Pilonidal Sinus Pilonidal sinus is a condition where a small cavity or hole forms in the skin over the tailbone. It can lead to pain, discomfort, and infection. Causes: Congenital or acquired, excessive hair growth, poor hygiene, or trauma. Types of surgery: Open excision, closed excision, and flap surgery. Open excision: Removal of the sinus and surrounding tissue. Closed excision: Removal of the sinus and stitching the wound. Flap surgery: Flap procedures involve moving tissue from elsewhere on the body to cover the wound.