There are two types of bone healing: primary and secondary. Which type occurs depends largely on the stability of the fracture and the amount of movement between the fragments. The fixation strategy that you choose determines whether relative stability is created, leading to secondary bone healing, or absolute stability, leading to primary bone healing.

Complications of fracture management in open fractures for an overview of which fixation strategies provide relative stability and which provide absolute stability.

Primary or secondary healing?

At first glance, it may seem that primary bone healing is always the preferred outcome. However, this is not necessarily the case. The goal in fracture treatment is not to force a specific type of healing, but to choose a fixation strategy that fits the fracture pattern and the clinical situation. In fact, most fractures treated worldwide heal through relative stability with secondary bone healing.

How to make an open fracture management plan, to see what fixation strategy fits best in your situation.

Primary bone healing

Primary bone healing refers to fracture healing without visible callus formation. It occurs when internal fixation with plates and/or screws compresses the fracture fragments against each other, creating absolute stability. This brings the fragments into direct contact and minimizes motion at the fracture site. Healing then proceeds through direct remodeling of the bone across the fracture line:

1 Osteoclasts
Bone remodeling starts at the microscopic level. Osteoclasts form cutting cones that resorb small tunnels through the bone and across the fracture line.

2 Osteoblasts
Osteoblasts follow these tunnels and deposit new lamellar bone. In this way the normal osteons (Haversian systems), containing blood vessels and nerves, reconnect across the fracture.

3 Remodeling
Over time the internal structure of the bone is restored, and the fracture heals without visible callus formation.

Secondary bone healing

Secondary bone healing refers to fracture healing in which the fracture gap is bridged by visible callus formation. It occurs when fracture fragments are adequately aligned but some motion remains at the fracture site. This is typical after non-operative treatment (e.g. plaster of Paris) or fixation strategies that allow micromotion, such as intramedullary nailing or external fixation, creating relative stability.

Secondary bone healing occurs through a sequence of processes that can be divided into four stages:

During open reduction of a fracture, preserve the fracture hematoma as it plays a key role in bone healing.

Crucial factors for bone healing

"Orthopaedics is not carpentry, it's gardening."

A gardener cannot make a plant grow without the right soil, water, and environment. In the same way, successful bone healing depends on more than reduction and fixation alone. It requires the right mechanical AND biological conditions for the bone to heal. In addition to treatment, these conditions are influenced by factors related to the injury, the patient, and the environment.

When encountering a delayed union or non-union: Always look for the underlying cause. Ask yourself whether the problem is related to fixation strategy, the injury, the patient, or the environment.

Injury-related factors

Fracture pattern and location

• Diaphyseal fractures have a higher risk of delayed union or non-union than metaphyseal fractures.
• Comminuted fractures are also more prone to healing problems than simple two-part fractures.

Soft-tissue condition

• Extensive soft-tissue damage compromises the biological environment required for bone healing.

Neurovascular status

• Impaired blood supply reduces delivery of oxygen, nutrients, and cytokines to the fracture site.

Presence of infection

• Infection (e.g. osteomyelitis) disrupts the healing process and is a major cause of delayed union and non-union.

Patient-related factors

Age ³

• Healing potential decreases with age.
• Older patients are more likely to have comorbidities that negatively affect bone healing.
• Postmenopausal women, for example, are more likely to develop osteoporosis, which alters bone quality and healing capacity.

Nutritional status ³

• Adequate nutrition is essential for bone healing. Malnutrition, vitamin deficiencies (particularly vitamin D), and chronic conditions associated with anemia can impair the healing process.
• Excessive alcohol use may further reduce nutritional intake.

Smoking ³

• Smoking negatively affects bone healing. Nicotine impairs collagen production, inhibits alkaline phosphatase activity, and reduces cellular proliferation during fracture repair.

Muscle mass ³

• Healthy surrounding soft tissue contributes to fracture stability and protects the developing callus.

Comorbidities ³

Several medical conditions influence bone healing, including:

• Osteoporosis
• Diabetes mellitus
• HIV/AIDS
• Tuberculosis
• Anemia
• Peripheral vascular disease.
• Chronic stress
• Immunosuppressive medications such as corticosteroids can impair the inflammatory phase of healing and increase infection risk.

Sociocultural factors ³

• Patients may prefer traditional or non-medical treatment options, which can influence the timing and type of care.

Financial situation ³

• Limited financial resources or out-of-pocket healthcare costs may affect access to treatment and follow-up care.

Medical environment-related factors

Resources ¹

• The availability of surgical equipment, implants, antibiotics, and microbiological diagnostics influences treatment options and healing outcomes. Limited resources may restrict fixation strategies and postoperative care.

Hygiene ¹

• Standards of hygiene and infection control directly affect the risk of infection and therefore the success of fracture healing.

Experience of the medical team ¹

• The experience of the team influences healing and outcome. Longer procedures may increase tissue exposure and the risk of contamination.