Surfer's knots are a cutaneous condition caused by chronic pressure over bony prominences leading to thick fibrotic nodules on knees, knuckles, dorsal feet, often seen with those who perform surfing, boxing, football, and marbles.
- Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. p. 1371. ISBN 1-4160-2999-0.