The purpose of this study is to test for significant differences in functional outcomes, specifically pre-operative ROM and post-operative ROM obtained by using a NexGen CR versus a NexGen CR-Flex knee implant. Specifically, it is predicted that an increase in post-operative range of motion will be experienced by patients treated with the NexGen CR-Flex knee implant.

This study will compare the clinical results of the NexGen CR femoral component with the higher flexion potential of the NexGen CR-Flex femoral component in all patients with degenerative joint disease that require total knee arthroplasty. The primary variable of interest is post-operative range of motion achieved with the two devices, which are implanted with slightly different surgical techniques in patients who may also be subjected to different rehabilitation programs depending on the device they are assigned.

Inclusion Criteria:

• Age, 21-80 years
• Sex, Male and Females will be included
• BMI less than or equal to 39
• Stable Health, the patient would be able to undergo surgery and participate in a follow-up program based on physical examination and medical history.
• Patient is willing and able to cooperate in follow-up therapy.
• Patient exhibits pre-operative radiographic evidenced of joint degeneration consistent with TKA that cannot be treated in non-operative fashion.
• Patient has stable and functional posterior cruciate and collateral ligaments.
• Patient has potential to perform higher than average range of motion activities.
• Operative side range of motion flexion greater than or equal to 120 degrees.
• Severe knee pain and disability due to degenerative joint disease.
• Patient or patient's legal representative has signed the Informed Consent form.

Exclusion Criteria:

• Previous history of infection in the affected joint.
• Previously failed knee endoprosthesis of any kind.
• Charcot joint disease or other severe neurosensory deficits.
• Previous patellectomy
• Patient is skeletally immature.
• Grossly insufficient femoral or tibial bone stock.
• Patient is pregnant.
• Varus or valgus deformity greater than 20 degrees.
• Fixed flexion deformity greater than 15 degrees.
• Previous high tibial osteotomy.
• Previous femoral osteotomy.
• Patient is a poor compliance risk, currently treated for ethanol or drug abuse, physical or mental handicap, etc.
• Loss of musculature or absence of musculoligamentous supporting structures required for adequate soft tissue balance.