30-year-old male to female trans-gender patient with 2 month history of progressively worsening right hip pain.
Initial hip radiograph was unremarkable.
Subsequent Tc-99m MDP bone scan showed increased activity within the proximal right femur on immediate flow and blood pool images. There was intensely increased activity in the proximal right femur, particularly within the femoral head, on the delayed images.
Pelvis MRI showed a marked oedema within the proximal right femur, particularly at the head, extending into the femoral neck. There was no evidence of fracture or femoral head collapse.
Infection was excluded by a negative joint aspiration. The patient was managed conservatively, with interval resolution of her symptoms.
Follow-up Tc-99m MDP bone scan performed 1.5 years later demonstrated some decreased activity within the right femoral head and neck.
MRI performed 4 months after the bone scan showed complete interval resolution of the previously noted oedema within the right femoral head and neck, with normal appearance of the marrow. Concurrent pelvis radiograph was unremarkable.
Transient osteoporosis of the hip (TOH) is a rare disease, with approximately 200 reported cases in the literature. It typically affects middle aged men and pregnant women. Patients present with relatively acute onset hip pain. Most patients recover within 6 months to 2 years with conservative therapy, often including protected weight-bearing [1-4].
The aetiology of TOH is unclear. It has been theorised that it may represent an early, reversible osteonecrosis. Differentiating this disease entity from early osteonecrosis may therefore be difficult on both clinical examination and imaging. TOH may represent a subset of a general clinical entity known as transient bone marrow oedema syndrome [3].
The differential diagnosis for TOH includes both early osteonecrosis, as well as subchondral fracture. Clinically, an infectious or inflammatory arthropathy also remain in the differential diagnosis.
Radiographs are often initially negative. Diffuse osteopenia may be seen in the affected femoral head and neck.
Tc-99m MDP bone scan findings may vary depending on the stage of the disease. Typically, there is marked increased activity within the femoral head, with lesser degrees of increased activity within the femoral neck. The bone scan typically normalises 1-2 years after symptom onset.
MRI findings also show marked oedema within the femoral head, with lesser amounts of oedema within the femoral neck. These findings are best seen on STIR and T1 weighted images. Of note, stress fractures can develop in patients, particularly those who do not adequately protect the hip. These should be excluded on MRI.
Transient osteoporosis of the right hip.
1. X-ray Plain Film:
● The contour of the affected (right) femoral head is generally intact, with no obvious collapse or clear fracture line on the articular surface.
● Mild diffuse osteoporosis can be observed in the right femoral head and neck, but the boundaries are not well-defined, and no obvious soft tissue swelling is noted.
2. MRI (T1, T2/STIR, coronal, sagittal, and axial sequences):
● The right femoral head shows a marked abnormal signal, with high signal on the STIR sequence (indicative of intramedullary edema) and relatively low signal on T1; the femoral neck region also shows relatively mild edema signals.
● The cartilage surface remains intact, and no obvious subchondral fracture line is seen.
● There is no significant increase in joint effusion, but mild reactive changes can be observed in the soft tissues around the joint.
3. Bone Scan (Tc-99m MDP):
● Elevated tracer uptake in the right femoral head, with relatively increased uptake in the femoral neck area as well, though primarily involving the femoral head.
● No obvious widespread lesions or abnormal uptake in other areas.
Based on the patient's symptoms (right hip pain worsening over 2 months), imaging findings (especially bone marrow edema-like changes on MRI and increased uptake in the femoral head on Tc-99m MDP), and the patient's age background, possible diagnoses include:
1. Transient Osteoporosis of the Hip (TOH)
● Commonly occurs in middle-aged men or pregnant women, although it has been reported in other specific populations.
● Characteristic features include diffuse bone marrow edema in the femoral head, sometimes accompanied by osteoporosis.
● Clinical symptoms generally resolve gradually over several months to one and a half years.
2. Early Avascular Necrosis of the Femoral Head (AVN)
● Presents with hip pain and abnormal signals in the femoral head on MRI, but typically shows subchondral lines or collapse in later stages.
● Imaging differentiation points include the presence of a typical necrosis band or a subchondral crescent line.
3. Subchondral Fracture or Occult Fracture
● Can present with severe pain; MRI may show edema signals. Requires careful exclusion of obvious fracture lines or deformities.
4. Infectious and Inflammatory Joint Lesions
● Often accompanied by an increase in joint effusion and elevated inflammatory markers in laboratory tests, but still need to be considered in differential diagnoses.
Considering the patient’s clinical history (male-to-female transgender, 30 years old, with no recent significant trauma or history of corticosteroid use), the findings from MRI and X-ray indicating bone edema/osteopenic signs in the right femoral head and neck, and the significantly increased uptake on bone scan without classic collapse or necrosis band features, the most likely diagnosis is: Transient Osteoporosis of the Hip (TOH).
Currently, there is no imaging evidence to support typical early necrosis with a necrosis band or collapse, nor clear subchondral fracture line or severe inflammatory damage, making early hip necrosis and severe subchondral fracture less likely.
1. Conservative Treatment:
● For transient osteoporosis of the hip, usual management involves reducing weight-bearing or partial weight-bearing activities. Crutches or walkers may be used, and strenuous exercise should be avoided to reduce stress-related damage to the femoral head.
● Pain can be managed with nonsteroidal anti-inflammatory drugs (NSAIDs) or other analgesics if needed.
● In cases with marked osteoporosis, calcium and vitamin D supplementation can be considered. Bisphosphonates may be used to improve bone metabolism depending on the situation.
2. Observation and Follow-up:
● Symptoms typically improve gradually over 6 months to 1 year, with imaging findings also returning closer to normal.
● Reassessment with MRI or X-ray in 3 to 6 months is recommended to monitor femoral head trabecular repair, potential collapse, or progression of other pathologies.
3. Rehabilitation Exercise Prescription (following the FITT-VP principle):
● Frequency: 3–5 times per week.
● Intensity: Begin with low-intensity activities, avoiding high-impact loads on the hip joint. Start with range-of-motion exercises and low-intensity strength training.
● Time: 20–30 minutes per session initially, gradually increasing to about 40 minutes as tolerated.
● Type:
- Non-weight-bearing or low-weight-bearing exercises such as swimming, range-of-motion training for the lower limbs in sitting or semi-reclining positions, and light resistance exercises with resistance bands.
- Gentle range-of-motion exercises: Active or passive hip range-of-motion exercises within a tolerable pain level to enhance joint flexibility.
● Progression: Gradually increase the intensity and duration of training based on pain relief and functional improvement. Avoid rapidly increasing the load.
● Precautions:
- For those at risk of osteoporosis or with hip edema and tenderness, carefully control activity volume and prevent falls.
- If pain worsens or any significant discomfort occurs, stop or reduce the load and seek medical re-evaluation promptly.
This report is an advisory analysis based on existing imaging and case history information and does not replace a face-to-face clinical diagnosis or treatment. The patient should consider their individual circumstances and follow up with further examinations and personalized treatment advice from a specialist or orthopedic physician.
Transient osteoporosis of the right hip.
