1. Imaging Findings

Based on the X-ray, MRI, ultrasound, and CT images of the patient’s right hand fourth finger (ring finger) proximal interphalangeal joint (PIPJ), the main observations are as follows:

• X-ray: At the initial examination, only soft tissue swelling of the affected joint was observed, without obvious bone destruction or sclerosis. No typical “radiolucent focus” or periosteal sclerosis was noted.
• MRI: Bone marrow edema was observed in both the proximal and middle phalanges near the joint surfaces with a small amount of joint effusion and signs of tenosynovitis. On T1-weighted images, a tiny (about 1–2 mm) low signal lesion was suspiciously seen near the articular surface of the proximal phalanx, suggesting possible calcification or a “nidus” (the core of an osteoid osteoma).
• Ultrasound: Showed synovial thickening of the affected joint with markedly increased blood flow signals (“high blood flow signal”) and a small amount of effusion, indicating synovitis.
• CT (postoperative follow-up): After the placement and subsequent removal of crossed Kirschner wires, no typical sclerosis or evident bone defects were noted in the adjacent bone. However, due to the small lesion size and its deeper location, pinpointing the core lesion postoperatively remains difficult.

Overall, the imaging features are atypical: there is a lack of obvious sclerotic changes or the classic “nidus” structure often associated with osteoid osteomas across various imaging modalities. On MRI, only a tiny (1–2 mm) low signal area is suggestive, accompanied by joint effusion and synovitis, leading to diagnostic challenges.

2. Potential Diagnoses

Based on the patient’s history (2.5 years of persistent pain and swelling, partially relieved by NSAIDs), imaging features, and repeated exclusions of infection and inflammatory joint diseases, the following differential diagnoses are considered:

1. Osteoid Osteoma
   • Features: Common in young adults, typically characterized by worsening nighttime pain and good response to NSAIDs. Intra-articular locations can present atypically.
   • Imaging: Typically, a “nidus” surrounded by reactive sclerosis can be seen on X-ray or CT. If the lesion is too small or located intra-articularly, imaging findings may be atypical.
2. Infectious Arthritis (including Tuberculous Arthritis)
   • Features: Chronic joint swelling, pain, and dysfunction. More caution is needed with a history of tuberculosis exposure.
   • However, in this case, two synovial biopsies showed no evidence of tuberculosis or other bacterial infection.
3. Rheumatoid Arthritis or Other Inflammatory Joint Diseases
   • Features: Can present as chronic mono- or oligoarticular swelling with synovial hyperplasia and effusion. However, disease course and histopathology did not strongly suggest typical rheumatoid arthritis.
   • Other joints are not characteristically involved, and there are no significant abnormalities in immunological lab results.
4. Other Rare Benign Bone Tumors
   • Such as enchondroma, osteochondroma, etc. Usually, some degree of calcification, exostosis, or typical cartilage matrix findings can be seen on X-ray or CT.
   • These features are absent in this case.

3. Final Diagnosis

Considering the patient’s age, clinical symptoms (joint pain, partial response to NSAIDs), local joint swelling, and imaging (only a vague tiny low-signal lesion on MRI, with bone marrow edema and synovitis, and no evidence of typical infection or rheumatic markers), the most likely diagnosis is:

• Intra-Articular Osteoid Osteoma (Proximal Phalanx)

This condition is relatively rare and can be easily delayed in diagnosis. Intra-articular lesions often lack the typical reactive sclerosis and can mimic arthritis or synovitis. For precise localization or confirmation, a high-resolution CT scan or a targeted biopsy during symptomatic periods may be considered.

4. Treatment Plan and Rehabilitation

If osteoid osteoma is confirmed or highly suspected, the following treatment strategies and subsequent rehabilitation plans may be considered:

1. Treatment Strategies
   • Conservative Pharmacological Treatment: If symptoms are relatively mild and well-controlled by NSAIDs, symptomatic management and regular follow-up may be chosen. Small lesions can sometimes resolve spontaneously.
   • Minimally Invasive Ablation or Curettage: For significant symptoms and a well-localized lesion, CT-guided radiofrequency ablation or curettage can quickly relieve pain and restore joint function.
   • Joint Fusion or Internal Fixation: If the lesion is located on a weight-bearing surface and significantly damages joint structure, more aggressive surgical intervention may be required. However, given the small lesion in this case, thorough curettage or ablation should effectively alleviate symptoms if recurrence is confirmed.
2. Rehabilitation / Exercise Prescription
   • Acute Phase: During severe pain, reduce joint activity and use anti-inflammatory medications along with local cold therapy. Avoid excessive loading or repetitive hyperextension movements.
   • Recovery Phase:
     • Once symptoms improve, gradually begin active and passive finger joint exercises, such as gentle fist-making and finger extension 2–3 times a day, 10–15 repetitions each time.
     • Performing these movements in warm water can help reduce pain and enhance tissue flexibility.
   • Strengthening Phase:
     • Gradually increase load, for example using elastic bands for finger flexion and extension exercises 2–3 times a week, 2–3 sets per session, 10 repetitions per set.
     • Increase fine gripping exercises if pain-free, such as pinching small balls or modeling clay, to improve joint mobility and muscle strength.
   • Maintenance Phase:
     • If joint function shows significant improvement, incorporate handheld grip exercises and joint mobility exercises into daily life; maintain at least 2–3 sessions of hand stretching or strengthening each week.
     • If pain or discomfort recurs, discontinue training and seek medical evaluation as needed.

Throughout rehabilitation, exercise intensity and range of motion should be individualized based on the patient’s age, bone quality, overall health status (especially any cardiovascular or chronic conditions), ensuring safety and comfort.

Disclaimer

This report is provided as a reference based on the available imaging and clinical information. It does not replace an in-person consultation or professional medical advice. Actual diagnosis and treatment must be determined by qualified medical professionals after reviewing the patient’s full medical history, physical examination, laboratory tests, and other diagnostic findings.