Various local and systemic factors affect the duration and effectiveness of the healing process. Abnormalities in any of these areas may lead to abnormally slow healing (delayed union) or failure to heal (non union). These include:

Systemic factors

1. Age: Children heal more quickly than adults; healing potential is decreased with advancing age
2. Nutrition: Poor nutrition and/or vitamin deficiency adversely affects healing
3. General health: Chronic illness depresses healing response (diabetes, anemia, systemic infection)
4. Generalized atherosclerosis: Decreases healing
5. Hormonal factors: Growth hormone enhances healing; corticosteroids depress healing
6. Drugs: Non steroidal anti-inflammatory drugs (e.g. ibuprofen) depress healing
7. Smoking: Decreases healing

Local factors

1. Degree of local trauma/bone loss: A comminuted fracture with more soft tissue injury is slower to heal
2. Area of bone affected: Metaphyseal fractures heal faster than diaphyseal
3. Abnormal bone (infection, tumour, irradiated): Slower to heal
4. Degree of immobilization of fracture: Motion at site delays healing
5. Disruption of vascular supply: Delays healing