The interdependency of peak pressure and pressure-time integral in pressure studies on diabetic footwear: no need to report both parameters.

BACKGROUND: In plantar pressure studies on diabetic footwear, both the maximum peak pressure (MPP) and peak pressure-time integral (PTI) are often reported. However, specific conclusions for each parameter are not commonly reported, suggesting these parameters may be interchangeable. The aim was to explore the interdependency of MPP and PTI in diabetic patients wearing different types of footwear.
METHODS: In-shoe plantar pressure was measured in 69 neuropathic diabetic patients who walked in custom made footwear, forefoot offloading shoes, cast shoes, and/or standard footwear. For each of six anatomical foot regions, correlation coefficients were calculated between MPP and PTI. To assess parameter congruency, the percentage of patients showing correlation coefficients >0.7 or coefficients of variation for both MPP and PTI <10%, was calculated.
RESULTS: Across all footwear conditions, MPP and PTI were highly correlated in the forefoot and midfoot (r>0.78 in all but one foot region in one footwear condition). Lower correlations coefficients were found in the rearfoot (r=0.43-0.45). Across regions, between 46% and 87% of patients (mean 72%) showed parameter congruency in the forefoot and midfoot.
CONCLUSIONS: The results showed that the MPP and PTI are highly interdependent in those foot regions most at risk for plantar ulceration in patients wearing commonly prescribed footwear. Since MPP has been shown to date to be the clinically more relevant parameter of the two, these results suggest that the value of reporting PTI in addition to MPP in the same diabetic footwear study is small.