Medial Branches and L5 Dorsal Ramus

Fig. 14.1

Dual neural supply of the facet joint. Oblique parasagittal view of overlapping segmental innervation of the facet joint. (1) Ventral branch of spinal nerve, (2) dorsal branch of spinal nerve, (3) ascendant branch of dorsal ramus, (4) medial branch of dorsal ramus, (5) distal branch of medial ramus to facet joint, (6) proximal branch of medial ramus to facet joint, (7) posterior ramus (sinuvertebral nerve of Luschka), (8) facet joint. (Reproduced with permission from Dr. Danilo Jankovic)

From there, they run beneath the mamilloaccessory ligament before they innervate the multifidus muscle, interspinous ligament, and the periosteum of the neural arch.

The L5 dorsal ramus differs from the other lumbar dorsal rami, in that it itself runs along the junction of the sacral ala and superior articular process of the sacrum and gives off the medial branch only as it reaches the caudal aspect of the L5–S1 zygapophyseal joint. Therefore, the target for injection or ablation at this level is the dorsal rami.

Patient Selection

No clinical or radiological test is specific enough to enable reliable diagnosis of low back pain of facetogenic in origin. Diagnosis of facetogenic pain can only be established by pain reduction and mobility improvement after the local anesthetic blocks.

Pain of facetogenic origin typically presents as unilateral or bilateral back pain with or without nondermatomal leg pain above the knee. Hyperextension and lumbar rotation are often painful in those individuals as well as local paraspinal tender points upon pressure. Motor function and reflexes are usually preserved and straight leg raise test is negative. Referred pain patterns from the upper lumbar joints can extend into the flank, hip, and upper lateral thighs. Groin pain can also be caused by L3–S1 facet joints. In very rare cases, pain from the lower lumbar joints may also extend into the lower lateral leg and even to the foot. The facet joint L5/S1 is the single one most commonly affected. After lumbar stabilization operations, facet joints of the adjacent segments can often be pain generators.

Ultrasound Scanning

Position: Prone;
Probe: Curvilinear 2–6 MHz

Five Basic Views

To understand the sonoanatomy of the lumbar spine, one can start with the five basic views of spine sonogram described by Chin, Karmakar, and Peng.

../images/457420_1_En_14_Chapter/457420_1_En_14_Fig2_HTML.jpg — Fig. 14.2

Paramedial sagittal transverse process view. (Reprinted with permission from Philip Peng Educational Series)

Paramedian Sagittal Transverse Process View

This is a sagittal view but not in the midline (median) but paramedian plane (Fig. 14.2). The transducer is placed 3–5 cm away from the midline. Two to three hyperechoic bone shadows of transverse process (TP) are seen deep to the erector spinae muscle (ESM) with open windows to reveal psoas muscles (PM) deep to TP. Deep to the psoas muscle, the peritoneum (P-indicated by arrows) can be seen.

../images/457420_1_En_14_Chapter/457420_1_En_14_Fig3_HTML.jpg — Fig. 14.3

Paramedian sagittal articular process view. (Reprinted with permission from Philip Peng Educational Series)

Paramedian Sagittal Articular Process View

Moving the transducer medially 1–2 cm reveals an image with continuous hyperechoic bone shadow (no gap) from the articular process (AP) (Fig. 14.3).

../images/457420_1_En_14_Chapter/457420_1_En_14_Fig4_HTML.jpg — Fig. 14.4

Paramedian sagittal oblique view. (Reprinted with permission from Philip Peng Educational Series)

Paramedian Sagittal Oblique View

Maintaining the transducer in the same position as Fig. 14.3 but tilting it medially will yield a view that reveals the interlaminar window (Fig. 14.4). Through this window, the intrathecal space (ITS) can be seen between the laminae (L). The ligamentum flavum (∗) is usually not clearly seen due to the orientation of the structure relative to the transducer but the posterior dura (PD) can be usually seen clearly in young patient. The other side of the ITS reveals a dense hyperechoic shadow from the posterior cortex of the vertebra, posterior longitudinal ligament, and anterior dura. Since the three structures cannot be differentiated in ultrasound, they are termed anterior complex.

../images/457420_1_En_14_Chapter/457420_1_En_14_Fig5_HTML.jpg — Fig. 14.5

Transverse spinous process view. ESM-erector spinae muscle. (Reprinted with permission from Philip Peng Educational Series)

Transverse Spinous Process View

By placing the transducer behind the spinous process (SP), the structures deep in the spine will not be seen (Fig. 14.5).

../images/457420_1_En_14_Chapter/457420_1_En_14_Fig6_HTML.jpg — Fig. 14.6

Transverse interlaminar view. (Reprinted with permission from Philip Peng Educational Series)

Transverse Interlaminar View

This is the most useful view (Fig. 14.6). The transducer is placed behind the interspinous ligament (ISL) which allows a window to reveal the intrathecal space (ITS). Typically, inferior articular process (IAP) is closer to the midline than the superior articular process (SAP), the hyperechoic shadow of which is seen continuous to the transverse process laterally (right side of Fig. 14.6). Practitioner should be careful in discerning the difference between TP and intertransverse ligament (line arrows) which is the ligament joining the transverse process dorsal to the psoas muscle.