Cervical Spine Research Society-Cervical Stiffness Disability Index (CSRS-CSDI): Validation of a Novel Scoring System Quantifying the Effect of Postarthrodesis Cervical Stiffness on Patient Quality of Life

Study Design. Cross-sectional study. Objective. The aim was to create and validate a novel patient-reported outcome measure (PROM) focusing on stiffness-related patient functional limitations after cervical spine fusion. Summary of Background Data. Cervical arthrodesis is a common treatment for myelopathy/radiculopathy, however, results in increased neck stiffness as a collateral outcome. No current PROM exists quantifying the impact of postoperative stiffness on patient function. Methods. The Cervical Spine Research Society-Cervical Stiffness Disability Index (CSRS-CSDI) was created through a modified Delphi process. The resultant 10-item questionnaire yields a score out of 100 with higher scores indicating increased functional difficulty related to neck stiffness. Cross-sectional study of control and postoperative patients was completed for CSRS-CSDI validation. Retest reliability (intraclass correlation coefficient), internal consistency (Cronbach alpha), responsiveness (levels fused vs. CSRS-CSDI scores), and discriminatory validation (CSRS-CSDI vs. neck disability index) scores) were completed. Results. Fifty-seven surgical and 24 control patients completed the questionnaire. Surgical patients underwent a variety of procedures: 11 (19%) motion preserving operations, nine (16%) subaxial 1-2 level fusions, seven (12%) subaxial 3-5 level fusions, five (9%) C1-subaxial cervical spine fusions, 20 (35%) C2-upper thoracic spine fusions, five (9%) occiput-subaxial or thoracic spine fusions. The questionnaire demonstrated high internal consistency (Cronbach alpha=0.92) and retest reliability (intraclass correlation coefficient=0.95, P<0.001). Good responsiveness validity with a significant difference between fusion cohorts was found (P<0.001, r _s=0.63). Patient CSRS-CSDI scores also correlated with neck disability index scores recorded (P<0.001, r=0.70). Conclusion. This is the first study to create a PROM addressing the functional impact of cervical stiffness following surgical arthrodesis. The CSRS-CSDI was a reliable and valid measure of postoperative stiffness impact on patient function. This may prove useful in counseling patients regarding their expected outcomes with further investigation demonstrating its value in a prospective fashion.