You have a pars defect at L5-S1 this is a separation of the bony ring that surrounds the spinal cord at the rear of the vertebrae. Your MRI report states that it has not changed since it was last imaged.
A pars defect can result in spondylolisthesis this is when one vertebra slips forward in relation to the others. this probably has not happened in your case as the bone has only separated on one side but that may change in the future. A successful outcome from surgery is never guaranteed but the best person to know whether you need surgery is an highly qualified surgeon if you choose surgery make sure the surgeon is highly recommended and get a second opinion.
The other problem you have is the abnormal curvature of your spine this probably needs to be addressed as well if you see any phsios chiros or osteopaths make sure they are aware of your pars defect or they could aggravate it.