Hi Aussie ~ The thecal sac is a membrane of dura matter that surrounds the spinal cord and the cauda equina. The thecal sac is filled with cerebral spinal fluid.
I would imagine if it's gone, the spinal cord is more open to injury & damage. I'm not sure tho ~ I'm just assuming.
There is still the spinal cord at L5. I don't know what he's thinking.
You need to think strongly about ANY injection that a doctor wants to do. ANY injection can cause problems such as infection, arachnoiditis, etc. I've never had any luck with any of the injections but my pain doc made me have them anyway. When I didn't show up for one because my husband DIED - he fired me!!! Nice, huh?
Anyway ~ best of luck in whatever you decide. God bless. Hugs, Lee