A Modified Type III Keystone Flap for Digital Mucous Cyst of the Eponychium

Digital mucous cysts (DMCs), also known as myxoid cysts, periungual ganglion cysts, and myxomatous cutaneous cysts, commonly occurr at the distal interphalangeal joint (DIPJ) of the fingers and toes. Due to the dense and inflexible skin at the dorsal fingertip, wound dehiscence and necrosis may sometimes be caused by tension sutures. The keystone flap (KF), designed as a curvilinear-shaped trapezoidal keystone with two V-Y advancements at the exterior peripheral corners, has been gaining popularity as a local flap that can close defects with a lower tension. In the reported case, while facing the DMC at the eponychial fold, we applied a modified type III KF with minimal elevation of the eponychium and internal rotation of the opposite flaps to cover the triangular defect. Postoperative outcomes showed that the flap was viable with sufficient perfusion and no wound dehiscence or infection. During follow-up, the grooving deformity of the nail was corrected, and no tumor recurrence was noted. Moreover, there were no restrictive scars or limited range of motion on the DIPJ.