Knee-ankle connector (4)
I believe the answer is:
shin
'knee-ankle connector' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for shin that I've seen before include "bit of leg" , "Front part of the leg between knee and ankle" , "letter from Israel" , "Cut of beef; part of leg" , "Part of the lower leg" .)