Force, pressure, and motion measurements in the foot: current concepts

Modern foot-pressure measurement studies have successfully debunked the tripod theory; on the contrary, the highest peak loads under the forefoot occur as often as not under the third metatarsal head and not the first and fifth. This does not necessarily mean that the first metatarsophalangeal joint does not sustain the highest pressures; calculations based on the measured pressures under the metatarsals and digits show that it does. One must bear in mind that the hallux consistently bears significantly more pressure than any of the other toes. It is likely that the pressure borne by the first metatarsal head and hallux combined consistently exceed that for the other four metatarsal heads and their respective digits. In other words, the first ray probably has the consistently highest load in normal feet, even when the second or third metatarsal head achieves a greater peak pressure than the first metatarsal head. Three lines of evidence suggest the role that pressure plays in forefoot pathology. First, metatarsalgia is commonly associated with hallux valgus. It often arises following or is exacerbated by hallux valgus surgery (especially arthroplastic procedures). Patients with hallux valgus demonstrate increased peak pressure under the lateral metatarsal heads that actually increases following the Keller procedure. Second, the peak pressure under callosities are, on the average, higher than normal. Third, diabetic plantar ulcers occur at sites of high pressure. The correlations between peak loads on the lateral column and both age and weight merit some attention, since it is common experience that the prevalence of symptomatic foot lesions is higher in older populations. The correlation with body weight may be unexpected. One would expect that, on the average, body weight would correlate with the weight-bearing surface area of the foot and, therefore, the pressure would be relatively constant. The increased pressure under the medial column suggests a relative instability of the medial column with advancing age and weight. Pressure should not be construed as the only factor. The large overlap in peak pressures found under diabetic ulcers and intact skin in both normal and diabetic feet makes this apparent. However, while peak pressures have been extensively studied, there has been no attempt to measure the duration or frequency of loading on a day-to-day basis. According to Brand, it is not the absolute loads applied to a part but repetitive pressure that is responsible for tissue breakdown, especially when such repetitive loads are applied without any interim period for the tissues to recover.(ABSTRACT TRUNCATED AT 400 WORDS)