Fracture Nonunion

Fracture nonunion is a fracture that has failed to unite and shows no progression toward union over successive assessments; delayed union is the softer label for healing that is late but still advancing. Definitions are conventional — often six to nine months without union — because healing is a continuum, and the clinically useful question is whether the picture is changing, not whether a calendar threshold has passed.

Three failures dominate. Motion across the fracture repeatedly tears the fragile bridging tissue, so Bone Remodeling restarts instead of maturing. Gapping leaves a distance the callus cannot span, whether from distraction, interposed soft tissue, or bone loss. Vascular insult starves the site, the mechanism set out in Watershed Blood Supply.

The standard division is diagnostic rather than cosmetic, and behaves like Root Cause Analysis: a hypertrophic nonunion shows abundant callus that never bridges — the biology is willing and the mechanics are wrong, so better Fracture Fixation usually suffices. An atrophic nonunion shows sparse callus and sclerotic ends — the biology is failing, so revision typically adds bone graft, autograft from iliac crest being the reference against which substitutes are measured.

Several risks are modifiable. Nicotine causes vasoconstriction and independently impairs union, which is a pharmacological effect separate from the Physical Dependence that makes cessation difficult. Poor glycaemic control, malnutrition, and some anti-inflammatory regimens also feature.

Detection is imperfect: plain radiographs are moderately sensitive, and computed tomography resolves ambiguous cases, so the trade-offs of Sensitivity and Specificity apply directly to deciding whether a quiet fracture is healing or stalled.