Relationship between interlaminar angle and the superior articular process removal range in patients with lumbar disc herniation during Percutaneous Endoscopic Interlaminar Discectomy: a cross-sectional study

doi:10.21203/rs.3.rs-3457783/v1

Objective:

Explore the relationship between the superior articular process removal range (SAPR) during Percutaneous Endoscopic Interlaminar Discectomy （PEID）and the interlaminar angle (ILA). In addition, we assessed the relationship between other imaging parameters and surgical difficulty.

Methods:

Collect the data of 237 patients who underwent PEID at Qilu Hospital of Shandong University. Measure the imaging data, such as ILA, facet angle (FA), facet joint medial distance (FMD), and the SAPR, and compare their statistical difference.

Results:

SAPR is negatively related to ILA(P<0.05). For patients with the L4/L5 segment operation, the average SAPR is 6.15±3.02mm. The SAPR of the patients with surgical segment ILA of 47.50-72.52° was 9.06±1.70mm. That of the patients with surgical segment ILA of 72.71-86.06° was 7.30±1.22mm. That of the patients with surgical segment ILA of 86.31-96.37° was 6.50±1.48mm. That of the patients with surgical segment ILA of 97.10-118.68° was 1.86±1.17mm. For patients with the L5/S1 segment operation, the average SAPR is 4.81±2.17mm. The SAPR of the patients with surgical segment ILA of 54.48-86.22° was 7.22±0.79mm. That of the patients with surgical segment ILA of 87.30-98.60° was 5.72±1.06mm. That of the patients with surgical segment ILA of 98.80-107.06° was 4.43±0.90mm. That of the patients with surgical segment ILA of 108.53-141.00° was 1.98±1.26mm. Interestingly, the ILA is also closely related to the operation time and operation difficulty score(P<0.05).

Conclusions:

Smaller ILA tends to be associated with more SAPR during the PEID. In addition, The smaller the ILA, the more difficult it is to expose the key anatomical structures, which leads to an increase in operation difficulty and longer operation time.

LDH

Interlaminar approach

decompression

difficulty scores

Lumbar intervertebral disc herniation (LDH) is a prevalent clinical condition that poses significant challenges to healthcare, society, and the economy in the present era^1-3. Compared to the central type, the paracentral type of LDH has a higher incidence rate within the population, and it is more likely to cause nerve root compression, resulting in severe low back and leg pain symptoms. Among the various techniques available, percutaneous endoscopy has emerged as one of the common approaches⁴. This procedure can be performed using either the interlaminar approach or the transforaminal approach⁵. In cases involving disc herniation with spinal stenosis, the Percutaneous Endoscopic Interlaminar Discectomy (PEID) is often preferred. This preference arises from the fact that the interlaminar approach provides easier access to the dorsal aspect of the spinal canal⁶. Moreover, the PEID is particularly well-suited for LDH with large herniated discs⁶.

During the PEID procedure, the removal of bony structures to expose the lateral edges of the nerve root has traditionally been carried out. However, effectively judging the range of superior articular process removal (SAPR) can be challenging due to the presence of adipose tissue and the ligamentum flavum surrounding the dural sac. Excessive removal of facet joints can lead to complications such as lumbar facet joint disorder and lumbar instability^7-9. Moreover, if the ligamentum flavum is removed first in PEID surgery, there is a higher risk of injuring the dural sac and nerve root when they are exposed without the protection of the ligamentum flavum¹⁰.

In comparison to the transforaminal approach, several studies have demonstrated that the interlaminar approach has a more genlter learning curve for operators but may pose greater difficulty for beginners^11-13. Consequently, finding ways to enhance intraoperative understanding through preoperative data has become a crucial consideration. We propose the potential possibility of predicting SAPR during the operation using preoperative data. We selected 3 common imaging parameters: interlaminar angle (ILA), facet angle (FA), facet joint medial distance (FMD), and analyze the correlation with the SAPR during PEID surgery. Such predictions could minimize unnecessary structural damage and enhance operators' preoperative comprehension.

Participants

This study prospectively collected data of 237 patients from January 2022 to June 2023. This study was approved by the our hospital ethics committee, and all studied subjects gave their informed consent.

Eligibility criteria for this study were: Patients with clinically diagnosed paracentral LDH, patients with complete preoperative and postoperative clinical data, visual analogue scale (VAS) for back and leg pain, Oswestry disability index (ODI), MRI and CT imaging data, patients whose responsible segment is L4/5 or L5/S1 undergoing PEID surgery. The exclusion criteria were as follows: the patient has prior lumbar surgery of the same segment in the past; the patient with vertebral fracture, spinal infection, tumor or immune diseases.

Surgery

All operations were done by 2 doctors titled with an associate chief physician or above. The two clinicians remained blinded to the study. The surgical instruments use the ilessys-Delta system (produced by Joimax, Germany). The outer diameter of the Delta spinal endoscope is 10 mm and the diameter of the working channel is 6 mm. The operation steps are as follows: After successful anesthesia, the patient is placed in a prone position. Mark the puncture point about 0.8 cm beside the spinous process on the side with severe symptoms using the X-ray fluoroscopy. Puncture and insert the working channel layer by layer (Figure 1). Remove the hypertrophic ligamentum flavum. Then resect the cranial and caudal laminae, articular process. The superior articular process（SAP）was cut off until the lateral edge of the nerve root was fully exposed（Figure 2）. Then the herniated disc tissue was carefully removed with nucleus pulposus forceps.(video1，video2)

Radiographic evaluation and definition

ILA, FA, FMD were measured by two experienced spine surgeons in duplicate and averaged as shown in Figure 3. All of these parameters were measured in the axial cut of the CT scan at the level of the upper border of the lower vertebral body at the surgical segment.

CT scan was performed 2 days after the operation. Use IMPAX 6.5.5.3020 software of AGFA company to measure the SAPR of the lower vertebral body in the coronal position by bilateral comparison. Figure 4 and Figure 5 show the imaging data and Radiographic evaluation including ILA, FA, FMD, and SAPR of two patients participating in the study.

Surgical Difficulty Score

Referring to the questionnaire on the difficulty of pancreatoduodenectomy surgery designed by Professor Hisashi Kosaka¹⁴, we made a questionnaire on the difficulty of PEID surgery, as shown in Table1.

The operation process is divided into channel establishment, exposure of key anatomical structures, such as nerve roots and herniated intervertebral discs, and decompression. The difficulty of each process was scored on a scale of 1 to 9 (higher scores indicate greater difficulty), and was classified as simple (scored 1-3), moderate (scored 4-6), or difficult (scored 7-9). Finally, the three scores are added to get the total difficulty score. After surgery, the chief surgeon scored the operation difficulty of all patients according to the subjective experience of the operation.

Statistical analyses

Analyses were performed using IBM SPSS Statistics version 23. All data are shown as mean ± standard deviation or ± standard error of the mean. Patients were then split by quartile groups according to the SAPR and ILA respectively. When the data were normally distributed, one-way ANOVA was used for comparison between groups. When the data were not normally distributed, the rank-sum test was used. Chi-squared test and Fisher’s exact test were used to analyze counting data. For correlation analyses between the data and the SAPR, Pearson correlation coefficients (Pearson r) and p values are reported, and P ≤ 0.05 was regarded as a statistically significant difference.

Baseline data

A total of 237 patients were included in this study. Grouped by surgical segment, 134 patients underwent surgery at L4/L5, and 103 patients underwent surgery at L5/S1. There was no significant difference in gender, age, BMI, preoperative and postoperative VAS score, preoperative and postoperative ODI score, length of hospital stays, and intraoperative blood loss of the two groups. The surgery time and total difficulty scores of operations of the L4/5 segment were higher than that of the L5/S1 segment (P<0.05) The ILA, FA, and FMD of the L4/5 segment were smaller than that of the L5/S1 segment (P<0.05). The SAPR in the L4/5 segment operation was larger than that in the L5/S1 segment operation (P<0.05). (Table 2)

Comparison of patients’ baseline data and imaging data.

The average SAPR in the PEID of L4/5 was 6.15±3.02mm. The maximum SAPR is 11.3mm; the minimum SAPR is 0.5mm. The patients were divided into 0.5-3.8mm group, 4.3-6.8mm group, 6.9-8.2mm group, and 8.3-11.3mm group via the interquartile method. There was no significant difference in gender, age, BMI, herniation type, preoperative and postoperative VAS scores, preoperative and postoperative ODI scores, length of hospital stays, and intraoperative blood loss among the 4 groups (P>0.05). Change in surgery times is with no significant difference between 0.5-3.8mm and 4.3-6.8mm groups, 6.9-8.2mm and 8.3-11.3mm groups. However, compared with 6.9-8.2mm and 8.3-11.3mm groups, the 0.5-3.8mm and 4.3-6.8mm groups had a significantly shorter operative time. The total operation difficulty score of patients with different SAPR and the surgical difficulty score of exposure of key anatomical structures were statistically significant, those of 8.3-11.3mm group were significantly higher than the other groups (P<0.05). In terms of imaging data, there was no statistical significance in the FA and the FMD in different patient groups (P>0.05). The ILA of 8.3-11.3mm group< 6.9-8.2mm group< 4.3-6.8mm group< 0.5-3.8mm group (P<0.05). (Table 3)

The average SAPR in L5/S1 patients was 4.81±2.17mm. The maximum SAPR is 8.6mm; the minimum SAPR is 0.3mm. The patients were divided into 0.3-3.4mm group, 3.5-4.9mm group, 5.0-6.6mm group and 6.7-8.6mm group using the interquartile range method. Gender, age, BMI, herniation type, preoperative and postoperative VAS scores, preoperative and postoperative ODI scores, length of hospital stay, and intraoperative blood loss were not statistically significant in patients with different SAPR (P>0.05). In terms of total surgical difficulty score, the scores of the 6.7-8.6mm group were significantly higher than that of the other three groups (P<0.05). There was no significant statistical difference among the other three groups (P>0.05). In addition, there was no statistically significant difference in the surgical difficulty scores of each procedure (P>0.05). In terms of imaging data, there were no significant differences in the FA and the FMD of different groups (P>0.05). The ILA of 6.7-8.6mm group < 5.0-6.6mm group < 3.5-4.9mm group < 0.3-3.4mm group (P<0.05). (Table 3)

Comparison of perioperative data in patients with different ILAs.

The comparison of perioperative data in patients with different ILAs of L4/5 is shown in Table 4: There were no significant differences in preoperative and postoperative VAS scores, preoperative and postoperative ODI scores, length of hospital stays, and intraoperative blood loss in patients with different ILAs. The surgery time of the 97.10-118.68° group was significantly shorter than the other 3 groups (P<0.05). In terms of surgical difficulty scores, there was a statistically significant difference in the total and the exposure of key anatomical structures difficulty scores (P<0.05). Inter-group analysis showed that 47.50-72.52° and 72.71-86.06° groups are higher than 86.31-96.37° and 97.10-118.68° groups in total surgical difficulty scores (P<0.05), 47.50-72.52° group is higher than the other 3 groups in the exposure of key anatomical structures difficulty scores (P<0.05). And there was no significant statistical difference among the other 3 groups (P>0.05). Besides, clinical groups did not differ on difficulty scores of the other 2 procedures (P>0.05).

The comparison of perioperative data in patients with different ILAs of L5/S1 is shown in Table 4: There were no significant differences in preoperative and postoperative VAS scores, ODI scores, length of hospital stays, and intraoperative blood loss in patients with different ILAs. Inter-group analysis showed that the surgery time of 108.53-141.00° group < 54.48-86.22° group (P<0.05). In terms of surgical difficulty score, there was a statistically significant difference in the total and the exposure of key anatomical structures difficulty scores (P<0.05). Inter-group analysis showed that the two scores of the 54.48-86.22° group were significantly higher than those of the other 3 groups (P<0.05), and there was no significant statistical difference among the other 3 groups (P>0.05). Besides, clinical groups did not differ on difficulty scores of the other 2 procedures (P>0.05).

Comparison of imaging data in patients with different ILAs.

The imaging data of patients with different ILA in L5/S1 PEID are compared as shown in Table 5. The patients were grouped via the interquartile method according to the ILA. The average ILA of L4/5 patients is 85.73±16.29°. The maximum is 118.68°, and the minimum is 47.50°. There were significant differences in the SAPR in different groups (P<0.05). The average SAPR in patients with an ILA of 47.50-72.52° is 9.06±1.70mm. That in patients with an angle of 72.71-86.06° is 7.30±1.22mm. That in patients with an angle of 86.31-96.37° is 6.50±1.48 mm. That in patients with an angle of 97.10-118.68° is 1.86±1.17mm. There was a statistical difference in the FMD among the groups (P<0.05). FMD of the 97.10-118.68° group was significantly longer than the other 3 groups (P<0.05).

The imaging data of patients with different ILA in L5/S1 PEID are compared as shown in Table 5. The patients were grouped via the interquartile method according to the ILA. The average ILA of L5/S1 patients is 97.54±16.59°. The maximum is 141.00°, and the minimum is 54.48°. There were significant differences in the SAPR in different groups (P<0.05). The average SAPR in patients with an ILA of 54.48-86.22° is 7.22±0.79mm. That in patients with an angle of 87.30-98.60° is 5.72±1.06mm. That in patients with an angle of 98.80-107.06° is 4.43±0.90mm. That in patients with an angle of 108.53-141.00° is 1.98±1.26mm. There was a statistical difference in the FMD among the groups (P<0.05). Compared with 54.48-86.22° and 87.30-98.60° groups, the 98.80-107.06° and 108.53-141.00° groups had a significantly shorter FMD (P<0.05).

Correlation analysis between the SAPR and imaging data.

Pearson correlation analysis was performed between the SAPR and the imaging data. There was a significant negative correlation between the SAPR and ILA in L4/5 PEID (P<0.05). Besides, the SAPR is negatively correlated with the FMD in L4/5 PEID (P<0.05). There was no significant correlation with FA (P>0.05). Interestingly, there was also a significant negative correlation between the SAPR and ILA in L5/S1 PEID (P<0.05). But there was no significant correlation between the FA and the FMD (P>0.05). (Table 6, Figure 6)

With the advancement of technology, there has been a growing preference for minimally invasive surgery ^15,16. To enlarge the interlaminar space and sufficiently decompress, the cranial lamina can be partially resected, including the distance between cranial and caudal laminae, and the distance between medial borders of processes articular and the midline¹⁷. However, due to the ligamentum, flavum and the obstruction of the view field during the operation, the surgeon could not correctly estimate the extent of removal of bony structures such as the SAP. Relying solely on previous experience to determine the amount of SAP removal can sometimes result in excessive removal, leading to lumbar spine instability, persistent low back pain symptoms, and potential long-term complications like spondylolisthesis^18,19. The ligamentum flavum and adipose tissue play a crucial role in protecting the nerve structures during exposure. If the ligamentum flavum is removed as the initial step, it increases the risk of complications such as cerebrospinal fluid leakage and iatrogenic injury to the dural sac and nerve roots²⁰.

Preserving the original structure and minimizing damage to normal anatomical structures has been a focal point for surgeons in the past. Initially, Caspar introduced the microsurgical discectomy technique, which involved extensive laminectomy or laminectomy combined with partial or total arthrectomy, all performed under direct vision²¹. Later on, Daniele Vanni discovered that approximately 10% of patients with lumbar disc herniation (LDH) experience upward or downward migration of the herniated nucleus pulposus, which can be effectively treated while preserving the ligamentum flavum, still requiring direct visualization²¹. Furthermore, Juichi Tonosu conducted a comprehensive analysis of different patients and concluded that only individuals with an interlaminar space measuring 20 mm or more are suitable candidates for the interlaminar approach²². The aim of such approaches was to maintain the integrity of the natural anatomical structures and minimize unnecessary tissue disruption.

Our research findings indicate a notable correlation between the ILA and the SAPR. This indicated ILA has potential value in predicting SAPR. Besides, there is a correlation between FMD and SAPR in the L4/5 segment, but the correlation disappears in L5/S1, which indicates that the predictive value of FMD for SAPR is lower than that of ILA. The reason for this remains to be discussed, and may be due to SAP and intervertebral disc anatomical differences between related structures.

We found that the smaller the ILA is, the operation time is longer and the difficulty score of the operation is higher, especially the exposure process. These findings highlight the importance of assessing ILA as a preoperative factor in predicting the difficulty of the operation and guiding surgical decision-making. Surgeons should take into account the ILA measurement when planning and performing PEID surgeries, as it can provide valuable insights into the anticipated challenges. Junior doctors may consider selecting patients with larger laminar angles when performing PEID.

Furthermore, we discovered a lack of existing studies specifically addressing the removal of bony structures during PEID. This novel result was obtained through our experimental investigation. However, it is important to acknowledge some limitations in our trial, such as potential slight biases in comparing the width of the bilateral articular processes.

ILA is negatively correlated with SAPR and has potential value in predicting SAPR. Furthermore, we observed a correlation between ILA and surgical difficulty. Specifically, when the ILA is smaller, exposure of critical anatomical structures during surgery becomes more challenging. Therefore, this results in increased surgical difficulty and prolonged operative time.

Ethical Approval

Scientific Review Committee of Qilu Hospital of Shandong University (QLCR20230399). All patients gave informed consent and signed a consent form.

Funding

The study was not funded.

Availability of data and materials

The datasets used/or analyzed during the current study are available from the corresponding author upon reasonable request.

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Table1.Questionnaire on the difficulty of spinal endoscopic surgery.

Category of difficulty	Simple			Moderate			Difficult
Difficulty score: Channel establishment	1	2	3	4	5	6	7	8	9
Difficulty score: Exposure of key anatomical structures	1	2	3	4	5	6	7	8	9
Difficulty score: Decompression	1	2	3	4	5	6	7	8	9

Table 2. Comparison of baseline data and imaging data of patients with different operation segments.

Tmers	L4/L5 (n=134)	L5/S1 (n=103)	P-value
Gender（Male/Female）	77/57	58/45	0.895
Age（y）	40.29±11.11	39.11±9.54	0.388
BMI（kg/m²）	24.68±3.88	25.36±3.60	0.170
VAS（Preoperative）	6.94±1.23	6.93±1.02	0.956
VAS（Postoperative）	2.33±1.33	2.59±0.99	0.093
ODI（Preoperative）	69.52±8.22	71.31±6.72	0.074
ODI（Postoperative）	29.39±8.49	27.70±6.51	0.095
Length of hospital stays（d）	3.25±0.76	3.07±0.77	0.065
Surgery time (min)	87.48±17.35	76.55±13.12	＜0.0001
Intraoperative blood loss (ml)	28.69±8.18	30.78±10.02	0.079
Difficulty of operation (Total)	13.04±1.79	11.92±2.24	0.012
(Channel establishment)	2.74±1.06	2.49±0.51	0.179
(Exposure of key anatomical structures)	4.85±1.74	4.62±1.37	0.501
(Decompression)	5.46±1.35	4.82±1.62	0.051
ILA（°）	85.73±16.29	97.54±16.59	＜0.0001
FA（°）	41.62±8.44	45.54±10.43	0.02
FMD（mm）	22.23±2.46	26.27±3.93	＜0.0001
SAPR (mm）	6.15±3.02	4.81±2.17	＜0.0001

Table 3. Comparison of baseline data and imaging measurements in patients with different SAPR in L4/5 and L5/S1 PEID.

Terms					P-value
L4/5 group	0.5-3.8mm	4.3-6.8mm	6.9-8.2mm	8.3-11.3mm
Gender（Male/Female）	14/20	15/19	14/20	14/18	0.991
Age（y）	42.26±11.69	37.21±8.98	39.15±11.65	42.69±11.47	0.135
BMI（kg/m²）	23.76±2.63	25.26±4.14	24.68±4.67	25.04±3.80	0.406
VAS（Preoperative）	7.03±1.22	6.71±1.17	6.74±1.05	7.31±1.42	0.152
VAS（Postoperative）	2.21±1.34	2.32±1.41	2.59±1.08	2.19±1.47	0.585
ODI（Preoperative）	70.88±6.13	68.76±8.12	67.59±8.37	70.94±9.80	0.258
ODI（Postoperative）	28.79±8.16	29.88±8.09	30.09±7.47	28.75±10.37	0.877
Length of hospital stays（d）	3.18±0.76	3.38±0.74	3.26±0.79	3.19±0.78	0.672
Surgery time (min)	83.09±17.19	80.18±14.88	92.38±18.15	94.69±15.19	0.001
Intraoperative blood loss (ml)	29.71±7.17	31.03±8.69	27.35±8.28	26.56±8.08	0.093
Difficulty of operation (Total)	11.77±1.42	13.18±1.08	12.91±1.92	14.55±1.57	0.001
(Channel establishment)	2.54±0.66	2.36±0.81	3.00±1.48	3.09±1.13	0.302
(Exposure of key anatomical structures)	3.85±1.57	4.91±1.58	4.64±1.63	6.18±1.47	0.008
(Decompression)	5.38±1.04	5.82±1.78	5.36±1.57	5.27±1.01	0.791
ILA（°）	106.33±6.40	85.77±8.37	81.90±9.08	67.88±11.07	＜0.0001
FA（°）	41.60±9.30	41.61±8.25	41.49±7.90	41.78±8.62	0.999
FMD（mm）	22.83±1.89	22.27±2.57	21.95±2.88	21.85±2.38	0.355
L5/S1 group	0.3-3.4mm	3.5-4.9mm	5.0-6.6mm	6.7-8.6mm
Gender（Male/Female）	16/11	15/10	15/12	12/12	0.890
Age（y）	41.3±8.32	36.24±8.42	38.78±11.44	40.00±9.39	0.273
BMI（kg/m²）	25.11±3.82	25.22±4.00	25.71±3.39	25.38±3.34	0.936
VAS（Preoperative）	6.96±1.13	6.84±1.07	6.93±0.96	7.00±0.98	0.955
VAS（Postoperative）	2.52±0.94	2.68±0.95	2.44±1.09	2.75±1.03	0.678
ODI（Preoperative）	71.81±6.68	72.48±7.30	70.67±6.73	70.25±6.28	0.631
ODI（Postoperative）	27.48±6.34	28.52±7.39	26.96±6.33	27.92±6.20	0.853
Length of hospital stays（d）	3.19±0.79	2.88±0.83	3.00±0.78	3.21±0.66	0.378
Surgery time (min)	73.33±12.79	72.00±8.42	77.41±12.20	83.96±15.60	0.005
Intraoperative blood loss (ml)	28.70±9.96	33.40±11.6	28.52±9.98	32.92±7.51	0.148
Difficulty of operation (Total)	11.44±1.88	11.25±1.75	11.25±2.09	13.70±2.36	0.029
(Channel establishment)	2.44±0.53	2.38±0.52	2.58±0.52	2.50±0.53	0.838
(Exposure of key anatomical structures)	4.00±0.71	4.25±1.04	4.58±1.31	5.50±1.78	0.081
(Decompression)	5.00±1.73	4.63±1.77	4.08±1.24	5.70±1.57	0.126
ILA（°）	116.76±10.84	100.22±6.23	92.98±8.47	78.26±10.62	＜0.0001
FA（°）	46.23±9.30	44.74±13.69	47.10±8.40	43.87±10.10	0.692
FMD（mm）	26.96±4.51	27.10±4.20	25.47±3.12	25.53±3.68	0.271

Table 4. The comparison of imaging data and baseline data among patients with different ILA in L4/5 and L5/S1

Terms					P-value
L4/5 group	47.50-72.52°	72.71-86.06°	86.31-96.37°	97.10-118.68°
Gender（Male/Female）	14/20	15/19	14/20	14/18	0.991
Age（y）	42.26±11.69	37.21±8.98	39.15±11.65	42.69±11.47	0.135
BMI（kg/m²）	23.76±2.63	25.26±4.14	24.68±4.67	25.04±3.80	0.406
VAS（Preoperative）	7.18±1.31	6.79±1.14	6.74±1.21	7.06±1.25	0.390
VAS（Postoperative）	2.30±1.51	2.18±0.95	2.53±1.48	2.29±1.31	0.752
ODI（Preoperative）	69.91±7.95	68.91±9.10	68.21±9.04	71.06±6.65	0.514
ODI（Postoperative）	29.76±10.86	28.52±5.36	29.94±9.13	29.32±7.98	0.908
Length of hospital stays（d）	3.30±0.73	3.24±0.71	3.35±0.92	3.12±0.69	0.619
Surgery time (min)	94.39±16.38	89.91±16.39	82.35±17.85	83.53±16.63	0.012
Intraoperative blood loss (ml)	28.18±9.09	27.88±7.81	27.94±8.54	30.74±7.19	0.417
Difficulty of operation (Total)	14.55±1.57	13.33±1.78	12.70±1.16	11.77±1.42	0.001
(Channel establishment)	3.09±1.13	2.58±0.79	2.80±1.62	2.54±0.66	0.596
(Exposure of key anatomical structures)	6.18±1.47	4.75±1.60	4.80±1.62	3.85±1.57	0.008
(Decompression)	5.27±1.01	6.00±1.04	5.10±2.13	5.38±1.04	0.418
L5/S1 group	54.48-86.22°	87.30-98.60°	98.80-107.06°	108.53-141.00°
Gender（Male/Female）	16/11	15/10	15/12	12/12	0.890
Age（y）	41.3±8.32	36.24±8.42	38.78±11.44	40.00±9.39	0.273
BMI（kg/m²）	25.11±3.82	25.22±4.00	25.71±3.39	25.38±3.34	0.936
VAS（Preoperative）	6.88±0.93	7.04±0.96	6.88±1.03	6.92±1.20	0.941
VAS（Postoperative）	2.72±0.98	2.65±1.16	2.46±0.95	2.54±0.91	0.797
ODI（Preoperative）	69.36±6.37	73.04±5.74	71.42±7.63	71.35±6.85	0.282
ODI（Postoperative）	27.52±5.33	28.46±8.26	27.5±6.23	27.31±6.12	0.922
Length of hospital stays（d）	3.00±0.65	3.15±0.88	2.88±0.77	3.23±0.77	0.373
Surgery time (min)	83.60±15.58	77.31±11.33	73.27±10.67	72.31±12.10	0.007
Intraoperative blood loss (ml)	33.60±7.97	30.19±7.80	29.04±13.34	30.38±9.89	0.413
Difficulty of operation (Total)	13.75±2.05	11.00±1.77	11.15±2.08	11.17±1.60	0.005
(Channel establishment)	2.58±0.52	2.50±0.54	2.46±0.52	2.33±0.52	0.808
(Exposure of key anatomical structures)	5.67±1.72	4.38±1.06	4.23±0.83	3.67±0.52	0.006
(Decompression)	5.50±1.51	4.13±1.13	4.46±1.81	5.17±1.72	0.215

Table 5. The comparison of imaging data among patients with different ILA in L4/5 and L5/S1 PEID.

Terms					P-value
L4/5 group	47.50-72.52°	72.71-86.06°	86.31-96.37°	97.10-118.68°
SAPR（mm）	9.06±1.70	7.30±1.22	6.50±1.48	1.86±1.17	＜0.0001
FA（°）	40.83±8.75	42.54±7.48	41.11±8.52	41.99±9.15	0.836
FMD（mm）	22.00±2.49	22.13±2.41	22.72±2.68	23.04±1.86	0.007
L5/S1 group	54.48-86.22°	87.30-98.60°	98.80-107.06°	108.53-141.00°
SAPR（mm）	7.22±0.79	5.72±1.06	4.43±0.90	1.98±1.26	＜0.0001
FA（°）	44.95±8.07	48.32±13.13	42.90±7.74	46.0±11.53	0.306
FMD（mm）	25.52±4.43	24.88±1.54	27.12±3.51	27.54±4.96	0.042

Table 6. Correlation analysis between the SAPR and imaging data.

Terms	R-value	P-value
L4/5
ILA	-0.867	＜0.0001
FA	-0.017	0.849
FMD	-0.182	0.035
L5/S1
ILA	-0.901	＜0.0001
FA	-0.027	0.790
FMD	-0.137	0.169

No competing interests reported.

Relationship between interlaminar angle and the superior articular process removal range in patients with lumbar disc herniation during Percutaneous Endoscopic Interlaminar Discectomy: a cross-sectional study

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