Compare the medium-term effectiveness and tolerance between joint lavage (JL) in combination with triamcinolone hexacetonide (TH) intra-articular injection (IAI) and IAI with TH alone for treatment of primary osteoarthritis (OA) of the knee. A randomized, double-blind, controlled study was carried out on 60 patients with primary OA of the knee, randomized into two intervention groups: JL/TH group, joint lavage in combination with TH intra-articular injection and TH group, TH intra-articular injection. Patients were followed for 12 weeks by a blind observer using the following outcome measurements: visual analogue scale for pain at rest and in movement, goniometry, WOMAC, Lequesne's index, timed 50-ft walk, perception of improvement, Likert scale for improvement assessment, use of nonsteroidal anti-inflammatory drugs and analgesics, and local side effects. There were no statistical differences in the inter-group analysis for any of the variables studied over the 12-week period. Although both groups demonstrated statistical improvement in the intra-group evaluation (except for Likert scale according to patient and the use of anti-inflammatory drugs). In the Kellgren-Lawrence scale (KL) 2 and 3 sub-analysis, there was a statistical difference regarding joint flexion among patients classified as KL 2, favoring the TH group (p=0.03). For the KL 3 patients, there were statistical differences favoring the JL/TH group regarding Lequesne (p=0.021), WOMAC pain score (p=0.01), and Likert scale according to the patient (p=0.028) and the physician (p=0.034). The combination of joint lavage and IAI with TH was not more effective than IAI with TH alone in the treatment of primary OA of the knee. However, KL 3 patients may receive a major benefit from this combination.