Transforaminal full-endoscopic ventral facetectomy: mid-term results and factors associated with poor surgical outcomes

BACKGROUND CONTEXT: 
Full-endoscopic spine surgery (FESS) is a well-established procedure for herniated nucleus pulposus. It is a minimally invasive surgery that can be performed under local anesthesia through only an 8-mm skin incision. With improvements in surgical equipment such as high-speed drills, the indications for FESS have expanded to include lumbar spinal stenosis (LSS). We perform transforaminal full-endoscopic ventral facetectomy (TF-FEVF) for unilateral nerve root-type lateral recess stenosis (LRS) using a transforaminal approach under local anesthesia.
PURPOSE
The aim of this study was to examine the postoperative results of TF-FEVF for LRS and to identify factors associated with poor surgical outcomes.
STUDY DESIGN 
Retrospective study.
PATIENT SAMPLE 
85 patients who underwent TF-FEVF for LRS under local anesthesia.
OUTCOME MEASURES
Clinical outcomes were determined by visual analogue scale (VAS) and the modified MacNab criteria. Evaluation was performed using magnetic resonance imaging (MRI), computed tomography (CT), and flexion-extension radiographs.
METHODS
This study involved 85 patients (47 male, 38 female) who underwent TF-FEVF for LRS. The mean age was 70.5 years and the mean follow-up duration was 14.8 months. Data were collected on sex, age, level of operation, diagnosis, history of spine surgery at the same level, and duration of follow-up. The diagnosis was categorized as lumbar spinal stenosis with or without disc bulging. Clinical evaluation was performed using the VAS and modified MacNab criteria. MRI was used to evaluate the degree of disc degeneration, vertebral endplate degeneration, disc height, thickening of the ligamentum flavum, and stenosis. Bony stenosis was evaluated using CT. Sagittal translation and sagittal angulation were also measured by flexion-extension radiographs, and Cobb angle was measured using a standing front view radiograph. All variables were compared between patients with excellent/good outcomes (E/G group) and those with fair/poor outcomes (F/P group) using the modified MacNab criteria.
Results
Postoperative VAS showed that leg pain decreased from 59.0±28.6 preoperatively to 17.9±27.2 at final follow up (P<0.01), and that lower back pain also decreased from 60.7±26.6 preoperatively to 27.3±28.6 at final follow up (P<0.01). According to the modified MacNab criteria, the results during the final follow-up were excellent in 39 cases, good in 21 cases, fair in 13 cases, and poor in 12 cases. There were no significant differences in sex, age, diagnosis, history of spine surgery, and duration of follow-up periods between the 60 cases (70.6%) in the E/G group and the 25 cases (29.4%) in the F/P group. Imaging evaluation revealed statistically significant differences between the E/G group and the F/P group in intervertebral angle flexion (3.2° vs 0.4°, P<0.05), sagittal angulation (4.3° vs 8.1°, P<0.05), slip in flexion (0.9mm vs 2.8mm, P<0.05), sagittal translation (0.7mm vs 1.6mm, P<0.05), and Cobb angle (−0.5° vs −1.9°, P<0.05).
Conclusion
Mid-term results of TF-FEVF were generally favorable; factors contributing to good or poor TF-FEVF outcomes were large sagittal angulation, large sagittal translation, and concave side. 
