Minimally-invasive tubular surgery is an emerging technique applied in the treatment of patients with spinal metastasis. Previous studies reported that spine metastatic tumor could be safely resected through a tubular retractor with even less tissue destruction and quicker functional recovery than mini-open and conventional surgery. The present study provides a more comprehensive analysis to evaluate the perioperative safety and efficacy of this technique for patients with primary tumor of different vascular supply and guide surgeons to select the best candidates.
In this study, VAS, Karnofsky score, and ECOG of both groups were significantly improved after surgery. The difference between two groups was not statistically significant in VAS, Karnofsky score, ECOG, AIS and ambulatory status. Besides, HGB, Hct, and Alb were significantly declined post-operation in both groups. We attempted to compare the change of HGB, Hct, and Alb in both groups that may reflect the degree of surgical trauma. The results showed that HGB decreased more significant in conventional group after surgery. Similar to previously study [15–19], tubular surgery had significantly less blood loss, less blood transfused, less drainage and shorter postoperative hospitalization compared with the conventional surgery. However, we found intraoperative cauterize was difficult for patients with hyper-vascular tumor, such as renal cell cancer. Hyper-vascular tumor usually bleeded until they are completely resected. This finding encouraged us to conduct a sub-analysis of our current data and the result showed that compared with hyper-vascular tumor such as renal cell, patients with hypo-vascular tumor would benefit more tubular surgery. This result was different from mini-open surgery and was mainly due to the limited vision under the tubular [7, 9]. Compared with mini-open surgery, tubular surgery had more stricter criteria on tumor type. For patients with hyper-vascular tumor, mini-open technique should be given priority. However, considering the advantages of more fast recovery of tubular surgery, preoperative arterial embolism or other intervention maybe performed to control the bleeding during operation for patients with hyper-vascular tumor. Although preoperative arterial embolism had been proven to reduce blood loss in conventional surgery, its role in tubular surgery remains to be confirmed by further studies.
The incidence of surgical complications for conventional surgery is higher in patients with symptomatic spinal metastases. Surgical trauma and perioperative complications often affect the continuity of subsequent treatment . All minimally invasive spine surgeries are characterized by less physiological insult and early mobilization and rapid recovery. Our results suggested that patients who underwent tubular surgery recover faster than patients underwent conventional surgery. They would have more opportunity to receive adjuvant therapy such as radiotherapy at early stage postoperative, which played an essential role in the local tumor control . Regrettably, our study showed tubular surgery had no significant advantage on operation time compared with the conventional surgery. Besides, the operation time and complication rate were relatively higher than the previous study performed by  and Nzokou A et al . The complications of the tubular surgery were mainly dural tear. The learning curve for the utilization of an emerging technique must be taken into account when performing such a surgical strategy. Previous study focused on the learning curve of Mis TLIF and suggested that decompression through a tubular retractor was a higher technical requirement with relatively long operation time and more complications at the early stage. Silva PS et al. analyzed 150 patients with the degenerative lumbar disease who underwent MI-TLIF. The most frequent complication was a dural tear (5.32%), and the complication rates were 33% and 20.51% for 50% and 90% learning milestones, respectively. They reported that 90% of the learning curve would be achieved around the 40th case . The Operation time and complication rate will improve with the growth of this technique's learning curve in the future.
Short-segment fixation, not including the decompressed segment, was used at the initial stage in trans-channel decompression surgery. Besides, the transverse connection could not be applied due to limited exposure. Because of the poor holding power of the screws for patients with spinal metastasis and osteoporosis, displacement of the pedicle appeared during follow up. In order to avoid the occurrence of internal fixation failure, Harel et al.  and Zirai et al.  recommended extending the internal fixation segment or applying the cement screw technique. Besides, Harel et al.  suggested screw should be placed on the healthy side of the decompressed segment to convert the bridge structure into a classic three-point fixation, thereby increasing the holding power of the screws and overall stability.
There are limitations to the present study. First, it was limited by its retrospective and non-randomized nature and there would be a particular bias in patient selection. To minimize the selective bias, we strictly limited the screening criteria for patient’s selection. Table 1 showed that there were no significant differences in the baseline characteristic between two groups. Second, the relatively small sample size may affect the outcomes available for analysis. A large-scale, prospective, randomized study should be carried out to validate these results. However, this study provides important information regarding applying this technique to treat spinal metastasis. In addition, this technique's characters make itself more suitable for patients with multiple comorbidities who are at high risk of perioperative complications .
In conclusion, this study showed that minimally-invasive tubular surgery is safe and effective for selected cases with spinal metastasis. Patients with hypo-vascular tumor were more suitable for this technique with less blood loss, less blood transfused, less drainage and shorter postoperative hospitalization.