swelling,fluid around the knee cap,housemaids got it years ago,when they had to scrub floors on their knees and other cleaning duties or damaged cartlidge or ligamants.wear and tear inside of knee.Rest,Ice Compression and Elevation =RICE,anti inflammatory,
drugs,if it does not settle down after a few weeks,they will use a syringe to drain the fluid off,then the leg will fall off easily.lol

www.gowerstreetpractice.org.uk/health-information/?arturi=aHR0cDovL2FwaS5wYXRpZW50LmNvLnVrL2NvbnRlbnQvcGlsL2hvdXNlbWFpZHMta25lZS1wcmVwYXRlbGxhci1idXJzaXRpcz9hcGlrZXk9MWQ3Yjg1ZWEtMDIxZi00MTIzYWI1MA==