Comparisons of venous and diabetic plantar ulcer shape and area.

That diabetic plantar ulcers are "round-like" and venous ulcers are "irregularly" shaped is well known. However, these notions have not been quantified or substantiated systematically. In this retrospective analysis, geometric parameters--including area (A), perimeter (p), and shape factor (SF)--of 255 venous and 305 plantar ulcers have been determined using length (L) and width (W) in specific calculation models; these calculations then were compared with computer planimetry. Length was the maximum dimension and width was the maximum dimension perpendicular to length. Results show that venous ulcers, when compared with plantar ulcers, have significantly smaller shape factors and smaller W/L ratios. An optimized calculation model (A = KoLW) then was used, in which Ko was adjusted to minimize root-mean-square (rms) error among venous and plantar ulcers. Values of Ko differed for venous (Ko = 0.67) and plantar (Ko = 0.73) ulcers, with no significant overall paired-differences in actual vs. calculated area. Overall, these models correctly identified 91.8% of venous and 95.1% of plantar ulcer areas within 20% of actual areas. If venous ulcer SF was > 0.35, 3% of the ulcers exceeded the 20% error limit; if SF was < or = 0.35, then 56% exceeded the 20% error. If plantar ulcer SF was > 0.65, no ulcers exceeded the 20% error limit; if SF was < or = 0.65, 15% did. These findings provide quantitative data of absolute and comparative ulcer shapes and clarify the impact of shape on area assessment accuracy when estimated by simple length by width measures.