A Novel Inextensible Endoscopic Tube Versus Traditional Extensible Retractor System in Single-Level Minimally Invasive Transforaminal Lumbar Interbody Fusion: A Prospective Observation Study.

BACKGROUND Currently, various retractor systems are widely used for access to the lumbar spine in minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF). Nevertheless, studies concerning the comparison of extensible retractor and inextensible tube systems are quite rare. OBJECTIVES This article was to compare perioperative characteristics, clinical outcomes, and multifidus muscle injury of obconic inextensible tube versus extensible retractor system for single-level MIS-TLIF. STUDY DESIGN A prospective observational study on 91 patients with a mean follow-up of 20.0 ± 4.1 months. SETTING This study was conducted by a university-affiliated hospital in a major Chinese city. METHODS From April 2015 to May 2016, 91 consecutive patients who underwent MIS-TLIF procedure using an obconic inextensible endoscopic tube or extensible retractor system were enrolled in this study. Operation parameters such as incision length, blood loss, postoperative drainage volume, surgical time, analgesic use rate, time to ambulation, and postoperative hospitalization days were evaluated. The concentration of white blood cells, interleukin-6, interleukin-8, tumor necrosis factor alpha, and creatine phosphokinase (CPK)-MM of the enrolled patients were measured for postoperative traumatic stress and muscle injury. Multifidus muscle edema and atrophy were evaluated by T2-weighted magnetic resonance imaging (MRI) at 3 different time points (preoperative, postoperative, and 1-year follow-up). Clinical outcomes such as Visual Analog Scale (VAS) score, Japanese Orthopedic Association (JOA) score, Oswestry Disability Index (ODI) score, fusion rates, and MacNab criteria were assessed for patients' symptoms. RESULTS In terms of baseline characteristics, the 2 groups were similar regarding sample size, gender, age, symptoms duration, operation level, body mass index, physical examination, and all the clinical outcomes measures (P > 0.05). Perioperative analysis showed that the inextensible group had comparative incision length, blood loss, operation time, time to ambulation, and postoperative hospitalization (P > 0.05). The inextensible tubular group had less postoperative drainage volume and analgesic use rate (P < 0.05). The concentration level of CPK-MM and c-reactive protein (CRP) was lower in the inextensible tubular group compared with the extensible retractor group.No significant difference was found between the 2 groups regarding MRI T2 signal intensity ratio of multifidus muscle at the immediate postoperative period. The MRI T2 signal intensity ratio of multifidus muscle was lower in the inextensible tubular group than the extensible retractor group at the 1-year follow-up period. The VAS scores for low back pain and leg pain improved significantly in both groups after surgery, as did the JOA and ODI scores. However, there were no significant differences between the 2 groups regarding the preoperative and final follow-up VAS, JOA, and ODI scores, fusion rates, and the distribution of the MacNab criteria. LIMITATIONS This was not a randomized controlled trail, which could provide more evidence-based medicine conclusions. CONCLUSIONS The obconic inextensible endoscopic tube system via the transforaminal approach for lumbar interbody fusion is a safe and sufficient technique. When compared with the extensible retractor system, it has comparable clinical outcomes, with additional significant benefits of less postoperative drainage volume and analgesic use rate, less multifidus muscle injury in terms of lower CPK-MM levels at immediate postoperative period, less change in CRP, and less change in MRI T2 signal intensity ratio of multifidus muscles at 1-year follow-up. KEY WORDS Minimally invasive, endoscopic, lumbar interbody fusion, tubular, multifidus muscle.