The purpose of this study is to compare the performance and safety of medial UKA and HTO in the treatment of AMOA in term of functional outcome, radiographic assessment, range of motion, postoperative complications, revision rate and relevant health economics outcome.

The purpose of this study is to compare the outcomes of medial UKA and HTO in the treatment of AMOA by investigating the performance of these 2 procedures in terms of functional outcome, radiographic assessment, range of motion, postoperative complications, revision rate and relevant health economics outcome, then identify factors associated with better clinical performance. It is aimed to provide evidence-based guidelines for selecting the appropriate procedure in managing AMOA in Chinese population based on the findings of this study.

The secondary endpoints will include:

1. Pain Numerical Rating Scale (NRS)
2. SF-12 Health Survey
3. Radiographic assessment includes pre-op and post-op mechanical femorotibial angle (mFTA), patella height, patellofemoral medial and lateral articular surfaces, and displacement angle of patella
4. Range of motion
5. Adverse event rate and classification (including complication)
6. Operating time
7. Total blood loss (BRECHER formula)
8. Revision rate

Health economic outcomes based on hospital discharge days, recovery time, physiotherapy and complications/ reoperations will also be analyzed.

Inclusion Criteria:

1. Patient is aged 18 to 85 years old, inclusive;

2. Patients who diagnosed with AMOA of the knee, and have undergone Open Wedge HTO, or primary unilateral partial knee arthroplasty with Oxford Partial Knee with Microplasty® instrumentation in accordance to indications of UKA and the following radiographic assessments in the knee joint:

   • exposed bone on both the femur and tibia in the medial compartment.
   • functionally intact ACL
   • full thickness lateral cartilage (ignore osteophytes)
   • functionally normal MCL: correctable deformity (normal medial opening)
   • acceptable patellofemoral joint: normal, medial facet OA with or without bone loss, lateral facet OA without bone loss.

3. UKA or HTO procedure completed one year prior to study participation;

4. Patient provides written informed consent by signing and dating the Institutional Review Board/Ethics Committee (IRB/EC) approved informed consent form.

Exclusion Criteria:

1. Has undergone UKA but met any of the contraindications included in the product labeling of Oxford Partial Knee system;
2. Has rheumatoid arthritis or other forms of inflammatory joint disease;
3. Uncooperative or with neurologic disorders who are incapable of following directions;
4. Has a diagnosed systemic disease that could affect his/her safety or the study outcome;
5. Anterior cruciate ligament and posterior cruciate ligament injury, collateral ligament instability;
6. Known to be pregnant;
7. Prisoner or known alcohol / drug abuser.

Patients who underwent either primary UKA with Oxford Partial Knee with the Microplasty® instrumentation or Open Wedge HTO for AMOA, and meet the inclusion criteria and do not meet any exclusion criteria will be screened to this study.