For years, I used something very similar. It was a wire saw with rings on both ends. Sold in the plumbing supply area of Home Depot, etc. Nothing worked better on a pelvic bone.
Nowadays, I've gone to what some call the "Indian style" or "gutless field dressing" method for my deer and elk. Completely avoids the whole bladder/anus/pelvic issue altogether.
Fred EIchler Field Dressing an Elk - YouTube