Surface analysis of retrieved bilateral UHMWPE tibial inserts under varus malalignment condition

•Our findings revealed that in vivo oxidation is a main contributing factor to the failure of implants, but not varus malalignment.•Highest surface roughness on the medial part for both polethylene tibial inserts was due to varus malalignment knee.•Our data demonstrated a strong association between the change of molecular weight and surface damage mode formation [delamination and crater] with oxidation.