Intervertebral disc space narrowing occurs as the disc degenerates and loses hydration. The change in segment height can cause subluxation of the facet joints, resulting in abnormal stresses on the joint and nerve root impingement. Other sequelae, such as capsular irritation and local inflammation, may result in reflex spasm of the erector spinae muscles. As degeneration proceeds, abnormal motion leads to osteophyte production, further exacerbating the symptoms [16]. That the facet joint is a source of nociception has yet to be universally accepted. Opponents submit that local anesthetic blockade of the facet joint with subsequent pain relief lacks validity. This position is supported by observations of contrast injection spilling over into the epidural space or intervertebral foramen [7]. Pain elicited with hypertonic saline or relief with local anesthetic administration may be due to action on neural structures or on other pain-sensitive tissues. Proponents for the facet joint as a site of nociception point to the presence of substance P in facet capsule neurons [17]. In addition, most of the mechanosensitive somatosensory units in the facet joint are group-III high-threshold, slow-conduction units, which are thought to mediate nociception [18–20]. Chronic inflammation may lead to fluid accumulation and distension, stimulating the richly innervated synovial villi inside the capsule, resulting in pain.

Lumbar facet arthropathy is characterized by low back pain, unilateral or bilateral, with or without radiation. The pain is described usually as a deep, dull ache; is difficult to localize; and frequently is referred into the buttock, groin, hip, or posterior thigh to the knee. Fukui et al. described referral patterns for thoracic facet joints [21].

Some patients describe a sudden onset of pain, usually associated with twisting or bending. There is no exacerbation of the pain with Valsalva maneuver. In contrast to discogenic pain, sitting does not severely aggravate pain secondary to facet arthropathy. The cervical facet joints also cause pain described as deep and aching. Referral patterns vary, depending on which level is of concern. The C1–C2 facet joint may refer pain to the occipital and postauricular region [22]. The C2–C3 facet joint may cause pain referred to the occiput, ear, vertex, forehead, or eye [23, 24]. The C3–C4 facet joint refers pain over the posterolateral cervical region, following the course of the levator scapulae. The lower cervical facet joints refer pain to the base of the neck and down to the scapulae (Fig. 17.3) [23]. Physical examination often reveals tenderness over the facet joints and involves associated muscle spasm. The pain is exacerbated by extension or lateral bending as opposed to flexion as well as prolonged sitting. A few patients may exhibit mechanical hyperalgesia over the associated innervated skin. Whereas range of motion in all directions may be reduced, extension and rotation are most uncomfortable. Straight leg raise is usually negative. To make the diagnosis of a painful facet joint requires the typical history and physical findings already described in combination with diagnostic blocks. The use of facet block for diagnosis is hampered by certain pitfalls. There is a lack of a corresponding cutaneous innervation to the facet joint and thus an inability to determine when complete blockade has occurred. Injection into the joint often results in joint capsule rupture and spillage of local anesthetic into the epidural space or intervertebral foramen, which can interrupt nociceptive impulses from alternative sites [20, 25–27]. The medial branch nerve innervates muscles, ligaments, and periosteum in addition to the facet joints, again limiting specificity of the test. Facet blocks should be avoided in patients with systemic infection, infection at the site, or coagulopathies or in patients who refuse the procedure. Needle placement for facet injection as well as local anesthetic delivery can result in pain provocation. A provocative response that is concordant with the patient’s ongoing complaints lends further support to the notion that the facet joint is the pain generator. Facet injections are commonly used for both therapeutic and diagnostic interventions. Intra-articular steroid injection often produces significant pain relief that outlasts the action of a local anesthetic [26, 28–30]. Although therapeutic benefit from steroid has been demonstrated, duration of outcomes is limited, similar to intra-articular steroids delivered to other joints [31–33]. Intra-articular block also does not correlate well with the success of radiofrequency denervation (only 64 %); therefore, medial branch block is the preferred procedure as a trial prior to facet denervation [34].