The purpose of this prospective study is to explore whether maximal and self-selected walking speed in individuals with knee arthroplasty is a useful and applicable clinical measure that can provide new insights into physical function after prosthetic surgery. We will examine the progression of walking speed and other measures of physical function, and investigate if walking speed can predict postoperative function. Individuals over 55 years, scheduled for knee arthroplasty will be invited to participate. Standardized functional tests such as walking speed, sit to stand and one legged stance along with patient reported outcomes will be assessed preoperatively, three months and 12 months after surgery. The study may provide useful knowledge that can be aplied clinically in the assessment and follow-up of this patient group.