Minimise outcome measures after knee replacement

In a previous study the "performance variability" of 15 different assessment systems after knee replacement was analysed. The notion that different knee evaluation systems measure different underlying factors was suggested. Three systems that seemed to have different underlying factors were selected, and a factor analysis was carried out to reduce the number of items in each group. The number of items could be reduced by 70%-82% with a minor loss of discriminating capacity. All instruments could be separated into items of pain, strength, mobility or stability. Pain measured on a visual analogue scale and self-selected walking speed were recommended for longitudinal monitoring of the treatment effect after knee replacement.