Radiological Analysis Of Spino-Pelvic Parameters Before And After Postero-Lateral Instrumentation And Fusion In Case Of Degenerative Lumbar Spinal Disease

Technical Summary: Radiological Analysis of Spino-Pelvic Parameters Before and After Postero-Lateral Instrumentation and Fusion in Degenerative Lumbar Spinal Disease

Problem Statement
Degenerative lumbar spinal disease (DLSD), encompassing conditions such as degenerative disc disease, intervertebral disc herniation, spinal canal stenosis, and spondylolisthesis, is a leading cause of disability and lower back pain. While surgical intervention, specifically posterior lumbar interbody fusion (PLIF), is a standard treatment for these pathologies when conservative management fails, the impact of such procedures on global sagittal and spino-pelvic balance remains a critical area of investigation. Previous literature suggests that maintaining or restoring sagittal equilibrium is vital for improving health-related quality of life (HRQOL) and reducing adjacent segment disease. However, there is a need to objectively quantify changes in specific spino-pelvic parameters (Pelvic Incidence [PI], Pelvic Tilt [PT], Sacral Slope [SS], Lumbar Lordosis [LL], and intervertebral disc angles) following PLIF in patients with degenerative conditions to determine if the surgery successfully restores or alters these biomechanical alignments.

Methodology
This prospective study evaluated 49 patients (11 male, 38 female) treated at Tianjin Hospital between March 2019 and December 2020. The cohort included patients diagnosed with lumbar spinal stenosis (41 patients), intervertebral disc herniation (6 patients), and degenerative spondylolisthesis (2 patients) who underwent single-surgeon postero-lateral instrumentation and fusion (PLIF) after failing conservative therapy.

• Surgical Procedure: All patients underwent PLIF under general anesthesia. The technique involved a midline incision, Wiltse muscle-slicing approach, laminotomy, and decompression. Polyaxial pedicle screws were utilized for reduction and stabilization, followed by interbody fusion with bone grafts. Patients were mobilized on postoperative day three and wore braces for 6–8 weeks.
• Data Collection: Clinical outcomes were assessed using the Visual Pain Analog Scale (VPAS), Oswestry Disability Index (ODI), and Japanese Orthopedic Association (JOA) scores. Radiological evaluation was performed using standing, full-length lateral and anteroposterior X-rays taken preoperatively and within 7 days postoperatively.
• Radiological Metrics: Six sagittal parameters were measured using Surgimap software: PT, PI, SS, LL, individual lumbar intervertebral disc angles, and the lumbar apex.
• Statistical Analysis: Data were analyzed using SPSS (version 16). A paired t-test was employed to compare preoperative and postoperative values, with a p-value < 0.05 considered statistically significant.

Key Results

• Clinical Outcomes: The study reported significant improvements in VPAS, ODI, and JOA scores from preoperative baselines to immediate postoperative and follow-up assessments.
• Radiological Findings:
  • Statistical Significance: Among all measured parameters, a statistically significant change was observed only in the L4-L5 intervertebral disc angle (Pre-op: 11.667° ± 3.582 vs. Post-op: 12.414° ± 3.724; P = 0.008).
  • Non-Significant Findings: No statistically significant differences were found for the other global parameters, including Pelvic Incidence (PI), Pelvic Tilt (PT), Sacral Slope (SS), and total Lumbar Lordosis (LL) (all P > 0.05).
  • Complications: The study noted minor complications including dural tears (4 cases), one case of incision site infection managed with debridement, and one case of increased radiating pain requiring reoperation. No severe complications such as hematoma-induced cord compression or pseudoarthrosis were observed.

Key Contributions and Claims
The paper contributes to the literature by prospectively analyzing the specific radiographic changes in spino-pelvic parameters following PLIF in a mixed cohort of degenerative lumbar diseases. The authors claim that:

1. Surgical Efficacy: PLIF is a successful treatment for degenerative spondylolisthesis, stenosis, and disc herniation, yielding satisfactory radiographic characteristics and clinical improvements without serious complications.
2. Parameter Stability: Contrary to the hypothesis that global sagittal parameters might shift significantly, the study found that global parameters (PI, PT, SS, LL) remained largely stable postoperatively, with the exception of the specific L4-L5 disc angle.
3. PI Variability: The authors noted a change in Pelvic Incidence (PI) values between pre- and post-operative measurements. They attribute this to a potential change in the patient's upright posture rather than a true anatomical change, as PI is theoretically a constant morphological parameter after skeletal maturity. They also note that fusion to the sacrum without pelvic fixation may result in a small increase in postoperative PI.

Significance
The study supports a multifaceted approach to lumbar surgery, emphasizing that while correcting the deformity is primary, surgeons must remain mindful of the spine's anatomical features to regain original balance. The findings suggest that while PLIF effectively treats symptoms and improves clinical scores, it may not drastically alter global spino-pelvic alignment in the short term, except for specific segmental angles. The authors conclude that sagittal equilibrium is a significant factor that should not be overlooked, and objective dimensions of spinopelvic parameters are essential for assessing surgical outcomes, even if the statistical changes in global parameters are minimal in this specific cohort.