Synovitis and Effusion

The Story

Every so often, usually alongside a fever, one of Stina’s joints — a knee, an ankle — would balloon overnight: hot, tight, hard to bend, clearly full of fluid. Once, a clinician drew the fluid off with a needle. It was sterile and inflammatory, with no infection to explain it. The episode was labeled reactive arthritis, the joint settled in a few days, and the pattern repeated — a swollen joint that came with the fevers and left with them, again and again, for years.

A synovial joint is a small fluid-filled chamber, and this page is about its lining. The bone ends are capped with hyaline cartilageThe most abundant cartilage type, found in joints, ribs, and the nose. and enclosed in a joint capsule; the inside of that capsule is lined by the synovium (synovial membrane), which secretes synovial fluid to lubricate and nourish the avascularTo be devoid of blood capillaries. Epithelial tissue is avascular, kind of like a cap of dead cells cartilage. When the synovium becomes inflamed — synovitis — it thickens and pours out excess fluid, producing the warm, swollen, tense joint of an effusion. In Stina, IL-1β and IL-6 inflamed the synovium directly, so her joints flared in lockstep with her fevers: same cytokines, same thermostat, two different tissues. The fluid was sterile because there was no germ — only inflammation. Her recurring “reactive arthritis” was inflammatory synovitis, one more tissue catching the same fire.

From Stina’s chart: Recurrent: single swollen, warm joints (knee, ankle) during attacks, with effusion; fluid tapped once — sterile, inflammatory. Read as “reactive arthritis.” Resolved between attacks.