CONTEXT AND OBJECTIVE: Osteoarthritis causes pain and disability in a high percentage of elderly people. The aim of the present study was to compare the analgesic effect of intra-articular bupivacaine and morphine in patients with knee osteoarthritis.

DESIGN AND SETTING: A randomized and double-blind study was performed at a Pain Clinic of São Paulo Federal University.

METHODS: Thirty-nine patients with pain for more than 3 months and an intensity higher than 3 on a numerical scale (zero to 10) were included. G1 patients received 1 mg (1 ml) morphine diluted in 9 ml saline by the intra-articular route, and G2 patients received 25 mg (10 ml) 0.25% bupivacaine without epinephrine. Pain was assessed on a numerical scale and knee flexion and extension angles were measured after administration of the drugs at rest and during movement. The total amount of analgesic complementation with 500 mg paracetamol was also determined.

Among the 39 patients selected, two patients from group 1 and five from group 2 were excluded from some of the analyses because they did not return on the day of assessment or because they used a complementary analgesic different from that standardized in the study

Inclusion Criteria:

• Older than 50 years with a radiological confirmation of chronic knee osteoarthritis
• Pain lasting for more than 3 months either at rest or under strain, morning stiffness
• Absence of heat at the site
• Crepitation during movement and a pain score ranging from three to ten.

Exclusion Criteria:

• Patients with coagulopathy
• Infection or malignant disease
• Patients who underwent knee or hip surgery; AND
• Patients using opioids 24 hours prior to the study