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A subungual hematoma is a collection of blood (hematoma) underneath a toenail or fingernail (black toenail). It can be extremely painful for an injury of its size, although otherwise it is not a serious medical condition. It is sometimes known as runner's toe or tennis toe. ==Causes== Runner's toe is a common condition seen in runners caused by downward pressure or horizontal separation of nail plate from the nail bed. This repetitive traumatic injury leads to bleeding and pooling of blood underneath the nail plate. Clinically, it is characterized by reddish-black discoloration of the toe nail. The nail plate may also become thicker and more brittle as a result of the injury (onychochauxis). Fortunately, the deformed nail plate will gradually grow out and be replaced by new, normal-appearing nail plate in several months time. Infrequently, the toe may become painful and require surgical drainage. Runner's toe is often associated with malfitting shoes and insufficient space for the toes. Some susceptible runners may also have Morton's toe. In this variant of human foot anatomy, the second toe extends further out than the great toe. The key to prevention of runner's toe is to purchase properly fitted shoes. The condition also results from a traumatic injury, such as slamming a finger in a door, or from sports activities, such as climbing or hiking rugged terrain. A subungual hematoma that results from the repetitive thrusting of the longest toe into a shoe's toe box is called jogger's toe or runner's toe. The bleeding comes from the (vascular) nail bed underlying the (avascular) nail plate. A laceration of the nail bed causes bleeding into the constricted area underneath the hard nail plate. Throbbing pain is common. The nail develops a black discoloration overlying the nail bed but under the nail plate. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Subungual hematoma」の詳細全文を読む スポンサード リンク
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