Posterior longitudinal ligament resection during microscopic anterior cervical discectomy: technique and safety consideration
- 53 Downloads
Herniation of the cervical disk material results in interruption of the posterior longitudinal ligament (PLL) in the majority of patients. Routine opening of the PLL during ACDF is a necessary step for complete removal of all disk fragments.
Safety measures during PLL opening during microscopic anterior cervical discectomy and risk-free surgery
A retrospective clinical case series
Patients and methods
The study was conducted on 145 patients. The main symptom was radicular pain. Pre-operative identification of PLL was assessed by MRI. All patients were operated upon by ACDF. We started dissection off the midline in patients with intact ligament while we used the site of disruption to start and complete dissection in patients with interrupted ligament. Follow-up was done monthly.
Ninety-seven percent of patients underwent single level surgery. The most commonly operated level was C5-6. PLL was interrupted in 60.7% of patients. There was a statistically significant difference between median VAS in immediate, early, and late post-operative period. Bleeding was encountered in 46% of patients. Saline irrigation was a suitable method for hemostasis.
Conventional MRI is the modality of choice for pre-operative identification of PLL. It is better to use the site of ligament interruption to start sharp dissection and to start lateral to the midline in intact ligament. Sharp dissection is better with curved knife. Thin foot plate Kerrison is suitable for excision of the remaining parts. Hemostasis using saline irrigation is better and non-risky than using bipolar coagulation.
KeywordsPosterior longitudinal ligament dissection Safety measures
Magnetic resonance imaging
Posterior longitudinal ligament
Visual analog scale
Cervical disk herniation results from a tear in the posterior annulus and the posterior longitudinal ligament (PLL). Consequently, there is a sequestrated disk fragment inside the spinal canal causing cord and/or root compression .
During microscopic anterior cervical discectomy with fusion (ACDF), violation of the PLL aiming at dural exposure and subligamentous disk fragment removal is indispensable surgical step to ensure complete removal. The structural integrity of the PLL broadens at the level of the disk through incorporation with the posterior annulus onto its thick deep layer. It has also a thin superficial layer that is related to the dura matter [2, 3, 4]. The superficial and deep layers are separate laterally while adherent in the mid-line. Fibers are running as a band in the mid-line but are dispersed laterally [5, 6].
The extradural veins are anastomosed beneath the PLL. The contribution with the internal veins forms a confluence at the intervertebral foramen. The nerve roots, as they leave the intervertebral foramen, have accompanying veins that receive contribution ventral radicular veins, which pierce the dura [7, 8]. The venous plexus lies between the two layers of PLL [9, 10].
The advantage of PLL dissection requires not to overlook its intimate relation to the dural sac to avoid a troublesome unintended durotomy or bleeding. Safety considerations aim at risk-free surgery which are the core of this study.
Patients and methods
This is a retrospective clinical case series conducted on 74 males and 71 females (total=145) in the Department of Neurosurgery, Tanta University Hospitals. Those patients were operated upon for anterior cervical discectomy and fusion in the period between December, 2016, and February, 2019. The main symptoms were radicular pain (73.8%) (measured by visual analog scale), motor weakness (47.6%), radicular hypoesthesia (39.3%), myelopathic symptoms (29.7%), diminished reflexes (19.3%), and lastly, interscapular pain (6.2%) (Table 1). All patient’s data, diagnosis, and treatment outcomes are confidentially kept private and patients had specific codes. An informed consent for surgery was taken from all patients . An approval from the research ethics committee of the Faculty of Medicine, Tanta University [reference number 33038], was obtained on April, 2019. Furthermore, being a retrospective study, patients’ consents for participation and for publication were not applicable. Additionally, the co-authors had neither financial nor non-financial competing interest to report.
The patient was put in a supine position. In patients with myelopathic picture, we took the precaution of awake positioning to avoid direct cord compression at the time interval between the start of anesthesia and the proper surgical resection. A rounded roll was put between the patient scapulae in the mid-line. An intra-operative image was initially taken for localization of the desired level and the proper site of skin incision.
With communication with the anesthesiology team, considerations executed by avoidance of neck extension through insertion of the endotracheal tube via the fiberoptic techniques and use of a low-pressure cuff with inflation of air below the maximum volume that is labeled on the cuff, thus avoidance of the risk of compression on the recurrent laryngeal nerve. In addition, we also recommended insertion of the cuff below the level of the vocal cord .
A transverse skin crease incision was done followed by platysma muscle incision. Identification of the sternocleidomastoid muscle was done to work just medial to it. Blunt dissection of the investing layer of deep cervical fascia was done. Care was taken to keep the carotid sheath intact. The plane between the carotid sheath laterally and trachea and esophagus medially was gently dissected till reaching the anterior aspect of the cervical spine.
Identification of the planned level was done by intraoperative imaging. The operating microscope was finally introduced. Under magnification, the longus colli muscles were separated using bipolar cauterization. Following resection of the anterior annulus and central disk material and using the back of micro-tumor knife, a peculiar resection of the cartilaginous end plates above and below created an additional space and obviated the need to marked Caspar distraction which switches the strands of PLL, bringing it more intimate to dura. The magnification power was increased at this step to identify the posterior annulus and the PLL.
Great cautions were taken near and beneath the uncovertebral joint where the exit of the root and the surrounding veins. When there was venous bleeding, irrigation with saline under gentle pressure was done. In spite of spending some time, it was a successful maneuver to stop that bleeding .
Post-operative care and follow-up
Analysis was done using IBM SPSS® statistics for windows.
Characteristics of the studied patients who underwent anterior cervical discectomy and fusion (n = 145)
Mean ± SD
44 ± 10
Preoperative motor grade
Operative details, complications, and degree of pain and motor grade (n = 145)
All patients (145)
Timing till surgery (days)
< 24 h–36
Level of surgery
PLL in MRI
location of disk fragments
No subligamentous fragment
Subligamentous central and lateral
Bleeding from vascular cuff around root
Postoperative VAS (early)
Postoperative VAS (late)
Postoperative motor grade
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.  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  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.  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.  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.  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.  and Terry and Michael  recommended routine removal of PLL, so as to be sure that no residual disk material is left behind. On the other hand, Cloward  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  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.  had an opinion that recommends partial removal to protect the dura unless the disk fragment is large. Scott et al.  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.  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.  supported this maneuver. Moreover, Ohyama et al.  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  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  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  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.  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.  reported one patient with CSF leak. Gabriele et al.  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.  had similar results. Lin et al.  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.  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.  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.  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.
Conventional MRI is the modality of choice for pre-operative identification of PLL. It is better to use the site of ligament interruption to start sharp dissection and to start lateral to the midline in intact ligament. Right angled blunt microhook is suitable to separate the longitudinal strands of the PLL using high magnification then to start sharp dissection using curved knife. Both 1- and 2-mm thin foot plate Kerrison is suitable for excision of the remaining parts without traction. Routine removal is the optimum for adequacy of disk removal and improvement of pre-operative symptoms. Hemostasis using saline irrigation is better and non-risky than using bipolar coagulation.
The authors sincerely thank El-Mahalawy M and all of the department members of Neurosurgery, Tanta University Hospital, for their help in doing this work.
Both authors equally participated in operating patients, data collection, data analysis, and scientific writing. Both authors read and approved the final manuscript.
There was no funding for this study.
Ethics approval and consent to participate
Approved from the research ethics committee of Faculty of Medicine at Tanta University [reference number 33038 obtained in April 2019]. Consent for participation was not applicable as this is a retrospective study, so the ethics committee waived the consent to participate.
Consent for publication
The authors declare that they have no competing interests.
- 1.Terry JC, Michael GF. Surgical management of cervical disc disease and spondylosis. In: Tindall GT, Cooper P, Barrow DL, editors. The Practice of Neurosurgery; Vol. 1, Chapt 158; 1997. p. 2409–22.Google Scholar
- 2.Wardak Z, Lavelle ED, Lavelle WF. Functional anatomy of the spine. In: Steinmetz MP, Benzel EC, editors. Benzel’s spine surgery: techniques, complication avoidance, and management, vol. chap. 5: Elsevier; 2017. p. 43.Google Scholar
- 3.Aebi M, Arlet V and Weeb JK: AOSPINE Manual Clinical Applications 2007; Vol. 2, chap 7: 545Google Scholar
- 4.Nelson Moussazadeh and Kai-Ming Gregory Fu: Spinal anatomy, in Youmans and Wenn neurological surgery, 2017: Part I, 273, 3916Google Scholar
- 6.Wiltse LL, Fonseca AS, Amster J, Dimartino P, Ravessoud FA. Relationship of the dura, Hofmann’s ligaments, Batson’s plexus, and a fibrovascular membrane lying on the posterior surface of the vertebral bodies and attaching to the deep layer of the posterior longitudinal ligament. An anatomical, radiologic, and clinical study. Spine. 1993;18(8):1030–43.CrossRefGoogle Scholar
- 7.Parke WW, Bono CM, and Garfn SR: Applied anatomy of the spine in Rothman-Simeone (ed): the spine, ed.6, Elsevier Saunders, chapter, 2, section 1, p:15-53, 2011Google Scholar
- 9.Williams KA, Jr, Rauschning W, Prasad S: Applied anatomy of the cervical spine In: Steinmetz MP and Benzel EC, editors. Benzel’s spine surgery: techniques, complication avoidance, and management. Elsevier 2017; chap. 8, p. 87Google Scholar
- 10.Girolami M, Ghermandi RM. Gasbarrini GA and Boriani S: Anatomy of the subaxial cervical spine in: Boriani S, et al, Editors. Atlas of craniocervical junction and cervical spine surgery © Springer International Publishing Switzerland 2017; chapter 6, P: 69Google Scholar
- 19.Heary RF, Karimi RJ, Jalan D and Benzel EC: Single- and multiple-level interbody fusion techniques. In: Steinmetz MP and Benzel EC, editors. Benzel’s Spine Surgery: Techniques, Complication Avoidance, and Management. Elsevier 2017; chap. 59, p. 519-531Google Scholar
- 22.Cloward R. Anterior cervical discectomy and fusion: the Cloward technique. In: Rengashary, Wilkins, editors. Neurosurgical Operative Atlas, vol. 2. 2nd ed. Chicago: The American Association of Neurological Surgeons; 1992. p. 229–40.Google Scholar
- 24.Charles H, Crawford K III, Riew D. Cervical discectomy. In: Steinmetz MP, Benzel EC, editors. Benzel’s spine surgery: techniques, complication avoidance, and management, vol. chap. 71: Elsevier; 2017. p. 608.Google Scholar
- 25.Meyer SA, Knightly JJ. Evaluation and treatment of cervical disk herniations. Youmans Wenn. 2017;283:4043.Google Scholar
- 28.Weinstein PR. Anterior cervical discectomy and fusion: Smith-Robinson technique. In: Rengashary, Wilkins, editors. Neurosurgical Operative Atlas, vol. 3. 2nd ed. Chicago: The American Association of Neurological Surgeons; 1993. p. 344–57.Google Scholar
- 33.Gabriele Molteni, Marco Giuseppe Greco and Pierre Guarino: Complications of cervical spine surgery in Boriani S, et al, (Editors) Atlas of Craniocervical Junction and Cervical Spine Surgery © Springer International Publishing Switzerland 2017, chapter, 2; PP: 19-24Google Scholar
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.