The optimal method of total knee replacement component fixation to the bone remains a challenge. The use of bone cement is considered the gold standard and is the preferred technique for most surgeons. However, uncemented fixation methods have been developed in an attempt to tackle problems that can be seen when cement is used. The cement-bone interlock can deform and degrade over the years and can lead to aseptic loosening, especially in young and active patients. A loosened prosthesis results in an impaired functioning and painful knee in daily life for which a revision of the prosthesis may be necessary. To prevent aseptic loosening and subsequent revision surgery, new methods of uncemented fixation have been developed.

One of these methods is to use a highly porous metal called Tritanium®. It can improve the biologic fixation by resembling the characteristics of trabecular bone. It is expected that this surface aids bone ingrowth and to have similar or even better results concerning early fixation properties and long-term durability compared with cemented fixation. Excellent results using this highly porous Tritanium have been seen in total hip surgery already.

This single-blinded, randomized clinical trial will assess clinical and radiological outcomes including Roentgen Stereophotogrammetry (RSA) measurements of a newly approved uncemented Triathlon Tritanium CR total knee prosthesis compared with a standard cemented Triathlon metal-backed CR total knee prosthesis (both by Stryker Orthopaedics). Two arms of each 35 patients will be included.

The primary outcome measure will be prosthetic migration after two years of the uncemented Triathlon Tritanium CR Total Knee and the cemented Triathlon CR Total Knee by means of RSA. It is hypothesized that the new uncemented Tritanium prosthesis will perform at least equally good in terms of migration and clinical parameters compared with the standard cemented Triathlon.

The secondary outcome measure will be long-term (10-year) survival based on the two-year migration patterns combined with clinical factors and radiographic aspects. In order to identify other clinical parameters besides the fixation of the prosthesis components, clinical scores and radiographic aspects will be correlated with the RSA outcome. The 10-year results will be used to verify the predicted long-term survival results.

Inclusion Criteria:

1. Patient is able to understand the meaning of the study and is willing to sign the Ethics Commission (EC) approved, study specific Informed Patient Consent Form.

2. Patients eligible and scheduled to undergo primary total knee replacement with any of the following indication.

   • Painful and disabled knee joint resulting from osteoarthritis (Ahlbäck stage II to V)
   • One or more compartments are involved.

3. Ability and willingness to follow instructions, including control of weight and activity level, and to return for follow-up evaluations.

4. A good nutritional state of the patient.

5. The subject is a male or non-pregnant female between 40 and 75 years of age.

Exclusion Criteria:

1. The subject is morbidly obese, defined as Body Mass Index (BMI) of > 37.
2. Previous major knee surgery
3. Patients who had a Total Knee Arthroplasty (TKA) on contralateral side within the last 6 months that is considered to have an unsatisfactory outcome. (Patients with contralateral TKA > 3 months ago with good outcome can be included in the study).
4. Patients with other severe concurrent joint involvements that can affect their outcome.
5. Patient has a flexion contracture of 15° and more.
6. Patient has a varus/valgus contracture of 15° and more.
7. The subject will be operated bilaterally.
8. The subject has an active or suspected latent infection in or about the knee joint.
9. Osteomyelitis
10. The subject has a neuromuscular or neurosensory deficiency, which would limit the ability to assess the performance of the device.
11. The subject has a systemic or metabolic disorder leading to progressive bone deterioration.
12. The subject is immunologically suppressed or receiving steroids in excess of normal physiological requirements.
13. Female patients planning a pregnancy during the course of the study.
14. The patient is unable or unwilling to sign the Informed Consent specific to this study.

Secondary exclusion criteria: when there are less than five tibia-bone markers or less than three insert markers visible in the baseline RSA photograph and it will not improve by placing the patient in another position, the patient will be excluded from the study.