The Effect of Arch Height and Body Mass on Plantar Pressure

Carine HM van Schie, MSc, PhD; , Andrew JM Boulton, MD, FRCP

Disclosures

Wounds. 2000;12(4) 

In This Article

Abstract and Introduction

High plantar foot pressure is one of the important risk factors for diabetic foot ulceration. Several factors have been associated with increased foot pressures; however, the effect of arch height and body mass on plantar pressure is not entirely clear from the available literature. Therefore, the aim of this study was to investigate the effect of the arch index (a measure of arch height) and body mass on plantar pressure in a group of 34 non-diabetic and diabetic subjects. Arch height was measured as the arch index -- a ratio of midfoot to whole foot ground contact area. Foot pressures were measured during barefoot walking. The arch index was not found to be significantly associated to peak pressure or pressure time integral at any region of the foot. However, there was a non-significant trend towards higher plantar pressure at the medial side of feet in subjects with low arches. In addition, subjects with low-arched feet had significantly higher body mass indexes (BMI) compared to subjects with high-arched feet (28.6 ± 4.8 vs 24.3 ± 3.3 kg/m2, p<0.05), and BMI was associated to arch index (r = 0.36, p<0.05). Body mass was significantly associated with peak pressure and pressure time integral at several regions of the foot (0.33 < r <0.47, p<0.05). To conclude, both body mass and arch index (arch height) contribute to increased foot pressures. The effect of arch height on foot pressures can possibly be explained by the effect of BMI on the arch of the foot during weight bearing.

An important risk factor for the development of diabetic foot ulceration is high plantar foot pressure.[1,2] High foot pressures have been associated with callus, foot deformities, reduced plantar tissue thickness, and limited joint mobility.[3,4,5,6] However, the effect of foot structure characteristics on plantar pressure is not as clearly defined.

The structure of the medial longitudinal arch (MLA) has been described as one of the most important structural characteristics of the foot, which greatly influences dynamic foot function.[7,8] Variations in the structure of the MLA will influence the shape of a footprint taken from that foot.[7] The use of footprints has therefore been suggested to be used for measuring foot structure characteristics, such as arch height.[7,8,9,10]

Preliminary evidence for an association between arch heights and foot pressures comes from the following two studies. Calcaneal inclination and first metatarsal inclination, which are both indicators of the height of the medial longitudinal arch (r = 0.64) were reported to be one of the predictive factors of foot pressures under the first metatarsal head (MTH).[11,12] A greater calcaneal inclination and first metatarsal inclination (with reference to standing surface), indicating a higher arch, was positively associated with higher pressure under the first MTH. Contradicting results come from the following study demonstrating that subjects with high arched, cavus-type feet tended to laterally load-bear and experienced high pressures on the lateral side of the forefoot.[13] However, the authors do not describe whether the pressures under the medial side were also increased in the cavus feet in this latter study. Alignment of the forefoot and rearfoot has also been associated to pressure loading pattern.[14] It was reported that both non-diabetic and the diabetic planus feet (valgus or everted rearfoot, varus or inverted forefoot, and low-arch morphology) experienced significantly greater peak pressures than the non-diabetic rectus feet (neutral rearfoot and forefoot with normal arch morphology).[14] No significant difference in peak pressure was seen between the diabetic and non-diabetic planus feet.

There are only two studies that have looked at the relationship between arch index and foot pressures.[15,16] Cavanagh, et al.,[15] reported weak correlations between peak pressure and arch index, for both diabetic neuropathic patients and healthy controls (r=0.17 and r=0.16), indicating higher pressures are related to a higher arch index (lower arch). McPoil and Cornwall16 observed that high-arched feet exhibited a significant delayed loading of the hallux compared to normal and low-arched feet, while low-arched feet exhibited earlier loading of the fifth MTH compared to normal and high-arched feet.

As pressure is defined as force by area, it could be speculated that subjects with a higher arch and subsequently a relative smaller foot contact area may have greater plantar pressures than subjects similar in body mass but with a lower arch and subsequently greater foot contact area. Some indirect evidence to support this hypothesis comes from Low, et al.,[17] who investigated the ratio area of foot print to area of foot outline, a measurement moderately similar to the arch index. A significantly lower ratio was noted in ulcerated feet compared to contralateral non-ulcerated feet in diabetic patients and compared to diabetic patients without ulcers and healthy control subjects.[17] Thus, these results indicate that ulcerated feet have a reduced foot contact area, which could contribute to foot ulcer development.

The reporting of the association between body mass and peak pressure has been very inconsistent, with some authors observing significant correlations but concluding that the functional relationship is weak,[15,18,19,20] some observing very low or no correlations,[21,22] or one reporting that body mass was the only predictive factor of high foot pressure at two or more sites of the foot (pressure > 1SD above the mean for each area).[5] In addition, patients with a history of neuropathic ulceration have been reported to be heavier.[23]

Thus, the relationship between arch index and body mass and peak pressures is not entirely clear from the available foot pressure literature. As foot pressures are considered to be an important risk factor for diabetic foot ulceration, it is important to investigate all factors that could increase foot pressures in these patients. Therefore, the aim of this study was to investigate the effect of arch height (arch index) and body mass on plantar foot pressures in diabetic and non-diabetic subjects.

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