100 knees with primary osteoarthritis and scheduled for a total knee replacement (TKR) will be recruited from our waiting list. The patients will be randomized to become operated with the Attune or PFC total knee arthroplasty. Randomisation will be done using envelopes. Patients can only participate with one knee.

The Attune total knee replacement is a recently developed implant with the intention to improve the outcome after this procedure. One of the primary aims is to improve the kinematics of the knee in order to more closely mimic the normal knee. Thereby the patients are expected to experience improved function, better stability and less pain during activity. So far there are no randomized studies which have demonstrated this potential superior performance when compared to its predecessor, the PFC Sigma TKR. This study aims to evaluate the clinical outcome and the knee kinematics of the Attune knee using recognized clinical outcome parameters and dynamic radiostereometry. The PFC sigma knee will be used as control.

100 knees with primary osteoarthritis and scheduled for a total knee replacement (TKR) will be recruited from our waiting list. The patients will be randomized to become operated with the Attune or PFC total knee arthroplasty. Randomization will be done using envelopes. Patients can only participate with one knee.

Surgical procedure: The operations will be done according to our routines without use of bloodless field. Local analgesia will be infiltrated periarticulary during the operation. Cemented fixation will be used in all cases. So-called "fast-track"principles will be applied in both Groups.

Patients will be followed for five years.

Patients with degenerative joint disease of the knee on our waiting list for a total knee replacement will be asked to participate in this study

Inclusion Criteria:

• Medial or lateral primary osteoarthritis (OA) Ahlbäck Grade 2-4
• Varus or valgus deformity ≤15 degrees, extension defect ≤15 degrees
• BMI <35
• ASA 1-3.
• Coming from independent living in own home
• Written informed consent

Exclusion Criteria:

• Cortisone treatment during the last 6 months before operation
• Neurological diseases with symptoms, stroke with sequel
• Endocrine diseases with symptoms
• OA secondary to trauma, infection, inflammatory disease or congenital and acquired deformities
• BMI >=35
• OA of the hip with symptoms. (Patients operated with total hip arthroplasty are accepted)
• Ongoing infection
• Unable or unwilling to participate in the follow-up.

Data will be shared with the sponsor (DePuy).