Notes from – Uptodate and https://emedicine.medscape.com/article/782537-treatment
Fingertip pulp is divided into numerous small compartments by vertical septa that stabilize the pad. Infection occurring within these compartments can lead to abscess formation, edema, and rapid development of increased pressure in a closed space. This increased pressure may compromise blood flow and lead to necrosis of the skin and pulp.
Wooden splinters, thorns, or minor cuts are common predisposing causes, yet no history of injury exists in over one half of patients. Infection also may spread from a paronychia.
Photos from uptodate –