Last week I saw a dog for some vaccines. The owner happened to mention that he had been limping for a few days (often seems to work that way..."Oh, by the way, doc..."). When I was looking at him I quickly noticed that he didn't want to put any weight on this left hind leg, and some manipulation isolated the problem to his hip. I was able to put a finger of each hand on the point of the femur and noticed that my fingers were uneven. So my first thought was that somehow he had dislocated his hip. A quick set of radiographs confirmed my suspicion.
Looking at the images you can see that the hip is completely out of the socket and displaced slightly dorsal ("up") and cranial ("forward"). It takes a pretty good injury to move a hip this far, as the femur is normally very tightly held in the socket. There is a short, tough ligament connecting the bones, as well as a capsule around the joint. Displacing a hip this far requires a tear of that ligament and likely a tear in the joint capsule.
Depending on the severity of the injury, it can be possible to put the hip back into place without surgery. However, extensive damage to the connective tissues can mean that the hip will dislocate again easily. In cases like this, surgery is the only option for a cure. In this case it seemed like a pretty bad dislocation so I referred the dog to a specialist for a further consultation. With proper treatment, these cases can have a very good outcome.