Radiographic Analysis of the Alignment of Lower Extremity after Total Knee Arthroplusty

Abstract：Objective The radiologic parameter after total knee replacement is very important to estimate surgical tech-niques and to find early prosthetic loosening. However,the radiologic parameter will be influenced by lower limb position change. The aim of the study is to investigate the relationship of lower limb position and the radiologic parameter after total knee replacement. Methods There was retrospectively study of twelve patients after total knee replacement in our hospital from September 2014 to May 2015. The full-length radiographs were taken from external rotation 20° to internal rotation 25°. The lower limb mechanical axis angle,lower limb anatomical axis and tibia anatomical axis angle were measured to define the relationship of lower limb position and the radiologic parameter after total knee replacement. Results The lower limb mechani-cal axis angle varied from varus 3° to valgus 2° when tibia position changes from external rotation 20° to internal rotation 20°. The lower limb anatomical axis varied from valgus 7. 57° to valgus 3. 71°when tibia position changes from external rotation 20° to internal rotation 20° with leg full extended. Tibia anatomical axis angle varied from varus 1. 6° to valgus 1. 4°when tibia po-sition changes from external rotation 20° to internal rotation 20°. Conclusion The rotation of anatomical landmarks on full length film should be carefully evaluated to avoid the mistakes caused by rotation of the lower extremities.