Nonunion

Nonunion is the failure of a fractured bone to heal within the expected time, resulting in a persistent fracture line, instability, pain, and impaired function. It is distinguished from delayed union, where healing is slower than usual but may eventually occur. In practice, nonunion is often considered when there is no radiographic progression toward healing over several months.

Nonunion can be classified by biology and biology plus instability. Hypertrophic nonunion shows abundant Callus formation, indicating good biological potential but mechanical instability. Atrophic nonunion has little or no callus, reflecting poor biology. Oligotrophic nonunion lies between these, with reduced biological activity. Infected, or septic, nonunion involves ongoing infection that impairs healing and complicates management.

Causes are multifactorial. Mechanical factors such as inadequate stabilization, malalignment, motion at the fracture site, or large bone gaps contribute. Biological factors include poor blood supply, infection, large soft-tissue injury, and systemic conditions (smoking, diabetes, malnutrition, steroid use). Patient factors, such as age and comorbidities, and prior surgeries can also influence healing.

Diagnosis relies on clinical and radiographic assessment. Clinically, persistent pain, tenderness, and functional limitation are common. Radiographs and computed tomography are used to document lack of healing progression over time; MRI can evaluate biology and blood supply. Infection should be ruled out with appropriate laboratory testing when indicated.

Treatment focuses on restoring stability and stimulating biology. Options include surgical revision with stable fixation, bone grafting (autograft is common), allografts or bone substitutes, and biologics or growth factors as appropriate. Infected nonunion requires infection control, debridement, and staged reconstruction. Smoking cessation and optimization of nutrition and comorbidities improve outcomes.