The majority of the report is age related degenerative changes consistent with what you would expect for a 42 year old man. An L5 transitional vertebrae is a congenital anomaly found in a small portion of the population, I pasted in a small paragraph that explains a little bit about what it is.
In transitional lumbosacral vertebrae, usually the last lumbar vertebra (L5) or the first sacral vertebra (S1) are formed improperly. People are born with this condition. Normally, when the vertebrae develop, they are clearly formed to represent different sections (for example, lumbar vertebrae or sacral vertebrae). In transitional lumbosacral vertebrae, one of the vertebrae does not form as part of the lumbar or sacral area. It is as if this one vertebra cannot make up its mind whether to be become a lumbar vertebra or a sacral vertebra. The result is that this vertebra winds up taking on characteristics of both the lumbar and sacral vertebrae. In other word, it is like a combination of the two. This is where the term transitional comes in because transitional means to be in a state of becoming something else.
Source : http://www.medfriendly.com/transitionallumbosacral.html
It has previously been shown that there is a relationship between the presence of a transitional vertebra and low back pain, with or without pain in the leg. Hopefully his Doctor's taking a look at this.
Take Care
Back pain radiating down legs.
Exactly what type of pain is he having, is it all in his low back or does it go down his leg or what?