The Validity and Reproducibility of the Flexicurve in the Evaluation of Cervical Spine Lordosis

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The purpose of this study was to measure the validity and reliability of flexicurve measurements of cervical curvature in the sagittal plane in adults.


One hundred thirteen adults were assessed in the seated position with flexicurve radiographs. Two groups were measured: (1) the validity group (n = 55), and (2) the reliability group (n = 58). Both groups were subdivided into 3 subgroups according to body mass index: underweight, normal weight, and overweight. Radiographs were simultaneously taken with flexicurve molded on the cervical spine. Pearson’s correlation and the root mean square error were used for the concurrent validity. The reliability of the flexicurve was assessed by 3 raters using the intraclass correlation coefficient (ICC), the standard error of the measurement (SEM), and minimal detectable change (MDC).


For the concurrent validity, a high correlation (r = 0.570, P < .001, root mean square error = 9.8°), and excellent results were obtained for intra-rater (ICC = 0.771, P < .001, SEM = 4.4°, MDC = 8.6°) and inter-rater (ICC = 0.775, P < .001, SEM = 4.3°, MDC = 8.5°) reliability. The subgroups had different results, whereas the underweight subgroup consistently had the best results.


These findings suggest that the flexicurve can be a valid instrument for evaluating the curvature of the cervical spine in the sagittal plane in adults classified according to the body mass index as underweight and normal weight. Reliable measurements were provided for its use whether by the same or different raters. The flexicurve can be recommended for use both in clinical practice and in research settings as long as the suggested protocol is followed.

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