Clinical Efficacy of Unilateral Dual‐channel Endoscopic Lumbar Interbody Fusion for Lumbar Spondylolisthesis with Spinal Scoliosis

Abstract

Objectives

Scoliosis associated with spondylolisthesis is a common phenomenon. Recent research has reported that scoliosis can spontaneously disappear after lumbar spinal fusion surgery. Researchers have advocated that, for scoliosis associated with vertebral slippage, surgery for the latter may be the only necessary intervention, while unnecessary surgery for scoliosis should be avoided. So we propose that minimally invasive techniques can achieve treatment effects similar to those of open surgery. Therefore, in this study, we aimed to investigate the clinical efficacy of unilateral dual‐channel endoscopic lumbar interbody fusion (ULIF) for treating lumbar spondylolisthesis with spinal scoliosis.

Methods

This study retrospectively analyzed patients with lumbar spondylolisthesis and spinal scoliosis who underwent ULIF between September 2021 and September 2023. Measurements of the Cobb angle, lumbar lordosis (LL) angle, sacral slope (SS), slip percentage (SP), slip angle (SA), L1 plumb line‐S1 distance (LASD), and average intervertebral height (AIH) were taken preoperatively, immediately following surgery, 3 months after surgery, and at the final follow‐up. The visual analogue scale (VAS), Oswestry disability index (ODI), and Japanese Orthopaedic Association (JOA) scoring systems were used to assess clinical results. The surgical efficacy was evaluated by comparing these parameters before and after surgery. Comparison of indicators within the same group was conducted using one‐way repeated‐measures analysis of variance or paired sample t‐tests, whereas between‐group differences were compared using an independent t‐test.

Results

This study included 31 individuals who underwent surgery and completed follow‐up. The follow‐up period did not show a significant loss of corrective angles. Furthermore, the Cobb angle, SP, SA, and LASD significantly decreased after surgery, whereas the LL angle, SS, and AIH significantly increased (all p < 0.05). SP did not differ between the immediate postoperative period and the 3‐month and final follow‐up periods (p > 0.05). However, other parameters significantly improved during the follow‐up period at all time points, except from 3 months to the final follow‐up period (p > 0.05). Throughout the follow‐up period, the lower back and leg pain VAS, ODI, and JOA scores considerably improved compared with the preoperative levels (p < 0.05).

Conclusion

ULIF effectively treated lumbar spondylolisthesis with scoliosis, thereby reducing the degree of slip and scoliosis. By performing surgical reduction, fusion, and fixation only on the slipped segment, ULIF also had a corrective effect on the spinal lateral curvature, thereby avoiding the need for unnecessary scoliosis surgery. Moreover, the short‐term efficacy was satisfactory, but the long‐term efficacy requires further study.

This study aims to explore if unilateral dual‐channel endsocopic lumbar interbody fusion (ULIF), which focuses solely on addressing slippage, can achieve similar spinal scoliosis correction as in open surgery. Additionally, we will compare the therapeutic effects of ULIF for different segments of spondylolisthesis and evaluate its clinical efficacy and safety.

Introduction

Lumbar spondylolisthesis is the relative displacement of the adjacent upper and lower vertebral bodies, with isthmic and degenerative spondylolisthesis being the most common. ¹ Scoliosis is a deformity of the spinal structure typically diagnosed by measuring the Cobb angle, with angles ≥10° indicating a definitive diagnosis. ² With a 15%–48% incidence rate, scoliosis is strongly associated with symptomatic vertebral spondylolisthesis. ³ Scoliosis and spondylolisthesis are complex conditions that can be grouped into three main categories: idiopathic, radicular, and olisthetic. ⁴ , ⁵ Khashab et al. ⁶ found that for patients with scoliosis caused by spondylolisthesis, surgery may only be needed for the latter condition, greatly improving symptoms and spinal curvature and avoiding unnecessary scoliosis surgery. In the treatment of L5 spondylolisthesis with accompanying scoliosis, Du et al. ⁷ achieved a satisfactory reduction of slippage and correction of spinal curvature through transforaminal lumbar interbody fusion (TLIF).

Although open vertebral fusion surgery can effectively address spondylolisthesis with accompanying scoliosis and achieve favorable clinical outcomes, ⁷ , ⁸ , ⁹ it significantly disrupts the spinous processes and paraspinal muscles, which can result in acute back pain after surgery, muscular atrophy, and a longer recovery period. ¹⁰ , ¹¹ , ¹² In contrast, unilateral dual‐channel endoscopic lumbar interbody fusion (ULIF) has become increasingly popular among spine surgeons because of its ability to considerably reduce or eliminate the negative outcomes associated with open surgery. ¹³ , ¹⁴ Studies ¹⁵ , ¹⁶ have demonstrated the unquestionable effectiveness of ULIF in the management of lumbar spondylolisthesis, revealing that it can help patients recover from surgery more quickly, maintain the natural structure of the spine, and minimize harm to the lower back tissues. Although the ULIF technique for treating lumbar spondylolisthesis is well‐established, there are few reports on its application in cases combined with spinal scoliosis. Consequently, we investigated the viability of ULIF in this field, offering patients with scoliosis and spondylolisthesis a less intrusive surgical option.

In this study, we explored whether ULIF, which focuses solely on addressing slippage, can achieve spinal scoliosis correction similar to open surgery. We also compared the therapeutic effects of ULIF for different segments of spondylolisthesis and evaluated its clinical efficacy and safety.

Materials and Methods

Patients

This retrospective study included patients with lumbar spondylolisthesis and associated spinal scoliosis who underwent surgical treatment at our institution between September 2021 and September 2023. The benefits, drawbacks, and potential consequences of the operation were discussed with the patients prior to surgery. This study was approved by the ethics committee of the Second Hospital of Shanxi Medical University (2020YX No. 128). Written informed consent was obtained from all participants. The ULIF procedure was approved by each patient, and the same surgeon performed each procedure. Clinical data and population demographics were gathered, including follow‐up duration, complications, blood loss, amount of drainage, degree of scoliosis, level and severity of spinal slippage, age, body mass index, sex, surgical time, and length of hospital stay.

The inclusion criteria were as follows: (i) lumbar spondylolisthesis with clinical symptoms and signs consistent with the imaging results and ineffective conservative treatment; (ii) associated degenerative scoliosis (Cobb angle ≥10°); (iii) age at surgery of >18 years; (iv) follow‐up duration of ≥1 year; and (v) underwent ULIF surgery.

The exclusion criteria were as follows: (i) a history of infections, fractures, or lumbar vertebral malignancies in the afflicted segment; (ii) severe osteoporosis, severe adjacent diss degeneration, or leg length discrepancy; and (iii) previous surgical procedures for the lumbar spine.

Surgical Approach

The surgical approach is explained by considering segments L4/L5 as a reference. After general anesthesia, the patient was placed in a prone position with the chest and abdomen elevated to suspend the abdomen. The C‐arm was employed to position and project the bilateral spinous processes of the vertebral bodies at the L4 and L5 levels onto the skin surface. At L4 and L5, the incision line was marked on the right side of the spinous processes. After routine disinfection and draping, two incisions of approximately 1–2 cm each were made, and guidewires were inserted to establish a triangular relationship. The working and observation channels were gradually dilated. Under arthroscopic observation, the right lower facet joint of L4 was removed to expose the ligamentum flavum, dura mater, and L5 nerve root. A nerve hook was used to protect the dura mater and nerve root, and the diseased intervertebral disc was removed. The intervertebral area was treated using bone files and scrapers, and a fusion cage was subsequently inserted. Percutaneous puncture was performed to place the bilateral pedicle screws. Decompression within the spinal canal was rechecked to ensure that there was no significant compression of the dura mater or bilateral nerve roots. The rod and fusion cage positions were checked under fluoroscopic guidance. Finally, the drainage tube was secured, and the wound was cleaned and stitched.

Postoperative Treatment and Variables

During and after surgery, antibiotics were administered to prevent infection, and the patient's condition was closely monitored. The drainage tube was removed based on the drainage fluid output within 2 days postoperatively (< 40 mL/24 h), and the patient was instructed to wear a waist belt and engage in weight‐bearing activities. Immediately following the surgery, lumbar spine computed tomography (CT), anterior and posterior lateral X‐ray films of the lumbar spine, and magnetic resonance imaging were performed. Follow‐up radiographs of the anteroposterior and lateral views of the lumbar spine were repeated 3 months postoperatively and at the final follow‐up visit. The Cobb angle, lumbar lordosis (LL) angle, sacral slope (SS), average intervertebral height (AIH), slip percentage (SP), slip angle (SA), and L1 plumb line to S1 distance (LASD) were among the radiographic measures. The intervertebral space fusion status was assessed using the Bridwell criteria during the final follow‐up, with grades I and II denoting successful fusion. Lumbar spine CT was performed if the fusion status could not be determined. The visual analogue scale (VAS), Oswestry disability index (ODI), and Japanese Orthopaedic Association (JOA) scoring systems were used to evaluate clinical results.

Three independent investigators not involved in the surgery performed clinical outcome evaluation and data recording. Measurements of the spinal pelvic and deformity parameters were based on radiographs. Every measurement was double‐checked by two observers, and the analysis was based on the average results. The measurement methods for the sagittal plane spinal radiographic parameters were as follows:

1. SP: the slip distance of the upper vertebra on the lower vertebra divided by the anteroposterior diameter of the lower vertebra multiplied by 100% (Figure 1A).

2. SA: angle formed by the slid vertebra's lower endplate and the lower vertebra's higher endplate (Figure 1B).

3. AIH: mean of the most posterior and anterior intervertebral disc heights (Figure 1C).

4. Cobb angle: the angle formed by the perpendicular lines drawn along the upper endplate of the cranial vertebra and the lower endplate of the caudal vertebra (Figure 1D).

5. LL angle: the angle between the upper endplates of L1 and S1 (Figure 1E).

6. SS: angle between the horizontal line and a line parallel to S1's top endplate (Figure 1E).

7. LASD: the length measured horizontally between the posterior superior corner of S1 and the plumb line drawn from the center of L1. When the plumb line is ahead of the sacral promontory, LASD is positive; when it is behind the sacral promontory, LASD is negative (Figure 1E).

FIGURE 1.

Sagittal plane spinal imaging parameter measurement methods. (A) Slip percentage (SP): the slip distance between the upper and lower vertebrae divided by the anteroposterior diameter of the lower vertebra multiplied by 100%. (B) Slip angle (SA): the angle between the lower endplate of the upper vertebra with slip and the upper endplate of the lower vertebra. (C) Average intervertebral height: the average height of the most anterior and posterior intervertebral discs. (D) Cobb angle: the angle between the perpendicular lines drawn on the upper and lower endplates of the upper and lower vertebrae. The upper and lower endplates refer to the vertebrae with maximum inclination toward the concave side of the scoliosis. (E) Lumbar lordosis (LL) angle: Cobb angle between the upper endplates of L1 and S1. Sacral slope (SS): the angle between the line parallel to the upper endplate of S1 and the horizontal line. L1 plumb line to S1 distance (LASD): The horizontal distance from the plumb line drawn from the center of L1 to the posterior superior corner of S1; LASD is positive when the plumb line is anterior to the sacral promontory and negative when the plumb line is posterior to the sacral promontory.

Statistical Analyses

SPSS version 26.0 software (IBM, Armonk, NY, USA) was used for statistical analysis. Normally distributed continuous data are presented as mean ± standard deviation. The interobserver comparisons were analyzed using the consistency test. Comparisons of radiographic parameters and efficacy evaluation indicators at different time points were performed using paired t‐tests or one‐way repeated‐measures analysis of variance. An independent sample t‐test was employed to compare the L4/L5 and L5/S1 groups. The chi‐squared test was used to assess categorical data. A significance level of α = 0.05 was established, with p‐values <0.05 deemed statistically significant.

Results

General Indices

Thirty‐one patients (13 male and 18 female) were included in this study. The study sample consisted of patients aged 64.45 ± 10.49 years with a mean body mass index of 25.29 ± 3.82 kg/m², followed up for 13.5 ± 3.9 months. L4/L5 and L5/S1 spondylolisthesis were present in 20 and 11 cases, respectively. The mean length of hospital stay was 9.55 ± 2.67 days, and the mean surgical duration was 206.35 ± 35.23 min. Using the Bridwell interbody fusion grading system, 20 patients were categorized as grade I, eight as grade II, and three as grade III at the final follow‐up, yielding a fusion rate of 90.3%. Serious complications did not occur peri‐ or postoperatively (Table 1), and throughout the follow‐up period, surgical site infection, internal fixation device loosening, and significant subsidence or displacement of the fusion cages did not occur (Figure 2).

TABLE 1.

Patient demographic and clinical data (n = 31)

Characteristics	Value
Age (years)	64.45 ± 10.49
BMI (kg/m2)	25.29 ± 3.82
Sex (M:F)	13:18
Slip segment
L4/L5	20
L5/S1	11
Slippage grade
I	23
II	8
Spinal curvature degree
Mild (10°–20°)	28
Moderate (20°–40°)	3
Severe (>40°)	0
Surgical time (min)	206.35 ± 35.23
Hospital stay (days)	8.55 ± 2.67
Blood loss (mL)	94.97 ± 9.85
Drainage volume (mL)	110.94 ± 61.53
Complications (n)
Nerve injury	0
Dural tear	0
Screw loosening	0
Fusion rate (%)	90.32 (28/31)
Follow‐up duration (months)	13.52 ± 3.94

Note: Data are presented as means ± standard deviations or as numbers, as appropriate.

Abbreviations: BMI, Body mass index, M, Male, F, Female.

FIGURE 2.

A 59‐year‐old female patient presented with lower back pain accompanied by left leg pain for 7 months, which worsened for 2 months. (A, B) Preoperative X‐ray shows pars interarticularis fracture at the L5 vertebra, Grade II spondylolisthesis at L5–S1, and moderate right‐sided scoliosis. (C) Preoperative magnetic resonance imaging demonstrates vertebral and intervertebral inflammation signals. (D, E) Three‐dimensional reconstruction computed tomography (CT) shows intervertebral space narrowing, and coronal CT demonstrates a pars interarticularis fracture at L5. (F–I) Intraoperative microscopic view shows reduction of the fracture site, bone cutting with an ultrasonic scalpel, interbody space management, and insertion of the fusion device. (J–L) Immediate postoperative images demonstrate reduced spondylolisthesis, an improved degree of scoliosis, a restored intervertebral disc height, and satisfactory position of the fusion device. (M, N) One‐year postoperative DR shows good correction of the spondylolisthesis and scoliosis, effective fixation, and no obvious loosening. LASD, L1 plumb line to S1 distance; LL, Lumbar lordosis angle; SS, Sacral slope.

Imaging Index

No significant loss of the correction angle was observed during the follow‐up period. Postoperatively, the LL angle, SS, and AIH considerably increased; in contrast, the Cobb angle, SP, SA, and LASD were substantially lower than the preoperative values (all p < 0.05, Figure 3). Within the follow‐up period, SP did not change (p > 0.05), but all other parameters improved with time, except between the 3‐month postoperative and final follow‐up visits (p > 0.05, Table 2). The intraclass correlation coefficient (ICC) value and Kappa coefficients of the two observers were > 0.75 (p < 0.05), indicating high repeatability.

FIGURE 3.

A 68‐year‐old female patient presenting with lower back pain accompanied by bilateral leg pain and numbness for 1 year. (A, B) Preoperative digital radiography shows Grade I spondylolisthesis at L4–5 vertebrae. (C, D) Preoperative whole spine lateral view shows moderate left‐sided scoliosis. (E–H) Immediate postoperative images demonstrate reduced spondylolisthesis, improved degree of scoliosis, restored intervertebral disc height, and satisfactory position of the fusion device. AIH, Average intervertebral height; LASD, L1 plumb line to S1 distance; LL, Lumbar lordosis angle; SS, Sacral slope.

TABLE 2.

Radiographic parameters (n = 31)

Item	Segment	Preoperative	Immediate postoperative	Postoperative at 3 months	Last follow‐up
Cobb angle (°)	L4/L5	15.27 ± 4.42 ‡ , §	9.63 ± 3.52 † , §	6.37 ± 3.25 † , ‡	6.24 ± 2.21 † , ‡
	L5/S1	13.92 ± 6.04 ‡ , §	9.28 ± 4.45 † , §	6.24 ± 2.74 † , ‡	5.42 ± 2.14 † , ‡
	Statistical values (F, P)	0.000, 0.486	0.026, 0.793	0.361, 0.914	0123, 0.364
LL angle (°)	L4/L5	39.83 ± 8.65 ‡ , §	45.42 ± 8.65 † , §	42.58 ± 8.73 † , ‡	42.29 ± 7.84 † , ‡
	L5/S1	40.92 ± 7.24 ‡ , §	49.85 ± 9.93 † , §	46.42 ± 8.65 † , ‡	45.74 ± 8.75 † , ‡
	Statistical values (F, P)	0.027, 0.705	0.651, 0.198	0.151, 0.240	0.526, 0.380
SA angle (°)	L4/L5	10.47 ± 3.52 ‡ , §	7.62 ± 3.43 † , §	6.84 ± 2.85 † , ‡	6.75 ± 2.56 † , ‡
	L5/S1	9.94 ± 4.24 ‡ , §	7.32 ± 4.13 † , §	5.73 ± 3.41 † , ‡	5.24 ± 2.87 † , ‡
	Statistical values (F, P)	0.415, 0.720	0.244, 0.660	0.167, 0.371	0.093, 0.103
SP (%)	L4/L5	22.93 ± 6.14 ‡ , §	7.35 ± 3.92 †	6.74 ± 2.57 †	6.95 ± 2.33 †
	L5/S1	20.84 ± 7.32 ‡ , §	7.26 ± 4.24 †	6.35 ± 2.72 †	6.12 ± 2.38 †
	Statistical values (F, P)	0.585, 0.406	0.438, 0.961	0.521, 0.728	0.007, 0.344
SS angle (°)	L4/L5	35.37 ± 5.52 ‡ , §	44.26 ± 7.74 † , §	40.72 ± 7.94 † , ‡	40.45 ± 7.76 † , ‡
	L5/S1	34.54 ± 6.95 ‡ , §	45.28 ± 3.73 † , §	41.85 ± 5.36 † , ‡	40.92 ± 5.18 † , ‡
	Statistical values (F, P)	1.330, 0.750	1.402, 0.693	0.926, 0.671	1.058, 0.852
LASD (mm)	L4/L5	23.52 ± 8.13 ‡ , §	19.02 ± 5.98 † , §	13.53 ± 4.78 † , ‡	13.64 ± 4.42 † , ‡
	L5/S1	22.56 ± 5.52 ‡ , §	16.74 ± 8.55 † , §	12.44 ± 3.96 † , ‡	11.37 ± 3.12 † , ‡
	Statistical values (F, P)	2.978, 0.733	1.762, 0.477	0.109, 0.490	0.364, 0.138
AIH (mm)	L4/L5	7.64 ± 2.53 ‡ , §	13.62 ± 2.27 † , §	11.84 ± 2.13 † , ‡	11.32 ± 1.63 † , ‡
	L5/S1	6.18 ± 1.63 ‡ , §	12.45 ± 1.74 † , §	11.27 ± 1.54 † , ‡	10.74 ± 1.72 † , ‡
	Statistical values (F, P)	1.877, 0.082	0.519, 0.128	1.270, 0.379	0.005, 0.343

Notes: Data are presented as means ± standard deviations.

Abbreviations: AIH, Average intervertebral height; LASD, L1 plumb line to S1 distance; LL, Lumbar lordosis angle; SA, Slip angle; SP, Slip percentage; SS, Sacral slope.

^† Compared to the preoperative values: p < 0.05,

^‡ compared to the immediate postoperative values: p < 0.05,

^§ compared to the 3‐month postoperative values: p < 0.05.

Clinical Indices

At all time points, there was a substantial improvement in the VAS for back and leg pain, ODI, and JOA scores after surgery compared with preoperative values (p < 0.05; Table 3). However, the scores did not differ significantly between the 3‐month postoperative and final follow‐up visits (p > 0.05).

TABLE 3.

VAS, ODI, and JOA scores (n = 31)

Item	Segment	Preoperative	Immediate postoperative	Postoperative at 1 month	Postoperative at 3 months	Last follow‐up
LBP VAS	L4/L5	9.52 ± 0.92 ‡ , § , ¶	3.18 ± 1.02 † , § , ¶	1.86 ± 0.71 † , ‡ , ¶	0.95 ± 0.51 † , ‡ , §	0.75 ± 0.44 † , ‡ , §
	L5/S1	8.65 ± 0.67 ‡ , § , ¶	2.62 ± 0.93 † , § , ¶	1.68 ± 0.52 † , ‡ , ¶	0.64 ± 0.51 † , ‡ , §	0.45 ± 0.52 † , ‡ , §
	Statistical values (F, P)	0.430, 0.259	0.072, 0.147	0.287, 0.299	1.851, 0.111	3.132, 0.107
Leg pain VAS	L4/L5	8.94 ± 0.81 ‡ , § , ¶	3.22 ± 0.89 † , § , ¶	1.95 ± 0.61 † , ‡ , ¶	1.04 ± 0.46 † , ‡ , §	0.85 ± 0.48 † , ‡ , §
	L5/S1	8.72 ± 0.47 ‡ , § , ¶	2.86 ± 0.75 † , § , ¶	1.67 ± 0.52 † , ‡ , ¶	0.82 ± 0.60 † , ‡ , §	0.55 ± 0.52 † , ‡ , §
	Statistical values (F, P)	1.685, 0.650	0.722, 0.240	0.676, 0.072	2.687, 0.193	2.212, 0.188
ODI (%)	L4/L5	63.54 ± 12.57 ‡ , § , ¶	34.96 ± 6.83 † , § , ¶	17.43 ± 4.95 † , ‡ , ¶	12.64 ± 4.52 † , ‡ , §	12.13 ± 4.12 † , ‡ , §
	L5/S1	61.58 ± 9.23 ‡ , § , ¶	35.62 ± 5.87 † , § , ¶	20.42 ± 2.31 † , ‡ , ¶	15.48 ± 2.32 † , ‡ , §	14.86 ± 2.44 † , ‡ , §
	Statistical values (F, P)	2.224, 0.723	0.461, 0.749	10.841, 0.064	9.788, 0.067	4.238, 0.054
JOA scores	L4/L5	4.42 ± 1.18 ‡ , § , ¶	9.13 ± 1.74 † , § , ¶	13.93 ± 2.04 † , ‡ , ¶	18.65 ± 2.18 † , ‡ , §	19.53 ± 1.64 † , ‡ , §
	L5/S1	4.62 ± 0.92 ‡ , § , ¶	8.83 ± 1.71 † , § , ¶	13.65 ± 1.62 † , ‡ , ¶	19.68 ± 1.71 † , ‡ , §	19.82 ± 0.87 † , ‡ , §
	Statistical values (F, P)	0.959, 0.562	0.231, 0.714	0.533, 0.716	0.344, 0.152	4.356, 0.857

Notes: Data are presented as means ± standard deviations.

Abbreviations: JOA, Japanese Orthopedic Association; ODI, Oswestry Disability Index; VAS, Visual Analog Scale.

^† Compared to the preoperative value: p < 0.05,

^‡ compared to the immediate postoperative value: p < 0.05,

^§ compared to the 1‐month postoperative value: p < 0.05,

^¶ compared to the 3‐month postoperative value: p < 0.05.

Discussion

In this study, we observed significant improvements in the degree of lumbar spondylolisthesis, clinical symptoms, and spinal curvature after reduction, fusion, and fixation of the lumbar spondylolisthesis segment. The Cobb angle decreased significantly after surgery, and no serious complications occurred during the surgery. In addition, spontaneous regression of the spinal curvature and related symptoms helped avoid unnecessary spinal deformity surgery. We hypothesize that this could be due to the significant relief of nerve stimulation and pain after correcting for lumbar spondylolisthesis, which gradually improved the compensatory scoliosis caused by sciatic nerve pain. Du et al. ⁷ also confirmed this observation in their study on the mechanism of TLIF treatment for L5 spondylolisthesis with accompanying scoliosis. In addition, restoring vertebral translation and rotation after vertebral reduction, fusion, and fixation repairs the abnormal spinal structure, leading to spontaneous regression of the spinal curvature. Furthermore, spinal curvature can also progress to vertebral spondylolisthesis due to changes in the isthmus of the vertebra, and scoliosis can cause intervertebral disc degeneration, resulting in vertebral slippage. Previous studies have also indicated that patients who have undergone surgical and non‐surgical scoliosis treatments tend to develop intervertebral disc changes and subsequent vertebral slippage. ¹⁷ , ¹⁸ Therefore, close attention and appropriate treatment measures should be taken to prevent and address the development of vertebral spondylolisthesis in patients with scoliosis, particularly those with intervertebral disc degeneration. Understanding the complex relationship between spinal curvature and vertebral spondylolisthesis, as well as the etiology and symptoms associated with vertebral slippage related to scoliosis, will help treat patients with these spinal conditions.

Treatment for Lumbar Spondylolisthesis with Spinal Scoliosis

The role of surgery for treating scoliosis with lumbar spondylolisthesis remains unclear. Early treatment of lumbar spondylolisthesis may help reduce triggering factors and avoid or improve the development of scoliosis because it is thought to be a potential cause of sciatic nerve or spondylolisthesis scoliosis. ¹⁹ For the treatment of scoliosis, the traditional view ²⁰ is that treatment should be managed depending on its classification and flexibility. Crostelli and Mazza ⁵ advocate that spondylolisthesis‐associated scoliosis, especially severe scoliosis, should be considered idiopathic scoliosis and treated with the same principles as idiopathic scoliosis. According to their viewpoints, more scoliotic curves associated with spondylolisthesis require surgical or conservative treatment. Zhou et al. ³ reported that the relationship between scoliosis and vertebral slip is complex. If scoliosis is considered to be caused by vertebral slip, surgery for the latter may be the only intervention needed. Unnecessary surgery for scoliosis should be avoided. Spondylolisthesis and scoliosis have complicated and occasionally ambiguous interactions. Reducing their different associations to simple relationships might be a better solution. ⁵ Therefore, careful evaluation of the patient's specific condition and the doctor's professional judgment are required to assess the need for surgical intervention when creating a treatment plan.

Evolution of Sagittal Parameters and Spinopelvic Parameters

This study explored the clinical effectiveness and feasibility of ULIF in 31 patients with lumbar spondylolisthesis and scoliosis, revealing that SP and LASD were important surgical outcome indicators for spondylolisthesis. Increased risk of spondylolisthesis and possible worsening of the degree of slippage have been linked to abnormally high LASD, which reflects the sagittal balance of the spine. In addition, patients with a higher residual LASD after surgery often experience severe back pain. ²¹ Therefore, ensuring effective reduction of spondylolisthesis is crucial for improving sagittal balance, indirectly decompressing nerve roots, and alleviating back and leg pain. SS was another relevant parameter that describes the pelvic spatial position and reflects the orientation of the sacrum in the sagittal plane. The mechanical equilibrium of the spine is derailed in patients with lumbar spondylolisthesis, and the body compensates by increasing the physiological LL angle to adapt to the anterior downward tilt of the sacrum. ²² Lower back discomfort is thought to be largely caused by the loss of both SS and LL, ²³ which have a close association with LL increasing as SS increases. ²⁴ In addition, the normal physiological LL angle may be reduced by degenerative abnormalities in the lumbar spine, which reduce the anterior and middle columns' ability to support weight and increase the load on the posterior column. This imbalance affects the mechanical structure of the vertebral bodies and intervertebral discs leading to lumbar instability and back and leg pain. ²⁵ Moreover, restoring SA aids in correcting the SS and LL angles, which are strongly related to SA. ²⁶ Specifically, recovering the LL angle reduces back and leg pain and decreases the incidence of adjacent segment diseases. ²⁷ Therefore, treatment strategies that restore the LL angle promote postoperative recovery and back pain symptom relief.

Our investigation examined the SP, SA, Cobb angle, and LASD of the L4/L5 and L5/S1 groups, which were significantly lower in the postoperative period relative to preoperative values, indicating that ULIF corrected slippage, reduced the risk of slippage progression, and elicited corrective effects on scoliosis by restoring the spine's sagittal balance. Furthermore, significantly higher postoperative values were found for SS, LL, and AIH in both groups compared with preoperative values. These results suggest that ULIF improved the physiological curvature of the lumbar spine, restored intervertebral disc height, prevented slippage progression, and inhibited the occurrence of adjacent segment disease. The preoperative and postoperative parameters did not differ between the L4/L5 and L5/S1 groups (p > 0.05), demonstrating that ULIF had similar clinical effectiveness for treating lower lumbar spondylolisthesis and associated scoliosis. These clinical results are consistent with those of previous studies ⁶ , ⁷ on open surgical treatment of slippage combined with scoliosis, further confirming that patients with lumbar spondylolisthesis and spinal scoliosis undergoing ULIF surgery can achieve similar safe and effective treatment outcomes as those treated with open surgeries such as TLIF and PLIF. Additionally, ULIF surgery is minimally invasive and offers advantages such as reduced blood loss and quicker recovery.

Precautions for ULIF Treatment of Spondylolisthesis Combined with Scoliosis

Our results indicate that ULIF treatment is effective, minimally invasive, and safe. However, this technique has some limitations. For example, this technique may require more time for surgical landmark localization, increasing the surgical risk for patients with multilevel spinal slippage or adjacent segment degeneration with lumbar disc protrusion and spinal stenosis. Therefore, physicians may select cases with a single segment, unilateral symptoms, or mild degeneration in the initial phases of ULIF. After reviewing and analyzing clinical data from patients and combining our operational experience, we have summarized the key technical points for ULIF treatment of lumbar spondylolisthesis as follows: first, it is crucial to pay attention to the details of the ULIF operation during surgery to improve surgical efficiency and safety. For instance, preoperative adjustment of patient positioning to align the intervertebral space of the surgical segment as vertically as possible to the ground facilitates easier handling of the intervertebral space, thereby reducing the incidence of vertebral body resection. It also simplifies vertical manipulation during placement of the fusion device. Moreover, after appropriately positioning the interbody fusion device, partial reduction of vertebral slippage can generally be achieved, thereby reducing stress during subsequent pedicle screw placement for slip reduction. Second, based on the patient's symptoms and imaging findings, if bilateral symptoms or severe spinal canal stenosis are present preoperatively, after ipsilateral decompression and fusion device placement, unilateral laminotomy for bilateral decompression can be performed to remove hypertrophied or thickened ligamentum flavum on the contralateral side. This approach fully releases the contralateral nerve roots, including the traversing and exiting roots, and helps avoid postoperative contralateral nerve symptoms. Finally, there is controversy surrounding the reduction of spondylolisthesis, and we suggest making a judgment based on the individual case, aiming to reduce it as much as possible without over‐pursuing anatomical reduction. Several studies ²⁸ , ²⁹ have shown that in situ fusion or reasonable reduction for lumbar spondylolisthesis yields positive results. Blindly pursuing anatomical reduction for the sake of imaging esthetics may lead to many complications.

Prospects for Clinical Application

Our research has demonstrated the clear effectiveness of the ULIF technique in treating lumbar spondylolisthesis combined with scoliosis. By addressing lumbar spondylolisthesis alone, the ULIF technique also provides good correction of scoliosis. Compared to traditional open surgeries, ULIF is minimally invasive. Additionally, it avoids the need for additional scoliosis surgeries, significantly reducing patient discomfort and decreasing hospitalization time and medical costs, allowing patients to return to normal life and work earlier. The ULIF technique provides spine surgeons with a new surgical option or treatment approach for the management of combined spondylolisthesis and scoliosis. It is worth noting that not all patients with slippage combined with scoliosis can benefit from ULIF despite its advantages over open surgical procedures. Sometimes, scoliosis may not improve after slippage correction because both partial slippage and scoliosis can be extremely rigid. Our understanding of the complex pathological mechanisms underlying spinal slippage and scoliosis is currently limited, and our understanding of their relationship has certain biases. However, our future studies will explore the etiology and manifestations of spinal slippage and scoliosis to enhance our knowledge of these two spinal conditions, aiming to develop effective treatment plans and inform more accurate preoperative decisions for patients.

Limitations

This study has some limitations. First, the sample size was small; hence, future studies with larger sample sizes and multicenter designs are needed to confirm the effectiveness of ULIF. Second, this study only included patients with mild scoliosis accompanying lumbar spondylolisthesis and did not analyze the effects in patients with severe scoliosis (>40°). Finally, the clinical follow‐up time was restricted, which may not be sufficient to fully evaluate the long‐term efficacy and complications of ULIF. Therefore, further studies, including more cases, longer follow‐up times, and high‐quality randomized controlled trials, are needed to explore the long‐term efficacy and safety of ULIF for treating lumbar spondylolisthesis combined with scoliosis.

Conclusions

ULIF is a promising treatment method for lumbar spondylolisthesis combined with spinal scoliosis, which reduces slippage and scoliosis. In addition to greatly improving the clinical symptoms of patients experiencing slippage, ULIF significantly reduced the degree of spinal curvature, thereby preventing needless scoliosis surgery. Meanwhile, ULIF offers benefits such as less trauma, less bleeding, and a shorter recovery period following surgery. Consequently, ULIF is an effective surgical therapy option for scoliosis and lumbar spondylolisthesis. Nevertheless, while the effectiveness in the short term was adequate, more research is needed to determine the long‐term usefulness of ULIF.

Funding

Funding for this study was obtained from the General Program of Natural Science Research of Shanxi Basic Research Program (202203021211040) and the Youth Science Research Program of Shanxi Basic Research Program (20210302124670).

Conflict of Interest Statement

The authors declare no conflict of interest.

Ethics Approval and Consent to Participate

This study was a prospective and clinical study approved by the Second Hospital of Shanxi Medical University, Shanxi Medical University Institutional Review Board. Consent to participate was obtained from the participants.

Author Contributions

Xuanjun You contributed to the conception and design of the study, acquisition of data, analysis, interpretation of data, and drafting of the manuscript. Bin Zhao, Yongfeng Wang, and Tao Zhang reviewed and edited the manuscript for important intellectual content and provided critical revisions. All authors have read and approved the final manuscript before submission. All authors contributed to the study's conception and design. This study was designed by Yongfeng Wang. Data collection was performed by Xuanjun You, Tao Zhang, and Chaojian Xu. Data interpretations were performed by Xuanjun You, Jie Yuan, and Ruxing Liu. Literature searches were performed by all authors. Fund collection was provided by Bin Zhao and Yongfeng Wang. Finally, the first draft of the manuscript was written by Xuanjun You, and all authors have commented on previous versions of the manuscript. All authors have read and approved the final manuscript.

Supporting information

Figure S1. An acceptable depth and good position of the pedicle screws are visible on the postoperative lumbar spine CT scan of the Main Figure 2 patient. No significant deviation is observed.

Figure S2. A postoperative lumbar spine CT scan of the Main Figure 3 patient shows that the position of the pedicle screws is good, with appropriate depth. No significant deviation is observed.