What’s the difference between a lumbar floating fusion and a lumbosacral fusion? My surgeon has talked to me about the pros and cons of these two procedures but I can’t keep them straight in my mind. Please remind me which is which. Oh, I have something called degenerative spondylolisthesis.

Low back pain from degenerative spondylolisthesis is often treated with spinal fusion when conservative (nonoperative) care fails to improve symptoms or function. In this condition, one of the vertebrae (spine bones) slips forward over the one below it.

Normally, the bones of the spine (the vertebrae) are neatly stacked on top of one another. Ligaments and joints support the spine. Spondylolisthesis alters the alignment of the spine and creates a narrowing of the spinal canal. As the bone slips forward, the nearby tissues and nerves may become irritated and painful. Low back pain and leg pain are the main symptoms but there can be sensory changes with numbness, tingling, and loss of sensation as well.

The degenerative aspect of spondylolisthesis tells us the condition develops over time as we age. Adults over age 50 are affected most often. There are degenerative changes in all parts of the spine including the joints, discs, and soft tissues. Slippage at the L4-L5 segment is the most common in this age group with this condition.

Without the normal alignment, spacing, and proper shock absorption, load is transferred through the spine. The disc at the L5S1 spinal level takes the brunt of it, so this is the area where degenerative disc disease is the worst in many patients.

Removal of the disc between L4-L5 with fusion of the same segment is referred to as a lumbar floating fusion or LFF. LFF is separate from a lumbrosacral fusion (LSF) where the L5 segment is fused to the main body of the sacral bone.

The procedures are used to reduce pain, increase activity level, and improve daily function. There is some speculation that extending the L4-L5 floating fusion down to include the L5-S1 segment (making it a lumbosacral fusion) might improve the results.

But according to a recent study comparing these two fusion levels, the extended fusion increased the risk of adjacent segment disease above the start of the fusion. Without this extension, the surgery was shorter and with less blood loss. There is also the advantage of less bone graft and a lower risk of pseudoarthrosis (failed fusion with spine motion still present) with the lumbar floating fusion.