Those suggesting that the object was a lawn edging tool are wrong, though I see the similarity. The object is remotely medical though more of a post mortem instrument than a therapeutic one. And you have to think big.
It is in fact a flensing knife, used by 19th century whalers to strip the blubber from a dead whale. It was also known as a blubber spade. In those days the entire whale could not be lifted onto the ship and the flensers had to do their job on the whale while it was still in the water. The instrument had a secondary use, that of fending off sharks attracted to the carcass.
This has a relevance to my last post. If you could get 3 litres of biodiesel from liposuction you could possibly get ten times that much by flensing and rendering a deceased obese person.