Shape and area measurement considerations for evaluating diabetic plantar ulcer progression

Ulcer shape is an important determinant of the suitability of clinically used length by width measurements to assess ulcer area. Herein accuracies of area calculations are determined for elliptical (ELP) and rectangular (REC) shapes whose dimensions are obtained from actual plantar ulcers using a consistent measurement rule. The rule assigns the maximum ulcer dimension (L) to the maximum model dimension and the maximum dimension perpendicular to L as W. Accuracies were tested with data from 83 plantar ulcers in which area tracings were made over 16 weeks (1034 assessments). Results show overall errors for both models as similar, (ELP 7.46 +/- 0.30 %, overestimate and REC 6.90 +/- 0.51%, underestimate). Weekly errors were < 10% for ELP and < 12% for REC models. Empirical optimization of models reduced overall error to near zero. For the optimized ELP model the formula for calculating ulcer area was 0.73LW. The results (strictly applicable to plantar ulcers) show good weekly and overall accuracies and suggest that this simple and consistent method of wound documentation and tracking as an attractive alternative when more complex methods are not needed, possible or cost-effective.