Introduction
The high prevalence of low back pain has made it a common cause of outpatient and inpatient healthcare visits. Lumbar facet joint pain is a common challenge presented to the interventional pain physician, with prevalence as high as 50% in systematic reviews. ,
Treatment includes pharmacological, physical therapy, psychiatric, weight loss, and lumbar medial branch nerve interventions. Intervention for lumbar facet pain represents the second most common procedure done by the interventional pain physician.
Understanding the anatomy of the lumbar medial branches is critical for interventional management of lumbar facet pain. Facet pain can be managed interventionally with either a block at the facet joint or, now more commonly, a therapeutic and diagnostic medial branch nerve block with local anesthetic with corticosteroids. After successful diagnostic medial branch blocks, with short-term pain relief and functional improvement, a subsequent radiofrequency ablation can be performed.
Facet pain is the result of degenerative changes as a result of aging, but can be related to work or sports injuries, trauma, and mass compression by tumors or other lesions. The lumbar region is of particular significance, as it consists of the most commonly affected facet joints resulting in pain.
Anatomy
The lumbar medial branch nerve is a major target of blockade for treatment of low back pain caused by the facet joints.
The dorsal ramus of a specific spinal-level branches off to the lateral and medial branches and sits on the superior border of the transverse process. The lumbar medial branch continues to the lateral border of the superior articular process and enters a fibro-osseous canal between the dorsal aspect of the superior articular process and the base of the transverse process, the bony groove. The bony groove runs in an oblique direction and is formed by the mammillary process and the accessory process. It continues on the lamina where it divides to innervate the joint, along with innervating the multifidus muscle and interspinous ligament and muscle. The medial branches run on the deep aspect of the multifidus muscle ( Fig. 7.1 ), which provides spinal stability. ,
The L5 dorsal ramus itself is amenable to ablation. The L5 dorsal ramus is unique because it runs on the sulcus of the groove formed by the S1 superior articular process and the sacral ala. This then forms the medial and lateral branches. The medial branch runs medially and goes around the lateral aspect of the lumbosacral facet joint.
The lumbar facet joint is a synovial joint that receives innervation from the medial branch of the dorsal rami from the spinal segment above and below, and thus blocking the medial branches at the level above the facet would be most beneficial. ,
The anatomical landmarks used to target the medial branch nerves via an RFA cannula would be ideal through fluoroscopy. Use of fluoroscopy allows the pain physician the opportunity to identify the superior articular process in an oblique angulation and to target the RFA cannula in the groove between the superior articular process and the transverse process.
Diagnosis
Facet joint pain can be difficult to diagnose, and treatment and management are not always clear. Diagnosis is dependent on a history and a physical exam, imaging, and use of a diagnostic or prognostic block. There has been considerable difficulty finding a consensus for understanding which patient characteristics would benefit from intervention at the lumbar medial branches. While stringent criteria improve overall outcomes for denervation, it comes at the expense of more false negatives.
Facet pain can present in a variety of different ways. Pain is generally associated in the back and not predominantly midline and/or in the buttocks, leg, and groin. Pain that radiates below the knee is associated with a negative response to intervention at the facet joints. The nature of the back pain that was associated with positive outcomes (defined as relief lasting >6 months after intervention) includes radiation to the groin, exacerbation with extension rotation, and paraspinal tenderness that is well localized. Pain that is radicular in nature may be more associated with negative outcomes to medial branch blockade. ,
Physical exam findings suggestive of relief from intervention include pain reproduced by lumbar hyperextension with absence of pain from forward flexion, rising from forward flexion, or extension rotation. Paraspinal tenderness showed a sensitivity of 95%, and well-localized paraspinal tenderness is correlated to positive relief from facet blockade.
A straight leg test manifesting as back pain would suggest relief from facet blockade, while a test manifesting as leg pain would not. Facet loading, or pain worsened by extension-rotation, was more prevalent in patients who had relief with RFA. Chronic opioid use was associated with a poor outcome with RFA. ,
Imaging can be a useful tool to determine low back pain pathology but as a diagnostic tool should be used with caution. MRI is a common modality to identify lesions correlating with low back pain including facet joint pathology, although there is overall no evidence suggesting positive correlation between MRI findings and positive outcomes from RFA. ,
Single photon emission computed tomography (SPECT) is a nuclear medicine imaging technique with considerable radiation and gamma-emitting radioisotopes to produce a three-dimensional image. Computed tomography (CT) scans similarly create a three-dimensional image with considerable radiation. Both SPECT and CT findings were found to have no significant association with response to facet joint injections.
A positive medial branch block (MBB) is defined as greater than 50% pain reduction with the duration of the local anesthetic administered. A diagnostic and prognostic MBB is often used by a provider to possibly isolate the specific anatomical structures that are the source of pain. Limitations to this include the potential for false-positive and false-negative relief, as the intended target of the medial branches must have been blocked. Pain on injection or capsule distention can manifest as back pain not relieved from medial branch blockade. Intraarticular facet joint injection can be considered as a diagnostic and prognostic tool but is limited by its high rate of failure.
The use of sedation before diagnostic facet blocks is subject to substantial debate. This controversy is based on the question of whether sedation and/or providing analgesic medication will alter the patient’s “true” response to the intervention. If sedation needs to be performed to decrease procedure-related discomfort or anxiety, the physician should give the lowest dose of short-acting sedation, ideally without opioids.
The MBB should be considered as a prognostic tool but is of course associated with denervation of the medial branch block, resulting in blockade of the innervation of the multifidus muscle, interspinal muscle, and ligament and periosteum of the neural arch. A younger patient could thus have an impact on their daily activities due to muscle atrophy, and this should be considered prior to RFA.
There is no single pathognomonic test result or exam finding that would suggest a patient would benefit from intervention at the facet joint or the lumbar medial branches. Instead, the clinician should look at the overall picture and understand the limitations of each diagnostic tool to determine if a patient would have success from RFA of the lumbar medial branches.
Diagnostic lumbar medial branch block (MBB) technique
Positioning
The patient is placed in a prone position, with the head turned to one side. A pillow can be placed under the lower abdomen in order to tilt the pelvis backward and swing the iliac crests posteriorly away from the lumbosacral junction ( Fig. 7.2 ).
