Fracture Healing
The type of fracture healing is determined by movement around the fracture site.
Movement around the fracture site and healing
| Degree of movement | Consequence |
|---|---|
| Absolute stability and compression | Primary healing |
| Relative stability | Secondary healing |
| Excessive movement | Delayed or non-union |
Primary fracture healing
Healing is by direct union, without callus formation. It occurs in absolutely stable fracture sites e.g. A fracture held by a metal plate or impacted fracture in cancellous bone
Types of primary fracture healing
| Primary fracture healing | Description |
|---|---|
| Contact healing | Fracture surfaces are in intimate contact and are held by absolute stability. Internal bridging may occasionally occur without any intermediate stages |
| Gap healing | There are gaps between the fracture surfaces. Gaps are invaded by new capillaries and osteoprogenitor cells and new bone is laid down on the exposed surface |
- Disadvantages of rigid (metal) fixation
- There is no callus formation since the bone depends entirely on the implant for its integrity, hence an increased risk of implant failure.
- The implant diverts stress away from the bone causing it to become osteoporotic. It may not recover fully until the metal is removed.
Secondary fracture healing
This is healing with callus formation. Surgical stabilisation of the fracture site is necessary in secondary bone healing to prevent malunion.
Stages of secondary fracture healing
| Stage | Time | Event |
|---|---|---|
| Hematoma formation | At the time of injury | Bleeding from bone and soft tissue |
| Inflammation | 1-7 days post-fracture | Osteoclasts remove necrotic ends of bone fragments |
| Soft callus formation | 2-3 weeks post-fracture | Fracture can still angulate but is stable in length |
| Hard callus formation | 12 – 16 weeks post-fracture | |
| Remodeling | Months to several years | Woven bone is remodeled to lamellar bone |
- Advantage of secondary fracture healing
- Ensures mechanical strength while the bone ends heal
- Increasing stress allows the callus to grow stronger and stronger (Wolff’s law)
Factors affecting fracture healing
Factors affecting fracture healing
| Classification | Examples |
|---|---|
| Biological factors | Age (fracture in children unite quicker), blood supply, type of fracture, type of bone, smoking, alcohol, and radiation |
| Mechanical factors | Degree of stability at the fracture site |
Union, delayed union, and non-union
If the fracture is not properly stabilised and aligned, it can undergo delayed union, non-union, or malunion
| Outcome | Description | Clinical feature | Radiological |
|---|---|---|---|
| Union | Complete repair. The ensheathing callus is calcified | The fracture site is painless on palpation and weight bearing. Clinical union occurs 4-8 weeks after injury (but can take much longer in the tibia) | Bridging callus, obliterated fracture line which is crossed by bone trabeculae |
| Delayed union | Fracture healing is not taking place at the expected rate and time. But healing is still possible | Fracture site has local swelling and pain on movement or partial weight bearing 4-6 months post-injury | Absence of radiographic progression of healing on 3 different occasions over 4 months |
| Non-union | Bone fails to unite. There is no progress of healing in the last 9 months. | The fracture has not healed in 9 months post-injury, pseudoarthrosis | Hypertrophic or atrophic non-union |
- How are long bones examined clinically for union?
- Feel the fracture site for tenderness – tender fracture has not united
- Feel the fracture site for warmth – warm fracture has not united
- With one hand over the callus, move the distal end of the distal fragment from side to side. If the fracture has united the proximal fragment will move in the opposite direction
Non-union
Non-union is a permanent arrest in the fracture repair process.
- Types of non-union according to cause
- Septic non-union
- Aseptic non-union (due to mechanical instability or impaired vascularity)
- Stiff aseptic non-union
- Mobile aseptic non-union (including pseudoarthrosis)
Types of non-union radiographically
| Non-union | Description |
|---|---|
| Hypertrophic non-union | Exuberant callus trying -but failing- to bridge the gap |
| Atrophic non-union | No callus at all. Bone ends are tapered or rounded with no indication of new bone formation |
Types of hypertrophic non-union
| Hypertrophic non-union | Cause |
|---|---|
| Elephant foot non-union | Excess callus associated with poor stability but good blood supply |
| Horse foot non-union | Moderate stability with adequate blood supply |
| Oligotrophic non-union | Minimal callus and no hypertrophy due to fragment distraction or internal fixation with no apposition |
- What is meant by pseudoarthrosis in aseptic non-union
- The fracture site is freely mobile and painless (like a joint)
Delayed union
In delayed union, there is prolonged time before the fracture unites. There is failure to reach bony union by 6 months post-injury. It can also include fractures that take longer than expected to heal e.g. distal radial fracture
- Biological factors causing delayed union
- Inadequate blood supply: poorly reduced fracture of long bones causing tearing periosteum and interruption of intramedullary supply
- Severe soft tissue damage: Reduces muscle splintage, damages local blood supply, and diminished osteogenic input from mesenchymal stem cells in muscles
- Periosteal stripping: overenthusiastic stripping during internal fixation is an avoidable cause
- Biomechanical factors causing delayed union
- Imperfect splintage: excessive traction creating a gap or excessive movement at fracture site delays callus formation. In-tact fellow bone in arm or leg can hold the fracture apart.
- Over-rigid fixation: union by primary bone healing is slow, but occurs eventually (provided stability is maintained)
- Infection: affects both biology and stability via bone lysis, necrosis, pus formation and implant failure
- Other causes of non-union
- Local infection
- Drug abuse
- Anti-inflammatory or cytotoxic immunosuppressant medication, anticoagulants, and anticonvulsants
- Non-compliant patient
- What 4 questions must be addressed when trying to figure out the cause of non-union?
- Contact: Was there sufficient contact between the fragments?
- Alignment: Was the fracture adequately aligned to reduce shear?
- Stability: Was the fracture held with sufficient stability?
- Stimulation: Was the fracture sufficiently stimulated?
Malunion
Malunion is when fragment joint in an unsatisfactory position. There may be an unacceptable degree of angulation, rotation or shortening.
| Type of malunion | Description |
|---|---|
| Rotational deformity | Can be caused by internal or external rotation of broken bone due to intramedullary nailing. Manage by transverse osteotomy |
| Angular deformity | In the frontal and lateral plane due to valgus or varus deformity. Manage by a wedge osteotomy |
| 2 plane deformity | Deformity in both the frontal and lateral axis |
| Multidirectional deformity | 3 or 4 planes of deformity eg. distal femur with varus, valgus flexion and shortening. Complex and requires multiple osteotomies for correction |
| Length malunion | Occurs when the proximal and distal fragments are overridden, resulting in shortening. |
- Causes of malunion
- Failure to reduce a fracture adequately
- Failure to hold reduction while healing proceeds
- Gradual collapse of comminuted or osteoporotic bone
