With the advancement of technology in recent years, for some cervical spondylotic radiculopathy, the posterior endoscopic cervical foraminoplasty can also alleviate pain very well without increasing the repair rate and complications[20]. Cervical disc replacement can preserve the motor function of surgical segments and theoretically reduce the probability of degeneration of adjacent segments. A prospective randomized controlled 10-year follow-up study[21] revealed that ACDF does not significantly increase the surgical rate of adjacent segments compared with cervical disc replacement. The practical clinical advantages of disc replacement are not obvious, only showing a better employment status[22]. Another 7-year follow-up study[23] also confirmed that single-segment cervical disc replacement and ACDF both have relatively good cost effectiveness, but the total cost of ACDF is lower. Therefore, ACDF surgery will still play an irreplaceable role about cervical disorders for a long time in the future. Changes in Modern work and lifestyle, including the long-term use of mobile phones and so forth and the extension of a low head state will lead to reduced cervical lordosis or cervical kyphosis, and the incidence of degenerative cervical diseases may also gradually increase. Cervical disc herniation and the degree of cervical spinal cord compression are negatively correlated with cervical lordosis[24]. The research on the prevention and treatment methods of ACDF comorbidities is still of great significance.
The risk factors of CSF leakage during ACDF surgery include increased age, increased surgical segments, ossification of the posterior longitudinal ligament, ankylosing spondylitis, combined posterior surgery, obesity, glucocoticoid use, race, and so forth[2,9,25,26]. Therefore, for these cases with a relatively high risk of CSF leakage, the intraoperative operation should be more careful and meticulous to avoid accidental dural injury. Direct suturing is theoretically most effective for the relatively small tears of the dural sac caused by unintentional iatrogenic injury. However, limited to the narrow space, routine suture operation is very difficult. Currently, the mainstream management method is to use a fascia patch or biological patch and glue to repair the dural tears directly[15,16,27] to prevent CSF leakage. For CSF leakage with incomplete resection of the posterior longitudinal ligament, even using fibrin glue alone can effectively avoid postoperative CSF leakage[28]. The posterior longitudinal ligament itself plays a role similar to a patch, and cerebrospinal fluid is blocked behind the posterior longitudinal ligament.
In fact, the strategy of patch and glue is to block the tears on the surface of the dural sac to avoid CSF leakage. The patch needs to be slightly larger than the rupture site. The glue is evenly sprayed on the patch and the attaching place of the dura . The success of this strategy depends on two points: first, whether the glue evenly adheres the patch to the dura completely, and whether there is any omission, second, whether the adhesive force between the glue and dural sac surface can resist cerebrospinal fluid pressure. Therefore, some cases may also need to coordinate with the adjustment of body position[15,25], such as raising the head of the bed and getting down early for activities, or they also coordinate with lumbar cistern drainage[5,15,17] to reduce the pressure of cerebrospinal fluid in the cervical segment, which is conducive to the repair of tears. In order to avoid iatrogenic spinal cord compression, the scope and number of layers of the used glue and patch need to be controlled[16,27]. Most CSF leakage can have a better prognosis after proper management, but still some needs resurgery and repair due to improper management[17,29].
The Principle and Effectiveness of Bone Wax Occlusion
Bone wax occlusion is to move the occlusion of the dural tears from the surface of the dural sac to the front of the intervertebral space(Fig. 1). Bone wax occlusion of the space between the fusion cage and the surroundings endplate of the upper and lower vertebral bodies directly physically isolates the front and back of the intervertebral space. The posterior intervertebral space are relatively narrow after bone wax occlusion and cage or fusion block implantation, and the amount of cerebrospinal fluid that they can contain is limited. The dural sac clings to the posterior wall of the spinal canal after bulging. The pressure of the cerebrospinal fluid leaking out of the dural sac will not be higher than that inside the dural sac, which is not enough to push away the dural sac to diffuse toward the surroundings. Therefore, the space for staying of the leaked cerebrospinal fluid is limited to the intervertebral space and a very small space around it(Fig.e). Cerebrospinal fluid pressure in the gap can quickly reach equilibrium inside and outside the dural sac, and the pressure gradient of cerebrospinal fluid diffusing to the surrounding space of the dura disappears. The amount of the leaked cerebrospinal fluid remains relatively constant. Whether there is the presence of low intracranial pressure after surgery depends only on the amount of the leaked cerebrospinal fluid before occlusion. Once there is no one-way flow of cerebrospinal fluid from it after the balance of the pressure inside and outside the rupture mouth, and the healing of dural tears is only a matter of time.
Postoperative MRIs (Fig.e) confirmed that the leaked cerebrospinal fluid mainly stays and accumulates behind the corresponding intervertebral space, and can not enter the prevertebral area through the intervertebral space, nor can it flow up and down the spinal canal in the front direction of the dural sac.
The position of occlusion operation was the anterior intervertebral space, with large operation space and wide view, good plasticity of bone wax shape and convenient operation. Additionally, it was far away from the spinal canal, and spinal cord safety was also relatively high. Thus, there was no need to worry about spinal cord compression. The fusion cage was surrounded by bone structure, so the adhesion stability of bone wax was relatively high. Judging from the research cases, this was enough to resist the pressure of the leaked cerebrospinal fluid. Bone wax is insoluble in water. Moreover, it does not decompose in the body, and the occlusion effect is also durable.
The Advantages and Side Effects of Bone Wax
Currently, the commercially available bone wax is mainly composed of a mixture of beeswax and partial softeners,etc. Its advantages are cheap and easy to obtain, convenient to apply, insoluble in water, non-degradable, and good adhesion. In spinal surgery, bone wax is mainly used for hemostasis of bone surface and cavity, and its major action mechanism is physical isolation. Its side effects are rare, mainly including inflammatory reaction and granuloma formation, which increases the infection probability, hinders bone healing and so forth[30,31].
The occurrence of complications is directly related to the site and amount of bone wax application. In this study, bone wax was only used to occlude the gap between the fusion cage and the surrounding bone tissue. The scope and amount of the used bone wax were both limited and the application site was not the intervertebral fusion one. Therefore, the probability of the side effects as mentioned above should be relatively low in theory. With the improvement of bone wax composition, the incidence of related side effects will be further reduced[32,33].
Research Limitations
There are different reports on the impact of CSF leakage on bone graft fusion[5,34], and there is currently a lack of literature with relatively large samples. In this study, the number of cases was small, so it was difficult to answer whether CSF leakage has an impact on cervical intervertebral fusion. Theoretically, after proper management of CSF leakage cases, the bone graft material is only soaked in cerebrospinal fluid for a short period time, which should have little effect on intervertebral fusion.
Due to the small number of cases in this study, the research objects were all unintentional iatrogenic dural injury and there have been yet no evidence and experience on the tears of the dural sac at the relatively large scale. However, the method for bone wax occlusion can at least be used as a useful auxiliary one for patch and glue. In addition, the prevertebral space is physically isolated from the intervertebral space and spinal canal by this method. If the hemostasis is not complete effectively after intraoperative decompression, the possibility of new compression caused by hematoma formation due to the inability to drain accumulated blood can not be ruled out. Therefore, there is a relatively high requirement for hemostasis behind the intervertebral space during surgery.