Hello Moyra

A baker's cyst is an excess (effusion) of the fluid that usually lubricates your knee joint.  If the joint gets irritated for any reason - arthritis, an injury etc - extra fluid is produced that makes it feel stiff, swollen and often hot.  If too much fluid builds up in the delicate membrane that surrounds the joint, it can eventually burst out of the fibrous bag that protects the membrane.  This is a bit like a bicycle tyre that has split and the inflated inner tube bulges through it.  It usually splits in the back of the knee and causes the painful bulge.  Treating the cyst is futile, you have to deal with whatever is irritating your knee.  I would suggest using ice on the front and sides of your knee for 5 to 10 minutes at a time (a bag of frozen peas wrapped in a tea towel).  Don't put the ice at the back of your knee, this might interfere with the fluid drainage from the lower part of your leg leading to swelling or even thrombosis.  Put your leg up whenever you can but keep it moving. 

A light compression bandage may help especially when you are driving.  If you don't want to take anti-inflammatories by mouth (NSAID) then you can get them in  a gel or cream form that you can rub around your knee - wash your hands after applying so you don't absorb the drug anywhere you don't need it.  You may get some relief from gentle manipulation of your knee by an osteopath, physio or chiropractor.  Other people reading this may be able to suggeat natural remedies to do the same thing - that isn't my expertise.

Sometimes if there is too much pressure within the membrane it can be drained off (aspirated) by a doctor;  few GPs do this simple procedure now, so unless you can afford to go privately you may have to wait months for an appointment to see a specialist to do a simple 5 minute procedure.  As you say you have had it many years, it may be that you have some debris in your knee that occasionally causes irritation and leads to the effusion and cyst.  This may need to be washed out, a simple surgical procedure done in outpatients (you may have difficulty walking for a few days after though).

Anyway, hope this helps and that you will soon be galloping around instead of hopping!

Regards

Peter, osteopath