Study finds three knee pain subgroups of osteoarthritis

MADRID — A 10-year investigation of knee pain in osteoarthritis revealed three general pain subgroups, suggesting the individualized process of pain may be categorized, according to findings presented at the EULAR Annual Congress.

Feng Pan, MD, of the Musculoskeletal Unit at Tasmania University Hospital in Australia, said as many as 35% of people older than 45 years with osteoarthritis experience knee pain.

“However, there is widely differing pain course and level over time,” he said. “Successful determinants of pain course may help define pain subgroups.”

He added that defining these groups has been challenging because it is an “individualized process,” often dependent on environmental, genetic, psychological, structural and socioeconomic factors. “No study has comprehensively investigated these factors in pain trajectory over the long term,” he said.

Pan and colleagues studied 1,099 patients aged 51 years to 81 years. At 2.6 years, the population was 875 patients. There were 768 patients included at 5.1 years and 543 patients remained at 10.7 years.

The investigators measured pain by WOMAC. Results showed 51.7% of the cohort had mild pain as determined by this scale, while 33.2% reported moderate pain and 15.1% reported severe pain.

The curve for mild pain remained relatively stable with time, whereas a slight increase was reported for moderate pain. The severe pain trajectory began high and leveled off with follow-up.

Patients in the severe pain group were more likely to be women, have lower physical activity levels, report more emotional difficulties, have poor employment status and low education levels. Severe pain was also associated with more structural problems and comorbidities.

High BMI and emotional difficulties were reported more frequently in the moderate pain group compared with the mild pain group. Pan suggested that associations with factors, such as BMI and psychological problems, highlight the complexity of pain trajectory.

No significant association was reported between effusion-synovitis and moderate pain. The number of structural abnormalities in the knee was associated with both moderate pain and severe pain.

The study was limited by the fact that imaging analysis was only available for the right knee, according to Pan.

“This is the first long-term study with a good assessment of potential risk factors for knee pain,” he concluded. “Three distinct pain trajectory groups were identified, suggesting that homogeneity of subgroups exists and follows a specific trajectory over time, despite large individual variations in pain.” — by Rob Volansky

Reference:

Pan F, et al. Abstract #OP0334. Presented at: EULAR Annual Congress; June 14-17, 2017; Madrid.

Disclosure: The researchers report no relevant financial disclosures.