But I love information, so I've been trawling for sites about problems in dogs' limbs. I've come across a chapter, presumably for vets, on observing dogs moving in order to diagnose an illness. There are interesting line drawing of the walk, the trot, the pace and the gallop. The article says:
As a quadruped, the dog has the ability to spare an injured joint or sore leg in such a way that the abnormality may be almost unnoticeable; the ability to shift the center of mass in an attempt to decrease weight bearing to any limb is remarkable...the clinician can be misled regarding forelimb and hindlimb weight-bearing modes. It is possible for a dog to move from a sitting to a standing position and begin walking without touching its hind limbs to the ground.Okay, so now I don't feel so silly that we can't make out what is going on with Penny's movements!
It also says:
Dogs with subtle gait changes or lameness may exhibit these signs only to their owners or handlers who notice the change in the dog's gait...The owner or handler may be able to describe his impression of the dog's problem quite accurately. It is important to know the duration of the dog's problem, if the onset was acute or chronic, and if the condition is improving or deteriorating.