Patient data
The inclusion criteria were as follows: 1. Single-segment degenerative disc herniation and spinal canal stenosis with neurological symptoms. 2. Age over 65 years. 3. More than one radiographic examination(X-ray, computed tomography (CT),MRI or DTI)confirming nerve root compression. 4. Good general condition
The exclusion criteria were as follows: 1. More than one segmental disc herniation. 2. Lumbago and no clear nerve root symptoms. 3. Advanced age (over 95 years). 4. Tumors. 5. Serious postoperative complications.
Lumbar disc herniation was combined with stenosis in L4/5 in 53 patients, L3/4 in 2 patients and L5/S1 in 5 patients. Group A received bilateral decompression via a unilateral approach surgery, and group B received conventional transforaminal lumbar interbody fusion approach. All patients underwent lumbar X-ray, three-dimensional CT, and magnetic resonance imaging (MRI) before surgery. After surgery, all patients were followed up for 26.2 months, with a range of 20–36 months.
Surgical methods
Bilateral decompression via unilateral approach (BDUA) group
Each patient was placed in prone position and intubated under general anesthesia. A paravertebral incision was made in the lesion intervertebral space. The paravertebral muscle space was obtusely separated, With the help of mini-retractor designed by ourselves[10], multifidus and the longissimus muscles were separated and the pedicle entry point was exposed clearly(Figure 1 A,B,C).The pedicle screw was inserted into the target vertebra, and the articular process was removed with bone biting forceps. The vertebral plate after c-arm X-ray fluoroscopy confirmed that the reduction was satisfactory. During this process, the nerve root and dural sac were protected. Then the inferior facet and approximately 1/3 of the superior facet were removed, the spinal canal was exposed, and the upper and lower laminar margins were removed depending on the specific conditions of spinal stenosis. Meanwhile, the protruded nucleus was removed, the intervertebral space was opened, and the cartilage of the vertebral endplate was removed for use in the bone graft fusion. The extracted articular process and lamina were used for granular packing in the intervertebral space, and the cancellous bone was compressed and placed into the intervertebral fusion cage. Wiltse's approach was used to implant a contralateral pedicle screw. Finally, the incision was sutured after a negative pressure flow tube was placed. Figure 2A,C shows an intraoperative photographs and schematic diagram of this surgical approach.
Control group: conventional approach transforaminal lumbar interbody fusion.
Each patient was placed in prone position and intubated under general anesthesia. The pedicle screws were placed into the upper and lower vertebral bodies. The spinous process and bilateral lamina and ligaments were removed with bone biting forceps, whereas the ligamentum flavum and the medial edge of the articular process were removed according to the specific conditions of the disease. The nerve root canal and lateral crypt were expanded, and the dural sac and nerve root were protected intraoperatively. Then the annulus fibrosus was cut open, the nucleus pulposus was removed, upper and lower cartilage endplates were removed, and autologous bone particles were implanted between the vertebral bodies. The dural sac and nerve roots were then explored. Finally, the incision was sutured after a negative pressure flow tube was placed. Figure 2B, D shows a schematic diagram and intraoperative photographs of this surgical approach.
Postoperative management
All patients in the two groups had the drainage tube removed within 72 hours and rested in bed for 3 days. Then, they were allowed to ambulate with the assistance of a lumbar brace within at least the next six weeks. All patients were followed up every three months, and X-ray, CT and MRI scans were reviewed.
Clinical and radiological assessment
All patients were assessed with Japanese Orthopedic Association (JOA), Visual Analogue Scale (VAS) and Oswestry Disability Index(ODI)scores before and after surgery. In addition, all patients were followed up every 3 months after surgery with X-ray, CT and MRI of the lumbar spine. X-ray and CT were used to calculate the lumbar spine fusion rate, and X-ray was used to measure L1-S1 lumbar lordosis (Figure 3 A, B). As shown in Figure 4 A,B, MRI was used to detect the fatty degeneration and muscle/vertebral body ratio[11]. VB represents the vertebral body size, CSA represents the cross-sectional area, and SC indicates subcutaneous fat. The gray-scale range of the CSA and SC areas was analyzed in Image J software (National Institutes of Health, MD, USA), as shown in Figure 4C, D. The grayscale value of the CSA region overlap with the SC region(Figure 4E)was used as an index of fatty degeneration of the multifidus muscle. In addition, the CSA/VB ratio indicated the degree of multifidus muscle atrophy. The surrounding layers of the lumbar fusion area were chosen to avoid metal interference.
Statistical analysis
All data were analyzed in SPSS 22.0 software (IBM Corporation, NY, USA) and are presented as mean ± standard deviation. A P-value of < 0.05 was considered statistically significant. The clinical and radiological assessments were analyzed with paired-sample t-tests to compare the changes.