Transforaminal approach to the epidural space has been utilized for several decades for proper placement of injectates at the site of inflammation. Initially called selective nerve root blocks, these injections are more recently called transforaminal injections. The main advantages include (1) ability to place the medication closer to the area of the pain generator and inflammation (the neuro-discal interface) and (2) the use of less medication to achieve similar or better results than an interlaminar approach.
Lumbar transforaminal injections are commonly performed at most pain practices, but recently the cervical transforaminal injections are now infrequently used to do an increase of the recognition of complications from these injections. This includes catastrophic outcomes secondary to intravascular (arterial) injections within the radicular arteries and intraneural injections leading to neuralgia and spinal cord injuries. This chapter will focus on the lumbar transforaminal approach.
Following are some of the specific indications for these injections:
The lumbar intervertebral foramen is the exit route for the spinal nerve roots at all the levels. The anatomic boundaries are:
Anteriorly by the body of the vertebra superiorly and the intervertebral disc inferiorly—lined by the posterior longitudinal ligament
Pedicle of the superior vertebra above and the pedicle of the inferior vertebra below
Lamina and the inferior articular process of the superior vertebra posteriorly
Lamina and the superior articular process of the inferior vertebra—lined by the ligamentum flavum (Figures 22-1, 2, and 22-3)
Spinal column. (Gray’s Anatomy.)
Sagittal section of the lumbar spine. (Gray’s Anatomy.)
Coronal section of the lumbar spine. (Gray’s Anatomy.)
The contents of the lumbar spinal intervertebral foramen include:
The spinal nerve root and the dorsal root ganglion and the sinuvertebral nerve.
The radicular artery (segmental artery) (Figure 22-4). These arteries are not fixed in their position relative to the foramen. These arteries enter the spinal cord through the nerve. One of the largest arterial branches is called the arteria radicularis magna (Artery of Adamkiewicz), which enters the spinal canal anywhere from the T9 through L1 levels. It merges with the anterior spinal artery, usually at about T4-T6 level to supply the anterior position of the spinal cord. As it is an end-artery (without anastomoses), blockage of this artery can lead to paralysis.
Veins connecting the external and internal venous plexuses (Figure 22-5).
Ligaments and meninges.