Severe deformation of the nails, most often involving the nails of the great toes. The involved nail becomes greatly thickened and curved, presenting a claw-like shape. Onychogryphosis may be due to trauma and permanent shoe pressure. Anomalies of foot position have a promoting effect. Onychogryphosis may also occur in patients suffering from psoriasis, ichthyosis hystrix and other epidermal dysplasias.