Jul 31, 2016
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why does a callus or corn form a round shape? Either on top of PIPJ or plantarly, it seems always circular. If you don't wear shoes, does it take certain shape?
 

FootAndAnkle

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Jul 6, 2013
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why does a callus or corn form a round shape? Either on top of PIPJ or plantarly, it seems always circular. If you don't wear shoes, does it take certain shape?
It's a reaction to pressure, so the callus formation reflects how the pressure is distributed. At other sites, such as pinch calluses from adductovarus 4th and 5th digits that underride the adjacent pulp, they don't take the circular/oval form you've mentioned. Same at the 1st MTPJ where they can form more of a crescent pinched shape with shearing/twisting forces or at clefts like you see with ectrodactyly.