I had knee replacement surgery around April 1, everything healed really well, but two weeks ago, while bending over, I got a sharp pain in my upper thigh. When I put weight on that leg now, it feels as if the leg will give out, but it is not in a joint. It is in the upper side of my high. I also had a hip replacement in that leg 17 years ago. Do you have any idea if this is a strain or something more serious.