Knee osteoarthritis (OA) is a common problem in clinical settings. Knee OA is well known for its association with the wear and tear of the cartilage and osteophyte formation. Evidence has suggested the importance of the infrapatellar fat pad, known as Hoffa's fat pad, during the development of knee OA. Some studies have demonstrated the protective role of the infrapatellar fat pad, whereas others have suggested an inflammatory role such as increased fibrosis and proinflammatory cytokine levels. Ultrasound is exceptionally convenient in the assessment of the musculoskeletal system, and elastography is a tool to evaluate tissue texture. Therefore, in this study, we investigated the Hoffa's fat pad in knee OA patients by using elastography.

This was an observation study that included a control group. We enrolled 20 patients with knee OA, as well as 10 healthy individuals. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Kellgren-Lawrence X-ray grading were employed to determine disease severity. All the study participants received elastography assessment, including strain and shear wave elastography in the knee extension and flexion position. The strain elastography contained color mapping that enabled the calculation of the relative texture and strain ratio. The shear wave elastography revealed the qualitative velocity, which was measured 3 times. Each patients with knee OA received elastography examination twice: once before hyaluronic acid injection and once 1 month after the injection.

Inclusion Criteria:

OA group

• Kellgren-Lawrence grading I-IV proved by knee X-ray Healthy group
• No knee pain or received injection during the past 1 year
• No history of knee OA

Exclusion Criteria:

• History of knee surgery, trauma or malignancy
• History of patellar tendinopathy or patellofemoral pain syndrome
• Refused informed consent

individuals with knee osteoarthritis diagnosis is classified as K-L grading I - IV individuals in control group has no knee pain or osteoarthritis history