Endoscopic Contralateral Transaxillary Discectomy for Recurrent Disc Herniation
Article information
Abstract
This video aims to describe an endoscopic surgical approach for accessing difficult to reach pathology such as disc herniations after previous surgery. The relatively small size of endoscopic instruments facilitates significant freedom of movement inside the spinal canal. The authors have experience with interlaminar approaches for contralateral pathology such as disc herniations, recurrent disc herniations, spinal stenosis, and facet cysts. The advantages of starting from the opposite side of the canal in a revision situation include the ability to establish a clear plane between the dura and the borders of the canal and visualize the disc from a different angle than the index operation. Contralateral approaches to residual or recurrent herniations can be performed with an “over the top” technique, navigating dorsal to the thecal sac to reach the far side of the canal. In the associated video we demonstrate a novel technique, a contralateral transaxillary endoscopic approach to a recurrent disc herniation at the L5–S1 level in a young male collegiate wrestler. In our experience, we have found this particular approach to be useful in patients with an early take off of the S1 nerve root which creates a large axillary window. In several instances this technique has allowed us to inspect the area of the reherniation from both the axilla and over the top of the thecal sac. This particular patient has a large recurrence 2 years after an open microscopic hemilaminotomy and discectomy. In this instance, an approach was chosen that navigates dorsal to the S1 nerve root and ventral to the thecal sac, starting on the opposite side of the spinal canal from the herniation. This approach is described as a contralateral interlaminar transaxillary discectomy.
INTRODUCTION
Endoscopic spine surgery for herniated nucleus pulposus is an established surgical technique, using both transforaminal and interlaminar approaches [1,2]. Recurrent disc herniations are common after both open and endoscopic approaches [3,4]. An endoscopic approach in the context of a previous microscopic decompression via an ipsilateral interlaminar approach is possible, but adhesions and scar tissue make the approach difficult and there are risks of dural injury, difficulty mobilizing the nerve root, and difficulty visualizing and removing the sequestration.
There is the possibility of approaching the disc herniation by starting on the contralateral side of the spinal canal. This allows the surgeon to establish a position inside the spinal canal starting in a tissue plane that is free of adhesions. From there, the disc herniation can be approached by navigating over the top of the thecal sac, requiring a careful release of the previous scar and an often difficult mobilization of the affected nerve root. There is also the possibility of a transaxillary approach in certain situations, exploiting the plane between the ventral surface of the dura and the dorsal surface of the annulus (Fig. 1A and B). This approach requires an early take off of the S1 nerve root which creates a relatively large axillary window. While it is possible to identify patients in advance who have morphometric features that make this approach anatomically possible (Fig. 2A and B), we have found that this potential trajectory is best assessed once the surgeon is inside the spinal canal. In this case, the cannula was navigated dorsal to the S1 nerve root and ventral to the thecal sac, through the axillary window, in order to reach the area of the reherniation on the opposite side (Fig. 3). This approach is relatively direct and is free of any scar tissue or adhesions from previous surgery and leads directly to the site of the herniation.
Preoperative magnetic resonance imaging scan demonstrating the sagittal view of a large recurrent disc herniation at L5–S1 (A) and approach path illustrated with a yellow curved arrow on the axillary image (B).
Midsagittal magnetic resonance imaging scan (A) and most proximal axial image (B) where the budding of the S1 nerve root from the thecal sac can be seen is located 1.6-cm cranial to the center of the L5–S1 disc. Axial image at the level of the intended resection (C) demonstrates the canal to be ellipsoid as opposed to triangular, 26 mm in diameter, with coronally oriented facets, and 3.8 mm of separation between the S1 nerve root and the thecal sac (D).
The axillary window as seen from the left side of the canal prior to approaching the recurrent disc herniation in the right lateral recess.
CASE REPORT
In this case, we present a 23-year-old male patient, former competitive collegiate wrestler, who underwent an open hemilaminotomy and discectomy 2 years prior to the endoscopic operation. He experienced recurrent symptoms relatively soon after the index microscopic operation but chose to live with his symptoms of radicular pain in the right S1 distribution rather than undergo a revision microscopic procedure. His stated reasons for choosing nonoperative care after the recurrence of symptoms was that the recovery of truncal strength and flexibility after the first operation was more difficult than anticipated and he struggled to return to sport. Eventually, however, he found his symptoms of numbness, tingling, and pain in the S1 distribution intolerable, especially with sitting, and he sought surgical relief. A magnetic resonance imaging (MRI) scan obtained shortly before the endoscopic operation reveals a recurrence of the herniated nucleus pulpous with compression of the right S1 nerve root in the lateral recess root and distortion of the normal tissue planes dorsal and lateral to the root consistent with the previous microscopic hemilaminotomy.
The axial images of this MRI scan also reveal an early take off of the S1 nerve root with budding of the root and an S1 nerve root sheath separating from the thecal sac approximately 1.6 cm proximal to the center of the L5–S1 disc. At the axial level of the herniation, the S1 nerve root is separated from the thecal sac by a distance of 3.8 mm. The mid canal width from facet to facet at the level of the intended resection measured 26 mm and the facets are relatively coronally oriented.
The patient was operated upon in an ambulatory surgery center using general anesthesia in the prone position without neurological monitoring. A standard interlaminar approach with a 7-mm Arthrex central channel endoscope was made, starting on the left side. The incision was made slightly more lateral and caudal than for an ipsilateral posterolateral or lateral recess herniation in order achieve the desired trajectory. The ligamentum flavum was identified and opened to the medial wall of the facet complex. Entering the canal, the traversing S1 nerve root was identified and the epidural fat in the axilla was gently removed. The axillary window between S1 and the thecal sac was identified and the cannula was gently advanced into this interval until the fragment could be visualized. The fragment was removed without difficulty. The patient was discharged home on the same day and made an uneventful recovery with resolution of his S1 symptoms. A postoperative scan obtained 6 weeks after this operation demonstrated resection of the fragment and complete decompression of the S1 nerve root (Fig. 4A and B).
A postoperative scan obtained 6 weeks after the revision endoscopic operation with a parasagittal image aligned with the previously seen herniation (A) and axial image at L5–S1 (B) demonstrating decompression of the S1 nerve root.
Written informed consent was obtained from the patient to share the images of the preoperative MRI scan and the intraoperative video.
DISCUSSION
Interlaminar approaches for contralateral pathology are useful techniques in the endoscopic armamentarium. Once the surgeon has navigated through the ligamentum flavum and established a tissue plane between the dura and surrounding spi-nal canal, hydrodissection with the endoscopic irrigant helps develop the planes between the dura and the surrounding anatomic structures. Navigating over the top of the thecal sac and then through the previous surgical plane requires sharp release of the adhesions which carries risk of dural and neural injury. There is also another approach to a recurrent disc herniation from the opposite side, one that is free from adhesions and scar and offers a unique angle on the area of recurrence. In situations where there is favorable anatomy consisting of an early take off of the S1 nerve root and a relatively large axillary window, it is also possible to approach the recurrence via this trajectory. We have found this approach to be useful in a number of cases.
Retrospective analysis of cases where we have utilized this approach demonstrate several morphological features of the canal, thecal sac, and S1 nerve root that are associated with successfully navigating through the axillary window. (1) The S1 nerve root buds from thecal sac and is visibly separate at least 1 cm cranial to the disc space. (2) There is at least 2–3 mm of lateral separation between the root and the thecal sac at the axial level of intended resection. (3) The mid canal width is greater than 24 mm and has an ellipsoid rather than triangular cross section. (4) The facets are coronally oriented and not enlarged by arthropathy. When these features are present, the approach is straight forward.
We acknowledge that there are risks of stretch injury to the central cauda equina and S1 nerve root with this approach. So far, we have not encountered any postoperative neurological deficits, but more study is needed to evaluate the relative safety of this approach and the key anatomic variants that make it possible. The contralateral transaxillary approach in this case is narrated in the accompanying video for a recurrent disc herniation. There are pros and cons to this approach as detailed in Table 1.
Advantages and disadvantages of an ipsilateral versus contralateral approach
Contralateral approaches have been successfully used for caudally migrated disc fragments using a transforaminal technique [5], for foraminal stenosis with O-arm assistance [6], for facet cysts using a biportal technique [7], for foraminal and lateral recess stenosis [8], and using a biportal technique for asymmetric stenosis [9]. To our knowledge, there are no reports of navigating to the contralateral aspect of the spinal canal via the transaxillary approach as described here. This technique is commonly used for central or axillary herniations on the same side as the initial approach. With a 7-mm diameter endoscope, it is also possible to reach the subarticular zone on the opposite side since there are marginal benefits of the relatively small endoscopic cannulas and instruments that increase the utility of this approach. We have had experience with approaching recurrent disc herniations on the contralateral side of the canal by navigating both ventral to the ipsilateral traversing root and via the axilla. In patients with an early take off of the S1 nerve root and a large axillary window, the transaxillary approach offers a direct route to the site of residual or recurrent herniation with minimal displacement of the ipsilateral S1 traversing root and thecal sac. Anatomic and radiographic studies have demonstrated significant variation in the distance from the L5–S1 disc at which the S1 nerve root buds from the thecal sac [10,11].
In our experience, we have observed several morphological features visible on the MRI scan that suggest a large axillary window that may permit access to the far side of the canal. These features include an early take off of the S1 nerve root (at least 1 cm proximal to the L5–S1 disc space), 2–3 mm of separation between the S1 root and the thecal sac at the L5–S1 level, a midcanal width of 24 mm with an ellipsoid rather than triangular cross section, and coronally oriented facets.
In the evolution of endoscopic spine surgery there is increasing awareness of novel surgical approaches that exploit the relatively small size of the endoscopic instruments and the 15°–30° angulation of the commonly used lenses. We present this case in order to increase awareness about the possibility of navigating further across the spinal canal using the axillary window in order to reach recurrent disc herniations on the opposite side of the canal. We urge caution in using this technique until there is more information on how much a 7-mm diameter cannula stretches or compresses the traversing nerve roots or thecal sac with inserted in this manner. We have not used this technique above the L5–S1 level. We suggest that neuromonitoring should be used if available and that this approach be reserved for what appear to be free fragment herniations in relatively large spinal canals (midcanal width greater than 24 mm). With the limited experience we have now, we do not recommend this technique in the context of congenital spinal stenosis, severe facet arthritis, or triangular spinal canal cross sections that demand steeper approach angles.
Video File
The video file for this article is available at https://doi.org/10.14245/ns.2449020.510.
Notes
Conflict of Interest
The authors have nothing to disclose.
Funding/Support
This study received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors.
Acknowledgments
We acknowledge the support of the Endospine Academy, Balgrist University Hospital, Zurich, Switzerland.
Author Contribution
Conceptualization: SG, JY, FVI, MF; Formal analysis: SG; Investigation: SG; Methodology: SG; Project administration: SG; Writing – original draft: SG, JY, FVI, JSK, MF; Writing – review & editing: SG, JY, FVI, JSK, MF.