I have not had these, but my wife has had 3 CT guided injections (Aug 2006, Jan 07 and June 07) for Spondylolisthesis with associated stenosis at L4-5 L5-S1 arising from degenerative osteoarthritis. In the course of these injections she has not had any of the more apparent problems (ie infection which is apparently 1:20000 initially but with increasing risk with each injection). She has suffered intense pain for 1-2 weeks post injection with improvements being gained 3 weeks to 1 month later. For the first two treatments she was able to resume gardening (to some extent) and to limit her analgesia to Paracetamol/Codeine 500mg/15mg.
Coming up to the most recent injection (June), the pain increased rapidly necessitating analgesia escalating to 2xParacetamol/Codeine 500mg/30mg 4 hourly then to Oxycodone (5 mg 2x daily). After the last injection, she spent 2 weeks in bed with no improvement after 1 month - now on Oxycodone or SR morphine (which is not a good place to be)
Comments at this point from the rheumatologist: injections can provide relief for many - but 3 in 12 months is too much & inviting complications, particularly with the (complete) lack of efficacy seen in the latest treatment. It is appears that the preferred "conventional treatment" ends with the injections and that these are continued until no benefit is obtained. The more radical approach (surgery) is only considered when the injections fail.
The issues of infection appear to be of paramount concern in this procedure as many doctors in general practice fail to realise what is going on. If one has any symptoms of infection urgent informed treatment is recommended.
Not sure if this helps, but reflects my wife's experiences to date. Next stop the neurosurgeon.