This study has the primary goal of evaluating the efficacy of corticoid infiltration in the quadratus lumborum syndrome, aiming to determine if there are benefits with the use of corticosteroids and if they exist, if this improvement comes only from the systemic effects of corticosteroid administration.

This study has the primary goal of evaluating triamcinolone's efficacy on the ultrasound- guided infiltration in the quadratus lumborum syndrome, aiming to determine if there are benefits with the use of corticosteroids and if they exist, if this improvement comes only from the systemic effects of corticosteroid administration.

It is an interventional study, double-blinded and randomized, in a sample of patients followed in the Chronic Pain Unit (Hospital of Braga, Portugal), proposed for ultrasound infiltration of the quadratus lumborum muscle.

The selection of the patients will take into account the inclusion and exclusion criteria, until reach the required sample size (66 patients). The confirmation of the inclusion criteria will be done by a physiatrist blind to randomization.

Different protocols will be randomly applied to patients after obtaining written informed consent.

The techniques will be performed by two anesthetists. The data will be obtained through questionnaires filled out on the day of the technique and in the course of 1, 3 and 6 months in chronic pain consultation and by telephone call 72 hours after the procedure. It will be a psychologist, blind to randomization, to fill the questionnaires.

Patients will be also evaluated in consultation, at the same time, the course of 1, 3 and 6 months.

After the data collection it will be performed a statistical analysis.

Inclusion Criteria:

I) patients followed in the Chronic Pain Unit proposed to have ultrasound- guided infiltration of the quadratus lumborum muscle.

II) written informed consent.

III) presence of 4 of the following clinical criteria evaluated by a physiatrist:

• pain below the 12th rib and 5 cm lateral to the transverse process of L1 during palpation, with referred pain to the iliac crest;
• pain on palpation of the trigger points in the quadratus lumborum muscle;
• exacerbation of the pain with with postural changes when lying down, walking, sitting and/or squatting;
• lumbar pain with muscle stretching;
• painful palpation of trigger points at the level of L4 vertebral body, 1 to 2 cm above the iliac crest.

Exclusion Criteria:

• rheumatologic disease;
• psychiatric disease;
• neurological disease;
• history of anticoagulation use;
• pregnant patients;
• uncontrolled diabetes mellitus;
• patients on corticosteroid therapy;
• allergy to the medication to be used;
• anterior realization of ultrasound techniques for low back pain ;
• anterior realization, of invasive techniques, less than 6 months, with administration of medication.