Definition
Transient osteoporosis defines a disease of the bones with increased water retention, which, as the name suggests (transient = temporary), occurs for a limited period of time and is a special form of classic osteoporosis. Typical for transient osteoporosis is the affection of the hip bones. Other bony joint involvement, for example of the ankle and knee, occurs only in rare cases.
Transient osteoporosis is also listed under the synonym “Bone Marrow Edema Syndrome” (BMES). In the literature, transient osteoporosis is described on the one hand as a separate entity, but on the other hand as a still reversible precursor of osteonecrosis. Men are usually three times more likely to be affected by the bone disease than women. However, both sexes develop transient osteoporosis simultaneously in the third and fifth decade of life.
Cause
The exact causes for the occurrence of transient osteoporosis are not yet known, so that one often speaks of an idiopathic genesis. However, some possible explanations for the development of the disease pattern are available. For example, severe overloading of the hip joints can be the reason for transient osteoporosis, as well as traumatic events such as falls on the hip.
The aspect of reduced and disturbed blood circulation in the femoral head, i.e. a so-called microcirculation disorder, also causes transient osteoporosis in some cases. In contrast to femoral head necrosis, transient osteoporosis is characterized by a short-lived and not a final reduced blood supply of the femoral head, which is the basis for a better prognosis. However, transient osteoporosis can ultimately also occur secondarily as part of other underlying diseases such as Sudeck’s disease, rheumatism or other degenerative diseases. Pregnancy can also increase the probability of transient osteoporosis.
Diagnosis
The diagnosis of transient osteoporosis can already be made clinically. In a physical examination, an objective assessment of the mobility in the hip is carried out according to the neutral-zero method. Roughly speaking, the range of motion of abduction (abduction), flexion (flexion) and also internal rotation are reduced.
The subjective limitation of movement is usually felt much more extreme by those affected due to the severe pain. One might think that X-rays are the most suitable diagnostic tool for bone disease, but this is not the case. Only after a loss of 40% of bone density can meaningful findings be made on X-rays.
Instead, magnetic resonance imaging (MRI) plays a decisive role in diagnosing transient osteoporosis. Depending on the weighting, MRI can be used to describe the typical fluid accumulations, i.e. bone edema. In the so-called T1 sequence, the signal intensity is reduced, but in the T2 sequence it is increased.
A sharp demarcation of the signals and the typical localization in the femoral head and parts of the femur are characteristic for the bone marrow edema syndrome or for transient osteoporosis. In order to exclude an important differential diagnosis of femoral head necrosis, both an MRI scan and a skeletal scintigraphy can be performed. In comparison to transient osteoporosis, femoral head necrosis additionally forms a “necrosis zone”, i.e. an area where bone loss occurs.
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