15 Extraforaminal Surgical Approach

Since the first description of extraforaminal disk herniations (EFDHs) in the lumbar spine by Abdullah et al1 in 1974, it is only recently that these herniations have been given their due importance in the diagnosis and treatment of sciatica of lumbar disk origin. One of the main reasons for this discrepancy has been the lack of better imaging tools in the past to diagnose these extracanalicular herniations as the myelographic contrast failed to reach the lateral areas.²

With wider availability of modern imaging methods such as high-resolution computed tomography (CT) and magnetic resonance imaging (MRI), the frequency of diagnosis for EFDH is on the rise. Despite this increased awareness about its existence, the optimal treatment for this disease entity is still a matter of contention. Conventional posterior laminectomy may not provide good access to a herniation that lies laterally to the lateral margin of the pedicle. Some reports have also mentioned extended facetectomy (partial or complete) or even complete resection of the pars to remove these EFDHs.^3–7 Facetectomy affects the stability of the motion segment sooner or later, ultimately leading to increased morbidity and late complications such as recurrent back pain due to instability and spondylolisthesis.²

The introduction of the paraspinal muscle splitting approach to treat such extraforaminal herniations has definitely changed the outcome for the better. The reported success rate for EFDH has been cited as 71 to 88% using the various paraspinal approaches.^2–4

The approach-related morbidity is also reduced with the reduced amount of facet resection and muscle elevation. However, some bone resection and muscle retraction as well as some handling of the exiting nerve root and its dorsal root ganglion (DRG) is still needed to perform adequate decompression. Handling of the exiting nerve root and its DRG may be the source of irritating dysesthesia, reflex sympathetic dystrophy, and chronic back pain in some patients, thus adding to approach-related morbidity.² Because EFDH usually occurs in older patients, the risk of general anesthesia when performing microscopic diskectomy in such patients cannot be overemphasized.

In the evolution of spine surgery, the endeavor has always been to develop surgical techniques that would provide the maximum benefit with minimal damage to the surrounding neural and musculoskeletal structures. Employment of an endoscopic technique through a percutaneous approach, especially to treat such EFDH patients, can further cut down on the surgical morbidity while achieving similar or better outcomes. The recent development in optics and allied tools like laser and flexible radiofrequency probes has further made it possible to use percutaneous techniques for the treatment of spinal disorders.^8–10 Yeung and Tsou have reported favorable outcomes by applying transforaminal endoscopic diskectomy to a mixed group of 307 patients, of whom 30 were extraforaminal/foraminal disk herniations.⁹ Similarly, Lew et al also reported their technique and results for foraminal/extraforaminal disk herniations with a transforaminal endoscopic technique.¹⁰

In our practices a different technique is recommended that we refer to as extraforaminal targeted fragment-ectomy. With this technique, the target point for needle insertion is identified first from preoperative images, and the needle track and starting point are determined according to the location of the hernia mass. The skin entry point is relatively medial, and the approach angle is also relatively steep in our technique as compared with the earlier described techniques. This gives a wider safety margin and makes the procedure less painful and better tolerated by the patients. We refer to this procedure as an extraforaminal targeted fragmentectomy technique because the main focus is the removal of the herniated disk fragment lying in the extraforaminal territory first, with little, if any, removal of the intradiskal contents. This extraforaminal technique has certain safeguards to prevent the catastrophe of extraforaminal nerve root (ENR) injury:

• The skin entry point is kept more medial.

• The needle angle is relatively steep.

• The needle target point is identified as the midpedicular line near the superior end plate of the caudal vertebra.

In this way, we can easily avoid even the posteriorly displaced ENR. This technique increases simplicity and expands the safety margin and can be easily adopted by a wider group of the spine surgeons who would otherwise be interested in this approach but are reluctant to adopt it for fear of injuring the ENR.

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