This study aims to compare the postoperative clinical outcomes of Infrapatellar Fat Pad (IPFP) preservation versus resection after total knee arthroplasty (TKA) in patients with knee osteoarthritis. Participants will be identified as normal IPFP or abnormal IPFP based on MRI findings before randomization. The primary outcome is the change from baseline to 12 months in the mean score on five Knee Injury and Osteoarthritis Outcome Score (KOOS) subscales (KOOS5), covering pain, symptoms, activities of daily life, sport & recreation, knee-related quality of life, with scores ranging from 0 (worst) to 100 (best). The secondary endpoints will be included: KOOS subscales, Knee Society Score (KSS), 100 mm Visual Analogue Scale (VAS) Pain, timed up-and-go test, depression, patellar tendon shortening, 100 mm VAS self-reported efficacy of reduced pain and increased quality of life. Adverse events will be recorded. Primary and secondary outcomes will be evaluated or reported blindly at baseline and at postoperative 3 months, 6 months, and 1 year. Intention-to-treat analyses will be used.

Knee Osteoarthritis (KOA) is a common chronic disease, which often leads to joint pain and limited function in the elderly, and thus affects participants' quality of life. Total knee arthroplasty (TKA) has been developed as a mature surgical procedure to relieve end-stage osteoarthritic joint pain and improve limb function. Although more than 80% of the patients reported in the literature are satisfied with the postoperative efficacy of TKA, there are still a large number of patients whose daily life is affected by persistent knee pain and limited function after the operation of the affected limb.

The IPFP is a fat mass located behind the patellar ligament, between the lower part of the patella and the tibial tubercle. The function of IPFP is controversial at present. It is reported that IPFP can provide blood supply for anterior cruciate ligament, patella and patellar ligament through the arterial network of the knee joint. In addition, it can fill the joint gap to lubricate the surface of the joint, reduce friction and absorb impulse so as to play a physiological protective role. On the contrary, studies have pointed out that abnormal IPFP could produce various pro-inflammatory cytokines such as interleukin (IL)-1β, tumour necrosis factor (TNF)-α, IL-6 and IL-8, as well as adipokines such as leptin and resistin, and thus might play a detrimental role in knee OA. Traditionally, the IPFP has been removed in order to improve surgical exposure and to prevent interposition during baseplate implantation. Despite the significant evolution of TKA technology which no longer requires the resection of IPFP for better surgical access, IPFP is still partially or totally resected in around 88% of TKAs.

The investigators' previous population-based cohort study revealed that IPFP maximal area and volume were associated with reduced knee pain, decreased loss of cartilage volume and reduced risks of cartilage defect progression, indicating a beneficial effect of IPFP size. On the other hand, the investigators' further investigation demonstrated that IPFP signal intensity alteration was negatively associated with maximum area of IPFP, and moreover, associated with increased knee cartilage defects, subchondral bone marrow lesion (BML) and knee pain, suggesting IPFP with abnormal quality may play a detrimental role in knee OA. Based on these findings, the investigators proposed that IPFP with normal quality should be preserved or not damaged during TKA, while IPFP with abnormal quality should be resected. This multicentre randomised controlled trial is designed to test the investigators' hypotheses: in patients with normal IPFP quality, preservation of IPFP during TKA procedure will reduce postoperative knee symptoms and improve joint function, comparing with IPFP resection during TKA procedures; in patients with abnormal IPFP quality, resection of IPFP during TKA procedure will reduce postoperative knee symptoms and improve joint function, comparing with IPFP preservation during TKA procedures. The results would provide evidence-based recommendations on clinical practice to improve OA patients' postoperative outcomes.

Three hundred and sixty eligible participants will be recruited and identified as having normal IPFP quality (signal intensity alteration score ≤ 1) or abnormal IPFP quality (signal intensity alteration score ≥ 2). Participants in each site will be randomly allocated to IPFP resection group or preservation group using computer-generated block randomisation.

Inclusion Criteria:

• Participants diagnosed with knee osteoarthritis by X-ray plain film (Kellgren-Lawrence score of ≥ 2)
• The need for TKA was confirmed after evaluation by the orthopedic surgeon
• One week before surgery, knee pain 100mm pain visual analogue scale score was greater than 20mm
• Understanding of the study requirements and willing to participate in this study

Exclusion Criteria:

• Rheumatoid arthritis,psoriatic arthritis,lupus,malignant tumor
• Requiring contralateral TKA within one year
• The visual analogue score of 100mm of knee pain before operation was less than 20mm
• Having a possible or planned pregnancy
• With poor compliance
• Suffering from somatic disease, psychiatric or cognitive disorders, neurological disorders that will compromise the safety, compliance, consent, participation, follow-up and the interpretation of the results
• Severe knee valgus
• Contraindications with TKA or MRI

participants, outcome assessors, data analysts and chief investigators are masked during the study procedure.