Rule Out Facet Arthropathy Before Initiating Expensive and Invasive Maneuvers for Back and Spine Pain
Amit Sharma MD
Spinal pain is one of most common and most intricate problems faced by physicians today. Pain of just the lumbar back alone is believed to be the most common etiology of chronic pain syndrome. In addition to the significant personal morbidity, spine-related pain has an enormous economic impact on society—the total cost of low back pain exceeds $100 billion per year in the United States alone. About one third of the overall costs are direct health care expenditures due to overuse of unnecessary diagnostic modalities and therapeutic maneuvers with unproven benefits. The remaining two thirds of the cost are indirect, due to lost wages and reduced productivity. Given this scenario, it is important to formulate precise evidence-based diagnostic and therapeutic plans for patients with spinal pain.
Facet arthropathy has been implicated as the etiology in 67% of patients with chronic neck pain, 48% of patients with chronic thoracic pain, and as many as 40% of patients with chronic lumbar pain. Thus, the high prevalence of facet arthropathy makes it a leading differential cause of almost all spinal pain issues. The facet (or zygapophyseal) joints are true synovial joints connecting the adjacent vertebra posteriorly. They are formed by the inferior articular process of superior vertebra and the superior articular process of inferior vertebra. Two adjacent vertebral bodies thus have a pair of facet joints preventing axial movements of one vertebra over another. The articular surfaces of each facet joint are covered with cartilage, and its edges are covered with synovial membrane and fibrous capsule. Primary dorsal rami of spinal nerves exit from the neural foramen just above and medial to the facet joints and send off medial and lateral branches. This medial branch, in turn, supplies corresponding facet joint and paraspinous muscles. Each facet joint receives innervation from the medial branch of exiting nerve root of corresponding vertebral level and from the level above. Facet joints can develop degenerative changes under certain circumstances (trauma, osteoarthritis, inflammation of synovial capsule, or joint subluxation) and can become quite painful. This painful degeneration of facet joints is known as facet syndrome or arthropathy.
PRESENTATION
Cervical facet arthropathy pain presents as pain involving the head, neck, shoulder, suprascapular and scapular area, and upper arm. Distribution of pain varies, depending on the specific facet joint involved. For instance, involvement of the C2-3 joint leads to pain in the occipital area, C3-4 in the neck, and C4-5 along the lateral aspect of the nape of the neck and shoulder area. The associated physical findings may include decreased range of movements at the neck, exacerbation of pain with neck extension, and some degree of alleviation with flexion. Palpation over the specific facet joint may also aggravate pain. Thoracic facet arthropathy presents mainly as thoracic pain along with paraspinous tenderness. The presentation of lumbar facet arthropathy is often as axial lumbar back pain with stiffness, especially in the morning. Pain also involves the hips, buttocks, or thighs and is often exacerbated by prolonged sitting or standing. Similar to cervical facet syndrome, paraspinous tenderness over the affected joint may be elicited. Movements such as hyperextension and lateral rotation over the spine (facet loading maneuver) that stress the facet joints will also aggravate the pain.
DIAGNOSIS
The differential diagnosis for pain that mimics facet arthropathy includes migraine and tension headaches, degenerative disc disease (discogenic pain), spondylosis, spondylolysis, spondylolisthesis, myofascial pain, and sacroiliitis. Unfortunately, the clinical picture is similar in most of these conditions, and it is difficult to distinguish between them by symptomatology or physical signs alone. Laboratory data and imaging studies are not helpful in diagnosing facet arthropathy because degenerative changes of the facet joints are seen on the plain films and on the computed tomography and magnetic resonance imaging scans in asymptomatic subjects. The only reliable way to identify the presence of facet arthropathy is if amelioration of symptoms occurs after local anesthetic blockade of the facet joint’s nerve supply. Historically, this was done by injecting the local anesthetic solution inside the facet joint itself under fluoroscopic guidance. In current practice, the same effect is achieved by injecting the anesthetic solution adjacent to the nerve branches (medial branches) supplying these joints.
This catch-22 situation involving a high prevalence of facet arthropathy and only a single invasive mode of diagnosis would seem to indicate that all patients with spinal pain should be subjected to the intervention of facet block. In fact, this scenario is probably too aggressive and would cause discomfort in many patients with other etiologies of spine pain. Hence, identification of the predictive factors for facet arthropathy became imperative to avoid imposing this rather uncomfortable testing on every patient. In 1998,
Helbig and Lee formulated a scoring system to predict a positive response to facet joint injection. Based on a limited study on 12 subjects, 30 points were allocated to back pain associated with groin or thigh pain, and to the reproduction of pain with extension-rotation at spine (positive facet loading). Similarly, 20 points were given to the presence of well-localized paraspinal tenderness and to corresponding positive radiographic changes, while a negative score of 10 was assigned to the existence of pain below the knee. Using this system, a score of 60 points or more was shown to indicate a very high probability of satisfactory response to facet injections. This scoring system can be used as a clinical guide to decide whether diagnostic facet injections are indicated for any given patient.
Helbig and Lee formulated a scoring system to predict a positive response to facet joint injection. Based on a limited study on 12 subjects, 30 points were allocated to back pain associated with groin or thigh pain, and to the reproduction of pain with extension-rotation at spine (positive facet loading). Similarly, 20 points were given to the presence of well-localized paraspinal tenderness and to corresponding positive radiographic changes, while a negative score of 10 was assigned to the existence of pain below the knee. Using this system, a score of 60 points or more was shown to indicate a very high probability of satisfactory response to facet injections. This scoring system can be used as a clinical guide to decide whether diagnostic facet injections are indicated for any given patient.
Diagnostic nerve blocks have limitations. Single diagnostic facet injections or medial branch blocks have been shown to have a high sensitivity but a low specificity. False-positive results have been shown in 63% of single local anesthetic blocks at cervical level, and these numbers are as high as 62% and 30% at thoracic and lumbar levels, respectively. Presence of placebo response and spread of local anesthetic solution in the adjacent epidural space have been reasoned as the probable causes of these high numbers. Many authors thus recommend double diagnostic blocks using different local anesthetic solutions such as lidocaine and bupivacaine. A differential duration response (lidocaine block being short lasting and vice versa) is taken as dual confirmation before aggressive therapeutic options are exercised.
The blocks are always done under fluoroscopic guidance. Because every facet joint has a dual innervation, it is crucial to block both nerves. At cervical level, C2-3 facet joint is supplied predominantly by the medial branch of C3 dorsal ramus (also called the third occipital nerve). The remaining joints are supplied by medial branches of the dorsal rami exiting at that vertebral level and from the level above. Thus, C4-5 facet joint is supplied by medial branches of C4 and C5 dorsal rami (C4 being exiting from C3-4 neural foramen). Likewise, at lumbar levels, each facet receives nerve supply from the dorsal rami of the same level and from the level above. Because L4 dorsal ramus exit from L4-5 neural foramen, medial branches of L3 and L4 dorsal rami need to be blocked to achieve L4-5 facet block. The interventional pain physician should also be aware of the correct positions of these medical branches to optimally perform these blocks. At cervical level, the target area is the central part or “waist” of the articular pillar on the A-P view (Fig. 169.1) and the midpoint of articular pillar projection on the lateral view (Fig. 169.2). At the lumbar levels, the target area is the junction of superior articular process and superior border of transverse process of the level below (Fig. 169.3) for L1-4 medial branches. The L5 medial branch lies at the junction of the sacral ala and superior articular process of S1.
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