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.