It does appear that your isthmic spondylolisthesis needs to be repaired surgically. Your transitional segment is probably stable unless there is a full separation between S1 and S2 (very unlikely). Many times, the X-ray is obvious in that there is a large transverse-alar articulation which generally means this transitional level is stable. See Bertolotti’s syndrome on this website. If there is any question, a CT scan can settle this question.
I almost always use a TLIf for these cases. It allows the nerves to be fully decompressed, allows both an anterior and a posterior fusion through only a posterior approach, allows great fixation through instrumentation and there is no need for bone graft as the broken lamina should be removed and acts as a wonderful bone graft. I like that the TLIF surgeon does not want to reduce the slip. Generally, any reduction can stretch the L5 nerve roots and cause some injury.
Just a posterolateral fusion without the TLIF is not enough fusion mass and has a high pseudoarthrosis rate. The ALIF without posterior fixation has a higher pseudoarthrosis rate and even the ALIF with posterior fixation has a higher chance of residual nerve pain.
The ALIF will not reduce your chances for ASD (adjacent segment disease).
Dr. Corenman
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.