GCDH is a rare type of cervical disc herniation. The first case was reported in 1999[3]. The spinal canal invasion rate of GCDH is more than 50% and the spinal cord becomes seriously compressed. Patients often show weakness of the limbs, an unstable gait, and are prone to high paraplegia after trauma; this condition can even be life-threatening. Compared to patients with myelopathy caused by small disc herniation, the neurological deficits of patients with GCDH are more serious. The choice of an appropriate surgical approach is very important for patients with GCDH, but at present, there are few reports on the treatment of GCDH, and there is no gold standard treatment. Kong et al.[7] used posterior laminoplasty to expand the volume of the spinal canal and indirectly relieve spinal cord compression; this approach was satisfactory for patients with anterior and posterior spinal cord compression. Because most cases of intervertebral disc herniation are located in the anterior part of the spinal cord, posterior surgery does not directly relieve the anterior compression of the spinal cord, and the postoperative effects are not good[4]. For GCDH, the anterior approach is still the best approach because this is the only way that real anterior spinal cord decompression can be carried out. Williams et al.[21] used ACCF to directly remove the nucleus pulposus and other compression, and achieved complete decompression. ACCF is beneficial to the recovery of neurological function and relieves axial pain in the neck; it is also beneficial to the recovery of the physiological curvature of the cervical vertebrae. However, due to the lack of reliable stability of the bone graft interface, ACCF is prone to delayed union or even nonunion of the bone graft, which may lead to pseudarthrosis and serious bone graft shedding. Further, the surgical time, intraoperative blood loss, and postoperative complications of ACCF are higher than those of ACDF[12, 20], and this approach sacrifices one more normal intervertebral disc, requiring one more fusion segment. A recent cohort study showed that patients who underwent ACCF were more likely to undergo revision than those who underwent ACDF[13]. ACDF can also achieve the best pre-exposure through a less invasive approach[8]. Thus, the purpose of this study was to evaluate the feasibility of ACDF for the treatment of GCDH patients.
This study included 23 patients with GCDH (including three patients with disc herniation with calcification), all of whom underwent ACDF surgery and were followed up for more than 12 months. ACDF achieved satisfactory results, relieving neck and shoulder pain and improving neurological function. Moreover, its effects were maintained until the last follow-up evaluation.
There was no spinal cord injury, vertebral artery injury, or nerve injury in the 23 patients. The surgeons used a microscope when performing each surgery, which provided a good visual field for the surgery, reduced the risk of artery and nerve injury, and improved the safety of the surgery. Nonetheless, routine intraoperative nerve monitoring equipment may be beneficial for monitoring nerve signals in real-time and reducing the probability of nerve injury. While there is no clear consensus on intraoperative nerve monitoring in the literature, some scholars argue that cervical surgery is dedicated to spinal cord decompression, and spinal cord monitoring will not change the purpose of the surgery. On the other hand, Martin used neurological monitoring in 2728 patients with cervical intervertebral disc treatment and reported that the use of neurological monitoring can significantly reduce the risk of permanent nervous system injury[17, 18]. We believe that intraoperative nerve monitoring during cervical surgery is desirable, especially when the intervertebral disc is large.
In this study, the Frankel grade of 17 patients increased by one grade (74%), the grades of 3 patients increased by two grades (13%), and the grades of 3 patients did not change (13%). Despite no change in Frankel grade, these patients were satisfied with the results of the surgery because their neurological function did not deteriorate further and their pain was relieved as compared to before the surgery. In this group of cases, the symptom duration of patients without neurological improvement was longer than that of the other patients, and the average conservative treatment time was more than six months. Although the sample size was small, there was no statistically significant effect of conservative treatment duration on postoperative neurological function recovery, which still suggests that GCDH may require early surgical treatment.
Among our 23 patients with GCDH, one patient was admitted to hospital with sudden hemiplegia, suspected to be a cerebrovascular accident. However, a cerebrovascular accident was ruled out after examination. Upon cervical MR examination, huge cervical disc herniation was found to be compressing the spinal cord, resulting in Brown-Sequard syndrome. This patient was sent to our department for treatment. Brown-Sequard syndrome involves loss of ipsilateral motor and deep sensory function accompanied by contralateral pain and loss of temperature sensation. It is common in spinal trauma and tumors, but rarely caused by intervertebral disc herniation. In 1928, Stookey[16] reported the first case of Brown-Sequard syndrome caused by intervertebral disc herniation. Brown-Sequard syndrome caused by cervical disc herniation is rare and is often misdiagnosed. Jomin et al.[6] studied 230 cases of cervical disc herniation over 18 years and reported that the probability of cervical disc herniation causing Brown-Sequard syndrome was 2.6%. In this study, we treated the patient with Brown-Sequard syndrome using ACDF. By the time the patient was discharged, their limb function had returned to normal, their pain was greatly relieved, and their limb numbness was improved; however, their lower limb numbness did not disappear completely six months after surgery. This is similar to the results of ACDF for the treatment of Brown-Sequard syndrome caused by cervical disc herniation reported in the literature[14, 9]. Therefore, in order to avoid missed diagnosis and misdiagnosis, detailed medical history inquiry, careful physical examination, and in particular, cervical MR examination, are essential.
Previous studies[19] have reported that cervical spondylotic myelopathy is most commonly observed in C5-C6, followed by C6-C7, C4-C5, and C3-C4. Here, intervertebral disc herniation was most common in C3-C4 (6/23). This may be because the C3-C4 spinal canal space is relatively large, and thus, the symptoms of patients with mild disc herniation are not obvious. When giant disc herniation compresses the spinal cord, patients will only come to see a doctor when they have obvious medullary symptoms. The protrusions can be completely removed through the intervertebral space during ACDF, but as the surgical field is narrow, it is difficult to clearly identify the anatomical structure of the surgical area under traditional direct vision, and the surgery is difficult to perform; thus, a microscope is necessary.
In the current study, surgeries were performed with the aid of a microscope. The use of a microscope allowed for a bright, clear, and magnified field of vision during surgery. A high-speed grinding drill and ultrasonic bone knife were used to remove the osteophytes on the posterior edge of the vertebral body and enlarge the posterior edge of the vertebral body. Usually, 1/5 of the posterior edge of the vertebral body was removed in order to expand the operating space. This allowed clear vision of the posterior longitudinal ligament. The posterior longitudinal ligament is divided into a deep and shallow layer. The shallow layer is often broken due to disc herniation. Some disc fragments are in the deep and shallow layers of the posterior longitudinal ligament, so the free nucleus pulposus should be explored and removed. With ACDF, the deep layer of the posterior longitudinal ligament is usually removed, because 1) this can prevent omission of disc fragments, and 2) the posterior longitudinal ligament thickens and has high tension, which may still oppress the spinal cord. The high tension in the posterior longitudinal ligament may be due to the long-term compression produced by the huge cervical disc herniation. In short, all surgeries were performed with the assistance of a microscope and all surgeries achieved decompression of the spinal cord and nerve with good results.
This study has several limitations. Firstly, this study included only a small number of cases, the follow-up time was short, and there were no statistics on the long-term complications of the patients. Second, since this is only a preliminary study; a case-control design comparing the efficacy of ACDF with other procedures was not employed. Finally, the economy of the surgery was not considered. Therefore, future studies of patients with GCDH need to be designed more carefully to include more patients and longer follow-up times in order to verify the efficacy of this surgery.