Manifestation sites of transient osteoporosis

The main manifestation site of transient osteoporosis is the hip joints. The findings may be bilateral or unilateral. The latter is typical for transient osteoporosis in pregnancy.

The X-ray of the hip shows at most a slight decalcification in the area of the head of the femur with a bone cortex (corticalis) that is difficult to delimit. Since the X-ray image only shows changes with a loss of bone density of more than 40%, a reliable diagnosis cannot be made on the basis of the images. MRI images of the hip are much more specific for the diagnosis of transient osteoporosis.

Here the characteristic bone marrow edema can be detected. The edema is localized in the head of the femur, but can also travel as far as the femoral neck and between the two trochanteric mounds (greater and lesser trochanter). In the T1 weighted sequence, the signal intensity of the fluid accumulation, i.e. the edema, is greatly reduced.

In the T2 sequence, the signal intensity is typically increased.A special weighting (STIR) suppresses the fat signal so that the bone marrow edema can be imaged even better. In addition, in the area of the joint surface below the cartilaginous surface, i.e. subchondral, isolated changes can be seen, which are often evaluated as small fractures in the context of transient osteoporosis. Close monitoring is important to assess the reduction in bone marrow edema, which should be achieved within 10 months at the latest.

Especially the femoral head as the site of manifestation makes accurate diagnostics necessary to exclude possible differential diagnoses. These include femoral head necrosis, rheumatic diseases and koxitis, an idiopathic inflammation of the hip joint in childhood. Above all, femoral head necrosis must be excluded, since transient osteoporosis shows changes that can be considered a preliminary stage of necrosis.

In addition to the hip, transient osteoporosis can also manifest itself in the distal region of the lower extremity, i.e. the foot and ankle joint. In the rare cases in which such a localization of transient osteoporosis occurs, men are more frequently affected than women. The bone marrow edema typically develops in the ankle joint.

Here it manifests itself mainly in the lower ankle joint, more precisely in the talus (= ankle bone). As with the other manifestations, MRI is the most specific diagnostic tool for imaging bone marrow edema. The control and also the diagnosis are important because although there is actually a spontaneous healing of the transient osteoporosis at this point, the development of arthrosis in the ankle joint must be prevented by timely therapeutic intervention.