ankle
踝 centers on the ankle, the joint connecting foot and leg.
踝 combines 足 (foot) with 果, which likely contributes the sound and relates to the rounded shape of the ankle bone.
The left side 足 means foot, and the right side 果 looks like a fruit. Picture a fruit-shaped swelling at the foot: that's the ankle.
For カ, imagine a car running over your ankle: car -> カ, and the pain shoots through your foot.