Validation of PROMIS Physical Function Instruments in Patients With an Orthopaedic Trauma to a Lower Extremity

Objectives: To evaluate the reliability, convergent validity, known-groups validity, and responsiveness of the Patient-Reported Outcomes Measurement Information System (PROMIS) Mobility Computer Adaptive Test (CAT) and PROMIS Physical Function 8a Short Form. Design: Prospective cohort study. Setting: Two Level-I trauma centers. Patients: Eligible adults with an isolated lower extremity trauma injury receiving treatment were approached consecutively (n = 402 consented at time 1, median = 80 days after treatment). After 6 months, 122 (30.3%) completed another assessment. Intervention: Cross-sectional and longitudinal monitoring of patients. Main Outcome Measurements: Floor and ceiling effects, reliability (marginal reliability and Cronbach's alpha), convergent validity, known-groups discriminant validity (weight-bearing status and fracture severity), and responsiveness (Cohen's d effect size) were evaluated for the PROMIS Mobility CAT, PROMIS Physical Function 8a Short Form, and 5 other measures of physical function. Results: PROMIS PFSF8a and Foot and Ankle Ability Measure Activities of Daily Living Index had ceiling effects. Both PROMIS measures demonstrated excellent internal consistency reliability (mean marginal reliability 0.94 and 0.96; Cronbach's alpha = 0.96). Convergent validity was supported by high correlations with other measures of physical function (r = 0.70-0.87). Known-groups validity by weight-bearing status and fracture severity was supported as was responsiveness (Mobility CAT effect size = 0.81; Physical Function Short Form 8a = 0.88). Conclusions: The PROMIS Mobility CAT and Physical Function 8a Short Form demonstrated reliability, convergent and known-groups discriminant validity, and responsiveness in a sample of patients with a lower extremity orthopaedic trauma injury.