eli5: Why can we bend our index finger’s first joint freely but we can’t bend our other fingers first joint(thumb excluded) without the others slightly retracting?

Question

eli5: Why can we bend our index finger’s first joint freely but we can’t bend our other fingers first joint(thumb excluded) without the others slightly retracting?

In: Biology

Answer 1

… YOU can’t. I can do this with the first joint of my middle fingers just fine. With some practice and stretching, _probably_ so could you.

–Dave, and this is WITH the neuropathy making it impossible for me to cross my fingers any more without outside help