Long-Term Spinopelvic Alignment Following Unilateral Laminotomy with Bilateral Decompression for Lumbar Spinal Stenosis: A Retrospective Analysis Using Surgimap Digital X-Ray Imaging

Introduction

Lumbar spinal stenosis (LSS) is a disease resulting from the compression of neural elements, due to the narrowing of the lumbar spinal canal or neural foramina [1]. The diagnosis of LSS is based on radiological findings combined with clinical judgement. LSS is the most common reason for neurosurgical spine surgeries in individuals aged 65 years and older [2,3]. Neurogenic claudication, a hallmark symptom of LSS, is characterized by pain, numbness, and weakness in the lower limbs, which worsens with standing or walking and improves with sitting or lying down [4]. Surgical treatment is indicated when conservative methods, such as pharmacotherapy and rehabilitation, fail to alleviate symptoms [5]. The primary goal of surgery is decompression of nerve elements to relieve pressure and improve functionality [5]. In the surgical treatment of radiologically single-level LSS, decompression of the stenotic level with or without fusion has become the criterion standard [6]. However, outcomes vary based on patient age, comorbidities, and the extent of the disease [7]. Elderly patients can experience higher complication rates and slower recovery. Recurrent stenosis and the need for revision surgeries are common, with rates ranging from 9.3% to 28% [8]. Fusion procedures are usually not recommended in the absence of instability or deformities [9].

However, the selection of the optimal surgical procedure for multi-level LSS, particularly multi-level LSS with degenerative spondylolisthesis, remains controversial [10]. While decompression alone and decompression with fusion have been reported to yield comparable favorable outcomes in patients with degenerative LSS and spondylolisthesis [11], the debate over the best approach persists. This controversy underscores the need for further investigation into minimally invasive techniques, such as unilateral laminotomy for bilateral decompression (ULBD), which can offer advantages in cases without segmental instability.

It is well known that alignment of the lumbar spine has a significant impact on segmental motion, degenerative pathology, and health-related quality of life [12]. In recent years, the importance of sagittal balance in the treatment of spinal lesions has been emphasized [13–15]. Restoration of sagittal spinal alignment is necessary to achieve good clinical results in adult patients with spinal deformity [16]. In contrast, spinopelvic sagittal alignment can be the underlying cause of adjacent segment disease after fusion surgery [17,18]. Although several reports have documented changes in spinopelvic alignment and sagittal balance after microsurgical decompression without fusion in patients with LSS, most are short-term studies [19–23].

Surgimap (Version 2.3.0.1, New York, 2019) is a specialized medical imaging software used for planning and analysis of spinal alignment using radiographic images. Surgimap provides precise angle calculations and visual mapping of spinal curvatures, improving preoperative planning, postoperative evaluation, and standardization across cases [24]. Its high reproducibility makes it a valuable tool for evaluating spinal deformities in clinical and research settings [24].

The long-term effects of ULBD surgery on sagittal alignment, particularly in multi-level LSS cases, remain poorly understood. Therefore, in this retrospective study from a single center including 92 patients with LSS, we aimed to evaluate long-term sagittal spinopelvic alignment following multi-level unilateral laminotomy with bilateral decompression using digital X-ray image analysis with Surgimap software.

Material and Methods

ETHICS APPROVAL AND STUDY PARTICIPANTS:

This study was approved by the Medical Ethics Committee of Istanbul Kanuni Sultan Süleyman Training and Research Hospital (approval no: KAEK/2024.12.215). All methods were performed in accordance with the Declaration of Helsinki. The study was conducted using medical records of patients treated at the institution between 2016 and 2019. The inclusion criteria were (1) clinical symptoms of neurogenic claudication or radiculopathy with/without low back pain, (2) failure of conservative treatment for at least 3 months, and (3) radiological diagnosis of LSS with grade I spondylolisthesis without instability. The exclusion criteria were (1) segmental instability (>4 mm translation or >10° angular motion on flexion-extension X-rays), (2) grade II or higher spondylolisthesis, (3) degenerative scoliosis (Cobb angle >10°), and (4) prior lumbar surgery.

STUDY DESIGN:

This study was a retrospective cohort analysis conducted at a single institution. The medical records of patients who underwent unilateral laminotomy for bilateral decompression surgery for LSS were reviewed (Figure 1). Patients were selected based on predefined inclusion and exclusion criteria, to ensure homogeneity of the study population. Radiological and demographic data were collected from patient charts, surgical records, and the hospital Picture Archiving and Communication Systems. The study population was divided into 2 groups, based on the number of decompressed levels: single-level decompression group (n=48) and multi-level decompression group (n=44). Demographic data and radiological evaluations of the patients are shown in Table 1.

BASELINE CHARACTERISTICS:

Baseline demographic and clinical characteristics were recorded, including age, sex, decompressed levels, and sagittal alignment parameters: pelvic tilt (PT), lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), and pelvic incidence-lumbar lordosis (PI-LL) mismatch. These are summarized in Table 1 for each group. The mean age of the patients was 62.23±11.12 years (range: 37–80 years), with 33 men and 59 women.

DIGITAL X-RAY IMAGE ANALYSIS: Preoperative and postoperative sagittal balance parameters were measured using Surgimap software and digital X-ray images in JPEG format (http://www.surgimap.com/download/) [24]. The following parameters were assessed: LL, PT, SS, and PI (Figure 2).

MEASUREMENT PROTOCOL:

Evaluation of parameters were conducted by 2 spine surgeons with than 5 years of experience. X-ray scans of 10 patients were randomly chosen to evaluate intra-rater reliability and inter-rater repeatability. Additionally, the assessors were kept blind to the clinical and X-ray information. Each evaluator assessed the parameters 2 times, leaving 10 days between each session of measurement.

STATISTICAL ANALYSIS:

Statistical analyses were performed using SPSS software (version 20.0; IBM Corp, 2012, Armonk, NY, USA). For continuous variables, the paired t test was performed to compare the 5 years of radiological outcomes with the respective preoperative scores in both groups. Continuous variables were expressed as mean±SD and compared using the t test, while categorical variables were compared using the chi-square or Fisher exact test. Statistical significance was set at P<0.05.

Results

PATIENT DEMOGRAPHICS:

Data for patients who underwent single-level decompression were as follows. A total of 48 patients were evaluated. The mean age was 60.79 years (±11.51), consisting of 30 (62.25%) women and 18 men (37.5%). Eleven of the patients underwent surgery at the L3–4 level, 29 at the L4-L5 level, and 8 at the L5–1 level (Table 1).

Data for patients who underwent multi-level decompression were as follows. A total of 44 patients were evaluated, with 29 (65.91%) women and 15 men (34.09%), and a mean age of 63.8 years (±10.59). Twenty-seven patients underwent 2-level surgery and 17 underwent 3-level surgery (Table 1). There was no statistically significant difference between the groups in terms of age (P=0.197), sex (P=0.458), and follow-up duration (P=0.285).

BASELINE RADIOLOGICAL PARAMETERS:

Preoperative radiological data of the patients who underwent multi-level and single-level decompression are shown in Table 2. In patients with single-level LSS, the mean values were PT, 23.58°±5.09°; SS, 29.79°±7.65°; PI, 53.38°±9.02°; LL, 36.91°±9.91°; and PI-LL mismatch, 16.46°±11.62°. In patients with multi-level LSS, the mean values were PT, 23.40°±5.94°; SS, 28.96°±6.58°; PI, 52.36°±8.31°; LL, 33.58°±9.97°; and PI-LL mismatch, 18.78°±10.52° (PPT=0.197, PSS=0.579, PPI=0.577, PLL=0.109, PPI-LL=0.321). There was a trend toward improvement in LL and PI-LL mismatch values in both groups. The multi-level group exhibited a greater increase in LL (+3.82° vs +0.58°), although this was not statistically significant (P=0.065 within group).

LONG-TERM RADIOLOGICAL OUTCOMES:

All results are shown in detail in Table 2. The mean follow-up period of the single-level group was 5.27.±1.47 years (range 4–8 years), and the mean follow-up period of the multi-level group was 5.55±1.34 years (4–8 years; P=0.285) No statistically significant difference was found in all spinal parameters preoperatively and postoperatively in both groups (Table 2). Also, no significant differences were observed in the changes between the 2 groups. A minimal increase in LL and PT, and a decrease in PI-LL were observed in both groups.

SAGITTAL ALIGNMENT SUBGROUP ANALYSIS:

To further clarify sagittal alignment behavior over time, patients were subgrouped based on their baseline PI-LL mismatch and PT status (Table 3).

PI-LL SUBGROUPS:

Among patients with PI-LL <10° preoperatively, 75% of single-level and 84.6% of multi-level patients maintained this favorable alignment at the 5-year follow-up.

Among those with PI-LL >10° preoperatively, improvement to <10° was observed in 35.7% of single-level and 32.3% of multi-level patients.

PT SUBGROUPS:

Among patients with PT <20° preoperatively, 64.3% single-level and 57.1% multi-level patients retained PT <20° postoperatively.

Among patients with PT >20° at baseline, only 23.5% single-level and 20% multi-level patients achieved PT <20° at follow-up, indicating limited improvement in this subgroup.

Patients with better baseline alignment (either PI-LL <10° or PT <20°) were more likely to maintain that status. Correction from abnormal to normal alignment occurred more frequently in the multi-level group, but the difference was modest.

Discussion

LIMITATIONS:

This study has some limitations. First, this was a retrospective study and included a single-center cohort; all patients underwent surgery at the same institution. It is possible that different surgical approaches and surgeons’ experience levels can alter the outcomes of the interventions. Second, short-term follow-up data could not be evaluated, because of incomplete postoperative data. Third, clinical symptoms were not addressed, and we could not compare the improvement in sagittal parameters with the clinical outcomes. Finally, adequate lumbar extensor muscle strength is necessary to improve and maintain the sagittal balance. However, the present study did not evaluate lumbar extensor muscle strength.

Conclusions

ULBD surgery effectively preserves and modestly improves long-term sagittal spinopelvic alignment, particularly in multi-level cases, supporting the value of digital X-ray analysis for evaluating outcomes.