Cuối cùng, mô mềm thực sự có thể biến mất, đôi khi đi kèm với tái hấp thu của xương nằm bên dưới. Subungual exostosis có thể trình bày theo cách này: phần mở rộng của xương lưng sản xuất móng tay gọng kìm (exostosis) phải được cắt bỏ. Các biên giới bên của móng tay tác dụng một áp lực liên tục, | Nail configuration abnormalities 25 Figure a-d Varying degrees of pincer nail deformity. Pincer nail Pincer nail is characterized by transverse overcurvature that increased along the longitudinal axis of the nail and reaches its greatest proportion towards the tip Figure . At this point the lateral borders tighten around the soft tissues which are pinched without necessarily disrupting the epiderms. Eventually the soft tissue may actually disappear sometimes accompanied by resorption of the underlying bone. Subungual exostosis may present in this way the dorsal extension of bone producing the pincer nail the exostosis must be excised. The lateral borders of the nail exert a constant pressure permanently constricting the deformed nail plate unguis constringens . In extreme cases they may join together forming a tunnel or they may become rolled taking the form of a cone. In certain varieties the nails are shaped like claws resembling pachyonychia congenita. A text atlas of nail disorders 26 Figure a b Progressive worsening of the pincer nail deformity in 5 years. This morphological abnormality would be no more than a curiosity if the constriction were not occasionally accompanied by pain which can be provoked by the lightest of touch such as the weight of a bedsheet. There are a number of subtypes of this condition 1 The inherited form usually shows symmetrical involvement of both the great toe nails and of the lesser toe nails. The great toe nails typically have lateral deviation of their longitudinal axis the lesser toe nails being deviated medially. This dystrophy Figure a Transverse curvature of nail b transverse curvature of nail in yellow nail syndrome before colour change . Nail configuration abnormalities 27 Figure Transverse overcurvature in the pseudo yellow nail syndrome due to insecticide and weed killer. Figure Transverse overcurvature in the yellow nail syndrome. is a developmental abnormality which may be an autosomal
