The validity and reliability of the Perometer in evaluating human knee volume

Summary Background: Accurate knee swelling evaluation is important in monitoring the progress of a patient's condition and rehabilitation. Water volumetry is the current gold standard of volume assessment but can be time consuming and unsuitable for assessing patients with open wounds. No previous study has reported the potential use of an optoelectronic device in assessing knee volume. Objectives: To evaluate an optoelectronic device, the Perometer® in knee volume assessment in uninjured subjects and compare it to the current gold standard of volume assessment – water displacement. Materials and methods: Bilateral knee measurements were measured in 20 uninjured individuals with both methods on two separate days using a one‐way repeated measures design. A cylindrical object was also measured 10 times with both tools. Results: The mathematically calculated volume of the cylinder was 1568 ml. The mean volume obtained by the Perometer was 1602 and 1620 ml by the volumeter. This represented an over‐estimation of the true volume of 2·2% by the Perometer and 3·4% by the volumeter. A high correlation was found for repeated measures of knee volumes with both methods (r = 0·94, P