Defining clinically meaningful pain reduction after spinal injections using an 11-point numerical rating scale and patient-reported relative reduction of pain

BACKGROUND: We aimed to establish thresholds for assessing clinically meaningful pain improvement after spinal injections using numerical rating scale (NRS) and patient-reported relative reduction (PRR) of pain. METHODS: This single-center retrospective study included 1,828 patients who received spinal injections at our spinal intervention center and completed a 2-week follow-up telephone interview in 2017. NRS absolute and relative reductions were calculated using the NRS scores before injection and at follow-up. The PRR and 5-point global perceived effect (GPE; 1, completely recovered; 2, much improved; 3, slightly improved; 4, no change; and 5, worsened) were recorded. The mean ± standard deviation (SD) of NRS absolute reduction, NRS relative reduction, and PRR in the GPE 2 and 3 subgroups were calculated. Receiver-operating-characteristic curve analysis was used to determine the cutoffs for NRS absolute and relative reduction and PRR in predicting the substantial clinically important difference (SCID, GPE 1-2) and minimal clinically important difference (MCID, GPE 1-3). RESULTS: The mean ± SD of NRS absolute and relative reduction, and PRR in the GPE 2 and GPE 3 were 4.5 ± 1.8, 65.4% ± 21.1%, and 67.7% ± 14.8% and 2.4 ± 1.4, 36.8% ± 22.5%, and 35.7% ± 16.1%, respectively. The cutoffs for predicting SCID and MCID were NRS absolute reduction of ≥3 and ≥1, NRS relative reduction of ≥50% and ≥10%, and PRR of ≥50% and ≥20%, respectively. CONCLUSIONS: The NRS absolute and relative reduction and PRR thresholds were established to differentiate SCID and MCID in terms of pain improvement after spinal injections.