Larger back ankles are normal, (this is an adult male veiled with normal larger back ankles
http://s1293.photobucket.com/user/simca357/media/IMG_0603_zpstslvudfp.jpg.html) look at the first picture of OP chameleon's back ankles, there is a lot of swelling and slight buckling in the back part of the ankle facing us. Then is you look at the last one you see it follows into the front of the foot slightly. My panther has this (at a slightly worse amount) I have seen many veileds and other chameleons with this who were later diagnosed with MBD. The slight swelling is usually a sign of the beginnings of MBD.
As far as the 4 open feet, it's usually a resting position for the feet if one or just two are not gripping the branch while they are sitting on them. However all four not gripping when he is obviously uncomfortable is not normal in my opinion especially with the slight swelling and small bend in his ankle (i guess it would be his toes). Because this is not a normal thing for something that uses gripping to walk, it actually can cause pressure sores. If the OP did some close ups of the back feet I wouldn't be surprised to see swelling and bending.