Currently, long-level CS treatment is controversial. Several studies have compared the efficacy of anterior decompression and posterior decompression for the treatment of long-level CS; however, no consensus as to the best treatment strategy has been reached. ACDF is the most common surgical intervention for CS, especially for treating single-segment CS. ACDF can directly remove compression on the ventral side and open the intervertebral space, effectively restoring cervical lordosis, enlarging the intervertebral foramen, and reconstructing the stability of the degenerative segments. Treatment strategies such as the use of fusion cage and titanium plate fixation systems have been widely used in conventional ACDF. Clinically, ACDF has been used to treat 1-2 segments of CS and is considered a safe and effective surgical method for cervical degenerative diseases.  However, the posterior open-door can enlarge the practical volume of the spinal canal to decompress the spinal cord. Although the pathology due to compression is not eliminated, compression on the spinal cord can be indirectly reduced. This is because the spinal cord drifts backward like a bowstring after the decompression. Improving patients' neurologic symptoms is the ultimate goal of the operation, regardless of the operation method utilized. Previous clinical studies have shown that both surgical methods can effectively alleviate neurologic symptoms. In agreement with these data, we observed no significant differences between the two surgical methods in regards to their ability of alleviating neurologic symptoms. However, ACDF could be performed level by level through mini-incision resulting from the elasticity of neck skin and enough space between visceral sheath and cervical spine, and nearly no damage to paravertebral muscle occurred. In the ACDF group, the incision length was about 3cm, the bleeding was about 50ml, the drainage tube was removed 1-2 days after surgery, and the hospital stay was about 4 days, while the LAMP incision length was about 10cm, the average bleeding was over 300ml, and the drainage tube was removed about 5 days after surgery, and the hospital stay was about 7 days. The damage in mini-incision ACDF group was significantly less than that in LAMP group, and the recovery after ACDF was faster.
Consistent with previous studies, we found that cervical lordosis (C2-7) in the ACDF group increased significantly after the operation. Furthermore, the cobb angle of C2-7 in the LAMP group did not change significantly after the operation. ACDF has the advantage of reconstructing cervical lordosis. It can not only restore normal physiological curvature but also restore the height of fused segments. Although ACDF is superior to LAMP in reconstructing cervical lordosis, ACDF limits C2-7 movement to some extent. Wu et al. reported that the ROM of cervical flexion and extension decreased by 28.2% and that the range of cervical rotation decreased by 14.1% after 3-level or 4-level ACDF treatment.  In this study, the ROM of cervical lordosis hyperextension and hyperflexion was decreased by approximately 36% in the ACDF group. Theoretically, LAMP does not affect the movement of the cervical spine. However, lamina self-fusion, muscle degeneration, and the facet joint may be essential factors contributing to reduced ROM of cervical lordosis hyperextension and hyperflexion after LAMP treatment. The ROM loss of cervical lordosis hyperextension and hyperflexion after LAMP is common in clinical studies (47.3%).[25, 26] In this study, the ROM loss rate of cervical lordosis hyperextension and hyperflexion in the ACDF group was higher than that in the LAMP group. However, there was no significant difference in the ROM loss rate in all directions of the cervical spine after the operation between the ACDF and the LAMP groups. There was no significant difference in ROM in all directions of the cervical spine between before and after the operation in each group. This may be because the atlantooccipital and atlantoaxial joints play a significant role in flexion, extension, lateral flexion, and axial rotation. Hence, it can be concluded that 3-4-level ACDF and LAMP have a negligible effect on the ROM of the cervical spine. Previous studies suggest that the increased decompression and fusion segments contribute to the increased probability of postoperative non-fusion and pseudo-joint. In this study, the fusion rate was 99.3% (142/143) in ACDF group, indicating that the ROI-C plug-in self-locking fusion cage obtained robust and reliable fusion in the application of 3-4 segments. This observation may be associated with the unique anatomical design of the ROI-C plug-in interbody fusion system. Further, this design could provide ample bone graft space and make close bone contact with the endplate. Additionally, the titanium plug-in that is inserted into the vertebral body through the endplate may improve stability and facilitate early fusion. One case with the subsidence of the C6/7 segment fusion cage was defined as Grade IV fusion in 4-segment ACDF. The C6/7 was at the tail end and the tension generated by the mini-incision pushed the holder rod of the fusion cage to the head end. If the cage was inserted without following the direction of the intervertebral space, it was likely to enter the lower endplate of C7 or even the vertebral body resulting in subsidence. So the cage should be inserted parallelly to the intervertebral space, and if necessary, fluoroscopy could be used to confirm the position of cage. Then, the self-locking plug-in was knocked in when the cage was holded at the best position, which could avoid the subsidence of the fusion cage.
Both ACDF and LAMP are associated with several possible complications. Of such complications, axial pain is typical, especially in LAMP. In the current study, 42 patients in the ACDF group did not experience axial pain and 3 patients in the LAMP group reported posterior axial pain. It is understood that ligament injury of the posterior cervical muscle caused by LAMP is the main cause of potentially chronic axial pain.[28–30] Chiba et al. reported that up to 28% of patients treated with LAMP experienced axial pain 14 years after the operation. However, the anterior approach caused less muscle damage. Furthermore, these patients were less likely to develop axial pain and recovered faster after the operation.
Anterior cervical surgery usually causes dysphagia. Currently, it is considered that dysphagia may be related to increased esophageal pressure during plate implantation or postoperative soft-tissue edema, esophageal injury, postoperative hematoma, and the formation of adhesion around the implanted cervical plate, [17, 33] Several experts also indicate that dysphagia is related to the thickness of the titanium plate at the fusion level. In this study, no patients developed dysphagia following ACDF treatment. No profile higher than the surface of the vertebral body after the ROI-C plug-in fusion cage was completely inserted into the intervertebral space, could avoid contact between the implant and the esophagus or other soft tissues in front of the cervical spine. This separation could eliminate any mechanical stimulation of implantation against esophagus as well as potentially avoid dysphagia. From these observations, the ROI-C plug-in fusion cage is considered a safe and effective treatment for long-level cervical disc herniation .
C5 paralysis is a common complication of cervical surgery. Shou et al.  conducted a meta-analysis of available clinical data and found that the incidence of C5 paralysis in the ACDF and LAMP groups was 3.3% and 5.1%, respectively. In this study, the incidence of C5 paralysis in the LAMP group was 5.56%. The increased incidence may be attributed to the amplification of the spinal canal which in turn facilitates the drifting of the spinal cord to the dorsal side; thus, involving the C5 nerve root after the cervical posterior open-door surgery. The ACDF patients did not develop C5 paralysis, which may be explained by the fact that neurologic decompression in ACDF was limited to the intervertebral space, conventional enlargement of the bilateral intervertebral foramen and no overdistraction of intervertebral space. To avoid C5 paralysis, Tsuji et al.  limited the lamina opening angle to 53.5°to minimize spinal cord drift. Katsumi et al.  reduced the incidence of C5 paralysis by preventive decompression of the bilateral C4-5 intervertebral foramen. Large intervertebral height, over correction of cervical curvature, and a narrow C4-5 intervertebral foramen may be risk factors for C5 paralysis following ACDF treatment. Therefore, a reasonable plan of cervical sagittal reconstruction before the operation may reduce the incidence of C5 paralysis following ACDF treatment.