Clinical photographic observation of plantar corns and callus associated with a nominal scale classification and inter- observer reliability study in a student population

BACKGROUND The management of plantar corns and callus has a low cost-benefit with reduced prioritisation in healthcare. The distinction between types of keratin lesions that forms corns and callus has attracted limited interest. Observation is imperative to improving diagnostic predictions and a number of studies point to some confusion as to how best to achieve this. The use of photographic observation has been proposed to improve our understanding of intractable keratin lesions. METHODS Students from a podiatry school reviewed photographs where plantar keratin lesions were divided into four nominal groups; light callus (Grade 1), heavy defined callus (Grade 2), concentric keratin plugs (Grade 3) and callus with deeper density changes under the forefoot (Grade 4). A group of 'experts' assigned from qualified podiatrists validated the observer rated responses by the students. RESULTS Cohen's weighted statistic (k) was used to measure inter-observer reliability. First year students (unskilled) performed less well when viewing photographs (k = 0.33) compared to third year students (semi-skilled, k = 0.62). The experts performed better than students (k = 0.88) providing consistency with wound care models in other studies. CONCLUSIONS Improved clinical annotation of clinical features, supported by classification of keratin- based lesions, combined with patient outcome tools, could improve the scientific rationale to prioritise patient care. Problems associated with photographic assessment involves trying to differentiate similar lesions without the benefit of direct palpation. Direct observation of callus with and without debridement requires further investigation alongside the model proposed in this paper.