Study design and participants
This was a prospective study of 87 patients with a first diagnosis of lumbar spine stenosis at Shanxi Province People’s Hospital between June 2014 and January 2016.
The inclusion criteria were: 1) 25–85 years of age; 2) unilateral or bilateral symptoms of nerve root with (or without) cauda equina compression; 3) single or double segment stenosis symptoms (patients with three or more stenosed segments undergo open surgery were excluded); 4) intermittent neurogenic claudication; and 5) imaging findings consistent with clinical symptoms in terms of pain location or affected root nerve: i) lateral crypt and/or intervertebral pore stenosis; ii) central vertebral canal and/or mixed spinal stenosis; and iii) failure to 3–6 months of conservative treatment.
The exclusion criteria were: 1) intervertebral instability (in accordance with the White criteria, i.e., over-extension and over-flexion X-ray images in the standing position show that the horizontal displacement of adjacent vertebrae is ≥3 mm or the angle change is ≥15° [1]), osseous infection, mental abnormalities, tumor(s), or communication difficulties; or 2) symptoms of stenosis caused by pure intervertebral disc herniation.
The following rules were applied in the presence of stenosis in more than one segment. 1) If CT and MRI showed two-segment stenosis, and if the clinical symptoms and signs (according to the sensory manifestations and mobility in the innervated areas of the corresponding nerve roots) also met the clinical manifestations of two-segment stenosis, the patients were considered as having two-segment stenosis; they were then included. 2) If CT and MRI showed two-segment stenosis, the clinical symptoms and signs did not show any evident manifestations in the innervated areas of the corresponding nerve roots, and the patient only had the symptom of intermittent neurogenic claudication, but without being able to determine from which segment this symptom was from, the patients were also considered as being two-segment stenosis; they were then included. 3) If CT and MRI showed three or more segment stenosis, but the clinical symptoms and signs showed that they were caused by two-segment stenosis (meaning that the symptoms were restricted to the innervated areas of two segments), the patients were considered as having two-segment stenosis. They were included in the study. 4) If CT and MRI showed three or more segment stenosis, and the clinical symptoms and signs showed that they were caused by three-segment stenosis (meaning that the symptoms were determined as coming from three segments), the patients were considered as having three of more segment stenosis and were excluded. 5) If CT and MRI showed three or more segment stenosis, but the clinical symptoms and signs could not identify the responsible segments, and none of the segments could be ruled out for inducing the disease, the patients were considered with three of more segmental stenosis, and were excluded from the study.
Surgical methods
According to the patient’s preoperative CT and MRI parameters, and their clinical symptoms, the segment of interest for decompression was identified. A physician with experience in treating lumbar spinal stenosis by PELD performed the surgery routinely and ensured complete decompression during the operation. The operation was performed through the intervertebral foramen (Additional file 1: Figure S1).
Preoperative and postoperative functional assessment
Clinical symptoms were assessed using the visual analog pain score (VAS) [2, 3], Oswestry Disability Index (ODI) [4, 5], and claudication distance (m). These factors were evaluated independently by two orthopedic surgeons during the preoperative period and at 3 and 6 months postoperatively. The mean value was used as the standard for evaluating preoperative and postoperative clinical symptoms. The overall clinical efficacy was assessed using the MacNab scores [6]. The minimal clinically important difference for ODI is 12.4 [7].
Preoperative imaging parameter measurement
Patients were evaluated by MRI (Germany Siemens 3.0 T superconducting magnetic resonance instrument) and CT (Germany’s Siemens 64 layer spiral CT machine). The following indicators were measured by two radiologists who were blinded to the patient’s condition. CT and MRI analysis software was used to calculate the mean values. MRI was used to measure the yellow ligament thickness and area of the dural sac (Additional file 1: Figure S2). CT was used to measure the bony vertebral canal area, real spinal canal area, nerve root canal bony area, nerve root canal real area, distance between the articular joints, and vertebral canal sagittal diameter (Additional file 1: Figure S3).
Definitions
The soft tissue invasion ratio of the vertebral canal and invasion ratio of the nerve root canal were calculated as: the soft tissue invasion ratio of the vertebral canal = (bony vertebral canal area- the real spinal canal area)/bony vertebral canal area; the invasion ratio of the nerve root canal = (nerve root canal bony area - nerve root canal real area)/nerve root canal bony area.
Statistical analysis
SPSS 22.0 (IBM, Armonk, NY, USA) and GraphPad Prism 6 (GraphPad Software, San Diego CA, USA) were used for statistical analysis. Normally distributed data (according to the Kolmogorov-Smirnov test) are presented as means ± standard deviation, while non-normally distributed data are presented as median (IQR). Categorical variables are presented as frequencies. The Friedman analysis was used to compare efficacy indicators of different time points among multiple groups, and Dunn’s test was used for comparison between groups. The comparisons of sex and age groups were performed using two-way repeated measure ANOVA with the Bonferroni post hoc test. Correlation between sex, age, and CT/MRI parameters and correlation between CT/MRI parameters and therapeutic effects were analyzed by Spearman correlation. Multiple linear regression was used to analyze the association among various indicators. Two-sided P-values < 0.05 were considered statistically significant. No multiple testing adjustments were done.