Musculoskeletal Imaging

Nonunion, fracture

failure of fracture fragments to unite or heal. Nonunion is distinguished from healing of a fracture in an improper position (malunion, or healing that is significantly delayed beyond the normal time of union (delayed union). Nonunion is generally deemed to have occurred if the fracture site has failed to heal completely by approximately 6 9 months after an injury. Some of the causes of nonunion are listed in Table 1.

Nonunion, of fracture, Table 1. Some causes of fracture nonunion.

Insufficient or improper immobilization

Infection

Presence of soft tissue interposed between the edges of the fractured bone

Inadequate blood supply

Poor nutritional status

Metabolic bone disease

Fractures that are open, comminuted, segmental, or pathologic

Nonunion occurs most commonly after a scaphoid, tibial or femoral fracture, although it may also accompany fractures of the humerus, radius, ulna and clavicle. Nonunion of a type 2 odontoid fracture (i.e. a fracture occurring at the base of the bone) leads to an os odontoideum. Typically a pseudarthrosis (consisting of a synovium-lined cavity and presence of synovial fluid related to persistent motion at the nonunion site) or a fibrous union develops with nonunion.

The proximal pole of the scaphoid bone is the site at which nonunion occurs most frequently. On radiographs, abnormalities characteristic of scaphoid nonunion include bone sclerosis, cyst formation, widening of the scapholunate space, bone resorption, and osteoarthritis.

DR