Image Guided Percutaneous Facet Joint Infiltrations: Review of the Knowledge for Diagnostic and Therapeutic Approach

It is estimated that approximately 70-90% of the population will experience at least once during their lifetime an episode of back pain (neck pain, upper low back pain) with facet joints accounting as a causative agent in 25-40% of the cases [1,2]. Facet joints are frequently affected by osteoarthritis resulting in joint space narrowing, intraarticular vacuum phenomenon/fluid, osteophytes, synovial cyst formation and flaval ligaments hypertrophy [3].


Introduction
It is estimated that approximately 70-90% of the population will experience at least once during their lifetime an episode of back pain (neck pain, upper low back pain) with facet joints accounting as a causative agent in 25-40% of the cases [1,2]. Facet joints are frequently affected by osteoarthritis resulting in joint space narrowing, intraarticular vacuum phenomenon/fluid, osteophytes, synovial cyst formation and flaval ligaments hypertrophy [3].
Percutaneous facet joint steroid infiltrations are minimally invasive therapeutic or diagnostic procedures that involve injection of corticosteroid with or without local anesthetic inside the zygapophyseal joints of the spine. The procedure is performed under minimal or no anesthesia aiming to control painful symptoms during the acute phase. In addition infiltrations provide diagnostic verification of a certain facet joint acting as pain source.
The use of steroids for infiltrations goes back to 1950s [4]. Steroids decrease neutrophils aggregation and suppress inflammatory proteins release by mast cells and macrophages, thereby, decreasing inflammatory cells activity [5]. Nowadays, facet joint steroid infiltrations are used throughout the globe for low back pain treatment. They constitute a symptomatic treatment for low back pain and facet syndrome refractory to appropriate conservative medical therapy.

Facet Joint Syndrome
Facet joint syndrome is diagnosed in patients with local paralumbar tenderness occasionally radiating to thigh, iliac crest and rarely to the groin. Pain is usually worse when waking up from bed or trying to stand after prolonged sitting and could be exacerbated upon pressure, hyperextension, torsion and lateral bending. The correlation of physical examination findings to those of imaging and neurophysiologic studies will play a decisive role to proper patient selection. Emphasis must be given to the fact that apart from their therapeutic role, percutaneous corticosteroid infiltrations might as well provide diagnostic information concerning the origin of the pain.
Conservative therapy is initially proposed. Image guided infiltrations can either be combined to this course or solely performed as an intermediate step between any of the rest therapeutic options which are either percutaneous (ablation) or surgical [6]. The injectate in the vast majority of cases contains a long acting corticosteroid mixed to local anesthetic. Alternatively, sodium hyaluronate solutions or ozone were tested, however more and extensive studies are necessary [7,8].
Ideal candidate for percutaneous facet joint infiltration is any patient with low back or radicular pain refractory to a 2-3 weeks course of conservative medical therapy. The facet joint selection is usually made by identifying the point of maximal local tenderness to palpation over the joint of interest and considering the cutaneous distribution of the pain. There is no clear relation between the dose and the effect. In most cases, if pain reduction is more significant than 50%, a second injection is performed 1 week later, and a third injection at one month with a maximum of five injections per years [9].
Alternative minimally invasive therapies include median nerve block, radiofrequency ablation of the medial branch nerves of the dorsal rami innervating each facet and MR-guided HIFU [6,10,11]. • Patient has already received maximum allowed for a given period dose of steroids [6,12].

Pre-procedure set-up
At least 24 hours prior to the procedure, patient's physical examination and coagulation laboratory tests are performed and clinical symptoms are recorded on a visual-analogue scale (VAS) with the corresponding VAS score. Painful areas and other possible neurological defects (e.g. hypoesthesia) are drawn on a specific chart before and during the procedure [14].
Strict sterility measures are necessary. Sterile bags are used to cover image intensifiers and X ray tubes, whilst, the skin is cleaned with alcohol solution and iodide povidone and a full surgical drape is placed over the patient [6].

Technique Corticosteroid selection
The most commonly injected corticosteroids are derivatives of a cortisol analogue called prednisolone that can be either soluble (particulate preparation) or non-soluble (non-particulate preparation which contains highly insoluble in water corticosteroid esters that form microcrystalline suspensions) [15]. Non-soluble corticosteroids have a longer lasting effect than soluble ones due to the esters which require hydrolysis in order to release the active moiety [15,16]. On the other hand, controversy is raised on whether soluble corticosteroids have a quicker initiation of their effect due to the rapid cellular uptake [17].

Imaging guidance
Fluoroscopy, Computed Tomography or Magnetic Resonance can be used as guidance imaging methods for percutaneous spinal infiltrations. Fluoroscopy is governed by the advantage of real time imaging during needle progression and especially during contrast medium injection which will verify the extravascular and intrarticular needle positioning. Computed Tomography provides more detailed anatomy of the region of interest. Magnetic Resonance although lacking ionizing radiation is of higher cost and of longer duration. Recent study upon the cost of MR-guided infiltrations concluded that it is twice the cost of CT-guided ones [18] (Figures 1-3).

Cervical Spine Concerning C1-C2 infiltration
With the patient in prone position with neck extension, a strict posterior access aiming in the inferior external articulation of C1-C2 is the approach of choice.
For the rest cervical levels, a posterolateral access is used. In our department we perform facet joint infiltration in the cervical spine with the patient seated in the fluoroscopy unit and the controlateral shoulder against the X-ray table. A direct posterolateral access is performed under strict sterility measures. In most centres worldwide the injectate mixture for cervical spine includes corticosteroid mixed to normal saline instead of local anaesthetic in order to avoid inadvertent anesthetization of C4, C5 and C6 nerve roots.

Lumbar spine
Two approaches can be used: • The posterior access (patient is in strict prone position and needle tip is advanced at the inferior part of the articular recess.
• The oblique direct access: at 45º rotation, the facet joint is

Post-Procedure Care
Post-discharge instructions vary and depend upon the practicioner. In general, patient is usually allowed to return to his/her normal activities after the first 24 hours. Precaution of a diet without salt and sugar for 24-48 hours mast is taken for diabetics or patients with arterial hypertension. The injected corticosteroid may take 3-5 days to reach its anti-inflammatory effect thereby the initial pain relief (which is the local anesthetic) is followed by a baseline pain return and a secondary pain relief at 3-5 days [19]. Clinical evaluation is performed after 7-10 days. • Thecal sac puncture with subsequent headache • Allergic reactions to the medications given • Arterial puncture with subsequent dissection, thrombus, false aneurysm, perivascular hematoma, air or crystals embolisation [6,7,20,21].

Outcome Measures
Outcome of facet joint infiltration greatly depends upon proper patient selection (59-94% immediate and 27-54% long term relief) [6]. Level of evidence for therapeutic facet joint infiltrations is limited for cervical spine and limited to moderate for lumbar spine concerning short-and long-term improvement [22,23]. However, even in the most recent guidelines released from the American Society of Pain Physicians it is stated that the technique is the oldest and most commonly used one [23]. The moderate to high success rates of the technique, its safety profile and least invasiveness seem to constitute intra-articular facet joint infiltrations as an attractive therapy for facet joint syndrome. In addition, intra-articular facet joint infiltrations can be used to differentiate symptomatic from asymptomatic facet joint alterations in cases where diagnosis is controversial.