This is a jukugo word, which usually means on'yomi readings from the kanji. This word, however, uses the kun'yomi readings. This is possibly because of 手, because body parts often use kun'yomi. You learned both readings with the individual words, so you should be able to read this.
My older sister has a mole on her left hand.
Please raise your left hand.
I was stung by a bee on the elbow of my left arm.
What you can see on your left-hand side is the Sky Tree.