The purpose of this study is to compare the effect of post-operative ROM between Flex IM rod and Rigid IM rod, to collect bone morphology of Japanese lower extremity and to research the incidence of overhung with Flex IM rod.

Inclusion Criteria:

1. Patient has signed an Institutional Review Board (IRB) approved, study specific Informed Patient Consent Form.
2. Patient is a male or non-pregnant female age 20 years or older.
3. Patient is candidate for primary Total Knee Arthroplasty (TKA).
4. Patient whose preoperative range of motion (ROM) is over 110 degree.
5. Patient is willing and able to comply with postoperative scheduled clinical and radiographic evaluations and rehabilitation.

Exclusion Criteria:

1. Revision cases
2. Patients that use bone wedges or allograft due to bone loss.
3. Patient has a Body Mass Index (BMI) >40.
4. Patient has an active or suspected latent infection in or about the affected knee joint at time of study device implantation.
5. Patient has a neuromuscular or neurosensory deficiency, which limits the ability to evaluate the safety and efficacy of the device.
6. Patient is diagnosed with a systemic disease (e.g. Lupus Erythematosus) or a metabolic disorder (e.g. Paget's Disease) leading to progressive bone deterioration.
7. Patient is immunologically suppressed or receiving steroids in excess of normal physiological requirements (e.g. > 30 days).
8. Patient has failed unicondylar knee prosthesis.
9. Patient has a known sensitivity to device materials.
10. Patient who are inappropriate for participating in the study in the judgment of the investigator.