Nonunion is permanent failure of healing following a broken bone unless intervention (such as surgery) is performed.

The diagnosis is generally made when there is no healing between two sets of medical imaging, such as X-ray or CT scan.

In general, if a nonunion is still evident at 6 months post-injury it will remain unhealed without specific treatment, usually orthopedic surgery.

This type of nonunion is thought to occur when the body has adequate biology, such as stem cells and blood supply, but inadequate stability, meaning the bone ends are moving too much.

Failure of initial union, as when bone fragments are separated by soft tissue, may also lead to an atrophic non-union.

[7] Currently, there are different strategies to augment the bone-regeneration process, however, there is no standardised clinical treatment guideline yet.

[9] Surgical treatment options include:[citation needed] In simple cases, healing may be evident within 3 months.

Bone stimulation with either electromagnetic or ultrasound waves has been suggested to reduce the healing time for non-union fractures.

[14] The proposed mechanism of action is by stimulating osteoblasts and other proteins that form bones using these modalities.