If a bone has shown no evidence of healing for 3 months or has stopped healing for 3 months then it is likely that it will not unite without further intervention. Non-unions tend to be painful, internal fixation devices can break which displaces the fracture. Modern limb reconstruction techniques are individualised depending on the bone involved and the severity of the original injury. Treatment may include revising the fixation, using a bone graft or bone morphogenetic proteins to stimulate bone formation. In severe cases, external fixator frames such as the llizarov frame or Taylor Spatial Frame can be used to re-grow segments of bone that are not healing or stabilise infected non-unions. Limb reconstruction techniques are often long and complex, but are usually the last resort for healing problem fractures.