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.