Reason a dogs leg woud be tied to collar?

Neighbours sheepdog from a stable come over for a bit and I noticed the leg was in the collar, before I thought the dog was three legged but upclose its front right leg was stuck in its collar, obviously on purpose because its been like that for a while and they would of taken it out otherwise. Would there be any like reason for this...? maybe a sling..? I wouldnt want to untie the dogs leg if it was broken or something