Analytical approaches to the determination of pressure distribution under a plantar prominence.

INTRODUCTION:: The purpose of the current research was to develop an analytical model for the interface between the metatarsal head, surrounding soft tissue, and the shoe. Results of 'peak plantar pressures' computed from this model were compared to previous results obtained from clinical data and from a finite element (FE) model. METHODS:: An analytical model for determining the pressure distribution at the interface between the foot and shoe insole was developed based on the solution[Figure: see text] for a rigid cylinder and a single elastic layer mounted on a rigid half-space originally developed by Meijers (see Figure 1). The rigid cylinder was used to represent the metatarsal head region (including bone and soft tissue). Material properties and loading conditions were chosen to reflect those used by Lemmon et al. for 'Normal' and 'Reduced' soft tissue thickness cases. RESULTS:: Peak pressures computed from the analytical model are plotted against insole thickness in Figure 1, alongside experimental and FE model data from Lemmon et al. Correlations between analytical, FE, and experimental results for both the Normal and Reduced soft tissue cases were all highly significant (r(2) = 0.86, p < 0.01). DISCUSSION:: The analytical model produced unrealistically high peak pressures compared to the FE and experimental results, with differences of approximately one order of magnitude. This was not surprising, given that the entire metatarsal head region (soft tissue included) was modelled as a rigid cylinder. The soft tissue on the bottom of the foot, and the much greater surface area over which the loads are carried in the real case, contribute greatly to reducing these peak pressure values. However, the downward trend in peak pressure with increased insole thickness was retained. CONCLUSION:: It is anticipated that the use of more accurate and detailed models will greatly improve the initial results.