Construct validity and reliability of the Japanese Version of the Lumbar Stiffness Disability Index.

Study design Outcome study to determine the construct validity and reliability of the Japanese version of the Lumbar Stiffness Disability Index. Objective To evaluate the psychometric measurement properties of the Japanese version of the Lumbar Stiffness Disability Index (J-LSDI) following lumbar spinal surgery in order to assess its construct validity and reliability. Summary of background data The LSDI was designed and validated as a tool to assess functional impacts of lumbar spine stiffness and diminished spinal flexibility. A Japanese version has been developed, but its construct validity and reliability have not been evaluated. Methods A Pearson's correlation coefficient was calculated using flexion and extension range of motion, Oswestry Disability Index (ODI) and Tampa Scale for Kinesiophobia (TSK) as external standards to evaluate construct validity. An intraclass correlation coefficient (ICC) and a Bland-Altman analysis were used to evaluate test-retest reliability. Results A total of 244 patients following lumbar spinal surgery participated in the study. Fifty one of the 244 patients participated in the reliability study. The ICC of the J-LSDI for test-retest reliability was 0.89 (95% confidence interval, 0.79-0.93). There was no systematic error found in the results of the Bland-Altman analysis. One hundred ninety-three of the 244 patients participated in the validity study. There were significant correlations between the J-LSDI and trunk flexion range of motion (r = -0.66), extension (r = -0.51), ODI (r = 0.62) and TSK (r = 0.38). Conclusion The construct validity and reliability of the Japanese version of the LSDI were confirmed. The J-LSDI can be used to evaluate lumbar stiffness and associated disability in Japanese patients following lumbar spinal surgery. Level of evidence 2.