Facet joint injection in lower back pain–is its continued use justified?

The injection of local anaesthetic and/or steroids into the facet joint is being practiced widely throughout the NHS and worldwide as a means of treating patients in whom it is believed the facet joint is the cause of the symptoms of their back pain. However, the effectiveness of this therapy for short- and long-term pain relief requires evaluation, as this has far reaching financial and social consequences.

Ghormley ¹ originally used the phrase ‘facet joint syndrome’ to depict back pain caused by pathology at the facet joints. Intra-articular facet injections of hypertonic saline and subsequent pain reproduction were performed by Hirsch ² in 1963 and by Mooney and Robertson ³ in 1976–supporting the role of facet joints in lower back pain.

It is important to note that the facet joints have a richly innervated capsule and the medial branches of the posterior lumbar rami (themselves branches of the lumbar spinal nerves) provide this innervation. In addition, the joints have been shown to hold up to a maximum of 1-2 mL of injected fluid by anatomical studies. Above this level, rupture of the joint capsule occurs and a resultant extravasation into the back and epidural space leade to non-specific therapeutic effects.^4-6

Lower back pain which originates from the facet joints has not been shown by studies to relate to radiological or pathological changes.^7-10 The value of plain radiographs, computed tomography and magnetic resonance imaging scans in diagnosing facet joint disease remains inconclusive: degenerative facet joint changes may be seen in asymptomatic patients, and the converse is also true.^7-10 Bone scintigraphy with single photon emission computed tomography (SPECT) is more sensitive in detecting facet joint lesions and allows more accurate anatomical localization. A recent study suggested that SPECT could help to identify patients with low back pain who would benefit from facet joint injections. ¹¹

The advocates of the continuing use of facet joint injections suggest that pain relief in patients following the injection is a diagnostic tool for confirmation of facet joint pathology.^9,12 However, others insist that both a positive pain provocation response and pain relief are necessary as diagnostic criteria.^9,10 Furthermore, there is little evidence in any of the available literature that arthrogram is undertaken for confirmation of the correct placement of the needle into the facet joint. Care needs to be taken in order to limit the amount of contrast injected–bearing in mind the facet joint can only hold up to 1-2 mL and that the steroid or local anaesthetic must subsequently be introduced.

More objective assessment of facet joint injections is lacking. In a study by Holm et al., ¹³ an attempt was made to determine an objective and reliable measurement of the effectiveness of facet joint injections. The authors postulated that because the best responders to facet joint injections had the most pain on extension after forward flexion in the standing position, then, after pain relief, an expected measurable progress in muscle strength would be observed. Unfortunately, no influence on isokinetic muscle performance was found. An objective measurement of the effectiveness of facet joint injections remains elusive.

It can be argued that studies assessing the long-term effects of facet joint injections do not take into account confounding variables. Perhaps facet joint injections simply offer a window of pain relief during which more rigorous physiotherapy and other treatment modalities can be instituted? Thus, good long-term results obtained in some studies do not take into account other treatment modalities taken by patients (e.g. alternative medications, physiotherapy and exercise). In addition, the natural history of the facet joint pain diminishing with time needs to be considered when reviewing the results of long-term follow-up studies.

Two recent publications by Slipman ¹⁴ and van Tulder ¹⁵ performed critical analysis of all available literature and found that these injections were not clearly shown to be effective and hence cannot be recommended. These studies reviewed current evidence using the results of systematic reviews within the Cochrane database. This adds further weight to our argument that there is insufficient evidence in support of facet injections.^14,15 A systematic review by Boswell et al. ¹⁶ suggested that there is moderate evidence (level 3) of an improvement in symptoms following facet injection. Of the studies reviewed by the authors, only Carette et al. ¹⁷ performed a double blind, randomized placebo-controlled trial, and this in fact found no short- or long term improvement. In addition, no studies were performed which evaluated cost-effectiveness of therapeutic intra-articular facet joint injections.

We suggest that further well-designed, prospective, double-blind, randomized, controlled trials are required to evaluate the therapeutic uses of facet joint injections and provide level 1 evidence for their role. Future studies must look at short- and long-term pain relief, the benefit to quality of life of patients undergoing the therapy, the opportunities for rehabilitation during any potential windows of pain relief offered and the financial implications of the procedure. An attempt must be made to standardize or limit the influence of confounding variables during periods of long term follow-up (e.g. alternative analgesia, physiotherapy and exercise). Thus, a cost–risk–benefit ratio may be attained and an assessment made of the potential therapeutic use of facet joint injections. Only when the results of such well-designed randomized controlled trials are available can we be sure that the injection of facet joints in the treatment of lower back pain is clinically and financially justifiable.