Abstract and Introduction
Abstract
Object: By targeting the medial branches of the dorsal rami, radiofrequency ablation and facet joint injections can provide temporary amelioration of facet joint-producing (or facetogenic) back pain. The authors used CyberKnife radiosurgery to denervate affected facet joints with the goal of obtaining a less invasive yet more thorough and durable antinociceptive rhizotomy.
Methods: Patients with refractory low-back pain, in whom symptoms are temporarily resolved by facet joint injections, were eligible. The patients were required to exhibit positron emission tomography-positive findings at the affected levels. Radiosurgical rhizotomy, targeting the facet joint, was performed in a single session with a marginal prescription dose of 40 Gy and a maximal dose of 60 Gy.
Results: Seven facet joints in 5 patients with presumptive facetogenic back pain underwent CyberKnife lesioning. The median follow-up was 9.8 months (range 3-16 months). The mean planning target volume was 1.7 cm (range 0.9-2.7 cm). A dose of 40 Gy was prescribed to a mean isodose line of 79% (range 75-80%). Within 1 month of radiosurgery, improvement in pain was observed in 3 of the 5 patients with durable responses at 16, 12, and 6 months, respectively, of follow-up. Two patients, after 12 and 3 months of follow-up, have neither improved nor worsened. No patient has experienced acute or late-onset toxicity.
Conclusions: These preliminary results suggest that CyberKnife radiosurgery could be a safe, effective, and non-invasive alternative to radiofrequency ablation for managing facetogenic back pain. No patient suffered recurrent symptoms after radiosurgery. It is not yet known whether pain relief due to such lesions will be more durable than that produced by alternative procedures. A larger series of patients with long-term follow-up is ongoing.
Introduction
LOW-BACK pain is a major public health problem with significant socioeconomic impact that costs society upwards of $50 billion annually. About 80% of people will experience at least one episode of low-back pain in their lifetimes, and their pain will recur at rates of 20-44% annually, 80% over 10 years, and 85% over their lifetimes. For most patients, back pain has no clear, identifiable cause. In a significant number of patients there is evidence of degenerative spinal changes, but such changes may also be present in asymptomatic individuals. In only 1-2% of patients with back pain is there a clear underlying cause such as tumor, infection, or trauma.
Increasing attention has recently been focused on the role of facet joints in the pathogenesis of back pain. Goldthwait was the first to propose the concept of facet joint-producing (facetogenic) back pain in 1911, but the term 'facet syndrome' was not coined until 1933 when Ghormley used it to describe back pain starting in the midback and spreading laterally to proximal limbs in a sclerodermal fashion, often aggravated by hyperextension. The authors of several studies have confirmed the involvement of the facet joints in a significant number of patients with back pain. Schwarzer et al. estimated the prevalence of facetogenic back pain at 15-40%.
Medial branches of the lumbar dorsal rami supply the facet joints, with each joint receiving innervation from medial branches of two rostral dorsal rami. The medial branches of the dorsal rami relay pain impulses from the facet joint through their nociceptive terminal endings. Facetogenic pain may result from mechanical stresses in the joint due to joint degeneration or from inflammation in the joint. Back pain may also result from segmental instability due to incompetent facets. Reducing joint inflammation or destroying the nociceptive nerve fibers that supply the joint may lessen facetogenic pain.
Shealy first reported on the efficacy of RF ablation of the nerve to the facet joint for facetogenic back pain. Radiofrequency ablation of the medial branch to the facet joint has become a mainstay of the treatment of facetogenic back pain, but the results have been mixed. Many centers have not adopted the recommended guidelines for RF ablation, a situation that may have led to variable outcomes. Moreover, RF ablation has a reported complication rate of 1%, including a 0.5% incidence of new neuritic pain probably resulting from errors of placement of the needle electrodes. Finally, pain relief after RF ablation is usually not durable, and patients often require multiple RF ablation procedures.
The CyberKnife consists of a linear accelerator mounted on a robotic arm that can be manipulated through 6 degrees of freedom using image guidance technology. It employs real-time imaging that allows tracking of and adjustment for patient movements, ensuring submillimetric accuracy of targeting. It provides conformal radiosurgery capability to cranial as well as spinal and paraspinal targets. It has been used safely and successfully in the treatment of benign and malignant lesions of the spine, as well as trigeminal neuralgia.
In this study, we report preliminary results using CyberKnife (Accuray, Inc.) radiosurgical facetectomy for the treatment of facetogenic pain. The CyberKnife may overcome most of the disadvantages associated with an RF ablation procedure: compared with RF ablation, the CyberKnife system is inherently more amenable to the development and adoption of a standardized protocol established by primary investigators, and much more accurate through its image guidance capability. None of the complications associated with RF ablation, such as erroneous placement of the needle electrodes and secondary neuritis pain, would be relevant. The CyberKnife is also more capable of lesioning the entire joint, thereby perhaps ensuring a more comprehensive rhizotomy. We hypothesize that CyberKnife-induced denervation of the facet joint may be as effective as RF ablation and yield fewer complications.