• Jwo-Luen Pao, Wen-Chih Chen, Chih-Hung Chang, Chiang-Sang Chen, and Jaw-Lin Wang.
• *Institute of Biomedical Engineering, College of Medicine and College of Engineering, National Taiwan University, Taipei Departments of †Minimally Invasive Spine Surgery ‡Orthopedic Surgery, Far-Eastern Memorial Hospital, New Taipei §Department of Mechanical Engineering, College of Engineering, National Taiwan University, Taipei, Taiwan.
• J Spinal Disord Tech. 2014 Dec 1; 27 (8): E318-23.

Study DesignA retrospective case series study.ObjectiveTo investigate the clinical significance of postdecompression facet effusion (PDFE) after microendoscopic decompressive laminotomy (MEDL).Summary Of Background DataThe facet joint effusion noted on magnetic resonance imaging was considered as an indicator of degeneration of the facet joints and segmental instability. PDFE occurring after MEDL might imply postdecompression segmental instability. Its clinical significance has not yet been clarified.Materials And MethodsFrom 2005 to 2010, 165 patients with degenerative lumbar spinal stenosis (average age: 64.5, average follow-up: 25.8 mo) who received MEDL were reviewed. We investigated the incidence of PDFE with preoperative and repetitive magnetic resonance imaging at 6 months postoperatively. The clinical data and treatment courses were reviewed. The treatment outcomes were evaluated with Oswestry Disability Index and Japanese Orthopedic Association scores.ResultsThe incidence of PDFE was 17.0% (n=28), which was significantly higher in patients receiving multilevel decompression and patients with scoliosis or spondylolisthesis. The intensity of low back pain was similar between patients with and without PDFE, but "mechanical" low back pain was only noted in patients with PDFE. Of the 28 patients with PDFE, only 9 symptomatic patients required invasive treatment (5 facet joint steroid injection, 3 revision MEDL, and 1 spinal fusion). Although the postoperative Oswestry Disability Index and Japanese Orthopedic Association scores were significantly worse these 9 patients, the final outcomes were good. Progression of spondylolisthesis was noted in 2 patients without PDFE but no patients with PDFE during the follow-up period.ConclusionsThe relatively high incidence of PDFE after MEDL suggests that injury to the integrity of facet joint is inevitable during decompression of the stenosis, even using minimally invasive techniques. However, the overall stability is well preserved with very rare progression of spondylolisthesis. Most patients with PDFE are asymptomatic. The prognosis of PDFE is very good. Spinal fusion is rarely indicated.

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