Subungual Hematomas:

• Subungual hematomas are collections of blood that form under the nail with injuries to the distal phalanx. 
• Those that are < 25% of the nailbed can be drained via trephination and heal well.
• Up to 94%  of subungual hematomas that are are associated with a distal phalanx fracture have a nailed laceration.  It is commonly taught this hematomas should have the nail removed and the nailbed repaired.  However  studies from the 1990's have shown that as long as the nail is attached to the nailbed or paronychia and is not displaced; trephination alone can be done to achieve similar outcomes.

References

• Roser SE, Gellman H. Comparison of nail bed repair versus nail trephination for subungual hematomas in children. J Hand Surg [Am]. Nov 1999;24(6):1166-70.
• Meek S, White M. Subungual haematomas: is simple trephining enough?. J Accid Emerg Med. Jul 1998;15(4):269-71.
• Seaberg DC, Angelos WJ, Paris PM. Treatment of subungual hematomas with nail trephination: a prospective study. Am J Emerg Med. May 1991;9(3):209-10.