'Joints' in the Bible

A certain man drew his bow at random, and struck the king of Israel between the joints of the armor. Therefore he said to the driver of his chariot, "Turn your hand, and carry me out of the battle; for I am severely wounded."

A certain man drew his bow at random, and struck the king of Israel between the joints of the armor. Therefore he said to the driver of the chariot, "Turn your hand, and carry me out of the army; for I am severely wounded."

Then the king's face was changed in him, and his thoughts troubled him; and the joints of his thighs were loosened, and his knees struck one against another.