Fracture healing is the healing of a bone fracture. A distinction is made between primary and secondary fracture healing. Disruption of this process can lead to pseudarthrosis.
What is fracture healing?
Fracture healing is the healing of a bone fracture. The healing process after a bone defect is called fracture healing. There are two types of bone defects. Either it is a bone fracture with a complete severing of the bone or a fissure (bone crack) with an incomplete destruction of the bone structure. The healing of a bone defect depends on many factors. First, a distinction is made between primary and secondary fracture healing. In primary healing of the fracture, no visible callus tissue is formed. The bone heals directly. However, this requires that the fracture ends remain in contact with each other, for example through the periosteum (outer periosteum), which is not destroyed during the fracture. Secondary fracture healing occurs when both ends of the bone no longer have tissue contact. While in primary fracture healing the process is usually completed after three weeks, secondary fracture healing can take up to 24 months. In this case, the secondary healing process takes place over five phases. This process is also known as indirect fracture healing. Disruptions in fracture healing can result in deformed bones as part of pseudoarthrosis.
Function and task
Bones form the supporting tissue of all vertebrates and also have the task of protecting the internal organs as well as assisting the organism in locomotion. A bone fracture severely limits the function of the affected bone. Therefore, after destruction of the bone, fracture healing begins immediately. The course of fracture healing depends, as already mentioned, on the extent of the fracture. For example, if both ends of the bone are still connected by the periosteum, the severed bones will still be treated together after the fracture. In this case, fracture healing proceeds without visible formation of a callus (scar tissue of the bone). In primary fracture healing, the precursor cells of osteoblasts (bone cells) accumulate around the capillaries directly from the periosteum or endost (inner periosteum). In the process, they form osteons (bone lamellae around bone canal). The precursor cells of osteoblasts are called osteoprogenietor cells. The osteons restore the functionality of the bone after about three weeks. In secondary fracture healing, the healing process does not proceed directly, but intermediate tissue (callus) is formed, which is hardened and mineralized into bone substance over a longer process. Secondary fracture healing can be divided into five phases. These are the injury phase, the inflammation phase, the granulation phase, the callus hardening phase and the remodeling phase (modeling and remodeling). In the injury phase, the bone structure is destroyed by force, with the formation of a hematoma in the fracture gap. All bone tissues are separated from each other. During the inflammatory phase, the hematoma is infiltrated by macrophages, mast cells, and granulocytes. Within the hematoma, pluripotent stem cells give rise to osteoblasts, chondroblasts and fibroblasts. In the course of these processes, heparin and histamine on the one hand and growth factors and cytokines on the other are secreted into the hematoma. This results in the degradation of the hematoma with simultaneous build-up of bone-forming cells. The third phase of secondary fracture healing is characterized by the replacement of the hematoma by granulation tissue with fibroblasts, capillaries and further collagen. In this process, osteoblasts build new bone, while osteoclasts (multinucleated giant cells from the bone marrow) break down bone substance that has not been perfused. In the fourth phase, callus hardening takes place with formation of the woven bone. This results in mineralization of the callus. This process is completed after about three to four months. Finally, in the fifth phase, the process of remodeling transforms the braided bone into lamellar bone. In this process, the original bone structure is restored. However, it is not one hundred percent clear whether the primary and secondary bone healing processes represent different processes.Thus, the same remodeling processes may only occur to a lesser extent during primary fracture healing.
Diseases and complaints
In connection with fracture healing, there may also be disorders that delay the healing process. Delayed fracture healing is when bony healing of the fracture has not occurred after 20 weeks. Causes may include very large fractures, infections, inadequate bone immobilization, or poor blood supply to the affected area. If the bones have not grown together after several weeks, pseudoarthrosis often results. The term pseudoarthrosis means false joint. In this case, the pain in the area of the fracture does not decrease. Chronic swelling occurs and the ability to bear weight at the affected site is not given. Furthermore, a functional and movement impairment results, which is expressed by a permanent weakness of the affected joint. There are many factors that can promote pseudoarthrosis. In addition to underlying conditions such as infections, liver disease, malignancies, vascular disease, immunodeficiencies, obesity, or diabetes mellitus, external factors such as inadequate joint immobilization can also lead to delayed healing. The effects of delayed fracture healing range from delayed complete healing to complete failure to heal. In this case, the therapy is based on the underlying cause. Any underlying disease present must be treated. In addition to surgical treatment methods, ultrasound treatments, shock wave therapies, or even gene therapies are used, among others.
