For severe single-segment CSR, the long-term curative effect, revision rate and postoperative complications of MI-PCF and ACDF were the same after precise positioning of the V point. 12,16 However, MI-PCF reduces dissection of the neck muscles by simply removing the protruding nucleus pulposus, which reduces the postoperative axial symptoms, and the incidence of limited postoperative neck movement as a complication.17,18 Furthermore, this method is capable of preventing accidental injury to the trachea, esophagus, carotid artery and other adjacent tissues in the neck, and avoids the risk of acute suffocation caused by laryngeal oedema and tracheal compression after surgery.19 At the same time, MI-PCF retains most of the physiological and anatomical structure, affects the physiological curvature to a lesser extent, and maintains nearly normal overall biomechanical performance.20 Accordingly, this technique has been accepted by the majority of surgeons.
However, this technique requires extremely fine anatomical dissection and is limited by the field of view of the cervical spine that is obtained endoscopically. An in-depth understanding of the adjacent structures is important, especially during the search for the V point which is used as the starting point of the abrasion. Since the cervical laminae are small, there is a large amount of soft tissue adhesion between the laminae, which can be and changed in the flexion and extension of the cervical spine. Hence, it can be difficult to find and repeatedly confirm the V point of the surgical segment under C-arm fluoroscopy during the operation. Researchers have proposed that O-arm fluoroscopy could be used for 3D imaging to locate the V point during the operation,21,22 and cervical spine lateral mass vertical anchoring has shown promise for use in surgical positioning.14 The projection point on the inner upper edge of the pedicle is a bony structure, that does not change with dynamic changes in the position of the cervical spine during the operation. After defining this point as the positioning point, the point was found to extend inward by 1.43 ± 0.07 ~ 4.98 ± 0.22mm according to the measurement results, and the accuracy of the V point could be verified again. At the same time, this point could be easily found under C-arm fluoroscopy, and the support of expensive equipment such as an O-arm is not required to find this point. It is reasonable to expect that this novel method is ready for popularization.
In MI-PCF surgery, removing the bony structure around the V point by a drill would cause the V point to be lost, which could lead to surgical disorientation. To solve the above dilemma, Liu et al. used a translaminar approach to treat cervical disc herniation.23 The projection point on the inner upper edge of the pedicle was not lost after grinding. The inside of this point was the V point, and there was no need to look for the V point through the perspective again. Therefore, the average number of fluoroscopies in our study was only 4.0 ± 0.9, which is significantly less than the previously reported average of 12.6±2.0. Thus, this technique shortens the operation and reduces the radiation exposure of patients and medical staff.14
Based on the anatomical observations, the inner side of the V point is adjacent to the dura mater, and the nerve roots passed through the front of the V point, while the vertebral artery is located deep outside of the V point. If excessively deep grinding is performed in this area the vertebral artery may be damaged, the grinding path may deviate from the intervertebral disc and damage the pedicle. Kim et al. reported a case of spinal dural injury caused by the intraoperative drilling process,24 and Stephen et al. reported a case of vertebral artery injury during posterior cervical surgery.25 Based on the above complications, Nkamura S et al. designed an internal retractor to avoid nerve damage, but it was difficult to popularize.26 The technique of anchoring the projection point on the inner upper edge of the pedicle that was used in this study was performed under direct endoscopic vision. Comparatively, this method has the advantage of avoiding the possibility of iatrogenic injury caused by the Kirschner wire entering the spinal canal, intervertebral space, spinous process, or vertebral artery.
The abrasion range in MI-PCF extended outward to the lateral edge of the pedicle isthmus. To ensure the stability of the facet joint after the operation, the amount that was removed from the articular process on the affected side was less than 50% of the total articular process area.27 Through anatomical and CT measurements, it was concluded that the distance between the projection point on the inner upper edge of the pedicle and the V point gradually increased from C3/4 to C6/7, reaching a maximum at the C6/7 level. In the report by Cao, the range of horizontally outward abrasion from C3/C4 to C6/C7 was 2 mmཞ5 mm.15 Therefore, it was feasible to use the pedicle projection point as the critical point for outward abrasion, and this point provided an intraoperative reference for the scope of laminectomy. Using this point avoided both vertebral artery and nerve damage because the position of the nerve root was too low to cause the fenestration to be too large, which could damage the vertebral artery. Meanwhile, the use of this point also prevented excessive abrasion of the small joint area, which could lead to iatrogenic cervical instability postoperatively.
Although the operative duration in this study may not be superior to the results of published papers within the same period, the operative time significantly decreased with improvements in proficiency during the treatment of 21 patients.28In the future, additional data will be collected from more patients and the efficacy of this method will be compared with that of traditional MI-PCF. Accurate values of a were obtained by on imaging and verified in anatomical specimens. Unfortunately, due to the possibility of damage to normal anatomical structures, differences in the accuracy of measurement tools, and the differences between anatomical and imaging measurements, the data showed differences between the patients and specimens. There were numerous other restrictions during the processing of the specimens and the results that were measured anatomically differed from those measured on imaging. In future studies, physical specimens and corresponding CT scans will be used to further verify our results.
In brief, the modified MI-PCF technique is a safe and effective new surgical treatment for CSR, that involves little trauma and allows rapid recovery. However, this technique still needs improvement, which motivates us to perform continuous optimization towards a targeted, minimally invasive, fast, and easy-to-learn approach.