Dogs and knees

I have no cartilage in my right knee.  As a result of this I have to be careful with it.  I can run and do marathons etc, I just have to train carefully and build up slowly.  Once the surrounding muscles are strong enough I can pretty much do anything I want with the knee without pain or problems.  One thing that I can not do though is sleep with it twisted.  If I sleep with my knee twisted I will be in pain.  Guaranteed.  For the past 3 days my knee has been hurting pretty bad.  I hadn't run all week so wasn't sure what was going on.  I tried all my usual remedies to fix it and got nothing.  I went for a run yesterday and it was fine on the run but it hurt the rest of the day.  At some points the pain was pretty bad.  When I got home yesterday from some errands I laid down to rest my knee and as I rolled over on to my side it hit me what was wrong.  The last week or so Axl has been sleeping at the foot of the bed on my side.  Sometimes I can not put my legs straight and they end up twisted.  I realized I have been sleeping that way and that's what's wrong with my knee.  Sure enough, last night I made it a point to keep my leg and knee straight all night and it feels much better this morning.  Who knew sleeping dogs could cause knee pain???