This prospective observational study aims to collect and analyse data on functional outcomes, quality of life indicators, and costs in patients undergoing primary total knee arthroplasty (knee replacement) surgery.

Primary total knee replacement surgery (also called primary total knee arthroplasty) has been shown to be a safe and reliable procedure for the treatment of degenerative joint disease, which can improve the functional and overall quality of life among patients. This prospective observational study aims to explore how undergoing these surgeries affects patients' functional outcomes and quality of life indicators. Another purpose of this research is to evaluate the costs that generate from this surgical intervention and relate them to the gains in functional outcomes and quality of life measures by conducting cost-utility analysis (CUA).

Participants of this study will be men and non-pregnant women over the age of 18 who are undergoing primary total knee replacement surgery at the Traumatology, Orthopedics and Joint Pathology Clinic of the I.M. Sechenov First Moscow State Medical University (Sechenov University). At this facility, around 500 total knee replacement surgeries are performed annually.

Functional outcomes and quality of life indicators will be measured with validated questionnaires. The Western Ontario and McMaster Universities Arthritis Index (WOMAC) will be used to measure functional outcomes in patients undergoing knee arthroplasty, the 5-level version of the EuroQol-5 Dimension questionnaire (EQ-5D-5L) will be used to measure their health-related quality of life. Questionnaires will be administered to patients before they undergo the procedure and on several follow-up dates (6 weeks, 3 months, 6 months, 1 year after the procedure). Before the surgery the questionnaires will be provided to patients in print form. At other points in time the questionnaires will be administered over the phone or via online forms (way of questionnaire administration depends on the choices of patients).

In addition to tracking changes in patients' functional outcomes and quality of life indicators, patients will be surveyed about all direct and indirect costs generated from seeking treatment for their condition, undergoing the replacement surgery, and the rehabilitation process. A small sample of patients will be interviewed about the costs borne by them to produce a questionnaire which will be used to survey the other patients. Cost information will be collected at the same points in time and in the same formats as stated above (printed questionnaires, telephone surveys, online forms). Financial data for calculating costs borne by the clinic will be obtained from the cost accounting system of the facility after each patient's discharge. Afterwards, the collected cost information will be applied to the CUA. Using quality-adjusted life-years (QALYs) and monetary estimates of costs, Average Cost-Utility Ratios (ACURs) will be calculated for primary total knee replacement surgeries.

Inclusion Criteria:

• Patient is aged 18 years and over
• Patient is willing and able to provide written informed consent to participate in the study including the pre-surgery questionnaire and all post-surgical follow-up questionnaires
• Patients is diagnosed with degenerative joint disease and are admitted to the Traumatology, Orthopedics and Joint Pathology Clinic of the I.M. Sechenov First Moscow State Medical University (Sechenov University) to undergo primary total knee arthroplasty

Exclusion Criteria:

• Patient is unable to provide written consent due to illness or personal circumstances
• Patient is cognitively unable to complete study questionnaires
• Patient refuses to participate in any of the pre-surgery and post-surgical outcome measures (e.g., refuses to provide their contact information for follow-up surveys)
• Patient has an existing condition that would compromise their participation and follow-up in the study (e.g., neuromuscular and psychiatric disorders, musculoskeletal cancer)
• Patient is a pregnant woman

Patients with degenerative joint disease who are undergoing primary total knee arthroplasty at the Traumatology, Orthopedics and Joint Pathology Clinic of the I.M. Sechenov First Moscow State Medical University (Sechenov University)