Enhanced Recovery after an Innovative Percutaneous Endoscopic Transforaminal Lumbar Interbody Fusion for the Treatment of Lumbar Spinal Stenosis: A Prospective Observational Study

Background The objective of this study was to investigate the enhanced recovery clinical effects of an innovative percutaneous endoscopic transforaminal lumbar interbody fusion (PE-TLIF) for the treatment of patients with LSS and degenerative instability. Methods From January 2019 to March 2020, 51 patients with single-segment LSS and degenerative instability were prospectively included in our study (ChiCTR1900020679). The Oswestry Disability Index (ODI), the visual analogue scale (VAS) on lumbar and leg pain (VAS-LBP and VAS-LP), serum creatine kinase (CK), the peak intensity of sulphur hexafluoride microbubble contrast agent (PI), and the maximal cross-sectional area of multifidus muscle (Max-CSA) around the surgical incision were assessed preoperatively, postoperatively, and at regular follow-up. Results All patients were followed up. The mean postoperative bedridden time was 20.45 ± 2.66 hours. The ODI, VAS-LBP, and VAS-LP were improved significantly after operation compared to these data before operation in all the patients (P < 0.05). The CK at 1 day after operation was higher compared to the data before the operation (P < 0.05), and there was no significant difference on CK at 1 week after operation (P > 0.05). The PI at 1 week after operation was higher compared to this item before operation (P < 0.05), and there was no significant difference on PI at 1 month or 3 months after operation (P > 0.05). The Max-CSA at 1 week after operation was higher compared to this item before the operation (P < 0.05), and there was no significant difference in Max-CSA at 1 month or 3 months after operation compared with before the operation (P > 0.05). Conclusions Our results and systematic review presented the innovative PE-TLIF technique could obtain satisfactory and effective outcomes for the treatment of patients with LSS and degenerative instability. Our PE-TLIF technique also had the ability to decrease the MF injury and obtain an enhanced recovery.


Introduction
Lumbar spinal stenosis (LSS) is the most common type of lumbar degenerative disease for people with low back pain [1]. Several patients need to receive operation treatment due to the inefficiency of conservative treatment to alleviate the severe pain [2]. Conventional posterior lumbar fusion surgery is considered as the standard operation for patients with LSS [3]. However, extensive striping and retraction of muscle and other soft tissue usually caused some approachrelated complications, especially postoperative tremendous back pain [4]; meanwhile, postoperative bedridden time was always extended.
Some studies showed that paravertebral muscle atrophy was clinically related to low back pain [5,6]. e multifidus muscle (MF) is an important structure in paravertebral muscles, and MF atrophy is considered to be associated with low back pain [7]. Recently, it was reported that the volume of the multifidus muscle was dramatically decreased after the open posterior lumbar fusion [8]. Hence, it is necessary to perform a minimally invasive lumbar surgery to decrease the injury of the MF and shorten the postoperative rehabilitation period.
Endoscopic lumbar fusion techniques have gradually gained popularity in the past several years, and we have also developed an innovative minimally invasive surgery named percutaneous endoscopic transforaminal lumbar interbody fusion (PE-TLIF) [9]. e preliminary results of our technique were satisfactory, but the injury of the MF and enhanced recovery were not evaluated in our previous study.
Hence, we conducted a prospective observation study on the MF injury via contrast-enhanced ultrasonography after PE-TLIF for the treatment of patients with LSS to provide evidence of obtaining an enhanced recovery. Meanwhile, we further investigated the clinical effects of PE-TLIF in order to provide good evidence for clinical practice.

Material and Methods
From January 2019 to March 2020, 51 patients with singlesegment LSS and degenerative instability were included in our study (ChiCTR1900020679). e eligible criteria were as follows: (1) patients with LSS and degenerative instability on L4/5 level; (2) patients treated by PE-TLIF; (3) no lumbar surgery history; (4) no obvious multifidus muscle injury; and (5) no lumbar deformity. e exclusion criteria were as follows: (1) patients were unable to finish the follow-up; (2) patients with other comorbidity could affect the lumbar fusion; and (3) patients with other comorbidity could affect the serum creatine kinase. All patients were told all possible results during the study and signed written consent before the operation. e study was approved by the institutional review board of Beijing Chaoyang Hospital.
Appropriate perioperative assessments were conducted for all patients before the operation. 51 patients were operated by the PE-TLIF technique. ere were 37 females and 14 males, and the average age was 58.98 ± 8.64 years. Operative level was L4/5. Operation time, intraoperative bleeding volume, postoperative drainage volume, and postoperative bedridden time were recorded. e intervertebral fusion was evaluated via the Bridwell criteria at 6 months after the operation. e Oswestry Disability Index (ODI), visual analogue scale (VAS) on lumbar and leg pain (VAS-LBP and VAS-LP), serum creatine kinase (CK), the peak intensity of sulphur hexafluoride microbubble contrast agent (PI), and the maximal cross-sectional area of multifidus muscle (Max-CSA) around the surgical incision were calculated via contrast-enhanced ultrasonography at 1 week, 1 month, 3 months, and then at final follow-up ( Figure 1).

Surgical Techniques.
e patients were in a prone position. General anesthesia or low-dose epidural anesthesia combined with local anesthesia was applied during the PE-TLIF surgery. e C-arm fluoroscope was employed to confirm the surgical lumbar segment. e primary guide pin was inserted into the pedicle of the symptomatic side, and a specially designed SAP guider was used to put the secondary guide pin into fixation at the superior articular process (SAP). en, dilating cannulas were inserted gradually through the secondary guide pin. A hook-shaped front of the cannula was applied to ensure the majority of SAP was excised safely by trepan ( Figure 2). e endoscope system was connected after the working channel was placed through Kambin's triangle. e canal and nerve root were decompressed with the surveillance of the endoscopy (Figure 3), and then the complete endplate preparation was performed ( Figure 4). e acceptable extent of endplate preparation under endoscopy was the appearance of hemic exudation from the bone endplate. An expandable cage (Shanghai Reach Medical Instrument Co., Ltd, Shanghai, China) with iliac bone autograft was then inserted through the working channel. Iliac bone autografting and adequate bone graft size (≥5 mm 3 per intervertebral space). e nerve root was confirmed to be totally relieved via endoscopy once again. Finally, four pedicle screws and two rods were inserted percutaneously. e active bleeding was stopped under the surveillance of endoscopy, and the incisions were sutured. More details on the PE-TLIF technique were described in our previous study [9].

Statistical Analysis.
e data were analyzed by SPSS 17.0 software with chi-square and Fisher's exact test for nominal data and an independent t-test in continuous data. A statistically significant difference was determined when P < 0.05.

Results
All patients underwent PE-TLIF surgery successfully. e mean operation time was 202.65 ± 27.52 minutes. e average intraoperative bleeding volume was 125.20 ± 40.41 ml. e average incision length was 8.54 ± 2.22 cm. e mean postoperative bedridden time was 20.45 ± 2.66 hours.
All patients were followed up, and the average follow-up period was 18.70 ± 4.54 months. e ODI at 3 months after the operation and at final follow-up were improved significantly compared to the data before operation in all patients (P < 0.05). e VAS-LBP and VAS-LP at 1 week, 3 months, and 6 months after the operation and at final follow-up improved significantly compared to these data before operation in all the patients (P < 0.05) ( Table 1 and Figure 5). e CK at 1 day after the operation was higher compared to the data before the operation (P < 0.05), and there was no significant difference in CK at 1 week after the operation (P > 0.05). e PI at 1 week after the operation was higher compared to this item before the operation (P < 0.05), and there was no significant difference in PI at 1 month, 3 months after the operation, and also at final follow-up compared to this item before the operation (P > 0.05). e Max-CSA at 1 week after the operation was higher compared to this item before the operation (P < 0.05), and there was no significant difference in Max-CSA at 1 month 3 months after the operation, and also at final follow-up compared with this item before the operation (P > 0.05). More details are listed in Table 2.
All the patients finished the intervertebral fusion at 6 months after the operation. According to the Bridwell criteria, 23 patients were rated as Grade 1, 24 patients as Grade II, and 4 patients as Grade III. One patient suffered temporary knee tendon hyperreflexia after surgery and recovered within 24 hours after surgery.

Discussion
is is the first prospective observation study on the MF injury via contrast-enhanced ultrasonography after PE-TLIF for the treatment of patients with LSS and degenerative 2 Pain Research and Management instability at present. Our present results showed that the MF injury in the PE-TLIF technique could be recovered at 1 month after the operation, and the CK at 1 week after the operation was restored to the status before the surgery. e ODI and VAS were significantly improved for all the patients via the PE-TLIF surgery. e mean postoperative bedridden time was less than 24 hours. e MF plays an important role in the preservation of lumbar segmental stability and stiffness [10]. e MF is the most medial component of the lumbar paraspinal muscles and is only innervated by the medial branch of the dorsal ramus, without intersegmental nerve supply [11]. Hence, iatrogenic denervation of the MF usually occurs during the dissection and retraction in conventional posterior lumbar Figure 1: Contrast-enhanced ultrasonography was used to demonstrate the blood perfusion of the multifidus muscle microcirculation. Figure 2: Resection method of the superior articular process. e hook-shaped protective sleeve clings to the lateral periosteum of the superior articular process, reaches the ventral side of the articular process, protects the exiting nerve root and can control the cutting depth of the trephine at the same time, protects the dura mater and nerve root, and rotates the trephine to remove the superior articular process.
Pain Research and Management 3 fusion surgery. Some researchers believed that postoperative muscle atrophy was related to iatrogenic denervation of the paraspinal muscles during the operation [12]. e MF atrophy was mostly associated with postoperative low back pain [8]. erefore, most spine surgeons demonstrate that decreasing the MF injury is vital for the improvement of the postoperative functional outcomes and shortening the rehabilitation period. Hence, minimizing the MF injury during the surgery gradually became a pursuing goal. Minimally invasive spine surgeries (MISS) have gained popularity to decrease the muscle-related injury on the conventional open surgeries. Schwender et al. first described the minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF), and the technique showed the potential advantages in the aspect of soft tissue injury over conventional open techniques [13]. However, the placement of screws in the MIS-TLIF technique is very similar to conventional open surgeries, so the medial branch of the dorsal ramus is usually injured, which could increase the possibility of the MF atrophy. Regev et al. believed that percutaneous screw placement was able to decrease the indirect injury of the medial branch nerve from 84% to 20% [14]. erefore, more and more surgeons have begun to attempt endoscopic lumbar fusion techniques with percutaneous screw fixation for lumbar degenerative diseases.
In our study, we developed an innovative endoscopic fusion technique named PE-TLIF, and the initial clinical results were favorable [9]. Postoperative serum CK level was considered as a marker of intraoperative related muscle injury [15]. e CK level was recovered to the preoperative level in all the patients, which was consistent with the previous report [16]. e minimally invasive technique could reduce the injury extent of the muscle. CSA was rated as a valuable indicator of MF injury. Some studies showed that the postoperative CSA of the MF was significantly smaller than the preoperative status [16,17]. In our study, there was no difference in the Max-CSA via contrast-enhanced ultrasonography between the preoperative level and the level at 1 month after the PE-TLIF technique. We also investigated the PI through contrast-enhanced ultrasonography, and the PI was restored to the preoperative level at 1 month after the PE-TLIF technique. e CK, Max-CSA, and PI were higher than the preoperative items in the early postoperative stage, which was mostly associated with the intervertebral space is fully prepared and the appearance of exudation from the bone endplate is good, the bony endplate is fully exposed. e width of the bone graft bed is in a fan-shaped area greater than 13 mm at the proximal section and 15 mm at the distal end.       To obtain a comprehensive understanding on endoscopic lumbar interbody fusion, we did a systematic review on endoscopic lumbar interbody fusion for the treatment of lumbar degenerative diseases until December 2020. Finally, 20 studies were included in our present systematic review (SR) [9,[18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35][36]. Most studies presented that the endoscopic lumbar fusion technique was a promising treatment for lumbar degenerative diseases, with less muscle injury and quicker rehabilitation. e fusion rate was 59.6%-100%, and the complication rate was 0%-36%. However, there were no standard operating procedures and specific indications of endoscopic lumbar interbody fusion. More details are listed in Tables 3 and 4.
To the best of our knowledge, this is the first prospective observational study on MF injury via contrast-enhanced ultrasonography after PE-TLIF for the treatment of patients with LSS and degenerative instability at present. All surgeries were performed by one senior surgeon. Several data on the characteristics of patients and clinical effects were reported in our study. e core part of our innovative technique is to excise the majority of SAP safely and effectively. We innovated a hookshaped front of the cannula, which could be a very useful tool to excise SAP, while could protect soft tissues and nerves. e contradiction on our technique is the severe central type of LSS. However, certain limitations need to be addressed. Our study lacks the conventional control group, and the number of patients is relatively small. More prospective randomized controlled trials are needed to overcome the limitations of our study.
In conclusion, our results and SR presented the innovative PE-TLIF technique could obtain satisfactory and effective outcomes for the treatment of patients with LSS and degenerative instability. Our PE-TLIF technique also had the ability to decrease MF injury. Patients with PE-TLIF could have a quicker postoperative rehabilitation.

Data Availability
e data used to support the findings of this study are available from the corresponding author upon request. Disclosure e trial registration number is ChiCTR1900020679. e small parts of involved items have been published in a preprint [37].

Conflicts of Interest
e authors declare that they have no conflicts of interest.

Authors' Contributions
Peng Yin and Haifeng Gao contributed equally to the study.