A chronic fracture is a broken bone that has failed to heal within the normal expected timeframe. Rather than describing a specific type of break, the term refers to any fracture where the healing process has stalled or stopped entirely. In medical settings, this is most often called a “nonunion,” and the FDA defines it as a fracture that persists for at least nine months without signs of healing for three consecutive months. In practice, many orthopedic surgeons begin treating a fracture as a nonunion as early as six months after the injury.
How Normal Healing Stalls
When a bone breaks, the body immediately begins repairing it. Blood clots form at the fracture site, new blood vessels grow into the gap, and specialized cells gradually lay down soft callus tissue that eventually hardens into bone. Under normal circumstances, visible improvement appears on X-rays within about three months.
When that process slows significantly, the fracture enters a gray zone called “delayed union,” typically between three and six months after the injury. The bone is still trying to heal, just not fast enough. If healing stalls completely and the gap between bone fragments remains visible on imaging beyond nine months, the fracture is classified as a nonunion, or chronic fracture. At that point, the bone is unlikely to heal on its own without intervention.
Stress fractures can also become chronic. These small cracks develop from repetitive strain rather than a single traumatic event. Without adequate rest, the cycle of damage outpaces the body’s ability to repair it. The microfractures accumulate, potentially progressing to a complete fracture or a nonunion that resists healing.
What a Chronic Fracture Feels Like
The hallmark symptom is persistent pain at the fracture site, especially with weight-bearing or movement. Months after the initial injury, you may still feel a deep ache when walking, gripping, or putting pressure on the affected area. In some cases, the bone fragments remain slightly mobile. You might feel a subtle shifting sensation or instability where the break occurred. This movement at the fracture site is one of the key signs doctors look for during a physical exam.
Unlike the sharp, acute pain of a fresh break, chronic fracture pain tends to be more of a constant, wearing discomfort. It often leads people to favor the injured limb, which over time can cause muscle weakness, stiffness, and problems in nearby joints.
Why Some Fractures Don’t Heal
Chronic fractures develop when the biological environment at the break site can’t support bone regeneration. Several factors raise the risk.
- Smoking: Smokers face roughly 2.5 times the odds of developing a nonunion compared to nonsmokers. Nicotine constricts blood vessels and limits the oxygen supply that healing bone tissue desperately needs.
- Vitamin D deficiency: Vitamin D plays a critical role in calcium metabolism and bone formation. In one study of spinal fusion patients, those with deficient vitamin D levels (below 20 ng/mL) had a nonunion rate of 38%, compared to 20% in patients with adequate levels. The deficient group also took twice as long to achieve fusion. In ankle surgery patients, every reoperation for nonunion occurred in the vitamin D deficient group.
- Poor blood supply: Certain bones and fracture types are inherently vulnerable because they receive limited blood flow. The scaphoid bone in the wrist, the neck of the femur, and the lower tibia are common trouble spots.
- Inadequate stabilization: If a fracture isn’t held still enough, whether from an insufficient cast or hardware that loosens, the constant micro-movement disrupts the delicate healing process.
- Infection: Bacteria at the fracture site create an inflammatory environment that diverts the body’s resources away from bone repair.
- Diabetes and vascular disease: Conditions that compromise circulation or immune function slow bone healing at a cellular level.
Three Types of Nonunion
Not all chronic fractures look the same on imaging, and the differences matter because they guide treatment decisions.
Hypertrophic nonunions show abundant callus tissue forming around the fracture gap. The body is clearly trying to heal: blood supply is intact and new tissue is growing. But the bone fragments never fully bridge together, usually because the fracture site has too much movement. These are often the most treatable type because the biology is working. The bone just needs better stabilization.
Oligotrophic nonunions have adequate blood supply like hypertrophic types, but produce little to no visible callus. The healing response is present but sluggish, often because the bone ends aren’t in close enough contact to bridge the gap.
Atrophic nonunions are the most challenging. There’s no callus formation at all and no signs of bone consolidation within the fracture gap. The tissue at the break site lacks adequate blood supply, meaning the body has essentially stopped trying to repair the fracture. Treating these requires not just stabilizing the bone but restoring the biological capacity to heal.
How Chronic Fractures Are Diagnosed
Standard X-rays are the first step. Doctors look for a persistent fracture line, the absence of bridging bone between fragments, and how much (if any) callus has formed. For tibial fractures, a scoring system called RUST rates each of the four visible bone surfaces on a scale, producing a score between 4 and 16. A score of 4 means no callus is present on any surface.
When X-rays aren’t conclusive, a CT scan provides a more detailed three-dimensional view of the fracture gap. Blood tests for markers of inflammation help rule out infection as the underlying cause. Your doctor will also review risk factors: whether you smoke, have diabetes or vascular disease, take certain anti-inflammatory medications, or have low vitamin D levels.
Treatment Options
Treatment depends on which type of nonunion you have and what caused healing to stall in the first place.
Nonsurgical Approaches
For some chronic fractures, bone growth stimulators offer a noninvasive option. These devices use magnetic fields or low-intensity ultrasound pulses applied to the skin over the fracture site, aiming to jump-start the healing process. Results vary considerably. One study using combined magnetic field stimulation reported an 84% success rate with an average healing time of about 6.5 months. But other trials have shown union rates closer to 45% to 64%, and at least one randomized trial found no significant benefit over a placebo device. The UK’s National Institute for Health and Care Excellence considers the evidence for ultrasound-based devices inadequate and recommends they be used only under special clinical governance arrangements.
Addressing underlying deficiencies also matters. Correcting low vitamin D levels, improving nutrition, and quitting smoking can create a more favorable environment for bone repair.
Surgical Repair
Surgery is the most reliable path to healing a chronic fracture. The specific approach varies, but common strategies include removing dead or fibrous tissue from the fracture gap, improving fixation with plates or rods, and adding bone graft material to stimulate new growth.
Bone grafts taken from your own body (typically from the pelvis) consistently outperform donor bone or synthetic alternatives. In comparative studies, autografts produce significantly better union scores and more advanced healing at one year. The trade-off is a second surgical site, which comes with its own recovery pain.
For hypertrophic nonunions where the biology is healthy, surgery may be as straightforward as replacing loose hardware with more rigid fixation. Atrophic nonunions require a more involved approach, combining stable fixation with grafting to restore both the structural and biological conditions for healing.
Recovery After Treatment
Recovery from surgical repair of a chronic fracture takes longer than healing a fresh break. In studies of patients treated for delayed or nonunion fractures of the upper arm, the average time from surgery to confirmed bone union was about 17 weeks, though the range extended from 8 to 30 weeks depending on severity. Physical therapy typically begins around 10 weeks after surgery for these patients.
The total time from the original fracture to final healing in nonunion cases averaged about 180 days, or roughly six months, compared to about 113 days for fractures treated promptly. That extended timeline underscores a frustrating reality: the longer treatment is delayed, the longer overall recovery takes. Each month of delayed surgery tends to push back the start of physical therapy, which in turn delays the return to normal activity.
Full recovery also depends on how well you manage the factors that contributed to the nonunion in the first place. If you continue smoking or leave a vitamin D deficiency untreated, the surgical repair faces the same biological obstacles that prevented healing the first time.