ObjectiveTo investigate the effectiveness and indications of deferred dynamization for nonunion of femoral shaft fractures after static interlocking nail. MethodsBetween March 2006 and June 2012, 26 patients with nonunion of femoral shaft fractures after static interlocking nail were treated with deferred dynamization, and their data were analyzed retrospectively. There were 19 males and 7 females with a mean age of 38 years (range, 22-46 years). Nonunion was found at 10-29 months (mean, 16 months) after open reduction and static interlocking nail for fracture fixation. Referring to Papakostidis criteria for nonunion, there were 7 cases of stable/hyperplastic type, 3 cases of stable/atrophic type, 12 cases of unstable/hyperplastic type, and 4 cases of unstable/atrophic type. ResultsAll incision healed at first stage. Twenty-six patients were followed up 10-28 months (mean, 14 months). A total of 16 (61.5%) fractures healed at 4-11 months after deferred dynamization (7 cases of stable/hyperplastic type and 9 cases of unstable/hyperplastic type); the other 10 fractures failed to heal. The healing rate was 100% (7/7) in patients with stable/hyperplastic type nonunion, 75% (9/12) in patients with unstable/hyperplastic type nonunion, and 0 in patients with stable/atrophic type and unstable/atrophic type nonunion. ConclusionDeferred dynamization is an effective method for hyperplastic nonunion of femoral shaft fractures after static interlocking nail, but it is not suitable for atrophic nonunion of femoral shaft fractures.