|Other names||Runner's toe, tennis toe, skier's toe|
|Subungual hematoma of a toe|
|Specialty||Internal medicine, Podiatry|
|Symptoms||Discoloration of nail, pain|
|Risk factors||Poorly fitting foot wear, overtraining particularly hiking and running|
|Treatment||Usually unmerited, blood drainage or nail removal in serious cases|
|Prognosis||Usually self-resolving as nail grows out|
A subungual hematoma is a collection of blood (hematoma) underneath a toenail or fingernail (subungal hematoma). It can be extremely painful for an injury of its size, although otherwise it is not a serious medical condition.
A laceration of the nail bed causes bleeding into the constricted area underneath the hard nail plate. The blood pools under the nail, giving a reddish, brownish, blueish, or grey/blackish discoloration. The blood puts pressure to the nailbed causing pain which can be throbbing in quality and disapperas when the pressure on the nail bed is relieved. 
Subungual hematomas typically heal without incident, though infection may occur. The pressure of the blood blister may cause separation of nail plate from the nail bed (onycholysis), but the nail should not be pulled off, as this can cause scarring of the nailbed and deformed nails. Nail discolouration may last some months.
The nail plate may also become thicker and more brittle as a result of the injury (onychochauxis). The deformed nail plate will gradually grow out and be replaced by new, normal-appearing nail plate in several months' time. Infrequently, the nail may become painful and require surgical drainage.
The condition is caused by a traumatic injury, such as slamming a finger in a door, 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,[better source needed] and ill-fitting footwear.:52,135
Repeatedly thrusting the toes against a shoe's toe box can cause a subungual hematoma called jogger's toe runner's toe, or black toenail. In a marathon, several percent of runners may be affected. Wearing footwear which fits helps prevent runner's toe.
If the shoe is too loose on the midfoot, the foot can slide forwards in the shoe, especially when going downhill. This may jam the toes into the end of the toebox. 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).:86–87,128,142 Excessively tight or uneven fit around the midfoot may, however, cause tendon problems.:125[better source needed]
Separately, if there is not enough space around the toes, the toes will also hit the toebox repeatedly. Feet become longer and wider when weight is put on them, because the arches flatten, and the toes also splay and bend.:p15,18,72–73 At the end of a long journey on foot, the arches flatten, the metatarsals spread, and the foot swells more than after a short one.:52 The toes also need vertical space; a toe cap which is low enough to press on the top of the toe may also cause bruising under the nail, especially if the toe cap is stiff. If the toebox is pointed, the toes may be wedged forwards into the area with inadequate height.:52–53,135
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. This can make it harder to find shoes with adequate space around the toes.
Subungual hematomas are treated by either releasing the pressure or conservatively, pressure (under the nail and over the nailbed) can be released by making a hole through the nail into the hematoma (trephining) within 48 hours of injury, or by removing the entire nail.
In hospital or medical setting Trephining is generally accomplished by using an electrocautery device or an 18-gauge needle if any of these is not available a heated (red hot) paper clip can be used to drain the blood underneath of the nail, to do this the tip of a paper clip needs to be heated till it's red hot and (the red hot) paper clip gently placed on the center of the hematoma (center of the black area underneath of the nail), as a result of (red hot) tip of the paper clip gently touching the nail a hole will appear in the nail and the blood will be drained, pressure will be relieved, the hole has to be covered with sterile dressing and nail be kept dry afterward. 
Removal of the nail is typically done when the nail itself is disrupted, a large laceration requiring suturing is suspected, or a fracture of the tip of the finger occurs. Although general anesthesia is generally not required, a digital nerve block is recommended if the nail is to be removed. For trephination, the block is often more painful than the procedure.
- Selbst SM, Attia M (2006). "Lacerations". Textbook Of Pediatric Emergency Medicine. Hagerstown, MD: Lippincott Williams & Wilkins. p. 1571. ISBN 978-0-7817-5074-5.
- "3 Tips to Protect Your Toenails If You're a Hard-Core Runner". Health Essentials from Cleveland Clinic. 3 December 2015.
- Mailler, EA; Adams, BB (August 2004). "The wear and tear of 26.2: dermatological injuries reported on marathon day". British Journal of Sports Medicine. 38 (4): 498–501. doi:10.1136/bjsm.2004.011874. PMC 1724877. PMID 15273194.
- Pingel, C; McDowell, C (January 2019). "Subungual Hematoma Drainage". Statpearls. PMID 29494114.
- "Subungual Hematoma: Care Instructions". myhealth.alberta.ca.
- "Subungual Hematoma: Causes, Symptoms, Pictures, Treatment, and More". Healthline.
- Munson, Edward Lyman (1912). The soldier's foot and the military shoe; a handbook for officers and noncommissioned officers of the line. Menasha, Wis.: Press of the George Banta publishing company. (this is the publication of a four-year review into the footwear of the US military by the Army Shoe Board, of which the author, a physician and senior officer of the United States Army Medical Corps, is president.
- Mailler, E A; Adams, BB (2004). "The wear and tear of 26.2: dermatological injuries reported on marathon day". British Journal of Sports Medicine. 38 (4): 498–501. doi:10.1136/bjsm.2004.011874. PMC 1724877. PMID 15273194.
- Dean, B; Becker, G; Little, C (2012). "The management of the acute traumatic subungual haematoma: a systematic review". Hand Surgery. 17 (1): 151–4. doi:10.1142/S021881041230001X. PMID 22351556.