When a bone breaks, the body initiates a repair process to restore its integrity. The initial stage is inflammation, where a blood clot forms at the fracture site, providing a scaffold and releasing chemical mediators that recruit healing cells. This is followed by the reparative phase, where specialized cells begin to bridge the gap by first forming a soft, fibrocartilaginous callus. Over several weeks to months, this soft tissue is gradually replaced by woven, immature bone, creating a hard callus that provides initial mechanical stability. If this biological cascade is interrupted, the bone may fail to heal correctly, leading to chronic complications that severely impact function and quality of life.
Understanding Nonunion and Malunion
When the normal timeline for fracture healing is disrupted, the outcome is classified into distinct categories. A delayed union occurs when the fracture is taking longer than average to heal, but the process is still visibly progressing on imaging studies. This situation often resolves with continued immobilization and time. A nonunion is defined by the complete cessation of the healing process, meaning the fracture will not fuse without therapeutic intervention. A malunion occurs when the bone successfully heals, but it does so in an incorrect anatomical position. This misalignment can involve angular, rotational, or length deformities that change the mechanics of the limb.
Key Factors That Disrupt Healing
The body’s ability to repair a fracture depends on a combination of local and systemic factors.
Local Factors
Inadequate blood supply, or ischemia, is a major local factor because blood delivers the necessary oxygen, nutrients, and growth factors to the fracture site. Another requirement for healing is a stable environment, and excessive movement at the fracture site prevents the soft callus from maturing into hard bone. This mechanical instability can be due to insufficient external immobilization or failure of internal surgical hardware. Infection, specifically a bone infection known as osteomyelitis, introduces bacteria that actively impede the formation of new bone tissue.
Systemic Factors
Beyond the local injury, systemic patient factors can significantly hinder the biological process. Smoking and nicotine use are strongly associated with impaired healing, as they constrict blood vessels and reduce blood flow to the injury. Chronic diseases like diabetes and poor nutritional status also compromise the body’s ability to produce the cells and chemical signals required for effective bone repair.
Physical Symptoms and Functional Limitations
A failed fracture repair results in chronic symptoms. The most common and enduring symptom is persistent pain at the site of the break, which is frequently aggravated by movement or when attempting to bear weight on the affected limb. In cases of nonunion, the lack of bony fusion can cause instability or abnormal motion at the fracture gap, sometimes creating a false joint, or pseudoarthrosis. Malunion, where the bone has healed crookedly, results in a visible deformity or misalignment of the limb. These structural problems inevitably lead to functional limitations, making activities like walking, gripping, or lifting difficult. Over time, the abnormal stresses caused by a malunion can also lead to premature arthritis in nearby joints.
Interventions for Failed Fracture Repair
Treating a failed fracture is complex, aiming to restore both mechanical stability and the biological capacity for healing.
Malunion Treatment
For a malunion, the primary treatment is usually a surgical procedure called an osteotomy, which involves deliberately re-breaking the healed bone and realigning it to the correct anatomical position. This corrected alignment is then maintained using rigid internal fixation, typically involving metal plates, screws, or rods, to hold the bone stable while it heals properly.
Nonunion Treatment and Grafting
Nonunions, which represent a biological failure, require both stability and a biological stimulus to restart bone growth. Surgical intervention involves debridement, or the removal of fibrous tissue that is preventing the bone ends from connecting. This is followed by the application of bone grafting, which is the placement of new bone tissue into the nonunion site to bridge the gap and encourage fusion.
Autograft, bone harvested from the patient’s own body, is considered the gold standard because it possesses three properties: it provides a scaffold (osteoconduction), growth-stimulating proteins (osteoinduction), and living bone-forming cells (osteogenesis). The main drawback of autograft is the additional surgical site, which can result in pain and a limited amount of available tissue. Allograft, bone tissue from a deceased donor, is more readily available and avoids donor-site complications, but it is primarily osteoconductive, lacking the living cells and potent growth factors of autograft.
Non-Invasive Stimulation
In addition to surgery, non-invasive treatments like electrical or ultrasonic bone stimulation may be used, often as an adjunct to surgery or as a first-line treatment for less severe cases. Electrical stimulators generate low-level electrical fields that promote bone cell proliferation and calcification. Low-intensity pulsed ultrasound devices apply a mechanical pressure wave to the bone, which stimulates cells and increases the expression of growth factors, accelerating the formation of soft callus.