Is the Oswestry Disability Index a valid measure of response to sacroiliac joint treatment?

Purpose Disease-specific measures of the impact of sacroiliac (SI) joint pain on back/pelvis function are not available. The Oswestry Disability Index (ODI) is a vali-dated functional measure for lower back pain, but its responsiveness to SI joint treatment has yet to be estab-lished. We sought to assess the validity of ODI to capture disability caused by SI joint pain and the minimum clini-cally important difference (MCID) after SI joint treatment. Methods Patients (n = 155) participating in a prospective clinical trial of minimally invasive SI joint fusion under-went baseline and follow-up assessments using ODI, visual analog scale (VAS) pain assessment, Short Form 36 (SF-36), EuroQoL-5D, and questions (at follow-up only) regarding satisfaction with the SI joint fusion and whether the patient would have the fusion surgery again. All out-comes were compared from baseline to 12 months post-surgery. The health transition item of the SF-36 and the satisfaction scale were used as external anchors to calculate MCID. MCID was estimated for ODI using four calcula-tion methods: (1) minimum detectable change, (2) average ODI change of patients ’ subsets, (3) change difference between patients ’ subsets, and (4) receiver operating characteristic (ROC) curve