The facet joints are the only true joints of the vertebral column. They allow movement of two adjacent vertebrae of our spine. They are bilateral, paired, diarthrodial articulations. Facet joints are composed of the inferior articular process of the vertebra above and the superior articular process of the vertebra below (Fig.). The superior pars /articular process is large, concave, and face postero-medially. The inferior pars are smaller and face antero-laterally. The facet joints in the lumbar vertebral column form the posterior aspect of the neural foramen. The facet joints have a space with a maximal volume of 1 to 2 ml of joint fluid. The facet joint is intimately related to the neural root sleeve. This relationship explains why the nerve root can be compromised in some instances of severe arthritis and joint deformity. The articular surfaces are covered with cartilage that is relatively thick and prone to degeneration with advances in age.
The facet joints have diffuse, overlapping of sensory innervation. In the interervertebral foramen a nerve root diverge into posterior and anterior primary rami. The posterior ramus passes dorsaly and caudally through a foramen in the intertransverse ligament. Then it divides into medial, lateral, and intermediate branches. The medial branch supplies the lower pole of the facet joint at its own level and the upper pole of the facet joint below. Therefore, each of the facet joints receives its innervations from a medial branch nerve of two posterior primary rami. One branch arises from the nerve at the same level as the joint and the other arises from the segmental level above. For example, the facet joint between the L3 and L4 vertebra is innervated by the medial branch nerves from the L2 and L3 nerve roots.
Therefore, each joint has dual segmental innervation, and each segmental nerve supplies two facet joints plus the soft tissues overlying them. Because of the duality of segmental innervation, each joint must be denervated at two segmental levels (and perhaps three for the L5-51 joint), both at and above the level of the involved joint.
Indications for facet joint block:
Indications for facet joint injection are
- Local tenderness over a facet joint,
- To evaluate chronic low back pain with or without radiation but without any radiï¿½ographic clue
- Back pain with radiographic evidence of disc disease and facet arthritis,
- Postlaminectomy syndrome/Failed back surgery syndrome
The only absolute contraindication to facet joint block is infection in the overlying soft tissues. A relative contraindication is allergy to injecting drugs. The newer non-ionic contrast agents decrease the risk of allergy.
The diagnosis of lumbar facet joint pain on clinical grounds is a difficult task. A patient who presented with low back pain and a normal neurologic examination may be suffering from facet joint arthropathy.
Following features are present:
- Low back pain with non-radicular referral pattern. The pain originating in a single lumbar facet joint is usually described as a unilateral, dull ache in the paraspinal region, occasionally radiating to the buttocks and proximal lower extremity. Referral pattern for the high lumbar facet joints (Ll-L2 and L2-L3) were more frequently observed in the lumbar area, whereas the lower lumbar joints referred pain into the gluteal area, groin area, and posterolateral thigh.
- Usually, no neuro-deficit is present and if a deficit is detected, other causes of back pain have to be ruled out before arriving at the diagnosis of facet joint pain.
- Physical examination (on palpation) can reveal paraspinal pain & muscle spasm in the lower back.
- Patients suffering from lumbar facet arthropathy experience less pain flexion movement. During the examination, the greatest pain is produced during three-dimensional movements that lock the facets (combined movement of extension, side bending, and ipsilateral rotation).
- Pain is usually reduced in the morning and worsens as the day progresses.
- Clinical examination provides maximum diagnostic clue. X-ray, CT scan, MRI are used mainly to exclude other possible causes.
- In facet joint pain, there may be no radiographic changes of facet joint and reverse is also true. There may be radiographic changes without any pain and they do not need any treatment.
- Diagnostic facet joint block confirms diagnosis.
Patient lies prone on the fluoroscopy table. Antiseptic dressing and draping is done. The level chosen to be blocked is identified under fluoroscopic view in the postero-anterior projection. Once the level is identified, the fluoroscopy ray is rotated obliquely until a view of the “Scottie dog” is obtained. The “Scottie dog” is formed by the superior as well as the inferior pars of the same vertebra. The “ear” of the dog is the superior articular process (pars) and the “front legs” of the dog are formed by the inferior articular process (pars) Once this view has been obtained, the optimal point of contact with the bone by the needle should be the “eye of the dog”.
The skin is anesthetized and the 22-gauge spinal needle is directed vertically toward the facet joint. Local anesthesia is achieved in the soft tissues overlying the facet joint by injection of lidocaine through the spinal needle while it is advanced. Care should be taken to pass the tip of the needle directly to the facet joint by observing its tip frequently with fluoroscopy. Sometimes puncture of the joint capsule can be felt. More often, however, the bone prevents further advance of the needle after entering the joint. 1 mL of iodinated contrast medium is injected. A spot film is exposed, with each facet injection to document the intra-articular position of the needle tip. Once the needle position has been documented, 1.5 mL of 0.5% bupivacaine and 20 mg of methylprednisolone acetate are injected into each joint, and the needles are removed.
Median branch block:
After a skin weal is raised and the skin is properly anesthetized, then in a gun-barrel fashion a spinal needle is advanced toward the eye of the “Scottie dog”. It should be emphasized that there should always be bone in front of the needle to avoid complications. Once bone contact is made, then the needle position should be confirmed by the lateral proï¿½jection, at which point the needle should be seen at the level of the facet line and not beyond this point, posteï¿½rior to the foraminal opening, and finally below the level of the intervertebral disc. If desired, an anteroposterior view can also be used to confirm the position of the needle. In this view the needle should be seen at the junction of the superior articular process and the medial-most aspect of the transverse process. At this point then, after careful aspiï¿½ration, the local anesthetic solution is to be injected. This should be repeated at the level corresponding to the medial branch innervating the facet joint targeted.
Complications are rare. These include bruising, backache, muscle spasm, neuriï¿½tis, and very rarely numbness of the leg. Treatment of infections are done with antibiotics. Expectant treatment should be sufficient, but patient should be followed closely.