Transient osteoporosis of the hip (TOH), also known as transient bone marrow edema syndrome (BMES), is a self-limiting condition characterized by transient bone marrow edema in the femoral head and neck. It most commonly affects the hip and occurs in middle-aged men and women in the third trimester of pregnancy. On MRI, diffuse bone marrow edema in the femoral head (hyperintense on STIR, hypointense on T1) is characteristic but unlike AVN, there are NO subchondral changes (no double-line sign, no crescent sign). It typically resolves spontaneously in 6-12 months without permanent damage. Treatment is conservative: pain management and weight-bearing reduction.
Age Range
25-55
Peak Age
40
Gender
Male predominant
Prevalence
Uncommon
The exact pathophysiology of transient osteoporosis is not fully understood but several theories have been proposed: (1) Vascular theory — transient ischemia of the femoral head leads to bone marrow edema but unlike AVN, ischemia is at a reversible level and does not progress to necrosis. This is consistent with the 'aborted AVN' concept. (2) Neural theory — local dysregulation of the sympathetic nervous system leads to vasomotor tone changes → increased intraosseous pressure → edema. (3) Mechanical theory — pelvic changes in pregnancy and increased load apply excessive stress to the femoral head → bone marrow edema as a stress response. MRI pathophysiological correlates: increased capillary permeability and increased interstitial fluid in bone marrow → fat cell displacement by water → signal drop on T1 (fat loss), signal increase on T2/STIR (free water increase). Subchondral bone REMAINS INTACT because osteocyte necrosis does not occur — this is the fundamental distinguishing feature from AVN.
Diffuse hyperintense bone marrow edema in the femoral head and neck on STIR/T2, WITHOUT any AVN findings such as double-line sign, crescent sign, or focal necrotic zone in the subchondral region. This 'pure edema' pattern is the most characteristic finding for transient osteoporosis and forms the basis of differential diagnosis from AVN.
On STIR and T2 fat-sat images, diffuse bone marrow edema (hyperintense signal) is seen in the femoral head and usually extending to the femoral neck. The edema is homogeneous and diffuse with NO focal subchondral abnormality — no double-line sign, no subchondral fracture, no necrotic zone. This is the most critical MRI finding distinguishing transient osteoporosis from AVN. The edema typically involves the entire femoral head and may extend to the intertrochanteric region. Joint effusion may accompany.
Report Sentence
Diffuse hyperintense bone marrow edema is seen in the femoral head and neck on STIR without subchondral changes; consistent with transient bone marrow edema syndrome.
On T1-weighted images, diffuse low signal is seen in the femoral head and neck. Normal bone marrow shows high T1 signal due to fat, but in the edema area, displacement of fat cells by water leads to signal drop. Unlike AVN, signal loss is diffuse and homogeneous — it does not show a geographic (band-like) pattern. T1 signal loss shows parallel distribution with STIR signal increase.
Report Sentence
Diffuse low signal is noted in the femoral head on T1, consistent with bone marrow edema; no focal necrotic changes are identified.
On post-contrast T1 fat-sat images, diffuse enhancement is seen in the edema area of the femoral head. Enhancement reflects increased vascular permeability and capillary dilation. Distinguishing feature from AVN: enhancement in transient osteoporosis is diffuse and homogeneous — there is NO non-enhancing necrotic zone as in AVN.
Report Sentence
Diffuse homogeneous enhancement is noted in the femoral head on post-contrast images without non-enhancing necrotic area; a finding favoring transient osteoporosis.
On T2-weighted images, hip joint effusion frequently accompanies. Effusion is usually mild to moderate and relates to reactive synovitis. Joint effusion alone is not specific but combined with diffuse bone marrow edema, supports transient osteoporosis.
Report Sentence
Mild to moderate joint effusion is noted in the hip joint.
On CT and conventional radiography, diffuse osteopenia (decreased bone density) may be seen in the femoral head but there is no subchondral fracture, sclerotic band, or femoral head contour disruption. On radiograph, 'phantom bone' appearance has been described — marked demineralization appearance of the femoral head. CT and radiography help exclude AVN but may be normal in early-stage transient osteoporosis.
Report Sentence
Diffuse osteopenia is noted in the femoral head on CT without structural bone changes.
Criteria
Single hip involvement, spontaneous recovery in 6-12 months, no recurrence.
Distinct Features
Diffuse edema in femoral head on MRI, MRI normalizes with recovery. Most common form.
Criteria
Sequential joint involvement — edema resolves in one joint while beginning in another. Lower extremity joints most commonly affected.
Distinct Features
Migratory pattern: hip → knee → ankle sequence. Each episode resolves in 6-9 months. May continue for years. More common in men.
Criteria
Femoral head bone marrow edema developing in the 3rd trimester of pregnancy or postpartum period.
Distinct Features
Left hip more commonly affected. MRI is safe in pregnancy (gadolinium contraindicated). Spontaneous resolution 2-6 months postpartum.
Distinguishing Feature
AVN shows pathognomonic double-line sign (T2) and geographic necrotic zone (T1) in subchondral region with non-enhancing necrotic area on contrast, while transient osteoporosis has no subchondral changes and enhancement is diffuse and homogeneous
Distinguishing Feature
Stress fracture shows a linear low signal fracture line within marrow edema on T1, while transient osteoporosis has no fracture line and edema is diffuse and homogeneous
Distinguishing Feature
Metastasis shows focal or multifocal bone lesions with irregular margins and diffusion restriction, while transient osteoporosis has diffuse homogeneous edema without focal mass or diffusion restriction
Urgency
routineManagement
conservativeBiopsy
Not NeededFollow-up
3-monthTransient osteoporosis is a self-limiting condition and treatment is conservative: weight-bearing reduction on the affected extremity (crutches), pain management (NSAIDs), physical therapy. Spontaneous recovery is expected in 6-12 months. Follow-up MRI confirms edema resolution — if MRI does not normalize, AVN differential should be re-evaluated. In pregnancy-associated cases, rapid postpartum recovery is typical. The migratory form may continue for years but each episode is transient.
Transient osteoporosis is self-limiting and resolves spontaneously in 6-12 months. Conservative treatment (weight bearing restriction, analgesia) is sufficient. Differential diagnosis from AVN is critical because AVN may require surgical intervention. Follow-up MRI should confirm resolution of edema.