Background: The Knee Injury and Osteoarthritis Outcome Score (KOOS) was constructed in Sweden. This questionnaire has proved to be valid for several orthopedic interventions of the knee. It has been formally translated and validated in several languages, but not yet in Dutch. The purpose of the present study was to evaluate the clinimetric properties of the Dutch version of the KOOS questionnaire in knee patients with various stages of osteoarthritis (OA).

Limitation in daily physical activity is one of the reasons for total hip arthroplasty (THA) or total knee arthroplasty (TKA). However, studies of the effects of THA or TKA generally do not determine actual daily activity as part of physical functioning. We determined the effect of THA or TKA on patients' actual physical activity and body function (pain, stiffness), capacity to perform tasks, and self-reported physical functioning. We also assessed whether there are differences in the effect of the surgery between patients undergoing THA or TKA and whether the improvements vary between these different outcome measures. We recruited patients with longstanding end-stage osteoarthritis of the hip or knee awaiting THA or TKA. Measurements were performed before surgery and 3 and 6 months after surgery. Actual physical activity improved by 0.7%. Patients' body function, capacity, and self-reported physical functioning also improved. The effects of the surgery on these aspects of physical functioning were similar for THA and TKA. The effect on actual physical activity (8%) was smaller than on body function (80%-167%), capacity (19%-36%), and self-reported physical functioning (87%-112%). Therefore, in contrast to the large effect on pain and stiffness, patients' capacity, and their self-reported physical functioning, the improvement in actual physical activity of our patients was less than expected 6 months after surgery.

The Dutch HOOS questionnaire has a good internal consistency and reliability. Moreover, the construct validity is good and no floor and ceiling effects were found. The HOOS is a good instrument for patients with different stadia of hip OA.

The impact of end-stage OA on the level of actual physical activity is equal for hip and knee OA patients. The actual physical activity for both of the OA groups was significantly and clinically relevantly lower compared to controls. However, this difference was smaller than expected and less dominant than patients' perception of limitations in daily life. Clinicians must be aware that the patients' perception of physical functioning in daily life does not always correspond to the actual physical activity.