The goal of this clinical trial is to evaluate the effectiveness and safety of Antarctic Krill Oil (AKO) as a dietary supplement in managing pain associated with knee osteoarthritis (OA). The main questions it aims to answer are:

①Does AKO reduce daily pain intensity in participants with moderate knee OA?

②What adverse effects do participants experience when taking AKO?

Researchers will conduct a randomized, double-blind study comparing AKO to a placebo (identical appearance without active components) to assess:

• Changes in joint pain severity; ②Functional improvement in daily activities; ③Biochemical safety parameters,etc.

Osteoarthritis (OA) is a chronic degenerative disease affecting the entire joint apparatus, characterized by pathological alterations in articular cartilage, subchondral bone, synovium, and joint capsule, clinically manifested by high rates of disability and deformity. With the accelerating aging population in China, the prevalence of OA has risen significantly, garnering substantial academic attention. Current management for early-to-moderate OA predominantly relies on oral non-steroidal anti-inflammatory drugs (NSAIDs), intra-articular hyaluronic acid injections, and glucocorticoids. For advanced cases, total joint arthroplasty remains the definitive intervention, while no disease-modifying therapies have been established to date.

Antarctic krill oil, a nutrient-dense marine extract, contains clinically relevant bioactive components including phospholipids, eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA), which are critical mediators of its therapeutic potential. Despite emerging interest, clinical evidence regarding krill oil's efficacy in alleviating OA-related pain and improving joint function remains limited, underscoring the need for further exploration of its role in OA management.

This clinical trial aims to evaluate the efficacy and safety of Antarctic krill oil supplementation in reducing pain severity among patients with knee osteoarthritis (KOA), with the ultimate goal of expanding evidence-based therapeutic options for KOA pain management.

Inclusion Criteria:

• Aged 45-75 years；
• Clinically diagnosed with knee osteoarthritis per the Chinese Guidelines for the Diagnosis and Treatment of Osteoarthritis (2018 edition) issued by the Chinese Medical Association, with Kellgren-Lawrence grade 1-3；
• Knee pain Visual Analog Scale (VAS) score between 4.0 and 8.0；
• Ability to comprehend and complete VAS and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) assessments；
• Willingness and ability to undergo knee MRI examinations.

Exclusion Criteria:

• Ipsilateral hip osteoarthritis;
• Diagnosis of rheumatoid arthritis (RA), ankylosing spondylitis, sarcoidosis, amyloidosis, or any other inflammatory arthritis (e.g., gout, pseudogout);
• Chronic pain syndromes, fibromyalgia, or comorbidities that may confound knee pain assessment;
• Pain intensity in the lower extremities or back equal to or greater than knee pain;
• Arthroscopic or open knee surgery within the preceding 12 months or planned during the study period;
• Oral, intra-articular, or intramuscular corticosteroid use within 6 months prior to screening or during the study;
• Intra-articular hyaluronic acid injection within 6 months prior to screening or during the study;
• High-dose NSAID use (≥ maximum recommended daily dose for osteoarthritis pain relief) within 1 month prior to screening, including but not limited to: Diclofenac ≥150 mg/day; Aceclofenac ≥100 mg/day; Meloxicam ≥15 mg/day; Naproxen ≥1,000 mg/day; Piroxicam ≥20 mg/day; Ibuprofen >2,400 mg/day (Exempt if a ≥4-week washout period is completed prior to Day 1);
• Bleeding disorders or anticoagulant use within 1 month (except low-dose aspirin ≤150 mg/day);
• Regular use of glucosamine, fish oil, or other supplements unless a ≥4-week washout period (≥3 months for fish oil) is completed prior to Day 1;
• Hypersensitivity to trial medications or seafood;
• Administration of any medication within 6 months prior to Day 1 that may interfere with study outcomes, as judged by investigators;
• Pregnancy (positive urine test at screening or Day 1), lactation, or inadequate contraception;
• History of alcoholism, substance abuse, major systemic diseases (e.g., renal, cardiac, hepatic, or gastrointestinal disorders), or conditions deemed by investigators to compromise study participation or data integrity;
• Uncontrolled hypertension (screening blood pressure ≥140/90 mmHg) unless confirmed as non-hypertensive or well-controlled by a specialist;
• Inability to provide informed consent.