This clinical trial aims to evaluate the use of a handheld Magnetic Particle Imaging (MPI) device for real-time, non-invasive monitoring of human umbilical cord-derived mesenchymal stromal cells (UC-MSCs) in patients with knee osteoarthritis (OA). The primary objective is to visualize and quantify the distribution, retention, and survival of SPIO (superparamagnetic iron oxide)-labeled MSCs within the joint space following intra-articular injection. By correlating MPI signal dynamics with established clinical outcomes (e.g., WOMAC, VAS scores) and anatomical MRI assessments, the study seeks to predict treatment efficacy and optimize therapeutic strategies for OA.

Current assessment of MSC therapy relies largely on MRI for structural evaluation, which has limited sensitivity for tracking early cell viability and migration. MPI offers high-contrast, radiation-free functional imaging capable of directly detecting SPIO-labeled cells. This study will enroll patients with mild-to-moderate OA (Kellgren-Lawrence grade II-III). Participants will receive a single injection of ferumoxytol-labeled UC-MSCs into the affected knee. MPI scans will be performed at multiple timepoints (day 1, 3, 7, and 30) to monitor cell homing, retention rate, and signal decay. MRI will be used in parallel to evaluate cartilage morphology and synovial changes.

The study expects to demonstrate that MPI can effectively track MSC behavior in vivo, providing a novel tool to understand cell therapy mechanisms, assess treatment response early, and potentially guide personalized OA management.

Inclusion Criteria:

1. Diagnosis of knee osteoarthritis according to internationally accepted criteria (e.g., American College of Rheumatology criteria).
2. Age between 18 and 75 years, inclusive.
3. Radiographic Kellgren-Lawrence grade II or III in the target knee.
4. Chronic knee pain of arthritic origin.
5. Absence of local or systemic infection.
6. No contraindications to joint cavity puncture as determined by hematological and biochemical tests.
7. Willing and able to understand the study, provide informed consent, and comply with all study procedures.

Exclusion Criteria:

1. Lack of legal capacity or impaired capacity to provide informed consent.
2. Known active infection with HIV, hepatitis B virus, hepatitis C virus, or syphilis (positive serology).
3. Body mass index (BMI) > 30 kg/m².
4. Congenital or acquired deformity of the target knee.
5. Pregnant or breastfeeding women.
6. History of or current active malignancy.
7. Known immunodeficiency disorder.
8. Intra-articular injection (e.g., corticosteroids, hyaluronic acid) in the target knee within the past 3 months.
9. Concurrent participation in another interventional clinical trial.
10. Any other condition that, in the opinion of the investigator, would make the participant unsuitable for the study (e.g., significant comorbid illness).

De-identified individual participant data (IPD) that underlie the results reported in the primary publication of this study will be made available. This will include clinical outcomes (e.g., WOMAC, VAS scores), MRI assessment data, and quantitative MPI-derived metrics (e.g., signal retention rate, decay rate).

Beginning 3 months after main results publication. Ending 36 months after publication.

Data access requests should be directed to the corresponding author or the designated data custodian at Hainan Provincial People's Hospital. Requestors will need to submit a methodologically sound research proposal for review by the study's Steering Committee. Access will be granted upon approval of the proposal and execution of a Data Use/Transfer Agreement.