"Pressure gradient" as an indicator of plantar skin injury

Peak plantar pressures (PPPs) have been studied extensively as a contributing factor to skin breakdown, especially in the forefoot where most plantar neuropathic ulcers occur. The purposes of this article were to 1) describe an additional pressure variable, the peak pressure gradient (PPG), 2) determine whether the PPG is higher in the forefoot than in the rearfoot (even when compared with PPP), and 3) determine the correlation between the PPG and PPP at the forefoot and rearfoot in subjects with diabetes, peripheral neuropathy, and a history of plantar ulcer.

Twenty subjects (12 male and 8 female) with diabetes, peripheral neuropathy, and a mean +/- SD age of 57 +/- 9 years participated. Plantar pressures were collected during walking in footwear. The PPP and the PPG (defined as the spatial change in plantar pressure across adjacent sites of the foot surface around the PPP) were determined for the forefoot and rearfoot, and the forefoot-to-rearfoot ratios for each variable were calculated.

The mean PPG was 143% higher in the forefoot than in the rearfoot, whereas the mean PPP was only 36% higher in the forefoot than in the rearfoot (P < 0.0001). The PPG forefoot-to-rearfoot ratio (2.84 +/- 1.36) was nearly two times greater than the PPP forefoot-to-rearfoot ratio (1.48 +/- 0.58) (P < 0.0001). The correlation between PPP and PPG was r = 0.59 at the forefoot and r = 0.75 at the rearfoot.

The PPG was substantially higher in the forefoot than in the rearfoot even when compared with the PPP. The PPG appears to be providing additional information about the stresses experienced by the soft tissues of the foot, especially in the forefoot. The PPG may be a useful indicator of skin trauma because spatial changes in high plantar pressures may identify high stress concentrations within the soft tissue.