INTRODUCTION

Cervical intervertebral disc herniations occur when a part of the nucleus pulpous or annulus fibrosus occupies space within the spinal canal and are an important pathology that causes neck pain, radiculopathy, and myelopathy. It may limit working life and daily activities, and cervical spine surgery is effective when conservative treatment is not sufficient to reduce pain^(1,2). The most appropriate method for treating symptomatic cervical disc herniation is microsurgical anterior cervical discectomy.

In recent years, with the introduction of the microscope, non-fusion or fusion techniques have been used^(1,3). Discectomy with fusion relieves the pressure on the spinal cord and nerve roots, and autologous or heterologous bone grafting and cervical cage (CC) are applied to achieve appropriate cervical vertebra alignment and solid arthrodesis with minimal risk^(4-6). Although there are many surgical options for cervical disc herniation, cervical disc prosthesis (CDP) is now an established and validated option that has demonstrated its safety and effectiveness with good clinical results⁽⁴⁾. In the posterior approach, posterior cervical foraminotomy (PCF) can be performed openly or endoscopically^(7-9).

In this study, in 57 patients with single- and double-level cervical disc herniation who were operated on using a microscope with an anterior approach in our clinic, posterior longitudinal ligament excision was performed and cage and/or CDP were used instead of bone graft. In cases of double-level degenerative disc herniation, a hybrid cage or cage and CDP were used together.

MATERIALS AND METHODS

The information of 57 patients who underwent surgery with a diagnosis of cervical disc herniation in our clinic between 2015 and 2020 was collected from the nucleus database. In patient groups, age, gender, motor and sensitive deficits, disc nature (hard, soft), osteophyte formation, the most common disc level, two or more affected levels, the relationship of the disc with the posterior longitudinal ligament and postoperative cervical vertebra curvature, early and postoperative 6^th-month Visual Analogue Scale (VAS) results, healing status according to Odom’s criteria, reoperation, and developing complications were evaluated. It was questioned whether there might be other reasons for symptoms such as neck pain, pain radiating to the arm, and shoulder pain. Preoperative plain radiographs, cervical magnetic resonance imaging (MRI), and computer tomography were examined in all patients. Cervical lordosis changes, intervertebral level stenosis, and osteophyte formation in the posterior vertebra were recorded. Patients with fractures, infections, deformities, tumors, and chronic systemic illnesses, such as rheumatoid arthritis and neurodegenerative diseases, were not included in this study. Postoperative cervical vertebral sagittal alignment was compared between the groups (Figure 1). The number of patients meeting the criteria was 29 males (50.9%) and 28 females (49.1%), and the follow-up period was 2 years.

Patients according to the type and level of fusion; were divided into 4 groups: group I, CC; group II, CDP at one level; group III, CC+CDP; and group IV, CC+CC at two levels. In cases with CC, 1 cc canceled bone allograft was placed inside the cage and placed at the level to achieve better fusion. Patients with cervical trauma, neoplasm, infection, bleeding tendency, and chronic systemic disease were not included in the study. The patients had neck pain before and after surgery. Severity was evaluated using VAS results, and postoperative quality of life was evaluated using Odom’s criteria.

This study was approved by the Başkent University Medicine and Health Sciences Research Board (approval number: KA23/267, date: 22.08.2023) and supported by the Başkent University Research Fund.

Statistical Analysis

Statistical Package for Social Sciences for Windows 11.0 program (SPSS Inc., Chicago) was used. While evaluating the data, descriptive statistics were given as mean, standard deviation, and n (%). Categorical variables were compared using the chi-square (X²-test). If the alpha value was less than 0.05 (p<0.05), the data were considered statistically significant.

RESULTS

When the groups were evaluated, the average age of the group I cases was 46.5 years, 20 (66.7%) of whom were female, and in the II, III, and IV group cases, the average age was over 55 years, 19 (70.3%) of whom were male. In preoperative cases, brachial neuropathy (pain radiating to the arm) in group I was found in 10 (33.3%), reflex disorders in 7 (23.3%), paresis in the upper extremity in 12 (40.0%), and Brown-Séquard findings in 1 (3.3%). In groups II and IV, brachial neuropathy and paresis were more frequent. It was determined that cord compression findings (clonus) developed in 2 (6.7%) cases. Because of the comparisons, there was no statistically significant difference (p>0.05) (Table 1).

In operated cases, in all groups, the affected disc space was frequently C 5/6 in 37 cases (64.9%) and C 6/7 in 23 cases (40.4%). In those who underwent CDP, soft disc was observed in 24 (80.0%) patients and hard discs in 6 (20%) cases. Hardness was detected in the entire group with CC, CDP+CC, and CC (two distances). There was a statistically significant difference according to the affected disc nature and spacing (p<0.001) (Table 2).

In the preoperative cervical MRI reports of the cases; In the CDP group, protrusion and extrusion were reported in the midline in 13 (22.8%) patients and in the lateral location in 17 (29.8%) patients. Osteophyte formation was more frequently encountered in the midline and lateral locations in the CC group (17.5%). Osteophyte formation and autofusion were not observed in the CDP group. Due to restrictions set by the Social Security Institution in Turkey, patient selection for CDP was limited to those who met certain criteria. However, if used in a single distance, at C3/4, C4/5, C5/6, and C6/7 disc distances, over the age of 18, it can be used in patients with no degenerative changes in the posterior elements (such as facet arthropathy, osteoporosis), no listhesis, no infection, and traumatic disc herniation. CDP was applied to patients who met all the criteria, such as having no cervical kyphosis or cervical lordotic, and showing on MRI that the height of the disc space to be applied was at least half of the height of the healthy adjacent disc. There was a statistically significant difference between the preoperative cervical MRI results (p=0.006) and the postoperative cervical spinal alignment averages (p=0.021)   was determined to be 4.28°-5.84° on average in the single-level CDP and CC groups and 4.66°-7.22° in those who underwent two-level CDP+CC and CC hybrid surgery (Table 3).

Although the operation time was performed at an average of 115.50-141.60 min in all 4 groups, postoperative VAS results showed a significant decrease and excellent improvement was detected in 47 (82.45%) cases. As a result of the surgeries in all cases, temporary dysphagia was observed in 2 (3.50%) cases, and only 1 patient (1.75%) who underwent hybrid CC was re-operated because of cage displacement (CD). When all groups are compared according to operation times, operation results, and complications, there is no statistically significant difference between the groups (p=0.074) (Table 4).

DISCUSSION

Cervical intervertebral disc herniations occur when part of the nucleus pulposus or annulus fibrosus occupies space within the spinal canal. Disc degeneration can lead to symptoms such as osteophyte formation, disc narrowing, subluxation, instability of one cervical vertebra relative to another, or disc protrusion, i.e., pathological changes. Symptoms such as neck pain, radicular, motor, and sensory disorders, and signs of cord compression may occur, whereas MRI shows signs of radicular and cord compression. C3-4, C4-5, and often C5-6, C6-7 levels are affected^(3,10).

In surgical treatment, discectomy without fusion with the anterior approach or cervical discectomy with fusion (mACDF), in which different bone grafts and devices are used to obtain good bone fusion, and PCF with the posterior approach are the preferred surgical techniques^(1,2,10). Anterior contralateral microdiscectomy without fusion is a minimally invasive technique that can be recommended in foraminal or lateral disc lesions, ventral osteophytes, and instability of the affected disc space⁽¹¹⁾. Although titanium cages, carbon fiber-reinforced polymer cages, polyetheretherketone, and polymethylmethacrylate cages are frequently used in mASDF surgery to provide mechanical support to the spine, preserve disc height, and restore sagittal lordosis, negative results have also been reported in some studies⁽¹⁾. In recent years, microsurgical cervical surgery with anterior intervention has been reported. CDP surgeries were preferred over mACDF, and good results were obtained⁽⁴⁾.

It has also been reported that there is an increase in the number of hybrid surgeries in which mACDF and CDP are used together in patients with multilevel cervical degenerative disc disease^(12,13). Such hybrid surgeries are performed because the degree of degeneration at each level is different and fusion or arthroplasty is applied equally to all levels. It is recommended in cases where application is difficult. Such hybrid surgeries limit the hypermobility of adjacent segments while preserving the segmental motion of each segment. In patients with multilevel cervical degenerative disc disease, several studies have reported better outcomes with combined mACDF and CDP than with mACDF or CDP alone. In addition, postoperative evaluation has shown that the complication rate and functional score are excellent or similar, the arthroplasty level is above the fusion level, or there is no significant difference in the pressure applied to the adjacent disc⁽¹³⁾.

Although successful clinical outcomes can be achieved with mACDF, postoperative complications such as pseudoarthrosis, instrumentation failure, and adjacent segment degeneration (ASD) have been the biggest concerns^(4,14,15,16). However, pseudoarthrosis is not observed in CDP, new problems such as heterotopic ossification and bone loss occur, and it has proven to be cost-effective compared with long-term follow-up^(4,17,18). In CDP, selecting the appropriate patient group is important to achieve a good prognosis. In addition, the postoperative prognosis of patients with one-or two-segment radiculopathy or myelopathy caused by soft disc herniation is excellent⁽¹⁶⁾.

There are many studies in the literature comparing long-term results after CDP and mACDF. In these studies, no significant difference was found in the results of CDP and mACDF when comparing patients followed for short periods of up to 2 years. However, in the 4-7-year patient follow-up results, CDP results were superior to mACDF in outcomes such as neck disability index, 36-item short health form survey results, and dysphagia, and the incidence of postoperative ASD was found to be lower in the CDP group than in the mACDF group^(19,20,21) Hilibrand and Robbins⁽¹⁴⁾ It has been reported that 2.9% of patients undergoing anterior interbody fusion will most likely develop ASD requiring cervical intervention⁽¹⁴⁾. Again, in studies comparing mACDF and PCF, although there is no difference in clinical outcomes, complication, and reoperation rates, PCF has a lower rate. Cervical alignment, which is costly, is better and does not increase the risk of adjacent segment disease (ASD)⁽²²⁾. Although ASD was not encountered in our four-group case series, long-term follow-up over 2 years could not be performed because of the distribution of the cases to different centers and the patients’ non-compliance with the long-term follow-up protocol.

Long-term prognosis results are important in the fusion of the operated segment after mACDF surgery. The surgeon should also consider the instruments and techniques used in surgery and patient factors. Diabetes, smoking, body mass index, vitamin D deficiency, and cortisone use are factors that negatively affect surgical results⁽¹⁾. To achieve bone fusion in mACDF surgeries, products such as autologous spongy bone and demineralized bone matrix combined with bone substitute tricalciumphosphate or bone morphogenic protein can be used; however, high fusion cannot be achieved with bone substitutes, and infection may develop⁽⁵⁾.

In recent years, different cages have been discussed to achieve osteosynthesis^(2,5). Better fusion was achieved using self-locking cages. Different types of anchors and screws (passing through the cage and settling on adjacent vertebrae) were designed for the cages. In our cases, cages with anchors were mostly used, and in fewer cases, cages with screws were used. Only in 1 case in hybrid surgery in the IV group, a decrease in the height of the vertebral body due to the displacement of the screw cage, pseudoarthrosis and CD, and spinal cord compression findings were detected, and the patient was re-admitted for surgery. In this case, dysphagia, vocal cord paresis, and right upper extremity paresis were detected in the early postoperative period after reoperation, and the vocal cord paresis resolved within 45 days.

CDP is preferred because it facilitates vertebral movement at the operation level and is less likely to cause ASD⁽⁴⁾. With CDP, patients can return to work early and the neck can maintain its natural range of motion. In recent years, disc prostheses made of titanium, chrome cobalt, ceramics, and hard silicone have been introduced⁽⁴⁾.

During CDP surgery, which is similar to mACDF surgery, discectomy is performed using an anterior approach. After foraminal decompression, an appropriate disc prosthesis is placed between the intervertebral level. However, some results may be encountered after CDP, such as pseudoarthrosis, ASD, and height loss at the intervertebral level^(17,23). Nevertheless, there have been no long-term consequences related to CDP and cage use in our cases.

Anterior bone loss (ABL) is a potential complication that occurs mid-term at the 5-year follow-up and has been reported in >50% of cases. It can cause disability, increased pain, and loss of the anterior part of the implant, among other issues. The cause of ABL is unknown, but it may be related to infection, debris accumulation, micromotion, and stress protection⁽²³⁾.

In our hybrid case, there was a displacement of the CD and ABL within the first 3 weeks. It is unclear whether the subchondral collapse and ABL in the upper and lower vertebrae of our patient were caused by the surgical technique or the screw cage used. In the relevant retrospective evaluation, it was believed that the bone cancellous structure of the case developed because of the screw cage compression applied at a softer and double distance.

In the last two decades, many randomized controlled trials have been conducted on SDP. The results indicate that CDP helps reduce ASD. It also prevents complications such as pseudoarthrosis and ABL. Moreover, it helps in achieving a more appropriate movement of the spine^(2,4).

CONCLUSION

Microdiscectomy with an anterior approach is the preferred surgical method for the treatment of cervical disc disease. Advances in minimally invasive techniques, imaging, microsurgery, and endoscopy techniques have led to the development of current surgical approaches. In the 2-year follow-up of our cases, it was determined that the results were excellent in the CDP patient groups after microdiscectomy. Therefore, in mACDF and CDP surgery, preoperative clinical and radiological evaluation, surgical team skill, instrument characteristics, and early and late postoperative follow-ups are the main factors affecting prognosis.

Ethics

Ethics Committee Approval: This study was approved by the Başkent University Medicine and Health Sciences Research Board (approval number: KA23/267, date: 22.08.2023) and supported by the Başkent University Research Fund.

Informed Consent: Retrospective study.

Authorship Contributions

Surgical and Medical Practices: F.A., B.L., G.Ö.S., Y.Ö.P., Concept: F.A., Design: F.A., Data Collection or Processing: F.A., B.L., G.Ö.S., Analysis or Interpretation: F.A., B.L., G.Ö.S., Literature Search: F.A., B.L., G.Ö.S., Y.Ö.P., Writing: F.A., Y.Ö.P.,

Conflict of Interest: The authors have no conflicts of interest to declare.

Financial Disclosure: The authors declared that this study received no financial support.