INTRODUCTION
Lumbar foraminal stenosis (FS) is a common degenerative spinal condition that affects approximately 8%–11% of individuals, making it a significant cause of lumbar radiculopathy [1]. This condition results from structural changes, including intervertebral disc degeneration, facet hypertrophy, and osteophyte formation, leading to nerve root compression and symptoms such as pain, numbness, and functional impairment [2].
In patient with degenerative lumbar scoliosis (DLS), FS occurs more frequently due to scoliosis-related biomechanical changes, including narrowing of the foraminal space on the concave side of the major scoliotic curve and increased load on the fractional curve. DLS, defined as a Cobb angle (CA) ≥10°, affects approximately 10% of the elderly population and often overlaps with FS. The treatment of FS in DLS remains challenging due to the dual pathologies of scoliosis and stenosis. Various techniques are usually utilized depending on the specific pathology [3-13]. These surgical interventions, whether decompression or fusion, often share overlapping techniques and considerations, highlighting the importance of a nuanced approach to treatment planning.
Endoscopic decompression has emerged as a minimally invasive alternative surgery to traditional open surgery for FS, offering reduced soft tissue trauma and faster recovery [6,7,9-11,13-16]. Despite these advantages, its role in treating FS in patients with DLS, particularly in relation to lesion location—major scoliotic curve versus fractional curve—has not been clearly established. Additionally, disc wedge angle (DWA) has been proposed as a risk factor for restenosis, but DWA to CA ratio has not been explored before.
This study aims to evaluate the clinical outcomes of uniportal endoscopic decompression for FS in DLS patients. Specifically, it investigates whether lesion location within the fractional curve or major scoliotic curve groups influences surgical outcomes, recurrence rates, and the need for revision surgery. By incorporating lesion-specific analyses and exploring the predictive value of the DWA/CA ratio, this study seeks to provide insights that could contribute to more personalized treatment strategies for FS in DLS.
MATERIALS AND METHODS
1. Patient Group
This retrospective case series study included 22 patients with radicular pain treated at one local hospital and one medical center between September 2019 and November 2023. All patients were diagnosed with FS and DLS. DLS was defined as a CA ≥10° based on standing coronal radiographs. FS diagnosis and grading were based on the criteria described by Lee et al., which classified FS into 4 grades using magnetic resonance imaging (MRI) [17]. Patients with prior spinal surgery at the affected level, or with segmental instability, or adjacent spinal disorders, were excluded. To facilitate treatment planning, the lumbar spine is divided into 2 distinct regions: the major scoliotic curve is located in the upper lumbar spine, characterized by scoliotic curves that significantly contribute to the overall spinal deformity. This region often requires targeted interventions, such as discectomy, to address disc extrusion. The second region, known as the fractional curve, is in the lower lumbar curve and plays a role in balancing the deformity caused by the major curves and often involves the concave side of the region (Figure 1).
All patients underwent uniportal endoscopic foraminotomy, with or without discectomy, under general anesthesia performed by a single surgeon. For patients with L5 radiculopathy and MRI findings indicating ipsilateral L4–5 lateral recess and L5–S1 FS, combined interlaminar decompression for L4–5 and foraminotomy L5–S1 were performed. Data were collected from medical records. All the data collection was authorized by Taipei Medical University Office of Human Research (IRB No. N202312127).
2. Surgical Technique
Under general anesthesia, the patient was placed in a prone position on the operating table with spinal pads for support, ensuring relief of all pressure points. The table was adjusted to maintain a straight back. The surgical area was disinfected with iodine and covered with a waterproof drape. A 1-cm skin incision was made 5–7 cm lateral to the spinous process. The procedure utilized a 12°/8.4 mm outer diameter percutaneous stereoscopic lumbar decompression endoscopic system (TECHCORD, Korea). The spinal endoscope was docked at the superior articular process (SAP) of the affected facet joint (Figure 2A), oriented toward the target neuroforamen, and normal saline irrigation was used to expand the surgical field.
First, the Harrison point was identified. The SAP was partially removed to access the facet joint line, and the lateral margin of the inferior articular process (IAP) was exposed (Figure 2B). The lateral border of the affected lamina was resected from the IAP to the isthmus using a high-speed burr and Kerrison punches. Bone resection proceeded medially until the ligamentum flavum was detached and cephalically until the inferior cortex of the affected pedicle was reached (Figure 2C).
A probe was used to confirm that the detached ligamentum flavum was free from the nerve root. The ligamentum was then removed piece by piece with punches (Figure 2D). For adequate decompression, partial resection of the SAP and a discectomy may be required until the pulsation of the nerve root and the reappearance of epidural vessels are noted (Figure 2E). After decompression, visible bleeding points were coagulated, and the wound was closed in layers.
3. Data Analysis
Data retrieved from medical records included patient characteristics such as age, sex; radiological parameters including CA, DWA, and lesion location (categorized as fractional or major scoliotic curve). The DWA, calculated as the angle formed by the superior and inferior endplates of a disc, was used to evaluate localized segmental angulation and its potential contribution to biomechanical instability. Surgical outcomes assessed using the MacNab criteria, which classified results as “excellent,” “good,” “fair,” or “poor.” Additionally, recurrence and revision data were collected, with recurrence defined as a symptom relapse requiring revision surgery within the follow-up period.
4. Statistical Methods
Statistical analyses were performed using IBM SPSS Statistics ver. 24.0 (IBM Co., USA). The chi-square test compared satisfaction rates and revision rates between groups, the Mann-Whitney U-test evaluated differences in the DWA/CA ratio, and the Pearson correlation test assessed the relationship between the DWA/CA ratio and the time to achieve fusion in revision surgery patients. Statistical significance was set at p<0.05.
RESULTS
A total of 22 patients diagnosed with FS and DLS were included in this study, with 6 patients in the major scoliotic curve group and 16 in the fractional curve group. The mean age of patients in the major scoliotic curve group of 60.3±12.3 years was younger than the fractional curve group mean age of 69.1±12.7 years. The sex distribution was 4 males and 2 females in the major scoliotic curve group, compared to 9 males and 7 females in the fractional curve group. Radiological assessment showed that the mean CA was 13.8°±3.7° in the major scoliotic curve group and 15.0°±5.0° in the fractional curve group (Table 1).
Clinical outcomes were evaluated using the MacNab criteria. In the fractional curve group (n=16), 18.7% of patients achieved “excellent” outcomes, 62.5% were rated as “good,” 18.8% as “fair,” and 0% as “poor.” In the major scoliotic curve group (n=6), 16.7% of patients achieved “excellent” outcomes, 16.7% were rated as “good,” 33.3% as “fair,” and 33.3% as “poor.” Overall, the fractional curve group demonstrated better outcomes, with 81.3% of patients rated as “good” or “excellent,” compared to only 33.4% in the major scoliotic curve group but without significant difference (p=0.102). The revision rate was significantly higher in the major scoliotic curve group (66.7%, 4 of 6) compared to the fractional curve group (12.5%, 2 of 16) (p=0.011) (Table 1).
Within the major scoliotic curve group, the DWA/CA ratio did not differ significantly between patients requiring or not requiring revision, with mean values of 32.1%±8.7% and 4.5%±1.9%, respectively (p=0.133). A negative correlation was observed between the DWA/CA ratio and the time to achieve fusion in revision surgery patients, with a correlation coefficient of r=-0.752 and p=0.248, indicating no statistically significant association (Table 2). All patients who underwent revision surgery did not require a third surgery during the study period.
DISCUSSION
In navigating the treatment landscape for FS, spine surgeons must adopt a nuanced approach. Uniportal endoscopic decompression stands out as a viable option, particularly for patients with normal alignment and stable segments. Conversely, fusion surgery becomes a compelling consideration in specific scenarios, such as deformity exceeding 20% in the coronal CA, segmental instability, adjacent segment disorders, burst fractures with neurologic deficits, and situations where non-fusion options may be inappropriate [4,5,18].
The rapid development of uniportal endoscopic surgery has introduced various new approaches and techniques [11,12,14,16]. However, there is still no clear consensus on the optimal treatment approach for patients, particularly those with FS. Spine surgeons are often faced with the dilemma of whether to perform a simple decompression or proceed directly with a fusion [5]. This decision-making process remains challenging due to the lack of definitive guidelines.
Seo et al. [19] highlighted the importance of identifying risk factors for restenosis after full endoscopic lumbar foraminotomy in treating lumbar FS. Factors such as a higher DWA, larger coronal CA, and smaller segmental lumbar lordosis have been associated with increased risks of restenosis. Additionally, the inclusion of discectomy during full endoscopic lumbar foraminotomy has been linked to higher recurrence rates. These findings underscore the need for careful patient evaluation and surgical planning to minimize the risk of restenosis and optimize patient outcomes.
In this study, patients in the fractional curve group achieved better clinical outcomes compared to those in the major scoliotic curve group. Specifically, 75% of patients in the fractional curve group were rated as “good” or “excellent” according to the MacNab criteria (Figure 3), whereas only 33% of patients in the major scoliotic curve group achieved similar results. These findings are consistent with the understanding that the fractional curve serves as a compensatory region, where biomechanical stress is less pronounced. In contrast, the major scoliotic curve, characterized by significant structural deformity, is associated with high recurrence and revision rates (66.7% vs. 12.5%, p=0.011) (Figure 4).
The DWA/CA ratio was explored as a potential predictor of surgical outcomes. In the major scoliotic curve group, patients requiring revision surgery exhibited a higher mean DWA/CA ratio (32.1%±8.7%) compared to those who did not (4.5%±1.9%). Although this difference was not statistically significant (p=0.133), it suggests that a higher DWA/CA ratio may indicate greater segmental instability, necessitating fusion for long-term stability. Furthermore, the negative correlation between DWA/CA ratio and fusion timing (r=-0.752, p=0.248) warrants further investigation to clarify its clinical implications.
One notable case in this study involved an 83-year-old female with DLS and left L5–S1 FS demonstrated postoperative progression of coronal imbalance after foraminotomy, leading to a "fair" outcome. Preoperative x-rays showed a truncal shift towards the concave side of the fractional curve, suggesting that isolated decompression may not suffice in such cases (Figure 5). Recent findings by Ransom et al. [20] highlighted the importance of addressing coronal imbalance in degenerative scoliosis. They recommended short-segment fusion for cases with truncal shift ipsilateral to the concave side of the fractional curve to prevent imbalance progression and improve stability.
The results of this study suggest that lesion location should be a critical consideration in surgical planning. For FS in the fractional curve group, uniportal endoscopic decompression can provide effective symptom relief with low recurrence rates. However, for FS in the major scoliotic curve group, isolated decompression may be insufficient, as evidenced by the high revision rate. In these cases, adjunctive fusion should be considered, particularly when the DWA/CA ratio exceeds 20%. These findings highlight the importance of integrating lesion-specific and biomechanical assessments into preoperative planning.
This study has several limitations. The small sample size, particularly in the major scoliotic curve group, limits the statistical power of subgroup analyses. Additionally, the retrospective design introduces potential selection bias and limits the generalizability of the findings. Finally, while the follow-up period was sufficient to evaluate recurrence, longer-term outcomes, including adjacent segment disease, were not assessed.
CONCLUSION
This study demonstrates that uniportal endoscopic decompression is an effective surgical option for FS in DLS, particularly for lesions located in the fractional curve. However, FS in the major scoliotic curve group with high DWA to CA ratio, or the presence of coronal imbalance may require adjunctive fusion to achieve long-term stability. This finding supports a tailored, lesion-specific surgical approach in DLS patients, integrating radiological parameters such as DWA/CA ratio and coronal alignment into preoperative planning. Further prospective studies are warranted to validate the findings and refine treatment algorithms for this complex patient population.
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