Stereophotogrammetry for measuring rates of cutaneous healing: a comparison with conventional techniques

A portable stereocamera linked to a computer has been developed capable of taking photographs in the clinical situation. The accuracy and precision of this system has been measured and compared with direct tracing and simple photography, the two systems currently in use for this type of work. It was found to have a precision of better than 2% and to be accurate to within 1% for edge length and area in models of chronic leg ulcers whose dimensions were known exactly. These results are between five and ten times better than direct tracing and simple photography measured under similar circumstances. When used on patients' ulcers, stereophotogrammetry was found to have a precision of 2% for edge length and 3.4% for area, again between five and ten times more accurate than the other two systems. The accuracy with which an epithelial edge can be identified with the naked eye, a possible limiting factor in any visual measuring system, was measured on fixed preparations of healing wounds on pigs. The mean error was found to be 240 micron with a confidence limit of 440 micron. Finally, the rate of healing of chronic leg ulcers was measured in a clinical trial on patients. Only stereophotogrammetry had errors consistently smaller than the changes being measured in the clinical trial, making it the only system which can validly be used to study rates of healing in this model. It is also able to measure volume to within 5% and is unique in being able to do this noninvasively.