Lower back pain is a common and widespread public health problem ¹. Amongst the causes of medical consultation for pain, only headache exceeds those in number compared to low back pain. Low back pain has a greater socioeconomic impact and is responsible for 10-15% of work disabilities in people between 18 and 55 years of age, surpassed only by the common cold as a cause of absenteeism from work ^2,3. The highest incidence of low back pain occurs in the most productive years and the global prevalence is 12% ^1,4,5. In Colombia, this type pf pain is the third cause of consultation in emergency services, the fourth in general medicine and the first for workplace relocation, Comparing this national panorama with the world, many similarities are observed and the figures have changed little in recent years ^6,7.

More than 80% of people suffer from low back pain throughout their lives ^8-10, and this type of pain is non-specific in 85% of patients, since the source that generates it is not identified. Many factors have been associated as possible causes of the pain, however, including degeneration in the intervertebral or facet discs, obesity, sedentary lifestyle, and hereditary factors ^11,13. A low percentage of cases can be attributed to specific factors such as cancer (0.7%), spinal infection (0.01%), Cauda Equina Syndrome (0.04%), fracture (4%), ankylosing spondylitis (0.3-5%), spinal stenosis (3%) or herniated disc with radiculopathy (4%) ^14,15. Joint pain is responsible for 10-15% of chronic low back pain. The pain generally begins insidiously with predisposing factors, such as spondylolisthesis, degenerative disc disease and advanced age.

Micro-trauma caused by falls or repetitive actions cause bone fissures, capsular tears or articular cartilage tears, micro-hemorrhages, entrapment of the meniscus, inflammation of the synovial capsule, or enthesopathies at the insertion points of the multifidus muscle ^16-19.

Of the people who suffer from low back pain, 65% recover during the first six weeks, 85-90% during the first eight weeks, while 10% develop permanent disability ^20-23. After twelve weeks, recovery is unlikely; Less than half of the people who have been disabled for 26 weeks return to work and the return is almost nil in those who have been absent from work for more than 104 weeks ^24-27. Low back pain affects quality of life by increasing psychological stress, partner dysfunction, and reducing social and physical activity ^28-31.

At present, it is accepted that the treatment of choice for the management of lumbar pain is thermal radiofrequency. In this procedure, an electrode is guided towards the articular facets of the vertebrae, creating an alternating electric field that generates heat at the tip of the electrode. A fluoroscopic radiographic evaluation is performed to verify that the orientation of the electrode is parallel to the course of the medial branch nerves. The electrode is heated to 42°C, then the current flows from the tip of the electrode to the tissue, and if the cause of the pain is of facet origin, it would be eliminated.

Given the importance of low back pain as a cause for medical consultation and its influence on the quality of life of patients, finding an effective treatment for this condition is crucial. The aim of our study was to describe the short-term clinical, therapeutic and evolutionary data of thermal radiofrequency of the medial branches in the relief of facet-based low back pain.

A cross-sectional study of the cohort of patients with low back pain from the consultation in the UNIDOLOR pain unit of the Rafael Uribe University Clinic was carried out, in the period from November 2011 to October 2013.

59 medical records were selected for analysis. Patient identification was kept hidden. The demographic and clinical variables of the patients in baseline conditions are presented in Table 1. Low back pain of facet origin primarily affected people over 55 years of age (63%), who were mainly retired. The gender ratio was 1.3: 1, being higher in women. In 80% of the patients, the evolution of pain was greater than one year. Radiated pain was observed in 41% of the population. In 83% the intensity of pain was equal to or greater than 6/10. Regarding the variables related to the treatment, it was found that 54% ³² underwent a diagnostic block before performing radiofrequency, 12% were operated on without a previous diagnostic block and 34% ²⁰ underwent two or more blocks diagnostics. In 66% ³⁹ bilateral radiofrequency was performed, while in 22% ¹³ only the left side was operated and 12% ⁷ were operated on the right side; in 80% (47) more than 4 medial branches were intervened, while in 20% ¹² there were less than 4 branches.

The procedure was effective in 80% ⁽⁴⁷⁾ of the patients in the first control; effectiveness gradually decreased over time: at three months it reached 70%, at six months 61%, at nine months 44%, while at one year there was effectiveness in only 25% of the patients. In the five controls, including the one performed at one year, the difference was statistically significant considering the percentage of patients who maintained a 50% improvement (p: <0.001) (Table 2).

Table 2

Time (months)	Change n (%)
1	47 (79.7)	0.00000
3	41 (69.5)	0.00000
6	36 (61.0)	0.00000
9	26 (44.0)	0.00000
12	15 (25.4)	0.00018

Evaluation of the response by group, comparing the baseline and subsequent

The mean time to relapse was 194 +137.7 days. Two patients (3%) reported adverse effects: one reported an initial increase in pain and another manifested weakness in walking that recovered spontaneously during the first week.

A study was carried out to describe the short-term clinical, therapeutic and evolutionary data of the thermal radiofrequency of the medial branches in the relief of low back pain of facet origin. It was found to be a safe method, and with clinical improvement in 80% of the patients one month after it was performed, however, the effects of the procedure diminish over time, until only 25% improvement is achieved at one year of follow-up.

The results derived from lumbar facet denervation published by other researchers show great differences in the successful results of treatment, ranging from 9% to 83%; Explanations to support these large differences are based on the presence of different research designs, inadequate radiofrequency techniques, or differences in inclusion criteria. Similar data were reported by other authors ^33,34; an improvement of 76% was found at 21 days, 32% at 6 months and at one year it decreased to 22%; These results coincide with those of our study, since 80% improvement was found at one month and 25% at one year of treatment. A shorter duration of relief in patients with depression, previous surgery, and a greater number of joints treated, although only depression was statistically significant ³³.

In relation to gender, in our study more women were intervened with a H: M ratio of 1: 1.3. Other studies showed an inverse relationship 16: 1 ³⁵ and 1.4: 1 ³⁶. Studies carried out in Spanish communities also found a higher prevalence of low back pain in women (24.5%) than in men (15.1%), affecting more people between 31 and 50 years of age, in full productive age ^37-39; the great difference with respect to the age of our patients is possibly due to the fact that we selected people who clinically suffered from low back pain of facet origin, this entity being more prevalent in elderly people. A possible bias in the results can be generated by the fact that the physicians who carried out the controls belong to the same team that performed the procedure. The results obtained in the present study are not generalizable, since they are obtained from a captive sample, belonging to the patients who attend the Pain Unit of the Rafael Uribe Uribe Clinic.

Thermal radiofrequency of the medial branches reduces chronic low back pain of facet origin. However, the improvement gradually diminishes. The low incidence of collateral effects and complications of radiofrequency justify its use.