Decompression versus decompression and fusion for degenerative lumbar stenosis: analysis of the factors influencing the outcome of back pain and disability.

BACKGROUND The objective of this study is to evaluate the factors influencing the outcome of back pain and disability in patients operated for lumbar stenosis without instability and deformity using two classical surgical techniques: decompression alone and decompression plus fusion. METHODS This is a retrospective cohort study of patients who underwent lumbar surgery with standard posterior decompression or standard posterior decompression plus pedicle screw fixation for degenerative lumbar stenosis without deformity, spondylolisthesis or instability at our department from June 2010 to January 2014. They were divided into two groups: decompression group (D) and decompression-fusion group (F). We analyzed the following factors: age, gender, levels of stenosis, pre-surgical "micro-instability", and post-surgical "micro-instability". RESULTS A total of 174 patients were enrolled in the study. Both Graphic Rating Scale (GRS) and Oswestry Disability Index (ODI) scores were significantly decreased after surgery (P<0.001). Female patients appeared to have lesser improvements from surgery, for both D and F groups. An analysis of variance using the decrease of pain (GRS pre-post) as dependent variable and type of surgery, age, gender and their interaction as factors showed that the main effects of type of surgery and gender were significant. The analysis of variance for the decrease of pain (GRS) and disability (ODI) according to the levels of stenosis showed a significant interaction for GRS scores. Female patients that underwent fixation surgery reported the least improvement in disability. A significant interaction was found on the one-way analysis of variance for the D group without pre-surgical micro-instability using post-surgical micro-instability as factor. CONCLUSIONS Our study supports posterior decompression alone as the gold standard option as treatment for lumbar stenosis without instability and deformity. Additional fusion should be considered only to prevent post-surgical instability. The "micro-instability" is a radiological finding that has its clinical surrogate but is not able to guide the choice of the type of surgery. Moreover the significance of "micro-instability" is still unclear. We suggest a prospective study following patients with asymptomatic micro-instability to definitively understand the clinical history.