Plantar skin callus plaques are a common, frequently painful hyperkeratotic condition affecting a number of the population and these hard, dense, yellowish, cutaneous lesions may even be sufficiently severe to limit working practices and social activities. Pathological callus formation is thought, empirically from clinical observation, to be due to excess intermittent pressure during gait, associated frequently with a structural or functional anomaly of the foot and leg.
Studies into callus pathology are relatively few and have been concerned mainly with the structure and ultrastructure of callus tissue. The biomechanical features of plantar skin callus have been studied and results show it behaves differently from normal plantar and hairy skin. The current work extends the understanding of plantar skin calluses, their aetiology and pathology, utilising techniques, with some novel applications, from a number of fields.
The mechanical forces exerted on the callused foot at the time of lesion loading were studied using the Kistler force and Musgrave pressure measurement plates. The duration of loading of the lesion was found to be increased compared with that of a normally functioning foot (p = 0.05). It was not possible to attribute reactive forces exerted on the foot at the time of loading to the lesion site, as appropriate technological advances have yet to be made. No predominant force vector was found which could be associated with the clinical appearance of plantar callus plaques. The clinical appearance of the callus lesion cannot therefore be used as an indicator of influential mechanical stresses. There is no relationship between either the dominant side and callus incidence on left or right feet or the different skin ridging patterns (dermatoglyphics) of callus lesions and their viscoelasticity. However, the results from rheological studies of this tissue suggested that the viscoelastic properties of areas of the stratum corneum within the callus plaque may be influential in the formation of the dermatoglyphic patterns found in these lesions.
Fourier Transform Infrared Spectrometry was used to provide fundamental information for the rheological studies on plantar skin callus tissue and also confirmed the clinical assumption that callus tissue had a lower water content than normal plantar skin. A-scan ultrasound skin imaging (Dermal Depth Detector) with which it was hoped to quantify the topographical features of the lesion was not successful, probably due to the limitations of the instrument and transducer in this application, rather than the technique in general. Light microscopical examination of plantar callus sections was in general agreement with previous studies. The most notable feature was the disruption or absence of the granular layer in callus and corns respectively.
A model for callus formation has been proposed partly as a result of the information generated during the course of study. An accelerated transit rate of callus keratinocytes is likely to result in cell immaturity on reaching the stratum corneum since differentiation will not have had time to be completed. Thus a number of differences in plantar callus will be evident, such as altered cell cohesion and desquammation.
The results of this work will provide useful data which may direct further studies into suitable therapeutic modalities, thus extending the range of methods available for treatment of this common condition.
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