I was born with Spina Bifida Occulta at L5... and had tight hamstrings since childhood. Over time (years), due to multiple microtraumas of life, L5 fractured away from the pars bilaterally, resulting in unstable spondylolisthesis. It is now what is considered Grade 2-3.
However, I wasn't diagnosed (officially) until I was 50 years old. By then, I had already been going to a doctor of Physical Medicine and Rehabilitation for seven years... and he thought I had multiple sclerosis... even though lesions did not show up on MRIs. I found the word on an old accident report I had saved from when I was 21 and brought it to my doctor's attention. He ordered MRIs and said, "Whatever you do, don't get surgery."
The rest is in my book titled: Living With Symptomatic Spondylolisthesis: A Personal Survival Guide, available on Amazon. You can view the Table of Contents and introduction when you click on Look Inside.