The present randomized controlled trial is designed to compare one novel total knee replacement (TKR) design and two conventional TKR designs in terms of functional outcome. 80 patients will be randomized in each of the three arms (240 altogether).

The study will compare the short-term functional outcome (at 2 years) of TKR performed with a novel TKR design (Persona , Zimmer, Warsaw, IN, USA) against TKRs performed with two conventional designs (PFC, DePuy, Warsaw, IN, USA and Nexgen, Zimmer, Warsaw, IN, USA).

Inclusion Criteria:

• patients undergoing total knee replacement surgery for primary osteoarthritis
• no previous open major surgery in the joint ( e.g. osteotomy)
• unilateral operative treatment, with no plans for surgical treatment of the contralateral knee in the near future
• patients living in the local hospital district (Pirkanmaa Hospital District)
• Kellgren-Lawrence grade 3-4 knee osteoarthritis in plain radiographs

Exclusion Criteria:

• Unwilling to provide informed consent
• > 15 degrees varus or valgus, or >15 degree fixed flexion deformity
• predominantly patellofemoral osteoarthritis
• Physical, emotional or neurological conditions that would compromise the patient´s compliance with postoperative rehabilitation and follow-up (e.g. drug or alcohol abuse, serious mental illness, general neurological conditions such as Parkinson, MS, etc.)

Patients will be operated upon using the implant allocated in randomization. Participants are blinded to the implant design used for their operation. Staff at the ward is also blinded. And the physiotherapists conducting the follow-up visits (at 2-3 months, 1 year and 2 years, i.e. the outcome assessors) are also blinded to the allocation.