Application of Percutaneous Endoscopic Interlaminar Discectomy or Open Lumbar Microdiscectomy in Treating Senile Patients Over 60 Years Old with Symptomatic Lumbar Disc Herniation: A Two-year Retrospective Study



Background: Percutaneous endoscopic interlaminar discectomy (PEID) had been successfully used in the treatment of lumbar disc herniation. However, few reports have focused on the treatment of senile lumbar disc herniation (SLDH) in patients aged over 60 years via PEID.

Methods: We included 42 patients with SLDH from January 2019 to June 2020 in this retrospective study. The patients were divided into the PEID group (n = 19) and the open lumbar microdiscectomy (OLM) group (n = 23) according to the type of surgical procedure they underwent. Basic clinical information, surgical information, and clinical effects were compared between the two groups.

Results: The estimated blood loss, bed-rest time, and hospital stay in the PEID group were less than those in the OLM group (P < 0.05 each) but the surgery time in the PEID group was longer than that in the OLM group (P < 0.05). The visual analgesia scores for back pain (VAS-BP), visual analgesia scores radiating to the lower legs (VAS-LL), and Oswestry disability index (ODI) scores of the two groups were significantly decreased after surgery compared to the baseline scores (P < 0.05). The VAS-BP at the 1st week and 3rd month post-operation and the ODI at the 12th month and 24th month in the PEID group were lower than those in the OLM group (P < 0.05 each).

Conclusion: Both PEID and OLM are safe and efficacious methods of treating SLDH. Compared with OLM, PEID has more advantages in reducing surgical trauma and decreasing postoperative low back pain in the early postoperative period. The long-term clinical results of both techniques seem to be effective without any of them being superior to the other in elderly patients.


With the development of the economy and society, aging has become an irreversible trend of globalization in the 21st century. According to the World Health Organization, the number and proportion of people aged over 60 years are increasing rapidly. In 2019, the number of people over 60 years worldwide was one billion, and this number will reach 1.4 billion by 2030 and 2.1 billion by 2050 [1]. Treatment for patients with senile lumbar disc herniation (SLDH) aged over 60 years is often more complex than that in young and middle-aged patients. SLDH is commonly associated with complex medical diseases such as hypertension, diabetes, and pulmonary dysfunction. Therefore, patients with SLDH exhibit poor tolerance to anesthesia and major surgery. Prolonged postoperative bedridden states also increase the risk of complications such as pulmonary infections and thrombosis [2, 3]. Furthermore, open surgery can also increase the risk of postoperative incision infection, low back pain, and medical complications [4].

In 1978, Williams described open lumbar microdiscectomy (OLM) [5]. Because of the limited paraspinal muscle dissection involved, the range of laminectomy and facet joint resection achieved, and the fact that it circumvents discectomy and fusion, OLM is still considered one of the classic and reliable treatments for lumbar disc herniation [6]. All of these benefits also effectively reduce surgical trauma, postoperative scar formation around nerve roots, and lumbar instability. Therefore, OLM has been widely adopted by clinicians [79].

Percutaneous endoscopic lumbar discectomy (PELD), including percutaneous endoscopic interlaminar discectomy (PEID) and percutaneous endoscopic transforaminal discectomy (PETD), has become one of the most rapidly-developed mini-invasive surgical procedures because it is associated with minimal injury to spinal structures and rapid postoperative recovery [10]. Compared with OLM, PELD is associated with less damage to soft tissues and bony structures, and patients can recover more quickly after surgery [1114]. Kim et al. compared the clinical efficacies of PELD and open lumbar discectomy [OLD] in the treatment of lumbar disc herniation through a meta-analysis and found that more studies were needed to compare the efficacies of these two surgical approaches [15]. With advancements in related pieces of technology, PELD has successfully overcome technical limitations such as, fifth lumbar vertebral to first sacral vertebra (L5–S1) segments, the dissociation of portions of the nucleus pulposus, and spinal canal stenosis at the early stages of lumbar disc herniation [13, 1618].

A study by Kim et al. [19] demonstrated that the re-operation rate of PELD was not higher than that of OLM when the patients were below 57 years and that PELD for older patients should be performed after careful consideration. However, another study by Zhu et al. [20] reported that percutaneous transforaminal endoscopic diskectomy had shown satisfactory clinical effectiveness in both elderly and younger patients. Lumbar degeneration and radiographic lumbar spinal stenosis are common conditions in elderly patients. Therefore, the treatment of SLDH using PELD via the interlaminar approach has remained a challenge. Also, it is not entirely clear whether PEID is more effective than OLM in treating SLDH. In the present study, data from 42 patients with SLDH treated via either PELD or OLM were retrospectively analyzed to explore the safety and efficacy of PELD in the treatment of SLDH.


Inclusion criteria, and exclusion criteria

We collected clinical data for a series of patients with SLDH who underwent either PEID or OLM from January 2019 to June 2020. We included the following categories of patients: 1) those aged at least 60 years (≥ 60 years); 2) those diagnosed with single-segment soft lumbar disc herniation (LDH) of L4–L5 or L5–S1; 3) those who exhibited significant clinical symptoms and signs, such as: radiating pain, radiating numbness or tingling, weakened muscles, decreased extensor/flexor muscle strength, an attenuated Achilles tendon reflex, and a positive (30°) angle in the straight-leg-raise test and the muscle strength test; 4) all patients received conservative treatment for at least 6 weeks, underwent either PEID or OLM and were followed up for more than 24 months. We excluded the following categories of patients: 1) those aged below 60 years (< 60 years); 2) those who had previously undergone lumbar surgery; 3) those with spinal infections, intraspinal tumors, severe lumbar scoliosis, or spinal deformities; 4) those with symptomatic lumbar spinal stenosis, such as neurogenic intermittent claudication; 5) those who were diagnosed with lumbar instability and required fusion surgery; 6) Those whose symptoms and signs of nerve injury were not relieved after conservative treatment or whose symptoms and signs of nerve injury continued to worsen during conservative treatment.

Surgical methods

The surgical techniques for PEID and OLM used in the present study were consistent with those previously reported in the literature [5, 13, 18]. During PEID [18], the patient was placed in a prone position on a carbon-fiber operating table with slightly elevated hips, with the hip and knee joints flexed to increase the space between the lamina and the foramen. In brief, under general anesthesia, the C-arm was used to determine the lesion’s segment. A working channel for percutaneous full endoscopy was implanted into the medial side of the inferior articular process at the junction of the upper and lower laminae through the posterior median approach under the guidance of the C-arm. The inclined plane of the working channel was oriented toward the side of the ligamentum flavum as shown in Figs. 1A and 1B. With the assistance of endoscopy, the proliferative osteophytes were removed using bone rongeurs and a grinding drill to expand the lamina space appropriately. The ligamentum flavum was cut off using a pair of scissors and the nerve root was separated and protected by the nerve stripper. The working channel was then rotated and gently inserted into the epidural cavity. Clear exposure and removal of the herniated/extruded nucleus pulposus were then performed(Figures 2G and 2H). The spinal canal and lateral recess were explored carefully. An Ellman bipolar radiofrequency electrode was used for annulus fibroplasty.

OLM was performed using a technique similar to a previously published one [5, 13]. In brief, under general anesthesia, the patient was placed in a prone position on a carbon-fiber operating table. The lesion segment was located by the C-arm, and a 3-cm incision was made at the posterior median lesion. The paraspinal muscles were stripped to expose the facet joints and the adjacent upper and lower laminae of the diseased segment. A bone window (2 cm in length × 1 cm in width) was made using a bone-nibbling rongeur at the disc herniation location shown by preoperative imaging. The facet joints were carefully protected when opening the bone window. The ligamentum flavum was excised carefully, and the nerve root was separated and protected by the nerve stripper. The herniated or free fragments of the nucleus pulposus were exposed clearly and removed carefully. The nerve root was loosened and uncompressed. After confirming the absence of active bleeding, a drainage tube was placed and the incision was closed layer by layer.

Postoperative management and follow-up evaluations

Training of leg lifting was performed while the patient remained in bed after surgery and was allowed to get out of bed with the protection of lumbar support belts according to the clinical situation. All the patients were followed up in the 1st week, 3rd month, 12th month, and 24th month after surgery. VAS scores were used to evaluate the low back pain and leg radiation pain. The ODI scores (ODI% = (the actual score/(number of answered questions) ⋅ 5) ⋅ 100%, 0–100%) (26) and the MacNab scale (21) were used to evaluate the clinical efficacy of the patients.

Statistical Analysis

SPSS 23.0 (IBM Corp., Armonk, NY, USA) was used to analyze the data. The independent-samples t-test was used to compare the efficacies of the surgical techniques used in the two groups. The one-way analysis of variance (ANOVA) was used to perform comparisons between different periods in the same group. When the results showed a difference, Fisher’s protected LSD tests were used for pairwise comparisons. The chi-square test or Wilcoxon’s rank-sum test was used to compare Continuous/quantitative data. Paired t-tests were used for comparing preoperative and postoperative parameters. The threshold for statistical significance was set to a two-tailed P-value of < 0.05.


Sociodemographic characteristics of the study participants

According to the inclusion and exclusion criteria, 42 patients with SLDH, including 25 men and 17 women aged 71.9 ± 8.2 years (range: 60–89 years), were included in this study. The 42 patients were divided into the following two groups: (1) the PEID group (n = 19 cases) in which patients underwent PEID; and (2) the OLM group (n = 23) in which patients underwent OLM.

The general characteristics of the patients included the following: age (PEID: 67.5 ± 7.5 years; OLM: 70.4 ± 8.5 years), sex (M/F, PEID: 9/10; OLM: 16/7), disease durations (PEID: 15.9 ± 10.3 weeks; 20.4 ± 15.5 weeks), follow-up durations (PEID: I30.4 ± 3.9 months; 28.4 ± 3.7 months), surgical segments (L4–L5/L5–S1, PEID: 12/7; OLM: 9/14), preoperative medical diseases (Yes/No, PEID: 13/6; PLM: 15/8), preoperative VAS-BP and VAS-LL scores (PEID: 3.3 ± 1.0/5.0 ± 1.3; OLM: 3.7 ± 1.3/5.1 ± 1.5), and ODI scores (PEID: 65.2 ± 12.9; OLM: 60.4 ± 11.3). There were no significant differences in any of the above parameters between the two groups (P > 0.05; Table 1 and Table 2).

Table 1

Basic clinical information of the two groups



(n = 19)


(n = 23)



Age (years)

Mean ± Standard Deviation

67.5 ± 7.5

70.4 ± 8.5















Disease duration (weeks)

Mean ± Standard Deviation

15.9 ± 10.3

20.4 ± 15.5



Follow-up period(mouths)

Mean ± Standard Deviation

39.4 ± 3.9

28.4 ± 3.7



Surgical level












Internal Medical diseases












The χ2 test was used to compare the sex, surgical level, and comorbidities;

The independent-samples t-test was used to compare the age, disease duration, and follow-up period;

Table 2

The clinical effects comparison of the two group



(n = 19)


(n = 23)

PEID versus OLM

t/Z (P)


Mean ± Standard Deviation


Before surgery

3.3 ± 1.0

3.7 ± 1.3

t=-1.045; P = 0.302

1st week

1.6 ± 0.9***

2.3 ± 1.0***

t=-2.349; P = 0.024

3rd month

1.1 ± 0.8***&

1.7 ± 0.8***&

t=-2.688; P = 0.010

12th month

0.9 ± 0.7***&&

1.1 ± 0.6***&&&#

t=-0.992; P = 0.327

24th month

0.7 ± 0.5***&&

0.7 ± 0.6***&&&###

t = 0.523; P = 0.604


Mean ± Standard Deviation


Before surgery

5.0 ± 1.3

5.1 ± 1.5

t=-0.325; P = 0.747

1st week

1.7 ± 1.3***

1.3 ± 1.1***

t = 1.110; P = 0.274

3rd month

1.3 ± 0.9***

1.0 ± 0.9***

t = 0.761; P = 0.451

12th month

1.0 ± 0.8***&

0.8 ± 0.7***

t = 0.703; P = 0.486

24th month

0.7 ± 0.6***&&

0.7 ± 0.5***&

t = 0.194; P = 0.847

ODI (%) (Mean ± Standard Deviation)


Before surgery

65.2 ± 12.9

60.4 ± 11.3

t = 1.276; P = 0.209

12th month

20.2 ± 3.3***

23.4 ± 5.7***

t=-2.146; P = 0.038

24th month

19.6 ± 3.1***

22.3 ± 4.6***

t=-2.175; P = 0.036

MacNab level

24 months post-operation


successful results






Z=-.625; P = 0.532

unsuccessful results






The independent-samples t-test was used to compare the VAS and ODI scores between the two groups; One-way analysis of variance (ANOVA)was used perform comparisons between different periods in the same group; When the results showed a difference, Fisher’s protected LSD tests were used for pairwise comparisons. Wilcoxon’s rank-sum test was used to compare the MacNab level.

*** P < 0.001, compared with before surgery; & P < 0.05, && P < 0.01, &&& P < 0.001 compared with 1st week postoperation; # P < 0.05, ### P < 0.001 compared with 3rd month postoperation;

VAS-BP: Visual analgesic score for back pain; VAS-LL: Visual analgesic score radiating to the lower leg;

ODI: Oswestry Disability Index; ODI%= [the actual score/(number of answered questions) X 5] X 100%, 0–100%.

Surgery and complications

Surgical operations were completed successfully for all the patients in the two groups. The mean surgery time of the PEID group was 45.3 ± 18.1 min, which was longer than the 33.9 ± 11.3 min of the OLM group (P < 0.05). However, the estimated blood loss (27.4 ± 18.0 ml), postoperative bed time (2.9 ± 2.6 days), and duration of hospitalization (4.1 ± 2.5 days) in the PEID group were all less than the corresponding parameters (43.9 ± 15.1 ml, 4.4 ± 1.3 days, and 5.8 ± 1.9 days, respectively) in the OLM group (Table 3).

Table 3

Comparison of surgery dates


PEID (n = 19)

Mean ± Standard Deviation

OLM (n = 23)

Mean ± Standard Deviation



Surgery time (minutes)

45.3 ± 18.1

33.9 ± 11.3



Blood loss (mL)

27.4 ± 18.0

43.9 ± 15.1



Bed-rest time (days)

2.9 ± 2.6

4.4 ± 1.3



Hospital stays (days)

4.1 ± 2.5

5.8 ± 1.9



Independent t-test was used to compare between the 2 groups.

Dural tearing and cerebrospinal fluid leakage were identified in two patients in the PEID group. A transient nerve-root irritation was found in three patients in the PEID group. These three patients presented with transient nerve-root irritation that manifested as numbness or tingling in the body parts served by the affected nerves after surgery. However, the symptoms of numbness or tingling disappeared after the administration of mecobalamin (0.5 mg po tid, for three months) and celecoxib (200 mg po qd, for one week), and there were no neurological sequelae. However, each of the instances was no longer present at the follow-up appointments and there were no neurological sequelae. No incision-induced infections or intervertebral space infections were found in either of the two groups.

Clinical outcomes

Patients in both groups were followed up for more than 24 months. The VAS-BP and VAS-LL scores in the PEID group and OLM group before surgery decreased in the PEID group and OLM group postoperatively and further decreased at the follow-up appointment (P < 0.05). The ODI scores also decreased from the preoperative period to the 12th month and 24th month in the PEID group and OLM group. The VAS-BP and ODI scores of the two groups differed significantly during the different postoperative periods. VAS-BP scores in the 1st week and 3rd month after surgery and ODI scores at the 12th month and 24th month appointment in the PEID group were lower than those in the OLM group (P < 0.05). However, there were no significant differences in VAS-BP scores at the 12th month and 24th month, VAS-LL scores at postoperative periods, MacNab levels at 24 months after surgery (P > 0.05; Table 2).

Preoperative imaging examinations revealed the degeneration and osteophyte formation of the lumbar region and disc herniation or prolapse (Figs. 2A-2F Figs. 3A–3F). Postoperative imaging examinations revealed that the herniated or free-fragment nucleus pulposus had been completely removed and that nerve root decompression was sufficient (Figs. 2I and 3G-3I). During follow-up, none of the patients had a re-recurrence of disc herniation or required additional surgery.


Patients with SLDH commonly present with muscle atrophy, especially of the erector spinae and iliocostalis lumborum muscles. The injury and lipogenesis of the paraspinal muscles after open lumbar surgery are the primary causes of long-term low back pain [2224]. With PELD, the surgeon can perform a discectomy via a channel that measures 0.7–12 mm in diameter, which can effectively reduce muscle injury and the incidence of postoperative low back pain [25, 26]. Comparisons of surgery durations, postoperative VAS scores, ODI scores, and hospitalization periods between PELD and OLM patients have yielded inconsistent results across previous studies. Through a meta-analysis, Manyoung Kim [15] found that VAS scores of the lower back and leg, ODI scores, surgery durations, and hospitalization periods of patients who underwent PELD were all better than those of patients who underwent OLM, whereas there were no differences in the MacNab grading, complication rates, recurrence rates, or repeat surgery rates between the patients who underwent the two procedures. However, another meta-analysis showed that when the parameters of patients who underwent OLM were compared with those of patients who underwent PELD, those who underwent the latter procedure had shorter surgery durations and hospital stays; however, there were no significant differences in postoperative VAS scores, ODI scores, surgical complications, or reoperation rates between the two groups [27]. In the present study, VAS-BP scores, VAS-LL scores, and ODI scores in both groups were significantly improved after surgery (P < 0.05). The VAS-BP scores at the 1st week and 3rd month after surgery and the ODI scores at the 12th month’s and 24th month’s appointment in the PEID group were lower than those in the OLM group (P < 0.05); however, there were no differences in the VAS-LL score at the postoperative appointment, the VAS-BP score at the 12th month and 24th month, or in the MacNab level at the 24th month after surgery (P > 0.05). We believe that the lower VAS-BP scores at 1st week and 3rd month, and the ODI scores at the 12th month and 24th month appointment in the PEID group may be related to the fact that the patients included in this study were elderly patients. Compared with PELD, OLM has a wider range of paravertebral muscle dissection, laminectomy, and facet arthrotomy. A previous study reports that 23% of patients required conservative treatment for moderate back pain, and 9% of patients underwent fusion surgery at the primary discectomy site for severe back pain [28]. Another study reported that 70% of the patients experienced back pain during the 4–17-year follow-up period [29]. Elderly patients exhibit muscle atrophy and spinal degeneration. Therefore, OLM surgery should aggravate the back muscle injury, which affects the patient’s low back pain and lower back function, and show higher VAS-BP scores and ODI scores in the OLM group than in the PEID group. Our results demonstrate that both PEID and OLM exhibit good clinical efficacy in the treatment of SLDH and that PELD may play a role in reducing postoperative low back pain.

According to previous studies, PELD has advantages in terms of inducing minimal surgical trauma and minimal intraoperative bleeding and being associated with short surgery durations and fast postoperative recovery [3032]. In the present study, the estimated intraoperative blood loss, postoperative bed stay, and duration of hospitalization of patients in the PEID treatment group were all less than those of patients in the OLM group (P < 0.05), which is similar to the findings of previous studies [27]. Previous studies have shown that PELD is associated with less paraspinal muscle damage and more bony structure preservation than OLM [12, 33]. In the present study, patients could get out of bed with the protection of lumbar support belts according to the clinical situation after surgery in the PEID and OLM groups. All the above reasons could lead to the shortening of postoperative bed stays and hospitalization durations; however, it also confirmed that PEID was characterized by less intraoperative trauma and faster postoperative recovery than OLM. The above factors could also be the reasons why the PEID group had lower VAS-BP scores at the 1st week and 3rd month after surgery and lower ODI scores at the 12th month’s and 24th month’s appointments than the OLM group. In our study, the mean surgery duration in the PEID group was higher than that in the OLM group. The reasons for this finding may be as follows: first, SLDH is often accompanied by the degeneration and hyperplasia of facet joints, both of which make PEID harder in SLDH than in younger patients with lumbar disc herniations. Second, before this study, our team had performed 111 PEIDs, and most of the patients involved were young patients with lumbar disc herniation and without lumbar spinal stenosis. The surgeon did not have much experience when it comes to PEID for senile patients. In contrast, OLM is a classical technique. Prior to this study, OLM had been used to treat more than four hundred patients with disc herniation, including young and elderly patients. The surgeon was already skillful at performing this procedure at the early stage of the present study. The surgeon was able to quickly finish a discectomy even with the presence of severe spinal degeneration. The results all confirm that the surgeon’s proficiency in PEID for SLDH could be further improved.

Nerve injury, dural tearing, and cerebrospinal fluid leakage were severe complications of PELD [34]. Li et al. showed that intraoperative nerve injury may be related to the compression of nerve roots by surgical instruments during the separation of adhesions or the stimulation of nerve roots during hemostasis with a radiofrequency knife head [35]. The elderly patients had lumbar degeneration, which leads to osteophytic hyperplasia, which, in turn, leads to stenosis of the foramina and spinal canal. All three patients had nerve root injury during the implantation of the working channel into a narrow spinal canal. The elderly patients always suffered severe lumbar degeneration and had a thickened ligamentum flavum and adhesions to the dura, all of which resulted in dura injury in two patients during the separation of the ligamentum flavum and dura and also in postoperative cerebrospinal fluid leakage. All the complications had been successfully treated with oral mecobalamin and celecoxib, and there were no neurological sequelae. The incidence of complications in PELD is approximately 4.0–12.5% in the literature [13, 36]. In the present study, 19 patients with SLDH were treated via PEID, and two (10.5%) of them incurred dural injuries and experienced cerebrospinal fluid leakage during surgery while three (15.8%) of them experienced transient nerve-root irritation. The complication rate in the present study was higher than that reported in previous studies, and we believe that this discrepancy is mainly related to spinal degeneration in elderly patients and the paucity of surgical experience at the early stage.

With a combination of our review of the literature and our personal experiences, we can suggest measures to reduce the incidence of complications of PEID. (1) Detailed X-ray, CT, and MRI examinations to understand the location of the disc herniation preoperatively; (2) repeated simulation of the implantation position and the angle of percutaneous endoscopy with the help of images before surgery; (3) careful manipulations during the operation and the flexible use of grinding under the endoscope to remove the degenerative hyperplasia of osteophytes; (4) gentle insertion of the working channel into the lamina space and remembering to avoid excessive force while inserting the channel into the lamina space; and (5) careful removal of the disc after clearly identifying the target nerve and disc, and the avoidance of the blind removal of the disc.

PEID and OLM have the advantages of inducing less trauma, enabling rapid postoperative recovery, and yielding satisfactory clinical results in the treatment of SLDH. However, surgical pointer manipulations should be strictly controlled. Lumbar degeneration and radiographic lumbar spinal canal stenosis are common conditions in elderly patients that render PELD difficult and result in significantly long learning curves for surgeons, especially beginners [27, 37]. OLM enables extensive decompression of the narrow spinal canal visually; however, at the same time, it increases the risk of postoperative lumbar instability and persistent low back pain [8, 9, 38]. Therefore, we recommend that PEID or OLM be used for the treatment of SLDH.


Our present study had some limitations. First, it was a retrospective study and not a prospective study that could provide a higher level of clinical evidence for the comparison of two surgical approaches in SLDH. Second, it had a small sample size.


The application of PEID in the treatment of ELDH achieved satisfactory clinical efficacy. PEID and OLM are both safe and efficacious methods of treating ELDH. PEID has more advantages in reducing surgical trauma, and there was no significant difference in the recurrence rates between the two methods. The long-term clinical results of both techniques seem satisfactory without any of them being superior to the other in elderly patients. PEID is an effective technique for the treatment of ELDH.



Percutaneous endoscopic interlaminar discectomy


Percutaneous endoscopic lumbar discectomy


OLM:open lumbar microdiscectomy

senile lumbar disc herniation

visual analgesia scores for back pain


visual analgesia scores radiating to the lower legs


Oswestry disability index



The manuscript submitted does not contain information about medical device(s) / drug(s)

Author Contributions

Ye-Hui Liao, Chao Tang, Ru-Pei Ye collected the data, analyzed the data, and wrote the manuscript. Dejun Zhong, Fei Ma, Qiang Tang were involved in the design and data management of the study. Dejun Zhong, Gaoju Wang, and Qing Wang performed all surgical procedures. Dejun Zhong critically reviewed and edited the manuscript.

Data Availability Statement

The original contributions presented in the study are included in the article materials, and further inquiries can be directed to the corresponding author.

Ethics statement

This study was approved by the ethics committee of Southwest Medical University, which approved the study and procedures of data collection. All procedures in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Declaration of Helsinki and its amendments, or comparable ethical standards. Prior to enrolment in the study, participants provided their signed informed consent after receiving written and oral information.


The study was supported by a grant from Southwest Medical University (2019ZQN053)

Consent for publication

All participants provided their written consent to publish their data and accompanying images.

Disclosure of Competing Interests

The authors declare that they have no competing interests.


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