Avascular necrosis

Bone necrosis or osteonecrosis ( ON abbreviation, English: osteonecrosis; colloquially bone infarction) describes a tissue death ( infarction) of the bone or a bone section with death (necrosis ) of bone or bone affected section, which is subsequently washed off or rebuilt. The result is thereby a weakened location in the bone structure, the extent of the infarct and the subsequent resulting defect in the bone may be different.

In all forms is an insufficient blood supply to the bone defect with underlying supply of oxygen, nutrients and minerals. Therefore, the term avascular necrosis, avascular osteonecrosis English (AVN ) is in use.

If you want to exclude only infection-related bone necrosis, one speaks of an aseptic bone necrosis ( aseptic osteonecrosis alternative name; Abbreviation: AON, AKN; aseptic osteonecrosis or aseptic english bone necrosis ).

• 4.1 diagnostics
• 4.2 Differential Diagnosis

Clinic

The tissue defects of the bone can sometimes have consequences or cause serious, irreversible damage to joints and bones, the course is variable depending on the location, the extent, the possible presence of risk factors, the age and the final trigger, both spontaneous healings as well as complete joint destruction are known. In principle, all bones of the body can be affected. Are both single-sided and double-sided lesions known. Bone necrosis can occur at any age.

Molding

Aseptic bone necrosis can be divided into different forms the basis of several factors. The allocations are made according to

Cause

According to the probable underlying cause of osteonecrosis of the following forms can be distinguished from osteonecrosis:

• Post-traumatic osteonecrosis, by an injury.
• Septic bone necrosis, under or as a result of infection.
• Aseptic bone necrosis, not triggered by an infection.

Risk Factors

Certain medical conditions or external factors favor the occurrence of aseptic bone necrosis. These include:

Classification on the affected bone or joint

Severity ( stages )

The staging of aseptic bone necrosis can be classified according to the Association for Research of Circulation Osseous ( ARCO ). This combines a Japanese classification, which is based on the localization of necrosis, with a classification of Philadelphia (USA), which is based primarily on the size of the necrosis.

The ARCO classification is the most widely studied for aseptic bone necrosis of the femoral head ( femoral head ) and mainly refers to lesions of the pineal gland, so near the joint bones chunks that can lead in the area of ​​necrosis at a joint degeneration through the collapse of the cartilage. Osteonecrosis of the diaphysis and the metaphysis can at best be classified analogously to the ARCO stages.

In the early stages there are no pathological changes can be seen in conventional X-ray. In rare cases, a subtle loosening of the bone fine structure ( trabecular ) can be seen in the affected area: however, the extent of this loosening is usually so low that it can not be reliably detected. In magnetic resonance imaging (MRI ) is an image analogous to bone marrow edema ( KMÖ, transient osteoporosis, bone marrow edema, BME) is at this stage to be recognized. By using the short tau inversion recovery ( STIR ) imaging sequence a signal hyperintensity ( bright lighting in grayscale MRI image) is observed (see Figure 1a and 2 bright edges ). A reliable distinction between the principle reversible image of a KMÖ / BME and the ARCO stage I of aseptic bone necrosis is not possible by means of the Kernspintomogramms.

Reversible early stage ( MRT-positiv/reaktive edge zone )

Irreversible early stage (X-ray positive)

Transitional stage ( subchondral fractures)

Late stage ( Kalottenimpression )

Late stage (secondary osteoarthritis )

Late stage ( joint destruction )

Symptoms

None of the symptoms specific to the disease, as well as many other conditions may be responsible for the symptoms. Pain over the affected bone necrosis through the bone or joint section are frequently encountered. The pain can suddenly occur. However, he also develops gradually -increasing in its intensity. A broadcast in adjacent unaffected skeletal structures is possible. Typically, the pain already occurs at rest and during exercise strengthens the bone segment or joint affected. However, it may be present, which occur in disease progression even at rest and pain only on loading of the affected bone or joint section. The pain can often only weeks, partly also occur months after the infarction in the bone.

Restricted movement of the affected joint or bone are less frequent than pain. They also occur in the course of the disease typically later than the pain and are mostly already signs of advanced deterioration. But this is not necessarily so; Movement restrictions can also occur in parallel with pain. In children - particularly in young children - the order of the symptoms sometimes be reversed. The affected infant falls, for example, the first time by a limp or lack of movement of the leg or the affected arm.

Diagnosis

Diagnostics

The diagnosis of aseptic bone necrosis involves the physical examination of the likely affected joint section with functional testing of the joints and bones as well as imaging techniques. As a rule, go pathological bone changes stress or trauma of different kind ahead. This is when the bone necrosis differently, the symptoms develop insidiously. Conventional imaging techniques such as X-rays or ultrasound arise only clues to the diagnosis when it came to the first bone remodeling or bone destruction. In the use of MRI contrast agents with a diagnosis can also be provided, if it is merely come to a typical bone remodeling activity.

Differential Diagnosis

From a bone necrosis other diseases must be distinguished:

Therapy

The therapy is dependent on the stage and involves the mechanical relief (eg crutches ), Hüftkopfentlastungsbohrung, osteotomies and (hip ) Implants. In the initial stage the hyperbaric oxygen therapy can be administered concomitantly or alone. Especially the painful bone marrow edema is thereby positively influence .. The treatment of osteonecrosis are also governed by the aforementioned prognostic factors: the larger and closer joint bone necrosis are, the more likely a surgical treatment is required. If, in the context of joint near bone necrosis in damage to or destruction of the articular surfaces, surgery is usually not be avoided. Depending on the extent of osteonecrosis are drillings ( Pridie drilling), bone grafting (with and without cartilage ) and carried out at greater or less extent also with artificial joint replacement ( endoprosthesis ). Conservative treatment consists of weight support and protection but are also spontaneous healings described.