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OBJECTIVE -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.RESEARCH DESIGN AND METHODS -Twenty subjects (12 male and 8 female) with diabetes, peripheral neuropathy, and a mean Ϯ SD age of 57 Ϯ 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.RESULTS -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 Ͻ 0.0001). The PPG forefoot-to-rearfoot ratio (2.84 Ϯ 1.36) was nearly two times greater than the PPP forefoot-torearfoot ratio (1.48 Ϯ 0.58) (P Ͻ 0.0001). The correlation between PPP and PPG was r ϭ 0.59 at the forefoot and r ϭ 0.75 at the rearfoot.CONCLUSIONS -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. Diabetes Care 28:2908 -2912, 2005P eak plantar pressure (PPP) has been investigated extensively in the literature as a surrogate measure of trauma to the plantar foot and is known to be an important contributing factor to skin breakdown in people with diabetes and peripheral neuropathy (1-3). High PPP repeated many times has been associated with the location of skin breakdown (4). There does not, however, appear to be a specific threshold of PPP that predicts skin breakdown (5). If one considers only mechanical trauma to the foot, other important variables besides PPP include direction of stress (normal versus shear), number of repetitions (steps), and duration of plantar pressures (sometimes estimated as the pressure time integral) (6). This threshold of injury also appears to vary among individuals, depending upon other factors that include amount of foot deformity (7), prior activity level (8,9), type of footwear, vascular status (3), history of ulcer (6), and type of measuring device.Besides these variables, we believe that the peak pressure gradient (PPG) is another important pressure variable to consider. We define the PPG as the spatial change in plantar pressure aroun...

Experimental study Level III.

A mixed-lubrication model considering the oil supply was developed. The elastoplastic model was applied in the asperity contact simulation. The oil-film thickness at the ring-cylinder liner interface was determined using a mass conservation algorithm. The modeling results were compared with experimental results for verification on a reciprocating wear tester. It is found that, under the fully flooded condition, the results of the Greenwood-Trip model and the current model in the middle of the stroke are in accordance with the experimental results, but the results of the current model at the ends of the stroke are closer to the experimental results than the Greenwood-Trip model results are. Under the starved-lubrication condition, the friction coefficient of the current method is closer to the experimental result than that of the Greenwood-Trip model in the entire stroke. Therefore, the model developed in this study is appropriate for mixed lubrication under the fully flooded condition and the starved-lubrication condition. Furthermore, the model was applied to the ring pack of a diesel engine to study the effect of the oil supply on the tribological performance. The results show that the frictional forces under the 1 mm oil supply condition are far larger than those under the sufficient oil supply condition in the middle of the stroke, and so the increase in the frictional force may be used to identify scuffing failure in future studies if the relationships between the frictional forces and the measured vibration signals of the engine are obtained.