Extra Foraminal Approach

Tarek P. Sunna’

Daniel Shedid

Fahed Zairi

Extraforaminal lumbar disk herniations represent 7% to 12% of all lumbar disk herniations.¹ Historically the pathology was first described in a cadaveric study in 1944 by Lindblom, then Macnab in 1971 published the first two case reports of L5 nerve compression in an extraforaminal herniation at L5-S1, Abdullah et al. in 1974 described the extreme lateral syndrome for the first time (Fig. 25.1).

Extraforaminal lumbar disk herniation more commonly occurs in the upper lumbar spine² and in patients between 50 and 60 years of age.², ³, ⁴, ⁵ It often presents with anterior thigh and groin pain,²,⁶, ⁷, ⁸ quadriceps weakness, and may be accompanied by a positive femoral stretch test.⁹,¹⁰ Curiously, there is often little back pain¹¹ and the Lasègue’s sign is usually negative.²,¹²,¹³

Over the years, the surgical approach has changed mainly because of two requirements: good exposure of both the foramen and the herniated disk and the necessity of preserving stability of the spinal column.

Currently two surgical approaches are commonly used for the treatment of this type of disk herniation: (1) a conventional approach via a midline laminotomy/fenestration, or one of its modifications, and (2) a paramedian (extraforaminal) approach. Removal of a truly extraforaminal herniated disk via the midline approach necessitates sacrificing a significant portion, if not all, of the facet joint, which can lead to subsequent instability. The paramedian approach, which is performed at the level of the facet joint, provides a more direct route to this lesion.

The paraspinal or paramedian approach to the lumbar spine was first described by Watkins in 1959.² The surgical plane is developed between the lateral border of the sacrospinalis muscles and the quadratus lumborum muscle. Wiltse described a modified trans-muscular paraspinal approach³,⁴ consisting of a longitudinal separation of the sacrospinalis muscle between its multifidus and longissimus parts. The original description of this approach was for spinal fusion, for spondylolisthesis treatment.¹⁴ Through this approach, a one-level or a multilevel fusion can be performed, leaving the supraspinous and interspinous ligaments intact. However now it is more commonly used for removing a far lateral disk herniation which will be discussed in this chapter.

MINIMALLY INVASIVE EXTRA FORAMINAL APPROACH FOR EXTRA-FORMAINAL LUMBAR DISK HERNIATIONS

Far lateral disk herniations are predominantly encountered at L3-L4 and L4-L5 levels followed by L5-S1.¹,¹⁵,¹⁶ Cephalad involvement of L1-L2 or L2-L3 is reportedly rare; however,

An et al.³ noted a higher incidence of 28% at those levels. The anatomy of the lumbosacral junction presents unique challenges. Reulen et al.¹⁷ described the bony anatomy bordering the intertransverse operative corridor, which narrows caudally in the lumbar spine. This is due to a wider pars interarticularis at L5, a shorter distance from the caudal transverse process to the superior edge of the inferior articulating process, and a higher frequency of a prominent accessory process.¹⁷,¹⁸ Sometimes the access can be difficult at this level due to compression of the L5 nerve root by the sacral ala.¹⁸, ¹⁹, ²⁰ Depending on the anatomic constraints in the individual patient, it is sometimes necessary to drill the superior aspect of the sacral ala to create a functional working space.²¹ Pirris et al.²¹ presented a small series of four patients and concluded that for complex extraforaminal disk herniations at the lumbosacral junction a viable surgical option is to perform the nerve root decompression and diskectomy via a minimally invasive, muscle-splitting approach using a tubular retractor and operating microscope.

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