What is a sinew?
A sinew is a piece of tough fibrous tissue uniting muscle to bone; a tendon or ligament.
This does not appear to be a direct commandment, rather, it seems to be recognition of a traditional way of honoring the patriarch Jacob— not eating the sinew of the hip which is on the socket of the thigh— since that is the place where G-d touched Jacob as they wrestled (Genesis 32:25).
Here you can also find the question: Why don’t we eat the sciatic nerve? The person’s question actually makes more sense to me than the answer. This is my honest point of view; yet I would really appreciate your feedback and help on this Mitzvot.
According to an article written in blogspot, epistoli.blogspot.hk,
This particular duty or obligation belongs to the mitzvoth of kashrut, a set of duties that may or may not make a lot of sense but are required in order to help the Jewish believer tame his/her ego, or to help them set boundaries or limits in life.
I find the above statement more sensible. Furthermore, here is an interesting read on the significance of the Sinew to the children of Israel and Israel as a nation. The symbolism behind can well be read below:
The symbolism of this mitzvah is that the Jews will endure suffering at the hands of other nations – including our brother Eisav – but that we will always persevere and never disappear. This message is driven home by attaching it to a mitzvah.