INTRODUCTION
Minimally invasive decompression (MID) is an established, reliable surgical option for lumbar spinal stenosis (LSS) with degenerative spondylolisthesis (DS). However, simple decompression is characterized by degenerative changes, such as slip progression and secondary instability, leading to negative surgical outcomes and revision surgery. The precise post-decompressive courses in this context are not well known. The purpose of this study was to prospectively evaluate the advantages and disadvantages of MID for LSS with DS.
METHODS
We conducted a 2-year follow-up. The inclusion criteria were LSS with a slip rate ≥10% at L4-5 in the neutral position on a standing radiograph, disruption of daily activities by radiculopathy or neurogenic claudication without previous lumbar surgery, and microscopic bilateral decompression using a unilateral approach at L4-5. This study enrolled 46 patients (14 males and 32 females) with an average age of 70.9 ± 8.4 years. The average slip rate in the neutral position was 17.2% ± 5.8%. Clinical evaluation included the Japanese Orthopedic Association (JOA) 15-point scoring system (where 0 indicates the greatest severity) and a VAS for low back pain, pains in buttocks and lower limb, and numbness in buttocks and lower limb (0–10, where 10 indicates the most severe symptom). For radiographic evaluation, the slip rate and lumbar lordosis (LL) were calculated on standing lateral radiographs in flexion, neutral position, and extension. For mobility, the difference between the slip rate measured in flexion and extension, the range of motion at L4-5, and the difference in LL between flexion and extension were used. The Wilcoxon signed-rank test with Bonferroni correction was carried out to determine the differences in each parameter across three different time points (before, 1 year after, and 2 years after surgery). A risk of 5% was considered significant.
RESULTS
Two patients dropped out of the study. Leg symptoms recurred in six patients; four of them had temporary deterioration due to a juxtafacet cyst at L4-5 (n=2) or L5-S (n=1), or an intraforaminal disc herniation (IFDH) at L4/5 (n=1). They responded well to facet joint block or selective nerve root block without reoperation. The other two patients required reoperation due to IFDH at L4/5 or LSS at L2/3 and L3/4. In 42 patients (excluding the dropouts and reoperated patients), the VAS for clinical symptoms improved 1 year after decompression but did not change thereafter. In contrast, the JOA score improved each year. LL in the neutral position and extension increased 1 year after decompression, whereas the other radiographic parameters did not change during follow-up.
DISCUSSION
MID preserving facet joints and spinous processes can be a reliable surgical option for LSS with DS, leading to satisfactory outcomes without slip progression or secondary instability. In addition, MID can improve posture from forward bending, facilitating back extension, which can also counteract post-decompressive slip progression. Degenerative changes at the decompressed and adjacent segments could cause symptom deterioration, many of which are temporary and curable by conservative treatments, and the reoperation rate may be lower than expected.