Safety considerations and risk-free surgery were the core of this study. Our study included 9.7% of patients had C3-4 disk, 22% had C4-5 disk, 53.1% had C5-6 disk (the most common), and 15.2% had C6-7 disk. Kienapfel et al. [16] reported also that the most commonly affected levels were C5-6 and C4-5.
In our study, we depended upon MRI for assessment of PLL pre-operatively, which was interrupted in 60.7% while it was intact in 39.3%. Takhtani and Melhem [17] demonstrated the sensitivity of MRI to assess PLL interruption in both sagittal T1 and T2. It is hypointense in both T1 and T2. PLL is usually interrupted by the ruptured disk fragment. Moreover, Yamazaki et al. [18] reported that disk herniation usually induces tears in both the superficial and deep layers. Consequently, there is fibrous tissue reaction and vascular proliferation. So, cautions should be taken during dissection of the ligament. Heary et al. [19] reported that pre-operative MRI may eliminate the need to open PLL provided that it is of high resolution and in T1 and there’s continuous PLL.
In our study, we found that PLL is interrupted in 60.1% (Table 2). Interruption of PLL was recognized intraoperatively after introduction of the operating microscope using its high magnification power. The ligament was known by its longitudinal yellowish fibers. We found that the ruptured disk fragment induced a tear through which it penetrated through the epidural space. By right-angled blunt microhook, we completed sharp dissection of the remaining parts of the ligament on both sides, irrespective of the site of the tear whether central or lateral. We used the right-angled blunt hook to explore beneath the PLL, then completing excision by thin foot plate 1- and 2-mm Kerrison (Fig. 3). Sonntag et al. [20] depended upon micro-curettes and bipolar coagulation, then completing the excision using 1 mm Kerrison. Our opinion is that 1- and 2-mm thin foot plate Kerrison has the advantages of being not only non-traumatic through its thin foot plate but also sharp in cutting the ligament in situ without traction.
Tu et al. [21] and Terry and Michael [1] recommended routine removal of PLL, so as to be sure that no residual disk material is left behind. On the other hand, Cloward [22] did not recommend the routine removal of PLL due to its protecting effect on the dura matter in addition to the fact that the herniation of posterolateral disk is beyond the lateral border of PLL and the central disk usually herniated through a tear in the PLL. On the other hand, Shapiro [23] reported that it is possible to find calcification of PLL. In such situation, it is advised to leave an island of the ligament adherent. Charles et al. [24] had an opinion that recommends partial removal to protect the dura unless the disk fragment is large. Scott et al. [25] stated that the PLL must be elevated laterally using right-angled blunt microhook and then excised with a thin footplate Kerrison. Precautions should be carried out during resection because of being thin and weak.
In our work, we were convenient with the opinion of routine removal based upon the study of Yamazaki et al. [26] who found an interruption of PLL in all of their patients intraoperatively. In patients with an intact PLL, we started dissection at its lateral border, based upon the anatomical features of the fiber orientation [5, 6, 22]. Optimum Casper distraction was not applied except after adequate visualization of the dura so that the dura is not in direct contact with the PLL.
In our study, bleeding was more common with those patients in whom PLL was resected and had no pre-operative radiologic signs of interruption in MRI. Bleeding near the root exit was encountered in 46% of our patients (Table 2). We tried to stop it using saline irrigation with a fine irrigation cannula. Okada et al. [15] supported this maneuver. Moreover, Ohyama et al. [27] reported that saline irrigation also minimizes the risk of root due to bipolar cauterization which if necessary, the bipolar forceps must be perpendicular to the root. We did not try to use bipolar coagulation. The only disadvantage of saline irrigation in our work was an additional operative time because using saline needed some patience to stop bleeding.
Weinstein [28] advocated that when venous bleeding occurs, it is possible to debride the PLL of adherent or thickened calcified material and could be left intact. They also recommended cautious coagulation of bleeding coming from the epidural venules or putting a hemostatic agent and augmented with a small piece of cottonoid. On the other hand, he did not recommend bone wax because it prevents fusion. In our work, we used the hemostatic agent after the effect of saline irrigation and a temporary small piece of cottonoid. At the same time, we prepared the hardware for fusion. Thus, exploiting this time for complete hemostasis.
Bertalanaffy and Eggert [29] reported postoperative cervical spinal extradural hematoma following ACDF. They attributed the source of bleeding to the arterial supply of PLL. They advised cauterization of the edges of the PLL. They partially resected the PLL in the majority of their series. Sang and Wilson [30] reported that extradural hemorrhage could result after ACD, and they attributed it to the injury of the arterial arcade. They concluded that the avoidance might be through partial resection and coagulation of the edges. Protzman et al. [31] reported that extradural hematoma could complicate ACDF. They attributed it to local trauma at the operative site and hypertension. Moreover, remote subdural hemorrhage to the thoracic spine was attributable to propulsion of the blood.
In our work, we had only one patient with intra-operative incidental durotomy (Table 2). We put a small piece of graft and no post-operative sequalae. Lin et al. [32] reported one patient with CSF leak. Gabriele et al. [33] reported spinal cord injury, CSF leak after dural injury, and meningitis in addition to nerve root injury. Our opinion is that the sharp dissection of the PLL might be risky with the straight knife because its blade is directed downwards to the dura. On the other hand, the curved knife may be less risky than the straight one because its blade is directed slightly upwards, so it may dissect through the potential space between the dura and PLL. Also avoiding Casper distraction initially may minimize the direct contact of the PLL with the dura. Moreover, starting at the lateral border is better than mid-line.
In our work, the postoperative degree of pain as measured by VAS score had a median of 4 (IQR 0–4), but decreased later to a median of 2 (IQR 0–2). The postoperative motor grade had a median of 5. The median VAS score for pain in preoperative had significantly decreased in early postoperative period, then decreased significantly also in late postoperative period (Friedman’s test was performed followed by pairwise comparisons, (p < 0.001). Figure 4b shows a significant increase in motor grade postoperatively compared with the preoperative grade (Wilcoxon signed rank test, p < 0.001). Elayouty et al. [34] had similar results. Lin et al. [32] pointed out that the excision of the PLL may help improve axial neck pain, where they defined axial neck pain as pain which included both nuchal, periscapular, and shoulder regions and its source is debatable. Lin et al. [32] postulated that PLL and the disk may be a source of axial pain, and therefore, PLL resection may help improve axial neck pain. On the other hand, Kienapfel et al. [16] reported that 24% of their patients had pain, 17% showed no improvement of radicular pain, and 19% were dependent upon medications. They reported motor weakness in 17% of their patients and 11% had myelopathic features.
It is to be mentioned that Nassr et al. [35] reported that the risk of post-operative C5 palsy after resection of PLL was dependent upon tethering of the nerve by the retropulsed disk fragment and non-cautious manipulation during resection of PLL. They recommended the use of intra-operative monitoring. In our work, we used thin footplate Kerrison and cut the ligament without traction, and also, we separated cautiously the disk fragment using microhook and under high magnification. This was planned to any disk level to avoid incidental durotomy or injury to the venous plexus around the root and also to minimize the risk of root injury. Accordingly, we did not catch such complication.
