The goal of this clinical trial is to learn whether partial knee replacement (unicompartmental knee arthroplasty, UKA) or total knee replacement (total knee arthroplasty, TKA) leads to better clinical and functional outcomes in adults with medial knee osteoarthritis who are candidates for knee arthroplasty.

The main questions the study aims to answer are:

• Does UKA or TKA result in better patient-reported outcomes, such as knee pain, function, and quality of life (measured by Oxford Knee Score, WOMAC, and Knee Society Score)?
• Does UKA or TKA lead to differences in complications or revision rates during follow-up?

Researchers will compare UKA to TKA to see whether one procedure provides superior postoperative recovery, knee function, and long-term outcomes under standard clinical care conditions.

Participants will:

• Receive either a unicompartmental or total knee replacement, assigned by randomization.
• Undergo routine postoperative examinations, including standardized questionnaires (e.g., Oxford Knee Score, WOMAC, Knee Society Score, VAS).
• Attend follow-up visits at standard clinical intervals (e.g., 6 weeks, 6 months, 1 year, 2 years, and beyond).

Medial knee osteoarthritis is a common degenerative joint disease that often leads to significant pain, loss of function, and reduced quality of life. When conservative treatments are no longer effective, surgical joint replacement is a standard therapeutic option. Two established procedures are unicompartmental knee arthroplasty (UKA), which replaces the diseased medial compartment, and total knee arthroplasty (TKA). Both procedures are widely used, but it remains unclear which option provides better outcomes for patients who specifically present with isolated medial osteoarthritis.

This prospective, randomized, controlled clinical trial aims to systematically compare the functional, radiological, and patient-reported outcomes of UKA and TKA performed under routine clinical care conditions. The study is conducted at the Department of Orthopaedics and Traumatology at the Medical University of Graz. Adult patients with isolated medial knee osteoarthritis who meet established clinical and radiographic criteria for knee arthroplasty are eligible for participation.

All surgical procedures are performed using standard techniques and implants currently approved and used in routine practice. Postoperative follow-up follows the usual clinical schedule (e.g., 6 weeks, 6 months, 1 year, 2 years), with additional long-term clinical and radiological assessments as part of institutional standard care. During these visits, participants complete validated patient-reported outcome measures, including the Oxford Knee Score, WOMAC, Knee Society Score, Forgotten Joint Score, and Visual Analog Scale for pain. Radiographs are collected to assess implant position and alignment.

The study seeks to determine whether one of the two surgical approaches results in superior knee function, less postoperative pain, faster recovery, or lower complication and revision rates. Findings from this trial may support evidence-based decision-making for surgeons and patients considering knee arthroplasty for isolated medial knee osteoarthritis.

Inclusion Criteria:

• written consent, 4th degree medial osteoarthritis, max 1st degree lateral osteoarthritis, max. 2nd degree osteoarthritis in patellofemoral joint

Exclusion Criteria:

• from 2nd degree lateral osteoarthritis, from 3nd degree osteoarthritis in patellofemoral joint, non-compensatable varus or valgus misalignment above 10 degrees, non-consent, age under 40 / over 90, st.p. fracture of the femur and or tibi, infection, st.p. joint replacement or osteotomy in the area of the knee joint, simultaneus bilateral care, pregnany