88-0.99). In contrast, the limits of agreement showed that all measures exhibited random error. The magnitude of random error was typically greater in the symptomatic subjects, suggesting that low-back pain may influence the reliability of typical measures used in this population.

The magnitude of error must be interpreted in relation to analytical goals and the expected magnitude of change. In the authors' opinion the error presented appears acceptable for the serial monitoring of patients, although this will depend on the differences in mobility typically found.