Full endoscopic laminotomy decompression versus anterior cervical discectomy and fusion for the treatment of single-segment cervical spinal stenosis: a retrospective, propensity score-matched study

Cervical spinal stenosis (CSS) is a common clinical spinal disorder with a high prevalence in the aging population [1]. The reduction in the effective volume of the cervical spinal canal can be due to factors such as cervical disc herniation, hypertrophy of the ligamentum flavum, ossification of the posterior longitudinal ligament, and degeneration of the facet joints, resulting in compression of the spinal cord and nerve roots, and producing symptoms of neurological dysfunction [2, 3]. The clinical manifestations of CSS patients principally include neck-shoulder pain and weakness or sensory loss, and lower limb numbness and weakness [4, 5]. In severe cases, urinary and rectal sphincter dysfunction and quadriplegia may occur [5]. For patients with mild symptoms, conservative treatment (neck immobilization, physiotherapy, medication, etc.) may provide symptomatic relief. However, for patients with progressive exacerbation of symptoms, surgery is required to prevent the progression of neurological deterioration [1, 6, 7].

Surgical approaches for CSS patients mainly include traditional open surgery and minimally invasive surgery. Anterior cervical discectomy and fusion (ACDF) is a classic open surgical procedure for the treatment of CSS, with the advantages of adequate decompression of nerves, reestablishment of cervical stability and restoration of cervical physiological lordosis [8, 9]. However, ACDF still has some limitations including potential complications such as degeneration of adjacent segments, restriction in neck movement, and displacement of the fusion device [5, 9]. In recent years, with the continuous development and refinement of minimally invasive concepts, spinal endoscopic surgery has been increasingly used in the clinical treatment of CSS due to its advantages of less trauma, faster recovery, and fewer complications, aiming to reduce soft tissue damage and achieve the same therapeutic effect as open surgery [6, 10, 11]. Nevertheless, the feasibility, indications, and clinical efficacy of spinal endoscopic surgery still need to be further investigated and clarified due to the limited literature available. Our team has previously applied full endoscopic laminotomy decompression to treat lumbar spinal stenosis with satisfactory clinical efficacy [12], and our guiding hypothesis was that this approach could also be applied to CSS with good clinical outcomes. In this study, full endoscopic laminotomy decompression or ACDF was performed for the treatment of CSS, with the aim of evaluating the clinical safety and superiority of the two surgical approaches.

CSS is the most common cause of spinal cord dysfunction in the middle-aged and elderly populations, with significant disability rates [24, 25]. The pathological basis of CSS is progressive compression of the spinal cord and nerve roots caused by cervical stenosis, leading to a series of neurological dysfunction symptoms due to ischemic changes in the nerves [1‐3]. The clinical symptoms of CSS are complex, including myelopathy, radiculopathy, and myelo-radiculopathy [16, 26]. For CSS patients whose conservative treatments are ineffective or have progression of neurological symptoms, surgical intervention is usually recommended [27]. The main objectives of spine surgery are to relieve spinal cord compression, improve neurological function, maintain cervical sagittal sequence, correct deformities, and prevent further neurological deterioration.

ACDF is the standard, well-accepted open surgical procedure for treating CSS, with proven therapeutic efficacy [28, 29]. From an anterior cervical approach, ACDF can remove herniated disc tissue, posterior osteophytes, and calcified posterior longitudinal ligaments that compress the spinal cord and nerve roots without manipulating the spinal cord, thereby achieving adequate decompression of the spinal canal [30]. Furthermore, ACDF can also effectively correct cervical kyphosis deformity [31]. However, despite the many advantages of ACDF, complications can still occur. The anatomy of the anterior cervical spine is complex and variable, and prolonged intraoperative traction on structures such as the vascular sheath, trachea and esophagus is likely to lead to postoperative complications such as throat pain, hoarseness, and dysphagia [2, 6]. Dysphagia is the most common complication following anterior cervical spine surgery [16, 32], with a prevalence of ACDF ranging from 1.7 to 67% [32]. In addition, long-term complications of ACDF, such as pseudoarthrosis formation, implant nonunion, and instrumentation failure, are also important factors that can severely impair patient prognosis [2, 9]. The fusion rate of a single-level ACDF has been reported to reach approximately 92%, while the fusion rates for two-level and three-level ACDF have diminished success at 75% and 56%, respectively [30].

In recent years, with continuous innovation and refinement of minimally invasive endoscopic techniques, spinal endoscopy applied to lumbar degenerative diseases has matured, and has recently been gradually transitioning to the treatment of cervical degenerative diseases. Several studies have shown that minimally invasive endoscopic techniques in the cervical spine could be applied to treat CSS with good clinical outcomes [10, 15]. In a proof-of-concept in vitro trial, Eicker et al. [27] performed full-endoscopic arcocristectomy on 55 segments of cervical stenosis in 10 cadaveric specimens, resulting in an average increase of 4.1 mm (± 1.2 mm) in the sagittal diameter of the cervical canal postoperatively. The authors concluded that this technique for CSS was feasible, achieved sufficient decompression of the spinal canal, and preserved the integrity of most of the posterior structures. Currently, posterior cervical endoscopic techniques are becoming increasingly accepted and adopted. The posterior approach avoids the complex anatomical structures encountered with the anterior cervical approach, eliminating any related surgical complications, while sufficiently enlarging the spinal canal for successful decompression [6]. Additionally, compared with posterior open surgery, the posterior endoscopic technique does not require extensive removal of cervical bony tissue and extensive stripping of paravertebral muscles, which effectively avoids postoperative disruption of spinal stability and potential intractable neck and back pain caused by denervation of posterior cervical muscle groups [3, 33]. Studies have documented that maintenance of the normal sagittal sequence of the cervical spine following posterior surgery principally relies on the function of a dynamic system, incorporating muscles and ligaments, rather than bony fusion or other rigid structures [34]. Therefore, posterior cervical endoscopic surgery can ideally maintain the normal physiological state of the cervical spine while avoiding the possibility of postoperative cervical kyphosis deformity associated with posterior open surgery and adjacent segment degeneration caused by fusion and internal fixation.

In the present study, there were no significant differences between the two groups in A-VAS, N-VAS, JOA and NDI scores, and all postoperative patient clinical scores improved markedly compared with preoperative scores, meeting the clinical significance criteria of the MCID. Therefore, we concluded that both surgical techniques for the treatment of CSS achieved satisfactory clinical outcomes, significantly relieving patient pain and improving neurological function postoperatively. However, referring to the principal aim of the study, the endoscopic group had significantly superior results in terms of operative time, intraoperative blood loss, incision length, and hospital stay compared to ACDF, which indicated reduced operative trauma and quicker recovery, quite in line with the concept of enhanced recovery after surgery (ERAS). Notably, our team has extensively applied full endoscopic laminotomy decompression for the treatment of lumbar spinal stenosis in previous cases, accumulating substantial clinical experience [12]. The expertise has enabled us to facilitate more efficient reduction and maintenance of operative time when using this technique to treat CSS in the present study. Prolonged operative time is one of the essential risk factors contributing to increase the risk of surgical site infection [35]. The impact of surgery as documented on cervical spine imaging is closely related to patient prognosis, and spine stability and sagittal sequence balance affects cervical micromotor joint motion, which is key to postoperative symptom relief and maintenance. Fusion techniques can lead to reduced range of motion of the cervical vertebral body, which significantly increases stress loading on adjacent segments and accelerates the progression of disc degeneration [16, 36]. Postoperative ROM changes in adjacent segments in this study were less in the endoscopic group, whereas the ACDF group had a significantly increased change in ROM at 12 months postoperatively and at the last follow-up, with a statistically significant difference. In addition, cervical GROM was significantly reduced and cervical mobility was limited after ACDF due to internal fixation. There was a trend of decreasing disc signals in adjacent segments between the two groups, but the decrease in RVG was more pronounced in the ACDF group at the last follow-up, which may be mainly due to segmental hypermobility with excessive disc pressure.

The postoperative disc height was increased and was maintained at a good level in the ACDF group, whereas in the endoscopic group there was a gradual decrease in disc height over time. The change in disc height after endoscopic surgery was attributed to the natural degradation of the disc tissues as well as to disc degeneration aggravated by surgical disruption of the normal disc structure. These changes may lead to localized loss of cervical curvature and poor spinal alignment [16]. In addition, we did not observe any evidence of fracture of the lamina and facet joints or significant spondylolisthesis in the endoscopic group, and the ST was < 3 mm in all the patients. These results suggest that cervical segmental stability can remain well maintained throughout the follow-up period. Nevertheless, there was a trend of gradual increase in ST, which poses the possibility of cervical spine instability with decrease in disc height. Therefore, longer-term follow-up is still necessary to assess ultimate segmental stability. Notably, compared with the ACDF technique, endoscopic surgery confirmed better preservation of the disc structure. While this helps to maintain physiological mobility of the cervical spine, it could theoretically lead to an increased risk of recurrent disc herniation, especially when the annulus fibrosus structure is not intact. In the present study, we did not identify any cases of recurrence, with several possible explanations: cervical discs bear less load in body mechanics, endoscopic surgery has relatively limited effect on cervical spine biomechanics, or limited sample size of the study. Nevertheless, this potential complication is worthy of clinical attention.

All patients in the endoscopic group were successfully operated under local anesthesia without any case converted to open surgery. Regarding intraoperative complications in the endoscopic group, one neurological dysfunction case was attributed to prolonged intraoperative nerve root retraction, and two cerebrospinal fluid leakage cases were likely due to dense adhesion of osteophyte or ligamentum flavum at the posterior margin of the vertebral body to the dural sac, leading to a dural sac tear during the decompression procedure. In the ACDF group, there were two cases of axial pain or neurological dysfunction, two cases of cerebrospinal fluid leakage, one case each of dysphagia and hoarseness. There was no statistically significant difference in the complication rate between the two groups, and no serious complications such as spinal cord injury, wound and surgical site infection, recurrence of disc herniation, or epidural hematoma occurred in any of the patients.

Full endoscopic laminotomy decompression is a relatively new technique for the treatment of CSS, in which spinal stenosis segments and degree can be precisely targeted for decompression. This technique provides adequate decompression of the cervical spine with less surgical trauma than the standard open technique. From the results of this study, full endoscopic laminotomy decompression was demonstrated to have the following advantages over ACDF: (i) less surgical trauma, quicker recovery, and earlier postoperative functional exercises facilitating more rapid patient rehabilitation; (ii) under local anesthesia, endoscopic surgery allowed the surgeon to communicate with the patient intraoperatively, which helped to reduce the risk of injury to nerve roots and dural sac; in contrast, ACDF was performed under general anesthesia, which is associated with some risks and higher overall costs; (iii) spinal endoscopy was a safer surgical option for older patients who could not tolerate open surgery due to underlying medical conditions; (iv) endoscopic surgery provided a clear, magnified field of view that allowed for precise identification of structures such as the ligamentum flavum, nerve roots, dural sacs, and enabled precise decompression of target tissues, with less risk of injuring nerves and blood vessels; (v) endoscopic surgery for single-segment CSS eliminated the need for fusion and internal fixation, which preserved cervical motion segment mobility, and greatly reduced the impact of adjacent segment degeneration. However, cervical endoscopic techniques still have some limitations and obstacles, such as intraoperative difficulties, high technical requirements, and a long learning curve. In this study, local anesthesia is the preferred choice for CSS patients who underwent full endoscopic laminotomy decompression, but it necessitates a high level of operator proficiency and patient tolerance. This can be primarily attributed to the potential iatrogenic injury to nerve roots and/or spinal cord when neck movement occurs during the decompression process. The success of the procedure relies on effective collaboration between the surgeon and patient. Prior to surgery, patients should be informed about the possibility of a stress response in the neck due to decompression. Furthermore, patients were required to actively communicate with the surgeon of any discomfort during surgery. Importantly, surgeons must provide advance notice and exercise caution while decompressing areas (e.g., nerve roots, dural sacs) that may induce a stress response. Besides, it is inevitable that part of the vertebral plate and facet joints need to be removed during cervical endoscopy, which can lead to biomechanical changes of the cervical segments when improperly handled, and may accelerate degenerative changes of the cervical spine and vertebral instability in the long term. Previous studies have shown that stability of the cervical spine is put at significant risk when more than 50% of the facet joints are removed [37]. Raynor et al. [38] demonstrated in a cadaveric specimen experiment that a fracture occurred at 159 pounds of pressure when 70% of cervical facet joints were removed, whereas no fracture occurred at 208 pounds of pressure when only 50% of facet joints were removed. Therefore, to adequately enlarge the spinal canal for decompression while preserving the facet joints as much as possible is a key to the efficacy of cervical endoscopic surgery.

There are some limitations in the current study. Firstly, it is a retrospective study, which could not compare to one with double-blinding in the selection of surgical approaches, and was also liable to bias from subjective factors. Although we used PSM to minimize confounding factors between the two groups, some biases in the study results may still exist. Secondly, the sample size was relatively small, the follow-up period was short, and it was limited to a single center. Thirdly, although all imaging results were averaged over 3 measurements by 3 independent reviewers, measurement error could still exist.

Full endoscopic laminotomy decompression is demonstrated to be an efficacious alternative technique to traditional ACDF for the treatment of single-segment CSS, with the advantages of less trauma, faster recovery, and less impact on cervical spine kinematics and adjacent segmental degeneration.