Jinchao Xu and Dong Wang contributed equally to this study as co-first authors.
The purpose of this study was to investigate the learning curve and complications of unilateral biportal endoscopy (UBE) in the treatment of lumbar disc herniation (LDH) and lumbar spinal stenosis (LSS).
This was a retrospective cohort analysis of 197 consecutive patients who received UBE unilateral laminotomy bilateral decompression (UBE-ULBD) or lumbar discectomy (UBE-LD) surgery, including 107 males and 90 females with an average age of 64.83±14.29 years. Cumulative sum (CUSUM) and risk-adjusted cumulative sum analysis (RA-CUSUM) were used to evaluate the learning curve, with the occurrence of complications defined as surgical failure, and variables of different phase of the learning curve were compared.
The cutoff point of learning curve of UBE surgery was 54 cases according to CUSUM analysis. The learning curve of UBE-ULBD and UBE-LD were divided into 3 phases. The first cutoff points were 31 and 12 cases, and the second cutoff point were 67 and 32 cases respectively. With the progress of the learning curve, the operation time and postoperative hospital stays decreased. The visual analogue scale and Oswestry Disability Index at the last follow-up were significantly lower than that before surgery. The incidence of surgical failure was 6.11% and began to decrease after the 89th case based on RA-CUSUM analysis. The surgical failure rate decreased from 10.11% to 2.78 after the 89th case with significant different.
UBE surgery is effective in the treatment of LDH and LSS with low incidence of complications. But a learning curve of at least 54 cases still required for mastering UBE surgery.
With increasing age, the incidence of lumbar disc herniation (LDH) and lumbar spinal stenosis (LSS) gradually increases. The herniated intervertebral disc, hyperplastic facet joint, thickened ligamentum flavum (LF) and lamina lead to a reduction in spinal canal volume and compression of the central spinal canal, lateral recess or foramen, causing symptoms such as intermittent claudication, low back pain and lower limb pain. LDH and LSS are the most common indications for lumbar surgery [
Recently, the unilateral biportal endoscopy (UBE) technique was used for the treatment of LDH and LSS, and several articles have reported satisfactory effect of UBE surgery [
The purpose of this study was to analyze the learning curve of UBE surgery through cumulative sum (CUSUM) analysis based on operation time and risk-adjusted cumulative sum (RA-CUSUM) analysis based on surgical failure rate [
Consecutive patients who underwent UBE surgery in the Department of Orthopedics, Hangzhou Hospital of Traditional Chinese Medicine from December 2019 to December 2020 were analyzed retrospectively. The operation methods included unilateral laminotomy bilateral decompression (UBE-ULBD) and lumbar discectomy (UBE-LD). All operations were performed by the same surgeon who had extensive experience in percutaneous endoscopic lumbar discectomy (PELD) but had never performed arthroscopic surgery.
The institutional review committee of Hangzhou Hospital of Traditional Chinese Medicine (No. 2022KY087) approved the study. This study was not considered to require informed consent. There was no treatment other than that routinely implemented during hospitalization, as well as no additional risk for the patients involved.
Inclusion criteria: (1) Patients presented with low back pain (visual analogue scale [VAS]≥ 6), with or without lower limb radiation pain or intermittent claudication (walking distance≤ 100 m). (2) Magnetic resonance imaging (MRI) showed stenosis of the central spinal canal, lateral recess or nerve root canal. (3) Systematic conservative treatment for more than 3 months was unsuccessful. (4) Patients undergoing UBE-ULBD or UBE-LD surgery performed by the same surgeon.
Exclusion criteria: (1) More than 2 surgical levels. (2) Lumbar spondylolisthesis greater than grade Ⅰ (Meyerding grade). (3) Lumbar scoliosis (Cobb angle> 20°). (4) Patients with a history of lumbar spinal canal decompression surgery or lumbar interbody fusion surgery at the same level. (5) Patients with spinal infection, tumor, tuberculosis.
The patient was placed in a prone position under general anesthesia with the abdomen suspended. The midline, horizontal line of the intervertebral space and surface projection of pedicles were identified on the anteroposterior (AP) view of the fluoroscope. By adjusting the operating table, the horizontal line of the intervertebral space of the targeted level was ensured to be perpendicular to the ground on lateral view of the fluoroscope.
Taking the left approach as an example, the viewing portal was located on the cranial side and the working portal on the caudal side. The left-side approach was easier to perform given that most surgeons had the dominant hand on the right side. Two 1-cm incisions were made 1.5 cm above and below the horizontal line of the intervertebral space of the ipsilateral pedicular medial line (
Multifidus muscles were dissected from the spinous process (SP) and the lamina space to form a primary workspace. The tubular dilators were inserted to expand the portals until the tips met at the junction between the base of the SP and the lamina on AP view, and were replaced by the endoscope and instrument subsequently (
Laminectomy was performed with a burr until reaching the insertion of the LF. The LF was carefully dissected and completely resected in pieces. In UBE-LD surgery, the axillary and shoulder areas of the traversing nerve root were explored to confirm the position of the herniated disc. The annulus fibrosus was incised by a radiofrequency probe or scalpel, and the nucleus pulposus was removed by pituitary forceps. In UBE-ULBD surgery, the lateral recess was decompressed with a straight Kerrison punch, and the range of decompression reached the inner wall of the pedicle. Then, the base of the SP was partly removed with the osteotome. Decompression of the contralateral spinal canal and lateral recess was performed using the curved Kerrison punch, with the inner wall of the contralateral pedicle as a reference. Finally, the contralateral LF was removed. The radiofrequency probe was used for hemostasis after confirming complete decompression. Then, the incision was closed, and a drain was placed. The instruments and schematic of UBE surgery was showed in
Basic information from all patients was collected, including age, sex, type of stenosis, surgical segment, body mass index (BMI), and hypertension. The operation time, estimated blood loss (EBL), complications and postoperative hospital stays were recorded after the operation. The operation time was calculated from the beginning of anesthesia to the closure of the incision. Since UBE surgery was performed under continuous fluid irrigation, and saline permeates into the soft tissue, the amount of bleeding was estimated by the surgeon. The VAS was used to evaluate the degree of low back pain and leg pain, and the Oswestry Disability Index (ODI) was used to evaluate limb function. Records were made before the operation, 1 month after the operation and at the last follow-up.
The learning curve based on operation time was calculated by CUSUM analysis. The formula was defined as:
In this study, surgical failure was defined as occurrence of complications, including nucleus pulposus residue, dural tear, epidural hematoma, nerve root injury, and infection. Univariate bivariate logistic regression was used to analyze potential risk factors, such as sex, age, surgical segment, EBL, BMI, hypertension and operation time. The variables with p<0.05 were included in the multivariate logistic regression model to predict the probability of surgical failure in each case. The scatter diagram of RA-CUSUM was drawn according to the following formula:
Continuous variables with a normal distribution are expressed as the mean±standard deviation. A t-test was used to compare the 2 groups of variables. One-way analysis of variance (ANOVA) and repeated measures ANOVA followed by the least significant difference test was used to compare multiple groups of variables. Continuous variables with a skewed distribution are expressed as the median (interquartile range, IQR), and the rank sum test was used for comparisons between groups. The classified variables were expressed as percentages, and comparisons between groups were performed by the chi-square test followed by Bonferroni correction. A p-value of < 0.05 was considered statistically significant.
The average operation time was 143.61±47.25 minutes (
In our study, a total of 12 cases were regarded as surgical failure because of complications (
Residual nucleus pulposus was found in 3 patients with highly migrated LDH in early phase (3rd, 13th, 68th), all of which were reoperated by PELD surgery and satisfactory results were obtained. Four patients with dural tears were fixed with gelatin sponges during the operation, and no cerebrospinal fluid leakage, lumbar pseudomeningoceles or meningitis was observed after the operation. Among them, 1 patient developed irritability, increased heart rate, hyperextension of both lower limbs and hypertonia in the recovery of general anesthesia, which relieved spontaneously after 2 hours. A case of epidural hematoma suddenly developed radiation pain in the right lower limb on the third day after the operation, and the symptoms were relieved immediately after the hematoma clearance operation (
Curve fitting was performed for the scatter diagram drawn according to the CUSUM value (
CUSUM analysis of different surgical methods showed that the first cutoff points of UBE-ULBD and UBE-LD were 31 cases and 12 cases, and the second cutoff point were 67 and 32 cases respectively. Therefore, the learning curve of UBE-ULBD and UBE-LD was divided into 3 phases respectively: the learning phase, practicing phase and mastery phase (
The comparison of patient characteristics and perioperative data in different phases are listed in
Univariate binary logistic regression showed that BMI, hypertension and operation time were risk factors for surgical failure (p<0.05; odds ratio [OR], 1.921, 5.551, 1.023) (
As listed in
To reduce the trauma and complications caused by surgery, spinal surgeons have been committed to the combination of endoscopic technology and minimally invasive concepts. The effectiveness of lumbar discectomy and decompressive laminotomy by posterior approach using the microendoscopy or full-endoscopy have been reported [
As an emerging technique, in the early proficiency phase of UBE surgery, surgeons must go through the process of learning and practicing. The learning curve reflects the rate of skills acquired within a certain period of time, which is usually determined by the number of surgical cases required for beginners' surgical techniques to achieve relative stability [
CUSUM is an average-based test method that was originally mainly used to monitor the continuous change trend of the industrial sector. Because this statistical method meets the requirements of clinical technical learning and quality control, it has been used to analyze learning curves in medicine since the 1970s [
Most of the evaluation indices used by CUSUM analysis were operation times, while the RA-CUSUM was used to evaluate other parameters that affect the outcome of the operation [
Research by Lin et al. [
The incidence of dural tears during surgery in LSS patients (3.7%) was significantly higher than that in LDH patients (2.1%), and the risk of dural tears in ULBD surgery was higher [
Symptoms of epidural hematoma were usually observed within 24 hours after surgery, but approximately 43% of cases did not develop symptoms until 4 days or later after operation [
This research was a single-center study and the surgery was performed by the same surgeon, so our experience does not apply to other surgeons. For the reason that the study of the learning curve should first be based on the subjective factor of the surgeon's experience. Moreover, objective factors such as the volume of patients, medical insurance policies, different equipment and devices all play important roles in the learning process. Therefore, other surgeons may have cutoff point earlier or later than ours.
We recommend that the deep layer of the contralateral LF be preserved during the operation and resected at the end. If the LF is removed first, the operation should be performed on the outside of the epidural fat as far as possible [
In the early phase of learning, we did not avoid some difficult cases deliberately, which leads to the prolongation of the operation time and the rapid rise of the learning curve in CUSUM analysis. The resection of LF is a relatively time-consuming and tricky step in the operation. Therefore, we suggest beginners to choose simple LD surgery by the left-side approach in early phase, which may reduce the difficulty of practicing. Apply of 0° endoscope in the early phase can make beginners adapt to UBE surgery more quickly. Additionally, standardized training and practicing on models or cadavers are of great help to shorten the learning curve.
In this work, the learning curve of UBE surgery was evaluated by CUSUM and RA-CUSUM analysis based on operation time and incidence of complications, and satisfactory clinical outcomes were achieved with low incidence of complications. Our data indicated that the number of cases for overcoming the learning curve of UBE surgery was 54 cases, and increased to 89 cases when the incidence of complications was taken into account. The appropriate early cases selection and standardized training are helpful to shorten the learning curve.
The authors have nothing to disclose.
(1) National Key R&D program of China (project number:2019YFC0121400). (2) Medical Health Science and Technology project of Zhejiang Province (project number: 2022KY997).
Conceptualization: JX, DW; Data curation: JB, WG; Formal analysis: JX, JB, WG; Methodology: JX, DW; Project administration: HP; Writing - original draft: JX, DW, JL; Writing - review & editing: WZ, HP.
Schematic of the incision design (A) and intersection of the 2 portals (B). Blue line: horizontal line of the intervertebral space. Yellow line: ipsilateral pedicular medial line. Red oval: viewing portal. Green oval: working portal.
(A) Instruments used in unilateral biportal endoscopy (UBE) surgery. (B) Schematic of UBE surgery.
The visual analogue scale (VAS) and Oswestry Disability Index (ODI) at each point in time. UBE-ULBD, unilateral biportal endoscopy unilateral laminotomy bilateral decompression; UBE-LD, unilateral biportal endoscopy lumbar discectomy.
(A, B) A case of epidural hematoma after UBE-LD surgery: a 52-year-old woman underwent UBE-LD surgery for lumbar disc herniation in the left foramen area (red arrows). (C, D) Radiation pain of the right lower limb with a visual analogue scale of 9 suddenly appeared on the third day after operation, the magnetic resonance imaging (MRI) showed the epidural hematoma (blue arrows). (E, F) The symptoms were relieved immediately after hematoma clearance operation, and MRI indicated that the epidural hematoma had been removed. UBE-LD, unilateral biportal endoscopy lumbar discectomy.
Cumulative sum (CUSUM) graph of the cohort. UBE-ULBD, unilateral biportal endoscopy unilateral laminotomy bilateral decompression; UBE-LD, unilateral biportal endoscopy lumbar discectomy.
Cumulative sum (CUSUM) graph of unilateral biportal endoscopy unilateral laminotomy bilateral decompression.
Cumulative sum (CUSUM) graph of unilateral biportal endoscopy lumbar discectomy.
Risk-adjusted cumulative sum analysis (RA-CUSUM) graph of the cohort. UBE-ULBD, unilateral biportal endoscopy unilateral laminotomy bilateral decompression; UBE-LD, unilateral biportal endoscopy lumbar discectomy.
Patient characteristics
Characteristic | UBE-ULBD | UBE-LD | p-value | χ2 | t |
---|---|---|---|---|---|
Age (yr) | 65.49 ± 13.34 | 64.06 ± 15.38 | 0.483 | - | 0.704 |
Sex (n) | 0.800 | 0.640 | - | ||
Male | 59 | 48 | |||
Female | 48 | 42 | |||
Body mass index (kg/m2) | 22.08 ± 2.31 | 21.65 ± 2.12 | 0.179 | - | 1.348 |
Hypertension | 31 | 26 | 0.990 | 0.000 | - |
Level (n) | |||||
L3/4 | 7 | 9 | 0.376 | 0.783 | |
L4/5 | 63 | 42 | 0.087 | 2.929 | |
L5/S1 | 37 | 39 | 0.209 | 1.581 | |
Postoperative follow-up duration (mo) | 10.57 ± 2.52 | 10.43 ± 2.35 | 0.696 | - | 0.391 |
Values are presented as mean±standard deviation.
UBE-ULBD, unilateral biportal endoscopy unilateral laminotomy bilateral decompression; UBE-LD, unilateral biportal endoscopy lumbar discectomy.
Variables related to surgery
Variable | UBE-ULBD | UBE-LD | p-value | χ2 | t | Z |
---|---|---|---|---|---|---|
Operating time (min) | 160.38 ± 53.98 | 123.68 ± 26.59 | 0.000 | - | 5.878 | |
EBL (mL) | 100 (50–100) | 50 (50–100) | 0.125 | - | - | 1.532 |
Postoperative hospital stays (day) | 6.36 ± 2.04 | 5.97 ± 2.91 | 0.276 | - | 1.092 | - |
Approach side (n) | 0.707 | 0.141 | ||||
Left | 67 | 54 | - | - | ||
Right | 40 | 36 | - | - | ||
Surgical failure | 7 (6.54) | 5 (5.56) | 0.773 | 0.083 | - | - |
Values are presented as mean±standard deviation, median (interquartile range), or number (%).
UBE-ULBD, unilateral biportal endoscopy unilateral laminotomy bilateral decompression; UBE-LD, unilateral biportal endoscopy lumbar discectomy; EBL, estimated blood loss.
Clinical outcomes
Variable | UBE-ULBD | UBE-LD |
---|---|---|
VAS leg | ||
Preoperative | 7.55 ± 1.20 | 7.33 ± 0.94 |
1 Month after surgery | 3.08 ± 0.84 | 2.95 ± 0.79 |
Last follow-up | 1.43 ± 0.49 | 1.32 ± 0.47 |
F | 1,362.07 | 1,402.56 |
p-value | 0 | 0 |
VAS back | ||
Preoperative | 7.45 ± 1.13 | 7.40 ± 1.19 |
1 Month after surgery | 3.90 ± 0.81 | 3.77 ± 0.79 |
Last follow-up | 2.05 ± 0.77 | 2.02 ± 0.82 |
F | 906.424 | 823.742 |
p-value | 0 | 0 |
ODI | ||
Preoperative | 58.76 ± 16.78 | 55.53 ± 15.46 |
1 Month after surgery | 29.29 ± 6.33 | 31.04 ± 6.35 |
Last follow-up | 21.39 ± 3.72 | 19.88 ± 3.03 |
F | 390.176 | 294.78 |
p-value | 0 | 0 |
Values are presented as mean±standard deviation.
UBE-ULBD, unilateral biportal endoscopy unilateral laminotomy bilateral decompression; UBE-LD, unilateral biportal endoscopy lumbar discectomy; VAS, visual analogue scale; ODI, Oswestry Disability Index.
Details of complications
Complication | No. | No. of cases occurred |
---|---|---|
Residue | 3 | 3rd |
Dural tear | 4 | 21st |
Epidural hematoma | 2 | 75th |
Nerve root injury | 3 | 36th |
Unilateral biportal endoscopy unilateral laminotomy bilateral decompression.
Unilateral biportal endoscopy lumbar discectomy.
Comparison of different phases according to the result of CUSUM analysis
Variable | Phases | p-value | χ2 | F/t | H/Z | |||
---|---|---|---|---|---|---|---|---|
Total | Learning phase (n = 54) | Practicing phase | Mastery phase (n = 143) | |||||
Operating time (min) | 168.37 ± 53.69 | - | 134.27 ± 41.04 | 0.000 | - | 4.225 | - | |
EBL (mL), median (IQR) | 100 (50–100) | - | 50 (50–100) | 0.359 | - | - | 0.917 | |
Postoperative hospital stays (day) | 7.01 ± 2.78 | - | 5.87 ± 2.28 | 0.003 | - | 2.972 | - | |
Surgical failure, n (%) | 6 (11.1) | - | 6 (4.20) | 0.093 | - | - | - | |
UBE-ULBD | ||||||||
Operating time (min) | 188.48 ± 55.61 |
162.19 ± 55.45 |
136.98 ± 39.85 |
0.000 | - | 9.220 | - | |
EBL (mL), median (IQR) | 100 (50–100) | 100 (50–100) | 100 (50–100) | 0.816 | - | - | 0.406 | |
Postoperative hospital stays (day) | 6.81 ± 2.35 |
6.50 ± 1.86 | 5.88 ± 1.85 |
0.140 | - | 2.006 | - | |
Surgical failure, n (%) | 3 (9.68) | 2 (5.56) | 2 (5) | 0.701 | 0.817 | - | - | |
UBE-LD | ||||||||
Operating time (min) | 152.92 ± 26.33 |
124.45 ± 37.07 |
117.36 ± 17.06 |
0.000 | - | 10.879 | - | |
EBL (mL), median (IQR) | 100 (100–200) |
100 (50–100) | 50 (50–100) |
0.004 | - | - | 11.226 | |
Postoperative hospital stays (day) | 7.92 ± 3.68 |
6.90 ± 3.40 | 5.26 ± 2.27 |
0.003 | - | 6.055 | - | |
Surgical failure, n (%) | 2 |
3 |
0 |
0.005 | 9.918 | - |
Values are presented as mean±standard deviation unless otherwise indicated.
CUSUM, cumulative sum; EBL, estimated blood loss; IQR, interquartile range; UBE-ULBD, unilateral biportal endoscopy unilateral laminotomy bilateral decompression; UBE-LD, unilateral biportal endoscopy lumbar discectomy.
p<0.05, pairwise comparison between groups.
Logistic regression analysis of risk factors for surgical failure
Variable | OR | p-value |
---|---|---|
Univariate analysis | ||
Sex | 0.375 | 0.151 |
Age | 0.974 | 0.208 |
BMI | 1.921 | 0.000 |
Hypertension | 5.551 | 0.007 |
Level | 0.858 | 0.750 |
EBL | 1.001 | 0.888 |
Operating time | 1.023 | 0.000 |
Operating methods | 0.840 | 0.773 |
Multivariate analysis | ||
BMI | 1.933 | 0.004 |
Hypertension | 6.484 | 0.017 |
Operating time | 1.022 | 0.002 |
Constant | 0.000 | 0.000 |
OR, odds ratio; BMI, body mass index; EBL, estimated blood loss.
Comparison of different phases according to the result of RA-CUSUM analysis
Variable | Learning phase | Mastery phase | p-value | χ2 | t | Z |
---|---|---|---|---|---|---|
No. of cases | 89 | 108 | ||||
Operating time (min) | 155.56 ± 53.49 | 133.77 ± 38.99 | 0.002 | 3.205 | ||
EBL (mL), median (IQR) | 100 (50–100) | 50 (50–100) | 0.315 | 1.006 | ||
Postoperative hospital stays (day) | 6.75 ± 2.71 | 5.71 ± 2.17 | 0.003 | 2.995 | ||
Surgical failure, n (%) | 9 (10.11) | 3 (2.78) | 0.032 | 4.589 |
Values are presented as mean±standard deviation unless otherwise indicated.
RA-CUSUM, risk-adjusted cumulative sum analysis; EBL, estimated blood loss; IQR, interquartile range.