Objective To evaluate the effectiveness of membrane induction technique in the treatment of Gustilo-Anderson ⅢB type injury of distal femur complicated with bone defect. Methods The clinical data of 20 patients with Gustilo-Anderson ⅢB type injury of distal femur complicated with bone defects admitted between January 2019 and December 2020 were retrospectively analyzed, including 15 males and 5 females, with an average age of 35 years (range, 19-70 years). Causes of injuries included 15 cases of traffic accidents and 5 cases of falling from height. Bone defect located at metaphyseal in 11 cases and at proximal metaphyseal in 9 cases. The time from injury to primary first-stage surgery was 4-28 hours, with an average of 11 hours. After primary radical debridement, the length of bone defect was 3-12 cm, with an average of 6 cm. Antibiotic-containing bone cement was implanted in the bone defect site to induce membrane formation. At 34-56 days (mean, 45 days) after the first-stage surgery, bone grafting was performed in the induced membrane for the repair and reconstruction of bone defects; 16 patients received a combination of autogenous cancellous and allogeneic bone grafts and 4 patients received cancellous bone grafts. The bone graft healing time after the second-stage surgery was recorded; the visual analogue scale (VAS) score and Lysholm score were compared before the second-stage bone graft and at last follow-up to evaluate the pain and functional improvement of the affected limb; and the knee joint range of motion at last follow-up was recorded. Results None of the patients had a second revision after the first-stage surgery, 1 patient recieved flap transfer and the flap survived well after operation. All patients were followed up 12-36 months after the second-stage surgery, with an average of 23 months. All patients achieved bone union, and the bone union time was 7-10 months (mean, 8.4 months). No bone nonunion or donor site related complications occurred. The Lysholm score and VAS score at last follow-up were 85.6±4.1 and 1.7±0.8, respectively, and they were significantly improved when compared with those before the second-stage bone defect repair (42.7±4.6 and 7.1±0.8, respectively) (t=37.410, P<0.001; t=21.962, P<0.001). Knee flexion range of motion was 60°-120°, with an average of 95°; the limit of elongation was 0°-10°, with an average of 5°. ConclusionFor Gustilo-Anderson ⅢB type injury of distal femur complicated with bone defect, induction membrane technique can effectively control infection, promote bone healing of the defect site, and effectively restore the function of lower limbs with satisfactory effectiveness.