Abstract: BACKGROUND: The Akagi line and range-of-motion (ROM) technique are widely used for locating the tibial prosthesis during total knee arthroplasty; however, there is still a lack of relevant research on the size and source of the difference between the two positioning methods.  
OBJECTIVE: To compare the differences of Akagi line and ROM technique in varus knee during total knee arthroplasty, and to discuss the causes of this difference.
METHODS:  Totally 70 patients with varus knee who underwent total knee arthroplasty in the Department of Orthopedics, Guangdong Hospital of Traditional Chinese Medicine from July to December 2021 were enrolled in this study. All operations were performed with the posterior cruciate-stabilizing total knee prostheses. The femorotibial angle, lateral distal femoral angle, medial proximal tibial angle, and joint line convergence angle were measured before operation. Its difference from normal was calculated. The angle α between Akagi line and ROM technique was measured during operation. The angles that measured preoperatively and α were statistically tested by using correlation analysis and multiple linear regression analysis.  
RESULTS AND CONCLUSION: (1) Before operation, Δ mechanical femoral-tibial angle was (10.90±4.82)°; Δ anatomic tibiofemoral angle was (10.81±4.34)°; Δ mechanical lateral distal femoral angle was (-3.26±2.68)°; Δ anatomic lateral distal femoral angle was (-3.00±2.30)°; Δ mechanical medial proximal tibial angle was (2.39±3.05)°; Δ anatomic medial proximal tibial angle was (2.98±3.31)°; Δ joint line convergence angle was (4.71±2.52)°; the α that measured during operation was (2.39±2.50)°. (2) Totally 53 cases selected Akagi line and 13 cases selected ROM technique for locating the tibial prosthesis finally. (3) Statistical analysis results showed that Δ mechanical medial proximal tibial angle and Δ anatomic medial proximal tibial angle had a significant positive effect on α (P < 0.01), and the regression equations were α=0.658±0.432×Δ mechanical medial proximal tibial angle and α=0.013±0.346×Δ anatomic medial proximal tibial angle respectively. (4) The results suggest that there is a difference between Akagi line and ROM technique when locating the tibial prosthesis for patients with varus knee undergoing total knee arthroplasty, and this difference (α) is positively correlated with the degree of proximal tibial varus deformity.

Key words: total knee arthroplasty, varus deformity, tibial prosthesis, rotational localization, Akagi line, ROM technique