Job description Reducing height of dead tree, Was straight forward, determined base of tree unsound to fell or rig safely due to rot, determined that attaching highline to tree behind to be safest option, due to tree behind having no head and being big mess decided that there was only two logical highpoint to provide adequate working access and chose one and set line. dead tree was collateral and removing of first main leader proved to be solid but there was bracken fungus up the second one and due to distance to lines I decided and unsure of tree safety I decided to cut from lower then anticipated earlier on ground during tree visual assessment. Spoke to observer if was safe to scarf he said he yes turn it up easement a bit. I did scarf clean and as was doing back cut I came around slightly more then intended and caused leader to turn a bit more and as it went it made contact with the end of the leader I was tied into on the tree behind which shock loaded and tore off the tree. A terrifying couple of seconds as I realised and thought I'm gone. Luckily my lanyard/pole belt was around the barrel of first leader and not a branch as the high ligh limb that I was tied into weighed around 200kg and ended up half way to the ground. It happened fast and I was left pinned to one side from the weight, Luckily the leader I scarfed out didn't stay attached to the highline leader or is have been ripped in half and dead one way or another. So I'm pinned by pole belt which had caught a side branch on dead tree and I'm struggling to breath due to the weight of the leader hanging, I tired to use my left arm to lower the leader wmbut my left arm wouldnt work. I realised i was in trouble I had searing pain from broken rib on left side and I'd torn my pectoralis major off the bone(humerus) completely which is called a complete avulsion and apprently a very very rare injury so much as the majority of physicians have never encountered one so I found out. Due to cutting with two hands and highline going through middle of arms as the leader i was tied into fell it ripped my left arm sideways and ripped my pec off bone instantly. I got rag dolled bit so I have no idea how the rib broke. So I'm hanging there and screaming out and left arm won't work and struggling to breath and everytime I try reach over with right arm I'm seperating my broken rib with the lanyard buckle on side of my harness and its causing me to almost blackout from pain. Some how I manage to lower the leader to the ground bit by bit but my offiader can't get it flat on ground. He's panicking hard and hyperventilating and tells me to cut my highline which I somehow managed to start chainsaw and cut it free and he came up and rescued me. Ironically the week before him and I both did our annual refresher aerial rescue from tree together at safety training refresher so it went smoothly and he was able to get me to hospital.