First off - love the signature.
Since you're talking injury, I assume jumping is out? If not, burpees are usually recommended around here. Also known as squat thrusts. You could also by-pass the the planking/push-up part and do high tuck-jumps. Start in squat, explode up and lift your knees up as if you were to cannonball into a pool (they do that in England too, right?) as you come back down break your fall by going into a squat again and jump right back up. Repeat 10-15 times for 3 sets or so.
Harder than it sounds.