The aims of this study is to compare the results between patients without severe patellofemoral arthritis and patients with severe patellofemoral arthritis after mobile bearing UKA.

The investigators prospective compute the results including anterior knee pain, knee society score, pain score, functional score, range of motion, operative time, blood loss, and component alignment.

The patients were performed surgery. The Oxford UKA was applied for all patient.

Inclusion Criteria:

• anteromedial osteoarthritis knee,
• older than 40 years old,
• range of motion > 90 degrees,
• varus deformity < 25degrees,
• flexion contracture< 20degrees,
• intact anterior cruciate ligament

Exclusion Criteria:

• younger than 40,
• osteonecrosis of knee,
• rheumatoid,
• posttraumatic arthritis,
• absent of anterior cruciate ligament