Assessment of Paraspinal Muscle Cross-sectional Area After Lumbar Decompression: Minimally Invasive Versus Open Approaches.

STUDY DESIGN A retrospective, blinded analysis of imaging studies. SUMMARY OF BACKGROUND DATA To evaluate changes in paraspinal muscle cross-sectional area (CSA) after surgical treatment for lumbar stenosis and to compare these changes between minimally invasive and standard open approaches. The open approach to lumbar stenosis is effective, but it involves retraction and resection of muscle from the spinous process, which can result in ischemia and denervation of paraspinal musculature and may lead to muscle atrophy and pain. OBJECTIVE It is hypothesized that the microendoscopic decompression of stenosis (MEDS) technique will better preserve the paraspinal muscles compared with the open procedure. MATERIALS AND METHODS A total of 18 patients underwent a 1-level posterior decompression for lumbar stenosis, (9 open, 9 MEDS). Lumbar magnetic resonance imaging was obtained before surgery and after surgery (open approach average 16.3 mo; MEDS average 16.6 mo). CSA of paraspinal muscles were averaged over the distance of the surgical site. RESULTS The mean age of patients treated with the open and MEDS approaches were 55.2 and 66.4 years, respectively (P=0.07). Paraspinal muscle CSA decreased by an average of 5.4% (SD=10.6%; range, -24.5% to +7.7%) in patients treated with the open approach and increased by an average of 9.9% (SD=14.4%; range, -9.8% to +33.1%) in patients treated with MEDS (P=0.02). For the open approach, changes in CSA did not differ significantly between the left and right sides for erector spinae (P=0.35) or multifidus muscles (P=0.90). After the MEDS approach there were no significant differences between the dilated and contralateral sides with regard to change in CSA for erector spinae (P=0.85) or multifidus muscles (P=0.95). CONCLUSIONS Compared with the open approach for lumbar stenosis, MEDS had significantly less negative impact on the paraspinal muscle CSA. Previous reports have documented negative effects of paraspinal muscle injury, including weakness, disability, and pain. Collectively, these data suggest that the MEDS approach for lumbar decompression is less destructive to the paraspinous muscles than the open approach and may facilitate better clinical outcomes.