To evaluate different Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain thresholds as eligibility criteria for a knee osteoarthritis (OA) trial and their effect on number of subjects recruited.
We screened subjects with knee pain using the Likert version of the WOMAC and scored all subjects based on the severity of pain with each of the 5 WOMAC activities. For each of 4 alternative definitions of eligibility, we tested how many subjects would be eligible for a trial.
Two hundred thirty-four subjects with chronic knee pain completed the WOMAC pain survey. If we required a score of > or = 4 and at least 2 activities with at least moderate pain, we found 128 of these subjects were eligible. If we required only one activity with moderate pain, the number increased to 139 (by 9%), and further to 161 (by 26%) if we required the same overall WOMAC score but no activity with at least moderate pain. The most common activity causing moderate or greater pain was going up or down stairs.
The number of subjects recruitable for an OA trial depends on the WOMAC pain threshold required. Raising the threshold will lower the number of subjects modestly, but include more persons with moderate to severe pain. Lowering it may include many with only mild pain with activity.