In 1944, Spurling et al. first described the effectiveness of p-PECD for the treatment of cervical foraminal stenosis induced by lateral CDH or osteophytes (32). Studies have proven that p-PECD is an effective treatment for cervical diseases, and the inner diameter of the working cannula has ranged from 3.7 mm to 6.9 mm (17, 22, 28). In our opinion, different diameters of the working cannula may lead to different surgical efficiencies. However, no comparative studies have been conducted to analyze the clinical outcomes of the application of a 3.7 mm endoscope or a 6.9 mm endoscope for p-PECD in patients with CDH. In this study, we analyzed the clinical results of 28 consecutive patients who were diagnosed with unilateral CDH and underwent p-PECD using a 3.7 mm endoscope or 6.9 mm endoscope.
Studies have suggested that both local and general anesthesia are effective strategies for PECD (17, 22, 23, 33). Wan et al. (17) announced that the use of local anesthesia in selected patients with CDH is a promising and feasible alternative. However, local anesthesia still has some unavoidable shortcomings, such as discomfort and psychentonia during the operation. Moreover, if the patient is awake, the noise produced by the surgical instrument may result in an elevated blood pressure, an increased heart rate, or an unpleasant surgical experience (17). General anesthesia has been explored in several previous studies, which all confirmed that it could offer patients a comfortable experience during p-PECD surgery (22, 23, 33).
In the present cohort, to minimize intraoperative anxiety and pain as well as to attain better cooperation by patients, general anesthesia was carried out in all patients. In addition, INM technology was applied in this study to prevent iatrogenic neurological deterioration intraoperatively. The detailed method has been described by Yu et al. (17, 34). No nerve compromise was observed in either of the groups postoperatively, and we attribute these positive results to the reasonable choice of anesthesia method and the application of INM.
The mean hospital stay for traditional posterior foraminotomy or ACDF in China is usually more than seven days (23). In our study, the mean hospitalization times of patients in whom the 6.9 mm endoscope or 3.7 mm endoscope was used were 5.1 (from 2 to 8) and 4.8 (from 3 to 6) days, respectively, and both groups showed an improvement in hospital stay compared with the average results in China. Since all the surgeries in this study were performed under general anesthesia, it took approximately 2 days to complete the preoperative examination and the assessment of the general condition of the patient to meet the requirements for conducting general anesthesia. Under normal circumstances, patients were discharged 2 days after the completion of the postoperative observation. Thus, the total length of hospital stay was approximately 5 days. However, no significant difference was observed between patients with the 3.7 mm endoscope and patients with the 6.9 mm endoscope in terms of the average hospital stay period (P>0.05). However, the use of the 3.7 mm endoscope (76.5 min) required longer operative times than the use of the 6.9 mm endoscope (61.5 min). We believe that this result may be because the small-diameter working cannula can only accommodate smaller-diameter endoscope instruments, such as RF probes, forceps and drills, which obviously limits the efficient identification of the “V” point, the removal of overlying soft tissue and the procedure of laminoforaminotomy.
On the basis of previous surgical experience (23, 35, 36), the average VAS score after surgery was significantly lower with the application of both endoscopes; however, the difference in the average VAS scores between the use of the 3.7 mm endoscope and the 6.9 mm endoscope was not obvious (P>0.05). Moreover, taking the modified MacNab criteria into consideration, the proportion of a satisfied result (excellent or good recovery) improved during the follow-up visit in the application of both endoscopes; nevertheless, the difference between the 3.7 mm endoscope and 6.9 mm endoscope was not significant (P>0.05). Therefore, the clinical outcomes of both endoscopes suggest similar efficiencies.
Identification of the “V” point
The identification of the V-point is an extremely critical operation step in determining the success or failure of p-PECD. Furthermore, the accurate and rapid confirmation of the V-point can provide sufficient confidence for surgeons in proceeding to the next step. In our study, the identification of the V-point was easier with the application of the 6.9 mm endoscope than with the application of the 3.7 mm endoscope (18.608±3.7607 min vs. 11.256±2.7161 min, p<0.001), which may be attributed to the large diameter of the working cannula in the 6.9 mm endoscope.
Potential of spinal cord injury
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.
Surgical-related complications, including headache, neck pain, dural damage, nerve root or spinal cord injury, seizures or neurological deterioration due to the highly increased cervical epidural pressure resulting from continuous saline irrigation, intraoperative bleeding or postoperative epidural bleeding, instability caused by surgery and infections, can occur after p-PECD for CDH patients (13, 23).
In 2007, Ruetten et al. (22, 30) stated a complication rate of 3% in 89 patients who underwent p-PECD, and in 2008, he reported three postoperative complications associated with transient, dermatome-related hypesthesia. In 2009, Joh et al. (37) demonstrated in a prospective study that 8 of 28 patients complained of neck pain caused by the increased pressure of the continuous irrigation system. In 2014, Yang et al. (23) observed a patient with transient pain on the contralateral side, which was due to excessive myelin dissection, and concluded that an incidence of 4.8% (2/42) of such symptoms occurred in patients who underwent p-PECD. In 2018, Wu et al. (27) reported that two patients suffered from bluntness of the pupillary light reflex, loss of consciousness, muscle weakness in the extremities and weak spontaneous respiration among those who underwent p-PECD under local anesthesia. The C6 lamina was perforated with the spinal needle, which then led to anesthetics passing through the iatrogenic hole and entering the subarachnoid space.
In the present cohort, the nerve root outer membrane was torn in one patient in whom the 6.9 mm endoscope was applied, but no cerebrospinal fluid leakage was observed during the operation, and no neurological deterioration was observed postoperatively. No other surgical complications were observed in either of the groups. The overall incidence of surgical complications in our study was 3.7% (1/28), and this result is similar to the results of previous studies (22) (23).
Despite all the positive clinical outcomes achieved in this study, there were still many limitations. The limitations of our study include the following: the small sample size, the lack of randomization, the use of a single surgeon, the deficiency of multicenter research and the comparably short-term follow-up period. In summary, multicenter randomized controlled trials with large sample sizes and long-term follow-up visits should be further established.