Hi XXXXXX,,.
Which leg is it that causes the problem ?
What did the x ray show?
Are the pain meds helping at all?
Did the Vet tell you to keep her well rested for a while?
When you say limp do you mean she lifts it and does not walk on it or does she fall over it like she is drunk?
My thought is a possible disc problem in the spine if the leg x rays came back with no torn ligaments, hip problems, or arthritis and usually strict rest and anti inflammatory meds as well as possible pain medication are given first, however this may not work and steroids may need to be tried if the rest and pain meds do not work. A regular x ray may not pick up a disc problem in the spine, sometime a myelogram needs to be done (x ray with dye). Boxers are prone to intervertebral disc disease and if the problem is in the lower spine the rear legs may be affected, if it is in the neck then the front legs may be affected.
My Newfoundland has it in the neck which makes him limp badly in the front leg and he was put on anti inflammatory drugs and pain meds when that did not work steroids from a neurologist were given and the problem was solved, until it comes back again which can happen.
Now the boser is also prone to degenerative myelopathy which is a progressive degeneration of the spine with sadly no cure.
http://www.petplace.com/dogs/degenerative-myelopathy/page1.aspx
Boxer prone illnesses http://www.petplace.com/dogs/choosing-a-boxer/page2.aspx
dog training consultant
24 years training & behavior,pet first aide, Therapy dog eval., PA Animal Response Team