The intervertebral disc height will be lost after the degeneration of the intervertebral disc, causing the instability of the spine and the relaxation of the ligamentum flavum, which could be regarded as one of the most important mechanism leading to the stenosis of the lumbar spinal canal[12]. At present, there are direct decompression and fusion operations such as PLIF and TLIF and indirect decompression surgery such as D/XLIF for the treatment of lumbar spinal stenosis. There are also cases of OLIF for the treatment of lumbar spinal stenosis reported in the literature[13–14]. To date, this is the first report of stand-alone OLIF in the treatment of lumbar spinal stenosis.
In this study, the effect of indirect neural decompression was evaluated by comparing the preoperative, postoperative and the final follow-up of DH and FH in terms of X-ray imaging. The results showed that both postoperative DH and FH were significantly higher than those of preoperation, which was contributed to the large OLIF cage. What’s more, we can clearly observed the excision of herniated intervertebral disc as well as the stretching and thinning of the ligamentum flavum through MRI image (Fig. 6). It indicated that the indirect spinal canal decompression of OLIF is achieved by increasing the height of intervertebral disc and intervertebral foramen and restoring the length and tension of ligamentum flavum. Previous literature also showed similar results. Lin et al[15] measured 25 patients who received OLIF with and without posterior internal fixation and found that average DH was significantly restored from 8.97 mm preoperatively to 13.44 mm postoperatively, and FH was significantly increased from a mean of 19.68 mm before surgery to 23.42 mm after surgery. In the authors’ experience, the cage could be placed as far back as possible for patients with lumbar spinal stenosis so as to distract the intervertebral space to the greatest extent. On the contrary, the cage should be put forward for patients with lumbar spondylolisthesis, which is conducive to the reduction of spondylolisthesis. Something interesting was found that the results of both DH and FH decreased at the last follow-up compared to those of postoperation, but still higher than those before surgery, with statistical significance. We thought it was due to cage subsidence without posterior pedicle screw fixation.
Complications played an important role in the clinical outcomes. In this study, there were a total of 27 cases of complications in the intraoperative and postoperative stages, including 8 patients with two or more combined complications. Therefore, there were actually 19 patients, and the complication incidence was 30.2%, which was similar to those reported in the previous literature[6, 16]. Herein, stand-alone OLIF complications can be divided into two parts, approach-related complications and cage-related complications included. There were 13 cases were approach-related complications, with a rate of 20.6%, including leg numbness 17.4% (11/63), vascular injury 1.6% (1/63) and peritoneal injury 1.6% (1/63). The similar result was also reported by Abe et al[17] who reviewed 155 patients received OLIF and found that approach-related complications were 16.1%. However, the most remarkable complications were cage-related complications for stand-alone technology. 10 patients (15.9%) with cage subsidence and 1 patient (1.6%) with cage displacement were observed. In a recent study, Zeng et al[18] found that the early complication incidence of stand-alone OLIF group was 36.26%, which was higher than that of OLIF combined posterior pedicle screw fixation group, being 29.86%. This was owing to the higher incidence of cage sedimentation in the stand-alone OLIF group than in the OLIF combined posterior fixation group. Therefore, some researchers advised posterior internal fixation in single stage for all patients undergoing the OLIF procedure because they worried about the limited relief or aggravation of clinical symptoms due to cage subsidence. As far as I'm concerned, stand-alone OLIF was sufficient for selected patients. It was believed that large cage could not only provide a more effective biological environment for the fusion process but also reduce the incidence of cage subsidence. Besides, the OLIF cage with 6 degrees of lordosis angle we used in the operation increased the lumbar lordosis from 38.0°±15.6° preoperative to 42.7°±13.0° at the final follow-up. In addition, Hresko et al[19] indicated that the recovery of lumbar lordosis was beneficial to increase the tension of anterior longitudinal ligament, which helped increasing the rate of spine fusion. Previous studies also exhibited the efficiency of stand-alone technology. Nitin Agarwal et al[20] investigated 55 patients with stand-alone LLIF with a ten year follow up and proved that stand-alone LLIF was a safe and effective surgical method. Solid arthrodesis and improvements in clinical symptoms using stand-alone XLIF were observed over 80% of patients in another study[21]. Zhang et al[22] analyzed a total of 45 segments in 22 patients using the OLIF procedure and found cage subsidence occurring in 15 fused segments. However, symptoms in all patients had been alleviated and pain were improved at the final follow-up. So he considered stand-alone OLIF as a safe and effective method for patients who require one- and two-level interbody fusion with the diagnosis excluding lumbar spondylolisthesis, degenerative scoliosis and spondylolysis. In the opinion of Schiffman, there was no direct relationship between the radiographic cage subsidence and clinical efficacy[23]. Ahmadian et al[24] investigated 59 patients with stand-alone LLIF and found that 9% of the patients remained clinically asymptomatic even if the their cage subsidence were high grade ( ≧ grade II). It was recommended that patients with osteoporosis, body mass index more than 30 kg/m2 or intraoperative endplate damage needed additional posterior internal fixation[18].
There are still some limitations in this study. Firstly, the cases were selected retrospectively. Secondly, the duration of follow-up was short. Further studies are required to ascertain the indications for single-stage or multistage internal fixation and posterior decompression.