This study was a prospective cohort study and was conducted at the General Hospital of Ningxia Medical University from May 2016 to June 2018. The Scientific Research and Ethics Review Committee of the General Hospital of Ningxia Medical University approved this study on April 26, 2019 (NO.2019-038). All participants in this study provided informed consent. The patients were assigned to different groups using the random number table method. The surgical operation was completed by only one doctor (Zhaohui. Ge), and the surgeon remained blinded to the group assignment of the patients before the operation started. Two independent radiologists evaluated the radiologic data, and the final result was the average of the two radiologists evaluations.
The inclusion criteria were: (1) the patient must have been over 40 years old; (2) diagnosed with lumbar degenerative diseases, such as degenerative lumbar scoliosis, lumbar spinal stenosis, lumbar disc herniation, lumbar spondylolisthesis (within Ⅱ°) and/or lumbar instability; (3) low back pain and/or radicular pain for more than 3 months and conservative treatment was ineffective, which seriously affected normal life; (4) need for multi-level fusion and fixation; (5) and at least 24 months of complete follow-up. The exclusion criteria were: (1) responsible segments that required fusion included L5-S1; (2) severely obese patients (BMI ≥ 35); (3) a history of lumbar fusion internal fixation and abdominal surgery.
After general anesthesia was successful, the patient took the standard right decubitus position, fixed the armpit, pelvis and left lower limb with adhesive tape, and slightly bent the hip and knee. The operative segments were determined using a "C" arm X-ray fluoroscopy machine, and a transverse incision was marked, with a length of about 3-5cm. After that, disinfection and laying of sterile towel were completed. The skin was cut, as well as the subcutaneous tissue and fascia sequentially, and the external oblique muscle, internal oblique muscle, and transversus abdominis were bluntly separated with a vascular forceps until the retroperitoneal space was reached. With the operator's index finger downward, and touching the internal wall of the iliac bone, the extraperitoneal fat was continued to be separated inward and downward bluntly, then the quadratus lumborum transferred and the extraperitoneal fat and ureter carefully separated forward. The upper and lower soft tissues were dissociated, and the extraperitoneal structures gently pushed forward after penetrating. The gap between psoas major and abdominal aorta was found by the end of index finger. Following the guidance of the index finger, the positioning guide needle was inserted into the anterior and middle 1/3 of the intervertebral space of the surgical segment for fluoroscopy positioning. Step by step, the casing was inserted and the working channel established, followed by the fixing of the cold light source firmly, then the working channel opened appropriately, and then the intervertebral disc bluntly separated and exposed. After resection of the annulus fibrosus, an osteotome was inserted into the intervertebral space and the contralateral annulus fibrosus was punctured. Reamer and curette were used to treat the intervertebral disc tissue, including the cartilage endplate, but the intact bony endplate was retained. Different size cage models were used to expand the intervertebral space to a satisfactory height step by step. After filling the allogeneic bone with the cage (Clydesdale Spinal System, Medtronic, Inc., Minneapolis, MN, USA) of appropriate size, the cage was inserted into the intervertebral space after being fixed with a silk thread to complete the segmental stretching, indirect decompression, and interface fixation.
After decompression and fusion, the patient was changed to a prone position and the surgical area was disinfected. The space between the multifidus muscle and the longissimus muscle (Wiltse approach) was used for unilateral or bilateral pedicle screw fixation (Medtronic, Inc., Minneapolis, MN, USA). Taking UPSF as an example: the "C" arm X-ray fluoroscopy machine located the target segment. The skin and lumbodorsal fascia were cut longitudinally at 2.5cm next to the spinous process. The index finger was used to bluntly separate the gap between the multifidus muscle and the longissimus muscle. With the aid of the retractor, the unilateral facet joints were exposed. Weinstein method was used for positioning, a unilateral pedicle screw was implanted, a titanium rod of appropriate length was taken to connect the tail of the pedicle screw, and the tail cap was used for compression and fixation. After washing the wound with saline, the wound was sutured layer by layer.
Antibiotics were routinely used for 3 days after operation, and no drainage tube was placed in all the patients. The patients were instructed to exercise moderately on the first 2-3 days after surgery. The two groups were given the same adjuvant medication and rehabilitation measures. The follow-up time was 6 months, 12 months, and 24 months after the operation.
Clinical and radiographical evaluation
The intraoperative blood loss, operation time, average length of stay, and hospitalization expenses were retrieved from the patient's electronic medical records. The data of VAS, ODI score, and intervertebral space height of fusion segment at 6 months, 12 months, and 24 months were collected. The fusion and cage subsidence of each segment at the 24th month of follow-up were recorded.
Disc height: the ventral and dorsal intervertebral space height of the fusion segment was measured on the standing neutral lateral radiographs, and the average value taken. Fusion status: mature trabeculae were observed between the endplate and cage. If the X-ray film was not clear, the lumbar spine CT was used for evaluation .
Cage subsidence: this was the difference between the height of intervertebral space within 1 week after operation and that at the 24 months. Mild was defined as the difference ≤ 1 mm, moderate was 1 mm to 3 mm, and severe was ≥ 3 mm .
Lumbar lateral radiographs with ≥1mm translucent bands on both sides of the screw were considered as screw loosening.
The Statistical Package for Social Science software was used for data processing (version 20, SPSS Inc., Chicago, IL, USA). The data are expressed as mean ± standard deviation. Fusion rate, cage subsidence rate, and complication rate are expressed as n (%). Student’s t-test was used for comparison between groups and within groups. Chi-square test or Fisher's exact test was used for the comparison between rates. P < 0.05 was considered statistically significant.