Osteolysis

Osteolysis ( gr ὀστέον osteon, bone ' and λύσις lysis, dissolution ') generally refers to a bone loss. Thus, on the one hand bone loss are referred to at the cellular level, as it occurs in the context of the physiological bone remodeling resistant in bone metabolism, on the other hand, one of excessive bone resorption in the context of a pathological bone remodeling are known. On the other designated especially in radiology and oncology circumscribed osteolysis a local bone defect with complete loss of bone within the defect.

Osteolysis in bone remodeling

In general, the osteoclasts, the cells can degrade the bone, which is why this type of osteolysis can be referred to as osteoclastic reaction. They are controlled via hormones on bone metabolism and are the physiological bone remodeling in activity in equilibrium with the bone-building osteoblasts.

In disorders of physiological balance two forms of osteopathy can be distinguished in which there is a reduced bone density:

• Osteoporosis and osteopenia with the precursor equally strong reduction of the organic substances and mineral content. These forms may occur systemically and affect all bones or only regionally occur.
• Osteomalacia with reduced mineral content with unchanged or less strongly reduced content of organic components by disturbance of phosphate metabolism or a deficiency of active vitamin D.

Umschriebe osteolysis

The circumscribed osteolysis occurs exclusively by osteoclasts, but they are locally heavily activated without concomitant osteoblastic activity. This results in bone sites without bone substance that can act as punched holes ( typical image of the plasmacytoma ).

The causes a circumscribed osteolysis are versatile and can sometimes can be inferred from the location of the osteolysis, underlying diseases, and age of the patient:

• For a mechanical loosening of implants, osteolysis can make as radiolucent lines or by foreign bodies (abrasion ). This can occur at endoprostheses, but also to osteosynthesis and often requires the removal of the internal fixation or with a prosthetic loosening a change of the endoprosthesis.
• Osteolytic processes in peri-implant loosening or lead to the loss of a dental implant, which is triggered by a mixed anaerobic microflora, are in the gram- negative bacteria in the foreground.
• Another form of osteolysis is the degradation of the alveolar processes of the jaw. Bone resorption of the jaw bone can be done by tooth loss, periodontal disease, or by the bearing pressure of dentures. In the latter case the Alveolarkammabbau is in the first year after tooth loss about 0.5 mm in the maxilla and 1.2 mm in the mandible. In subsequent years, the reduction is 0.1 mm in the maxilla and 0.4 mm in the mandible. The extent of degradation is distinguished in the Resorptionsklassen after Cowood and Howell.
• Also benign and malignant bone tumors can be represented as osteolysis that stand out in some cases only by a pathological fracture of the weakened by osteolysis, bone. They range from a simple bone cyst to osteosarcoma. Just enter osteolytic metastases by malignant tumors of other organs to, or as a manifestation of hematological tumors, ie with leukemia or lymphoma diseases such as multiple myeloma. There are radiological signs such as a Sklerosierungsrand to osteolysis suggestive of a benign cause. This is recognized in the Lodwick classification of the radiographic findings of osteolysis and bone tumors.
• In the context of metabolic disorders can also rarely occur osteolysis, an example are the " brown tumors " with an overactive parathyroid gland ( hyperparathyroidism ). In primary hyperparathyroidism osteolytic changes in the mouth, jaw and facial area, in contrast to the rest of the skeletal system rarely observed, but may represent the first clinical evidence of endocrine disease. Also in the context of amyloidosis osteolysis can be observed.
• Also near the joint bone cysts represent osteolysis and occur in advanced arthrosis than " rubble cysts " and inflammatory joint diseases such as rheumatoid arthritis.
• Infections as a Knochenmarkvereiterung ( osteomyelitis) also lead to osteolysis, sometimes at very low virulent germs, as in Brodie 's abscess. Very rare causes can also tuberculosis or a fungal infection be

Osteolysis of the entire bone

Very rarely the complete resolution of a single bone is observed. This referred to as Gorham - Stout syndrome or phantom bone disease is idiopathic osteolysis, so the cause is unknown.