The substantia spongiosa is the inner, bony network of bone substance. It primarily determines the load-bearing capacity of bones. In osteoporosis, the cancellous bone is increasingly broken down and the bone loses its load-bearing capacity.
What is cancellous bone substance?
Human bone tissue is also known as substantia spongiosa in its macroscopic structural form. This spongy substance consists of fine trabeculae. As such, the macroscopic bone platelets are known. The macroscopic structural form of the bone tissue is also abbreviated as cancellous bone. In the case of flat bones, on the other hand, the term diploë is sometimes used instead of cancellous bone. To be distinguished from these macroscopic bone forms is the so-called braided bone, which develops at the beginning of osteogenesis. Braided bone is made of cartilage or is formed directly from stem cells of connective tissue. Like cancellous bone, woven bone has fine bone bars. However, the bars of cancellous bone are not directly intertwined and, unlike those of woven bone, do not form a structurally organized whole. In addition to the substantia spongiosa in the interior, the bone is mainly formed by the substantia compacta in the exterior, which, unlike the adaptable cancellous bone, is rather static and corresponds to the stable portion of the bone.
Anatomy and structure
The cancellous bone is located within the bones. Outwardly, the substance is embraced by the cortical bone. Within the cavities, the bone marrow lies between the individual cancellous bone beams. Overall, the cancellous bone corresponds to an enormously tightly interconnected scaffold. The bars of cancellous bone are interconnected and form a lattice-like structure. Many of the little beams are located within the cancellous bone, especially along the load lines of individual bones. Stress trajectories are often referred to in this context. The architecture of the cancellous bone depends strongly on the pressure conditions in the bone. For example, if a certain section of the bone is subjected to excessive pressure, the cancellous bone in this area adapts to the pressure requirements. The same applies in the case of bending or torsional forces, such as those acting on the femoral head. Because of its lightweight construction principle, cancellous bone saves bone substance and thus ensures the minimum weight of the bones.
Function and tasks
During osteogenesis, first and foremost, the woven bone is formed. In chondral osteogenesis, osteoblasts form the woven bone from cartilage. This ossification is the indirect one. In direct ossification, the woven bone is formed directly from the stem cells of the connective tissue by the bone-building osteoblasts. For this reason, the process is referred to as direct or desmal osteogenesis. On the surface of each woven bone there is a densification of the substance. In addition, in the course of osteogenesis, further bone substance is deposited from the outside. This substance corresponds to the cortical bone. Internally, the bone substance remodels into cancellous bone. The bone-degrading osteoclasts are involved in this remodeling process. They break down parts of the bone matrix, while osteoblasts form new bone material at the same time. The work of the osteoblasts gives rise to the characteristic bone bars of cancellous bone in the interior. Once the work of osteogenesis is complete, the resulting lattice structure dynamically adapts to the newly developing loads on the individual bones for life. Thus, the function of cancellous bone corresponds primarily to bone stabilization and bone adaptation to changing loads. In particular, cancellous bone is thus partly responsible for the load-bearing capacity of a bone.
Diseases
One of the most important diseases of the substantia cancellosa is osteoporosis. Osteoporosis refers to a pathological loss of bone material that far exceeds the physiologically normal loss of bone during the natural aging process. The normal aging process usually does not break down more than half of the existing bone mass and begins at the age of 30. Vertebral fractures occur in the normal aging processes only when a corresponding accident occurs. In patients with osteoporosis, vertebral fractures occur even without external impact. Unlike age atrophy, osteoporosis breaks down all the aneils of the bone. Especially the spongy substance of the bones is affected by osteoporosis. Thus, the load-bearing capacity of the individual bones is considerably reduced.For a long time, the onset of osteoporosis does not cause any symptoms. Bone resorption progresses slowly and at a certain point causes atypical fractures. Preferably, the fractures occur in the vertebral bodies in the lower back. They are either preceded by slight impacts or occur without any identifiable cause. A vertebral fracture causes patients to experience pain, often as diffuse, vaguely localized pain. The vertebral fractures deform the spine and cause a so-called widow’s hump to develop. Sometimes the height of the body is also reduced by up to a few centimeters. Patients are more susceptible to any fractures than healthy people of the same age, and therefore also frequently suffer from fractures of the neck of the femur, for example, after a trivial household accident. Depending on its causes, osteoporosis is divided into two types. Primary osteoporosis occurs without the influence of chronic diseases. Besides old age, genetic components are discussed as a cause of its occurrence. The consumption of alcohol, coffee and cigarettes can negatively influence and accelerate the course of the disease. Lack of exercise also plays a role in primary osteoporosis. The same applies to a lack of calcium or vitamin D intake. Secondary osteoporosis occurs in the context of chronic diseases or is triggered by certain medications. Hormonal disorders, sugar disorders, and intestinal diseases are often associated with the onset.
