Hi Louise

Due to the long duration of your symptoms I would suggest there is more of a muscular imbalance at fault for your symtpoms, especially in the abscence of any trauma to the knee.

I would expect you would have some tightness in the hamstrings and calf muscles so would start with lots and lots of stretching for these muscles specifically and probably the quads/hipflexors, atleast 2-3 times daily, I usually prescribe 3x30seconds for each muscle in one set.

The weakness you describe going down stairs would suggest poor eccentric control of your quadriceps, start some strengthening for these with isometric VMO exercises, progressing to IRQ and SLR with good VMO contraction, then onto wall squats with emphasis on the lowering phase, double leg and then single leg and then single leg lowering on a step using affected leg. Knee alignment is very important, keep hip knee and toes straight! If any cause pain then your prob progressing to quick or going to low, take your time, strengthening takes a long time. Would also suggest some glut strengthening aswell as these are normally weak i.e. clamshell exercise, single leg wall push, single leg bridge.

If these help and pain reduces continue with regular stretches and add in some calf and hamstring strengthening once muscles are suitably lengthened.

Althou I agree heat, tens, ultrasound may help control pain, I dont see how these would give lasting relief in long standing symptoms like yours. Deep tissue massage would be useful along with the stretches if your feel certain muscles are particularly tight.

This is only going off what you have mentioned and from my experience, but hope it helps! Any questions then please ask. I appriciate you might not know some of the abbriviations I've used but if you type them in google it will come up as will the exercises!!

Glenn