Comparative evaluation of posterior percutaneous endoscopy cervical discectomy using a 3.7 mm endoscope and a 6.9 mm endoscope for cervical disc herniation: a retrospective comparative cohort study

After general anesthesia, the patient was placed in a prone position. Then, intraoperative neurological monitoring (INM) was performed by a surgeon who specialized in neurosurgery. The surgeon and the assistant stood on the same side as the pathology, and then the endoscope monitor was placed on the opposite side of the pathology. A Kerrison punch or endoscope drill was also applied to conduct laminoforaminotomy or foraminotomy. An endoscope with an inner diameter of 3.7 mm as well as a 30° optics angle was also utilized (Shanghai Maoyu Medical Equipment Co., Ltd., China). Furthermore, all the processes were carried out under continuous irrigation with saline solution. The lamino-facet junction should be observed on the radiograph with a true antero-posterior view to identify the entry point. An 18-gauge Kirschner needle with a length of 25 cm was inserted and placed at the level of the pathology. A 1 cm superficial skin incision was completed. Then, the obturator was implanted and served to palpate the “V” point, which is an anatomical landmark surrounded by the superior border of the inferior laminae, inferior border of the upper laminae, and medial point of the facet joint. Hence, the working cannula was advanced, and then the obturator was removed (Fig. 1). At this point, the endoscope was inserted through the working cannula. A radiofrequency probe (joimax® GmbH, Germany) as well as endoscope forceps were applied to coagulate and remove the overlying soft tissue under continuous irrigation with normal saline. Once the observation of the osseous anatomical structure was completed, the inferior border of the upper laminae was resected with an endoscope drill until the ligamentum flavum was exposed, and then the endoscope drill was directed caudally toward the cervical pedicle and laterally toward the facet joint. Finally, to expose the exiting nerve root, the ligamentum flavum and foraminal ligament were also removed. Subsequently, the underlying disc space was detected with a dissector. Intraoperatively, to prevent excessive removal of the facet joint, a nerve hook was applied to feel the medial wall of the pedicle. After the exiting nerve root was exposed successfully, the intervertebral disc was detected. The herniated cervical disc was removed through the shoulder or axilla of the exiting nerve root according to the lesion location (Fig. 2). It is critical to palpate the exiting nerve root using a nerve hook, and the patient should feel discomfort-free after adequate removal of the intervertebral disc [30, 31]. Figure 3 shows the case of a 60-year-old male with cervical discomfort and radiating pain to the right shoulder and upper extremity. The patient was diagnosed with C6–C7 CDH. The postoperative performance was satisfactory based on the clinical results achieved by the patient.

The surgical tools applied in this technique were slightly different from those applied for the 3.7 mm endoscope. A larger endoscope with a 6.9 mm inner diameter (Fig. 4) was used in this approach (Shanghai Maoyu Medical Equipment Co., Ltd., China). The procedures used for foraminotomy, laminoforaminotomy and discectomy (Fig. 5) remained unchanged compared with those used for the application of the 3.7 mm endoscope. A 54-year-old male patient presented with symptoms such as neck pain and right upper extremity numbness. He was diagnosed with C5–C6 right foraminal CDH (Fig. 6). Good postoperative clinical results were achieved by this patient.

In this study, the application of neither the 3.7 mm nor the 6.9 mm endoscope resulted in the surgical complication of spinal cord damage. However, our corresponding author argues that the use of the 3.7 mm endoscope has a higher risk of spinal cord injury than the use of the 6.9 mm endoscope. The minimal working cannula of the 3.7 mm endoscope has the potential to become trapped in the spinal canal via the iatrogenic hole, thus damaging the spinal cord. Moreover, the 6.9 mm endoscope has a working cannula with a wider outer surface, which can prevent it from being negligently inserted into the spinal canal, eventually increasing the safety of the operation. This idea was also agreed upon by Lin et al. [20], who suggested that increasing the outer diameter of the working cannula could reduce the risk of spinal cord injury.

The application of the 3.7 mm endoscope is better than that of the 6.9 mm endoscope in terms of anterior decompression of the intervertebral foramen due to the smaller outer diameter of the working cannula, which functions to reduce compression of the spinal cord. In contrast, the delta working channel, which has a large inner diameter, may lead to spinal cord injury.