Rasch analysis of Visual Analog Scale measurements before and after treatment of Patellofemoral Pain Syndrome in women.

The Visual Analog Scale (VAS) can be used to record subjectively experienced pain in different situations (items). By a mathematical method, the Rasch analysis, the original VAS recordings can be converted to an interval scale. Forty women with Patellofemoral Pain Syndrome (PFPS) reported their pain on the VAS from 12 different situations (items) before and after 12 weeks of rehabilitation. The items recorded pain during the last 3 months, during provocation tests, and during activities such as walking up stairs, jumping and strength testing. It was concluded that the items used for the patients with PFPS were hierarchically ordered in a statistically equivalent manner before and after rehabilitation. Subjectively reported pain after 12 weeks of rehabilitation was significantly alleviated for 23 (58%) of the 40 patients, compared with before rehabilitation. The patients with PFPS did not use the VAS as a linear scale over the full range. Rasch analysis of recordings made with the VAS gave a more detailed pain assessment.