In the accompanying paper, McCallum and colleagues report a systematic review of the effects of different surgical techniques for treating pilonidal sinus.1 Pilonidal disease is an infection in a “ditch” that results from mechanical stretch, which causes enlargement and rupture of hair follicles in the natal cleft.2 The disease is confined to skin and fat, can be acute or chronic, minor or major, and can range from an asymptomatic pinhole in skin to an abscess the size of an orange.

The disease affects mainly young men aged 15-30. McCallum and colleagues report an incidence of 26/100 000,1 but it varies by population—from 0.11% in women at college to 8.8% in Turkish soldiers. One large series reported that 78 924 US servicemen in the second world war were in hospital for an average of 55 days each with pilonidal problems, chiefly because of complications of …