Responsiveness of the numeric pain rating scale in patients with shoulder pain and the effect of surgical status.

Context: The Numeric Pain Rating Scale (NPRS) is commonly used to assess pain. Change in the NPRS across time can be interpreted with responsiveness indices. Objective: To determine the minimal clinically important difference (MCID) of the NPRS. Design: Single-group repeated measures. Setting: Outpatient rehabilitation clinics. Patients: Patients with shoulder pain (N = 136). Main Outcome Measures: At the initial evaluation patients completed the Penn Shoulder Score (PSS), which includes pain, satisfaction, and function sections. Pain was measured using an 11-point NPRS for 3 conditions of pain: at rest, with normal daily activities, and with strenuous activities. The NPRS average was calculated by averaging the NPRS scores for 3 conditions of pain. The final PSS was completed after 3–4 wk of rehabilitation. To determine the MCID for the NPRS average, the minimal detectible change of 8.6 points for the PSS function scale (0–60 points) was used as an external criterion anchor to classify patients as meaningfully improved (≥8.6 point change) or not improved (<8.6-point change). The MCID for the NPRS average was also determined for subgroups of surgical and nonsurgical patients. Cohen’s effect sizes were calculated as a measure of group responsiveness for the NPRS average. Results: Using a receiver-operating-characteristic analysis, the MCID for the average NPRS for all patients was 2.17, and it was 2.17 for both the surgical and nonsurgical subgroup: area-under-the-curve range .74–.76 (95%CI: .55–.95). The effect size for all patients was 1.84, and it was 1.51 and 1.94 for the surgical and nonsurgical groups, respectively. Conclusions: The NPRS average of 3 pain questions demonstrated responsiveness with an MCID of 2.17 in patients with shoulder pain receiving rehabilitation for 3–4 wk. The effect sizes indicated a large effect. However, responsiveness values are not static. Further research is indicated to assess responsiveness of the NPRS average in different types of patients with shoulder pain.