Determining threshold values for success after surgical treatment of lumbar spondylodiscitis using quality of life scores

OBJECTIVE: This study aimed to determine threshold values of validated quality of life (QoL) scores, including Oswestry Disability Index (ODI) and Core Outcome Measures Index (COMI), for predicting a successful outcome following surgical treatment of lumbar spondylodiscitis (LS). METHODS: Patients with lumbar spondylodiscitis (LS) undergoing surgery in a tertiary referral hospital were included prospectively from 2008-2019. Data were collected both before surgery (T(0)) and one year after surgery (T(1)). QoL was measured using ODI and COMI. The successful clinical outcome was defined by the combination of the following four criteria: no recurrence of spondylodiscitis, back pain ≤4 on visual analogue scale or relief of ≥3 points, absence of LS-related neurological deficit, and radiological fusion of the affected segment. For subgroup analysis, group 1 consisted of patients with a favorable treatment outcome (meeting all four criteria), while group 2 included patients with unfavorable treatment outcome (meeting ≤3 criteria). RESULTS: Ninety-two LS patients (median age = 66 years; age range = 57-74) were analyzed. QoL scores improved significantly. Threshold values for the ODI and COMI were calculated at 35 and 4.2 points, respectively. The area under curve for the ODI was 0.856 (95%-CI 0.767-0.945; P < 0.001) and 0.839 (95% CI-0.749-0.928; P < 0.001) for the COMI score. Eighty percent of patients achieved a favorable outcome. CONCLUSION: Objective measurement and evaluation of successful surgical treatment of spondylodiscitis require defined thresholds of quality of life scores. We were able to define such thresholds for Oswestry Disability Index and Core Outcome Measures Index. These can be useful to assess clinically relevant changes and therefore allow a more precise estimation of the post-surgical outcome.