Abstract
Objective
Unilateral biportal endoscopic (UBE) discectomy is a reliable endoscopic technique in the treatment of lumbar disc herniation. However, UBE discectomy involves a single-handed manipulation, which may compromise the utility of the procedure. The present study was performed to examine the efficacy and safety of a novel pin-assisted retraction technique.
Methods
This single-center retrospective cohort study involved 57 consecutive patients who underwent UBE lumbar discectomy from July 2021 to May 2022. The patients were randomly divided into the pin-assisted UBE discectomy group (P-UBE group) and the traditional UBE discectomy group (T-UBE group). The patients’ perioperative data, clinical outcomes, and radiologic outcomes were collected and compared between the two groups.
Results
The operative time, intraoperative blood loss, endoscopic irrigation volume, and overall complication rate were significantly lower in the P-UBE group than in the T-UBE group. There were no significant differences in the clinical outcome data between the two groups.
Conclusion
P-UBE discectomy may have superior safety and efficacy over the traditional technique, and it has the potential to serve as an optional method in UBE lumbar surgery.
Keywords
Introduction
Lumbar disc herniation (LDH) is the most common indication for spinal surgery. 1 The traditional open discectomy procedure has been widely replaced by minimally invasive surgery because of its advantages of less blood loss and faster recovery. 2 Among the various minimally invasive methods, the unilateral biportal endoscopic (UBE) decompression technique was first proposed in 2003 as a minimally invasive surgical technique for the treatment of LDH and spinal canal stenosis. 3 The UBE decompression technique is a percutaneous fully endoscopic technique performed through two separate small surgical wounds on either side of the spinous process. 3 The UBE technique is not confined by the working tube or working channel; therefore, it provides a larger field of vision and working space. 4 Furthermore, ordinary open decompression instruments such as dissectors, probes, and Kerrison rongeurs can be incorporated into the UBE procedure, lowering the instrument investment and shortening the learning curve. 5
UBE techniques have been successfully applied in patients with cervical, thoracic, and lumbar disorders.6–8 However, UBE techniques are single-handed manipulation procedures, which is a limitation. The surgeon must use one hand to constantly hold the endoscope and the other hand (sometimes the non-dominant hand) to hold the burr, Kerrison rongeur, or other instruments. When performing precise decompression and delicate manipulation of neural tissue, the surgeon must cooperate with a sophisticated assistant to maintain retraction or hold the endoscope, which increases the possibility of neural injury. 9 Furthermore, excessive insertion of the retractor into the working port may decrease the outflow of irrigation, resulting in a blurred visual field. 9 To overcome these limitations, use of an auxiliary port was reported in the UBE procedure, which improved the ease and safety of decompression and insertion of larger cages.10,11 However, such an auxiliary port results in an additional visible scar and compromises the cosmetic outcome.
In this study, a simple surgical technique was developed to overcome the above-mentioned limitations. A thin K-wire was passed through the port in the UBE device and pinned in the vertebral disc as a stable retractor for the nerve root. The present study was performed to evaluate the safety and efficacy of this technique in patients with LDH.
Methods
Patient population and grouping
This retrospective cohort study included 57 patients (37 male, 20 female) with one-level LDH from July 2021 to May 2022. The patients were consecutively enrolled and randomly assigned to either the pin-assisted UBE discectomy (P-UBE) group or the traditional UBE discectomy (T-UBE) group. The study was conducted in accordance with the guidelines of the Declaration of Helsinki and was approved by the ethics committee of Beijing Jishuitan Hospital (approval number: 202101-02). Written informed consent was obtained from each patient. All patients’ details have been de-identified. The reporting of this study conforms to the STROCSS 2021 guidelines. 12
The inclusion criteria were (1) neurogenic symptoms induced by LDH; (2) computed tomography and/or magnetic resonance imaging indicating single-level LDH and radiologic findings in accordance with the clinical neural distribution; (3) either progressive motor weakness or persistent disabling pain despite conservative treatment including physical therapy, nonsteroidal anti-inflammatory drugs, activity modification, and spinal steroid injections for 1 to 3 months; (4) follow-up for at least 6 months; and (5) enrollment in the study after the surgeon’s learning curve. The exclusion criteria were (1) lumbar instability, spondylolisthesis, or deformity; (2) tumors, infections, or other lesions; (3) a surgical history involving the corresponding segment; and (4) delayed treatment of cauda equina syndrome or other irreversible neural deficits.
All patients underwent operations by the same surgeon (J.XZ) to evaluate the surgical efficacy and complications of this new technique.
Instruments
The surgical procedure involved the use of a conventional 30° 4-mm rigid arthroscope (BD-1; Shenyang Shenda Endoscope, Shenyang, China), a 4.0-mm oval burr (Sterling; CONMED, Utica, NY, USA), a 3.75-mm radiofrequency ablation probe (Super TURBOVAC 90; Smith & Nephew, London, UK), and an instruments tool set for UBE decompression (Blon UBE tool set; Changzhou Blon Minimally Invasive Medical Devices Technology, Changzhou, China), including neural dissectors, soft tissue dilator, retractor, rotating Kerrison punches, and pituitary forceps (Figure 1(a)). A conventional K-wire (0.8 mm in diameter and 175 mm in length) and a K-wire bending clamp were also required (Figure 1(b) and (c)).
(a) UBE decompression tool set (Blon UBE tool set; Changzhou Blon Minimally Invasive Medical Devices Technology, Changzhou, China), including neural dissectors, soft tissue dilator, retractor, rotating Kerrison punches, and pituitary forceps. (b) and (c) K-wire bending clamp.
Surgical techniques
The patient was placed in the prone position on a radiolucent Jackson table after induction of general anesthesia. The skin and surgical field were prepared in the usual manner.
In the T-UBE discectomy group, surgical steps such as endoscopic port placement, preparation of the interlaminar space, laminotomy and ligamentum flavum removal, discectomy, and annulotomy were performed according to a description by Soliman. 3 Irrigation of normal saline was performed by the gravity method, with the saline placed 20 to 30 cm above the operation table.
In the P-UBE discectomy group, the surgical steps were in accordance with those in the T-UBE discectomy group except that after the nerve root was identified, a blunt dissector was used to ensure that the nerve root was free from adhesions and able to be retracted medially (Figure 2(a)). A retractor was then used to hold the nerve root to a desirable position. Next, the sharp end of a K-wire was slowly inserted into the working port under guidance by the retractor until it could be seen by endoscopy (Figure 2(b)). The K-wire was safely pinned into the intervertebral disc to a thumb-wide depth. Finally, the residual K-wire was bent at a right angle and hung on the incision (Figure 3(a)–(c)). If pin loosening occurred while performing the discectomy, a strip of adhesive surgical draping could be used to hold the pin in place (Figure 3(d)). Thus, the K-wire provided sufficient nerve retraction and optimal visualization of the herniated disc. Annulotomy and discectomy were performed with the assistance of the K-wire retractor (Figure 2(c)). At the end of the surgery, the K-wire was safely removed under endoscopic visualization, and the root decompression was confirmed using a 90° hook probe.
(a) The nerve root was retracted medially by a blunt retractor. (b) The sharp end of the K-wire was slowly inserted into the working port under guidance by the retractor until it could be seen with the endoscope. (c) Annulotomy could be safely performed under the protection of the pin retractor. (d) and (e) The position of the K-wire retractor was confirmed by biplanar fluoroscopy. White triangle: nerve root. White arrow: K-wire. White star: herniated disk.
(a) The K-wire was slowly inserted into the working port under guidance by the retractor. (b) The residual K-wire was bent at a right angle. (c) The pin was rotated and the bending point of the pin was hung on the incision, allowing the skin margin of the incision to cover the bending point and prevent the pin from loosening and (d) A strip of adhesive surgical draping was used to hold the pin in place. White arrow: K-wire.
Outcome evaluation
Data were collected perioperatively and at the 3-, 6-, and 12-month postoperative follow-ups. Perioperative data included the length of the operation, endoscopic irrigation volume, and complications. The complications were assessed via video records of the endoscopic procedure and clinical charts. Estimated blood loss was calculated by measuring the hemoglobin concentration in the washout fluid 13 and multiplying it by the irrigation volume. 14
Clinical outcomes were evaluated using the visual analogue scale for back pain and lower leg pain, the Oswestry Disability Index for functional recovery, and the modified MacNab criteria for overall treatment outcomes.
Radiologic outcomes were evaluated using preoperative, postoperative, and final follow-up magnetic resonance imaging and computed tomography (Figure 4). These imaging studies were used to verify the decompression effect and identify any possible postoperative complications, such as incomplete decompression, hematoma formation, or recurrent disc herniation.
A 36-year-old woman with L4/5 disc herniation underwent P-UBE discectomy and was followed up for 6 months. Preoperative and follow-up magnetic resonance imaging (MRI) and computed tomography (CT) results are shown. Preoperative MRI in the (a) axial and (b) sagittal planes. (c) Preoperative CT image. Six-month follow-up MRI in the (c) axial (d) sagittal planes and (e) Six-month postoperative CT image. White arrow: herniated disc.
Statistical analyses
Statistical analyses were performed using SPSS® for Windows, Version 17.0 (SPSS Inc., Chicago, IL, USA). Continuous variables are presented as mean ± standard deviation. For normally distributed variables, a two-sample t-test was used to compare the differences in perioperative data between the P-UBE and T-UBE discectomy groups. For non-normally distributed variables, the Wilcoxon rank sum test was performed. Categorical variables were compared using Pearson’s chi square test or Fisher’s exact test. A P value of < 0.05 was considered statistically significant.
Results
In total, 57 patients were retrospectively enrolled in this study. The follow-up period ranged from 8 to 16 months (mean, 12 months). The demographic data and preoperative clinical characteristics of the patients in both groups are summarized in Table 1. There were no significant differences in the baseline information between the two groups.
Baseline preoperative characteristics of patients in P-UBE and T-UBE discectomy groups.
Data are presented as mean ± standard deviation (range) or number of patients.
P-UBE discectomy, pin-assisted unilateral biportal endoscopic discectomy; T-UBE discectomy, traditional unilateral biportal endoscopic discectomy; VAS, visual analogue scale; ODI, Oswestry Disability Index.
No statistically significant between-group differences were found (P ≥ 0.05; two-sided Student’s t-test).
The clinical outcomes and operative findings are shown in Table 2. The operative time, intraoperative blood loss, and endoscopic irrigation volume were significantly lower in the P-UBE than T-UBE discectomy group (P = 0.003, 0.006, and 0.001, respectively). The 1-day postoperative evaluation revealed that all patients had substantial relief of their radicular pain. There were no significant between-group differences in the postoperative visual analogue scale score or Oswestry Disability Index score. In the final follow-up, patients in both groups showed similar pain relief and functional recovery. The overall clinical outcome evaluation according to the modified MacNab criteria revealed an excellent/good rate of 96.9% in the P-UBE discectomy group and 96.0% in the T-UBE discectomy group, and no statistically significant differences were found between the two groups.
Comparison of operative parameters and clinical outcomes between P-UBE and T-UBE groups.
Data are presented as mean ± standard deviation (range) or number of patients included in the statistical analysis.
P-UBE discectomy, pin-assisted unilateral biportal endoscopic discectomy; T-UBE discectomy, traditional unilateral biportal endoscopic discectomy; VAS, visual analogue scale; ODI, Oswestry Disability Index.
Continuous variables were compared using the two-sided Student’s t-test. Categorical variables were compared using Pearson’s chi square test or Fisher’s exact test. NS, not statistically significant (P ≥ 0.05).
Two patients in the T-UBE discectomy group developed small dural tears. Additionally, three patients in the T-UBE discectomy group developed a perineural hematoma detected by postoperative magnetic resonance imaging without any neural deficits, and the hematomas were fully absorbed during follow-up. No dural injury or hematoma formation was observed in the P-UBE discectomy group. No other complications occurred in either group. No reoperation was recorded during the follow-up period. The overall complication rate in the P-UBE discectomy group was significantly lower than that in the T-UBE discectomy group (P < 0.05).
Discussion
Traditionally, LDH is treated by open or microscopic discectomy via a midline lumbar incision. 15 However, extensive detachment of the paraspinal muscles from the lamina may cause postoperative pain, intraoperative blood loss, and muscle weakness. 16 Therefore, various minimally invasive and paraspinal muscle-sparing techniques have been developed to minimize injury to the posterior musculoligamentous structures.16–18 In 2013, Soliman 3 was the first to introduce the irrigation endoscopic discectomy procedure, which is now known as the UBE technique. Several studies have provided evidence supporting UBE discectomy as a reliable endoscopic technique in the treatment of degenerative lumbar diseases, including LDH 19 and lumbar stenosis. 20 A meta-analysis of the UBE technique reviewed 556 patients among 11 studies, and the average satisfactory outcome rate was 84.3%. 4 The mean overall complication rate was 6.7%, and the most frequently encountered complication in the UBE procedure was dural tear (mean incidence of 4.1%); other complications included epidural hematoma and incomplete decompression. 4 In the UBE technique, bleeding is controlled by the hydrostatic pressure of irrigation. 21 Bleeding vessels are sometimes covered by the nerve root or dural sac, making them unreachable without sufficient neural retraction; surgeons may thus misinterpret the status of hemostasis, resulting in postoperative hematoma formation.
According to our experience with the UBE discectomy procedure, the surgeon must become accustomed to single-handed manipulation and decompression. Because the surgeon needs one hand to hold the endoscope constantly, only the remaining hand (sometimes the non-dominant hand) is available to hold the burr, Kerrison rongeur, or other instruments. This situation is completely different from microdiscectomy. When performing precise hemostasis or delicate decompression of neural tissue, the surgeon must cooperate with a sophisticated assistant to maintain retraction or hold the endoscope, which can easily lead to neural injury. Furthermore, outflow of irrigation will be blocked by excessive insertion of the retractor into the working port, resulting in an unclear visual field. To overcome these limitations, auxiliary portals including the “quarterback portal,” 10 “far lateral portal,” 11 and “Zhang’s portal” 22 were reported in the UBE procedure, which improved the ease and safety of decompression and insertion of larger cages.10,11 However, auxiliary ports result in additional visible scars and compromise the cosmetic outcome. Other instruments, such as the scope retractor, 23 were inspired by uniportal endoscope, which allows the nerve to be retracted without the help of an assistant; however, such instruments cannot move freely and independently of the endoscope.
To maintain technical simplicity while not undermining the benefits of minimally invasive surgery, we developed the K-wire technique as a novel neural retractor. In our practice, a K-wire can be introduced from either portal of the UBE access depending on the surgeon’s preference. The whole process of placement and removal of the K-wire retractor occurs under direct endoscopic visualization. With the assistance of the K-wire retractor, the herniated disc was adequately exposed in the present study. Additionally, the residual K-wire was bent at a right angle and hung on the incision to prevent interference with the subsequent manipulation and dislocation of the K-wire retractor.
In this study, the operation time, irrigation volume, blood loss, and complications were all related to the surgeon’s experience and learning curve. In the early stage of practicing the UBE procedure, the surgeon must dedicate great time and effort to becoming accommodated to the new surgical setting and environment. To cope with the influence of the learning curve in this study, all cases managed during the learning curve and all cases involved in developing this new pin retraction technique were excluded from cohort enrollment. In other words, all cases in this study were enrolled after the period of the learning curve. To ensure scientific integrity and reliability, the cohort was continuously enrolled and randomly assigned to either group, and all procedures were performed by the same surgeon.
In endoscopic surgery, visual estimation of operative blood loss is unreliable and inaccurate.
24
In UBE surgery, the intraoperative hemorrhage is diluted in irrigation saline and collected in the washout. The simplest way to calculate the hemorrhage volume is to subtract the irrigation volume from the washout volume. However, hemorrhage in endoscopic surgery is relatively minimal, and the washout would soak the drapes and gauze and inevitably result in soft tissue edema; this would lead to inaccurate results. In the present study, the specimen was collected from the washout liquid and the hemoglobin concentration was measured in accordance with a previous report.
13
The blood loss volume was calculated according to the following formula:
14
The blood loss data are relatively accurate and reliable, which also explains why the irrigation volume makes sense.
In the present study, two dural tears and three epidural hematomas were observed in the T-UBE discectomy group, and all these complications were managed conservatively with no clinical sequalae. By contrast, no complication was recorded in the P-UBE discectomy group, and the overall incidence of complications was significantly lower in the P-UBE than T-UBE discectomy group; this indicates that use of a K-wire retractor may be a safe surgical technique. Moreover, with respect to the reduction in the operative time, intraoperative blood loss, and endoscopic irrigation volume, the surgical efficacy was significantly greater in the P-UBE discectomy group. There were no significant differences in the clinical outcomes during follow-up between the two groups. However, UBE discectomy is a relatively new technique, and long-term follow-up data are lacking. Compared with the currently available literature, the complication rate in the present study was average among similar follow-up periods. 4 Studies with much longer follow-up are critical to evaluate long-term outcomes such as recurrence and disc degeneration.
The general concept for disc health is preventing the healthy disc from undergoing any form of destruction. Because of the physiological and anatomical characteristics of the intervertebral disc, the healing potential of the intervertebral disc is relatively low. Nonfusion disc surgery should prevent unnecessary injury to the disc other than decompression. However, the disc still degenerates with age, which is why we should evaluate whether the destruction of the intervertebral disc will aggravate the degeneration of the disc. Several studies have shown that disc puncture and discography can increase the risk of clinical disc problems. 25 However, a more recent study concluded that patients with discogenic low back pain who underwent low-pressure provocative discography did not develop accelerated disc degeneration or new disc herniations. 26 Evidence on both sides can be reached, and it is difficult to draw a definite conclusion.
In the present study, in an effort to maximize patients’ benefit and minimize potential side effects, the finest K-wire currently available (0.8 mm in diameter) was chosen to minimize disc injury. The risks and benefits of the herein-described K-wire retraction technique should be carefully considered in terms of the long-term effects on disc degeneration. Two benefits are no need to inject toxic material, unlike in discography, and minimal invasiveness of K-wire puncture compared with discectomy performed simultaneously.
To minimize disc injury and annular defects caused by pin insertion, an 0.8-mm-diameter K-wire was used in this study. This is the finest K-wire currently available in our hospital, and it is strong enough to retract the nerve root. The working space of the UBE procedure is the inter-multifidus space. 27 The medial residual multifidus is close to the spinous process, which is thin and weak. Stronger muscle tissue and tension will be encountered during lateral retraction. The pin medially retracts the nerve root and medial residual multifidus, and little tension will be encountered at that moment.
The depth of pin insertion is based on the following three factors. (1) Excessive depth of K-wire insertion may penetrate the anterior annular and anterior longitudinal ligaments, which may induce vascular injury. (2) Compared with the nucleus pulposus, the annular ligament is much tougher and provides most of the holding strength for the pin. Thus, excessive advancement of the pin into the disc is unnecessary. (3) Deeper pin puncture can induce more severe disc injury and possibly more severe disc degeneration later.
An ideal technique to manage pin loosening while performing discectomy is as follows. First, the pin is bent at a right angle after insertion (Figure 3(b)). Attention should be given to the bending point of the pin, which is the indicator for pin loosening. Second, the pin is rotated and the bending point of the pin is hung on the incision (Figure 3(c)). The skin margin of the incision will thus cover the bending point and prevent the pin from loosening. Third, a strip of adhesive surgical draping should be used to hold the pin in place (Figure 3(d)).
During continuous traction of the nerve root, attention should be paid to the strength and duration of traction. Excessive retraction force and time applied to the affected nerve root may induce neuropraxia. The surgeon must accumulate adequate experience with nerve retraction in other lumbar decompression surgeries to become familiar with the tension limit of the nerve root. For surgeons in the learning curve, the most reliable method to prevent this complication is intraoperative electrophysiological monitoring. If the surgeon is sophisticated in manipulating the nerve root, the retraction force is relatively safe and under control. Clinical experience indicates that the retraction time should be less than 10 minutes; this is enough time in most situations of decompression. If decompression cannot be accomplished in 10 minutes, the surgeon should release the retraction and rest for 3 to 5 minutes. The position of K-wire insertion depends on the location of the herniated disc. The optimal position of pin insertion may be the point with complete exposure of the herniation. In cases of a huge herniation and high tension of the nerve root palpated under the retractor, limited retraction and partial decompression should be applied first; this will gradually alleviate the tension of the nerve root for further retraction and decompression. The surgeon should always make an effort to achieve a balance between the range of exposure and a safe amount of nerve root tension.
This study had several limitations. First, this was a retrospective study of a small cohort and had a short follow-up period, which prevented the detection of long-term outcomes such as herniation recurrence and disc degeneration. Second, this was an observational study performed in a single center, which may not have provided enough power to draw any definite conclusions. Third, the learning curve for this technique was not included in this study. The surgeon must dedicate great time and effort to accommodate the new surgical setting and environment. A further prospective clinical study is required to evaluate and compare the safety and efficacy of using a K-wire retractor in larger samples and multiple centers.
Conclusion
The P-UBE technique may be a simple surgical modification that provides better safety and efficacy than the T-UBE technique. Therefore, it has the potential to serve as an optional method in UBE lumbar surgery.
Footnotes
Author contributions
JXZ: conceptualization, design, formal analysis, funding acquisition, and writing. The author approved the submitted version of the manuscript.
Declaration of conflict of interest
The author has no conflicts of interest to declare in relation to this article.
Data availability statement
Funding
This study was funded by the Beijing JST Research Fund (code: YGQ-202208).