Mal-rotation　of　the　components　in　total　knee　arthorplasty　(TKA)　is　a　major　cause　of　postoperative　complications,　with　an　increased　propensity　for　implant　loosening　or　wear　leading　to　revision.　A　musculoskeletal　multi-body　dynamics　model　was　used　to　perform　a　parametric　study　of　the　effects　of　the　rotational　mal-alignments　in　TKA　on　the　knee　loading　under　a　simulated　walking　gait.　The　knee　contact　forces　were　found　to　be　more　sensitive　to　variations　in　the　varus-valgus　rotation　of　both　the　tibial　and　the　femoral　components　and　the　internal-external　rotation　of　the　femoral　component　in　TKA.　The　varus-valgus　mal-rotation　of　the　tibial　or　femoral　component　and　the　internal-external　mal-rotation　of　the　femoral　component　with　a　5　degrees　variation　were　found　to　affect　the　peak　medial　contact　force　by　17.8-53.1%,　the　peak　lateral　contact　force　by　35.0-88.4%　and　the　peak　total　contact　force　by　5.2-18.7%.　Our　findings　support　the　clinical　observations　that　a　greater　than　3　degrees　internal　mal-rotation　of　the　femoral　component　may　lead　to　unsatisfactory　pain　levels　and　a　greater　than　3　degrees　varus　mal-rotation　of　the　tibial　component　may　lead　to　medial　bone　collapse.　These　findings　determined　the　quantitative　effects　of　the　mal-rotation　of　the　components　in　TKA　on　the　contact　load.　The　effect　of　such　malrotation　of　the　components　of　TKA　on　the　kinematics　would　be　further　addressed　in　future　studies.　(C)　2015　Orthopaedic　Research　Society.　Published　by　Wiley　Periodicals,　Inc.