Definition
Self limiting syndrome of unknown aetiology
- hip pain associated with osteoporosis of proximal femur
DDx
AVN
- AVN of the hip in pregnancy is rare but possible
- TOH tends to be diffuse on MRI, while AVN is localised
- extends to neck and metaphysis
- transient osteoporosis has normal bone scan
Incidence
Rare
- M: F 3:1
Two Groups
1. Men 40-50 years old
2. Women usually 3rd trimester of pregnancy
Aetiology
Unknown / Theories
- ischaemia
- RSD
- virus / toxin
Only predisposing factor is pregnancy
Pathology
Biopsy shows many features in common with AVN, but it is non-specific
- edematous fluid & marrow
- inflammation
- fat necrosis
- reactive bone formation
- widely spaced trabeculae
Clinical Features
Acute onset
- AVN tends to be insidious
Mechanical hip pain
- usually FROM
Rarely sub-capital fracture results
Natural History
Three distinct temporal phases
1. Initial
- sudden onset severe pain
- disability >> signs
- lasts 1/12
2. Plateau
- symptoms stabilise
- osteopenia seen on xray
- lasts 2/12
3. Regression
- lasts 3/12
X-ray
Shows diffuse osteopenia of entire proximal femur
- 1/12 after onset
- may have "Phantom" appearance of proximal femur
- rarely the pelvis can be affected too
MRI
Key is that with TOH the MRI changes are diffusely affecting the proximal femur
- AVN it is localized to a portion of the head
Marrow oedema
- TI decreased SI
- T2 increased SI due to oedema
DDx
Radiologically
AVN
Osteoporosis 2° joint disease
Metabolic cause osteopenia
Permeative - neoplasia
Management
Pregnancy
NHx
Self limiting condition
- rapidly improves after delivery
Need to prevent fracture
- protected weight bearing in pregnancy
NOF
Management
- simultaneous pinning & LSCS
Non pregnancy
Bisphosphonates
Varenna et al Bone 2002
- 16 cases treated with IV pamidronate
- resolution of symptoms and normalisation of MRI findings