Transient Osteoporosis of the Hip
Bone marrow oedema syndrome is also referred to as "transient osteoporosis of the hip."
Terminology
The more appropriate term would be bone marrow oedema of the proximal femur as the more distal parts of the femur are not affected.
Aetiology
The aetiology is unknown. Risk factors are pregnancy, excess alcohol consumption, steroid use, and hypothyroidism.
Epidemiology
Originally described in pregnancy, but is most commonly seen in middle aged men with hip pain.
Investigations
Osteopaenia may be seen in hip radiographs but is often normal. Osteopenia may only show up 4-8 weeks after the onset of hip pain.
On MRI there may be increased T2 signal in the bone marrow of the femoral head and neck. There can be extension into the subtrochanteric region and there is also often a joint effusion. The main differential is osteonecrosis, but in osteonecrosis the signal change is focal rather than diffuse..
Bone scan shows diffuse and homogeneously increased uptake involving the femoral head and neck. MRI has made bone scan obsolete.
Prognosis
The condition is self-limiting in most cases and the osteopenia usually resolves within nine months of symptom onset. However it is a risk factor for potential progression to advanced avascular necrosis.
