Reliability and minimal detectable change for the figure-of-eight-20 method of, measurement of ankle edema

Abstract

Study design: Single-session, repeated-measures design, with 3 raters.

Objectives: To determine the intrarater and interrater reliability and the minimal detectable change score for a modified version of the figure-of-eight method of measurement of ankle edema (figure-of-eight-20) developed for patients with severe injuries.

Background: The precise quantification of ankle edema is necessary to determine the relative effectiveness of interventions aimed at reducing swelling, and to monitor individual progress during treatment.

Methods and measures: Thirty subjects (mean +/- SD age, 46 +/- 16 years; 9 female and 21 male) with ankle edema following surgery for malleolar fracture took part in the study. Each of 3 raters performed 3 measurements of the affected ankle without marking landmarks and 3 measurements of both ankles using skin markings. The order of the raters was randomized and the raters were blinded to each other's results.

Results: The figure-of-eight-20 method showed high intrarater and interrater reliability (intraclass correlation coefficients greater than .99). The minimal detectable change (MDC95%) for the swollen ankle was 9.6 mm when measured without skin marks and 73 mm with marks. The difference in circumference of the affected and unaffected ankle (mean +/-SD, 33.8+/-12.1 mm) consistently exceeded the MDC95,, even in patients with only mild edema.

Conclusions: The standardized figure-of-eight-20 offers a good option for reliably measuring ankle circumference in patients with severe ankle trauma. In repeated assessments, greater accuracy is likely to be obtained when the landmarks for measurement are marked and the same rater carries out the measurements.