What is the influence on adjacent segment lordosis after single-level PELD? – an observational study of radiological alignment changes

doi:10.21203/rs.3.rs-4825188/v1

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What is the influence on adjacent segment lordosis after single-level PELD? – an observational study of radiological alignment changes

https://doi.org/10.21203/rs.3.rs-4825188/v1

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Study Design:

Retrospective cohort study.

Purpose

To investigate the change in lumbar lordosis angle after single-level percutaneous endoscopic lumbar discectomy (PELD) and the difference in lordosis angle between L4/5 and L5/S1.

Methods

All patients were divided into L4/5 and L5/S1 groups according to surgical level. Lateral radiographs before and one year after surgery were collected to assess changes in lordotic angulation at all lumbar segments who underwent PELD at L4/5 and L5/S1.

Results

In total, 92 lumbar disc herniation patients (44 males and 48 females) treated with single-level PELD (52 at L4/5 and 40 at L5/S1) were enrolled. Fifty-two patients received the transforaminal approach (L4/5 21.7%, L5/S1 34.8%), and 40 patients received the interlaminar approach (L4/5 34.8%, L5/S1 8.7%). The L4/5 group had a mean 2° increase in operated segment lordosis (SL) (P < 0.001), the L5/L1 group had a mean − 1° change in the operated SL (P < 0.001), and the segmental lordosis gain was associated with lordosis changes at adjacent segments of -1° at L5/S1 (< 0.001) in the L4/5 group and 1° at L4/5 (< 0.001) in the L4/5 group. Modest gains in global lordosis (LL) angle were 2° (< 0.001) in the L4/5 group and 1° (< 0.001) in the L5/S1 group. The preoperative mean value of PI-LL was 15° in the L4/5 group and 18° in the L5/S1 group, and the postoperative mean value of PI-LL was 14° (P = 0.257) in the L4/5 group and 12° (P = 0.728) in the L5/S1 group.

Conclusion

There are subtle changes in lordosis at the operated segment and adjacent segments after single-level PELD surgery. The impact of surgery on LL is greater at the L4/5 segment than at the L5/S1 segment; additionally, the impact of surgery on lordosis is greater when the interlaminar approach is used than when the transforaminal approach is used.

PELD

Lordosis

Spinal alignment

LDH

Transforaminal

Interlaminar

Degenerative disc disease (DDD) in the lumbar spine is often accompanied by a change in spine lordosis^[1], and many studies have investigated segmental lordosis and a wide range of lordosis at each level ^[2–5]. These studies provide robust evidence of the correlation between sagittal spine‒pelvic balance and patient health-related quality-of-life (HRQOL) scores^{[2, 3]}. Percutaneous endoscopic lumbar discectomy (PELD), a minimally invasive surgery, has little impact on the structure of the spine and theoretically does not significantly impact lumbar lordosis; however, we found that a large proportion of patients still experience residual lumbar pain after endoscopy. We cannot be sure whether PELD surgery significantly affects lumbar lordosis (LL) and the pelvic incidence (PI), and these changes may be related to clinical outcomes. After excluding other potential factors of low back pain caused by compression ^{[4, 5]}, we hypothesized that a change in LL after PELD may be associated with patients’ symptoms.

In PELD surgery, two surgical approaches are usually used: (1) the transforaminal approach and (2) the interlaminar approach^{[6, 7]}. Compared with the interlaminar approach, the transforaminal approach causes different degrees of damage to the unilateral facet joint during foraminoplasty and may disrupt the coronal balance of the spine^{[8, 9]}. Therefore, we consider that different surgical approaches and surgical levels may result in varying degrees of radiographic changes in regional spinopelvic alignment and segmental lordosis (SL) at the operative level and adjacent levels.

This study aimed to observe SL at each level within the lumbar spine in patients undergoing single-level L4/5 or L5/S1 PELD treatment and changes in global lordosis to better comprehend whether preoperative LL is associated with postoperative clinical outcomes after single-level PELD.

Retrospectively collected data from all patients who underwent PELD surgery at our center from January 2020 to December 2023, excluding those who did not meet the study criteria. The exclusion criteria included: 1. Patients with incomplete preoperative or postoperative imaging data; 2. Patients who had undergone other types of spinal surgeries (e.g., spinal fusion) before or after lumbar endoscopic surgery; 3. Patients with concurrent spinal conditions that could affect imaging results, such as severe scoliosis, spinal tumors, or infections; 4. Patients who underwent endoscopic surgery on regions other than the lumbar spine; 5. Patients with a follow-up period of less than six months post-surgery; 6. Patients who underwent revision endoscopic surgery during the study period; 7. Patients who underwent surgery for trauma, infection, or tumors as a primary diagnosis. Ultimately, information from 92 patients who underwent single-level PELD surgery was selected, including 52 patients at the L4/5 segment and 40 patients at the L5/S1 segment. All patients were over 21 years of age and had a follow-up period of no less than six months.

All patients underwent PELD under fluoroscopic guidance at the prostrate position. In the transforaminal approach, the entry site is typically positioned on the outside of the herniated disc, approximately 8–12 cm from the midline of the spine. The front end of the puncture needle was placed in the intervertebral foramen, the guidewire was left in the goal place, a 1 cm skin incision was made, and an endoscopy sheath was inserted. The decompression process is carried out with continuous irrigation. For the intralaminar approach, the entry location was situated parallel to the disc space and at the inferior border edge of the superior lamina on the lesion side. A dilator was introduced and docked under the lower edge of the superior lamina, and the final position was checked on the AP and LAT fluoroscopic images.

The demographic variables collected from all patients included age, sex, body mass index (BMI) and diabetes mellitus diagnosis. The Cobb angle in the sagittal plane was calculated via ImageJ analysis of the radiological data. Preoperative lateral lumbar radiographs and one-year postoperative lateral lumbar radiographs were compared to determine the proper radiological angular change (Fig. 1). Measurements were performed by two of the physicians, with an assessment of concordance between the two.

The values are expressed as the means ± standard deviations. Statistical analysis was performed via the t test to evaluate age, BMI and angle date, and the chi-square test was used to analyze categorical data. A P value < 0.05 was considered statistically significant.

We identified 92 patients who underwent single-level PELD (52 at L4/5 and 40 at L5/S1). Descriptive statistics for all control variables by operative level can be found in Table 1.

Table 1

Basic patient characteristics preoperatively
	L4-5	L5-S1	P value
Age	54.67 ± 12.63	53.00 ± 12.59	.084 *
Sex			.926 #
Female	28(30.4%)	16(17.4%)
Male	24(26.1%)	24(26.1%)
BMI	27.39 ± 3.68	28.84 ± 4.34	.095 *
Diabetes diagnosis			.659✝
With	3(3.3%)	5(5.4%)
Without	48(52.2%)	35(38.0%)
Preoperative angle
Preoperative PI-LL	14.61 ± 10.07	12.91 ± 9.81	.458 *
Operative segment lordosis	10.81 ± 2.09	18.41 ± 3.53	< .001*
Adjacent segment lordosis	5.61 ± 1.34	10.74 ± 2.59	< .001*
Global lordosis	50.87 ± 9.57	50.86 ± 9.51	.929*
Surgery approach			< .001#
Intraluminal	20(21.7%)	32(34.8%)
Transforaminal	32(34.8%)	8(8.7%)
Note. Means with standard deviations in parentheses are shown for all continuous variables. Frequencies with percentages in parentheses are shown for all categorical variables.
*=t test
#=chi-square test
✝=Fisher’s exact test

The L4/5 PELD Group promoted lordosis at the surgical level(Table 2), with a mean SL gain of 1.89° at L4/5 and 0.98° at L5/S1 (P < 0.001). The adjacent segments of the patients who received PELD at L4/5 showed minimal changes in SL, and LL increased by a mean of 3.08° (p = 0.777) in line with the lordosis increase at the L4/5 level. There were no significant alterations at the superior level L1/2 of 0°, at L2/3 of 0° and at L1/2 of 2°. The mean PI-LL decreased from 0 to 10 degrees (p < 0.001).

Table 2

L4/5 PELD Group
Level	Mean SL Change (°)	P value	95% CI
L1-2	0	0.817	0.81
L2-3	0	0.085	1.35
L3-4	2	0.596	1.38
L4-5	2	<0.001	0.90
L5-S1	-1	<0.001	1.10

The LL increased by 2.86° (p < 0.001) in the patients who underwent PELD at L5/S1 (Table 3). The L4/5 level next to the operated level has a mean SL reduction of 1° (p < 0.001). The SL of L3/4 decreased by 0° (p = 0.816). The SL of the superior levels showed a 0° change at L2/3 (p = 0.280) and a 0° change at L1/2 (p = 0.976) as nonsignificant variations. The preoperative PI-LL was 2°, and the postoperative PI-LL was − 1° (p = 0.05) (Table 4).

Table 3

L5/S1 PELD Group
Level	Mean SL Change (°)	P value	95% CI
L1-2	0	0.976	1.32
L2-3	0	0.280	1.28
L3-4	0	0.816	1.10
L4-5	1	<0.001	0.95
L5-S1	-1	<0.001	0.90

Table 4

Comparisons of sagittal balance measurements preoperatively and postoperatively in both groups
	L4/5 group(°)	P Value	L5/S1 group(°)	P Value
Preop-LL	51		51
Postop-LL	53		52
Change of LL	+ 2	<0.001	+ 1	0.002
Mean pelvic incidence (Pl)	58		57
Preop-PI-LL	15		18
Postop-PI-LL	14	0.257	12	0.728

Measurement accuracy:

All metrics in the L4/5 cohort had R scores that were > 0.8. The R score for the measurements in the L5/S1 group ranged from 0.6 to 0.7. Scores > 0.6 were regarded as indicating good reliability. The angle measurements in this study were identified to be precise and repeatable.

The preliminary results of this study indicate that in single-level PELD surgery, different operative segments may have varying degrees of impact on adjacent segments and overall lordosis. In accordance with some of our previous clinical observations, we found that patients receiving PELD via the transforaminal approach have a greater chance of recurrence than those receiving via the interlaminar approach at our institution. We wondered whether the intrusion of the facet joint during foraminoplasty would lead to postoperative changes in lumbar lordosis. For the overall sample in this study, we did find more lordotic changes at the operative segment in the transforaminal group, which led to a greater compensatory reduction in lordosis at the infra-adjacent segment. Wang reported that overall radiological parameters, including disc height (DH), lumbar lordosis and segmental lordosis, significantly changed in both elderly and relatively young patients who underwent PELD^[10]. At L4/5, more lordotic changes at the operative segment led to more compensatory lordosis reduction at the infra-adjacent segment. It is also likely that adjacent segment compensation depends on the mobility of the remaining segments of the lumbar spine. Wu explained that the original integrity of the intervertebral disc and facet joint is destroyed^[11].

In this study, we also find that the radiograph results depend on different surgical approaches. When foraminoplasty is performed at L4/5, the superior articular process of L4 has different degrees of subsidence, which leads to an increase in L4/5 lordosis due to the decreasing supporting capacity of the posterior column of the vertebrae^[12] (Fig. 2). The lordosis gain of L4/5 matches the lordosis "loss" in the neighboring segments, which shows that the lumbar spine has a small amount of compensation for segmental hyperlordosis (2°) in the L4/5 group. Lordosis preservation is essential for achieving sagittal alignment balance and is associated with positive surgical outcomes^[13]. Schwab reported how crucial this relationship is for treating spinal deformity^[2], which may explain why the clinical outcome of the transforaminal group is slightly inferior to that of the interlaminar group.

In this study, we further explored the extent to which changes in lordosis at the surgical segment affect adjacent segments. In both groups, segmental lordosis at the operative level increased, but at the expense of a loss in segmental lordosis at the infra- and supra-adjacent segments, We usually believe that spinal endoscopy results in very little damage to the vertebral structure and hardly affects the lordosis of the spine. In this study, we did find that the global kyphosis of the spine did not change significantly after surgery, but the lordosis of adjacent segments did compensate (P < 0.001), which suggests the need for single-segment analysis of lumbar lordosis preoperatively and postoperatively rather than a crude measure of overall lumbar lordosis when motion segments work together, because Local segmental changes may not be evident as overall lordosis changes if they are compensated by other segments.

Patients in this study focused mainly on the L4/5 and L5/S1 segments. Compared with local lordotic angle change at L5/S1, PELD surgery for increased lordosis at L4/5 was associated with a greater reflection of LL change within the lumbar spine. Chevillotte studied the difference in LL between asymptomatic volunteers and reported that the mean difference in LL between L4/5 and other levels was − 4.6°^[14]. Similarly, Hasegawa studied differences in LL in patients with adult spinal deformity and reported that the mean LL values at L4/5 and L5/S1 were approximately 11° and 9°, respectively, indicating that L4/5 has greater compensation capability than other lumber does^{[15]; thus}, these patients are likely to have a greater risk of spondylosis throughout the lumbar spine, with stiffness in adjacent motion segments reducing the ability to compensate for the loss of primary lordosis at L4/5. In previous studies, the loss of preoperative lumbar lordosis was one of the factors influencing postoperative residual symptoms^[16].

Further research is necessary since there are a variety of patterns of lordosis variation preoperatively and patterns of response to lordosis restoration at the operated level, which are related to the diversity of pain sources and sagittal alignment. Different approaches at the same level cause different degrees of damage to the articular process, and the degree of relief of low back pain after decompression is also inconsistent. We also accept that it is possible that the ability of vertebral bodies to adapt to changes in lordosis is associated with pain relief ^[22–24], but longer follow-up studies are needed for verification.

We observed a change in the PI, but neither group was statistically significant (P = 0.257&0.728). Some studies have provided a certain understanding of the PI^[25–27], Roussouly demonstrated the importance of this relationship in the correction of spinal deformity in patients, in whom significant improvements in HRQL scores were correlated with a PI-LL mismatch of less than 9 degrees^[28]. Subsequent work by Robertson et al. revealed that achieving balanced spinopelvic alignment was protective against development^[9].

This study demonstrates that following PELD surgery, there are subtle changes in lordosis at both the surgical segment and adjacent segments. The impact of the surgery on LL is greater at the L4/5 segment compared to the L5/S1 segment. Additionally, the effect of the surgery on lordosis is more pronounced with the interlaminar approach than with the transforaminal approach.

Ethics approval and consent to participate:

This study was approved by the Ethics Committee of the First Affiliated Hospital of Harbin Medical University(Grant No. [IRB-AF/SC-08/06.0]). All procedures performed in this study involving human participants were in accordance with the ethical standards of the institutional research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.

Consent for publication:

All authors give consent for the publication of the manuscript titled “What is the influence on adjacent segment lordosis after single-level PELD? – an observational study of radiological alignment changes” in Journal of Orthopaedic Surgery and Research, published by Spinger. We confirm that this manuscript is original, has not been previously published, and is not under consideration elsewhere. All authors have reviewed and approved the final version for submission and publication.

Availability of data and materials:

The datasets used and analyzed during the current study are available from the corresponding author on reasonable request.

Competing interests:

The authors declare that they have no competing interests related to this manuscript. All authors have disclosed any potential conflicts of interest that could be perceived as influencing the results or interpretation of this study.

Funding:

This article is sponsored by the Bethune·Special Research Fund Project for Minimally Invasive Vertebral Intensive Treatment of Pathological Spinal Fractures(BK-JP2021001)

Authors' contributions:

L.SW. contributed to the study conception and drafted the manuscript; Q.Q. supervised the study and reviewed the final manuscript; W.WY. designed the study and conducted the literature review; L.Y. responsible for data acquisition, analysis, and interpretation; W.XY. assisted in data acquisition and contributed to the manuscript revision.

Acknowledgement:

Not applicable.

Clinical Trial Number : It is being reviewed by Chinese Clinical Trial Registry (ChiCTR) and will be announced later.

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No competing interests reported.

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You are reading this latest preprint version

What is the influence on adjacent segment lordosis after single-level PELD? – an observational study of radiological alignment changes

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Abstract

Study Design:

Purpose

Methods

Results

Conclusion

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1. Background

2 Methods

3 Results

4 Discussion

5 Conclusion

Declarations

References

Additional Declarations

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