Although, in most cases, fracture healing proceeds uneventfully, there are certain situations when the outcome is not normal. Several patterns of abnormal healing are described in this section.
Fracture non-union
Healing is described as 'delayed' if union is not seen within the expected time after initial treatment. At the six month mark, an unhealed fracture is termed a "non- union". There are two types of non-union: atrophic, where little callus has formed and hypertrophic, where there is obvious callus but continued instability. Atrophic non-unions respond to bone grafting. This involves transplantation of the patient's own healthy bone, often from the iliac crest, to the non-union site. An alternative is the implantation of donor bone or an artificial bone substitute. Hypertrophic non-unions often result from increased motion at the fractures site. These improve with by surgical stabilization of the non-union. If a non-union persists and remains mobile, the fibrous tissue at the fracture site may undergo transformation into synovial cells forming a "false joint" or pseudarthrosis.
Stress fractures
Stress fractures are the result of an imbalance of bone formation and bone healing, usually in young healthy individuals involved in repetitive physical activity. Common sites include the tibia, metatarsal and femoral neck. The diagnosis is often challenging as plain radiographs may be negative or may reveal calcification only in the late stages of healing. Bone scans and/or Magnetic Resonance Imaging scans are frequently diagnostic. Treatment with immobilization is usually successful.
The red arrow points to a stress fracture in this patient's calcaneus
Reactive bone formation
Reactive bone formation isn't true "healing" but instead a response of the bone to an underlying abnormality. Review this link from the University of Washington School of Medicine to learn more about the different patterns of reactive bone formation. "Sunburst" or "onion skin" patterns are growing rapidly and so are classified as "aggressive", while more solid patterns of periosteal reaction (such as are seen in children's fractures) indicate slower growths that are likely benign.
Click on headings below (on left side) to see examples of each term.
Benign periosteal reaction after fracture
Sunburst pattern of periosteal reaction
Benign periosteal reaction after fracture
This is an example of benign periosteal reaction seen as a normal part of fracture healing in a child four weeks after a supracondylar humeral fracture
Sunburst pattern of periosteal reaction
This child has an agressive humeral osteosarcoma. The sunburst reactive bone formation shown in this image is growing so rapidly that there is not enough time for a layer of bone to form over the periosteum. This is indicative of an aggressive growth and suggests, albeit not conclusively, the presence of a malignancy. In this case, the sunburst pattern is caused by an osteosarcoma.
