Prevalence and risk factors of axial neck pain in patients undergoing multilevel anterior cervical decompression with fusion surgery

Cervical spondylotic myelopathy (CSM) is a common clinical degenerative disease with an incidence of about 53.5% [1, 2], seriously impacting quality of life and even causing disability for the elderly population [3, 4], which can also lead to defecation dysfunction even paralysis if accompanied by cervical cord injury. For patients with multilevel CSM, anterior decompression and instrumentation, including anterior cervical corpectomy and fusion (ACCF), anterior cervical discectomy and fusion (ACDF), anterior cervical hybrid decompression and fusion (ACHDF), have grown in popularity due to improvement in technology and surgical skill that allows direct decompression and reconstruction with satisfied outcome [5‐8]. However, in many cases, anterior cervical decompression with fusion surgery is still associated with unresolved complications, including dysphagia, postoperative hematoma (neck), hoarseness, esophageal injury, injury to major vessels, wound infection (neck), graft extrusion, axial neck pain, C5 palsy, reduction in neck motion, pseudoarthrosis, nonunion, and revision and screw removal [9, 10]. Among them, axial neck pain as a common complication after surgery, especially in patients undergoing multilevel anterior or posterior cervical decompression, severely threatens the physical and mental health and life quality of the patients. Axial pain has been defined as a chronic, dull ache extending from the nuchal to the periscapular or shoulder region with the feeling of acid bilges, stiffness, oppression, and muscle spasm and is diagnosed after eliminating diseases associated with other related systems [11‐15]. Multilevel anterior decompression and instrumentation often needs to insert intervertebral graft, not only for fusion but also for reconstruction of intervertebral height to indirectly decompress by distraction. Previous literature has reported postoperative neck pain might come out of overdistraction by inserting a large instrumentation, which was considered to lead to posterior facet joint distraction or posterior neck muscle spasm. However, no evidence that supports the relationship between graft size and postoperative axial neck pain has been available. Persistent axial pain can be a major cause of dissatisfaction after surgery, even in patients with excellent neurological recovery. With the emerging appreciation of health-related quality of life, the symptom of pain merits attention by the virtue of it being commonly linked to ongoing disease in the mindset of patients. The incidence of axial pain in individuals with posterior cervical decompression is reportedly as high as 60–80% according to previous articles [16, 17]. Although axial pain has gradually been receiving more attention, compared with a monumental amount of coverage of posterior decompression, this complication associated with multilevel anterior cervical decompression is seldom described in large clinical series [18, 19]. The aim of this study was to explore prevalence and risk factors for axial neck pain in patients undergoing multilevel anterior cervical decompression with fusion surgery.

On the day before surgery, 88 patients (45 men and 43 women) were registered on the books for evaluation voluntarily. The cohort of patients was integrated before discharge. At the time of 1-year follow-up, no patient was lost to follow-up. Thus, 88 patients (45 men and 43 women) had entered into the final assessment phase. Based on the postoperative axial neck pain, the patients were classified into two groups: axial pain group, including patients with obvious pain and related pain treatment, and no axial pain group, including patients with no axial pain or with slight discomfort and without treatment.

There were 24 patients in the axial pain group and 64 patients in the no axial pain group, and the prevalence of axial neck pain was 27.3%. According to the statistical analyses of demographic variables, preoperative axial neck pain (62% vs 23%, P < 0.001) and preoperative kyphosis (42% vs 21.9%, P < 0.001) had a significant difference between the two groups (Figs. 2 and 3). However, no significant differences were found in age (59.5 ± 8.8 vs 60.7 ± 9.8, P = 0.600), sex (P = 0.542), body mass index (BMI) (25.3 ± 2.9 vs 23.8 ± 4.9, 0.143), smoking (P = 0.430), drinking (P = 0.219), heart disease (P = 0.580), hypertension (P = 0.551), diabetes (P = 0.683), JOA scores (9.95 ± 2.1 vs 9.98 ± 1.53, 0.248), DOI scores (0.52 ± 0.08 vs 0.54 ± 0.11, 0.378) (Table 1).

According to the statistical analyses of surgical-related variables, no significant differences were found on the following factors: course of disease (11.03 ± 2.45 vs 11.98 ± 4.13, P = 0.294), operation time (96.9 ± 16.5 vs 103.1 ± 30.6, P = 0.348), surgical option (P = 0.187), superior fusion segment (P = 0.499), incision length (8.87 ± 0.87 vs 9.25 ± 1.19, P = 0.156), blood loss (253.5 ± 19.2 vs 266.3 ± 30.0, P = 0.055), preoperative VAS-neck (4.35 ± 1.13 vs 4.00 ± 0.92, P = 0.069), and presence of IHSI on MRI (P = 0.563) (Table 2).

Additionally, for patients with preoperative cervical kyphosis, compared to the no axial pain group, the axial neck group was significantly more likely to exist a higher preoperative angle of C2–C7 (13.31 ± 2.33 vs 7.33 ± 2.56, P < 0.001) and a higher correction range for kyphosis (20.24 ± 4.12 vs 12.34 ± 3.12, P < 0.001) (Table 3). However, for all the patients with postoperative axial symptoms (n = 24), the improvement rate of axial pain was significantly higher for patients without cervical kyphosis at the early-term follow-up (3 weeks) (P = 0.032), and no significant differences were found at the medium-term (P = 0.554) and long-term follow-up (P = 0.902) (Table 4).

Degenerative spine diseases such as CSM are increasing among the geriatric population, and surgical treatment of CSM is becoming more common. Consensus has currently been reached on the surgical management of CSM involving one or two mobile segments; however, controversy remains regarding the selection of surgical procedures for treatment of multilevel CSM, especially 3- or 4-level CSM [21‐25]. Li et al. [26] reported that anterior techniques had become one of the most popular spinal surgeries for the treatment of CSM, which not only allowed direct decompression, but could also help restore the height of interbody spaces and restore cervical lordosis with careful intraoperative distraction, and the immediate stability of the cervical spine could be achieved with grafting and with anterior internal fixation. Axial neck pain has been recognized as one of the most important complications after cervical surgery. The incidence of axial pain in individuals with posterior cervical decompression is reportedly as high as 60–80% according to previous articles [16]. Kawaguchi et al. reported that postoperative axial pain for posterior cervical decompression was associated with the destruction of posterior cervical muscle complex and abnormal cervical curvature [17]. For patients undergoing anterior cervical decompression surgery, previous researches have investigated detailed complications, such as dysphagia, postoperative hematoma (neck), hoarseness, esophageal injury, injury to major vessels, wound infection (neck), graft extrusion, axial neck pain, C5 palsy, reduction in neck motion, pseudoarthrosis, nonunion, and revision and screw removal. To the best of our knowledge, however, few studies focus on the axial neck pain associated with anterior decompression, especially multilevel decompression with fusion surgery.

In this study, radiologic images of the patients showed that spinal cord compressions in the majority of multilevel CSM were mainly the result of protrusive intervertebral discs and osteophytes, and the pathophysiologic features of multilevel CSM make anterior decompression the most effective surgical option. We found that the prevalence of axial neck pain was 27.3% for patients undergoing multilevel anterior cervical decompression with fusion surgery, which was significantly lower than that of posterior decompression. This might suggest that the destruction of posterior cervical muscle complex had a significant effect on postoperative axial symptoms. On the basis of perioperative clinical and radiographic parameters, we compared three different anterior techniques, ACCF, ACDF, and ACHDF, for the treatment of 3- and 4-level CSM. The result shows that different surgical procedures for postoperative axial pain make no difference. The key finding of this study is that preoperative axial neck pain and kyphosis are the risk factors of axial neck pain for patients undergoing multilevel anterior cervical decompression with fusion surgery, and moderate correction of the kyphosis is more significant to avoid the axial pain.

The physiological curvature of the cervical vertebrae is an arcuate protuberance in the middle of the cervical segment of the human spine, which evolved over a long period of time to adapt to the upright walking posture of the human body. Lee et al. [27] pointed out that the normal value of cervical curvature in the middle position was 12~33°, and the C2–7 Cobb angle of cervical spine was abnormal in males with less than 20° and in females with less than 12°. In this study, the physiological curvature of cervical vertebrae was observed by preoperative and postoperative X-ray, on which the changes were obvious and easy to measure and could run through the whole process of cervical spine disease. The maintenance of normal cervical curvature includes static stability factors and dynamic stability factors. The former includes vertebral sequence, upper and lower facet joints, articular capsule, intervertebral disc, intervertebral ligament, and so on. The latter includes muscle group and ligaments around the cervical vertebrae. Dulor et al. [28] in animal studies found that the skeletal muscle led to denervated muscle during degeneration, causing muscle atrophy or replaced by adipose tissue. Previous research reported that changes in cervical curvature were accompanied by significant paraspinal muscle degeneration (fat infiltration). Thakar et al. [29] found that 93.50% of the patients with cervical spondylosis had abnormal cervical curvature, and in the control group without cervical spondylosis, only 38.50% had abnormal cervical curvature, which was significantly statistically different between the two groups. It can be seen that the changes of physiological curvature of cervical vertebrae can, to some extent, reflect the process of cervical degeneration. For patients with reversed cervical curvature, large interbody fusion cages are often needed to facilitate the recovery of cervical kyphosis. In the present study, cervical lordosis of fusion segments was significantly increased in all the patients with preoperative cervical kyphosis, but the correction range for kyphosis was greater in the axial pain group than that in the no axial pain group. Chang et al. [30] reported that a significant relationship between the increases in intervertebral disc height and interfacet distance, indicating that a large graft material lead to an increase in interfacet distance. Anterior approach allows the surgeon to distract and restore disc height, which can correct the in-buckling of the ligamentum flavum and restore alignment. It may be that multilevel ACDF can restore alignment by pulling the involved vertebral bodies toward the lordotic ventral plate, but long corpectomy grafts may straighten the cervical spinal column between the remaining vertebral bodies. Bogduk reported that provocative injection in the facet joint led to posterior neck and shoulder pains in asymptomatic volunteers [31]. The mechanism of action of pain provocation by the facet joint was suggested to be via the entrapment of synovial villi, nerve impingement by osteophyte, release of inflammatory mediators, and stretching of the facet joint capsule [32, 33]. Larger interbody fusion cages can reconstruct intervertebral space height to obtain higher cervical curvature recovery; however, overdistraction by inserting a large graft material was generally considered to lead to postoperative neck pain due to distraction of the posterior facet joint or spasm of the posterior neck muscle. We also found that for all the patients with postoperative axial neck, the absence of the axial pain was maintained at the 3-week follow-up, and improvements of clinical symptom have no obvious difference at the last follow-up. Axial symptoms gradually decrease or even disappear after a long period of adaptation. Thus, moderate cervical curvature recovery can avoid the occurrence of posterior cervical axial symptoms. Recovery of cervical kyphosis may contribute to the recovery of neural function, but may also suffer from short-term axial pain. And the exact critical values of height of intervertebral space and cervical curvature that cause postoperative axial symptoms still need further study.

This study is associated with several limitations. First, due to its retrospective design, our results did not rule out or compensate the diverse possible causes of postoperative neck pain. Therefore, further study is needed to prospectively evaluate the nature of postoperative neck pain after multilevel anterior cervical decompression with fusion surgery according to the fusion level and the nature and location of neck pain. Second, different people may have different subjective feelings about the same thing because of the different environment. In our study, only a part of all variables were selected to study which may lead to exist selection bias. Third, the effect of other postoperative complications on the postoperative neck pain was not taken into account.

Overall, preoperative axial neck pain and kyphosis could predict axial neck pain for patients undergoing multilevel anterior cervical decompression with fusion surgery, and recovery of cervical kyphosis may contribute to the long-term recovery of neural function, but may also suffer from risk of short-term axial pain, which could be reduced through moderate cervical curvature recovery.