Responsiveness of the Japanese version of the lumbar stiffness disability index.

Purpose: We aimed to investigate the psychometric characteristics of the Japanese version of the Lumbar Stiffness Disability Index (J-LSDI) in patients undergoing lumbar spinal surgery, with a focus on its responsiveness and minimal clinically important differences (MCID).

Methods: This prospective, single-institution cohort study enrolled adult individuals diagnosed with degenerative spinal pathologies who underwent surgical intervention approximately 1 year prior inclusion in the study. Participants were stratified into three groups according to the number of lumbar segments included in the arthrodesis construct: Group 1 (no fusion or single-level fusion); Group 2 (fusion across two to four levels); and Group 3 (fusion involving five or more levels). Within the distribution-based framework, responsiveness was quantified using effect size (ES) and standardized response mean (SRM). Areas under the receiver operating characteristic curves (AUCs) and MCID were determined for participants who reported either "minimal" or "moderate" improvement.

Results: A total of 488 participants completed the J-LSDI at baseline and 1 year. In Group 1, the LSDI scores improved from preoperatively to postoperatively, with moderate ES and SRM values (ES = 0.78; SRM = 0.59). In Group 2, the preoperative and postoperative LSDI scores did not differ, with low ES and SRM values (ES = 0.13; SRM = 0.12). In Group 3, the LSDI scores worsened from preoperatively to postoperatively, with high ES and SRM values (ES = 1.20; SRM = 0.90). The optimal cutoff points for the MCID in Groups 1, 2, and 3 were - 8.0, 0.2, and 17.1, respectively. The AUCs for the MCID in Groups 1, 2, and 3 were 0.72, 0.73, and 0.76, respectively, indicating moderate accuracy. Between-group analysis of variance revealed no significant differences in preoperative LSDI scores (p = 0.40), while significant differences were observed in postoperative scores at 1 year (p < 0.01).

Conclusion: This study underscores the clinical relevance and measurement reliability of the J-LSDI as an effective tool for evaluating the functional impact of spinal stiffness on activities of daily living among Japanese patients, in both the preoperative and postoperative phases of spinal surgery.