An Obturator Reduces Time for Volumetric Measurements of the Foot and Ankle

Nicholas Henschke, Robert A. Boland, Roger D. Adams

DOI: 10.2519/jospt.2004.1601

Increased volume of a body region is often described as swelling, and can be intra- or extra-articular. Swelling in the lower limb can follow immobilization, surgery, or trauma such as an ankle sprain. Assessment and reduction of swelling should be pursued vigorously, especially after trauma, because fibrinous exudation and swelling of capillary endothelial cells can result in scar tissue formation that impedes rehabilitation. Different methods are used to measure volume of the foot and ankle, such as the figure-of-eight method with a tape, and water displacement volumetry. Water displacement provides a direct measure of volume and is the gold standard or criterion reference for other methods. The foot is immersed into a water-filled tank and the volume of displaced water is measured. The advantage over tape methods is that volume can actually be determined, compared with indirect estimates of volume that only correlate with volume change. One significant disadvantage of water displacement volumetry is that measurements take longer than for tape methods, and it has been argued that volumetry is not efficient because of this extra time. One device that is sometimes used during volumetry is an obturator. An obturator is a device that can be placed within a volumeter to prevent water turbulence or waves from reaching the overflow spout and prolonging the time taken for water to drain. It has been proposed that an obturator (a) increases the volume of displaced water and possibly increases the accuracy of the method, (b) reduces water turbulence from leg movements, and (c) decreases surface tension of the water, thereby improving accuracy. None of these hypotheses has been evaluated, however, even in studies where an obturator was used to improve accuracy. In fact, Petersen et al stated that they did not use an obturator because they found it was of minimal importance in a pilot study. If an obturator does reduce water turbulence during volumetry, a reduction in drainage time (defined as time elapsed from when a body segment is immersed into the volumeter to when dripping ceases) might be observed. We could not find any data that quantify time effects attributable to an obturator, but any reduction in time required to complete a measurement (increasing time efficiency) would address a noted disadvantage of volumetry. In addition, an obturator would be a valuable tool if it did not compromise reliability. The aim of this study, therefore, was to evaluate the effects of an obturator on volumetric measurements, and the time efficiency of the water displacement method.

J Orthop Sports Phys Ther. 2004;34(12):800-804. doi:10.2519/jospt.2004.1601

Key Words: obturator, volumeter, measurement, foot, ankle

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