Objective To evaluate the therapeutic effect of extendable intramedullary nail on children with femoral deformity due to osteogenesis imperfecta.Methods From June 2009 to June 2012,21 patients with femoral deformity due to osteogenesis imperfecta were treated with extendable intramedullary nail.There were 13 males and 8 females,aged from 9 years and 6 months to 15 years and 7 months (average,12 years and 3 months).All children had been performed osteotomy on the shaft of femur and implanted with non-extendable nail before 2-4 years (average,3 years).All children had suffered refracture and deformity,including 9 children with femoral bending deformity and 12 with refracture.The deformity angle ranged from 10°to 30°,with an average of 15°.According to revised Sillence classifications,there were 6 cases with type Ⅲ and 14 with type Ⅳ and 1 case with type Ⅴ.Twenty-one patients were operated with extendable nail for fixing fracture and correcting deformity and incisions were 2-3 cm long and located on the great trochanter and distal osteotomy point.Results All of 21 children were followed up for 6-30 months (average,18 months).The bone healing time was 7-12 weeks (average,8.5 weeks).Patients started to walk after X-ray showing bone union.Parents of 21 children were satisfied with surgical operation effect and deformity correction.The Barthel index score improved from 72.85 (range,50-90 points) preoperatively to 91.42 (range,80-100 points) postoperatively at the latest follow-up of patients.WeeFIM index score increased from preoperative average of 55.42 points (range,40-70points) to postoperative average 79.00 points (range,70-86 points).Ten of all children with stick aid preoperative could walk independently after small incision repairing,and 6 of all children in sickbed preoperative,4 of 6 children could walk independently,2 of 6 children could walk with stick aid.Conclusion Small incision repair with extended intramedullary nail operation therapy is advantaged.It gets less bloody,less damages,less pain,less healing time and walking after removing plaster.