Metal ion release from metal implants may have side effects. It can be reduced by coating of the implant. This study compares coated and uncoated TKA.

Patients are randomized to receive a coated or uncoated TKA. Patients are assessed before surgery, after 3 month, 1 year and 5 years.

Blood samples are collected in 7.5 ml S-Monovette® tubes (for trace metal analysis, Sarstedt AG, Germany) using a specific steel needle for trace metal analysis (Sarstedt AG, Germany). Within one hour, plasma was separated by centrifugation at 2500g for ten minutes. Samples were stored at -20°C before being analysed for chromium, cobalt, molybdenum and nickel content using a graphite furnace atomic absorption spectrometer Z-8270 with Polarisation-Zeeman-Absorption (Hitachi Ltd., Japan). The accuracy and precision of the method is validated to < 10% using the control materials SeronormTM Trace Elements Serum (SERO AS, Norway). The detection limit of the method is estimated at 0.5µg/l for chromium, cobalt and molybdenum, 1.0µg/l for nickel (mean + 3 standard deviations from buffer). All probes having ion levels below the detection limit were adjusted to 0.25µg/l for chromium, cobalt and molybdenum and 0.5µg/l for nickel.

Clinical outcome is measured with the Knee Society Score, Oxford Knee Score, Short-Form 36 and University of Los Angeles Activity Score.

Inclusion Criteria:

• indication to TKA
• no other metal implant

Exclusion Criteria:

• no informed consent
• not able to understand study and/or questionnaires
• Need of a higher constrained implant

No masking