Abstract: Objective To study the changes in distal position of first metatarsal in correcting varus after the Ludloff osteotomy.Methods Ludloff Osteotomy was simulated on a wooden cylinder 86.56 mm in length and 30.65 mm in diameter and the experimental date were recorded.Results As the angle between the distal and proximal fragments increased,the length of the cylinder became shorter,and the distal cross section of the cylinder showed an internal rotation.When cutting it more plantar,the distal lowest point of the cylinder lowered first,then rose.However,if the cutting was more dorsal or horizontal,the distal lowest point rose constantly.Conclusion The distal cross section of the first metatarsal showed an internal rotation after Ludloff Osteotomy,which affects the positioning of the metatarsal-sesamoid joint.Across section of 15～20°angle plantar is suggested for patients with serious lateral metatarsalgia.

Key words: hallux valgus, Ludloff osteotomy, first metatarsal