Subungual exostoses are bony projections which arise from the dorsal surface of the distal phalanx, most commonly of the hallux (big toe). They are non-cancerous, benign bone tumours. They are composed of mature bone with a fibrocartilaginous cap.
Lee et al (2007) noted that half of their subungual lesions were actually osteochondromas arising from the proximal part of the distal phalanx and covered with hyaline cartilage organised as in a growth plate.
True exostoses are commonest in young adults with a female predominance. They mainly occur in the great toe, although they also occur in the lesser toes and fingers.
Signs & Symptoms
Typical clinical signs of this condition are painful raised firm lesions that are located deep to the free edge of the nail. This growth pushes the nail edge and, sometimes, the entire nail upward.
Pain is caused by the enlarging exostoses below and is exacerbated by the shoe pressure above.
The loosened, raised nail plate is typical of this entity.
The growth usually continues to grow so is best removed when diagnosed.
This can be done under local anaesthesia as a day case.
Sometimes the nail fold can be elevated and preserved, but usually it cannot be separated from the lesion and must be sacrificed.
Even with careful excision of the whole lesion, the recurrence rate averages about 10%.
A few patients require removal of so much nail bed that there is significant post-operative nail deformity, so that plastic nail bed reconstruction may be considered.
This picture shows the growth after the nail was removed: