1. Imaging Findings

Based on the provided MRI images, abnormalities in signal can be observed in both ankle joints (talus, calcaneus, and surrounding relevant structures) to varying degrees, primarily manifested as:

• Localized areas of heterogeneous signal in the bone marrow: On T1-weighted images, these appear as low or heterogeneous signals, while on T2-weighted or fat-suppression sequences, they may appear as relatively high signal areas, suggesting possible osteonecrosis or structural bone damage.
• Parts of the subchondral region may exhibit slight collapse or irregular contours, indicating potential damage to the local weight-bearing surface.
• In terms of soft tissues, there is no evident widespread edema or obvious soft tissue mass; however, the surrounding joint capsule or synovium may show a small amount of effusion or inflammatory changes.

Overall, these imaging findings are consistent with ischemic bone necrosis (osteonecrosis) in the ankle joint, particularly prominent in the talus.

2. Potential Diagnoses

Taking into account the patient's profile — 50-year-old female, HIV-positive and on HAART, a long history of ankle pain with recent exacerbation, no clear history of trauma, and the imaging findings — the following potential diagnoses are considered:

1. Osteonecrosis (Avascular Necrosis):
   The patient has been on long-term HAART. Although no glucocorticoids have been used, HIV infection and related treatments can lead to abnormal lipid metabolism and immunological changes, negatively affecting local blood supply and bone metabolism. The clinical presentation aligns with MRI findings, making it the primary consideration.
2. Osteoarthritis or Rheumatoid Arthritis:
   These can cause joint pain and dysfunction, but typically present with cartilage wear on the joint surface and narrowing of the joint space. MRI can show subchondral bone sclerosis and marginal osteophytes, and the imaging findings do not fully coincide with osteonecrosis. Bilateral involvement also calls for excluding inflammatory arthropathy.
3. Osteomyelitis or Other Infectious Lesions:
   Typically, this would present with more pronounced bony destruction, soft tissue swelling, and possible abscess formation. Although the patient is HIV-positive, current imaging does not indicate obvious signs of infection such as significant cortical destruction or soft tissue abscess near the bone, thus making this less likely.

3. Final Diagnosis

Combining the patient's medical history (HIV-positive, long-term on HAART), clinical symptoms (chronic bilateral ankle pain with a recent acute exacerbation), and imaging findings (MRI showing characteristics of ischemic necrosis of bone), the most likely diagnosis is:

Osteonecrosis affecting multiple areas, including the talus and calcaneus.

For further confirmation, additional clinical tests (such as blood lipids, coagulation function, and antiphospholipid antibody levels) and monitoring the progression of symptoms are recommended to exclude other possibilities.

4. Treatment Plan and Rehabilitation

4.1 Treatment Strategies

• Conservative Treatment: For early-stage or milder cases, consider reducing weight-bearing, using braces or crutches to relieve joint stress, and using anti-inflammatory and analgesic medications to alleviate pain and control intra-articular inflammatory responses.
• Pharmacotherapy: Under specialist guidance, emphasize bone protection and lipid-lowering treatment. If necessary, use bisphosphonates, vitamin D, and calcium supplements. If lipid metabolism is disturbed, consider adjusting the HAART regimen and prescribing lipid-lowering medication.
• Interventional or Surgical Treatment: For advanced cases, when conservative treatment fails or bone collapse is marked, drilling decompression, bone grafting, or joint fusion/replacement can be considered. A multidisciplinary evaluation by orthopedics and infectious disease specialists is needed to determine the specific plan.

4.2 Rehabilitation and Exercise Prescription

Rehabilitation should focus on protecting the joint, maintaining muscle strength, and promoting blood circulation, following the FITT-VP principles (Frequency, Intensity, Time, Type, Progression, and Individualization).

1. Frequency: It is recommended to perform low-intensity exercises 3–5 times per week, avoiding excessive weight-bearing.
2. Intensity: Based on pain levels and joint stability, initially choose low or non-weight-bearing exercises (e.g., ankle movements in a seated or supine position), then gradually progress to light resistance exercises (e.g., use of resistance bands, slight weight-bearing on the ankles).
3. Time: Start with 10–20 minutes of exercise per session, and gradually increase to 30 minutes or more if tolerated, adjusting according to symptom relief.
4. Type: Possible choices include:
   • Joint range of motion exercises: Ankle dorsiflexion, plantarflexion, and circumduction, to maintain or improve joint mobility.
   • Muscle strengthening: Heel raises and toe lifts in a seated or supported position, supplemented by light resistance band exercises.
   • Aquatic exercises: If available, swimming or walking in water to reduce joint loading while strengthening muscles.
5. Progression: Gradually increase the duration and weight-bearing intensity based on improvements in pain and function. Balance and proprioceptive training can be introduced under the guidance of a specialist or physical therapist.
6. Individualization: If the patient has other comorbidities (e.g., cardiovascular risks), closely monitor heart rate, breathing, and local pain, and modify the exercise prescription accordingly.

5. Disclaimer

This report is a reference analysis based on the existing medical history and imaging data; it cannot replace in-person consultations or professional clinical diagnostic and treatment advice. The patient should undergo further examinations and clinical assessment at professional medical facilities to obtain an individualized treatment plan.