Step I Rectus femoris abscess

[stronghold]

I have just encountered a UW question. In one of wrong choices explanation, it states that a patient with rectus femoris abscess would favor extension of the knee!
I am confused because I know that rectus femoris (supplied by femoral n.) flexes the thigh and extends the knee. Hence, extension of the knee means that muscle in action!
Why does a patient with rectus femoris abscess, according to UW, favor knee extension?

 

[Diagnose]

Maybe they would favor the knee to be in a extended position, but not necessarily favor the act of extending the knee.

 

[Moose A Moose]

I hear what you're saying. It has me scratching my head as well.

I would venture that the patient would prefer extension over flexion because in the position of knee flexion all the quadricep muscles are being stretched, and that must produce pain due to the pulling force on the muscle fibers vs abscess (the abscess may have some scar tissue surrounding it thus inhibiting proper function). Regarding the action of contraction/extension- that would be shortening the sarcomeres and pulling them in closer together thereby relieving pain due to strain [of flexion] in the muscle fibers of your rectus femoris.

That's the best i got.

 

[Morsetlis]

Well, punch yourself in the thigh and see whether it feels better with knee extended (muscle is loose) or flexed (muscle is stretched). Think about how people lie in hospital beds. 😉