Not a keratoma, just a blooming bad crack gone wrong. Original crack was due to trauma.
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The crack created an very unstable heal (the lameness and infection) which turned into a, very badly, sheared heal, this has improved hugely over the last shoeing. Possibly is showing up in the top half inch?
Top half inch suggests the shoe is making the foot grow at a different angle than it should be. If it doesn't change soon, I would want the shoes off.
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