In the cavity of human knee joint, there is a structure called synovium, which can nourish articular cartilage by secreting synovial fluid, lubricate the surface of cartilage and reduce the wear and tear during joint movement. Under normal circumstances, there is about 2 ml -5 ml synovial fluid in the knee joint cavity. Because the synovial fluid is small and distributed in all parts of the joint, it will not cause swelling and abnormality of the knee joint. If the patient's knee joint has hyperosteogeny, the cartilage surface is uneven, and even the cartilage is destroyed. At this time, when the knee joint is active, it can stimulate the synovium, leading to synovitis of the knee joint, which is mainly manifested as synovial vasodilation, congestion and edema, which significantly increases synovial fluid secretion and causes knee joint effusion.

Intra-articular effusion of knee joint hyperosteogeny often occurs in the early and acute stages of osteoarthritis. The liquid is clear and viscous, with low protein content and slightly higher cell number than normal. Calcium hydroxide or calcium pyrophosphate crystals can be found in the effusion of patients with knee osteoarthritis and hyperosteogeny, especially middle-aged and elderly patients. Because of osteophyte shedding caused by hyperosteogeny, synovial folds with rich blood supply bleed, sometimes the effusion in patients' joints is bloody effusion.

In a word, joint cavity effusion is one of the common signs of patients with knee osteoarthritis and hyperosteogeny, and there is an inevitable connection between them.