The goal of this study is to utilize physical activity monitoring to determine the trajectory of normal recovery as it relates to a patient's ability to get up and get moving. From this work, we hope to be able to define the range in patients' physical activity following knee replacement surgery, and thus, give clinicians a tool and the methodology to identify patients whose recovery is not progressing as quickly as expected. Data from physical activity monitors will allow the research team to identify how active patients are, how vigorous that activity is, and how well that activity correlates with standard and commonly used patient questionnaires.

This study is an observational study of the physical activity levels of adults who have been diagnosed with end-stage osteoarthritis of the knee and are undergoing knee replacement surgery at the Nuffield Orthopaedic Centre, Oxford. Data regarding patient activity and functional recovery will be collected using two methods. First, data will be collected through the extraction of three-axis accelerometer data, collected via a wrist-worn (and hip-worn for a subset of patients) physical activity monitor. This data will be collected in three intervals: pre-operatively, immediately postoperatively, and at 6 months postoperatively. Secondly, data will be collected by standard clinical assessment and patient reported outcome measures. These assessments will again take place pre-operatively, at 6 weeks postoperatively, and at 6 months postoperatively. Additional data will be collected through a simple activity diary, which asks the participants to log their monitor wear-time along with the times that they took bicycle rides or extended walks.

The expected duration of patient involvement is up to a total of 8 to 8.5 weeks over the course of up to 7 months. There are no clinical visits within this protocol beyond what is already within normal patient care. Patients will be asked to post their monitor back to the research centre for data collection and data processing twice during the study period.

The aim of this study is to assess the trajectory of recovery in terms of physical activity in the post-operative knee replacement population, and subsequently to define the expected path of early recovery.

Inclusion Criteria:

• Participant is willing and able to give informed consent for participation in the study.
• Male or Female, aged 18 years or above.
• Diagnosed with required late stage osteoarthritis, undergoing knee arthroplasty in the next 3 months.
• In Investigator's opinion, is able and willing to comply with all trial requirements.

Exclusion Criteria:

• Any other significant disease or disorder which, in the opinion of the Investigator, may either put the participants at risk because of participation in the study, or may influence the result of the study, or the participant's ability to participate in the study.
• Participants who are enrolled in another research study involving an investigational product or methodology that could alter physical activity.
• Participants are undergoing a revision arthroplasty surgery on the operative knee

Participants will be patients undergoing primary total or unicompartmental knee arthroplasty for treatment of end-stage osteoarthritis.

De-identified individual participant data for all primary and secondary outcome measures will be made available.

Data will be made available within 6 months following study completion.

Data access requests will be reviewed by the trial steering committee.