A nonunion fracture is a broken bone that has stopped healing and will not mend on its own without intervention. The FDA defines it as a fracture line still visible on imaging more than 9 months after the injury, though in practice many doctors begin treating it as a nonunion as early as 6 months. Under normal circumstances, a healing fracture should show visible improvement on X-rays within three months. When that progress stalls or never begins, the fracture is on a path toward nonunion.
How a Nonunion Differs From Slow Healing
Not every fracture that takes longer than expected is a nonunion. Doctors distinguish between delayed union and true nonunion based on timing and imaging. Delayed healing is typically identified between 3 and 6 months after the injury or surgery, when X-rays show less progress than expected but the bone is still actively trying to repair itself. A nonunion, by contrast, means the biological repair process has essentially given up. The fracture gap remains visible, no new bridging bone is forming, and without a change in treatment, the bone will stay broken indefinitely.
Types of Nonunion
Not all nonunions look the same on imaging, and the type determines how doctors approach treatment. The most widely used classification divides them into three categories based on what’s happening at the fracture site.
Hypertrophic Nonunion
In a hypertrophic nonunion, the body is actively trying to heal. Blood supply to the area is intact, and new bone is forming at the fracture ends, sometimes creating a bulging, elephant-foot appearance on X-rays. The problem is mechanical: the broken ends aren’t stable enough to bridge the gap. This type generally responds well to better stabilization because the biology is already working.
Atrophic Nonunion
Atrophic nonunion is the opposite scenario. The bone ends have lost their blood supply and are no longer producing new tissue. On imaging, the fracture ends may appear rounded, shrunken, or resorbed. This is essentially a bone defect, and treatment needs to restore both the biology (living bone cells and blood flow) and the stability to give healing a chance.
Oligotrophic Nonunion
Oligotrophic nonunion falls between the two. There’s moderate bone loss at the fracture ends, often caused by a combination of poor blood supply, soft tissue trapped in the fracture gap, or underlying metabolic problems. The healing potential is limited but not absent.
Which Bones Are Most Affected
Nonunion can happen in any bone, but some locations are far more prone to it. An epidemiological study across 18 human bones found that the scaphoid (a small bone in the wrist), the tibia and fibula (lower leg), and the femur (thighbone) have the highest nonunion rates. The scaphoid is particularly vulnerable because parts of it have a tenuous blood supply that’s easily disrupted by a fracture. The tibia, especially in its middle shaft, is at risk because it has relatively little soft tissue coverage to deliver blood to the healing site.
What a Nonunion Feels Like
The hallmark symptom is persistent pain at the fracture site that doesn’t improve over time, particularly with weight-bearing or use of the affected limb. Some people notice an inability to put weight on the leg or use the arm the way they could before, even months after the initial injury. In some cases, there’s abnormal movement or a subtle clicking at the fracture site, a sign that the two bone ends are shifting against each other rather than fusing together.
Interestingly, not all nonunions are painful. When a fibrous “false joint” (called a pseudarthrosis) forms at the fracture gap, the site may become relatively painless unless it’s stressed by repetitive use or complicated by infection. This can sometimes delay diagnosis because the patient assumes healing is progressing.
Risk Factors That Prevent Healing
Several factors increase the chance that a fracture won’t heal properly, and some of them are modifiable.
Smoking is one of the strongest risk factors. Smokers have significantly higher rates of nonunion and reoperation following fractures, particularly in the tibial shaft. Nicotine constricts blood vessels and reduces the oxygen delivery that bone cells need to regenerate. This effect persists even in former smokers, though the risk is highest in active smokers.
Nutritional deficiencies also play a role. Vitamin D deficiency has been linked to increased nonunion risk in multiple studies. One large study of over 237,000 pediatric fracture patients found that vitamin D deficiency nearly tripled the odds of nonunion. Low levels of calcium, iron, and albumin (a protein marker of overall nutrition) have also been associated with impaired bone healing. Clinically diagnosed malnutrition and sarcopenia (loss of muscle mass) raise the risk as well.
Other contributing factors include diabetes, infections at the fracture site, inadequate blood supply to the bone, and insufficient stabilization during initial treatment. If the broken bone ends aren’t held close together and kept still, or if soft tissue gets trapped between them, the healing process can fail from the start.
Do Anti-Inflammatory Drugs Cause Nonunion?
Common painkillers like ibuprofen and naproxen have long been suspected of interfering with bone healing because they block a chemical pathway involved in new bone formation. However, a recent systematic review and meta-analysis found no significant difference in nonunion rates between people who used these medications and those who didn’t. The pooled data showed only a minimal, statistically insignificant increase in risk. The evidence isn’t strong enough to say these drugs cause nonunion, though some surgeons still recommend limiting their use in the early weeks after a fracture as a precaution.
How Nonunion Is Diagnosed
Diagnosis starts with X-rays taken at regular intervals during recovery. The key findings that point to nonunion are a persistent fracture line that isn’t narrowing over time and the absence of bridging bone (callus) connecting the two fragments. When X-rays are inconclusive, CT scans provide a more detailed look at the fracture gap and can reveal whether the bone’s internal canal has sealed off or whether new bone is forming in areas that plain X-rays can’t capture clearly. Doctors also look at clinical signs: ongoing pain, inability to use the limb normally, and tenderness or motion at the fracture site during physical examination.
Non-Surgical Treatment Options
For some nonunions, particularly hypertrophic types where biology is intact but stability is the problem, non-surgical approaches can work. Bone growth stimulators that deliver pulsed electromagnetic fields through a device worn over the skin are one of the most established options. These devices are used at home, typically for several hours a day over weeks to months.
Success rates for electromagnetic bone stimulation range from 68% to 90%, depending on the fracture location and patient factors. A large follow-up study of 1,382 patients found an overall healing rate of 89.6%, and an independent audit of a subset confirmed an 86.4% success rate. In a controlled comparison, 85% of fractures treated with electromagnetic stimulation healed without surgery, compared to just 36% in a control group. These devices work best when the fracture ends are in reasonable alignment and the biological environment is favorable.
Surgical Treatment
When non-surgical approaches fail or aren’t appropriate, surgery is the standard path. The specific procedure depends on the type of nonunion, the bone involved, and the size of the gap between fragments.
For hypertrophic nonunions, the priority is mechanical. Surgeons re-stabilize the fracture with plates, screws, or an intramedullary nail (a rod placed inside the bone’s central canal) to provide the rigid fixation the healing process needs.
For atrophic nonunions, surgery must address both the mechanical problem and the biological one. This almost always involves bone grafting to introduce living bone cells and a scaffold for new bone to grow on. Autograft, bone harvested from the patient’s own body (usually the pelvis), remains the gold standard because it contains living cells that can form new bone, proteins that stimulate bone growth, and a natural scaffold all in one. The tradeoff is pain and potential complications at the donor site, and the amount of bone available is limited.
Allograft, bone from a donor, avoids the donor-site problems and comes in unlimited quantities. But because the sterilization and freezing process destroys living cells, it only provides a scaffold without the active biological signals. This means it has a lower success rate and higher risk of the graft itself failing to integrate. Synthetic bone substitutes face similar limitations. When used alone, synthetic materials have high failure rates; combining them with the patient’s own bone at a ratio of roughly 1:3 to 1:1 improves outcomes.
Even with the gold-standard autograft, failure rates of up to 26% have been reported, and the number of active bone-forming cells in the graft decreases with age. For large bone defects or patients who’ve already had a graft harvested, surgeons may use grafts with their own blood supply still attached (vascularized grafts) or supplement with bone marrow cells to boost the biological environment.
Recovery After Nonunion Treatment
Recovery from nonunion treatment is often longer and less predictable than recovery from the original fracture. After surgery, healing is monitored with serial X-rays to confirm that new bone is bridging the gap. Weight-bearing and activity are gradually reintroduced based on imaging progress. Addressing underlying risk factors, quitting smoking, correcting vitamin D or nutritional deficiencies, and managing diabetes, is just as important as the procedure itself. Without those changes, a second nonunion is a real possibility.