Multi-variable Prediction Model of Total Knee Replacement Outcome

Length of in-hospital rehabilitation

Patient Reported Outcome questionnaire to specifically assess the patient's perspective of outcome following Total Knee Arthroplasty. The OKS consists of twelve questions covering function and pain associated with the knee. Each question is scored from 0 to 4 (0 being the worst outcome and 4 being the best). The overall score is the sum of all items and can range from 0 to 48, with higher scores corresponding to better outcomes

This measure assesses the types of intensity of physical activity and sitting time that people do as part of their daily lives. It consists of open-ended questions surrounding individuals' last 7-day recall of physical activity. Total physical activity is estimated in metabolic (MET) MET-min/week and time spent sitting. Then three level or categories are proposed (1=low, 2=moderate and 3=high level of physical activity)

This is a measure of health-related quality of life. The EQ-5D consists of a descriptive system and the EQ VAS. The descriptive system comprises five dimensions: mobility, self-care, usual activities, pain/discomfort and anxiety/depression, with 3 possible answers; the score is obtained from the possible binary combination of answers, and interpreted using the visual analogue scale validation technique for the Spanish population.

Yesavage Scale. The short form of this questionnaire consists of a 15-item self-report assessment used to identify depression in older adults. Questions are answered "yes" or "no", and results consider and individual to be non depressed (normal<5), probably depressed (mild=5<10) and very likely to ve depressed (severe>10)

A visual analog scale is used to assess the perceived knee pain. The participant specifies their level of knee pain by indicating a position along a continuous line between 0, no pain, and 10, worse possible pain

The individual is asked: "How do you expect to feel after the operation?". The level of expectation is answered with a Likert scale ranging from much worse to much better.

Quadriceps isometric strength as measured with hand-held dynamometer

Knee range of motion as measured in degrees with a telescopic goniometer

A timed test used as a measure of mobility and dynamic balance in which the individual raises from an arm-chair, walks three meters, turn round a cone, and go back to sit again

A measure of physical performance. The functional strength of the lower extremities, the transition movements, the balance and the risk of falls are evaluated. The time spent in getting up from a chair for five times is recorded

A measure of static balance. The time the patient is able to stand on one leg keeping balance is recorded

A T-Plate pedometer will be used to register posturographic data. One trial of 30-s with open eyes, in which the individual has to stand over the platform and remain as static as possible during the test. Data extracted include the velocity of center of pressures (in mm/s), the center of pressure excursions (surface in mm2) and weight-bearing data measured as percentage of weight on each leg

Clinical history data of comorbidities (the individual is asked whether other diseases are present, i.e. osteoarthritis in other parts of the body, diabetes, and etc)