Validity of flexicurve for the assessment of spinal flexibility in asymptomatic individuals

Abstract

Introduction: Spine problems are common, and assessment of spine flexibility provides relevant information; however, alternative evaluation methods need to be validated. Objective: To evaluate the concurrent validity of the Flexicurve using 3D videogrammetry as a reference value to assess spinal flexion and extension in the lumbar and thoracic regions. Method: The consecutive sample consisted of 39 individuals aged between 18 and 50 years. Two consecutive evaluations were performed by the same rater on the same day and at the same location: (1) Flexicurve and (2) 3D videogrammetry. The assessments were performed with the spine in the neutral position, followed by maximum flexion and extension. The range of motion (ROM) in the maximum flexion and extension positions was calculated in MATLAB^® and defined as the difference between the maximum flexion or extension angle and that of the neutral position. Statistical analyses used were the Pearson Product-Moment Correlation coefficient, RMS error and Bland-Altman plot (α < 0.05). Results: The ROM between instruments was similar, with high correlations for thoracic flexion (r = 0.751), extension (r = 0.814) and lumbar flexion (r = 0.853), and RMS errors under 8°. The correlation for lumbar extension was moderate (r = 0.613) and the RMS error was more than 10°. The limits of agreement varied between ± 10º and ± 21º. Conclusion: The Flexicurve is valid for assessing maximum flexion and extension of the thoracic spine, and maximum flexion of the lumbar spine. We suggest caution in evaluating the maximum extension of the lumbar spine.