Hi Wobblyknee, thanks for your post. Essentially the main difference between climbing stairs and walking on the flat ground is the angle/range of movement that the joints are working in differs between the two. The knee joint is operating more flexed/bent state when climbing stairs and less so when walking on the flat. Also the load on the knee is being taken in a flexed state with the knee cap more secured in place on stairs and it is located in a different position when walking. The nerves running from the low back down the back of the leg at also on more stretch walking that on climbing stairs so if the pain is referred in origin, then this would also be taken into consideration.

All these factors would be useful to take to a followup examination and treatment plan with your therapist. Ahead of that you could try to refine the specific mechanics of the pain even more.e.g try to find out where in the motion of walking the pain becomes evident. Such as: As the leg is swinging, when the heal hits the ground, as you transfer the weight, when the leg is fully loaded...... Armed with that information your therapist should be able to do a few more tests to pin point the origin and provide you with the next steps in the progression of treatment.

What you are reporting is not uncommon although often people might be fine climbing stairs but have pain descending stairs.

Let us know what you find and how you get on.