1. Introduction

Cervical spondylosis is mainly manifested as a series of clinical symptoms caused by compression of the cervical spinal cord, cervical nerve root, and corresponding vascular tissue.[1,2] Under modern life and work styles, the morbidity of cervical spondylosis had increased with larger cervical lordosis angle and worse spinal bearing capacity.[3–5]Cervical spondylotic myelopathy (CSM) is one of the most serious types of cervical spondylosis, and early surgical intervention is an effective treatment method.[6,7] With the promotion of minimally invasive surgery, spinal endoscopic techniques have been gradually established and applied in clinical work.[8–11] Currently, the endoscopic cervical surgery with key-hole technique, and the endoscopic cervical surgery with trench and vertical anchoring techniques had achieved good clinical results in the treatment of cervical spondylosis.[12–16]

Patients suffering from the lateral cervical disc and foraminal disease can be treated using anterior and posterior techniques, such as anterior cervical discectomy and fusion (ACDF), cervical total disc arthroplasty, and minimally invasive posterior cervical foraminotomy.[17]

A potential minimally invasive technique for treating cervical spondylotic radiculopathy is navigated percutaneous endoscopic cervical discectomy. It has been regarded as a safe, effective, and less invasive treatment for radiculopathy patients, however, it has a high learning curve. Anatomic localization is challenging for surgeons because of their limited range of view until they use O-arm navigation.[18] The emergence of complete endoscopic techniques allows surgeons to properly see the operation field.[19]

Posterior endoscopic cervical foraminotomy is used to treat unilateral cervical nerve root compression that causes radiculopathy and does not improve with conservative treatments. There have been descriptions of both anterior and posterior techniques. The overall outcomes of either of these broad techniques are equal.[13] Posterior methods directly address cervical root compression and allow for decompression by enlarging the neural foramen and/or removing a lateral disc fragment. Following the success of the open procedure, modifications of it were developed to reduce approach-related difficulties.[13]

Endoscopic posterior foraminotomy was created as a minimally invasive method to avoid the complications of the anterior cervical approach and to retain segmental mobility without reducing the efficiency of nerve decompression.[19] The trenching technique simplified the positioning procedure and reduced iatrogenic damage to the facet joint and the risk of spinal nerve injury during the surgery.[15,16] It allows the endoscope with a working cannula to get closer to the sequestrated nucleus pulposus without irritating the exiting nerve root, and it allows the nucleus pulposus to be successfully removed under direct visualization. It is a safe, effective, and feasible surgical procedure for the treatment of CSM with very highly up-migrated nucleus pulposus.[20] According to our findings, the drill may still block intraoperative vision during the central spinal canal decompression procedure. It is also difficult to determine the decompression range (especially the central to the contralateral range), the position of the bleeding point, and the subsidence influence of the dura mater from an endoscopic perspective. Therefore, the clinical effectiveness of the posterior endoscopic cervical modified trench approach in the treatment of CSM was documented in this study.

2. Methods 2.1. Patient population

Between June 2021 and June 2022, 9 patients with CSM in our hospital were retrospectively studied. Five of them were male and 4 were female, with a mean age of (60.44 ± 16.49) years (32–85 years) and a mean disease duration of (10.33 ± 3.67) months (5–17 months). Table 1 showed the clinical data of patients. This study was approved by the intuitional ethical committee (# 2021-04).

Table 1 - The clinical data of the patients. VAS JOA MSDC Cases Sex Age (yr) Disease duration (mo) Segment Preoperative Postoperative Last follow-up Preoperative Postoperative Last follow-up Preoperative (mm) Postoperative (mm) Operation time (min) Blood loss Follow-up period (mo) 1 Male 32 9 C4/5 6 3 1 13 10 16 7.13 13.49 128 48 6 2 Male 48 11 C5/6 5 3 1 12 12 15 6.26 13.05 171 87 12 3 Male 62 14 C5/6 7 4 2 12 13 15 5.91 12.64 132 81 9 4 Male 54 10 C6/7 5 3 1 10 14 15 7.91 16.67 126 60 12 5 Female 85 17 C5/6 – – – 11 12 14 5.73 14.76 148 75 1 6 Female 80 6 C5/6 5 3 2 11 13 14 7.64 13.22 167 94 10 7 Female 52 11 C6/7 6 2 2 13 13 15 7.11 11.42 124 59 6 8 Female 71 10 C6/7 4 2 1 10 12 13 9.60 14.90 144 55 9 9 Male 60 5 C4/5 7 3 2 11 12 16 7.98 13.72 139 69 12

JOA = Japanese Orthopedic Association, MSDC = minimum sagittal diameter of the spinal canal, VAS = visual analog scale.

The inclusion criteria were as follows: clinical symptoms of spinal cord injury, such as limb numbness, fatigue, and staggering; compression of a single segment of the spinal cord caused by cervical intervertebral disc herniation, as demonstrated by the cervical MRI; ineffective conservative treatment for 3 months or worsening of symptoms to intolerable levels; and undergoing local + intravenous anesthesia and surgery.

The exclusion criteria were as follows: refusal of local + intravenous anesthesia; combination of contraindications to surgery determined by multidisciplinary joint consultation; segmental tumor, infection, or other cervical spine diseases; multi-segmental cervical disc herniation with difficulty in locating the main lesion segment; cervical instability; and refusal of surgical treatment due to personal factors.

Before surgery, all patients had X-rays, 3-dimensional CT (angiography was done as needed), MRI, and CTA exams to identify the lesions and operative section. Prior to surgery, all patients received instruction and prone position training. The same attending surgeon carried out every operation.

2.2. Surgical procedure

All operations were performed under intravenous + local anesthesia. The patient was placed in the prone position with the head slightly elevated and the feet low with a horizontal angle of about 20°. A square silicone headrest or a Mayfield headframe was used to immobilize the head, in the prone position with the neck slightly flexed. Guided by C-arm fluoroscopic, the skin mark was made at the point of cross projection between the outer edge of the lateral mass joint and posterior tubercle of the transverse process on the side of the main symptom (Fig. 1A).

Figure 1.:

Image data and intraoperative fluoroscopy. (A) Green circle was the area of posterior endoscopic cervical modified trench technique approach, red circle was the area of traditional trench approach, blue circle was V-point, yellow circle is the decompression area of lamina approach. (B) Oblique pedicle projection point. (C) Vertical anchoring technique. (D) Decompression had reached the central spinal canal. (E–G) Decompression range of posterior endoscopic cervical modified trench technique. (H) Decompression range of traditional trench technique, the red arrow showed the partial remove of posterior wall of the vertebral body.

After routine disinfection and anesthesia, a 2.0 mm Kirschner wire was punctured and fixed on the lateral mass surface along the oblique projection direction of the pedicle (convex angle of 45°–60°, Fig. 1B). After confirming the position with C-arm fluoroscopy, an 8-mm skin incision was made and the working trocar and endoscope were placed along the Kirschner wire. After clearing the soft tissue around the Kirschner line, the presence of large vessels on the surface of the lateral mass was observed.

After ensuring that the visual field was secure, the surgical region was marked in a circle with a trephine on the posterolateral surface of the lateral mass (Fig. 1C). The deep carotid artery that ran above the lateral mass was protected by having the trephine marks exposed to the dorsal side of the lateral mass from the central side, laterally to the parapophysis tubercle, and ventrally to the vertebral artery under continuous saline lavage. The spinal canal and nerve root were revealed under endoscopic view after progressively removing a portion of the lateral mass joints and the top border of the pedicle of the lower vertebral body with a burr. Then, a portion of the vertebral body’s posterior wall was cut away to reveal the dura’s ventral perspective. Intraoperative fluoroscopy confirmed that the surgical area reached the center of the spinal canal (Fig. 1D), allowing for resection of the ossified posterior longitudinal ligament, cervical disc herniation, and hyperplasia of the posterior and inferior edges of the vertebral body at the ventral edge of the dura to finish the decompression (Fig. 1E–G).

Under endoscopic observation, full decompression causes the dural sac and nerve root to decrease. The surgical region was flushed with 160,000 U of gentamicin sulfate injection and 5 mg of dexamethasone sodium phosphate injection after hemostasis. A drainage tube was inserted into the wound, and the entire thickness was stitched together and fastened. Figure 2 depicts the procedure performed using an endoscope.

Figure 2.:

Procedure under the endoscope. (A) Exposing the deep cervical artery, blue arrow showed the deep cervical arteries. (B) Exposing the anchoring point, blue arrow showed the deep cervical arteries, red arrow showed the anchoring point. (C) Exposing the spinal canal, blue arrow showed the back wall of the vertebral body, red arrow showed the dural sac. (D and E) Exposing the posterior longitudinal ligament, blue arrow showed the back wall of the vertebral body, red arrow showed the posterior longitudinal ligament. (F) Partial excision of posterior longitudinal ligament, red arrow showed the posterior longitudinal ligament, blue arrow showed the dural sac. (G) Exposing the back wall of the vertebral body and contralateral posterior longitudinal ligament, red arrow showed the dural sac, blue arrow showed the posterior longitudinal ligament after excision, green arrow showed the intervertebral disc. (H) Ventral vision of spinal canal after decompression, red arrow showed the nucleus pulposus, blue arrow showed the back wall of the vertebral body, yellow arrow showed the dural sac. (I) The operation of contralateral tissues decompression, the forceps can be seen clearly under endoscope, red arrow showed the mouth of forceps. (J) Subsidence of spinal nerves, red arrow showed the nucleus pulposus, blue arrow showed the back wall of the vertebral body, yellow arrow showed the dural sac.

2.3. Details regarding the surgical procedure

The segmental superior vertebral arch was positioned at the outer edge of the projection point of the body of the lateral mass joint, with an entry roadside opening angle of approximately 70 to 90° (Fig. 3A), and the bone surface was abraded from the lateral mass joint (Fig. 3B and C) to the lateral, ventral-inferior edge of the superior arch (internal) – superior edge of the inferior arch (internal) – posterior (external-internal) posterior superior wall of the vertebral body (Fig. 3D and E). The key anatomical landmarks were the lateral block dorsal deep carotid artery, the posterior transverse node, the segmental nerve root, and the vertebral artery.

Figure 3.:

The specific steps of the surgical procedure. (A) Position the segmental superior vertebral arch at the outer edge of the projection point of the body of the lateral mass joint. Angle the entry roadside opening at approximately 70° to 90°. (B–E) Abrade the bone surface from the lateral mass joint to the lateral, ventral-inferior edge of the superior arch (internal), superior edge of the inferior arch (internal), and posterior (external-internal) posterior superior wall of the vertebral body.

2.4. Follow-up

The operative time, intraoperative blood loss [hematocrit (HCT) algorithm: blood loss = (preoperative HCT − postoperative HCT) × body weight × 7%/HCT], visual analog scale (VAS),[8] Japanese Orthopedic Association (JOA) scores, JOA recovery rate (JOA recovery rate (%) = [(postoperative JOA score − preoperative JOA score)/(17 − preoperative JOA score)] × 100%, the score ≥ 75% is excellent, 74–50% is good, 49–25% is fair, <25% is poor),[9] and surgical complications were recorded and used to evaluate the surgical safety and efficacy of the procedure. A postoperative 3D CT examination of the cervical spine was performed. The minimum sagittal diameter of the spinal canal (MSDC) was measured pre and postoperatively[10] to evaluate the extent of decompression.

3. Statistical analysis

SPSS 25.0 (IBM SPSS Inc., Chicago, USA) and GraphPad Prism 9 (Dotmatics, CA) were used for statistical analysis and graph drawing. Paired t tests were used to compare pretest/posttest scores of VAS, JOA, and MSDC, and P < .05 was regarded as a positive significance level.

4. Results

All 9 patients successfully finished the operation. The operation time was 124 to 171min with an average of 142.11 ± 17.29 min. The intraoperative blood loss was 69.78 ± 15.57 mL (48–94 mL). Following surgery, patients were monitored for 1 to 12 months; the average follow-up period was 8.56 ± 3.68 months. In comparison to before surgery, the postoperative and final VAS values were considerably reduced (P < .01). Additionally, the JOA scores rose over time following surgery (P = .01). The JOA recovery rate at final follow-up was 75% in 2 instances, 74–50% in 6 cases, and 49–25% in 1 case. The percentage of JOA improvements that were excellent or good was over 90%. CT imaging demonstrated that it had significantly increased following surgery as compared to preoperative MSDC. Figure 4 (case 1) and Table 2 displayed the data of follow-up indicators.

Table 2 - The follow-up data of patients (mean ± SD). VAS JOA MSDC (mm) Preoperative 5.63 ± 1.06 11.44 ± 1.13 7.25 ± 1.21 Last follow-up 1.50 ± 0.53 14.78 ± 0.97 13.76 ± 1.51 t 13.981 10.00 12.568 P value .000 .000 .000

VAS 1.57 ± 0.41. JOA 15.01 ± 1.32.

JOA = Japanese Orthopedic Association, MSDC = minimum sagittal diameter of the spinal canal, VAS = visual analog scale.

Figure 4.:

Follow-up data of patients. After the operation, the (A) VAS score decreased apparently, (B) JOA score and (C) MSDC increased obviously, ***P < .01 compared with that prior to the operation. JOA = Japanese Orthopedic Association, MSDC = minimum sagittal diameter of the spinal canal, VAS = visual analog scale.

A 32-year-old male patient with a C4/5 responsible segment had right C5 nerve root palsy throughout the follow-up period, and his muscular strength fell to level 3 from level 4 prior to surgery. No significant nerve root tugging or damage occurred during surgery. And a postoperative CT evaluation revealed no evident aberrant compression. After receiving conservative care for a week, the symptoms dramatically subsided and there were no aftereffects found during the last checkup. During the follow-up period, there were no major complications such as artery damage, cerebrospinal fluid leak, or paralysis.

Figure 5 (case 2) presented the case 2 data, which was diagnosed with cervical spinal cord injury and spinal cord type cervical spondylosis. Preoperative CT suggested cervical 4/5 and 5/6 disc herniation with calcification and vertebral cervical 6/7 disc herniation with nerve outlet stenosis. Postoperative MRI showed good decompression of the cervical 4/5 and 5/6 discs, and good decompression of the cervical 6/7 disc, central spinal canal, and nerve outlets.

Figure 5.:

Comparison of imaging before and after staged endoscopic decompression of cervical 4/5 and cervical 6/7 in a 35-year-old male with cervical 4/5 and cervical 6/7 disc protrusion. Preoperatively: (A) sagittal CT suggested cervical 4/5 and 5/6 disc herniation with calcification and hyperplasia at the posterior border of the vertebral body; (B) suggested cervical 4/5 disc herniation in the central spinal canal with calcification to the right; (C) suggested cervical 6/7 disc herniation with calcification at the posterior border to the right to the central spinal canal and nerve outlet stenosis. Postoperatively: (D) sagittal MRI suggested good decompression of cervical 4/5 and 5/6 discs and basic resection of hyperplasia at the posterior edge of the vertebral body; (E) suggested good decompression of cervical 4/5 discs and central spinal canal and abrasion of calcified hyperplasia at the posterior edge of the vertebral body; (F) suggested good decompression of cervical 6/7 discs, central spinal canal, and nerve outlet.

5. Discussion

Cervical spondylosis is a common disease in spine surgery, and CSM is one of the most common types.[1,6] Posterior endoscopic cervical discectomy has achieved good clinical outcomes in the treatment of cervical spondylosis.[21,22] Studies have shown that it is comparable to the ACDF in terms of the clinical efficacy of cervical radiculopathy.[23,24] However, posterior endoscopic cervical discectomy is less invasive, recovery is faster, it preserves the motion of the operating segment, and it reduces the incidence of adjacent segment degeneration.[23–26] Recently, it has become an indispensable surgical treatment in clinical work.[27,28]

For the treatment of cervical spondylotic radiculopathy, the key-hole cervical endoscopic approach is frequently used.[24,29–31] Although it provided several benefits for foraminal decompression, the dura’s occlusion made it challenging to finish ventral decompression of the spinal canal.[31] A central disc herniation can be successfully treated with posterior percutaneous endoscopic cervical surgery using the trench approach, as shown in a recent study by Deng et al.[16] The surgical approach is made in the cervical lateral mass, which minimizes injury to the facet joint and improves the surgical segment’s postoperative stability.[16] Additionally, it can expand the decompression range to the top and posterior portions of the vertebral body, allowing the ventral dura to be decompressed with minimal nerve disruption during the procedure.[16] The complexity of localization and operation is significantly decreased with the aid of the vertical anchoring technique.[15]

We developed the posterior endoscopic cervical modified trench method based on clinical research. Although the usual trench method is a posterior approach, reaching the ventral and contralateral sides of the dura is challenging. When the lesions are concentrated in the center of the spinal canal, or when there is significant hyperplasia and bulging along the entire posterior edge of the vertebral body, it is necessary to enlarge the surgical tunnel laterally and remove more bony structures behind the vertebral body in order to complete decompression of the posterior wall and the contralateral side of the vertebral body (Fig. 1H). Also, the surgeon’s view may be obstructed by the dura during the procedure, which increases the risk of spinal cord injury to the patient. Moreover, it was difficult to directly observe the extent of decompression and bleeding point in the surgical area, which will also lead to inadequate decompression.

Our modified lateral combined trench approach provides direct access to the dura on both the ventral and contralateral sides. Using the lumbar endoscopic technique,[32] we exposed the spinal canal and nerve roots by expanding the intervertebral foramen region of the posterolateral border of the lateral mass from the outside to the inside. At this point, decompression can be limited to 1/3 to 1/2 of the vertebral body’s posterior wall. Under direct vision, the central or even opposite side of the spinal canal can be decompressed with a clear ventral view of the dura. Our procedure allows for the removal of osteophytes, posterior longitudinal ligaments, and ruptured intervertebral discs, and the partial grinding of the vertebral body’s posterior wall during the operation did not significantly raise the risk of postoperative instability. All the patients improved significantly in terms of VAS, JOA, and MSDC after surgery. Patients were followed up for 1 to 12 months after surgery, and the results indicated a substantial drop in VAS values (from 5.63 ± 1.06 to 1.50 ± 0.53) and an increase in JOA scores (from 11.44 ± 1.13 to 14.78 ± 0.97) over time compared to the preoperative period, with an overall JOA recovery rate of > 90%. When compared to preoperative MSDC, CT imaging revealed a substantial rise in postoperative MSDC in our study.

Our study demonstrated that our VAS results are comparable or superior to the other study. Specifically, the other study found that at postoperative final follow-up, VAS scores were 1.57 ± 0.41, and JOA scores were 15.01 ± 1.32.[33]

According to the results, the surgeries were completed smoothly without any serious complications such as arterial rupture, dural tear, cerebrospinal fluid leakage, or paralysis. However, one patient with a cervical disc herniation at C4/5 level experienced a decrease in strength in the right trapezius muscle after surgery (from grade 4 preoperatively to grade 3 postoperatively). Three days after surgery, the muscle strength had recovered to grade 4. This complication was thought to be related to spinal cord and nerve root sinking or hematoma irritation. It’s important to note that although surgical complications can occur, they are generally rare, and most patients do not experience any significant issues after surgery. As a clinician, it’s essential to inform patients about the potential risks and benefits of surgical intervention and to monitor patients closely during the postoperative period to ensure timely management of any complications that may arise.

We believe that the following points can help reduce the complexity of cervical endoscopic procedures: during the puncture process, the Kirschner wire initially contacted the dorsal bone surface of the lateral mass, then the needle tip moved outward to the posterolateral area for anchoring along the bone surface, minimizing injury to the nerve root and artery near the intervertebral foramen. Before marking with the trephine, the soft tissue around the Kirschner wire should be examined and cleansed to locate the big blood veins and limit the danger of bleeding. And it is not necessary to excessively clean the soft tissue on the bone surface for full ring marking. When the transverse process tubercle blocked the access, the bone resection range can be appropriately increased and the angle of the access can be adjusted. However, it is not necessary to expose the vertebral artery when it is not necessary. Under intravenous + local anesthesia, the patient can remain awake and give feedback during the procedure, which improves the safety of the procedure.

Our modified lateral combined trench approach offers a unique access approach that differs from the conventional cervical endoscopy procedures, which typically access the vertebral plate from the posterior side, intervertebral plate V-point, or vertebral plate grinding openings, and are generally suitable for soft protrusion or partial calcification protrusion near or next to the central intervertebral disc herniation. Using existing endoscopic techniques to treat myelopathy caused by osteophytes is challenging. The main problem is the limited operating space in the spinal canal, which is likely to result in iatrogenic nerve root or spinal cord injury.[34] This technique offers complete decompression and enhanced safety. However, it may not be effective for central spinal cord ventral or calcification that is too pronounced or when there is central posterior vertebral body bony hyperplasia compression. We developed a modified approach that accesses the lateral intervertebral foramen, offering advantages in entering from the nerve roots and the ventral side of the spinal cord, trenching to the ventral side of the dura mater, or even the opposite side, removing soft disc herniation, calcified discs, and bony growths in the region, and completing spinal cord decompression. The scope and effect of ACDF decompression can be achieved through this technique. However, the modified approach has some drawbacks, including a steep technical route and a long learning curve. It requires a team of highly qualified physicians with extensive experience in cervical endoscopy to perform the procedure.

5.1. Limitations of this study

While this study showed promising clinical outcomes, there are limitations that must be addressed. The small sample size, lack of randomization, and short follow-up period make it difficult to draw definitive conclusions about the long-term efficacy and complications of the procedure. Therefore, future studies should involve a larger sample size, longer follow-up periods, and a multicenter approach to enhance the generalizability of the results. Additionally, a randomized design would minimize bias and increase the validity of the study. Further research is necessary to confirm the safety and effectiveness of this surgical technique, as well as to identify any potential risks and limitations.

6. Conclusion

In our study, the posterior endoscopic cervical modified trench technique provides greater maneuvering space over the ventral dura and reduces nerve irritation from instruments. It achieves a more completed ventral decompression with better subsidence effect of dura mater and nerve root. Its short-term clinical outcomes for the treatment of CSM are satisfactory, and long-term effects still need to be further explored.

Author contributions

Conceptualization: Shuangquan Gong, Liqiang Cui.

Data curation: Shuangquan Gong, Liqiang Cui, Yu Ye.

Formal analysis: Shuangquan Gong, Hongjun Liu, Yu Ye.Methodology: Hongjun Liu, Yu Ye.

Supervision: Shuangquan Gong.

Writing – review & editing: Shuangquan Gong, Liqiang Cui.

Writing – original draft: Liqiang Cui.

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