[1] The blood pools under the nail, giving a reddish, brownish, blueish, or grey/blackish discoloration.

The deformed nail plate will gradually grow out and be replaced by a new, normal-appearing one in several months' time.

[5] The condition is caused by a traumatic injury, such as slamming a finger in a door,[6] or from sports activities, especially those involving sudden accelerations, such as soccer, basketball, and tennis, or going downhill, such as running or hiking rugged terrain, and ill-fitting footwear.

[4] If the foot is sliding forwards because the shoe is too loose around the midfoot, it may be restrained by lacing the shoe carefully, or placing bulky padding between the tongue and the lacing, or by wrapping a strap in a figure-eight around the foot and ankle (image).

[4] Feet become longer and wider when weight is put on them, because the arches flatten, and the toes also splay and bend.

[10] In a hospital or medical setting, trephining is generally accomplished by using an electrocautery device or an 18-gauge needle.

[5] Complication rates from both forms of treatment are low, and the nail generally recovers to a normal appearance.