My little Jack Russell has had an occasional limp (alwys her left front leg). I feel along the leg and she has no tender areas. Twice I took her in and she was not limping by the time of appointment so they could not see what I meant and her lef and hip checked out fine. This last appointment, I got her in the next day and she was still limping. I think they took me more serious and ordered xrays of her leg, hip and spine.
Leg and hip again are fine with no arthritis or other problems. But she does hve a narrowing between two vertebra in her neck. The disks get compressed just as peoples do. Since she is only 6, he thought it was not age related, but possibly from an old jumping injury. He said when she is extra active, it inflames the area and presses against the nerves, making her limp a bit. It is not a big problem, and he said she should be fine with a little anti-inflammatory for a few days whenever it bothers her.
I was relieved it was not a worse problem. I could also relate as I have disk problems too that seem to affect my left arm most. We have matching infirmaries!
Might not be the same for you, but if you want to check, all it takes is an xrqy of the spine. They did hers when she was getting her dental done and already sedated.