What is the best medication to increase the synovial fluid between knee joints ?

Synovial fluids: No proven medications.

Artificial : Joint fluid given by injection. There are several brands. It is only used when the joint arthritis is advanced and used in the knees.

Some options: Glucosamine tabs may help. There are also injections with a material called synvisc (hylan g-f 20). Staying hydrated is important.

Probably none: The best way to help large joints like your knees is regular exercise, like walking. Pounding, twisting, or wrenching your knees may make them worse. Bicycling may be best of all, but be sure your seat is high enough. Glucosamine sulfate (not the hcl version) has some scientific evidence of benefit; you need 1500-2500 mg per day. It has little risk. You have to take it for months before it works.

Synovial fluids : There are no medications that increase synovial fluid in knee joints. Proper hydration and plenty of fluids will be of help.