Mobile-bearing insert dislocation

The goal of this study is to compare the fixed bearing (FB) Triathlon knee (Stryker, USA) and the mobile bearing (MB) Triathlon knee (Stryker, USA) and study the effect of implant design on kinematics and micromotion. During two tasks the kinematics measured with fluoroscopy (kinematics and movement of the polyethylene bearing). Roentgen Stereophotogrammetric Analysis (RSA) will be used to evaluate micromotion between prosthesis and the bone for the MB and FB Triathlon knee.

The goal of this study is to perform a kinematic evaluation of a MB and FB knee prosthesis designs (Triathlon, Stryker, USA), by means of fluoroscopy and RSA and compare the different designs. The findings of this study will contribute to improve total knee designs and improve rehabilitation strategies.

Objectives:

1. To evaluate if there is micromotion of the prosthesis with respect to the bone and if there is a different migration pattern between the designs.
2. To assess and compare the in vivo kinematic patterns of the knee designs by means of fluoroscopy. This will be done on a subset of the patients (the first 20 patients able to perform step-up and lunge motions 6 months post-operatively in a controlled manner without the use of bars and walk more than 1 km)
3. To evaluate if the polyethylene bearing in the mobile bearing is rotating and if this changes over time.
4. Results of the RSA study will be used to correlate the kinematic parameters (fluoroscopy) with the migration results in order to identify factors of risk for the survival of total knee prostheses.

Inclusion Criteria:

• Patient (minimum age of 18 years old, no maximum age limit) is diagnosed with osteoarthritis or rheumatoid arthritis and requires primary arthroplasty.
• Patient is capable of giving informed consent and expressing a willingness to comply with this study
• Patient has no major deformities (i.e. sagittal and coronal deformities are less then 15 degrees)
• The ability to perform a lunge and step-up motion without the help of bars or a cane.
• No or slight pain during activity according to the Knee Society Pain Score

Exclusion Criteria:

• The patient is unable or unwilling to sign the Informed Consent specific to this study
• The individual has a functional impairment of any other lower extremity joint besides the operated knee
• Patient has a flexion contracture of 15° and more
• Patient has a varus/valgus contracture of 15° and more
• Patients requiring revision arthroplasty
• The patient does not understand the Dutch or English language good enough to participate.
• The use of walking aids
• The inability to walk more than 500 meters

IPD analysis is scheduled