A fracture, or broken bone, typically begins a predictable, self-repairing biological process immediately after the injury. This natural healing sequence usually progresses over weeks to months, ultimately restoring the bone’s strength and function. If the body’s repair mechanism stalls, the broken ends fail to fuse back together. When a fracture fails to achieve union within the expected time frame, it is categorized as a nonunion, a serious complication requiring specialized intervention to restart the healing cascade.
Understanding Fracture Healing Failure
The normal process of bone repair unfolds in several overlapping stages. It begins with the inflammatory phase, where a hematoma (blood clot) forms at the injury site, providing initial scaffolding for healing cells. This is followed by the formation of a soft callus, a temporary bridge of cartilage and fibrous tissue connecting the fragments within the first few weeks.
The soft callus gradually transforms into a hard callus, composed of woven bone, which provides structural stability and is usually visible on X-rays between four and eight weeks. The final stage is remodeling, where the woven bone is replaced by mature, lamellar bone, restoring the original shape and strength. A nonunion is defined as the complete cessation of this healing process, making bone fusion highly improbable without medical or surgical treatment.
It is important to distinguish a nonunion from a delayed union. A delayed union is a fracture taking longer than average to heal but still showing signs of progress, and it is expected to eventually unite without additional intervention. While the exact timeline varies, a fracture is generally classified as a nonunion if it persists without radiographic evidence of healing for at least three consecutive months, typically six to nine months post-injury. The diagnosis of nonunion confirms that the natural healing mechanism has failed and requires a change in management.
Why Fractures Fail to Unite
Nonunion results from mechanical and biological deficits preventing the formation of a solid bony bridge. A primary biological issue is insufficient blood supply (vascularity) to the fracture site, which starves the area of necessary oxygen and cells. Bones with naturally limited blood flow, such as the scaphoid or the neck of the femur, are inherently more susceptible to healing failure.
Infection at the fracture site can overwhelm healing resources, impeding new bone growth and damaging the local blood supply. Systemic conditions also compromise healing, including uncontrolled diabetes, malnutrition, or low Vitamin D levels. These factors disrupt the cellular environment required for bone-forming cells to function.
Mechanical instability is a major contributor, as excessive motion prevents the soft callus from maturing into hard bone. If initial fixation (cast or surgical hardware) allows too much movement, the repair tissue remains fibrous rather than ossifying. Lifestyle factors, particularly tobacco or nicotine use, also play a significant role by vasoconstricting blood vessels and inhibiting bone-forming cells. Additionally, certain medications, including nonsteroidal anti-inflammatory drugs (NSAIDs) or corticosteroids, may interfere with the early inflammatory steps required for healing.
Diagnosing Nonunion
Diagnosis relies on combining a thorough clinical assessment with detailed medical imaging. Patients typically report persistent pain and tenderness at the fracture site several months after the injury, sometimes describing instability or motion in the limb. The physical examination focuses on identifying localized pain during weight-bearing or movement, suggesting the fracture has not achieved biological union.
Radiographic studies, primarily X-rays, are the initial imaging tool used to assess healing progression. In a nonunion, X-rays show a persistent gap between the bone fragments, often with visible rounding or sclerosis (hardening and thickening) of the bone ends. To gain a more detailed three-dimensional view, a Computed Tomography (CT) scan is frequently employed. A CT scan definitively confirms the absence of a bony bridge across the fracture line, even when metal hardware is present.
If infection or underlying systemic issues are suspected, blood tests may be ordered to check for elevated inflammatory markers or nutritional deficiencies. For example, a blood test can reveal a low Vitamin D level or the presence of an active infection. This comprehensive diagnostic approach confirms the nonunion and identifies the specific biological or mechanical factors preventing the bone from healing.
Treatment for Nonunion Fractures
Treatment is tailored to address the identified cause of healing failure, focusing on restoring mechanical stability and biological activity. Non-surgical options are often considered first, particularly external bone stimulation devices. These devices apply low-intensity pulsed ultrasound or electromagnetic fields over the fracture site, generating a signal that encourages bone cells to resume the repair process. They can be used safely at home over several months.
If non-surgical attempts fail or a mechanical problem is identified, surgical intervention is necessary. The most common procedure is revision internal fixation, where existing hardware (plates, screws, or rods) is replaced with new, more rigid hardware to achieve absolute stability. This mechanical correction is frequently paired with a biological stimulus, usually a bone graft.
A bone graft introduces new bone-forming cells and a supportive framework into the nonunion gap, effectively jump-starting the stalled biological process. The gold standard is an autograft, which uses the patient’s own bone (often harvested from the pelvis) because it contains living cells and natural growth factors. Alternatively, allografts (processed donor bone) or synthetic bone substitutes may be used to provide a scaffold for new bone growth. In complex cases, the surgeon may debride the fracture site by removing scar tissue or sclerotic bone ends to create a fresh surface receptive to healing.