Objective To explore the method and effectiveness of index finger proximal dorsal island flap supplied by the nutrient vessels of superficial branch of radial nerve for treatment of thumb skin and soft tissue defect. Methods Between August 2019 and December 2024, 12 patients with thumb skin and soft tissue defects caused by trauma accompanied by variation of the first dorsal metacarpal artery were treated. There were 8 males and 4 females, aged 19 to 55 years, with an average age of 32 years. The wound area ranged from 2.2 cm×2.0 cm to 5.5 cm×3.5 cm. The time from injury to operation was 1.5 to 6.0 hours, with an average of 4.5 hours. After thorough debridement, the wound was repaired with a dorsal index finger island flap supplied by the nutrient vessels of the superficial branch of the radial nerve. The flap area ranged from 2.4 cm×2.2 cm to 6.0 cm×4.0 cm. The donor site was repaired with free skin grafting. Regular follow-up was conducted postoperatively to observe the appearance, texture, sensory recovery of the flap, and the condition of the donor site. Results The operative time ranged from 30 to 72 minutes, with an average of 47 minutes; intraoperative blood loss ranged from 30 to 70 mL, with an average of 46 mL. After operation, partial necrosis occurred at the skin edge of the radial incision on the dorsum of the hand in 1 case, which healed after dressing changes; all other flaps survived uneventfully, with primary wound healing. The skin grafts at the donor sites all survived. All 12 patients were followed up 5-36 months, with an average of 14 months. The appearance and elasticity of the flaps were good. At last follow-up, the two-point discrimination of the flaps ranged from 4 to 9 mm, with an average of 5.2 mm. According to the functional evaluation criteria for upper limb issued by the Hand Surgery Society of Chinese Medical Association, the results were excellent in 11 cases and good in 1 case. No scar contracture, pain, or joint movement limitation was observed at the donor sites. Conclusion For patients with skin and soft tissue defects of the thumb accompanied by variation of the first dorsal metacarpal artery, the index finger proximal dorsal island flap supplied by the nutrient vessels of the superficial branch of the radial nerve can be selected. This method has advantages such as shorter operative time, less intraoperative bleeding, and good postoperative appearance and sensation of the flap.