Hi,
"Arthropathy" means joint disease, so in your case it would mean there is joint disease in your facet joints on both sides of your spine. The facet joints are small joints that connect each vertebrae and there's one on each side of each vertebrae. So it's probably arthritic in there, though what you reported doesn't mention if the facets have any osteophytes (bone spurs) or enlargements. And it is occuring on both sides of the vertebrae at your 2 lowest lurabar vertebrae. Usually when the facet joints get too much strain on them (which could be due to degenerating disks), they have more than the usual stress on them. This in turn, can cause these joint bones to thicken and form bone spurs, and these spurs can end up taking up too much space around nearby nerves. This can end up causing lots of pain. And I can't be sure, but the fluid collection might be localized inflammation because it's all irritated in there. So yes, the L4 through S1 are in your lower spine..and yes, problems in your spine can radiated to other areas of your body. Plus you might start walking differntly or limping, and this causes more strain on other body parts. So it can be a vicious domino effect.
Did your doctor offer up any treatments to try?