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The Spine Blog

Monday, February 13, 2017

What are the benefits of MIS?

Minimally invasive surgery (MIS) techniques have been developed and widely adopted to treat lumbar degenerative conditions. However, there are no high quality RCTs comparing outcomes and complications between MIS and open surgery (OS) for lumbar spondylolisthesis, the most common indication for lumbar fusion. In an effort to fill this gap, Dr. Lu and colleagues from the Mayo Clinic performed a meta-analysis comparing MIS to OS for lumbar spondylolisthesis (both degenerative and isthmic spondylolisthesis were included). They identified 10 observational cohort studies, 5 of which were prospective and 5 of which were retrospective. The studies included 602 patients treated with MIS and 274 with OS. According to GRADE classification system, the 5 prospective studies offered low quality evidence and the 5 retrospective studies were of very low quality. Overall, the ages, gender distribution, and levels fused were similar for the MIS and OS groups, though some individual studies did have more pronounced baseline differences. Meta-analysis revealed the mean blood loss was 330 mL less and LOS was 1.7 days less for the MIS patients. No significant differences were observed for operative time, complications, or patient reported outcomes on the Oswestry Disability Index or visual analog scale.

This meta-analysis likely represents the highest quality evidence available comparing MIS to OS for lumbar spondylolisthesis. However, given the low and very low quality of the included papers, the overall strength of the evidence provided by this meta-analysis is also relatively low. It comes as no surprise that MIS offers the advantage of less blood loss, though given that transfusion following one level open decompression and fusion is uncommon, it is not clear that this provides a clinically meaningful benefit. The LOS advantage also needs to be scrutinized as half of the included studies had mean LOS over 6 days for both the MIS and OS groups, and one had a mean LOS of 10 days for MIS and 14 days for OS. Length of stay tends to be much lower in the United States, with 1-3 day stays being more typical for MIS or OS. Additionally, LOS is frequently affected by provider and patient expectations rather than more objective characteristics like mobility or analgesic requirements. An unbiased comparison of LOS differences would only be possible with a study design in which the patient and inpatient care team were blinded. The major limitation of the included studies, and thus the meta-analysis, is the risk of selection bias. Treatment type was determined by the patient and surgeon rather than by randomization, so the MIS and OS patients may have been very different. The authors provided very little baseline data (i.e. age, gender, number of fused levels), so it is not possible to compare factors known to affect outcomes such as comorbidities, psychosocial characteristics, body mass index, smoking status, work status, and baseline patient reported outcomes. The authors have done a nice job working with the low quality evidence that exists, though meta-analysis is not statistical alchemy, and the strength of its conclusions are limited by the quality of the included studies. This and other studies make it clear that MIS techniques decrease blood loss. Whether or not MIS leads to faster mobilization, decreased post-operative pain, and long-term outcomes equal to OS remains to be seen. The spine community awaits an RCT to answer these questions.

Please read Dr. Lu’s paper in the February 1 issue. Does this change how you view the benefits of MIS? Let us know by leaving a comment on The Spine Blog.

Adam Pearson MD, MS

Associate Web Editor