Yes, I have had the exact surgery that your ortho surgeon is recommending, which I am assuming is a fusion of L4-5.
I have to tell you that mine did not turn out well, but I also had other problems at that level and above and below L4-5 that were not addressed at the time of surgery that resulted in my having such a terrible outcome. So please take that into account when considering surgery.
Both a neuro and ortho spine surgeon who is fellowship trained and certified have completed the same training, just in different specialities.
The spine is a complex web of the spinal cord, vertebre, ligaments and tendons, as well as nerve roots that exit each spinal level in pairs. One nerve root exits on each side of the vertebra at the different levels.
An xray unfortunately is not going to tell you whether or not there is compression of the spines nerve roots. That can only be seen through MRI's and CT scans. A spondylolysthesis ( spond-ee-lol-lis-the-sis) is the slippage of one vertebral level over another one. The degree of slippage determines what, if anything needs to be done. There are 4 degrees of slippage- the first degree is a slippage of less than 25% of the vertebra's width, second degree is 50% or less and more than 25% , third degree is more than 50% but less than 75%, and the fourth degree is more than 75% but not 100%.....The reason that you are having trouble standing and walking is because the slippage causes the spinal nerves ( it is no longer a cord per se at the lumbar area of the spine- but it is instead the nerve roots before they pair off into the foramina- little holes that allow the nerve root to exit the spine proper), to be tugged upon by the vertebra's slippage. The more the nerve roots are tugged upon, the more the nerves become impacted and can be compressed.
A fusion would bring the vertebra at L4-5 back into the proper spinal alignment, which would also relieve the tugging on the nerves. This should fix the problems, and after recovery time, you should find that you are able to walk, shop and live your life without the problems that you are currently having.
I do want to encourage you, that the majority of spinal fusions do turn out well. That is the reason that they continue to do them. On forums , unfortunately, you find people like me who had problems that may have caused or contributed in some fashion to the surgery not turning out as planned. I am one of them.
I would do as Stray recommended, first, have the MRI and see what the report says and what the recommendations are from the surgeon you have seen.. It seems that you are comfortable with him and believe that he has the credentials to give you his best result.
But, you should also consult with a board certified spine neuro surgeon and see what he says. Don't be surprised if you find that you get slightly different recommendations from each surgeon. Since spondylolysthesis is a "structural " problem , at least so far, if you are comfortable with the ortho, I would tend to go with him.......
If I can be of any further help, just ask away.