Features of primary healing
It is important to understand that the nature of healing depends on the conditions of fragment apposition. During so-called primary healing, the connective tissue callus is capable of metaplasia (transformation) directly into mature bone tissue. In this scenario, the periosteal callus is not clinically pronounced.
Stage one: primary fusion of fragments
The initial stage lasts from 3 to 10 days. Morphologically, this period corresponds to the active formation and differentiation of immature mesenchymal tissue.
Clinical picture:
- The hematoma in the injury zone gradually resolves.
- The severity of local edema and manifestations of traumatic inflammation decreases.
- Pain syndrome noticeably subsides.
- Bone fragments still remain mobile and can easily be displaced with careless handling.
Practical significance: It is the subsiding of acute pain that opens the therapeutic window for performing delayed reduction of bone fragments if it was not performed on an emergency basis or if secondary displacement occurred against the background of resolving edema.
Stage two: soft callus
The duration of this phase ranges from 10 to 50 days.
By this point, the patient experiences practically no pain. The periosteal callus is already palpable, and in superficially located bones, it is visible visually and on radiographs. The fragments lose their previous mobility, but consolidation is not yet rigid.
The key marker of this stage is the springy deformation sign. The bone callus is pliable to bending, and under axial loading on the diaphysis, fragment mobility is clearly revealed.
Tactics: Performing an ideal closed reduction at this stage is practically impossible due to the formed adhesions, but the physician can still partially correct angular deformity or displacement along the length and width.
Stage three: bony union
The phase of osteoid callus mineralization, which lasts from 30 to 90 days (sometimes longer).
Reliable signs of union are detected clinically and radiologically. Pain is completely absent. The springy deformation sign disappears, as does fragment mobility under axial loading.
Despite this, the physiological integrity of the bone is not yet fully restored. Trophic changes and venous outflow disturbances persist in the soft tissues of the segment. External immobilization is removed at this stage, but loading on the limb is introduced in a strictly dosed manner, gradually increasing its force and duration.
Stage four and conditions for successful regeneration
The final phase—morphological and functional restoration of the damaged structure—can take up to 1 year or more.
Premature removal of restrictions and excessive loads before the completion of this stage can lead to fatal consequences:
- Delayed union or complete cessation of regeneration with the formation of a nonunion (pseudarthrosis).
- Re-fracture even with minimal traumatic impact.
Basic conditions for union The main rule of traumatology: the regeneration process needs not so much to be helped as not to be hindered. General conditions are necessary for the formation of a full-fledged callus:
- Adequate restoration of body homeostasis.
- Timely correction of injury complications and compensation for concomitant chronic conditions.
- Age consideration (the rate of physiological regeneration is directly dependent on the patient's age).
Briefly: answers to topical questions
How are long tubular bones (humerus, forearm bones, femur, leg bones) designated in the AO universal classification?
In the AO universal classification, long tubular bones are designated by corresponding numeric codes that indicate the localization of the injury. Each bone or group of bones is assigned a unique number:
- Humerus — 1
- Forearm bones — 2
- Femur — 3
- Bones of the leg (tibia and fibula) — 4
These numbers stand first in the alphanumeric code of the diagnosis, followed by the designation of the bone segment.
What do fracture types A, B, and C mean for diaphyseal segments in the AO classification?
For diaphyseal segments, fracture types indicate the severity of the injury and are classified by the degree of contact between the main bone fragments.
- Type A — simple fracture. Contact between the two main fragments is possible in more than 90%; this is a circular fracture without wedges.
- Type B — wedge fracture. Comminuted or multi-fragmentary fracture in which partial direct contact between the main fragments is possible.
- Type C — complex fracture. Comminuted or multi-fragmentary fracture where direct contact between the main fragments is impossible and occurs only through intermediary fragments.
How do fracture types A, B, and C differ for proximal and distal (articular) segments according to the AO classification?
Fracture types for proximal and distal segments differ by the degree of involvement of the articular surface and the preservation of its connection with the diaphysis.
| Type of fracture | Characteristic | Relationship to the articular surface |
|---|---|---|
| Type A | Extra-articular fracture | The fracture line does not run through the articular surface |
| Type B | Partial articular fracture | The fracture line runs through the articular surface, part of the epiphysis maintains connection with the diaphysis |
| Type C | Complete articular fracture | The articular surface is split and has completely lost connection withplayerPosition |
How are proximal, diaphyseal, and distal bone segments determined using the square rule in the AO classification?
According to the square rule, segments of a long tubular bone are determined based on the width of its epiphyses. The zone of the proximal and distal metaepiphyses (segments 1 and 3, respectively) is bounded by a square whose side is equal to the widest part of the corresponding epiphysis of this bone. The diaphyseal segment (segment 2) is located between these two proximal and distal squares. Exceptions to this rule are the proximal segment of the femur and the malleoli.
How does primary bone healing differ from secondary healing?
Primary and secondary bone healing differ in healing mechanisms and the types of bone callus formed.
| Characteristic | Primary healing | Secondary healing |
|---|---|---|
| Conditions | Maximum fragment immobilization, gap no more than 0.1 mm | Presence of mobility between fragments or persistent diastasis |
| Type of callus | Intermediary callus | Periosteal, endosteal, and paraosteal calluses |
| Features | Connective tissue callus metaplasizes directly into bone; periosteal callus is not pronounced | Direct vascular ingrowth is impossible; healing proceeds through the formation of external, internal, and bridging calluses |
To memorize the stage timeline: "A week for glue (3–10), a month for softness (10–50), a season for bone (30–90), a year for the finale (up to 1 year)."
Class and exam questions
Is it possible to perform reduction during the soft callus stage?
Ideal closed reduction is no longer possible, but partial correction of angular deformations and width/length displacements is permitted.
What is the elastic deformation sign?
This is a specific sign of the second stage of regeneration (10–50 days), where the callus is pliable to bending, and mobility of fragments persists under axial diaphyseal loading.
Why is full weight-bearing prohibited in the third stage even if pain is gone?
Because the process of consolidation and restoration of physiological bone integrity is not yet complete. The risk of delayed repair and pseudoarthrosis persists.
What else to study on this topic
- Mechanisms of connective tissue callus metaplasia into bone
- Differential diagnosis of pseudoarthrosis and delayed consolidation
- Radiological signs of each regeneration stage
- Methods of homeostasis correction to accelerate osteogenesis
- Impact of chronic diseases on callus formation timelines
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