Learning curve of percutaneous transforaminal endoscopic discectomy with visualized foraminoplasty for lumbar spinal stenosis

Abstract

Objective

This study aims to analyze the learning curve of percutaneous transforaminal endoscopic discectomy (PETD) with visualized foraminoplasty for the treatment of lumbar spinal stenosis (LSS).

METHODS

80 patients underwent PETD with visualized foraminoplasty between 1 January 2019 and 1 January 2022 were retrospectively reviewed. Clinical outcomes were evaluated by using the Visual Analogue Scale(VAS) of low back pain(LBP) and leg pain(LP), the Oswestry Disability Index (ODI), and Japanese Orthopaedic Association scores(JOA). The learning curve was assessed by CUSM analysis. According to the learning curve, of these 80 patients were divided into two groups: early group(38) and late group(n = 42) in chronological order for comparison.

Results

All cases were completed successfully with no conversion to open surgery. No major complications occurred, but 5 patients response to postoperative paresthesia. The mean follow-up time was 16.04 ± 2.62 months. The median operative time reduced from 92.5 (interquartile range(IQR), 80–100) minutes for the early group to 85 (IQR, 80–90) minutes for the late group (P < 0.05). After approximately 38 cases, the curve tends to plateau and is considered a learning plateau. Postoperatively, the VAS of LBP and LP, and ODI in the two groups decreased significantly, the JOA was considerably elevated during the follow-up. The total complication rate was 6.2%. There were no significant differences in ODI, VAS of LP and LBP, JOA and complication rates between the two groups.

CLUSIONS

PETD with visualized foraminoplasty for LSS performed by surgeons has a notable learning curve. The mastery level could be achieved with 38 cases.

INTRODUCTION

Lumbar spinal stenosis (LSS) is a common degenerative disease which can manifest in the central spinal canal, intervertebral foramen or lateral recess. Its major symptoms include radiating leg pain, back pain, and neurogenic intermittent claudication[1]. When long-term conservative therapy fails to improve the symptoms, surgical intervention is often considered as a treatment option.

Percutaneous transforaminal endoscopic lumbar discectomy (PTED) is initially used for treating lumbar disc herniation(LDH), but its usage has expanded to include the treatment of lumbar spinal stenosis(LSS) due to its capability to enlarge the spinal canal[2.3]. Many previous reports have confirmed that PETD has advantages in the treatment of LSS[1–6]. Nonetheless, PETD for LDH may have a steep learning curve for beginners[7]. Conversely, the pathological changes in LSS are more complex and pose a technical challenge for most surgeons. Therefore, the learning curve for PETD for LSS is different from that for LDH.

It is well known that foraminoplasty is a crucial aspect of PETD and is almost always necessary in cases of LSS. Yang et al[8] have published the learning curve of PETD with traditional foraminoplasty. Traditional foraminoplasty is usually performed under repeated fluoroscopy, which not only increases the radiation risk for the surgeon, but may also cause nerve injury and bone bleeding. To our knowledge, no paper has reported the learning curve of PETD with visualized foraminoplasty for LSS. In our study, a surgeon with experience in endoscopic surgery initiated PETD for LSS with visualized foraminoplasty, and our aim was to evaluate the learning curve and clinical outcomes of PETD with visualized foraminoplasty for LSS.

Materials and methods

Prior to the procedure, the surgeon received one year of training in PETD with visualized foraminoplasty under the guidance of Surgeon Liu. The surgeon has successfully performed over 100 PETD procedures for LDH. From 1 January 2019 to 1 January 2022, a total of 80 patients with LSS underwent PETD with visualized foraminoplasty, and their demographic information is detailed in Table 1.

The following were the inclusion criteria: (1) individuals with LSS, as proven by concordant imaging diagnosis and clinical symptoms; (2) unilateral radiating leg pain (3) more than three months of failed conservative therapy. The following were the exclusion criteria:(1) multilevel lumbar spinal stenosis (2) with segmental instability (3) previous surgery history for segmental lesions; (4) with pathologies such as infection or tumor. Our hospital's ethics committee accepted this retrospective study. all methods were carried out in accordance with relevant guidelines and regulations. 

Imaging 

Prior to the procedure, all patients underwent assessments through magnetic resonance imaging (MRI) and computed tomography (CT). Additionally, dynamic X-ray images were utilized to examine any spinal instability. The stenosis locations were classified as central canal, foraminal, and lateral recess.

Surgical Procedure 

All operations were performed under general anesthesia. A prone position was used for all patients. According to the patient's body dimensions, the skin entrance location of the needle was around 8-13 cm lateral from the midline. After general anesthesia was administered, an 18-gauge needle was punctured into the selected skin entry point. The final target point of the needle tip should be the lateral aspect of the superior articular process(SAP). After a series of dilators were inserted consecutively, the endoscope and trephine was introduced. A bipolar radiofrequency coagulator was used to ablate the ligamentous structures and for bleeding control to expose the lateral and ventral aspects of the SAP. As required the SAP were then ground with the endoscopic trephine while being seen directly endoscopically until a gap was produced that allowed the work tube to enter the spinal canal. The intervertebral disc was endoscopically removed when the visualized foraminoplasty was complete, exposing the nerve root. The extent of the SAP removal depends on the preoperative and intraoperative situation (Figure 1).

Clinical Evaluation 

Operation time, fluoroscopy times, hospital stay and post-operative complications were analyzed. All patients had post-operative three-dimensional reconstruction CT imaging. Clinical outcomes were evaluated by two independent observers preoperatively and postoperatively at 1 day, 3 months, 6 months, and 12months following surgery using the VAS of LBP and LP, and Oswestry Disability Index (ODI), Japanese Orthopaedic Association Scores(JOA). The learning curve in terms of duration of surgery, was visualized by creating scatter plots and CUSUM charts.

CUSUM analysis

CUSUM analysis is a statistical technique applied to surgical procedures for the quantitative estimation of the learning curve[9]. Operative time was utilized as an indicator of surgical proficiency and patients were classified based on the order in which they underwent the procedure. The results were presented using a CUSUM chart. The chart displays a curve that is the result of adding all these deviations, case after case, around 0. Cases appear as dots in the curve organized along the x-axis which is the timeline. Therefore, every point in the curve shows the sequential monitoring of cumulative performance over time. The progress of a surgeon in mastering a new skill can be measured by its slope. A higher slope indicates slower progress, and as the curve eventually flattens, the surgeon has achieved mastery of the skill[10]. The CUMUS chart was made with Minitab software.

Statistical Analysis

Statistical analysis was conducted with SPSS 23.0 (IBM Corporation, USA). The normality of data was tested with Shapiro–Wilk test. Continuous data were presented as mean ± standard deviation or interquartile range (IQR). Continuous data were compared with paired t test for parametric data, Wilcoxon or Mann-Whitney U test for non-parametric data. Pearson's chi-squared test was used for comparing the frequencies of categorical data. A P value < 0.05 was considered to indicate significance.

RESULTS

Clinical results of the patients (n = 80)

The patients' average follow-up time was 16.04 ± 2.62months (range, 12-23). None were lost in different time points during follow-up. The median operative time of all patients was 85 (IQR,80–93.8) minutes. The median fluoroscopy times was 7(IQR, 6-8) times. Blood loss during surgery was not monitored. The median hospital stay after surgery was 6(IQR, 5–7) days (Table1). The VAS of LP decreased from 7(IQR, 6–8) pre-operatively to 3(IQR, 2–3) post-operatively and to 1(IQR, 1–1) at the last follow-up. The VAS of LBP changed from 5 (IQR, 4–6) preoperatively to 3(IQR, 3–4) postoperatively and to 1(IQR, 1– 2) at the last follow-up. The ODI values decreased from 34(IQR, 32–36) pre-operatively to 26(IQR, 24–26) post-operatively and to 8(IQR, 6–8) at the last follow-up (Table2). The JOA increased from 12(IQR, 10–14) to 20(IQR, 18–21) post-operatively and to 27 (IQR, 26–27) at the last follow-up(Table2, figure2).

Learning curve of PETD with visualized foraminoplasty 

Fig. 2 gives an overview of the surgical learning curve through scatter plots and CUSUM charts. A steady state was assumed to have been achieved, which is defined as the asymptote of the learning curve. The scatter plot shows about 38 cases, and the operation time tends to be stable, while CUSUM charts showed no slope of the curve for the operative time after the 38th case(Figure3).

Comparison of outcome measures between the early group (n = 38) and late group (n = 42)

According to the basis of the learning curve findings, the 80 patients were divided into two groups: the early group (38 patients) and the late group (42 patients). There was no difference in the baseline data between the two groups before surgery. Operative time decreased significantly from 92.5 (IQR, 80–100) minutes in the early group to 85 (IQR, 80–90) minutes in the late group (P < 0.05). Fluoroscopy times decreased from 8 (IQR, 7–10) times in the early group to 6 (IQR, 5–6.3) times in the late group (P <0.05) (Table 3). Postoperatively, ODI and VAS scores of LBP and LP decreased considerably in both groups, but JOA was significantly elevated. There were no significant differences in the ODI, JOA and VAS scores of LBP and LP at the follow-up time between the groups(P> 0.05) (Table 4, Fig.2).

Complications

Postoperative paresthesia were the most prevalent in our study, with no dural tears, residual nucleus pulposus, or hematoma formation. The early and late groups had rates of 7.9% (3/38) and 4.8% (2/42), respectively. The number and rate of complications were higher in the early group, indicating a higher risk of complications during the early stages of learning this new technique. Nevertheless, there was no significant difference in complication occurrences between the two groups (P =0.357), which might be attributed to the limited sample size and the surgeon's experience in endoscopy surgery.

DISCUSSION

Percutaneous transforaminal endoscopic lumbar discectomy (PETD) is used to treat patients with LSS, which requires more specialized tools, skills and experience than LDH[10.11]. As a result, the learning curve for LSS and LDH is distinct. Actually, PETD for LSS should be considered a new and complex technique that should be explored the learning curve by surgeons with endoscopic experience [10]. Following this strategy, a senior clinician evaluated the PETD learning curve for LSS in the our study.

Operative time trends are a valuable statistical tool commonly used to evaluate a trainee's proficiency level. A chronological case series showed that surgeon comfort and technical proficiency were linked to a decrease in operative time. Traditional learning curve assessments have mainly relied on case numbers to assess proficiency[12]. The operation time should decrease with the increase of the number of operations performed by the surgeon, and finally reach a steady state. Previous literatures reported that the PETD learning curve used linear regression analysis and logarithmic regression analysis, but did not use CUSUM analysis[8.13]. In our study, the analysis of our learning curve showed that showed that the proficiency in PETD with visualized foraminoplasty was obtained after about 38 procedures. The learning stage of 38 cases of PETD is longer than that of other techniques with non-visualized foraminoplasty which ranged from around 20 to 35 cases[8, 14]. Despite variations in technology and illness, the lengthier learning period may suggest the new technology's complexity.

In the early group, the operative time was 92.5(IQR, 80–110) minutes, while in the late group, the time decreased to 85(IQR, 80–90) minutes. There was statistically significant difference in operation time when comparing the two groups. The slight difference in operative time between the early and late groups suggests that the learning curve for LSS is not steep for surgeons who have experience in PETD for LDH. However, the total operative time for all 80 patients was 85(IQR, 80-93.8)minutes which was higher than other findings in the literature[3.8.15]. This may be because visualized foraminoplasty requires more endoscopic manipulation. At the same time, surgeon’s skil and anatomical differences are also related. In addition, the early group had a higher frequency of intraoperative fluoroscopy at 8 (IQR, 7–10) times, which decreased to 6 (IQR, 5-6.3) times in the late group in our study. Radiation exposure has long been considered animportant index for assessing the effificiency of PETD[16]. As the number of surgical cases increases, reducing the number of intraoperative fluoroscopies provides advantages for both surgeons and patients. The use of PETD with visualized foraminoplasty has reduced the need for repeated puncture processes during the operation. This is because the puncture needle only needs to be positioned outside the SAP. Additionally, the risk of nerve injury caused by blind vision puncture is also reduced.

The learning curve was not only associated with a shortening of the operating time, but also influenced by factors such as demographic characteristics, clinic results, and complications. In order to ensure the reliability of statistical results, Fisher's test was used for discrete variables to exclude potential confounding factors from the demographic characteristics. Our study found that the clinic results included postoperative VAS of LBP and LP, ODI, and JOA scores were improved and remained so throughout the follow-up period. These results indicate that visual foraminoplasty PETD is an effective treatment for improving patient function. However, Yang et al.[8] discovered that the VAS of LBP increased from postoperative to the last follow-up. They attributed this phenomenon to two factors: progressive degeneration of the lumbar spine after the operation and damage to the facet joints of the lumbar vertebrae caused by the foraminoplasty. In fact, when performing a visual foraminoplasty, only the bone is removed when needed, without the injury of facet joints. Therefore, the resected SAP has less bone and will not cause lumbar instability[13.17].

Paresthesia is the most common complication after PETD[18.19], which is consistent with our study. We did not observe complications such as dural tear and cerebrospinal fluid leakage. The complication rate decreased from 7.9% in the early group to 4.8% in the late group. The incidence of complications in the early group and the late group was not statistically significant, indicating that surgical complications do not depend on the learning curve. Therefore, it was considered that surgical complications should not be used as a key outcome measure[7]. The overall complication rate was 6.2%. The operative complication rates in the early and late groups in our study were lower than those reported in the literature for non-visualized foraminoplasty PETD respectively[8]. This suggests that visual security may be better. Ahn et al. [20] noted that the dural sac cross-sectional area (DSCSA) on magnetic resonance imaging was found to be a useful measure for distinguishing between the early and late stages of the learning curve. because of the changes in the DSCSA significantly increased in the late group. This may be a shortcoming of our study.

The learning curves of surgical procedures are known to vary among surgeons, and this variation may be influenced by factors such as the experiences of the surgeons and their assistants, as well as the individual learning capacities of the surgeons themselves. Improvement in surgical technique and training before performing a new procedure are equally important in shortening the learing curve. However, it is important to note that the surgical data analyzed in this study was limited to a single surgeon. While the learning curve can provide valuable reference points for other surgeons in the learning process, it cannot be used as the sole criterion for determining when a surgeon has achieved a stable stage of surgical competence. In order to better understand the learning curve of PETD with visualized foraminoplasty for LSS, it is important to involve more surgeons in future research.

This study does have limitations. This study retrospectively analyzes cases performed by a single surgeon that already has rich experience In endoscopic spinal surgery before this procedure, while for young surgeons with less experience, the learning curve of PETD with visualized foraminoplasty for LSS may be longer. In addition, there is no classification of the severity of spinal canal stenosis and no comparison of the enlarged area of the spinal canal before and after surgery.

Conclusions

This study utilized CUSUM analysis to visualize the learning curve for PETD with foraminoplasty for LSS. The results indicate that the surgeon may become proficient in the procedure after 38 cases, while maintaining the safety and feasibility of PETD even in the initial stages of the learning curve.

Declarations

Competing interests

The authors report no conficts of interest in this work.

Ethics approval and consent to participate

The study received approval from the Clinical Trial Ethics Committee of the Yueyang Hospital of Traditional Chinese Medicine(YZYEC[2023P002]). Written informed consent was obtained from all participants. All methods were carried out in accordance with relevant guidelines and regulations.

Consent for publication

Not applicable.

Availability of data and materials 

The authors will allow the sharing of participant data. The data will be available to anyone who wishes to access them for any purpose. The data will be accessible from immediately the following publication to 6 months after publication, and contact should be made via the corresponding author by email.

Funding: The author(s) received no financial support for the research, authorship, and/or publication of this article.

Authors’ contributions 

Xin-Jian Feng contributed to the design of study, data analysis, and writing (original and revised draft) of the manuscript. Sheng-Hui YI and De-Ping Mo contributed to the data analysis, writing (original and revised draft) of the manuscript. Hui-Ming Chen contributed to the writing (review and editing) of the manuscript. Jian-Guo Liu contributed to surgeon training and study design.

Acknowledgments 

The authors would like to thank all the study participants.

Author ' information

¹Spinal Orthopedics, Yueyang Hospital of Traditional Chinese Medicine, 414000,Yueyang, China,

²Orthopaedic Surgery, Gulin People's Hospital, 646000, Luzhou, China,

³Joint Orthopedics, Yueyang Hospital of Traditional Chinese Medicine, 414000,Yueyang, China

⁴ Neurospinal Surgery, Luzhou People's Hospital, 646000, Luzhou, China.

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Tables

Table 1 Demographic characteristics of 80 Patients

Table 2 Clinical outcomes of the total 80 patients before and after surgery.

LP, leg pain; LBP, low back pain; VAS, visual analog score; ODI, Oswestry Disability Index; JOA, Japanese Orthopaedic Association. IQR, interquartile range; a, the P value between preoperation and 1 day after surgery ; b, the P value between pre-operation and 3 months after surgery; c, the P value between pre-operation and 6month after surgery; c, the P value between post-operation and 12 months after surgery; P, the P value of Wilcoxon test. 

Table 3 The comparison of demographic characteristics between two groups [Median (IQR) or mean ± SD or n (%)]

IQR, interquartile range; LP, leg pain; LBP, low back pain; VAS, visual analog score; ODI, Oswestry Disability Index; JOA, Japanese Orthopaedic Association; SD, standard deviation; BMI, Body Mass Index. 

Table 4 The comparison of clinic outcomes between two groups [Median (IQR) or mean ± SD or n (%)]

IQR, interquartile range; LP, leg pain; LBP, low back pain; VAS, visual analog score; ODI, Oswestry Disability Index; JOA, Japanese Orthopaedic Associ