Congenital Curved Nail of the Fourth Toe with Subungual Hyperkeratosis.

Congenital curved nail of the fourth toe (CNFT) is a rare nail deformity. We report a case of CNFT with thickening and hyperkeratosis at the hyponychium and peripheral nail bed that was successfully treated using a novel surgical technique. A 7-year-old Japanese boy had a clawed nail with thickening and hyperkeratosis at the hyponychium and peripheral nail bed on his bilateral fourth toes. His chief complaint was pain. The nails of the bilateral fourth toes curved plantarly and exhibited thickening and hyperkeratosis of the hyponychium and peripheral nail bed. A surgical approach was planned to improve the condition. The distal phalanges that deviated and formed a point toward the nail bed were partially shaved, and a soft tissue flap was created in the finger pad and shifted to cover the distal phalanges. The dorsal side of the distal phalanges was covered by the nail bed flap. Recurrence has not been observed for 3 years after surgery. There is limited evidence supporting surgical approaches for CNFT. This approach may be an effective treatment option for CNFT with thickening of the nail bed.