Different bones heal at different rates; the majority of wrist fractures heal in six weeks, whereas the average time for healing of the tibia (shin bone) is four months. If a bone has shown no evidence of healing for 3 months, or has stopped healing for 3 months, then it probably will not unite without further intervention.
What are the symptoms of non-union?
Most commonly, unhealed bones are painful at the fracture site. Internal fixation devices such as plates or internal nails cannot take weight indefinitely, and eventually metal fatigue occurs leading to breakage of screws or plates, and displacement of the fracture.
Treatment of non-union
Modern limb reconstruction techniques are individualised depending on the bone involved, the severity of the original injury and the reason for the bone failing to unite. Treatment might be a simple matter of revising the fixation for something more stable, to the use of bone graft or modern genetically engineered Bone Morphogenetic Proteins that can stimulate bone formation.
In severe cases, the use of complex external fixator frames such as the Ilizarov frame or the Taylor Spatial Frame can be used to re-grow dead segments of bone that are not healing, or stabilise infected non-unions. These limb reconstruction techniques are often long and complex, but are usually the last resort for the healing of problem fractures.