I believe there is a lack of bone for posterlateral fusion with MIS TLIF because surgeon is not removing the facet joints as in the open TLIF. The surgeon jsut removes the pars fractures on either side.
Does this sound accurate ?
IF you read sperryguy on your forum he had non fusion for the same reason. No gutter fusion and retractable cage was used. Kind of a stupid way to do the surgery in my opinion, Why take the risk?
In any event, when you start questioning details of the surgery like this with a surgeon they generally get angry and try to get rid of you. I have found that spine surgeons do not like to be told how to do the surgery. Even the most reputable.
Your method of open TLIF is the most conservative and logical that I have found. I have found couple other surgeons that do the same and they have great results.