The goal of this randomized controlled trial is to analyze the stability of a cementless Total Knee Arthroplasty (TKA) over time and compare it to a well-documented implant in patients with knee osteoarthritis. The main aim is to answer if there is a difference in stability over time as a measure of long time survivorship in these 2 implants.

50 participants will be randomly allocated to receive either the Triathlon Tritanium (Stryker) or the Global Medacta Knee Sphere (GMK Sphere, Medacta) 3D printed cementless TKAs.

Total joint replacement is an efficacious treatment for osteoarthritis of hips and knees. Both TKA and Total Hip Artrhoplasties (THA) have excellent implant survivorship. However, patients' satisfaction is lower in TKA than THA. A possible cause of the discrepancy is the unnatural knee kinematics after TKA. Various implants designs have been developed to solve the problem. The most common fixation mode is cemented TKA with good survival up to 15 years. However, newer series in younger patients also have shown lasting survival with cementless implants (Nilsson KG, Prudhon JL). Among various different designs, the medially stabilized total knee, which are designed to reproduce natural knee kinematics with a medial ball-in-socked design, is a promising implant design (No authors listed). Dynamically the medial pivot knee performs more naturally (Bragonzoni L,Petersen ET) compared to other designs. Most data for this design is available only for the cemented version. Up to now there is no safety study performed that confirms the stability over time for this implant with cementless fixation.

In this study, the investigators will therefore analyze the in vivo stability of an uncemented TKA with a medially stabilized design, and compare it with a well-documented comparable implant. In order to do this, the investigators will use the CT based micromotion analysis (Broden C, Broden C). This study will contribute to the understanding of fixation and lead to safety to the patient.

Inclusion Criteria:

• Patients referred to Kristiansund Hospital for primary total knee replacement surgery for osteoarthritis with Kellgren & Lawrence grade 3 or 4

Exclusion Criteria:

• Preoperative severe deformity (Hip-Knee-Ankle angle of >5 (valgus) or <-15 degrees (varus) on a full-length leg image at weight bearing
• Preoperative flexion contracture more than 15°
• Less than 50 and more than 75 years of age at the time of surgery
• Use of walking aids because of other musculoskeletal and neuromuscular problems
• Preoperative diagnosis other than osteoarthritis or avascular necrosis (e.g. rheumatoid arthritis, tumours)
• Revision arthroplasty
• Obesity with BMI>35 g/m2
• Lateral collateral ligament deficient knee
• Previous knee joint infection
• Cognitive dysfunction or severe psychiatric disorders.

Individual participant data that underlie the results reported in this article, after deidentification

Immediately following publication and 5 years

Researchers that want access to data

Double blinded study (patient and research nurse)