1.1. General information
From January 2017 to January 2019, 85 patients diagnosed with MCSMSS and treated with ACAF (45 cases) or HDF (40 cases) were selected for the study. X-ray, Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) of cervical spine were taken before operation. Selection criteria: (1) Confirmed by cervical spinal stenosis (the sagittal diameter of the spinal canal is less than 12 mm), and the conservative treatment is ineffective; (2) cervical spondylotic myelopathy involving segments≥3. Exclusive criteria: (1) deformity, ankylosing spondylitis, rheumatoid arthritis and other diseases involving the cervical spine; (2) cervical spine trauma, surgical history; (3) severe osteoporosis.
All patients agreed to the record of research data, and signed the informed consent.
1.2. Operative methods
ACAF group: (1) After general anesthesia, supine position was taken, cervical oblique incision was made through the anterior right side to expose deep structures. (2) The responsible intervertebral disc, anterior and posterior edge osteophyte were removed until the posterior longitudinal ligament (PLL) was exposed. Then, at the cephalic and caudal ends of the planned hoisting segments, the PLL should be bitten in intervertebral space, while the rest of PLL need not be deal with. (3) According to the requirement for decompression, the certain thickness of anterior part of the vertebra was removed, and the space was reserved for the responsible segment to be hoisted forward. (4) According to the decompression width needed, the grooving position was selected on the anterior surface of vertebra, where was usually the inner edge of Luschka's joint. Grinding drill was used to dig deep along the grooving lines on both sides, and the bone was chisel away to reach the cortex of the posterior wall of the vertebra. The posterior wall of the vertebra was bitten on one side. The other side was temporarily retained to maintain the stability of the vertebra. (5) Intervertebral fusion cages, pre-curved titanium plate and vertebral screws were installed, and then the posterior wall of the vertebra on the other side was resected to make the vertebra free. (6) The titanium plate was pulled forward. At this time, vertebrae and compression mater would move forward together until the vertebrae and the titanium plate were closely joined. Finally, the incision was flushed, hemostasis and drainage were performed, and suture was finished layer by layer. The diagram of the procedure of ACAF is presented as Fig 1.
HDF group: ACCF was performed at the segments with severe compression, and ACDF was performed at other segments. The specific steps are as follows:
(1) ACCF: Exposure process was the same as ACAF group.
Degenerative discs and osteophytes in the intervertebral space was removed, until reaching hook joints on both sides. Subtotal resection of adjacent vertebrae was performed, and osteophytes were removed. Titanium cages filled with broken bones were placed after decompression. Finally, titanium plate and screw were installed.
(2) ACDF: Other processes were the same as ACCF. After discectomy, the osteophytes at posterior margin of the vertebra were removed, and the intervertebral space was expanded by distractor to normal height. Intervertebral fusion cage was selected and inserted into the intervertebral space. Titanium plate and screw fixation was finally performed.
Postoperative management was as ACAF’s.
All operations were performed by surgeons of the same team. Negative pressure drainage tubes were placed and pulled out 24 to 48 hours after operation. All patients were fixed with external cervical bracket for 3 months.
1.3. Observation Indicators
1.3.1. General indicators
Age, sex, operative levels, operation time, and intraoperative bleeding volume and complications were recorded.
1.3.2. Functional evaluation
Before and 1 year after operation, neurological function was evaluated by Japanese Orthopaedic Association (JOA) score and Neck Disability Index (NDI) score.
1.3.3. CT transverse measurement
By utilizing the measuring tools embedded in software of picture archiving system, 3 parameters were measured on CT axis images to evaluate the effects of decompression. The definitions of the parameters were as follows:
(1) Transverse area of spinal canal: the area surrounded by the posterior edge of vertebra (in ACAF) or the titanium cage (in HDF), the inner side of vertebral plate and the inner side of pedicle.
(2) Decompression width: the distance between the double sides grooves at the anterior wall of spinal canal
(3) Sagittal diameter of spinal canal: the distance between the posterior edge of vertebra or the titanium cage, and the base of spinous process
The data was from all the operative segments, and were measured at the middle level of vertebra. The measuring diagram is depicted as Fig 2.
1.3.4. C2-7 Cobb’s angle
The a Cobb’s angle method was used to evaluate cervical curvature on the lateral images of X-ray, and the angle is formed by vertical lines of the upper edge of C2 and the lower edge of C7.
1.3.5. Kang’s grade
Kang's MRI grading system was used to assess the degree of cervical spinal cord compression[8, 9], and the specific criteria is : grade-0, no spinal canal stenosis; grade-1, subarachnoid compression exceeded 50％; grade-2, spinal cord compression deformed; grade-3, spinal cord T2 weighted signal changes.
All the parameters were measured by two senior spine surgeons independently, and the average value of each parameter at each level was taken for independent calculation.
1.4. Statistical methods
SPSS 22.0 was used for statistical analysis. Measurement data were expressed as mean ±standard deviation ( ). Paired t test was used for intragroup comparison. Two independent samples t-test for inter-group comparison, Chi-square test was for the categorical data comparison. Test level was α=0.05.